{"id":499,"date":"2024-12-18T07:20:23","date_gmt":"2024-12-18T07:20:23","guid":{"rendered":"http:\/\/192.168.10.18\/arslan\/Demo\/GeekyBot\/?p=499"},"modified":"2025-06-18T12:55:25","modified_gmt":"2025-06-18T12:55:25","slug":"telephone","status":"publish","type":"post","link":"https:\/\/demo.geekybot.com\/index.php\/telephone\/","title":{"rendered":"Telephone"},"content":{"rendered":"<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded\" data-topic-id=\"585993\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"grey-box w-100 grey-box-top\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"true\">\r\n<div class=\"reading-channel\">\r\n<section id=\"ref1\" data-level=\"1\" data-has-spy=\"true\">\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-prev-disabled rw-next-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"192158\" data-asm-type=\"video\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"video\"><a class=\"gtm-assembly-link d-flex justify-content-center\" href=\"https:\/\/www.britannica.com\/video\/Overview-invention-telephone-focus-work-Alexander-Graham\/-192158\" data-id=\"180119\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/180119-138-29F20103\/Overview-invention-telephone-focus-work-Alexander-Graham.jpg?w=800&amp;h=450&amp;c=crop\" alt=\"How the telephone was invented\" \/><\/a>\r\n<div class=\"btn btn-xl btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><span class=\"md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption\">How the telephone was invented<\/span>Overview of the invention of the telephone, with a focus on the work by Alexander Graham Bell.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<a class=\"font-14 mt-10 d-inline-block\" href=\"https:\/\/www.britannica.com\/technology\/telephone\/images-videos\">See all videos for this article<\/a><\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><\/div>\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref607751\"><\/span>telephone<\/strong>, an instrument designed for the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/simultaneous\" data-term=\"simultaneous\" data-type=\"EB\">simultaneous<\/a>\u00a0transmission and reception of the human voice. The telephone is inexpensive, is simple to operate, and offers its users an immediate, personal type of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0that cannot be obtained through any other medium. As a result, it has become the most widely used telecommunications device in the world. Billions of telephones are in use around the world.<\/p>\r\n<p class=\"topic-paragraph\">This article describes the functional components of the modern telephone and traces the historical development of the telephone instrument. In addition it describes the development of what is known as the\u00a0<span id=\"ref607752\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/public-switched-telephone-network\">public switched telephone network<\/a>\u00a0(PSTN). For discussion of broader technologies,\u00a0<em>see<\/em>\u00a0the articles\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\" data-show-preview=\"true\">telecommunications system<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/telecommunications-media\" data-show-preview=\"true\">telecommunications media<\/a>. For technologies related to the telephone,\u00a0<em>see<\/em>\u00a0the articles\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\" data-show-preview=\"true\">mobile telephone<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/videophone\" data-show-preview=\"true\">videophone<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/fax\" data-show-preview=\"true\">fax<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modem\" data-show-preview=\"true\">modem<\/a>.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279893\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\">The telephone instrument<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"122351\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/00\/71000-050-C336A099\/Alexander-Graham-Bell-ability-sound-telephone-electricity-1887.jpg\" data-href=\"\/media\/1\/585993\/122351\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/00\/71000-050-C336A099\/Alexander-Graham-Bell-ability-sound-telephone-electricity-1887.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/00\/71000-050-C336A099\/Alexander-Graham-Bell-ability-sound-telephone-electricity-1887.jpg?w=300\" alt=\"Alexander Graham Bell demonstrating the telephone\" data-width=\"1600\" data-height=\"1166\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/00\/71000-050-C336A099\/Alexander-Graham-Bell-ability-sound-telephone-electricity-1887.jpg\" data-href=\"\/media\/1\/585993\/122351\">Alexander Graham Bell demonstrating the telephone<\/a>Alexander Graham Bell demonstrating the ability of the telephone to transmit sound by electricity from Salem to Boston, Massachusetts, 1887.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The word\u00a0<em>telephone<\/em>, from the Greek roots\u00a0<em>t\u0113le,<\/em>\u00a0\u201cfar,\u201d and\u00a0<em>phon\u0113,<\/em>\u00a0\u201csound,\u201d was applied as early as the late 17th century to the string telephone familiar to children, and it was later used to refer to the megaphone and the speaking tube, but in modern usage it refers solely to electrical devices\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/derived\" data-term=\"derived\" data-type=\"EB\">derived<\/a>\u00a0from the inventions of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\" data-show-preview=\"true\">Alexander Graham Bell<\/a>\u00a0and others. Within 20 years of the 1876 Bell\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/patent\" data-show-preview=\"true\">patent<\/a>, the telephone instrument, as modified by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Augustus-Watson\" data-show-preview=\"true\">Thomas Watson<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Emil-Berliner\" data-show-preview=\"true\">Emil Berliner<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Edison\" data-show-preview=\"true\">Thomas Edison<\/a>, and others, acquired a functional design that has not changed fundamentally in more than a century. Since the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/invention-technology\" data-show-preview=\"true\">invention<\/a>\u00a0of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transistor\" data-show-preview=\"true\">transistor<\/a>\u00a0in 1947, metal wiring and other heavy hardware have been replaced by lightweight and compact microcircuitry. Advances in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/electronics\" data-show-preview=\"true\">electronics<\/a>\u00a0have improved the performance of the basic design, and they also have allowed the introduction of a number of \u201csmart\u201d features such as automatic redialing, call-number identification, wireless transmission, and visual data display. Such advances supplement, but do not replace, the basic telephone design. That design is described in this section, as is the remarkable history of the telephone\u2019s development, from the earliest experimental devices to the modern digital instrument.<\/p>\r\n<div class=\"mb-20\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"293440\" data-asm-type=\"infogram\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"infogram\" data-gtm-vis-first-on-screen1145433_1044=\"6632\" data-gtm-vis-recent-on-screen1145433_1044=\"154907\" data-gtm-vis-total-visible-time1145433_1044=\"100\" data-gtm-vis-has-fired1145433_1044=\"1\"><iframe title=\"Evolution of the Phone\" src=\"https:\/\/e.infogram.com\/_\/4vQBCMMalJU9axNsoagf?parent_url=https%3A%2F%2Fwww.britannica.com%2Ftechnology%2Ftelephone&amp;src=embed#async_embed\" frameborder=\"0\" scrolling=\"no\" allowfullscreen=\"allowfullscreen\" data-mce-fragment=\"1\"><\/iframe><\/div>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279894\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Working components of the telephone<\/h2>\r\n<p class=\"topic-paragraph\">As it has since its early years, the telephone instrument is made up of the following functional components: a power source, a switch hook, a dialer, a ringer, a transmitter, a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>, and an anti-sidetone\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/circuit\" data-term=\"circuit\" data-type=\"EB\">circuit<\/a>. These components are described in turn below.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/inventions-from-bayonets-to-jet-engines\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/28\/169428-131-820AF1D4\/ornithopter-Airplane-Aircraft-flying-machine-illustration-plans.jpg\" alt=\"ornithopter. Airplane and Aircraft. 3D illustration of Leonardo da Vinci's plans for an ornithopter, a flying machine kept aloft by the beating of its wings; about 1490.\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Inventions: From Bayonets to Jet Engines<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279895\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Power source<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120541\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/23\/60523-050-1D099B2F\/Alexander-Graham-Bell-version-Centennial-telephone-1876.jpg\" data-href=\"\/media\/1\/585993\/120541\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/23\/60523-050-1D099B2F\/Alexander-Graham-Bell-version-Centennial-telephone-1876.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/23\/60523-050-1D099B2F\/Alexander-Graham-Bell-version-Centennial-telephone-1876.jpg?w=300\" alt=\"actor portraying Alexander Graham Bell\" data-width=\"1600\" data-height=\"1306\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/23\/60523-050-1D099B2F\/Alexander-Graham-Bell-version-Centennial-telephone-1876.jpg\" data-href=\"\/media\/1\/585993\/120541\">actor portraying Alexander Graham Bell<\/a>An actor portraying Alexander Graham Bell in a short film, 1930.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In the first experimental telephones the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electric-current\" data-show-preview=\"true\">electric current<\/a>\u00a0that powered the telephone circuit was generated at the transmitter, by means of an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electromagnet\" data-show-preview=\"true\">electromagnet<\/a>\u00a0activated by the speaker\u2019s voice. Such a system could not generate enough voltage to produce audible speech in distant receivers, so every transmitter since Bell\u2019s patented design has operated on a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/direct-current\" data-show-preview=\"true\">direct current<\/a>\u00a0supplied by an independent power source. The first sources were\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/battery-electronics\" data-show-preview=\"true\">batteries<\/a>\u00a0located in the telephone instruments themselves, but since the 1890s current has been generated at the local\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">switching<\/a>\u00a0office. The current is supplied through a two-wire circuit called the\u00a0<span id=\"ref1251051\"><\/span>local loop. The standard voltage is 48 volts.<\/p>\r\n<p class=\"topic-paragraph\">Cordless telephones represent a return to individual power sources in that their low-wattage radio transmitters are powered by a small (e.g., 3.6-volt)\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/battery\" data-term=\"battery\" data-type=\"EB\">battery<\/a>\u00a0located in the portable handset. When the telephone is not in use, the battery is recharged through contacts with the base unit. The base unit is powered by a transformer connection to a standard electric outlet.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279896\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref1251050\"><\/span>Switch hook<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120258\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/22\/60522-050-C20A5F66\/transmitter-telephones-attachment-position-hook-operation-receiver-1897.jpg\" data-href=\"\/media\/1\/585993\/120258\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/22\/60522-050-C20A5F66\/transmitter-telephones-attachment-position-hook-operation-receiver-1897.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/22\/60522-050-C20A5F66\/transmitter-telephones-attachment-position-hook-operation-receiver-1897.jpg?w=300\" alt=\"1897 telephone\" data-width=\"942\" data-height=\"1000\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/22\/60522-050-C20A5F66\/transmitter-telephones-attachment-position-hook-operation-receiver-1897.jpg\" data-href=\"\/media\/1\/585993\/120258\">1897 telephone<\/a>Nineteenth-century telephones typically contained a transmitter that had to be in an upright position for proper operation, with the receiver located in an attachment that rested on a hook when not in use. The tall profile of AT&amp;T&#8217;s desk set, such as the 1897 model shown here, led many people to call them \u201ccandlestick\u201d phones.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The switch hook connects the telephone instrument to the direct current supplied through the local loop. In early telephones the receiver was hung on a hook that operated the switch by opening and closing a metal contact. This system is still common, though the hook has been replaced by a cradle to hold the combined handset, enclosing both receiver and transmitter. In some modern electronic instruments, the mechanical operation of metal contacts has been replaced by a system of transistor\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/relay-electronics\" data-show-preview=\"true\">relays<\/a>.<\/p>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120542\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/96\/80596-050-FE68106A\/Business-telephone-2000.jpg\" data-href=\"\/media\/1\/585993\/120542\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/96\/80596-050-FE68106A\/Business-telephone-2000.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/96\/80596-050-FE68106A\/Business-telephone-2000.jpg?w=300\" alt=\"telephone c. 2000\" data-width=\"1600\" data-height=\"1136\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/96\/80596-050-FE68106A\/Business-telephone-2000.jpg\" data-href=\"\/media\/1\/585993\/120542\">telephone\u00a0<em>c.<\/em>\u00a02000<\/a>Business telephone,\u00a0<em>c.<\/em>\u00a02000.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">When the telephone is \u201con hook,\u201d contact with the local loop is broken. When it is \u201coff hook\u201d (i.e., when the handset is lifted from the cradle), contact is restored, and current flows through the loop. The switching office signals restoration of contact by\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmitting\" data-term=\"transmitting\" data-type=\"EB\">transmitting<\/a>\u00a0a low-frequency \u201cdial tone\u201d\u2014actually two simultaneous tones of 350 and 440 hertz.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<div data-page-index=\"1\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"2\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279897\" data-level=\"3\" data-has-spy=\"true\">\r\n<h1 class=\"h3\"><span id=\"ref1251100\"><\/span>Dialer<\/h1>\r\n<p class=\"topic-paragraph\">The dialer is used to enter the number of the party that the user wishes to call. Signals generated by the dialer activate switches in the local office, which establish a transmission path to the called party. Dialers are of the rotary and push-button types.<\/p>\r\n<p class=\"topic-paragraph\">The traditional rotary dialer, invented in the 1890s, is rotated against the tension of a spring and then released, whereupon it returns to its position at a rate controlled by a mechanical governor. The return rotation causes a switch to open and close, producing interruptions, or pulses, in the flow of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/direct-current\" data-show-preview=\"true\">direct current<\/a>\u00a0to the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">switching<\/a>\u00a0office. Each pulse lasts approximately one-tenth of a second; the number of pulses signals the number being dialed.<\/p>\r\n<p class=\"topic-paragraph\">In push-button dialing, introduced in the 1960s, the pressing of each button generates a \u201cdual-tone\u201d signal that is specific to the number being entered. Each dual tone is composed of a low\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0(697, 770, 852, or 941 hertz) and a high frequency (1,209, 1,336, or 1,477 hertz), which are sensed and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/decoded\" data-term=\"decoded\" data-type=\"EB\">decoded<\/a>\u00a0at the switching office. Unlike the low-frequency rotary pulses, dual tones can travel through the telephone system, so that push-button telephones can be used to activate automated functions at the other end of the line.<\/p>\r\n<p class=\"topic-paragraph\">In both rotary and push-button systems, a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/capacitor\" data-show-preview=\"true\">capacitor<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/resistor\" data-show-preview=\"true\">resistor<\/a>\u00a0prevent dialing signals from passing into the ringer circuit.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279898\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref1251052\"><\/span>Ringer<\/h2>\r\n<p class=\"topic-paragraph\">The ringer alerts the user to an incoming call by emitting an audible tone or ring. Ringers are of two types, mechanical or electronic. Both types are activated by a 20-hertz, 75-volt alternating current generated by the switching office. The ringer is commonly activated in two-second pulses, with each pulse separated by a pause of four seconds.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">The traditional mechanical ringer was introduced with the early Bell telephones. It consists of two closely spaced bells, a metal clapper, and a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/magnet\" data-show-preview=\"true\">magnet<\/a>. Passage of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/alternating-current\" data-show-preview=\"true\">alternating current<\/a>\u00a0through a coil of wire produces alternations in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/magnetic-force\" data-show-preview=\"true\">magnetic attraction<\/a>\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/exerted\" data-term=\"exerted\" data-type=\"EB\">exerted<\/a>\u00a0on the clapper, so that it vibrates rapidly and loudly against the bells. Volume can be muted by a switch that places a mechanical damper against the bells.<\/p>\r\n<p class=\"topic-paragraph\">In modern electronic ringers, introduced in the 1980s, the ringer current is passed through an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/oscillator-electronics\" data-show-preview=\"true\">oscillator<\/a>, which adjusts the current to the precise frequency required to activate a piezoelectric transducer\u2014a device made of a crystalline material that vibrates in response to an\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/electric-current\" data-show-preview=\"true\">electric current<\/a>. The transducer may be coupled to a small loudspeaker, which can be adjusted for volume.<\/p>\r\n<p class=\"topic-paragraph\">The ringer circuit remains connected to the local loop even when the telephone is on hook. A larger voltage is necessary to activate the ringer because the ringer circuit is made with a high\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electrical-impedance\" data-show-preview=\"true\">electrical impedance<\/a>\u00a0in order to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/avoid\" data-term=\"avoid\" data-type=\"EB\">avoid<\/a>\u00a0draining power from the transmitter-receiver circuit when the telephone is in use. A capacitor prevents direct current from passing through the ringer once the handset has been lifted off the switch hook.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279899\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref607758\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transmitter\">Transmitter<\/a><\/h2>\r\n<p class=\"topic-paragraph\">The transmitter is essentially a tiny\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/microphone-electroacoustic-device\" data-show-preview=\"true\">microphone<\/a>\u00a0located in the mouthpiece of the telephone\u2019s handset. It converts the vibrations of the speaker\u2019s voice into variations in the direct current flowing through the set from the power source.<\/p>\r\n<p class=\"topic-paragraph\">In traditional\u00a0<span id=\"ref607765\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/carbon-transmitter\">carbon transmitters<\/a>, developed in the 1880s, a thin layer of carbon granules separates a fixed\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electrode\" data-show-preview=\"true\">electrode<\/a>\u00a0from a diaphragm-activated electrode. Electric current flows through the carbon against a certain\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/resistance-electronics\" data-show-preview=\"true\">resistance<\/a>. The diaphragm, vibrating in response to the speaker\u2019s voice, forces the movable electrode to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/exert\" data-term=\"exert\" data-type=\"EB\">exert<\/a>\u00a0a fluctuating pressure on the carbon layer. Fluctuations in the carbon layer create fluctuations in its\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/resistance-electronics\" data-show-preview=\"true\">electrical resistance<\/a>, which in turn produce fluctuations in the electric current.<\/p>\r\n<p class=\"topic-paragraph\">In modern\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electret\" data-show-preview=\"true\">electret<\/a>\u00a0transmitters, developed in the 1970s, the carbon layer is replaced by a thin plastic sheet that has been given a conductive metallic coating on one side. The plastic separates that coating from another metal electrode and maintains an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electric-field\" data-show-preview=\"true\">electric field<\/a>\u00a0between them. Vibrations caused by speech produce fluctuations in the electric field, which in turn produce small variations in voltage. The voltages are amplified for transmission over the telephone line.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279900\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Receiver<\/h2>\r\n<p class=\"topic-paragraph\">The\u00a0<span id=\"ref607760\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>\u00a0is located in the earpiece of the telephone\u2019s handset. Operating on electromagnetic principles that were known in Bell\u2019s day, it\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/converts\" data-term=\"converts\" data-type=\"EB\">converts<\/a>\u00a0fluctuating electric current into\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/sound-physics\" data-show-preview=\"true\">sound<\/a>\u00a0waves that reproduce human speech. Fundamentally, it consists of two parts: a permanent magnet, having pole pieces wound with coils of insulated fine wire, and a diaphragm driven by magnetic material that is supported near the pole pieces. Speech currents passing through the coils vary the attraction of the permanent magnet for the diaphragm, causing it to vibrate and produce sound waves.<\/p>\r\n<p class=\"topic-paragraph\">Through the years the design of the electromagnetic system has been continuously improved. In the most common type of receiver, introduced in the Bell system in 1951, the diaphragm, consisting of a central cone attached to a ring-shaped\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/armature-modeling\" data-show-preview=\"true\">armature<\/a>, is driven as a piston to obtain efficient response over a wide frequency range. Telephone receivers are designed to have an accurate response to tones with frequencies of 350 to 3,500 hertz\u2014a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamic\" data-term=\"dynamic\" data-type=\"MW\">dynamic<\/a>\u00a0range that is narrower than the capabilities of the human\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/ear\" data-show-preview=\"true\">ear<\/a>\u00a0but sufficient to reproduce normal speech.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279901\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref1251101\"><\/span>Anti-sidetone circuit<\/h2>\r\n<p class=\"topic-paragraph\">The anti-sidetone circuit is an assemblage of transformers, resistors, and capacitors that perform a number of functions. The primary function is to reduce sidetone, which is the distracting sound of the speaker\u2019s own voice coming through the receiver from the transmitter. The anti-sidetone circuit accomplishes this reduction by interposing a transformer between the transmitter circuit and the receiver circuit and by splitting the transmitter signals along two paths. When the divided signals, having opposite polarities, meet at the transformer, they almost entirely cancel each other in crossing to the receiver circuit. The speech signal coming from the other end of the line, on the other hand, arrives at the transformer along a single, undivided path and crosses the transformer unimpeded.<\/p>\r\n<p class=\"topic-paragraph\">The anti-sidetone\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/circuit\" data-term=\"circuit\" data-type=\"EB\">circuit<\/a>\u00a0also matches the low electrical impedance of the telephone instrument\u2019s circuits to the higher electrical impedance of the telephone line. Impedance matching allows a more efficient flow of current through the system.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"2\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279902\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\">Development of the telephone instrument<\/h1>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279903\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Early sound transmitters<\/h2>\r\n<p class=\"topic-paragraph\">Beginning in the early 19th century, several inventors made a number of attempts to transmit\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/sound-physics\" data-show-preview=\"true\">sound<\/a>\u00a0by electric means. The first inventor to suggest that sound could be transmitted electrically was a Frenchman,\u00a0<span id=\"ref607756\"><\/span>Charles Bourseul, who indicated that a diaphragm making and breaking contact with an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electrode\" data-show-preview=\"true\">electrode<\/a>\u00a0might be used for this purpose. In the 1850s Italian American inventor\u00a0<span id=\"ref1255480\"><\/span>Antonio Meucci had electrical devices in his home called\u00a0<em><span id=\"ref1255481\"><\/span>telettrofoni<\/em>\u00a0that he used to communicate between rooms, though he did not patent his inventions. By 1861\u00a0<span id=\"ref607757\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Johann-Philipp-Reis\" data-show-preview=\"true\">Johann Philipp Reis<\/a>\u00a0of Germany had designed several instruments for the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmission\" data-term=\"transmission\" data-type=\"EB\">transmission<\/a>\u00a0of sound. The transmitter Reis employed consisted of a membrane with a metallic strip that would intermittently contact a metallic point connected to an electrical circuit. As sound waves impinged on the membrane, making the membrane vibrate, the circuit would be connected and interrupted at the same rate as the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0of the sound. The fluctuating\u00a0<span id=\"ref607759\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electric-current\" data-show-preview=\"true\">electric current<\/a>\u00a0thus generated would be transmitted by wire to a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>, which consisted of an iron needle that was surrounded by the coil of an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electromagnet\" data-show-preview=\"true\">electromagnet<\/a>\u00a0and connected to a sounding box. The fluctuating electric current would generate varying\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/magnetic-field\" data-show-preview=\"true\">magnetic fields<\/a>\u00a0in the coil, and these in turn would force the iron needle to produce\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/vibrations\" data-term=\"vibrations\" data-type=\"EB\">vibrations<\/a>\u00a0in the sounding box. Reis\u2019s system could thus transmit a simple tone, but it could not reproduce the complex waveforms that make up speech.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279904\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Gray and Bell: the transmission of speech<\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279905\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">The first devices<\/h2>\r\n<p class=\"topic-paragraph\">In the 1870s two American inventors,\u00a0<span id=\"ref607761\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Elisha-Gray\" data-show-preview=\"true\">Elisha Gray<\/a>\u00a0and\u00a0<span id=\"ref607762\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\" data-show-preview=\"true\">Alexander Graham Bell<\/a>, each independently, designed devices that could transmit speech electrically. Gray\u2019s first device made use of a harmonic\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telegraph\" data-show-preview=\"true\">telegraph<\/a>, the transmitter and receiver of which consisted of a set of metallic reeds tuned to different frequencies. An electromagnetic\u00a0<span id=\"ref607763\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/coil\" data-show-preview=\"true\">coil<\/a>\u00a0was located near each of the reeds. When a reed in the transmitter was vibrated by sound waves of its resonant frequency\u2014for example, 400 hertz\u2014it\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/induced\" data-term=\"induced\" data-type=\"EB\">induced<\/a>\u00a0an electric current of corresponding frequency in its matching coil. This coil was connected to all the coils in the receiver, but only the reed tuned to the transmitting reed\u2019s frequency would vibrate in response to the electric current. Thus, simple tones could be transmitted. In the spring of 1874 Gray realized that a receiver consisting of a single steel diaphragm in front of an electromagnet could reproduce any of the transmitted tones. Gray, however, was initially unable to conceive of a transmitter that would transmit complex speech vibrations and instead chose to demonstrate the transmission of tones via his telegraphic device in the summer of 1874.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120543\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" data-href=\"\/media\/1\/585993\/120543\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg?w=300\" alt=\"telephone: Alexander Graham Bell's sketch of a telephone\" data-width=\"1600\" data-height=\"1077\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" data-href=\"\/media\/1\/585993\/120543\">telephone: Alexander Graham Bell&#8217;s sketch of a telephone<\/a>Alexander Graham Bell&#8217;s sketch of a telephone. He filed the patent for his telephone at the U.S. Patent Office on February 14, 1876\u2014just two hours before a rival, Elisha Gray, filed a declaration of intent to file a patent for a similar device.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Bell, meanwhile, also had considered the transmission of speech using the harmonic telegraph concept, and in the summer of 1874 he conceived of a membrane receiver similar to Gray\u2019s. However, since Bell too had no transmitter, the membrane device was never constructed. Following some earlier experiments, Bell postulated that, if two membrane receivers were connected electrically, a sound wave that caused one membrane to vibrate would induce a voltage in the electromagnetic coil that would in turn cause the other membrane to vibrate. Working with a young machinist,\u00a0<span id=\"ref1251053\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Augustus-Watson\" data-show-preview=\"true\">Thomas Augustus Watson<\/a>, Bell had two such instruments constructed in June 1875. The device was tested on June 3, 1875, and, although no intelligible words were transmitted, \u201cspeechlike\u201d sounds were heard at the receiving end.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120547\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/85\/115185-050-C6C92B40\/Alexander-Graham-Bell-patent-telephone-declaration-United-February-14-1876.jpg\" data-href=\"\/media\/1\/585993\/120547\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/85\/115185-050-C6C92B40\/Alexander-Graham-Bell-patent-telephone-declaration-United-February-14-1876.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/85\/115185-050-C6C92B40\/Alexander-Graham-Bell-patent-telephone-declaration-United-February-14-1876.jpg?w=300\" alt=\"Bell, Alexander Graham: telephone\" data-width=\"1137\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/85\/115185-050-C6C92B40\/Alexander-Graham-Bell-patent-telephone-declaration-United-February-14-1876.jpg\" data-href=\"\/media\/1\/585993\/120547\">Bell, Alexander Graham: telephone<\/a>Alexander Graham Bell filing the patent for his telephone at the United States Patent Office on February 14, 1876, two hours before declaration of a rival device by Elisha Gray. Bell&#8217;s telephone is on the table to the right.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">An application for a U.S.\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/patent\" data-show-preview=\"true\">patent<\/a>\u00a0on Bell\u2019s work was filed on February 14, 1876. Several hours later that same day, Gray filed a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/caveat\" data-term=\"caveat\" data-type=\"MW\">caveat<\/a>\u00a0on the concept of a telephone transmitter and receiver. A caveat was a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/confidential\" data-term=\"confidential\" data-type=\"MW\">confidential<\/a>, formal declaration by an inventor to the U.S. Patent Office of an intent to file a patent on an idea yet to be perfected; it was intended to prevent the idea from being used by other inventors. At this point neither Gray nor Bell had yet constructed a working telephone that could convey speech. On the basis of its earlier filing time, Bell\u2019s patent application was allowed over Gray\u2019s caveat. On March 7, 1876, Bell was awarded U.S. patent 174,465. This patent is often referred to as the most valuable ever issued by the U.S. Patent Office, as it described not only the telephone instrument but also the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/concept\" data-term=\"concept\" data-type=\"EB\">concept<\/a>\u00a0of a telephone system.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279906\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">The search for a successful transmitter<\/h2>\r\n<p class=\"topic-paragraph\">Gray had earlier come up with an idea for a transmitter in which a moving membrane was attached to an electrically conductive rod immersed in an acidic solution. Another conductive rod was immersed in the solution, and, as sound waves impinged on the membrane, the two rods would move with respect to each other. Variations in the distance between the two rods would produce variations in electric resistance and, hence, variations in the electric current. In contrast to the magnetic coil type of transmitter, the variable-resistance transmitter could actually amplify the transmitted sound, permitting use of longer cables between the transmitter and the receiver.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/inventions-from-bayonets-to-jet-engines\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/28\/169428-131-820AF1D4\/ornithopter-Airplane-Aircraft-flying-machine-illustration-plans.jpg\" alt=\"ornithopter. Airplane and Aircraft. 3D illustration of Leonardo da Vinci's plans for an ornithopter, a flying machine kept aloft by the beating of its wings; about 1490.\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Inventions: From Bayonets to Jet Engines<\/div>\r\n<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120549\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" data-href=\"\/media\/1\/585993\/120549\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg?w=300\" alt=\"Alexander Graham Bell\" data-width=\"1423\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" data-href=\"\/media\/1\/585993\/120549\">Alexander Graham Bell<\/a>Alexander Graham Bell, inventor who patented the telephone in 1876, lecturing at Salem, Massachusetts (top), while friends in his study at Boston listen to his lecture via telephone, February 12, 1877.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Again, Bell also worked on a similar \u201cliquid\u201d transmitter design; it was this design that permitted the first transmission of speech, on March 10, 1876, by Bell to Watson, which Bell transcribed in his lab notes as \u201cMr. Watson\u2014come here\u2014I want to see you.\u201d The first public demonstrations of the telephone followed shortly afterward, featuring a design similar to the earlier magnetic coil membrane units described above. One of the earliest demonstrations occurred in June 1876 at the Centennial Exposition in Philadelphia. Further tests and refinement of equipment followed shortly afterward. On October 9, 1876, Bell conducted a two-way test of his telephone over a 5-km (2-mile) distance between\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Boston\" data-show-preview=\"true\">Boston<\/a>\u00a0and Cambridgeport, Massachusetts. In May 1877 the first commercial application of the telephone took place with the installation of telephones in offices of customers of the E.T. Holmes burglar alarm company.<\/p>\r\n<p class=\"topic-paragraph\">The poor performance of early telephone transmitters prompted a number of inventors to pursue further work in this area. Among them was\u00a0<span id=\"ref607764\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Edison\" data-show-preview=\"true\">Thomas Alva Edison<\/a>, whose 1886 design for a voice transmitter consisted of a cavity filled with granules of carbonized\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/anthracite\" data-show-preview=\"true\">anthracite<\/a>\u00a0coal. The carbon granules were\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/confined\" data-term=\"confined\" data-type=\"EB\">confined<\/a>\u00a0between two\u00a0<span id=\"ref607766\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electrode\" data-show-preview=\"true\">electrodes<\/a>\u00a0through which a constant electric current was passed. One of the electrodes was attached to a thin iron diaphragm, and, as sound waves forced the diaphragm to vibrate, the carbon granules were alternately compressed and released. As the distance across the granules fluctuated, resistance to the electric current also fluctuated, and the resulting variations in current were transmitted to the receiver. Edison\u2019s carbon transmitter was sufficiently simple, effective, cheap, and durable that it became the basis for standard telephone transmitter design through the 1970s.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"3\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<section data-level=\"2\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279907\" data-level=\"3\" data-has-spy=\"true\">\r\n<h1 class=\"h3\">Development of the modern instrument<\/h1>\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"39853\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/29\/60529-050-65D05825\/telephone-1877.jpg\" data-href=\"\/media\/1\/585993\/39853\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/29\/60529-050-65D05825\/telephone-1877.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/29\/60529-050-65D05825\/telephone-1877.jpg?w=300\" alt=\"first commercial telephone\" data-width=\"1000\" data-height=\"697\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">1 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/29\/60529-050-65D05825\/telephone-1877.jpg\" data-href=\"\/media\/1\/585993\/39853\">first commercial telephone<\/a>The first commercial telephone, 1877.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69324\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/21\/60521-050-9EA01206\/ATT-magneto-wall-telephone-1907.jpg\" data-href=\"\/media\/1\/585993\/69324\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/21\/60521-050-9EA01206\/ATT-magneto-wall-telephone-1907.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/21\/60521-050-9EA01206\/ATT-magneto-wall-telephone-1907.jpg?w=300\" alt=\"AT&amp;T magneto wall telephone\" data-width=\"732\" data-height=\"1000\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">2 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/21\/60521-050-9EA01206\/ATT-magneto-wall-telephone-1907.jpg\" data-href=\"\/media\/1\/585993\/69324\">AT&amp;T magneto wall telephone<\/a>AT&amp;T magneto wall telephone, 1907.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20\"><\/button><\/div>\r\n<p class=\"topic-paragraph\">The telephone instrument continued to evolve over time, as can be illustrated by the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/succession\" data-term=\"succession\" data-type=\"EB\">succession<\/a>\u00a0of American instruments described below. The concept of mounting both the transmitter and the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>\u00a0in the same handle appeared in 1878 in instruments designed for use by telephone operators in a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/New-York-City\" data-show-preview=\"true\">New York City<\/a>\u00a0exchange. The earliest telephone instrument to see common use was introduced by\u00a0<span id=\"ref607767\"><\/span>Charles Williams, Jr., in 1882. Designed for wall mounting, this instrument consisted of a ringer, a hand-cranked\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/magneto\" data-show-preview=\"true\">magneto<\/a>\u00a0(for generating a ringing voltage in a distant instrument), a hand receiver, a switch hook, and a transmitter. Various versions of this telephone instrument remained in use throughout the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>\u00a0as late as the 1950s. As is noted in the section\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\/The-telephone-network#ref279913\" data-show-preview=\"true\">Switching<\/a>, the telephone dial originated with automatic telephone switching systems in 1896.<\/p>\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69325\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/20\/60520-050-7E3831A8\/ATT-E1A-handset-1928.jpg\" data-href=\"\/media\/1\/585993\/69325\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/20\/60520-050-7E3831A8\/ATT-E1A-handset-1928.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/20\/60520-050-7E3831A8\/ATT-E1A-handset-1928.jpg?w=300\" alt=\"AT&amp;T desk telephone with E1A handset\" data-width=\"1000\" data-height=\"730\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">1 of 3<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/20\/60520-050-7E3831A8\/ATT-E1A-handset-1928.jpg\" data-href=\"\/media\/1\/585993\/69325\">AT&amp;T desk telephone with E1A handset<\/a>AT&amp;T desk telephone with E1A handset, 1928.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69326\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/19\/60519-050-A8871231\/ATT-desk-telephone-1937.jpg\" data-href=\"\/media\/1\/585993\/69326\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/19\/60519-050-A8871231\/ATT-desk-telephone-1937.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/60519-050-A8871231\/ATT-desk-telephone-1937.jpg?w=300\" alt=\"AT&amp;T combined desk telephone\" data-width=\"1000\" data-height=\"797\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">2 of 3<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/19\/60519-050-A8871231\/ATT-desk-telephone-1937.jpg\" data-href=\"\/media\/1\/585993\/69326\">AT&amp;T combined desk telephone<\/a>AT&amp;T combined desk telephone, 1937.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69327\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/18\/60518-050-3DE3B696\/ATT-desk-telephone-1949.jpg\" data-href=\"\/media\/1\/585993\/69327\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/18\/60518-050-3DE3B696\/ATT-desk-telephone-1949.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/60518-050-3DE3B696\/ATT-desk-telephone-1949.jpg?w=300\" alt=\"AT&amp;T \u201c500\u201d desk telephone\" data-width=\"4835\" data-height=\"3792\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">3 of 3<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/18\/60518-050-3DE3B696\/ATT-desk-telephone-1949.jpg\" data-href=\"\/media\/1\/585993\/69327\">AT&amp;T \u201c500\u201d desk telephone<\/a>AT&amp;T \u201c500\u201ddesk telephone, 1949.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20\"><\/button><\/div>\r\n<p class=\"topic-paragraph\"><span id=\"ref607768\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/desk\" data-show-preview=\"true\">Desk<\/a>\u00a0instruments were first constructed in 1897. Patterned after the wall-mounted telephone, they usually consisted of a separate receiver and transmitter. In 1927, however, the American Telephone &amp; Telegraph Company (<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>) introduced the\u00a0<span id=\"ref607769\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/E1A-handset\">E1A handset<\/a>, which employed a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/combined\" data-term=\"combined\" data-type=\"EB\">combined<\/a>\u00a0transmitter-receiver arrangement. The ringer and much of the telephone electronics remained in a separate box, on which the transmitter-receiver handle was cradled when not in use. The first telephone to incorporate all the components of the station apparatus into one instrument was the so-called combined set of 1937. Some 25 million of these instruments were produced until they were superseded by a new design in 1949. The 1949 telephone was totally new, incorporating significant improvements in audio quality, mechanical design, and physical construction. Push-button versions of this set became available in 1963.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69328\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/17\/60517-050-EF7DB0D2\/ATTelephone-T-Touch-Tone-1968.jpg\" data-href=\"\/media\/1\/585993\/69328\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/17\/60517-050-EF7DB0D2\/ATTelephone-T-Touch-Tone-1968.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/17\/60517-050-EF7DB0D2\/ATTelephone-T-Touch-Tone-1968.jpg?w=300\" alt=\"AT&amp;T Touch-Tone telephone\" data-width=\"725\" data-height=\"1000\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/17\/60517-050-EF7DB0D2\/ATTelephone-T-Touch-Tone-1968.jpg\" data-href=\"\/media\/1\/585993\/69328\">AT&amp;T Touch-Tone telephone<\/a>AT&amp;T Touch-Tone telephone, 1968.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Modern telephone instruments are largely\u00a0<span id=\"ref607770\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/electronics\" data-show-preview=\"true\">electronic<\/a>. Wire coils that performed multiple functions in older sets have been replaced by\u00a0<span id=\"ref607771\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/integrated-circuit\" data-show-preview=\"true\">integrated circuits<\/a>\u00a0that are powered by the line voltage. Mechanical bell ringers have given way to electronic ringers. The carbon transmitter dating from Edison\u2019s time has been replaced by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electret\" data-show-preview=\"true\">electret<\/a>\u00a0microphones, in which\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/sound-physics\" data-show-preview=\"true\">sound<\/a>\u00a0waves cause a thin, metal-coated plastic diaphragm to vibrate, producing variations in an\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/electric-field\" data-show-preview=\"true\">electric field<\/a>\u00a0across a tiny air gap between the diaphragm and an electrode. The telephone dial has given way to the keypad, which can usually be switched to generate either pulses similar to those of the dial mechanism or dual-tone signals as in AT&amp;T\u2019s Touch-Tone system. Finally, a number of other features have become available on the telephone instrument, including last-number recall and speed-dialing of multiple telephone numbers.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279908\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref1117832\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/cordless-telephone\">Cordless telephones<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"69329\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/16\/60516-004-5D523557\/Cordless-telephone-1995.jpg\" data-href=\"\/media\/1\/585993\/69329\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/16\/60516-004-5D523557\/Cordless-telephone-1995.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/16\/60516-004-5D523557\/Cordless-telephone-1995.jpg?w=300\" alt=\"cordless telephone\" data-width=\"336\" data-height=\"300\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/16\/60516-004-5D523557\/Cordless-telephone-1995.jpg\" data-href=\"\/media\/1\/585993\/69329\">cordless telephone<\/a>Cordless telephone, 1995.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Cordless telephones are devices that take the place of a telephone instrument within a home or office and permit very limited mobility\u2014up to 100 metres (330 feet). Because they communicate with a base unit that is plugged directly into an existing telephone jack, they essentially serve as a wireless\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/extension\" data-term=\"extension\" data-type=\"EB\">extension<\/a>\u00a0to existing home or office wiring. The first cordless phones employed\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/modulation-communications\" data-show-preview=\"true\">modulation<\/a>\u00a0methods and operated over a pair of frequencies, 1.7 megahertz and 49 megahertz. Beginning in the 1980s, cordless phones operated over a pair of frequencies in the 46- and 49-megahertz bands, and in the late 1990s phones operating in the 902\u2013928-megahertz band began to appear. These phones employed either analog modulation, digital modulation, or spread-spectrum modulation. Some digital cordless telephones now operate in the gigahertz region\u2014for example, 5.8 gigahertz. Generally speaking, each successive generation of cordless phones has offered improved quality and range to the consumer.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279909\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref1117843\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/personal-communication-system\">Personal communication systems<\/a><\/h2>\r\n<p class=\"topic-paragraph\">In a number of countries throughout the world, a wireless service called the personal communication system (PCS) is available. In the broadest sense, PCS includes all forms of wireless communication that are interconnected with the public switched telephone network, including\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\" data-show-preview=\"true\">mobile telephone<\/a>\u00a0and aeronautical public correspondence systems, but the basic concept includes the following attributes:\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/ubiquitous\" data-term=\"ubiquitous\" data-type=\"MW\">ubiquitous<\/a>\u00a0service to roving users, low subscriber terminal costs and service fees, and compact, lightweight, and unobtrusive personal portable units.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-read-more-module\" href=\"https:\/\/www.britannica.com\/topic\/human-factors-engineering\/Applications-of-human-factors-engineering#ref106338\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"default rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/mendel-resources\/3-131\/images\/shared\/default3.png?v=3.131.7\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-navy-dark\">More From Britannica<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">human-factors engineering: Push-button telephone<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The first PCS to be\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implemented\" data-term=\"implemented\" data-type=\"MW\">implemented<\/a>\u00a0was the second-generation cordless telephony (<span id=\"ref1117844\"><\/span>CT-2) system, which entered service in the United Kingdom in 1991. The CT-2 system was designed at the outset to serve as a telepoint system. In telepoint systems, a user of a portable unit might originate telephone calls (but not receive them) by dialing a base station located within several hundred metres. The base unit was connected to the PSTN and operated as a public (pay) telephone, charging calls to the subscriber. Because of its limited coverage, the CT-2 system went out of service, giving way to the popular GSM digital cellular system (<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\" data-show-preview=\"true\">mobile telephone<\/a>).<\/p>\r\n<p class=\"topic-paragraph\">Meanwhile, the\u00a0<span id=\"ref1117845\"><\/span>European Conference on Posts and Telecommunications (CEPT) had begun work on another personal communication system, known as DECT (Digital\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/Enhanced\" data-term=\"Enhanced\" data-type=\"MW\">Enhanced<\/a>\u00a0Cordless Telecommunications, formerly\u00a0<span id=\"ref1117846\"><\/span>Digital European Cordless Telephone). The DECT system was designed initially to provide cordless telephone service for office\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environments\" data-term=\"environments\" data-type=\"MW\">environments<\/a>, but its scope soon broadened to include campus-wide communications and telepoint services. By 1999 DECT had reached 50 percent of the European cordless market.<\/p>\r\n<p class=\"topic-paragraph\">In\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Japan\" data-show-preview=\"true\">Japan<\/a>\u00a0a PCS based loosely on the DECT concepts, the\u00a0<span id=\"ref1117848\"><\/span>Personal Handy-Phone System (PHS), was introduced to the public in 1994. The PHS became popular throughout urban areas as an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/alternative\" data-term=\"alternative\" data-type=\"MW\">alternative<\/a>\u00a0to cellular systems. Supporting data traffic at 32 and 64 kilobits per second, it could perform as a high-speed wireless\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modem\" data-show-preview=\"true\">modem<\/a>\u00a0for access to the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Internet\" data-show-preview=\"true\">Internet<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">In the United States in 1994\u201395 the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Federal-Communications-Commission\" data-show-preview=\"true\">Federal Communications Commission<\/a>\u00a0(FCC) sold a number of licenses in the 1.85\u20131.99-gigahertz region for use in PCS applications.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"4\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279910\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\">The telephone network<\/h1>\r\n<p class=\"topic-paragraph\">In order to understand the many concepts represented in the public switched telephone network (PSTN), it is helpful to review the processes that take place in the making of a single call on a traditional wired telephone. To make a call, a telephone subscriber begins by taking the telephone \u201coff-hook\u201d\u2014in the process, signaling the local central office that service is requested. The central office, which has been monitoring the telephone line continuously (a process known as\u00a0<span id=\"ref1117743\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/attending\">attending<\/a>), responds with a dial tone. Upon receiving the dial tone, the customer enters the called party\u2019s telephone number. The central office stores the entered number, translates the number into an equipment location and a path to that location, and tests whether the called party\u2019s line is already in use (or \u201cbusy\u201d). The called party\u2019s number may lie in the same central office (in which case the call is\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/designated\" data-term=\"designated\" data-type=\"EB\">designated<\/a>\u00a0<span id=\"ref1117745\"><\/span>intraoffice), or it may lie in another central office (requiring an\u00a0<span id=\"ref1117744\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/interoffice-signaling\">interoffice<\/a>\u00a0call). If the call is intraoffice, the central office switch will handle the entire call process. If the call is interoffice, it will be directed either to a nearby central office or to a distant central office via a long-distance network. In the case of interoffice calls, a separate signaling network is employed to coordinate the call progression through a multitude of switches and telephone trunks. Assuming, however, that the call is an intraoffice call, if the called party\u2019s line is busy and does not have call waiting (in which the current call can be suspended), the telephone switch will return a busy signal until the calling party returns to the \u201con-hook\u201d condition. If the called party\u2019s line is not busy or does have call waiting, it will be alerted, or \u201crung.\u201d At the same time that the line is rung, an audible signal will be returned to the calling party to indicate that ringing is taking place. If the called party answers by going off-hook, ringing will be discontinued and a voice path will be established through the switching system to both the calling and called parties. The voice path is maintained until either party goes back on-hook. At that moment the voice path is disconnected, and call charging is recorded.<\/p>\r\n<p class=\"topic-paragraph\">From the example described above, it is evident that telephone systems consist of four major components:<\/p>\r\n<ol>\r\n<li>\r\n<div>Switching, between telephone sets and between trunks, as required.<\/div>\r\n<\/li>\r\n<li>\r\n<div>Signaling, between the telephone sets and the central offices as well as between central offices when needed.<\/div>\r\n<\/li>\r\n<li>\r\n<div><a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/Transmission\" data-term=\"Transmission\" data-type=\"EB\">Transmission<\/a>, between the central switching office and subscribers\u2019 telephone sets and also between central offices.<\/div>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"topic-paragraph\">Each of these major components of a telephone system is discussed in turn in this section.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279911\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref1117746\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">Switching<\/a><\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279912\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Switching systems<\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76187\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117747\"><\/span>Manual switching<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120260\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/44\/119544-050-CCD58608\/switchboard-city-American-1900.jpg\" data-href=\"\/media\/1\/585993\/120260\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/44\/119544-050-CCD58608\/switchboard-city-American-1900.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/44\/119544-050-CCD58608\/switchboard-city-American-1900.jpg?w=300\" alt=\"manual central switchboard\" data-width=\"1600\" data-height=\"1089\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/44\/119544-050-CCD58608\/switchboard-city-American-1900.jpg\" data-href=\"\/media\/1\/585993\/120260\">manual central switchboard<\/a>A manual central switchboard in an American city,\u00a0<em>c.<\/em>\u00a01900.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">From the earliest days of the telephone, it was observed that it was more practical to connect different telephone instruments by running wires from each instrument to a central switching point, or\u00a0<span id=\"ref1117748\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/central-office\">telephone exchange<\/a>, than it was to run wires between all the instruments. In 1878 the first telephone exchange was installed in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/New-Haven-Connecticut\" data-show-preview=\"true\">New Haven<\/a>, Connecticut, permitting up to 21 customers to reach one another by means of a manually operated central\u00a0<span id=\"ref1117749\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/switchboard\">switchboard<\/a>. The manual switchboard was quickly extended from 21 lines to hundreds of lines. Each line was\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/terminated\" data-term=\"terminated\" data-type=\"EB\">terminated<\/a>\u00a0on the switchboard in a socket (called a jack), and a number of short, flexible circuits (called cords) with a plug on both ends of each cord were also provided. Two lines could thus be interconnected by inserting the two ends of a cord in the appropriate jacks.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279913\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117750\"><\/span>Electromechanical switching<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120851\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/15\/60515-050-D8832FA9\/telephone-switching-system.jpg\" data-href=\"\/media\/1\/585993\/120851\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/15\/60515-050-D8832FA9\/telephone-switching-system.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/15\/60515-050-D8832FA9\/telephone-switching-system.jpg?w=300\" alt=\"crossbar-type electromechanical telephone switching system\" data-width=\"1600\" data-height=\"1287\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/15\/60515-050-D8832FA9\/telephone-switching-system.jpg\" data-href=\"\/media\/1\/585993\/120851\">crossbar-type electromechanical telephone switching system<\/a>A crossbar-type electromechanical telephone switching system from the 1960s.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The idea of\u00a0<span id=\"ref1117751\"><\/span>automatic switching appeared as early as 1879, and the first fully automatic switch to achieve commercial success was invented in 1889 by Almon B. Strowger, the owner of an undertaking business in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Kansas-City-Missouri\" data-show-preview=\"true\">Kansas City<\/a>, Missouri. The\u00a0<span id=\"ref1117752\"><\/span>Strowger switch consisted of essentially two parts: an array of 100 terminals, called the bank, that were arranged 10 rows high and 10 columns wide in a cylindrical arc; and a movable switch, called the brush, which was moved up and down the cylinder by one\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/ratchet\" data-term=\"ratchet\" data-type=\"EB\">ratchet<\/a>\u00a0mechanism and rotated around the arc by another, so that it could be brought to the position of any of the 100 terminals. The ratcheting action on the brush gave Strowger\u2019s\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/invention-technology\" data-show-preview=\"true\">invention<\/a>\u00a0the common name\u00a0<em>step-by-step switch<\/em>. The stepping movement was controlled directly by pulses from the telephone instrument. In the original systems, the caller generated the pulses by rapidly pushing a button switch on the instrument. Later, in 1896, Strowger\u2019s associates devised a rotary dial for generating the necessary pulses. (The rotary dialing system is described below in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\/Dialer#ref279897\" data-show-preview=\"true\">Rotary dialing<\/a>.)<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">In 1913\u00a0<span id=\"ref1117753\"><\/span>J.N. Reynolds, an engineer with\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/Western-Electric-Company-Inc\" data-show-preview=\"true\">Western Electric<\/a>\u00a0(at that time the manufacturing division of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>),\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/patented\" data-term=\"patented\" data-type=\"EB\">patented<\/a>\u00a0a new type of telephone switch that became known as the\u00a0<span id=\"ref1117754\"><\/span>crossbar switch. The crossbar switch was a grid composed of five horizontal selecting bars and 20 vertical hold bars. Input lines were connected to the hold bars and output lines to the selecting bars.<\/p>\r\n<p class=\"topic-paragraph\">The five selecting bars could be rotated either upward or downward to make connections with the hold bars, thus effectively providing the switch with 10 horizontal rows. With the appropriate movement of the hold and selecting bars, any column could be connected to any row, and up to 10 simultaneous connections could be provided by the switch. The first\u00a0<span id=\"ref1117755\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/crossbar-switching-system\">crossbar system<\/a>\u00a0was demonstrated by Televerket, the Swedish government-owned telephone company, in 1919. The first commercially successful system, however, was the AT&amp;T\u00a0<span id=\"ref1117756\"><\/span>No. 1 crossbar system, first installed in Brooklyn, N.Y., in 1938. A series of improved versions followed the No. 1 crossbar system, the most notable being the No. 5 system. First\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>\u00a0in 1948, the No. 5 crossbar system became the workhorse of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Bell-System\" data-show-preview=\"true\">Bell System<\/a>\u00a0and by 1978 accounted for the largest number of installed lines throughout the world. Originally designed to serve 27,000 lines, it was later upgraded to handle 35,000 voice circuits. Further revisions of the AT&amp;T crossbar systems continued until 1974, by which time new switching systems had shifted from electromechanical to electronic\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/technology\" data-show-preview=\"true\">technology<\/a>.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"5\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"2\">\r\n<section data-level=\"3\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279914\" data-level=\"4\" data-has-spy=\"true\">\r\n<h1 class=\"h4\"><span id=\"ref1117757\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/electronic-switching\">Electronic switching<\/a><\/h1>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120852\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/14\/60514-050-E004020D\/ATT-No-5-ESS-switching-system.jpg\" data-href=\"\/media\/1\/585993\/120852\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/14\/60514-050-E004020D\/ATT-No-5-ESS-switching-system.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/14\/60514-050-E004020D\/ATT-No-5-ESS-switching-system.jpg?w=300\" alt=\"AT&amp;T No. 5 ESS\" data-width=\"1600\" data-height=\"1290\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/14\/60514-050-E004020D\/ATT-No-5-ESS-switching-system.jpg\" data-href=\"\/media\/1\/585993\/120852\">AT&amp;T No. 5 ESS<\/a>The AT&amp;T No. 5 ESS, an electronic switching system from the 1980s.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">As telephone traffic continued to grow through the years, it was realized that large numbers of common control\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/circuits\" data-term=\"circuits\" data-type=\"EB\">circuits<\/a>\u00a0would be required to switch this traffic and that switches of larger capacity would have to be created to handle it. Plans to provide new services via the telephone network also created a demand for innovative switch designs. With the advent of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transistor\" data-show-preview=\"true\">transistor<\/a>\u00a0in 1947 and with subsequent advances in memory devices as well as other electronic devices and switches, it became possible to design a telephone switch that was based fundamentally on electronic components rather than on electromechanical switches.<\/p>\r\n<p class=\"topic-paragraph\">Between 1960 and 1962\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>\u00a0conducted field trials of a new\u00a0<span id=\"ref1117758\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/attending\">electronic switching system<\/a>\u00a0(ESS) that would employ a variety of devices and concepts. The first commercial version, placed in service in 1965, became known as the\u00a0<span id=\"ref1117759\"><\/span>No. 1 ESS. The No. 1 ESS employed a special type of reed switch known as a\u00a0<span id=\"ref1117760\"><\/span>ferreed. Normally, a reed switch is constructed of two thin metal strips, or reeds, which are sealed in a glass tube. When an electromagnetic coil surrounding the tube is energized, the reeds close, making an electrical contact. In a ferreed a magnetic alloy known as\u00a0<span id=\"ref1117761\"><\/span>Remendur is added to two sides of the reed relay. When the coil is energized, the Remendur material retains the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/magnetism\" data-show-preview=\"true\">magnetism<\/a>\u00a0and polarity, thus acting as a switch with a memory. In addition to this new switch device, the No. 1 ESS incorporated a new read-only memory device and a new\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/RAM-computing\" data-show-preview=\"true\">random-access memory<\/a>\u00a0device. These\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/innovations\" data-term=\"innovations\" data-type=\"MW\">innovations<\/a>\u00a0allowed the No. 1 system to serve as many as 65,000 two-way voice circuits, and it permitted hundreds of new features to be handled by the switching equipment. It underwent a number of revisions, including the adoption of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/semiconductor-memory\" data-show-preview=\"true\">semiconductor memory<\/a>\u00a0in 1977.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279915\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">Digital switching<\/h2>\r\n<p class=\"topic-paragraph\">All the automatic telephone switches, both electromechanical and electronic, discussed up to this point are classified as\u00a0<span id=\"ref1117762\"><\/span>space-division switches. Space-division switches are characterized by the fact that the speech path through a telephone switch is continuous throughout the exchange. That speech path is a metallic circuit, in the sense that it is provided entirely through the metallic contacts of the switch. Other forms of switching, however, are made possible by converting the fluctuating electric signal transmitted by the telephone instrument into digital format. In one of the first digital systems, known as\u00a0<span id=\"ref1117763\"><\/span>time-division switching, the digitized speech information is sliced into a sequence of time intervals, or slots. Additional voice circuit slots, corresponding to other users, are inserted into this bit stream of data, in effect achieving a \u201ctime multiplexing\u201d of several voice circuits. Switching essentially consists of interchanging the time position of one user\u2019s slot with that of another user in a determined manner. Time-division switches may also employ space-division switching; an appropriate mixture of time-division and space-division switching is advantageous in various circumstances.<\/p>\r\n<p class=\"topic-paragraph\">The first time-division switching system to be\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>\u00a0in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>\u00a0was the AT&amp;T-designed\u00a0<span id=\"ref1117764\"><\/span>No. 4 ESS, placed into service in 1976. The No. 4 ESS was a toll system capable of serving a maximum of 53,760 two-way trunk circuits. It was soon followed by several other time-division systems for switching local calls. Among these was the AT&amp;T\u00a0<span id=\"ref1117765\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Number-5-electronic-switching-system\">No. 5 ESS<\/a>, improved versions of which could handle 100,000 lines.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279916\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">The switching network<\/h2>\r\n<p class=\"topic-paragraph\">As the telephone network evolved, it became necessary to organize it into a hierarchical system that would permit any customer to call any other customer. In order to support such an organization,\u00a0<span id=\"ref1117766\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/switching-centre\">switching centres<\/a>\u00a0in the American telephone system were organized into three classes: local,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/tandem\" data-term=\"tandem\" data-type=\"EB\">tandem<\/a>, and toll. A local office (or\u00a0<span id=\"ref1117767\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/central-office\">end office<\/a>) was a switching centre that connected directly to the customers\u2019 telephone instruments. A\u00a0<span id=\"ref1117768\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/tandem-office\">tandem office<\/a>\u00a0was one that served a cluster of local offices. A<span id=\"ref1117769\"><\/span>toll office was involved in switching traffic over long-distance (or toll) circuits.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">During the 1990s the telephone network significantly changed, because of a combination of several trends: an increased amount of traffic due to new telephone subscribers and to use of the telephone network to access the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Internet\" data-show-preview=\"true\">Internet<\/a>; the advent of new \u201cpacket-switching\u201d techniques (described below); new\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/protocols\" data-term=\"protocols\" data-type=\"MW\">protocols<\/a>\u00a0for voice traffic over data networks; and the availability of a tremendous amount of bandwidth in the long-distance network. As a result of these developments, the hierarchical telephone network of the 1950s and \u201960s collapsed to mostly two levels of switching. End offices are now known as class 5 offices and are owned by the local service operators, or \u201clocal exchange carriers.\u201d The old toll and tandem offices are now known as class 4 offices; they are owned by long-distance service providers, or \u201cinterexchange carriers.\u201d Even this distinction between local and long-distance providers, however, became less clear with continued deregulation of the telephone industry.<\/p>\r\n<p class=\"topic-paragraph\">While much telephone voice traffic continues to flow through the class 5 and class 4 switches, several\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/alternatives\" data-term=\"alternatives\" data-type=\"MW\">alternatives<\/a>\u00a0have arisen for switching voice traffic through the telephone network. For instance, by digitizing, compressing, and packetizing voice signals, telephone traffic can be sent over conventional packet-switched data\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\" data-show-preview=\"true\">networks<\/a>\u00a0instead of dedicated circuits. Several approaches to\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/packet-switched-network\" data-show-preview=\"true\">packet switching<\/a>\u00a0are possible, based on whether variable-length or fixed-length packets are used. When variable-length packets are used and Internet\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/protocol\" data-term=\"protocol\" data-type=\"MW\">protocol<\/a>\u00a0(IP) is the underlying protocol for the data network, the mechanism is called \u201cvoice over IP\u201d (<span id=\"ref1117849\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/VoIP\" data-show-preview=\"true\">VoIP<\/a>). In such a configuration, voice traffic is switched over the Internet using a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/router-tool\" data-show-preview=\"true\">router<\/a>, a device consisting of input and output ports from the network, a switching fabric to switch between input and output, and a processor to execute the routing protocols and perform network management. When the digitized voice signal is packed into fixed-length packets and sent over an asynchronous transfer mode (ATM) network, the method is known as \u201cvoice over ATM\u201d (VoATM). Within the network, ATM switches direct packets from source to destination.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"6\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279917\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\">Signaling<\/h1>\r\n<p class=\"topic-paragraph\">A major component of any telephone system is signaling, in which electric pulses or audible tones are used for alerting (requesting service), addressing (e.g., dialing the called party\u2019s number at the subscriber set), supervision (monitoring\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/idle\" data-term=\"idle\" data-type=\"EB\">idle<\/a>\u00a0lines), and information (providing dial tones, busy signals, and recordings).<\/p>\r\n<p class=\"topic-paragraph\">In general, signaling may occur either within the subscriber loop\u2014that is, within the circuit between the individual telephone instrument and the local office\u2014or in circuits between offices.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279918\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref1117770\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/call-number-dialing\">Call-number dialing<\/a><\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279919\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117771\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/rotary-dialing\">Rotary dialing<\/a><\/h2>\r\n<p class=\"topic-paragraph\">The first automatic switching systems, based on the Strowger switch described in the section\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\/The-telephone-network#ref279913\" data-show-preview=\"true\">Electromechanical switching<\/a>, were activated by a push button on the calling party\u2019s telephone. More accurate call dialing was permitted by the advent of the rotary dial in 1896. A number of different dial designs were placed in service until 1910, when designs were standardized, and after 1910 the design and operation of the rotary dial did not change in its essentials.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"19586\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/31\/24331-050-1F98EE01\/methods-call-number-rotary-dial-tone-dialing-series-telephone-telephony.jpg\" data-href=\"\/media\/1\/585993\/19586\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/31\/24331-050-1F98EE01\/methods-call-number-rotary-dial-tone-dialing-series-telephone-telephony.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/31\/24331-050-1F98EE01\/methods-call-number-rotary-dial-tone-dialing-series-telephone-telephony.jpg?w=300\" alt=\"On the left, a hand dials a number on a green rotary phone above a graph showing pulses (interruptions in DC current) that represent the phone being dialed. On the right, a hand presses a button on a red tone-dial phone above a representation of a push-button pad showing frequencies corresponding to each button.\" data-width=\"1600\" data-height=\"831\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/31\/24331-050-1F98EE01\/methods-call-number-rotary-dial-tone-dialing-series-telephone-telephony.jpg\" data-href=\"\/media\/1\/585993\/19586\">Two methods of call-number signaling in a telephone system<\/a>A major component of any telephone system is signaling. (Left) For telephones with a rotary dial, the design of which became standardized in 1910, each digit is signaled by a corresponding series of pulses, or interruptions, in a direct-current connection between the user&#8217;s telephone and the local switching office. (Right) In telephones with a push-button pad, each digit is signaled by a \u201cdual tone,\u201d which is made up of two frequencies that correspond to the button&#8217;s location on the keypad. This type of signaling, which became a worldwide standard starting in the 1960s, is also referred to as tone dialing.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In a rotary dial, a number of pulses, or interruptions in current flow, are\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmitted\" data-term=\"transmitted\" data-type=\"EB\">transmitted<\/a>\u00a0to the switching office in proportion to the rotation of the dial. When the dial is rotated, a spring is wound, and when the dial is subsequently released, the spring causes the dial to rotate back to its original position. Inside the dial a governor device ensures a constant rate of return rotation, and a shaft on the governor turns a cam that opens and closes a switch contact. An open switch contact stops current from flowing into the telephone set, thereby creating a dial pulse. Each dial pulse corresponds to one additional digit\u2014i.e., two pulses correspond to the digit 2, three pulses correspond to the digit 3.<\/p>\r\n<p class=\"topic-paragraph\">The rotary dial was designed for operating an electromechanical switching system, so that the speed of operation of the dial was limited by the operating speed of the switches. Within the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/Bell-System\" data-show-preview=\"true\">Bell System<\/a>\u00a0the dial pulse period is nominally one-tenth of a second long, permitting a rate of 10 pulses per second. Modern telephones are now wired for push-button dialing (<em>see below<\/em>), but even they can usually generate pulse signals when the push-button pad is operated in\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/conjunction\" data-term=\"conjunction\" data-type=\"EB\">conjunction<\/a>\u00a0with electronic timing circuits.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279920\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117772\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/push-button-dialing\">Push-button dialing<\/a><\/h2>\r\n<p class=\"topic-paragraph\">In the 1950s, after conducting extensive studies,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>\u00a0concluded that push-button dialing was about twice as efficient as rotary dialing. Trials had already been conducted of special telephone instruments that incorporated mechanically vibrating reeds, but in 1963 an electronic push-button system, known as\u00a0<span id=\"ref1117773\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Touch-Tone-dialing-system\">Touch-Tone dialing<\/a>, was offered to AT&amp;T customers. Touch-Tone soon became the standard U.S. dialing system, and eventually it became the standard worldwide.<\/p>\r\n<p class=\"topic-paragraph\">The Touch-Tone system is based on a concept known as\u00a0<span id=\"ref1117774\"><\/span>dual-tone multifrequency (DTMF). The 10 dialing digits (0 through 9) are assigned to specific push buttons, and the buttons are arranged in a grid with four rows and three columns. The pad also has two more buttons,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/bearing\" data-term=\"bearing\" data-type=\"EB\">bearing<\/a>\u00a0the\u00a0<span id=\"ref1117775\"><\/span>star (*) and\u00a0<span id=\"ref1117776\"><\/span>pound (#) symbols, to accommodate various data services and customer-controlled calling features. Each of the rows and columns is assigned a tone of a specific\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>, the columns having higher-frequency tones and the rows having tones of lower frequency. When a button is pushed, a dual-tone signal is generated that corresponds to the frequencies assigned to the column and row that intersect at that point. This\u00a0<span id=\"ref1117778\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/signal\">signal<\/a>\u00a0is translated into a digit at the local office.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279921\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref1117779\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/interoffice-signaling\">Interoffice signaling<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Interoffice signaling also has undergone a notable evolution, changing over from simple \u201cin-band\u201d methods to fully digitized \u201cout-of-band\u201d methods.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279922\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117780\"><\/span>In-band signaling<\/h2>\r\n<p class=\"topic-paragraph\">In the earliest days of the telephone network, signaling was provided by means of\u00a0<span id=\"ref1117781\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/direct-current\" data-show-preview=\"true\">direct current<\/a>\u00a0(DC) between the telephone instrument and the operator. As long-distance\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/circuits\" data-term=\"circuits\" data-type=\"EB\">circuits<\/a>\u00a0and automatic switching systems were placed into service, the use of DC became obsolete, since long-distance circuits could not pass the DC signals. Hence,\u00a0<span id=\"ref1117782\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/alternating-current\" data-show-preview=\"true\">alternating current<\/a>\u00a0(AC) began to be used over interoffice circuits. Until the mid-1970s, interoffice circuits employed what has become known as in-band signaling, in which the same circuits that were used to connect two telephone instruments and serve as the voice path were also used to transmit the AC signals that set up the switches employed in the circuit.\u00a0<span id=\"ref1117783\"><\/span>Single-frequency tones were used in the switching network to signal availability of a trunk. Once a trunk line became available,\u00a0<span id=\"ref1117784\"><\/span>multiple-frequency tones were used to pass the address information between switches. Multiple-frequency signaling employed pairs of six tones, similar to the signaling used in Touch-Tone dialing.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279923\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117785\"><\/span>Out-of-band signaling<\/h2>\r\n<p class=\"topic-paragraph\">Despite the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/simplicity\" data-term=\"simplicity\" data-type=\"EB\">simplicity<\/a>\u00a0of the in-band method, this type of signaling presented a number of problems. First, because the in-band signals by necessity fell within the bandwidth of speech signals, speech signals could at times interfere with the in-band signals. Second, in-band signaling did not always make efficient use of the available telephone circuits. For example, if a called party\u2019s telephone instrument was in use, the called party\u2019s central office would generate a busy signal that was carried by the already established voice path through the public switched telephone network to the calling party\u2019s handset. Hence, a full voice-circuit path through the network would be tied up merely to convey a busy signal.<\/p>\r\n<p class=\"topic-paragraph\">In order to overcome these issues and to speed the call set-up process in long-distance calls, another form of interoffice signaling, known as\u00a0<span id=\"ref1117786\"><\/span>common channel signaling (CCS), was developed. In CCS an \u201cout-of-band\u201d circuit (that is, a separate circuit from that used to establish the voice connection) is dedicated to serve as a data link, carrying address information and certain other information signals between the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/microprocessor\" data-show-preview=\"true\">microprocessors<\/a>\u00a0employed in telephone switches. The first version of CCS was developed between 1964 and 1968 by the\u00a0<span id=\"ref1117787\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/International-Telegraph-and-Telephone-Consultative-Committee\">International Telegraph and Telephone Consultative Committee<\/a>\u00a0(CCITT), a predecessor of the Telecommunication Standardization Sector of the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/International-Telecommunication-Union\" data-show-preview=\"true\">International Telecommunication Union<\/a>. The first system was standardized internationally as\u00a0<span id=\"ref1117788\"><\/span>CCITT-6 signaling; within\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/North-America\" data-show-preview=\"true\">North America<\/a>, CCITT-6 was modified by AT&amp;T and became known as\u00a0<span id=\"ref1117789\"><\/span>common channel interoffice signaling, CCIS. CCIS was first installed in the Bell System in 1976.<\/p>\r\n<p class=\"topic-paragraph\">Although CCITT-6 was standardized by an international body, it was never universally\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>. Recognizing this shortcoming as well as the still-growing amount of international traffic within the worldwide telephone network, the CCITT between 1980 and 1991 developed a successor version known as CCITT-7. Within North America, CCITT-7 was\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implemented\" data-term=\"implemented\" data-type=\"MW\">implemented<\/a>\u00a0as\u00a0<span id=\"ref1117790\"><\/span>Signaling System 7, or SS7.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"7\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279924\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\"><span id=\"ref1117791\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transmission-communications\">Transmission<\/a><\/h1>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279925\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Development of\u00a0<span id=\"ref1117792\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/long-distance-transmission\">long-distance transmission<\/a><\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279926\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">From single-wire to two-wire circuits<\/h2>\r\n<p class=\"topic-paragraph\">The first telephone lines employed the same type of outdoor circuits as\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telegraph\" data-show-preview=\"true\">telegraph<\/a>\u00a0lines\u2014namely, a single noninsulated iron or steel wire supported by wooden poles with glass insulators. Since electric signals require two wires, the second \u201cwire\u201d was a ground return through the earth. Unfortunately, the use of a single wire made the telephone circuit extremely susceptible to interference by other signals. This problem was addressed by the use of a\u00a0<span id=\"ref1117793\"><\/span>two-wire, or \u201cmetallic,\u201d circuit; the first demonstration of such a system occurred in 1881 on a telephone line between\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Providence-Rhode-Island\" data-show-preview=\"true\">Providence<\/a>, Rhode Island, and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Boston\" data-show-preview=\"true\">Boston<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">As the distances between telephone instruments began to increase beyond those served by local exchange offices, a number of technical problems arose that had not been experienced in earlier telegraph systems. Even with the two-wire system, it soon became apparent that telephone signals could be\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmitted\" data-term=\"transmitted\" data-type=\"EB\">transmitted<\/a>\u00a0only a fraction of the distance of telegraph signals, because of the greater attenuation in iron and steel of the higher frequencies of telephone signals. The principal difference between telegraph systems and the telephone system was that the frequencies of the signals carried by telephone lines were as much as 30 times greater than those of telegraph signals. Several individuals noted that\u00a0<span id=\"ref1117794\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/copper\" data-show-preview=\"true\">copper<\/a>\u00a0wire greatly improved the situation, but manufacturing techniques produced brittle wire that was not self-supporting over the spans between poles. The problem was solved in 1877 with the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/invention-technology\" data-show-preview=\"true\">invention<\/a>\u00a0of hard-drawn copper wire. In 1884 the first test of hard-drawn copper wire for long-distance telephone service was conducted between\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/New-York-City\" data-show-preview=\"true\">New York City<\/a>\u00a0and Boston.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279927\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">Problems of interference and attenuation<\/h2>\r\n<p class=\"topic-paragraph\">Two-wire copper circuits did not solve all the problems of long-distance telephony, however. As the number of lines grew, interference (or cross talk) from\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/adjacent\" data-term=\"adjacent\" data-type=\"MW\">adjacent<\/a>\u00a0lines on the same crossarm of the telephone pole became significant. It was found that transposing the wires by twisting them at specified intervals canceled the cross talk. Another major problem was caused by distance: over the lengths of long-distance lines, even the two-wire copper circuit\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/attenuated\" data-term=\"attenuated\" data-type=\"MW\">attenuated<\/a>\u00a0the telephone signal significantly. In a series of theoretical papers published in book form in 1892,\u00a0<span id=\"ref1117795\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Oliver-Heaviside\" data-show-preview=\"true\">Oliver Heaviside<\/a>, an English physicist, developed the theory behind the transmission of signals over two-wire circuits. In the United States,\u00a0<span id=\"ref1117796\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Mihajlo-Pupin\" data-show-preview=\"true\">Michael I. Pupin<\/a>\u00a0of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Columbia-University\" data-show-preview=\"true\">Columbia University<\/a>\u00a0in New York City and\u00a0<span id=\"ref1117797\"><\/span>George A. Campbell of\u00a0<span id=\"ref1117798\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>\u00a0both read Heaviside\u2019s papers and realized that introducing inductive coils (<span id=\"ref1117799\"><\/span>loading coils) at regular intervals along the length of the telephone line could significantly reduce the attenuation of signals within the voice band (i.e., at frequencies less than 3.5 kilohertz). Both Campbell and Pupin applied for a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/patent\" data-show-preview=\"true\">patent<\/a>\u00a0on the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/concept\" data-term=\"concept\" data-type=\"EB\">concept<\/a>\u00a0of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/loading-communications\" data-show-preview=\"true\">loading<\/a>\u00a0coils; after extended patent interference proceedings, the patent was finally awarded to Pupin in 1904. The first long-distance application of loading coils occurred in 1900, over a 40-km (24-mile) circuit in Boston. It was followed later that year by a test over a 1,000-km (600-mile) circuit. By 1925 approximately 1.25 million loading coils were in use over 3 million km (1.8 million miles) of wire circuits.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"193928\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/13\/181413-050-3A6FF109\/Map-call-telephone-line-details-place-January-25-1915.jpg\" data-href=\"\/media\/1\/585993\/193928\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/13\/181413-050-3A6FF109\/Map-call-telephone-line-details-place-January-25-1915.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/13\/181413-050-3A6FF109\/Map-call-telephone-line-details-place-January-25-1915.jpg?w=300\" alt=\"first transcontinental telephone line\" data-width=\"1600\" data-height=\"1493\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/13\/181413-050-3A6FF109\/Map-call-telephone-line-details-place-January-25-1915.jpg\" data-href=\"\/media\/1\/585993\/193928\">first transcontinental telephone line<\/a>Map of the first transcontinental telephone line with details of the first transcontinental call, which took place on January 25, 1915.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Even with the use of loading coils, telephone\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0across countries as large as the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>\u00a0was not possible without some form of amplification. A mechanical\u00a0<span id=\"ref1117800\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/amplifier\" data-show-preview=\"true\">amplifier<\/a>, which made use of an\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/electromagnet\" data-show-preview=\"true\">electromagnet<\/a>\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>\u00a0and a carbon transmitter, was installed in a commercial\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/circuit\" data-term=\"circuit\" data-type=\"EB\">circuit<\/a>\u00a0between New York City and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Chicago\" data-show-preview=\"true\">Chicago<\/a>\u00a0in 1904, but it was not until the patenting of the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/electron-tube\" data-show-preview=\"true\">vacuum tube<\/a>\u00a0by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Lee-de-Forest\" data-show-preview=\"true\">Lee de Forest<\/a>\u00a0in 1907 that truly transcontinental telephone communication was possible. In 1915 the first transcontinental line, between New York City and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/San-Francisco-California\" data-show-preview=\"true\">San Francisco<\/a>, was placed in service. Although this system was commercially viable, its cost and limited capacity (only one two-way circuit) prevented substantial growth of transcontinental telephony until\u00a0<span id=\"ref1117801\"><\/span>carrier multiplexing techniques were introduced beginning in 1918. With carrier\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/multiplexing\" data-show-preview=\"true\">multiplexing<\/a>, four or more two-way voice channels could be transmitted simultaneously over two-wire or four-wire circuits. By 1927 more than 5 million km (3 million miles) of long-distance circuits covered the entire United States\u2014more than 10 times the circuitry present in 1900.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"8\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"3\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279928\" data-level=\"4\" data-has-spy=\"true\">\r\n<h1 class=\"h4\">From analog to digital transmission<\/h1>\r\n<p class=\"topic-paragraph\">Until the early 1980s the bulk of long-distance transmission was provided by\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0systems in which individual telephone conversations were stacked in four-kilohertz intervals across the transmission band\u2014a process known as\u00a0<span id=\"ref1117803\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-division-multiplexing\">frequency-division multiplexing\u00a0<\/a>(FDM). However, particularly with the development of fibre optics (<em>see below<\/em>), these\u00a0<span id=\"ref1117802\"><\/span>analog systems were rapidly replaced by digital systems. In\u00a0<span id=\"ref1117804\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/digital-transmission\">digital transmission<\/a>, which may also be carried over the coaxial and microwave systems, the telephone signals are first converted from an analog format to a quantized, discrete time format. The signals are then multiplexed together using\u00a0<span id=\"ref1117805\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/time-division-multiplexing\">time-division multiplexing<\/a>\u00a0(TDM), a method in which each digitized telephone signal is assigned a specific slot within a fixed time frame. In order to provide standard interfaces between transmission and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">switching<\/a>\u00a0equipment, multiplexed signals are further combined or\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/aggregated\" data-term=\"aggregated\" data-type=\"MW\">aggregated<\/a>\u00a0in hierarchical arrangements.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279929\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117806\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/coaxial-cable\" data-show-preview=\"true\">Coaxial cable<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"3695\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/20\/4620-050-85C12A49\/transmission-media-Cutaway-drawings-cable-fields-direction.jpg\" data-href=\"\/media\/1\/585993\/3695\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/20\/4620-050-85C12A49\/transmission-media-Cutaway-drawings-cable-fields-direction.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/20\/4620-050-85C12A49\/transmission-media-Cutaway-drawings-cable-fields-direction.jpg?w=300\" alt=\"cutaway drawings of multipair and coaxial cables\" data-width=\"1600\" data-height=\"807\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/20\/4620-050-85C12A49\/transmission-media-Cutaway-drawings-cable-fields-direction.jpg\" data-href=\"\/media\/1\/585993\/3695\">cutaway drawings of multipair and coaxial cables<\/a>Wire transmission mediaCutaway drawings of (top) multipair cable and (bottom) coaxial cable, showing direction of current flow and propagation of electric and magnetic fields.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Long-distance coaxial cable systems were introduced in the United States in 1946. Employing analog FDM methods, the first coaxial system could support 1,800 two-way voice circuits by bundling together three working pairs of cable, each pair transmitting 600 voice signals simultaneously. In the last analog coaxial system,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>\u00a0in 1978, each pair of cables transmitted 13,200 voice signals, and the cable bundle contained 10 working pairs; this combination supported 132,000 two-way voice circuits. Digital coaxial systems were introduced into the U.S. long-distance network beginning in 1962. TDM, a digital cable system first deployed in 1975, can support up to 40,320 two-way voice circuits over 10 working pairs of coaxial cable.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279930\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">Microwave link<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"138682\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/24\/4624-050-D2CAB6B1\/Radio-wave-dish-type-antennas-diameter-satellite-communications.jpg\" data-href=\"\/media\/1\/585993\/138682\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/24\/4624-050-D2CAB6B1\/Radio-wave-dish-type-antennas-diameter-satellite-communications.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/24\/4624-050-D2CAB6B1\/Radio-wave-dish-type-antennas-diameter-satellite-communications.jpg?w=300\" alt=\"radio wave dish-type antennas\" data-width=\"1225\" data-height=\"815\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/24\/4624-050-D2CAB6B1\/Radio-wave-dish-type-antennas-diameter-satellite-communications.jpg\" data-href=\"\/media\/1\/585993\/138682\">radio wave dish-type antennas<\/a>Radio wave dish-type antennas, varying in diameter from 8 to 30 metres (26 to 98 feet), serving an Earth station in a satellite communications network.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Long-distance transmission also has been provided by radio link in the form of\u00a0<span id=\"ref1117807\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/point-to-point-microwave-transmission\">point-to-point microwave<\/a>\u00a0systems. First employed in 1950,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/microwave-radiation\" data-show-preview=\"true\">microwave<\/a>\u00a0transmission has the advantage of not requiring access to all\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/contiguous\" data-term=\"contiguous\" data-type=\"MW\">contiguous<\/a>\u00a0land along the path of the system. Because microwave systems are line-of-sight media, radio towers must be spaced approximately every 42 km (25 miles) along the route. Point-to-point microwave systems generally operate in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0ranges of 3.7\u20134.2 gigahertz or 5.925\u20136.425 gigahertz; some systems operate at 11 or 18 gigahertz. Following the trend of coaxial cable systems, the first microwave links were analog systems. Early systems had a capacity of 2,400 two-way voice circuits, and later systems could support 61,800 two-way circuits. Beginning in 1981, digital microwave systems began to be deployed in the U.S. system that could support the wide range of digital services available over the PSTN.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279931\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117808\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/optical-fiber\">Optical-fibre<\/a>\u00a0cable<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120550\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/35\/24335-050-5A3036BC\/Cutaway-drawing-optical-fibre-cable-sheathing-types.jpg\" data-href=\"\/media\/1\/585993\/120550\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/35\/24335-050-5A3036BC\/Cutaway-drawing-optical-fibre-cable-sheathing-types.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/35\/24335-050-5A3036BC\/Cutaway-drawing-optical-fibre-cable-sheathing-types.jpg?w=300\" alt=\"optical fibres\" data-width=\"1600\" data-height=\"819\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/35\/24335-050-5A3036BC\/Cutaway-drawing-optical-fibre-cable-sheathing-types.jpg\" data-href=\"\/media\/1\/585993\/120550\">optical fibres<\/a>(Left) Cutaway drawing of an optical fibre cable, showing bundled fibres and protective sheathing; (right) schematic drawing of three types of optical fibres, showing propagation of light rays and refractive indexes.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Because of their great\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>, reliability, and low cost, optical fibres became the preferred medium in both short-haul and long-haul\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmission\" data-term=\"transmission\" data-type=\"EB\">transmission<\/a>\u00a0systems following their first deployment in 1979. Since 1990 there has been significant progress in the development of\u00a0<span id=\"ref1117809\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/fiber-optics\" data-show-preview=\"true\">fibre optics<\/a>, permitting transmission at ever higher data rates. Several different technologies have been essential in this development: so-called nonzero-dispersion optical fibres, which permit the transmission of multiple wavelengths of light at high data rates;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/erbium\" data-show-preview=\"true\">erbium<\/a>-doped fibre amplifiers, which use a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/laser\" data-show-preview=\"true\">laser<\/a>\u00a0pump source to amplify optical signals over long distances; and \u201ctunable\u201d lasers, which generate light at several frequencies, thereby permitting transmission of multiple\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/wavelength\" data-show-preview=\"true\">wavelengths<\/a>\u00a0over a single optical fibre. Multiple wavelength transmission, known as wave division multiplexing (WDM), allows higher data rates to be achieved over a single fibre; when 40 or more different wavelengths are multiplexed, the technique is known as dense wave division multiplexing (DWDM). DWDM\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/technology\" data-show-preview=\"true\">technology<\/a>\u00a0has permitted\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data transmission<\/a>\u00a0at rates of 400 gigabits per second, each wavelength supporting approximately 10 gigabits per second. These data rates are equivalent to some 6,000,000 voice circuits per fibre and 150,000 voice circuits per wavelength. Long-distance carriers in the developed world make use of optical fibre technology at a variety of data rates. Most systems employ the standardized\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/hierarchy\" data-term=\"hierarchy\" data-type=\"MW\">hierarchy<\/a>\u00a0of digital transmission rates known as the\u00a0<span id=\"ref1117810\"><\/span>synchronous optical network (SONET) or optical carrier (OC) in the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>\u00a0and as the synchronous digital hierarchy (SDH) elsewhere, as shown in the\u00a0<span id=\"ref2605\"><\/span>table.<\/p>\r\n<div class=\"md-drag md-table-wrapper\">\r\n<table summary=\"Standardized digital transmission rates for the synchronous digital hierarchy (SDH), the synchronous optical network (SONET), and the optical carrier (OC) hierarchy\">\r\n<thead>\r\n<tr>\r\n<th colspan=\"5\">Standardized digital transmission rates for the synchronous digital hierarchy (SDH), the synchronous optical network (SONET), and the optical carrier (OC) hierarchy*<\/th>\r\n<\/tr>\r\n<\/thead>\r\n<tfoot>\r\n<tr>\r\n<td colspan=\"5\">*SDH is the transmission hierarchy established by the International Telegraph and Telephone Consultative Committee (CCITT); SONET and OC are transmission hierarchies established by the American National Standards Institute (ANSI).<\/td>\r\n<\/tr>\r\n<\/tfoot>\r\n<tbody>\r\n<tr class=\"table-header\">\r\n<th scope=\"col\">SDH system<\/th>\r\n<th scope=\"col\">SONET system<\/th>\r\n<th scope=\"col\">OC level<\/th>\r\n<th scope=\"col\">transmission rate in megabits per second (Mbps) or gigabits per second (Gbps)<\/th>\r\n<th scope=\"col\">maximum voice channels per circuit<\/th>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"row\">\u00a0<\/th>\r\n<td>STS-1<\/td>\r\n<td>OC-1<\/td>\r\n<td>51.84 Mbps<\/td>\r\n<td>783<\/td>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"row\">STM-1<\/th>\r\n<td>STS-3<\/td>\r\n<td>OC-3<\/td>\r\n<td>155.52 Mbps<\/td>\r\n<td>2,349<\/td>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"row\">STM-4<\/th>\r\n<td>STS-12<\/td>\r\n<td>OC-12<\/td>\r\n<td>622.08 Mbps<\/td>\r\n<td>9,396<\/td>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"row\">\u00a0<\/th>\r\n<td>\u00a0<\/td>\r\n<td>OC-24<\/td>\r\n<td>1,244.16 Mbps<\/td>\r\n<td>18,792<\/td>\r\n<\/tr>\r\n<tr>\r\n<th scope=\"row\">STM-16<\/th>\r\n<td>STS-48<\/td>\r\n<td>OC-48<\/td>\r\n<td>2.4888 Gbps<\/td>\r\n<td>37,584<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"9\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 grey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<section data-level=\"2\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279932\" data-level=\"3\" data-has-spy=\"true\">\r\n<h1 class=\"h3\">Overseas transmission<\/h1>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279933\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\">Terrestrial radio<\/h2>\r\n<p class=\"topic-paragraph\">The extension of telephone service to other countries and continents was a goal set in the earliest days of telephone systems. In\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/North-America\" data-show-preview=\"true\">North America<\/a>, service to\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Canada\" data-show-preview=\"true\">Canada<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Mexico\" data-show-preview=\"true\">Mexico<\/a>\u00a0was a natural extension of the long-distance methods used within the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>, but transmission across the ocean to Europe called for a significant amount of ingenuity. While transatlantic\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telegraph\" data-show-preview=\"true\">telegraph<\/a>\u00a0cables had been in service since 1866, these same cables could not be used for voice\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmission\" data-term=\"transmission\" data-type=\"EB\">transmission<\/a>, because of bandwidth limitations. Instead, the first transatlantic telephone service made use of radio. Regular service via\u00a0<span id=\"ref1117811\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/radio\" data-show-preview=\"true\">radio<\/a>\u00a0between the United States and Europe was first established in 1927 using long-wave frequencies in the range of 58.5 to 61.5 kilohertz. Within the first year this system supported 11,000 calls. By 1929 additional circuits were added in the range of 6\u201325 megahertz.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279934\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117812\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/undersea-cable\" data-show-preview=\"true\">Undersea cable<\/a><\/h2>\r\n<p class=\"topic-paragraph\">It was soon realized that the number of transatlantic telephone calls would rapidly outgrow available radio spectrum. Accordingly, transoceanic cable\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/technology\" data-show-preview=\"true\">technology<\/a>\u00a0was developed that made use of amplifiers or repeaters placed at regular intervals along the length of the cable. Early deployment of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/undersea-cable\" data-show-preview=\"true\">undersea cables<\/a>\u00a0had been accomplished previously in 1921, with a 184-km-long (114-mile-long) cable between\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Cuba\" data-show-preview=\"true\">Cuba<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Key-West\" data-show-preview=\"true\">Key West<\/a>, Florida. The first\u00a0<span id=\"ref1117813\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transatlantic-cable\">transatlantic cable<\/a>\u00a0was laid in 1956 between Canada and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Scotland\" data-show-preview=\"true\">Scotland<\/a>\u2014specifically, between Clarenville,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Newfoundland-and-Labrador\" data-show-preview=\"true\">Newfoundland<\/a>, Canada, and Oban, Scotland, a distance of 3,584 km (2,226 miles). This system made use of two coaxial cables, one for each direction, and used\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0FDM to carry 36 two-way voice circuits. With the availability of the cable system, transatlantic telephone traffic increased dramatically, from 1.7 million calls in 1955 to 3.7 million in 1960. Six additional coaxial cables, representing four successive generations of cable design, were laid across the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Atlantic-Ocean\" data-show-preview=\"true\">Atlantic Ocean<\/a>\u00a0between 1956 and 1983. Each generation of cable system supported a greater number of voice circuits\u2014the last supporting 4,200. In order to improve the voice channel capacity of transoceanic cable systems, a method of voice data reduction known as\u00a0<span id=\"ref1117814\"><\/span>time assignment speech interpolation, or TASI, was introduced. In TASI the natural pauses occurring in speech were used to carry other speech conversations. In this way a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/coaxial-cable\" data-show-preview=\"true\">coaxial cable<\/a>\u00a0system designed for 4,200 two-way voice circuits could support 10,500 circuits.<\/p>\r\n<p class=\"topic-paragraph\">Developments in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/fiber-optics\" data-show-preview=\"true\">fibre optics<\/a>\u00a0also had a significant effect on the deployment of undersea cable. From 1989 to 2001 a total of 15 new transatlantic optical fibre cables were\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>, along with a similar number of transpacific cables. Many other short-segment undersea cables were deployed to connect various countries within a continent. Since 1996 many of these optical cables have employed erbium-doped fibre amplifiers and wave division\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/multiplexing\" data-show-preview=\"true\">multiplexing<\/a>, permitting the highest-quality\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data transmission<\/a>\u00a0at very high rates. One of the more ambitious programs, the TAT-14, deployed in 2001, connects the United States,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/France\" data-show-preview=\"true\">France<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Germany\" data-show-preview=\"true\">Germany<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Denmark\" data-show-preview=\"true\">Denmark<\/a>, and the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/United-Kingdom\" data-show-preview=\"true\">United Kingdom<\/a>\u00a0with a 15,428-km (9,581-mile) undersea cable. As deployed, the cable has four fibre pairs and has a protected capacity of 640 gigabits per second, corresponding to roughly 9.6 million voice circuits. Owing to such capacity, TASI is no longer needed to increase the number of voice circuits over undersea cable.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279935\" data-level=\"4\" data-has-spy=\"true\">\r\n<h2 class=\"h4\"><span id=\"ref1117815\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/satellite-communication\" data-show-preview=\"true\">Satellite<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"59816\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/35\/435-050-7DAECBE7\/communications-satellite-American-Telstar-1-television-signals-July-10-1962.jpg\" data-href=\"\/media\/1\/585993\/59816\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/35\/435-050-7DAECBE7\/communications-satellite-American-Telstar-1-television-signals-July-10-1962.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/35\/435-050-7DAECBE7\/communications-satellite-American-Telstar-1-television-signals-July-10-1962.jpg?w=300\" alt=\"Telstar 1\" data-width=\"615\" data-height=\"1185\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/35\/435-050-7DAECBE7\/communications-satellite-American-Telstar-1-television-signals-July-10-1962.jpg\" data-href=\"\/media\/1\/585993\/59816\">Telstar 1<\/a>American-built Telstar 1 communications satellite, launched July 10, 1962, which relayed the first transatlantic television signals.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">About the same time that transatlantic cables were being installed, another transmission method,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/satellite-communication\" data-show-preview=\"true\">satellite communication<\/a>, was being investigated. In 1962\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>\u00a0in conjunction with the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/NASA\" data-show-preview=\"true\">National Aeronautics and Space Administration<\/a>\u00a0(NASA) launched the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0satellite\u00a0<span id=\"ref1117816\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Telstar-communications-satellite\" data-show-preview=\"true\">Telstar<\/a>\u00a0into an elliptical medium Earth\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/orbit-astronomy\" data-show-preview=\"true\">orbit<\/a>, its\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/apogee\" data-term=\"apogee\" data-type=\"MW\">apogee<\/a>, or farthest distance from Earth, being some 5,600 km (3,500 miles). Telstar 1 served as a repeater in the sky; that is, it simply translated all frequencies within its receiving bandwidth in the six-gigahertz band to frequencies in its four-gigahertz transmitting band. The 32-megahertz transmission bandwidth of Telstar 1 could support one one-way\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/television-technology\" data-show-preview=\"true\">television<\/a>\u00a0signal or multiple two-way telephone conversations.<\/p>\r\n<p class=\"topic-paragraph\">Because of its low orbit, Telstar was not always in view of the communications ground stations. This problem was solved in July 1963 with the launch of the first\u00a0<span id=\"ref1117818\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/geostationary-orbit\" data-show-preview=\"true\">geostationary<\/a>\u00a0communication satellite,\u00a0<span id=\"ref1117819\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Syncom-2\">Syncom 2<\/a>, which followed a circular path some 35,900 km (22,300 miles) above the Earth. Syncom 2 was followed by a series of geostationary satellites, each providing a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/capacity\" data-term=\"capacity\" data-type=\"EB\">capacity<\/a>\u00a0greater than the previous generation. For instance, the Intelsat 11 satellite, launched October 5, 2007, which orbits above the Equator at longitude 43\u00b0 W (just east of Brazil), uses 12 active C-band transponders to relay digital data over most of North and South America and uses 18 Ku-band transponders primarily for relaying television broadcasts in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Brazil\" data-show-preview=\"true\">Brazil<\/a>.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Unfortunately, geostationary satellites, because of their great distance above the Earth, introduce a quarter-second signal delay, sometimes making two-way voice conversation difficult. For this reason, and also because of the availability of high-capacity undersea cables, geostationary satellites are no longer used for common-carrier telephone communication in much of the world. However, since optical-fibre connections are not available everywhere, geostationary satellites continue to be launched to support voice as well as\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>\u00a0traffic.<\/p>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/David-E-Borth\/4163\">David E. Borth<\/a><\/span><\/section>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<div data-page-index=\"10\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded\" data-topic-id=\"1482373\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\">mobile telephone<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<ul class=\"list-unstyled my-0\" data-level=\"h1\">\r\n<li class=\"\" data-target=\"#ref1\">\r\n<div class=\"pl-25\"><a class=\"link-gray-900 w-100\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\">Introduction<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref279849\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone#ref279849\">Cellular telephones<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-active\" data-target=\"#ref279853\">\r\n<div class=\"d-flex align-items-center\">\r\n<div class=\"ml-25\">\u00a0<\/div>\r\n<a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\/Satellite-based-telephone-communication\">Satellite-based telephone communication<\/a><\/div>\r\n<\/li>\r\n<\/ul>\r\n<a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/mobile-telephone\">Quick Facts &amp; Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\/images-videos\">Images<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg\" data-href=\"\/media\/1\/1482373\/105704\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/52\/95252-004-36E59AB6\/People-another-distances-mobile-phones-computers.jpg\" alt=\"computer and mobile phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/97\/128697-050-751CA10E\/girl-laptop-computer-telephone-2007.jpg\" data-href=\"\/media\/1\/1482373\/126837\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/97\/128697-004-F18062A6\/girl-laptop-computer-telephone-2007.jpg\" alt=\"Computer and Cell Phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg\" data-href=\"\/media\/1\/1482373\/19587\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg\" alt=\"Cell Relays of Cellular Phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg\" data-href=\"\/media\/1\/1482373\/126843\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg\" alt=\"1959 Car Phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg\" data-href=\"\/media\/1\/1482373\/126845\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg\" alt=\"Motorola car telephone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" data-href=\"\/media\/1\/1482373\/126847\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" alt=\"Motorola DynaTAC 8000X\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" data-href=\"\/media\/1\/1482373\/19225\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/12\/23612-004-6E3C2C07\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" alt=\"Motorola's MicroTAC flip cellular phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg\" data-href=\"\/media\/1\/1482373\/120524\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/125919-004-871D6673\/Cell-phones-world-classrooms-text-messages-images.jpg\" alt=\"Sending Text Messages\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" data-href=\"\/media\/1\/1482373\/126849\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/39\/128739-004-D2F94AF8\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" alt=\"2008 Nokia Videophone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/www.britannica.com\/topic\/communication\/The-psychology-of-communication\" data-href=\"\/media\/1\/1482373\/293440\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/85\/251485-049-CC839F13\/att-telecommuications-corporation.jpg\" alt=\"Evolution of the Phone\" height=\"50\" \/><\/a><\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-student-links\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">For Students<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/summary\/mobile-telephone\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"computer and mobile phone\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/summary\/mobile-telephone\">mobile telephone summary<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-quizzes\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Quizzes<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/electronics-amp-gadgets-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/01\/128701-131-74746B98\/nano-iPod-2007.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The iPod nano, introduced by Apple CEO Steve Jobs in San Francisco, May 2007. A revolutionary full-featured iPod that holds 1,000 songs and is thinner than a standard #2 pencil. MP3 player, music player, digital music\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/electronics-amp-gadgets-quiz\">Electronics &amp; Gadgets Quiz<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/why-do-you-have-to-turn-off-electronic-devices-on-an-airplane\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/38\/194838-131-C4080C2D\/Businessman-tablet-phone-airplane.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Businessman using tablet phone on airplane\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/why-do-you-have-to-turn-off-electronic-devices-on-an-airplane\">Why Do You Have to Turn Off Electronic Devices on an Airplane?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/what-are-the-differences-between-first--second--and-third-degree-murder\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/11\/238411-131-2CBFE7E4\/scales-of-justice-gavel.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Law legal system crime concept with gavel and scales of justice with books in the background. (mallet, judicial system).\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/what-are-the-differences-between-first--second--and-third-degree-murder\">What Are the Differences Between First-, Second-, and Third-Degree Murder?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/68\/152568-131-E6B869A4\/King-cobra-world-snake.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"King Cobra snake in Malaysia. (reptile)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\">9 of the World\u2019s Deadliest Snakes<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/12-novels-considered-the-greatest-book-ever-written\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/55\/142355-131-EFF621AF\/books-Stack-literature-pile-reading-entertainment-society-2010.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Close up of books. Stack of books, pile of books, literature, reading. Homepage 2010, arts and entertainment, history and society\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/12-novels-considered-the-greatest-book-ever-written\">12 Novels Considered the \u201cGreatest Book Ever Written\u201d<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191082-131-AD46C136\/threshold-office-Chester-A-Arthur-chromolithograph-Print-September-1881.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"&quot;On the threshold of office--what have we to expect of him?&quot; chromolithograph by Joseph Keppler, September 1881. Print shows the members of the assassinated James A. Garfield's cabinet looking at the new president, Chester Arthur. Chester A. Arthur.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\">The Surprisingly Disorderly History of the U.S. Presidential Succession Order<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-palaces-in-england\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/57\/177357-131-20A5B7AD\/Pond-Gardens-Hampton-Court-place-garden-London-England.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Pond Gardens, Hampton Court palace and garden, London, England. (horizontal)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-palaces-in-england\">9 Palaces in England<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191982-131-D3194343\/ball.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"magic 8 ball\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\">Where Did the Idea for the Magic 8 Ball Come From?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-of-the-worlds-deadliest-shipwrecks\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/41\/182141-131-32BD2459\/Lusitania-sinking-U-boat-German-May-1915.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Lusitania sinking, illustration from The War of the Nations (New York), December 31, 1919. World War I, WWI. This image is one of three on the page. (See source file for the other two.)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-of-the-worlds-deadliest-shipwrecks\">7 of the World\u2019s Deadliest Shipwrecks<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"false\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg\" data-href=\"\/media\/1\/1482373\/105704\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"computer and mobile phone\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/52\/95252-050-BBBB9B8F\/People-another-distances-mobile-phones-computers.jpg\" data-href=\"\/media\/1\/1482373\/105704\">computer and mobile phone<\/a>\u00a0People can quickly and easily communicate with one another over long distances using computers and mobile phones.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>mobile telephone<\/h1>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"1482373\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"caption alternate-titles\">Also known as: mobile phone<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">David E. Borth<\/span><\/div>\r\n<div class=\"font-serif font-12 text-gray-700\"><span class=\"qa-fact-checked-by\">Fact-checked by<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link font-12 \">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-12-16T00:00:00CST\">Dec 16, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Also called:<\/dt>\r\n<dd>mobile phone<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/iPhone\">iPhone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/smartphone\">smartphone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/BlackBerry-wireless-device\">BlackBerry<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/cell-phone\">cell phone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/MicroTAC\">MicroTAC<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/mobile-telephone\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false\">\r\n<div>\r\n<h2 class=\"font-weight-bold font-14 m-0 d-inline\">News\u00a0<span class=\"text-gray-600\">\u2022<\/span><\/h2>\r\n<div class=\"recent-news-item first-recent-news-item d-inline\"><a class=\"font-14 gtm-ap-news-link\" href=\"https:\/\/www.nytimes.com\/2024\/12\/15\/technology\/school-fight-videos-student-phones.html\" rel=\"nofollow\">How Student Phones and Social Media Are Fueling Fights in Schools<\/a>\u00a0<span class=\"font-14 text-gray-600\">\u2022\u00a0Dec. 15, 2024, 11:45 AM ET (New York Times)<\/span><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref1\" data-level=\"1\" data-has-spy=\"true\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref1007899\"><\/span>mobile telephone<\/strong>, portable device for connecting to a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\" data-show-preview=\"true\">telecommunications network<\/a>\u00a0in order to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmit\" data-term=\"transmit\" data-type=\"EB\">transmit<\/a>\u00a0and receive voice, video, or other data. Mobile phones typically connect to the public switched telephone network (PSTN) through one of two categories: cellular telephone systems or global satellite-based telephony.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279849\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\"><span id=\"ref1079017\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\" data-show-preview=\"true\">Cellular telephones<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"126837\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/97\/128697-050-751CA10E\/girl-laptop-computer-telephone-2007.jpg\" data-href=\"\/media\/1\/1482373\/126837\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/97\/128697-050-751CA10E\/girl-laptop-computer-telephone-2007.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/97\/128697-050-751CA10E\/girl-laptop-computer-telephone-2007.jpg?w=300\" alt=\"Computer and Cell Phone\" data-width=\"1173\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/97\/128697-050-751CA10E\/girl-laptop-computer-telephone-2007.jpg\" data-href=\"\/media\/1\/1482373\/126837\">Computer and Cell Phone<\/a>Teenage girl using a laptop computer and a cellular telephone,\u00a0<em>c.<\/em>\u00a02007.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Cellular telephones, or simply cell phones, are portable devices that may be used in motor vehicles or by pedestrians. Communicating by radio waves, they permit a significant degree of mobility within a defined serving region that may range in area from a few city blocks to hundreds of square kilometres. The first mobile and portable subscriber units for cellular systems were large and heavy. With significant advances in component technology, though, the weight and size of portable transceivers have been significantly reduced. In this section, the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/concept\" data-term=\"concept\" data-type=\"EB\">concept<\/a>\u00a0of cell phones and the development of cellular systems are discussed.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279850\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref1079023\"><\/span>Cellular communication<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"19587\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg\" data-href=\"\/media\/1\/1482373\/19587\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg?w=300\" alt=\"Cell Relays of Cellular Phone\" data-width=\"510\" data-height=\"300\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/32\/24332-004-056FB3E3\/telephone-system-location-Operation-cell-call-area.jpg\" data-href=\"\/media\/1\/1482373\/19587\">Cell Relays of Cellular Phone<\/a>Operation of a cellular telephone systemFrom a specific location within a geographic area, or cell, a subscriber places a call using a mobile telephone. The call is relayed by the base station serving that cell to the mobile telephone switching office (MTSO). The MTSO in turn relays the call to another base station within the cellular system or to a central office in the public switched telephone network. When telephone traffic within a cell exceeds capacity, the cell is split into a number of smaller cells, each with its own base station.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">All cellular telephone systems exhibit several fundamental characteristics, as summarized in the following:<\/p>\r\n<ol>\r\n<li>\r\n<div>The geographic area served by a cellular system is broken up into smaller geographic areas, or cells. Uniform hexagons most frequently are employed to represent these cells on maps and diagrams; in practice, though, radio waves do not confine themselves to hexagonal areas, so the actual cells have irregular shapes.<\/div>\r\n<\/li>\r\n<li>\r\n<div>All\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0with a mobile or portable instrument within a given cell is made to a base station that serves the cell.<\/div>\r\n<\/li>\r\n<li>\r\n<div>Because of the low transmitting power of battery-operated portable instruments, specific sending and receiving frequencies assigned to a cell may be reused in other cells within the larger geographic area. Thus, the spectral\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/efficiency\" data-term=\"efficiency\" data-type=\"MW\">efficiency<\/a>\u00a0of a cellular system (that is, the uses to which it can put its portion of the radio spectrum) is increased by a factor equal to the number of times a frequency may be reused within its service area.<\/div>\r\n<\/li>\r\n<li>\r\n<div>As a mobile instrument proceeds from one cell to another during the course of a call, a central controller automatically reroutes the call from the old cell to the new cell without a noticeable interruption in the signal reception. This process is known as handoff. The central controller, or mobile telephone\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">switching<\/a>\u00a0office (MTSO), thus acts as an intelligent central office switch that keeps track of the movement of the mobile subscriber.<\/div>\r\n<\/li>\r\n<li>\r\n<div>As demand for the radio channels within a given cell increases beyond the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/capacity\" data-term=\"capacity\" data-type=\"EB\">capacity<\/a>\u00a0of that cell (as measured by the number of calls that may be supported simultaneously), the overloaded cell is \u201csplit\u201d into smaller cells, each with its own base station and central controller. The radio-frequency allocations of the original cellular system are then rearranged to account for the greater number of smaller cells.<\/div>\r\n<\/li>\r\n<\/ol>\r\n<p class=\"topic-paragraph\">Frequency reuse between discontiguous cells and the splitting of cells as demand increases are the concepts that distinguish cellular systems from other wireless telephone systems. They allow cellular providers to serve large metropolitan areas that may contain hundreds of thousands of customers.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279851\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Development of cellular systems<\/h2>\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"126843\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg\" data-href=\"\/media\/1\/1482373\/126843\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg?w=300\" alt=\"1959 Car Phone\" data-width=\"550\" data-height=\"450\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">1 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/28\/128728-004-445E3315\/Motorola-push-button-car-telephone-control-unit-handset-1959.jpg\" data-href=\"\/media\/1\/1482373\/126843\">1959 Car Phone<\/a>Motorola push-button car telephone, control unit, and handset mounted under the automobile dashboard, 1959.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"126845\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg\" data-href=\"\/media\/1\/1482373\/126845\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg?w=300\" alt=\"Motorola car telephone\" data-width=\"520\" data-height=\"450\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">2 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/29\/128729-004-7EADB5E3\/Motorola-mobile-telephone-service-car-dial-push-1964.jpg\" data-href=\"\/media\/1\/1482373\/126845\">Motorola car telephone<\/a>Motorola improved mobile telephone service (IMTS) car telephone with push buttons and dial, control head with handset, and base unit, introduced in 1964.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20\"><\/button><\/div>\r\n<p class=\"topic-paragraph\">In the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>, interconnection of mobile transmitters and receivers with the\u00a0<span id=\"ref1079025\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/public-switched-telephone-network\">public switched telephone network<\/a>\u00a0(PSTN) began in 1946, with the introduction of\u00a0<span id=\"ref1079045\"><\/span>mobile telephone service (MTS) by the\u00a0<span id=\"ref1079046\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">American Telephone &amp; Telegraph Company<\/a>\u00a0(<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\" data-show-preview=\"true\">AT&amp;T<\/a>). In the U.S. MTS system, a user who wished to place a call from a mobile phone had to search manually for an unused channel before placing the call. The user then spoke with a mobile operator, who actually dialed the call over the PSTN. The radio connection was simplex\u2014i.e., only one party could speak at a time, the call direction being controlled by a push-to-talk switch in the mobile handset. In 1964 AT&amp;T introduced the\u00a0<span id=\"ref1079050\"><\/span>improved mobile telephone service (IMTS). This provided full duplex operation, automatic dialing, and automatic channel searching. Initially 11 channels were provided, but in 1969 an additional 12 channels were made available. Since only 11 (or 12) channels were available for all users of the system within a given geographic area (such as the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/metropolitan-area\" data-show-preview=\"true\">metropolitan area<\/a>\u00a0around a large city), the IMTS system faced a high demand for a very limited channel resource. Moreover, each base-station\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/antenna-electronics\" data-show-preview=\"true\">antenna<\/a>\u00a0had to be located on a tall structure and had to transmit at high power in order to provide coverage throughout the entire service area. Because of these high power requirements, all subscriber units in the IMTS system were motor-vehicle-based instruments that carried large storage batteries.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/electronics-amp-gadgets-quiz\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/01\/128701-131-74746B98\/nano-iPod-2007.jpg\" alt=\"The iPod nano, introduced by Apple CEO Steve Jobs in San Francisco, May 2007. A revolutionary full-featured iPod that holds 1,000 songs and is thinner than a standard #2 pencil. MP3 player, music player, digital music\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Electronics &amp; Gadgets Quiz<\/div>\r\n<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"126847\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" data-href=\"\/media\/1\/1482373\/126847\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg?w=300\" alt=\"Motorola DynaTAC 8000X\" data-width=\"304\" data-height=\"450\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" data-href=\"\/media\/1\/1482373\/126847\">Motorola DynaTAC 8000X<\/a>The Motorola DynaTAC 8000X, introduced in 1983, was the world&#8217;s first portable commercial handheld cellular phone.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">During this time a truly cellular system, known as the\u00a0<span id=\"ref1079047\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/advanced-mobile-phone-system\">advanced mobile phone system<\/a>, or AMPS, was developed primarily by AT&amp;T and\u00a0<span id=\"ref1079048\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/Motorola-Inc\" data-show-preview=\"true\">Motorola, Inc.<\/a>\u00a0AMPS was based on 666 paired voice channels, spaced every 30 kilohertz in the 800-megahertz region. The system employed an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/modulation-communications\" data-show-preview=\"true\">modulation<\/a>\u00a0approach\u2014<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-modulation\" data-show-preview=\"true\">frequency modulation<\/a>, or FM\u2014and was designed from the outset to support subscriber units for use both in automobiles and by pedestrians. It was publicly introduced in Chicago in 1983 and was a success from the beginning. At the end of the first year of service, there were a total of 200,000 AMPS subscribers throughout the United States; five years later there were more than 2,000,000. In response to expected service shortages, the American cellular industry proposed several methods for increasing capacity without requiring additional spectrum allocations. One analog FM approach, proposed by Motorola in 1991, was known as\u00a0<span id=\"ref1079049\"><\/span>narrowband AMPS, or NAMPS. In NAMPS systems each existing 30-kilohertz voice channel was split into three 10-kilohertz channels. Thus, in place of the 832 channels available in AMPS systems, the NAMPS system offered 2,496 channels. A second approach, developed by a committee of the\u00a0<span id=\"ref1079051\"><\/span>Telecommunications Industry Association (TIA) in 1988, employed digital modulation and digital voice compression in\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/conjunction\" data-term=\"conjunction\" data-type=\"EB\">conjunction<\/a>\u00a0with a\u00a0<span id=\"ref1079052\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/time-division-multiple-access\">time-division multiple access (TDMA) method<\/a>; this also permitted three new voice channels in place of one AMPS channel. Finally, in 1994 there surfaced a third approach, developed originally by\u00a0<span id=\"ref1079054\"><\/span>Qualcomm, Inc., but also adopted as a standard by the TIA. This third approach used a form of spread spectrum multiple access known as\u00a0<span id=\"ref1079058\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/code-division-multiple-access\">code-division multiple access<\/a>\u00a0(CDMA)\u2014a technique that, like the original TIA approach, combined digital voice compression with digital modulation. (For more information on the techniques of information compression, signal modulation, and multiple access,\u00a0<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\" data-show-preview=\"true\">telecommunications<\/a>.) The CDMA system offered 10 to 20 times the capacity of existing AMPS cellular techniques. All of these improved-capacity cellular systems were eventually\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>\u00a0in the United States, but, since they were incompatible with one another, they supported rather than replaced the older AMPS standard.<\/p>\r\n<p class=\"topic-paragraph\">Although AMPS was the first cellular system to be developed, a Japanese system was the first cellular system to be deployed, in 1979. Other systems that preceded AMPS in operation include the Nordic mobile telephone (NMT) system, deployed in 1981 in Denmark,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Finland\" data-show-preview=\"true\">Finland<\/a>, Norway, and Sweden, and the total access communication system (TACS), deployed in the United Kingdom in 1983. A number of other cellular systems were developed and deployed in many more countries in the following years. All of them were incompatible with one another. In 1988 a group of government-owned public telephone bodies within the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/European-Community-European-economic-association\" data-show-preview=\"true\">European Community<\/a>\u00a0announced the digital\u00a0<span id=\"ref1079060\"><\/span>global system for mobile communications, referred to as GSM, the first such system that would permit any cellular user in one European country to operate in another European country with the same equipment. GSM soon became\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/ubiquitous\" data-term=\"ubiquitous\" data-type=\"MW\">ubiquitous<\/a>\u00a0throughout\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Europe\" data-show-preview=\"true\">Europe<\/a>.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"19225\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" data-href=\"\/media\/1\/1482373\/19225\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg?w=300\" alt=\"Motorola's MicroTAC flip cellular phone\" data-width=\"1296\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" data-href=\"\/media\/1\/1482373\/19225\">Motorola&#8217;s MicroTAC flip cellular phone<\/a>Motorola&#8217;s MicroTAC flip cellular phone, introduced in 1989.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The analog cellular systems of the 1980s are now referred to as \u201c<span id=\"ref1079061\"><\/span>first-generation\u201d (or 1G) systems, and the digital systems that began to appear in the late 1980s and early \u201990s are known as the \u201c<span id=\"ref1079062\"><\/span>second generation\u201d (2G). Since the introduction of 2G cell phones, various enhancements have been made in order to provide data services and applications such as\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Internet\" data-show-preview=\"true\">Internet<\/a>\u00a0browsing, two-way\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/text-messaging\" data-show-preview=\"true\">text messaging<\/a>, still-image transmission, and mobile access by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/personal-computer\" data-show-preview=\"true\">personal computers<\/a>. One of the most successful applications of this kind is iMode, launched in 1999 in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Japan\" data-show-preview=\"true\">Japan<\/a>\u00a0by NTT DoCoMo, the mobile service division of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/Nippon-Telegraph-and-Telephone-Corporation\" data-show-preview=\"true\">Nippon Telegraph and Telephone Corporation<\/a>. Supporting Internet access to selected Web sites, interactive games,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/information-retrieval\" data-show-preview=\"true\">information retrieval<\/a>, and text messaging, iMode became extremely successful; within three years of its introduction, more than 35 million users in Japan had iMode-enabled cell phones.<\/p>\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120524\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg\" data-href=\"\/media\/1\/1482373\/120524\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg?w=300\" alt=\"Sending Text Messages\" data-width=\"1209\" data-height=\"1600\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">1 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg\" data-href=\"\/media\/1\/1482373\/120524\">Sending Text Messages<\/a>Cell phones became ubiquitous in classrooms around the world for exchanging images and text messages.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"126849\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" data-href=\"\/media\/1\/1482373\/126849\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg?w=300\" alt=\"2008 Nokia Videophone\" data-width=\"1054\" data-height=\"1600\" \/><\/picture><\/a>\r\n<div class=\"position-absolute top-10 left-10 assembly-slide-tag rounded-lg\">2 of 2<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" data-href=\"\/media\/1\/1482373\/126849\">2008 Nokia Videophone<\/a>A Nokia videophone showing MultiVu, a mobile video-delivery system, 2008.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20\"><\/button><\/div>\r\n<p class=\"topic-paragraph\">Beginning in 1985, a study group of the Geneva-based International Telecommunication Union (ITU) began to consider specifications for Future Public Land Mobile Telephone Systems (FPLMTS). These specifications eventually became the basis for a set of \u201c<span id=\"ref1079063\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/third-generation-data-network\">third-generation<\/a>\u201d (3G) cellular standards, known collectively as IMT-2000. The 3G standards are based loosely on several attributes: the use of CDMA technology; the ability eventually to support three classes of users (vehicle-based, pedestrian, and fixed); and the ability to support voice,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>, and multimedia services. The world\u2019s first 3G service began in Japan in October 2001 with a system offered by NTT DoCoMo. Soon 3G service was being offered by a number of different carriers in Japan,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/South-Korea\" data-show-preview=\"true\">South Korea<\/a>, the United States, and other countries. Several new types of service compatible with the higher data rates of 3G systems have become commercially available, including full-motion video transmission, image transmission, location-aware services (through the use of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/GPS\" data-show-preview=\"true\">global positioning system<\/a>\u00a0[GPS] technology), and high-rate\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data transmission<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">The increasing demands placed on mobile telephones to handle even more data than 3G could led to the development of\u00a0<span id=\"ref1246937\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/fourth-generation-data-network\">4G technology<\/a>. In 2008 the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/International-Telecommunication-Union\" data-show-preview=\"true\">ITU<\/a>\u00a0set forward a list of requirements for what it called IMT-Advanced, or 4G; these requirements included data rates of 1 gigabit per second for a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/stationary\" data-term=\"stationary\" data-type=\"EB\">stationary<\/a>\u00a0user and 100 megabits per second for a moving user. The ITU in 2010 decided that two technologies, LTE-Advanced (Long Term Evolution; LTE) and WirelessMan-Advanced (also called WiMAX), met the requirements. The Swedish telephone company TeliaSonera introduced the first 4G\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/long-term-evolution\" data-show-preview=\"true\">LTE<\/a>\u00a0network in Stockholm in 2009.<\/p>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279852\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Airborne cellular systems<\/h2>\r\n<p class=\"topic-paragraph\">In addition to the terrestrial cellular phone systems described above, there also exist several systems that permit the placement of telephone calls to the PSTN by passengers on commercial aircraft. These in-flight telephones, known by the generic name\u00a0<span id=\"ref1079064\"><\/span>aeronautical public correspondence (APC) systems, are of two types: terrestrial-based, in which telephone calls are placed directly from an aircraft to an en route ground station; and satellite-based, in which telephone calls are\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/relayed\" data-term=\"relayed\" data-type=\"EB\">relayed<\/a>\u00a0via satellite to a ground station. In the United States the\u00a0<span id=\"ref1079065\"><\/span>North American terrestrial system (NATS) was introduced by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/GTE-Corporation\" data-show-preview=\"true\">GTE Corporation<\/a>\u00a0in 1984. Within a decade the system was installed in more than 1,700 aircraft, with ground stations in the United States providing coverage over most of the United States and southern Canada. A second-generation system, GTE Airfone GenStar, employed digital modulation. In Europe the European Telecommunications Standards Institute (ETSI) adopted a terrestrial APC system known as the\u00a0<span id=\"ref1079066\"><\/span>terrestrial flight telephone system (TFTS) in 1992. This system employs digital modulation methods and operates in the 1,670\u20131,675- and 1,800\u20131,805-megahertz bands. In order to cover most of Europe, the ground stations must be spaced every 50 to 700 km (30 to 435 miles).<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<div data-page-index=\"11\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 grey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref279853\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\">Satellite-based telephone communication<\/h1>\r\n<p class=\"topic-paragraph\">In order to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/augment\" data-term=\"augment\" data-type=\"EB\">augment<\/a>\u00a0the terrestrial and aircraft-based mobile telephone systems, several\u00a0<span id=\"ref1079067\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/satellite-communication\" data-show-preview=\"true\">satellite-based systems<\/a>\u00a0have been put into operation. The goal of these systems is to permit ready connection to the PSTN from anywhere on Earth\u2019s surface, especially in areas not presently covered by\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\" data-show-preview=\"true\">cellular telephone<\/a>\u00a0service. A form of satellite-based mobile\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0has been available for some time in airborne cellular systems that utilize\u00a0<span id=\"ref1079068\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/International-Maritime-Satellite-Organization\">Inmarsat<\/a>\u00a0satellites. However, the Inmarsat satellites are geostationary, remaining approximately 35,000 km (22,000 miles) above a single location on Earth\u2019s surface. Because of this high-altitude orbit, Earth-based communication transceivers require high transmitting power, large communication antennas, or both in order to communicate with the satellite. In addition, such a long communication path introduces a noticeable delay, on the order of a quarter-second, in two-way voice conversations. One viable\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/alternative\" data-term=\"alternative\" data-type=\"MW\">alternative<\/a>\u00a0to geostationary satellites would be a larger system of satellites in\u00a0<span id=\"ref1079069\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/low-Earth-orbit\" data-show-preview=\"true\">low Earth orbit<\/a>\u00a0(LEO). Orbiting less than 1,600 km (1,000 miles) above Earth, LEO satellites are not geostationary and therefore cannot provide constant coverage of specific areas on Earth. Nevertheless, by allowing radio communications with a mobile instrument to be handed off between satellites, an entire constellation of satellites can assure that no call will be dropped simply because a single satellite has moved out of range.<\/p>\r\n<p class=\"topic-paragraph\">The first LEO system intended for commercial service was the\u00a0<span id=\"ref1079070\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Iridium-satellite-system\">Iridium system<\/a>, designed by Motorola, Inc., and owned by Iridium LLC, a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/consortium\" data-term=\"consortium\" data-type=\"MW\">consortium<\/a>\u00a0made up of corporations and governments from around the world. The Iridium concept employed a constellation of 66 satellites orbiting in six planes around Earth. They were launched from May 1997 to May 1998, and commercial service began in November 1998. Each satellite, orbiting at an altitude of 778 kilometres (483 miles), had the capability to transmit 48 spot beams to Earth. Meanwhile, all the satellites were in communication with one another via 23-gigahertz radio \u201ccrosslinks,\u201d thus permitting ready handoff between satellites when communicating with a fixed or mobile user on Earth. The crosslinks provided an uninterrupted communication path between the satellite serving a user at any particular instant and the satellite connecting the entire constellation with the gateway ground station to the PSTN. In this way, the 66 satellites provided\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/continuous\" data-term=\"continuous\" data-type=\"EB\">continuous<\/a>\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0communication service for subscriber units around the globe. However, the service failed to attract sufficient subscribers, and Iridium LLC went out of business in March 2000. Its assets were acquired by Iridium Satellite LLC, which continued to provide worldwide communication service to the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/US-Department-of-Defense\" data-show-preview=\"true\">U.S. Department of Defense<\/a>\u00a0as well as business and individual users.<\/p>\r\n<p class=\"topic-paragraph\">Another LEO system,\u00a0<span id=\"ref1079071\"><\/span>Globalstar, consisted of 48 satellites that were launched about the same time as the Iridium constellation. Globalstar began offering service in October 1999, though it too went into bankruptcy, in February 2002; a reorganized Globalstar LP continued to provide service thereafter.<\/p>\r\n<div class=\"mb-20\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"293440\" data-asm-type=\"infogram\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"infogram\">\u00a0<\/div>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/David-E-Borth\/4163\">David E. Borth<\/a><\/span><\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"12\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded\" data-topic-id=\"585829\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\">telecommunications network<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<ul class=\"list-unstyled my-0\" data-level=\"h1\">\r\n<li class=\"\" data-target=\"#ref1\">\r\n<div class=\"pl-25\"><a class=\"link-gray-900 w-100\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\">Introduction<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76410\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network#ref76410\">Types of networks<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent spy-active-parent\" data-target=\"#ref76413\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network#ref76413\">Network access<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76421\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\/Spread-spectrum-multiple-access#ref76421\">Open systems interconnection<\/a><\/div>\r\n<\/li>\r\n<\/ul>\r\n<a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/telecommunications-network\">Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\/images-videos\">Images<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/36\/24336-004-CB570885\/telecommunications-network-Network-switches-nodes-users-communications.jpg\" data-href=\"\/media\/1\/585829\/19591\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/36\/24336-004-CB570885\/telecommunications-network-Network-switches-nodes-users-communications.jpg\" alt=\"A simple closed telecommunications networkNetwork switches, or nodes, enable users (stations) to link to any number of network users through communications channels.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg\" data-href=\"\/media\/1\/585829\/68195\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg\" alt=\"local area networks (LANs)\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg\" data-href=\"\/media\/1\/585829\/19588\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg\" alt=\"open systems interconnection (OSI)\" height=\"50\" \/><\/a><\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-invented-the-internet\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/129488-131-09AB5E83\/Internet-blue-screen-blog-society-history-media-2009.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Internet http:\/\/www blue screen. Hompepage blog 2009, history and society, media news television, crowd opinion protest, In the News 2009, breaking news\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/who-invented-the-internet\">Who Invented the Internet?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/how-does-wi-fi-work\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/197118-131-00A7D6AF\/Computer-Code-Binary-Internet-Password-Data-Technology.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Binary Computer Code, Binary Code, Internet, Technology, Password, Data\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/how-does-wi-fi-work\">How Does Wi-Fi Work?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/11\/113311-131-8848D08B\/Victoria-Woodhull-woman-suffrage-US-House-of-1871.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Judiciary Committee of the U.S. House of Representatives receiving a deputation of female suffragists, January 11, 1871, a lady delegate (identified as Victoria Woodhull) reading her argument (cont'd)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\">Who Was the First Woman to Run for President of the United States?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/189145-131-45FF672E\/Secret-Service-Agent-Earpiece.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Secret Service Agent Listens To Earpiece\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\">Secret Service Code Names of 11 U.S. Presidents<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/which-religion-is-the-oldest\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/91\/223091-131-A986B08A\/relief-Zoroastrian-god-Ahura-Mazda-Persepolis-Iran.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Ahura Mazda - relief of the Zoroastrian god Ahura Mazda at the ancient ruins of Persepolis in Iran. Also known as Ormazd Zoroastrianism,\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/which-religion-is-the-oldest\">Which Religion Is the Oldest?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-mind-altering-plants\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/39\/123539-131-B5711E3A\/Hemp.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Hemp (Cannabis sativa).\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-mind-altering-plants\">9 Mind-Altering Plants<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/why-does-cilantro-taste-like-soap-to-some-people\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/63\/194863-131-E49C6B35\/Coriander-leaves-cilantro-herbs-background.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Coriander leaves, fresh green cilantro on wooden background, herbs\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/why-does-cilantro-taste-like-soap-to-some-people\">Why Does Cilantro Taste Like Soap to Some People?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/what-makes-a-species-endangered\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/152045-131-501AC122\/bald-eagle-conservation-efforts-species-numbers-list-2007.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Bald eagle in flight.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/what-makes-a-species-endangered\">What Makes a Species Endangered?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191082-131-AD46C136\/threshold-office-Chester-A-Arthur-chromolithograph-Print-September-1881.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"&quot;On the threshold of office--what have we to expect of him?&quot; chromolithograph by Joseph Keppler, September 1881. Print shows the members of the assassinated James A. Garfield's cabinet looking at the new president, Chester Arthur. Chester A. Arthur.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\">The Surprisingly Disorderly History of the U.S. Presidential Succession Order<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"false\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/36\/24336-004-CB570885\/telecommunications-network-Network-switches-nodes-users-communications.jpg\" data-href=\"\/media\/1\/585829\/19591\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/36\/24336-004-CB570885\/telecommunications-network-Network-switches-nodes-users-communications.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/36\/24336-004-CB570885\/telecommunications-network-Network-switches-nodes-users-communications.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"A simple closed telecommunications networkNetwork switches, or nodes, enable users (stations) to link to any number of network users through communications channels.\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\">A simple closed telecommunications networkNetwork switches, or nodes, enable users (stations) to link to any number of network users through communications channels.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>telecommunications network<\/h1>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"585829\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">Robert K. Morrow<\/span><\/div>\r\n<div class=\"font-serif font-12 text-gray-700\"><span class=\"qa-fact-checked-by\">Fact-checked by<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link font-12 \">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/packet-switched-network\">packet-switched network<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/circuit-switched-network\">circuit-switched network<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/computer-network\">computer network<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/switched-communications-network\">switched communications network<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/broadcast-network\">broadcast network<\/a><\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/telecommunications-network\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref1\" data-level=\"1\" data-has-spy=\"true\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref607973\"><\/span>telecommunications network<\/strong>, electronic system of links and switches, and the controls that govern their operation, that allows for\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>\u00a0transfer and exchange among multiple users.<\/p>\r\n<p class=\"topic-paragraph\">When several users of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/telecommunications-media\" data-show-preview=\"true\">telecommunications media<\/a>\u00a0wish to communicate with one another, they must be organized into some form of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/network-sociology\" data-show-preview=\"true\">network<\/a>. In theory, each user can be given a direct point-to-point link to all the other users in what is known as a fully connected topology (similar to the connections employed in the earliest days of telephony), but in practice this technique is impractical and expensive\u2014especially for a large and dispersed network. Furthermore, the method is inefficient, since most of the links will be idle at any given time. Modern telecommunications networks\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/avoid\" data-term=\"avoid\" data-type=\"EB\">avoid<\/a>\u00a0these issues by establishing a linked network of switches, or\u00a0<span id=\"ref607974\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/node-communications\">nodes<\/a>, such that each user is connected to one of the nodes. Each link in such a network is called a\u00a0<span id=\"ref607975\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/communication-channel\">communications channel<\/a>. Wire, fibre-optic cable, and radio waves may be used for different communications channels.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76410\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\">Types of networks<\/h2>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76411\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref607976\"><\/span>Switched communications network<\/h2>\r\n<p class=\"topic-paragraph\">A switched communications network transfers data from source to destination through a series of network nodes.\u00a0<span id=\"ref607977\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">Switching<\/a>\u00a0can be done in one of two ways. In a\u00a0<span id=\"ref607978\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/circuit-switched-network\" data-show-preview=\"true\">circuit-switched network<\/a>, a dedicated physical path is established through the network and is held for as long as\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0is necessary. An example of this type of network is the traditional (analog)\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0system. A\u00a0<span id=\"ref607979\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/packet-switched-network\" data-show-preview=\"true\">packet-switched network<\/a>, on the other hand, routes digital data in small pieces called\u00a0<span id=\"ref607980\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/packet-transmission\">packets<\/a>, each of which proceeds independently through the network. In a process called\u00a0<span id=\"ref607981\"><\/span>store-and-forward, each packet is temporarily stored at each intermediate node, then forwarded when the next link becomes available. In a\u00a0<span id=\"ref607982\"><\/span>connection-oriented transmission scheme, each packet takes the same route through the network, and thus all packets usually arrive at the destination in the order in which they were sent.\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/Conversely\" data-term=\"Conversely\" data-type=\"EB\">Conversely<\/a>, each packet may take a different path through the network in a connectionless or\u00a0<span id=\"ref607983\"><\/span>datagram scheme. Since datagrams may not arrive at the destination in the order in which they were sent, they are numbered so that they can be properly reassembled. The latter is the method that is used for transmitting data through the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Internet\" data-show-preview=\"true\">Internet<\/a>.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76412\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref607984\"><\/span>Broadcast network<\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"68195\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg\" data-href=\"\/media\/1\/585829\/68195\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg?w=300\" alt=\"local area networks (LANs)\" data-width=\"753\" data-height=\"300\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/37\/24337-004-B57997F0\/area-networks-bus-Ethernet-token-IBM-office.jpg\" data-href=\"\/media\/1\/585829\/68195\">local area networks (LANs)<\/a>\u00a0Simple bus networks, such as Ethernet, are common for home and small office configurations. The most common ring network is IBM&#8217;s Token Ring, which employs a \u201ctoken\u201d that is passed around the network to control which location has sending privileges. Star networks are common in larger commercial networks since a malfunction at any node generally does not disrupt the entire network.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">A broadcast network avoids the complex routing procedures of a switched network by ensuring that each node\u2019s transmissions are received by all other nodes in the network. Therefore, a broadcast network has only a single communications channel. A wired\u00a0<span id=\"ref607985\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/local-area-network\" data-show-preview=\"true\">local area network<\/a>\u00a0(LAN), for example, may be set up as a broadcast network, with one user connected to each node and the nodes typically arranged in a\u00a0<span id=\"ref607986\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bus-topology\">bus<\/a>,\u00a0<span id=\"ref607987\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/ring-topology\">ring<\/a>, or\u00a0<span id=\"ref829254\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/star-topology\">star topology<\/a>, as shown in the\u00a0<span class=\"link-blue media-overlay-link asmref\" data-href=\"\/media\/1\/585829\/68195\">figure<\/span>. Nodes connected together in a wireless LAN may broadcast via radio or optical links. On a larger scale, many\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/satellite-radio\" data-show-preview=\"true\">satellite radio<\/a>\u00a0systems are broadcast networks, since each Earth station within the system can typically hear all messages relayed by a satellite.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76413\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\">Network access<\/h2>\r\n<p class=\"topic-paragraph\">Since all nodes can hear each transmission in a broadcast network, a procedure must be established for\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/allocating\" data-term=\"allocating\" data-type=\"MW\">allocating<\/a>\u00a0a communications channel to the node or nodes that have packets to transmit and at the same time preventing destructive interference from collisions (simultaneous transmissions). This type of communication, called\u00a0<span id=\"ref607988\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/multiple-access\">multiple access<\/a>, can be established either by\u00a0<span id=\"ref607989\"><\/span>scheduling (a technique in which nodes take turns transmitting in an orderly fashion) or by random access to the channel.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76414\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Scheduled access<\/h2>\r\n<p class=\"topic-paragraph\">In a scheduling method known as\u00a0<span id=\"ref607990\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/time-division-multiple-access\">time-division multiple access<\/a>\u00a0(TDMA), a time slot is assigned in turn to each node, which uses the slot if it has something to transmit. If some nodes are much busier than others, then TDMA can be inefficient, since no data are passed during time slots\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/allocated\" data-term=\"allocated\" data-type=\"MW\">allocated<\/a>\u00a0to silent nodes. In this case a reservation system may be\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implemented\" data-term=\"implemented\" data-type=\"MW\">implemented<\/a>, in which there are fewer time slots than nodes and a node reserves a slot only when it is needed for transmission.<\/p>\r\n<p class=\"topic-paragraph\">A variation of TDMA is the process of\u00a0<span id=\"ref607991\"><\/span>polling, in which a central\u00a0<span id=\"ref607992\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/controller-technology\">controller<\/a>\u00a0asks each node in turn if it requires channel access, and a node transmits a packet or message only in response to its poll. \u201cSmart\u201d controllers can respond dynamically to nodes that suddenly become very busy by polling them more often for\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmissions\" data-term=\"transmissions\" data-type=\"EB\">transmissions<\/a>. A decentralized form of polling is called\u00a0<span id=\"ref607993\"><\/span>token passing. In this system a special \u201ctoken\u201d packet is passed from node to node. Only the node with the token is authorized to transmit; all others are listeners.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76417\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref607994\"><\/span>Random access<\/h2>\r\n<p class=\"topic-paragraph\">Scheduled access schemes have several disadvantages, including the large overhead required for the reservation, polling, and token passing processes and the possibility of long idle periods when only a few nodes are transmitting. This can lead to extensive delays in routing information, especially when heavy traffic occurs in different parts of the network at different times\u2014a characteristic of many practical communications networks. Random-access\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/algorithms\" data-term=\"algorithms\" data-type=\"MW\">algorithms<\/a>\u00a0were designed specifically to give nodes with something to transmit quicker access to the channel. Although the channel is\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/vulnerable\" data-term=\"vulnerable\" data-type=\"MW\">vulnerable<\/a>\u00a0to packet collisions under random access, various procedures have been developed to reduce this probability.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76418\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref607995\"><\/span>Carrier sense multiple access<\/h2>\r\n<p class=\"topic-paragraph\">One random-access method that reduces the chance of collisions is called carrier sense multiple access (CSMA). In this method a node listens to the channel first and delays transmitting when it senses that the channel is busy. Because of delays in channel\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/propagation\" data-term=\"propagation\" data-type=\"MW\">propagation<\/a>\u00a0and node processing, it is possible that a node will erroneously sense a busy channel to be idle and will cause a collision if it transmits. In CSMA, however, the transmitting nodes will recognize that a collision has occurred: the respective destinations will not acknowledge receipt of a valid packet. Each node then waits a random time before sending again (hopefully preventing a second collision). This method is commonly employed in packet networks with radio links, such as the system used by\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/amateur-radio\" data-show-preview=\"true\">amateur radio<\/a>\u00a0operators.<\/p>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">It is important to minimize the time that a communications channel spends in a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/collision\" data-term=\"collision\" data-type=\"EB\">collision<\/a>\u00a0state, since this effectively shuts down the channel. If a node can simultaneously transmit and receive (usually possible on wire and fibre-optic links but not on radio links), then it can stop sending immediately upon detecting the beginning of a collision, thus moving the channel out of the collision state as soon as possible. This process is called\u00a0<span id=\"ref607996\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/carrier-sense-multiple-access-with-collision-detection\">carrier sense multiple access with collision detection<\/a>\u00a0(CSMA\/CD), a feature of the popular wired\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/Ethernet\" data-show-preview=\"true\">Ethernet<\/a>. (For more information on Ethernet,\u00a0<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/computer\/Networking#ref235918\" data-show-preview=\"true\">computer: Local area networks<\/a>.)<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<div data-page-index=\"13\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 grey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<section data-level=\"2\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76420\" data-level=\"3\" data-has-spy=\"true\">\r\n<h1 class=\"h3\"><span id=\"ref607998\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/spread-spectrum-multiple-access\">Spread-spectrum multiple access<\/a><\/h1>\r\n<p class=\"topic-paragraph\">Since collisions are so\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/detrimental\" data-term=\"detrimental\" data-type=\"MW\">detrimental<\/a>\u00a0to network performance, methods have been developed to allow multiple transmissions on a broadcast network without necessarily causing mutual packet destruction. One of the most successful is called spread-spectrum multiple access (SSMA). In SSMA simultaneous transmissions will cause only a slight increase in bit error probability for each user if the channel is not too heavily loaded. Error-free packets can be obtained by using an appropriate control code. Disadvantages of SSMA include wider signal bandwidth and greater equipment cost and complexity compared with conventional CSMA.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76421\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\"><span id=\"ref607999\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/open-systems-interconnection\">Open systems interconnection<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"19588\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg\" data-href=\"\/media\/1\/585829\/19588\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg?w=300\" alt=\"open systems interconnection (OSI)\" data-width=\"400\" data-height=\"300\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/33\/24333-004-59ADD143\/open-systems-interconnection-model-network-communication-protocols-1983.jpg\" data-href=\"\/media\/1\/585829\/19588\">open systems interconnection (OSI)<\/a>The open systems interconnection (OSI) model for network communication. Established in 1983 by the International Organization for Standardization, the OSI model divides network protocols (standardized procedures for exchanging information) into seven functional \u201clayers.\u201d This communications architecture enables end users employing different operating systems or working in different networks to communicate quickly and correctly.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Different\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0requirements necessitate different network solutions, and these different network\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/protocols\" data-term=\"protocols\" data-type=\"MW\">protocols<\/a>\u00a0can create significant problems of compatibility when networks are interconnected with one another. In order to overcome some of these interconnection problems, the open systems interconnection (OSI) was approved in 1983 as an international standard for communications architecture by the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/International-Organization-for-Standardization\" data-show-preview=\"true\">International Organization for Standardization<\/a>\u00a0(ISO) and the\u00a0<span id=\"ref608024\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/International-Telegraph-and-Telephone-Consultative-Committee\">International Telegraph and Telephone Consultative Committee<\/a>\u00a0(CCITT). The OSI model, as shown in the\u00a0<span class=\"link-blue media-overlay-link asmref\" data-href=\"\/media\/1\/585829\/19588\">figure<\/span>, consists of seven layers, each of which is selected to perform a well-defined function at a different level of abstraction. The bottom three layers provide for the timely and correct transfer of\u00a0<span id=\"ref608000\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/data-computing\">data<\/a>, and the top four ensure that arriving\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>\u00a0are recognizable and useful. While all seven layers are usually necessary at each user location, only the bottom three are normally employed at a network node, since nodes are concerned only with timely and correct data transfer from point to point.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76422\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Data recognition and use<\/h2>\r\n<p class=\"topic-paragraph\">The\u00a0<span id=\"ref608001\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/application-level\">application layer<\/a>\u00a0is difficult to generalize, since its content is specific to each user. For example, distributed\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/database\" data-show-preview=\"true\">databases<\/a>\u00a0used in the banking and airline industries require several access and security issues to be solved at this level. Network transparency (making the physical distribution of resources irrelevant to the human user) also is handled at this level. The\u00a0<span id=\"ref608002\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/presentation-level\">presentation layer<\/a>, on the other hand, performs functions that are requested sufficiently often that a general solution is warranted. These functions are often placed in a software library that is accessible by several users running different applications. Examples are text\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/conversion\" data-term=\"conversion\" data-type=\"EB\">conversion<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/data-compression\" data-show-preview=\"true\">data compression<\/a>, and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/data-encryption\" data-show-preview=\"true\">data encryption<\/a>.<\/p>\r\n<p class=\"topic-paragraph\"><span id=\"ref608003\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/human-machine-interface\" data-show-preview=\"true\">User interface<\/a>\u00a0with the network is performed by the\u00a0<span id=\"ref608004\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/session-level\">session layer<\/a>, which handles the process of connecting to another computer, verifying user authenticity, and establishing a reliable communication process. This layer also ensures that files which can be altered by several network users are kept in order. Data from the session layer are accepted by the\u00a0<span id=\"ref608005\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transport-level\">transport layer<\/a>, which separates the data stream into smaller units, if necessary, and ensures that all arrive correctly at the destination. If fast throughput is needed, the transport layer may establish several\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/simultaneous\" data-term=\"simultaneous\" data-type=\"EB\">simultaneous<\/a>\u00a0paths in the network and send different parts of the data over each path. Conversely, if low cost is a requirement, then the layer may time-multiplex several users\u2019 data over one path through the network. Flow control is also regulated at this level, ensuring that data from a fast source will not overrun a slow destination.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76423\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Data transfer<\/h2>\r\n<p class=\"topic-paragraph\">The\u00a0<span id=\"ref608006\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/network-level\">network layer<\/a>\u00a0breaks data into packets and determines how the packets are routed within the network, which nodes (if any) will check packets for errors along the route, and whether congestion control is needed in a heavily loaded network. The\u00a0<span id=\"ref608007\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/data-link-level\">data-link layer<\/a>\u00a0transforms a raw communications channel into a line that appears essentially free of transmission errors to the network layer. This is done by breaking data up into data frames, transmitting them sequentially, and processing acknowledgment frames sent back to the source by the destination. This layer also establishes frame boundaries and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implements\" data-term=\"implements\" data-type=\"MW\">implements<\/a>\u00a0recovery procedures from lost, damaged, or duplicated frames. The\u00a0<span id=\"ref608008\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/physical-level\">physical layer<\/a>\u00a0is the transmission medium itself, along with various electric and mechanical specifications.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/Robert-K-Morrow\/4204\">Robert K. Morrow<\/a><\/span><\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"14\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content \" data-topic-id=\"1017653\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/technology\/VoIP\">VoIP<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<span class=\"toc-extra-link selected link-gray-900 mt-15\">Introduction<\/span><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/VoIP\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/VoIP\">Quick Facts &amp; Related Topics<\/a><\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-invented-the-internet\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/129488-131-09AB5E83\/Internet-blue-screen-blog-society-history-media-2009.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Internet http:\/\/www blue screen. Hompepage blog 2009, history and society, media news television, crowd opinion protest, In the News 2009, breaking news\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/who-invented-the-internet\">Who Invented the Internet?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/how-does-wi-fi-work\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/197118-131-00A7D6AF\/Computer-Code-Binary-Internet-Password-Data-Technology.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Binary Computer Code, Binary Code, Internet, Technology, Password, Data\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/how-does-wi-fi-work\">How Does Wi-Fi Work?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191982-131-D3194343\/ball.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"magic 8 ball\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\">Where Did the Idea for the Magic 8 Ball Come From?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/titanosaurs-8-of-the-worlds-biggest-dinosaurs\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/14\/196914-131-061D0CB0\/Patagotitan-mayorum-titanosaurs.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"illustration of the walking titanosaurus, Patagotitan mayorum\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/titanosaurs-8-of-the-worlds-biggest-dinosaurs\">Titanosaurs: 8 of the World&#8217;s Biggest Dinosaurs<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/whats-the-difference-between-modern-and-contemporary-art\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/16\/191216-131-B288FFB5\/Tulips-sculpture-group-colour-coating-stainless-steel-2004.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Jeff Koons tulips sculputure outside the Guggenheim Museums in Bilbao, Spain, Basque Country.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/whats-the-difference-between-modern-and-contemporary-art\">What\u2019s the Difference Between Modern and Contemporary Art?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/73\/150373-131-DB2CFBDD\/Teton-Range-Jackson-Lake-Wyoming-Grand-National.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Jackson (Wyoming, United States). Jackson Lake (also called Jackson Hole), southern end of the Teton Range (the Grand Tetons), Grand Teton National Park, Wyoming, USA\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\">7 Wonders of America<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/189145-131-45FF672E\/Secret-Service-Agent-Earpiece.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Secret Service Agent Listens To Earpiece\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\">Secret Service Code Names of 11 U.S. Presidents<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/8-deadliest-wars-of-the-21st-century\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/38\/168938-131-2FBA7C21\/Soldiers-Iraqi-Army-learning-9th-Mechanized-Division-2011.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Iraqi Army Soldiers from the 9th Mechanized Division learning to operate and maintain M1A1 Abrams Main Battle Tanks at Besmaya Combat Training Center, Baghdad, Iraq, 2011. Military training. Iraq war. U.S. Army\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/8-deadliest-wars-of-the-21st-century\">8 Deadliest Wars of the 21st Century<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/68\/152568-131-E6B869A4\/King-cobra-world-snake.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"King Cobra snake in Malaysia. (reptile)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\">9 of the World\u2019s Deadliest Snakes<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\r\n\t\t\tgrey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"false\">\r\n<div class=\"reading-channel\">\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>VoIP<\/h1>\r\n<\/div>\r\n<\/div>\r\n<div class=\"topic-identifier font-16 font-md-20\">communications<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"1017653\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"caption alternate-titles\">Also known as: Internet telephone service, voice over IP, voice over Internet protocol<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written and fact-checked by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-11-23T00:00:00CST\">Nov 23, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/technology\/VoIP\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>In full:<\/dt>\r\n<dd>Voice over Internet Protocol<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Also called:<\/dt>\r\n<dd>IP telephony<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/Skype\">Skype<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/protocol-computer-science\">protocol<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>On the Web:<\/dt>\r\n<dd><a href=\"https:\/\/www.academia.edu\/28758814\/Voice_over_Internet_Protocol_VoIP_The_Dynamics_of_Technology_and_Regulation\" target=\"_blank\" rel=\"noopener\">Academia &#8211; Voice over Internet Protocol (VoIP): The Dynamics of Technology and Regulation<\/a>\u00a0(Nov. 23, 2024)<\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/VoIP\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<section id=\"ref1\" data-level=\"1\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref1021539\"><\/span>VoIP<\/strong>, communications\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/technology\" data-show-preview=\"true\">technology<\/a>\u00a0for carrying voice\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0traffic over a data network such as the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Internet\" data-show-preview=\"true\">Internet<\/a>. VoIP uses the Internet\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/Protocol\" data-term=\"Protocol\" data-type=\"MW\">Protocol<\/a>\u00a0(IP)\u2014one half of the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/TCP-IP\" data-show-preview=\"true\">Transmission Control Protocol\/Internet Protocol<\/a>\u00a0(TCP\/IP), a global addressing system for sending and receiving packets of data over the Internet.<\/p>\r\n<p class=\"topic-paragraph\">VoIP works by converting sound into a digital signal, which is then sent over a data network such as the Internet. The conversion is done by a device, such as a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/personal-computer\" data-show-preview=\"true\">personal computer<\/a>\u00a0(PC) or special VoIP phone, that has a high-speed, or broadband, Internet connection. The digital signal is routed through the network to its destination, where a second VoIP device converts the signal back to sound. Because of the digital nature of VoIP, call quality is normally much higher than that of a standard telephone. Another advantage is that VoIP frequently costs less than standard telephone and long-distance service.<\/p>\r\n<p class=\"topic-paragraph\">Initially, there were problems with VoIP, not the least of which was how VoIP connected to 911 emergency systems. Because of this, the U.S.\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Federal-Communications-Commission\" data-show-preview=\"true\">Federal Communications Commission<\/a>\u00a0(FCC) required VoIP providers to provide connections to 911, although these systems sometimes worked differently from\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/conventional\" data-term=\"conventional\" data-type=\"EB\">conventional<\/a>\u00a0911 systems. Another, more persistent, problem that sometimes arises is that VoIP systems will often not work during a power outage.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Several companies provide VoIP service that allow people to use their PC or a special phone with the service. Larger organizations sometimes handle their own VoIP traffic.<\/p>\r\n<\/section>\r\n<span class=\"md-signature\">This article was most recently revised and updated by\u00a0<a href=\"https:\/\/www.britannica.com\/editor\/Erik-Gregersen\/6723\">Erik Gregersen<\/a>.<\/span><\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"15\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content \" data-topic-id=\"59564\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\">Alexander Graham Bell<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<span class=\"toc-extra-link selected link-gray-900 mt-15\">Introduction &amp; Top Questions<\/span><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/Alexander-Graham-Bell\">Quick Facts &amp; Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\/images-videos\">Images, Videos &amp; Interactives<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/65\/76465-050-4078CFBC\/Alexander-Graham-Bell.jpg\" data-href=\"\/media\/1\/59564\/76302\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/65\/76465-004-E1D9362E\/Alexander-Graham-Bell.jpg\" alt=\"Alexander Graham Bell\" height=\"50\" \/><\/a>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/19\/180119-138-29F20103\/Overview-invention-telephone-focus-work-Alexander-Graham.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"How the telephone was invented\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" data-href=\"\/media\/1\/59564\/120543\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/115188-004-C74C4644\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" alt=\"telephone: Alexander Graham Bell's sketch of a telephone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" data-href=\"\/media\/1\/59564\/120549\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/87\/115187-004-3BFD9598\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" alt=\"Alexander Graham Bell\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/84\/115184-050-40B64A5D\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg\" data-href=\"\/media\/1\/59564\/120540\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/84\/115184-004-9C9C534F\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg\" alt=\"Alexander Graham Bell and the New York City\u2013Chicago telephone link\" height=\"50\" \/><\/a>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/48\/24048-138-67ECC8F2\/groove-Columbia-Graphophone-wax-surface-Chichester-Bell-1886.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"How a Graphophone records and plays sound\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/www.britannica.com\/topic\/communication\/The-psychology-of-communication\" data-href=\"\/media\/1\/59564\/293440\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/85\/251485-049-CC839F13\/att-telecommuications-corporation.jpg\" alt=\"Evolution of the Phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/14\/6414-050-0A270F1D\/Alexander-Graham-Bell.jpg\" data-href=\"\/media\/1\/59564\/8821\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/14\/6414-004-4640C578\/Alexander-Graham-Bell.jpg\" alt=\"Alexander Graham Bell\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/64\/76464-050-9A264569\/Alexander-Graham-Bell.jpg\" data-href=\"\/media\/1\/59564\/96631\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/64\/76464-004-875D167E\/Alexander-Graham-Bell.jpg\" alt=\"Bell, Alexander Graham\" height=\"50\" \/><\/a><\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-student-links\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">For Students<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div 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src=\"https:\/\/cdn.britannica.com\/14\/6414-050-0A270F1D\/Alexander-Graham-Bell.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Alexander Graham Bell\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/summary\/Alexander-Graham-Bell-Timeline\">Alexander Graham Bell Timeline<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/summary\/Alexander-Graham-Bells-Achievements\"><img loading=\"lazy\" decoding=\"async\" class=\"default \" src=\"https:\/\/cdn.britannica.com\/mendel-resources\/3-131\/images\/shared\/default3.png?v=3.131.7\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/summary\/Alexander-Graham-Bells-Achievements\">Alexander Graham Bell\u2019s Achievements<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-quizzes\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Quizzes<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/spot-the-canadian-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/70\/250270-131-BAD87926\/figures-holding-hands-Canadian-flag.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Stick figure illustrations holding hands with the Canadian flag.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/spot-the-canadian-quiz\">Spot the Canadian Quiz<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/what-very-big-thing-happened-on-this-day\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/259288-131-D51AA72F\/quiz-thumbnail-what-happened-on-this-very-important-date.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Quiz thumbnail, &quot;What Happened on this Very Important Date&quot; quiz. A push pin on a calendar\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/what-very-big-thing-happened-on-this-day\">What Very Big Thing Happened on This Day?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/inventors-and-inventions\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/65\/166065-131-7C59DB40\/ball-bearing-friction-Automobile-Industry-Sphere-Wheel.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"ball bearing. Disassembled ball bearing. rotational friction Automobile Industry, Engineering, Industry, Machine Part, Metal Industry, Sphere, Steel, Wheel\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/inventors-and-inventions\">Inventors and Inventions<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/inventions-from-bayonets-to-jet-engines\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/28\/169428-131-820AF1D4\/ornithopter-Airplane-Aircraft-flying-machine-illustration-plans.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"ornithopter. Airplane and Aircraft. 3D illustration of Leonardo da Vinci's plans for an ornithopter, a flying machine kept aloft by the beating of its wings; about 1490.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/inventions-from-bayonets-to-jet-engines\">Inventions: From Bayonets to Jet Engines<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/a-history-of-everyday-technology-in-68-quiz-questions\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/171918-131-68E6E33A\/Postcard-Alberto-Santos-Dumont-dirigible-Brazilian-Eiffel-Tower-October-19-1901.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Alberto Santos-Dumont. Postcard of Brazilian aviator Alberto Santos-Dumont's (1873-1932) airship or dirigible and Eiffel Tower. The Santos Dumont Air-Ship rounding the Eiffel Tower; on Octoboer 19th 1901. airplane\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/a-history-of-everyday-technology-in-68-quiz-questions\">A History of Everyday Technology in 68 Quiz Questions<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-questions\">\r\n<div class=\"text-gray-900 p-5 pb-0 font-serif font-14 font-weight-bold mx-10 mb-15\">Related Questions<\/div>\r\n<ul>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/Who-was-Alexander-Graham-Bell\">Who was Alexander Graham Bell?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/What-did-Alexander-Graham-Bell-invent\">What did Alexander Graham Bell invent?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/How-did-Alexander-Graham-Bells-telephone-work\">How did Alexander Graham Bell\u2019s telephone work?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/When-was-the-telephone-patented\">When was the telephone patented?<\/a><\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/6-fast-facts-about-alexander-graham-bell\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/84\/115184-131-873E7847\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Alexander Graham Bell, inventor who patented the telephone in 1876, inaugurating the 1520 km telephone link between New York and Chicago, watched by a crowd on Oct. 18, 1892.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/6-fast-facts-about-alexander-graham-bell\">6 Fast Facts about Alexander Graham Bell<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/inventors-and-inventions-of-the-industrial-revolution\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/34\/193634-131-F5FF783D\/factories-Industrial-Revolution-workers-house-machines.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"A Factory Interior, watercolor, pen and gray ink, graphite, and white goache on wove paper by unknown artist, c. 1871-91; in the Yale Center for British Art. Industrial Revolution England\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/inventors-and-inventions-of-the-industrial-revolution\">Inventors and Inventions of the Industrial Revolution<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/10-inventions-that-changed-your-world\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/04\/24404-131-BA7B1B4F\/Apple-II.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Apple II\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/10-inventions-that-changed-your-world\">10 Inventions That Changed Your World<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-celebrities-you-didnt-know-were-inventors\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/79\/150379-131-19227925\/Prince.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Prince. musician Prince (Prince Rogers Nelson). Prince WELCOME 2 AMERICA tour. Exclusive North American Performances, 2010-11\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-celebrities-you-didnt-know-were-inventors\">7 Celebrities You Didn\u2019t Know Were Inventors<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/did-marie-antoinette-really-say-let-them-eat-cake\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/28\/188528-131-D58974EF\/Marie-Antoinette-Louis-XVI-unrest-monarchy-overthrow-France-August-1792.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Portrait of Marie Antoinette by Jean-Francois Janinet, 1777. Color etching and engraving with gold leaf printed on two sheets, 30x13.5 in.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/did-marie-antoinette-really-say-let-them-eat-cake\">Did Marie-Antoinette Really Say \u201cLet Them Eat Cake\u201d?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191082-131-AD46C136\/threshold-office-Chester-A-Arthur-chromolithograph-Print-September-1881.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"&quot;On the threshold of office--what have we to expect of him?&quot; chromolithograph by Joseph Keppler, September 1881. Print shows the members of the assassinated James A. Garfield's cabinet looking at the new president, Chester Arthur. Chester A. Arthur.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\">The Surprisingly Disorderly History of the U.S. Presidential Succession Order<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/what-makes-a-species-endangered\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/152045-131-501AC122\/bald-eagle-conservation-efforts-species-numbers-list-2007.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Bald eagle in flight.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/what-makes-a-species-endangered\">What Makes a Species Endangered?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/12-novels-considered-the-greatest-book-ever-written\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/55\/142355-131-EFF621AF\/books-Stack-literature-pile-reading-entertainment-society-2010.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Close up of books. Stack of books, pile of books, literature, reading. Homepage 2010, arts and entertainment, history and society\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/12-novels-considered-the-greatest-book-ever-written\">12 Novels Considered the \u201cGreatest Book Ever Written\u201d<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/11\/113311-131-8848D08B\/Victoria-Woodhull-woman-suffrage-US-House-of-1871.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Judiciary Committee of the U.S. House of Representatives receiving a deputation of female suffragists, January 11, 1871, a lady delegate (identified as Victoria Woodhull) reading her argument (cont'd)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\">Who Was the First Woman to Run for President of the United States?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/why-do-jeans-have-that-tiny-pocket\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/87\/238587-050-A11B8CBF\/Stylish-light-blue-jeans-on-wooden-background-closeup-of-inset-pocket.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Stylish light blue jeans on wooden background, closeup of inset pocket\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/why-do-jeans-have-that-tiny-pocket\">Why Do Jeans Have That Tiny Pocket?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191982-131-D3194343\/ball.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"magic 8 ball\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\">Where Did the Idea for the Magic 8 Ball Come From?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\r\n\t\t\tgrey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-BIOGRAPHY\" data-student-article=\"true\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/65\/76465-050-4078CFBC\/Alexander-Graham-Bell.jpg\" data-href=\"\/media\/1\/59564\/76302\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/65\/76465-050-4078CFBC\/Alexander-Graham-Bell.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/65\/76465-050-4078CFBC\/Alexander-Graham-Bell.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"Alexander Graham Bell\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/65\/76465-050-4078CFBC\/Alexander-Graham-Bell.jpg\" data-href=\"\/media\/1\/59564\/76302\">Alexander Graham Bell<\/a><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>Alexander Graham Bell<\/h1>\r\n<\/div>\r\n<\/div>\r\n<div class=\"topic-identifier font-16 font-md-20\">American inventor<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"59564\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">David Hochfelder<\/span><\/div>\r\n<div class=\"font-serif font-12 text-gray-700\"><span class=\"qa-fact-checked-by\">Fact-checked by<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link font-12 \">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-10-29T00:00:00CDT\">Oct 29, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"qf-title font-weight-bold font-14 mb-10 text-center\">Quick Facts<\/div>\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Born:<\/dt>\r\n<dd>March 3, 1847,\u00a0<a href=\"https:\/\/www.britannica.com\/place\/Edinburgh-Scotland\">Edinburgh<\/a>,\u00a0<a href=\"https:\/\/www.britannica.com\/place\/Scotland\">Scotland<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Died:<\/dt>\r\n<dd>August 2, 1922, Beinn Bhreagh,\u00a0<a href=\"https:\/\/www.britannica.com\/place\/Cape-Breton-Island\">Cape Breton Island<\/a>,\u00a0<a href=\"https:\/\/www.britannica.com\/place\/Nova-Scotia\">Nova Scotia<\/a>,\u00a0<a href=\"https:\/\/www.britannica.com\/place\/Canada\">Canada<\/a>\u00a0(aged 75)<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Founder:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/money\/ATandT-Corporation\">AT&amp;T Corporation<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Awards And Honors:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/topic\/Hall-of-Fame-for-Great-Americans\">Hall of Fame (1950)<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Inventions:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/Graphophone\">Graphophone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/telephone\">telephone<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"facts-list-show-more-btn mt-15 p-0 mx-auto btn font-14 d-block font-weight-normal\">\u00a0<span class=\"show-more-label\">Show More<\/span><\/button><\/div>\r\n<div class=\"top-questions qa-accordion d-flex flex-column module-spacing\">\r\n<div class=\"font-weight-bold font-14 mb-5\">Top Questions<\/div>\r\n<div id=\"intent-accordion\" class=\"md-intent-accordion\">\r\n<div class=\"top-question bg-gray-50 rounded\" data-value=\"1\">\r\n<div class=\"pe-none d-flex justify-content-between align-items-center\">\r\n<div>Who was Alexander Graham Bell?<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"top-question bg-gray-50 rounded\" data-value=\"2\">\r\n<div class=\"pe-none d-flex justify-content-between align-items-center\">\r\n<div>What did Alexander Graham Bell invent?<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"top-question bg-gray-50 rounded\" data-value=\"3\">\r\n<div class=\"pe-none d-flex justify-content-between align-items-center\">\r\n<div>How did Alexander Graham Bell\u2019s telephone work?<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<section id=\"ref1\" data-level=\"1\">\r\n<div class=\"assemblies multiple medialist slider js-slider position-relative d-inline-flex align-items-center mw-100\" data-type=\"other\">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex rw-slider rw-next-disabled rw-prev-disabled\">\r\n<div class=\"rw-track d-flex align-items-center\">\r\n<div class=\"position-relative rw-slide col-100 px-20\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"192158\" data-asm-type=\"video\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"video\"><a class=\"gtm-assembly-link d-flex justify-content-center\" href=\"https:\/\/www.britannica.com\/video\/Overview-invention-telephone-focus-work-Alexander-Graham\/-192158\" data-id=\"180119\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/180119-138-29F20103\/Overview-invention-telephone-focus-work-Alexander-Graham.jpg?w=800&amp;h=450&amp;c=crop\" alt=\"How the telephone was invented\" \/><\/a>\r\n<div class=\"btn btn-xl btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><span class=\"md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption\">How the telephone was invented<\/span>Overview of the invention of the telephone, with a focus on the work by Alexander Graham Bell.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<a class=\"font-14 mt-10 d-inline-block\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\/images-videos\">See all videos for this article<\/a><\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow btn-lg btn-blue-dark m-20 rw-disabled\" disabled=\"disabled\"><\/button><\/div>\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref19870\"><\/span>Alexander Graham Bell<\/strong>\u00a0(born March 3, 1847, Edinburgh, Scotland\u2014died August 2, 1922, Beinn Bhreagh, Cape Breton Island,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Nova-Scotia\" data-show-preview=\"true\">Nova Scotia<\/a>, Canada) was a Scottish-born American inventor, scientist, and teacher of the deaf whose foremost accomplishments were the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/invention-technology\" data-show-preview=\"true\">invention<\/a>\u00a0of the\u00a0<span id=\"ref19871\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0(1876) and the refinement of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/phonograph\" data-show-preview=\"true\">phonograph<\/a>\u00a0(1886).<\/p>\r\n<p class=\"topic-paragraph\">Alexander (\u201cGraham\u201d was not added until he was 11) was born to Alexander Melville Bell and Eliza Grace Symonds. His mother was almost deaf, and his father taught\u00a0<span id=\"ref19872\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/elocution\">elocution<\/a>\u00a0to the deaf, influencing Alexander\u2019s later career choice as teacher of the deaf. At age 11 he entered the Royal High School at\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Edinburgh-Scotland\" data-show-preview=\"true\">Edinburgh<\/a>, but he did not enjoy the compulsory curriculum, and he left school at age 15 without graduating. In 1865 the family moved to London. Alexander passed the entrance examinations for University College London in June 1868 and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/matriculated\" data-term=\"matriculated\" data-type=\"MW\">matriculated<\/a>\u00a0there in the autumn. However, he did not complete his studies, because in 1870 the Bell family moved again, this time immigrating to\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Canada\" data-show-preview=\"true\">Canada<\/a>\u00a0after the deaths of Bell\u2019s younger brother Edward in 1867 and older brother Melville in 1870, both of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/tuberculosis\" data-show-preview=\"true\">tuberculosis<\/a>. The family settled in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Brantford\" data-show-preview=\"true\">Brantford<\/a>, Ontario, but in April 1871 Alexander moved to Boston, where he taught at the Boston School for Deaf Mutes. He also taught at the Clarke School for the Deaf in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Northampton-Massachusetts\" data-show-preview=\"true\">Northampton<\/a>, Massachusetts, and at the American School for the Deaf in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Hartford-Connecticut\" data-show-preview=\"true\">Hartford<\/a>, Connecticut.<\/p>\r\n<p class=\"topic-paragraph\">One of Bell\u2019s students was\u00a0<span id=\"ref19883\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Mabel-Hubbard-Bell\">Mabel Hubbard<\/a>, daughter of Gardiner Greene Hubbard, a founder of the Clarke School. Mabel had become deaf at age five as a result of a near-fatal bout of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/scarlet-fever\" data-show-preview=\"true\">scarlet fever<\/a>. Bell began working with her in 1873, when she was 15 years old. Despite a 10-year age difference, they fell in love and were married on July 11, 1877. They had four children, Elsie (1878\u20131964), Marian (1880\u20131962), and two sons who died in infancy.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/spot-the-canadian-quiz\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/70\/250270-131-BAD87926\/figures-holding-hands-Canadian-flag.jpg\" alt=\"Stick figure illustrations holding hands with the Canadian flag.\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Spot the Canadian Quiz<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">While pursuing his teaching profession, Bell also began researching methods to transmit several\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telegraph\" data-show-preview=\"true\">telegraph<\/a>\u00a0messages simultaneously over a single wire\u2014a major focus of telegraph\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/innovation\" data-term=\"innovation\" data-type=\"MW\">innovation<\/a>\u00a0at the time and one that ultimately led to Bell\u2019s invention of the telephone. In 1868 Joseph Stearns had invented the duplex, a system that transmitted two messages simultaneously over a single wire.\u00a0<span id=\"ref19877\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/Western-Union-Corporation\" data-show-preview=\"true\">Western Union Telegraph Company<\/a>, the dominant firm in the industry, acquired the rights to Stearns\u2019s duplex and hired the noted inventor\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Edison\" data-show-preview=\"true\">Thomas Edison<\/a>\u00a0to devise as many multiple-transmission methods as possible in order to block competitors from using them. Edison\u2019s work culminated in the quadruplex, a system for sending four simultaneous telegraph messages over a single wire. Inventors then sought methods that could send more than four; some, including Bell and his great\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/rival\" data-term=\"rival\" data-type=\"EB\">rival<\/a>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Elisha-Gray\" data-show-preview=\"true\">Elisha Gray<\/a>, developed designs capable of subdividing a telegraph line into 10 or more channels. These so-called harmonic telegraphs used reeds or tuning forks that responded to specific acoustic frequencies. They worked well in the laboratory but proved unreliable in service.<\/p>\r\n<p class=\"topic-paragraph\">A group of investors led by Gardiner Hubbard wanted to establish a federally chartered telegraph company to compete with Western Union by contracting with the Post Office to send low-cost telegrams. Hubbard saw great promise in the harmonic telegraph and backed Bell\u2019s experiments. Bell, however, was more interested in transmitting the human voice. Finally, he and Hubbard worked out an agreement that Bell would devote most of his time to the harmonic telegraph but would continue developing his telephone concept.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120543\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" data-href=\"\/media\/1\/59564\/120543\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg?w=300\" alt=\"telephone: Alexander Graham Bell's sketch of a telephone\" data-width=\"1600\" data-height=\"1077\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/88\/115188-050-BA7F9D71\/Alexander-Graham-Bell-sketch-telephone-patent-declaration-February-14-1876.jpg\" data-href=\"\/media\/1\/59564\/120543\">telephone: Alexander Graham Bell&#8217;s sketch of a telephone<\/a>Alexander Graham Bell&#8217;s sketch of a telephone. He filed the patent for his telephone at the U.S. Patent Office on February 14, 1876\u2014just two hours before a rival, Elisha Gray, filed a declaration of intent to file a patent for a similar device.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">From harmonic telegraphs transmitting musical tones, it was a short\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/conceptual\" data-term=\"conceptual\" data-type=\"MW\">conceptual<\/a>\u00a0step for both Bell and Gray to transmit the human voice. Bell filed a patent describing his method of transmitting sounds on February 14, 1876, just hours before Gray filed a\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/caveat\" data-term=\"caveat\" data-type=\"MW\">caveat<\/a>\u00a0(a statement of concept) on a similar method. On March 7, 1876, the Patent Office awarded Bell what is said to be one of the most valuable patents in history. It is most likely that both Bell and Gray independently devised their telephone designs as an outgrowth of their work on harmonic telegraphy. However, the question of priority of invention between the two has been controversial from the very beginning.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120549\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" data-href=\"\/media\/1\/59564\/120549\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg?w=300\" alt=\"Alexander Graham Bell\" data-width=\"1423\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/87\/115187-050-431D5CA7\/Alexander-Graham-Bell-telephone-study-friends-lecture-February-12-1877.jpg\" data-href=\"\/media\/1\/59564\/120549\">Alexander Graham Bell<\/a>Alexander Graham Bell, inventor who patented the telephone in 1876, lecturing at Salem, Massachusetts (top), while friends in his study at Boston listen to his lecture via telephone, February 12, 1877.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"200311\" data-asm-type=\"audio\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"audio\"><audio src=\"https:\/\/cdn.britannica.com\/96\/99896-005-93EC718E\/Thomas-A-Watson-birth-Alexander-Graham-Bell.mp3\" controls=\"controls\" data-mce-fragment=\"1\"><\/audio><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/96\/99896-005-93EC718E\/Thomas-A-Watson-birth-Alexander-Graham-Bell.mp3\" data-href=\"\/media\/1\/59564\/200311\">Thomas A. Watson describing invention of the telephone<\/a>Thomas A. Watson, assistant to Alexander Graham Bell, discussing the birth of the telephone, including the first words spoken.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Despite having the patent, Bell did not have a fully functioning instrument. He first produced intelligible speech on March 10, 1876, when he summoned his laboratory assistant,\u00a0<span id=\"ref1220626\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Thomas-Augustus-Watson\" data-show-preview=\"true\">Thomas A. Watson<\/a>, with words that Bell\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transcribed\" data-term=\"transcribed\" data-type=\"EB\">transcribed<\/a>\u00a0in his lab notes as \u201cMr. Watson\u2014come here\u2014I want to see you.\u201d Over the next few months, Bell continued to refine his instrument to make it suitable for public exhibition. In June he demonstrated his telephone to the judges of the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Philadelphia\" data-show-preview=\"true\">Philadelphia<\/a>\u00a0Centennial Exhibition, a test witnessed by Brazil\u2019s Emperor\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Pedro-II\" data-show-preview=\"true\">Pedro II<\/a>\u00a0and the celebrated Scottish physicist\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/William-Thomson-Baron-Kelvin\" data-show-preview=\"true\">Sir William Thomson<\/a>. In August of that year, he was on the receiving end of the first one-way\u00a0<span id=\"ref1173216\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/long-distance-transmission\">long-distance<\/a>\u00a0call, transmitted from Brantford to nearby Paris, Ontario, over a telegraph wire.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"120540\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/84\/115184-050-40B64A5D\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg\" data-href=\"\/media\/1\/59564\/120540\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/84\/115184-050-40B64A5D\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/84\/115184-050-40B64A5D\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg?w=300\" alt=\"Alexander Graham Bell and the New York City\u2013Chicago telephone link\" data-width=\"1426\" data-height=\"1600\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/84\/115184-050-40B64A5D\/Alexander-Graham-Bell-telephone-link-Chicago-New-October-18-1892.jpg\" data-href=\"\/media\/1\/59564\/120540\">Alexander Graham Bell and the New York City\u2013Chicago telephone link<\/a>Alexander Graham Bell, who patented the telephone in 1876, inaugurating the 1,520-km (944-mile) telephone link between New York City and Chicago on October 18, 1892.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Gardiner Hubbard organized a group that established the\u00a0<span id=\"ref19876\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Bell-Telephone-Company\">Bell Telephone Company<\/a>\u00a0in July 1877 to commercialize Bell\u2019s telephone. Bell was the company\u2019s technical adviser until he lost interest in telephony in the early 1880s. Although his invention rendered him independently wealthy, he sold off most of his stock holdings in the company early and did not profit as much as he might have had he retained his shares. Thus, by the mid-1880s his role in the telephone industry was\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/marginal\" data-term=\"marginal\" data-type=\"EB\">marginal<\/a>.<\/p>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"19407\" data-asm-type=\"video\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"video\"><a class=\"gtm-assembly-link d-flex justify-content-center\" href=\"https:\/\/www.britannica.com\/video\/groove-Columbia-Graphophone-wax-surface-Chichester-Bell-1886\/-19407\" data-id=\"24048\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/48\/24048-138-67ECC8F2\/groove-Columbia-Graphophone-wax-surface-Chichester-Bell-1886.jpg?w=800&amp;h=450&amp;c=crop\" alt=\"How a Graphophone records and plays sound\" \/><\/a>\r\n<div class=\"btn btn-xl btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><span class=\"md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption\">How a Graphophone records and plays sound<\/span>The vertical \u201chill-and-dale\u201d groove, as played by a Columbia Graphophone, c. 1902. Patented by Charles Sumner Tainter, Chichester A. Bell, and Alexander Graham Bell in 1886, this vertically undulating groove, cut into a wax surface, was the most successful method employed in cylinder sound recording.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<a class=\"font-14 mt-10 d-inline-block\" href=\"https:\/\/www.britannica.com\/biography\/Alexander-Graham-Bell\/images-videos\">See all videos for this article<\/a><\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">By that time, Bell had developed a growing interest in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/technology\" data-show-preview=\"true\">technology<\/a>\u00a0of\u00a0<span id=\"ref19879\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/sound-recording\" data-show-preview=\"true\">sound recording<\/a>\u00a0and playback. Although Edison had invented the phonograph in 1877, he soon turned his attention to other technologies, especially\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/electric-power\" data-show-preview=\"true\">electric power<\/a>\u00a0and lighting, and his machine, which recorded and reproduced sound on a rotating cylinder wrapped in tinfoil, remained an unreliable and cumbersome device. In 1880 the French government awarded Bell the Volta Prize, given for achievement in electrical\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/science\" data-show-preview=\"true\">science<\/a>. Bell used the prize money to set up his\u00a0<span id=\"ref19878\"><\/span>Volta Laboratory, an institution devoted to studying\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/deafness\" data-show-preview=\"true\">deafness<\/a>\u00a0and improving the lives of the deaf, in Washington, D.C. There he also devoted himself to improving the phonograph. By 1885 Bell and his colleagues (his cousin Chichester A. Bell and the inventor\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Charles-Sumner-Tainter\" data-show-preview=\"true\">Charles Sumner Tainter<\/a>) had a design fit for commercial use that featured a removable cardboard cylinder coated with mineral\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/wax\" data-term=\"wax\" data-type=\"EB\">wax<\/a>. They called their device the\u00a0<span id=\"ref19880\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Graphophone\">Graphophone<\/a>\u00a0and applied for patents, which were granted in 1886. The group formed the Volta Graphophone Company to produce their invention. Then in 1887 they sold their patents to the American Graphophone Company, which later evolved into the Columbia Phonograph Company. Bell used his proceeds from the sale to endow the Volta Laboratory.<\/p>\r\n<div class=\"mb-20\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"293440\" data-asm-type=\"infogram\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"infogram\">\u00a0<\/div>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Bell undertook two other noteworthy research projects at the Volta Laboratory. In 1880 he began research on using\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/light\" data-show-preview=\"true\">light<\/a>\u00a0as a means to transmit sound. In 1873 British scientist Willoughby Smith discovered that the element\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/selenium\" data-show-preview=\"true\">selenium<\/a>, a\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/semiconductor\" data-show-preview=\"true\">semiconductor<\/a>, varied its electrical\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/resistance-electronics\" data-show-preview=\"true\">resistance<\/a>\u00a0with the intensity of incident light. Bell sought to use this property to develop the photophone, an invention he regarded as at least equal to his telephone. He was able to demonstrate that the photophone was technologically\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/feasible\" data-term=\"feasible\" data-type=\"MW\">feasible<\/a>, but it did not develop into a commercially viable product. Nevertheless, it contributed to research into the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/photovoltaic-effect\" data-show-preview=\"true\">photovoltaic effect<\/a>\u00a0that had practical applications later in the 20th century.<\/p>\r\n<p class=\"topic-paragraph\">Bell\u2019s other major undertaking was the development of an electrical bullet probe, an early version of the metal detector, for surgical use. The origin of this effort was the shooting of U.S. President\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/James-A-Garfield\" data-show-preview=\"true\">James A. Garfield<\/a>\u00a0in July 1881. A bullet lodged in the president\u2019s back, and doctors were unable to locate it through physical probing. Bell decided that a promising approach was to use an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/induction\" data-term=\"induction\" data-type=\"MW\">induction<\/a>\u00a0balance, a by-product of his research on canceling out electrical interference on telephone wires. Bell determined that a properly configured induction balance would emit a tone when a metal object was brought into proximity with it. At the end of July, he began searching for Garfield\u2019s bullet, but to no avail. Despite Garfield\u2019s death in September, Bell later successfully demonstrated the probe to a group of doctors. Surgeons adopted it, and it was credited with saving lives during the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/event\/South-African-War\" data-show-preview=\"true\">Boer War<\/a>\u00a0(1899\u20131902) and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/event\/World-War-I\" data-show-preview=\"true\">World War I<\/a>\u00a0(1914\u201318).<\/p>\r\n<p class=\"topic-paragraph\">In September 1885 the Bell family vacationed in Nova Scotia, Canada, and immediately fell in love with the climate and landscape. The following year, Bell bought 50 acres of land near the village of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/Baddeck\" data-show-preview=\"true\">Baddeck<\/a>\u00a0on\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Cape-Breton-Island\" data-show-preview=\"true\">Cape Breton Island<\/a>\u00a0and began constructing an estate he called Beinn Bhreagh,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Scots-Gaelic-language\" data-show-preview=\"true\">Scots Gaelic<\/a>\u00a0for \u201cBeautiful Mountain.\u201d The Scottish-born inventor had been an American citizen since 1882, but the Canadian estate became the family\u2019s summer retreat and later permanent home.<\/p>\r\n<p class=\"topic-paragraph\">During the 1890s Bell shifted his attention to heavier-than-air\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/history-of-flight\" data-show-preview=\"true\">flight<\/a>. Starting in 1891, inspired by the research of American scientist\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Samuel-Pierpont-Langley\" data-show-preview=\"true\">Samuel Pierpont Langley<\/a>, he experimented with wing shapes and propeller blade designs. He continued his experiments even after\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Wright-brothers\" data-show-preview=\"true\">Wilbur and Orville Wright<\/a>\u00a0made the first successful powered, controlled flight in 1903. In 1907 Bell founded the\u00a0<span id=\"ref19884\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Aerial-Experiment-Association\" data-show-preview=\"true\">Aerial Experiment Association<\/a>, which made significant progress in aircraft design and control and contributed to the career of pioneer aviator\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Glenn-Hammond-Curtiss\" data-show-preview=\"true\">Glenn Hammond Curtiss<\/a>.<\/p>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Throughout his life, Bell sought to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/foster\" data-term=\"foster\" data-type=\"EB\">foster<\/a>\u00a0the advance of scientific knowledge. He supported the journal\u00a0<em>Science<\/em>, which later became the official publication of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/American-Association-for-the-Advancement-of-Science\" data-show-preview=\"true\">American Association for the Advancement of Science<\/a>. He succeeded his father-in-law, Gardiner Hubbard, as president of the\u00a0<span id=\"ref19882\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/National-Geographic-Society\" data-show-preview=\"true\">National Geographic Society<\/a>\u00a0(1898\u20131903). In 1903 his son-in-law,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Gilbert-H-Grosvenor\" data-show-preview=\"true\">Gilbert H. Grosvenor<\/a>, became editor in chief of the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/National-Geographic-Magazine\" data-show-preview=\"true\"><em>National Geographic Magazine<\/em><\/a>, and Bell encouraged Grosvenor to make the magazine a more popular publication through more photographs and fewer scholarly articles. Bell died at his Nova Scotia estate, where he was buried.<\/p>\r\n<\/section>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/David-Hochfelder\/9206088\">David Hochfelder<\/a><\/span><\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"16\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content \" data-topic-id=\"101609\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\">cell phone<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<span class=\"toc-extra-link selected link-gray-900 mt-15\">Introduction<\/span><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/cell-phone\">Quick Facts &amp; Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\/images-videos\">Images<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/95\/128695-050-E396B0B0\/Cell-phone-use-2006.jpg\" data-href=\"\/media\/1\/101609\/126815\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/95\/128695-004-535BC8A6\/Cell-phone-use-2006.jpg\" alt=\"Cell phone in use, c. 2006.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/www.britannica.com\/topic\/communication\/The-psychology-of-communication\" data-href=\"\/media\/1\/101609\/314261\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/87\/261287-049-7FE742EA\/technology-timeline-banner.jpg\" alt=\"Britannica's 21st-Century Technology Timeline\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/54\/74854-050-78FBBFBC\/cell-phone-Nokia-users-video-clips-photographs.jpg\" data-href=\"\/media\/1\/101609\/68666\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/54\/74854-004-8F7DFC49\/cell-phone-Nokia-users-video-clips-photographs.jpg\" alt=\"Nokia cell phone that allows users to take still photographs and video clips.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/99\/137699-050-25930FB1\/Cell-phone-tower-cell-combination-microwave.jpg\" data-href=\"\/media\/1\/101609\/142292\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/99\/137699-004-801F8F48\/Cell-phone-tower-cell-combination-microwave.jpg\" alt=\"cell phone tower; microwave tower\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/19\/125919-050-02F1A73E\/Cell-phones-world-classrooms-text-messages-images.jpg\" data-href=\"\/media\/1\/101609\/120524\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/125919-004-871D6673\/Cell-phones-world-classrooms-text-messages-images.jpg\" alt=\"Sending Text Messages\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" data-href=\"\/media\/1\/101609\/126847\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/27\/128727-004-18D81A15\/Motorola-DynaTAC-8000X-world-1983.jpg\" alt=\"Motorola DynaTAC 8000X\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/30\/128730-004-C6BECB0F\/customer-Motorola-phone-DynaTAC-8000X-Asia-1984.jpg\" data-href=\"\/media\/1\/101609\/126859\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/30\/128730-004-C6BECB0F\/customer-Motorola-phone-DynaTAC-8000X-Asia-1984.jpg\" alt=\"Motorola customer using a cell phone in 1984\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/26\/128726-050-5AEFBB50\/businessman-Indian-cell-phone-train.jpg\" data-href=\"\/media\/1\/101609\/126827\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/26\/128726-004-060A9C99\/businessman-Indian-cell-phone-train.jpg\" alt=\"businessman with cell phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/12\/23612-050-9F8113FE\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" data-href=\"\/media\/1\/101609\/19225\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/12\/23612-004-6E3C2C07\/Motorola-flip-cellular-phone-MicroTAC-1989.jpg\" alt=\"Motorola's MicroTAC flip cellular phone\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/39\/128739-050-E5EC36BA\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" data-href=\"\/media\/1\/101609\/126849\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/39\/128739-004-D2F94AF8\/Nokia-videophone-MultiVu-video-delivery-system-2008.jpg\" alt=\"2008 Nokia Videophone\" height=\"50\" \/><\/a><\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-quizzes\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Quizzes<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/electronics-amp-gadgets-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/01\/128701-131-74746B98\/nano-iPod-2007.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The iPod nano, introduced by Apple CEO Steve Jobs in San Francisco, May 2007. A revolutionary full-featured iPod that holds 1,000 songs and is thinner than a standard #2 pencil. 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Also known as Ormazd Zoroastrianism,\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/which-religion-is-the-oldest\">Which Religion Is the Oldest?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\r\n\t\t\tgrey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"false\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/95\/128695-050-E396B0B0\/Cell-phone-use-2006.jpg\" data-href=\"\/media\/1\/101609\/126815\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/95\/128695-050-E396B0B0\/Cell-phone-use-2006.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/95\/128695-050-E396B0B0\/Cell-phone-use-2006.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"Cell phone in use, c. 2006.\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/95\/128695-050-E396B0B0\/Cell-phone-use-2006.jpg\" data-href=\"\/media\/1\/101609\/126815\">Cell phone in use,\u00a0<em>c.<\/em>\u00a02006.<\/a>\u00a0Cell phones are now more commonly referred to as smartphones, as most models offer Internet connectivity.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>cell phone<\/h1>\r\n<\/div>\r\n<\/div>\r\n<div class=\"topic-identifier font-16 font-md-20\">communications<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"101609\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"caption alternate-titles\">Also known as: cellular phone, cellular telephone, mobile cellular phone, mobile phone<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written and fact-checked by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-12-03T00:00:00CST\">Dec 3, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>In full:<\/dt>\r\n<dd>cellular telephone<\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Key People:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Martin-Cooper\">Martin Cooper<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/iPhone\">iPhone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/BlackBerry-wireless-device\">BlackBerry<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/global-system-for-mobile-communications\">global system for mobile communications<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/MicroTAC\">MicroTAC<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/advanced-mobile-phone-system\">advanced mobile phone system<\/a><\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>On the Web:<\/dt>\r\n<dd><a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC7425970\/\" target=\"_blank\" rel=\"noopener\">National Center for Biotechnology Information &#8211; PubMed Central &#8211; Mobile phones: The effect of its presence on learning and memory<\/a>\u00a0(Dec. 03, 2024)<\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/cell-phone\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"bg-gray-50 p-15 rounded module-spacing recent-news d-flex flex-column float-false\">\r\n<div>\r\n<h2 class=\"font-weight-bold font-14 m-0 d-inline\">News\u00a0<span class=\"text-gray-600\">\u2022<\/span><\/h2>\r\n<div class=\"recent-news-item first-recent-news-item d-inline\"><a class=\"font-14 gtm-ap-news-link\" href=\"https:\/\/www.bbc.com\/news\/articles\/c3dxxr15m78o\" rel=\"nofollow\">Humberside Police dogs to work alongside online investigation team<\/a>\u00a0<span class=\"font-14 text-gray-600\">\u2022\u00a0Dec. 7, 2024, 9:08 AM ET (BBC)<\/span><\/div>\r\n<\/div>\r\n<\/div>\r\n<section id=\"ref1\" data-level=\"1\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref1023929\"><\/span>cell phone<\/strong>, wireless\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0that permits\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\" data-show-preview=\"true\">telecommunication<\/a>\u00a0within a defined area that may include hundreds of square miles, using radio waves in the 800\u2013900 megahertz (MHz) band. To\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implement\" data-term=\"implement\" data-type=\"MW\">implement<\/a>\u00a0a cell-phone system, a geographic area is broken into smaller areas, or cells, usually mapped as uniform hexagrams but in fact overlapping and irregularly shaped. Each cell is equipped with a low-powered radio transmitter and receiver that permit\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/propagation\" data-term=\"propagation\" data-type=\"MW\">propagation<\/a>\u00a0of signals between cell-phone users.\u00a0<em>See also<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/mobile-telephone\" data-show-preview=\"true\">mobile telephone<\/a>\u00a0and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/smartphone\" data-show-preview=\"true\">smartphone<\/a>.<\/p>\r\n<div class=\"mb-20\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"314261\" data-asm-type=\"infogram\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"infogram\"><iframe title=\"Britannica's 21st-Century Technology Timeline\" src=\"https:\/\/e.infogram.com\/_\/JoLkXfU9lK081O737jAM?parent_url=https%3A%2F%2Fwww.britannica.com%2Fbiography%2FAlexander-Graham-Bell&amp;src=embed#async_embed\" frameborder=\"0\" scrolling=\"no\" allowfullscreen=\"allowfullscreen\" data-mce-fragment=\"1\"><\/iframe><\/div>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<\/section>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/editor\/The-Editors-of-Encyclopaedia-Britannica\/4419\">The Editors of Encyclopaedia Britannica<\/a><\/span><span class=\"md-signature\">This article was most recently revised and updated by\u00a0<a href=\"https:\/\/www.britannica.com\/editor\/tara-ramanathan\/12894283\">Tara Ramanathan<\/a>.<\/span><\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"17\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded\" data-topic-id=\"585799\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\">telecommunication<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<ul class=\"list-unstyled my-0\" data-level=\"h1\">\r\n<li class=\"\" data-target=\"#ref1\">\r\n<div class=\"pl-25\"><a class=\"link-gray-900 w-100\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\">Introduction<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76266\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication#ref76266\">Analog-to-digital conversion<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76270\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Bit-mapping#ref76270\">Source encoding<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76274\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Channel-encoding\">Channel encoding<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76278\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Modulation\">Modulation<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref76285\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Multiplexing\">Multiplexing<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent spy-active-parent\" data-target=\"#ref76288\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Multiple-access\">Multiple access<\/a><\/div>\r\n<\/li>\r\n<\/ul>\r\n<a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/telecommunication\">Quick Facts &amp; Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/images-videos\">Images &amp; Videos<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/15\/4615-004-75EA480A\/Block-diagram-telecommunications-system.jpg\" data-href=\"\/media\/1\/585799\/3691\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/15\/4615-004-75EA480A\/Block-diagram-telecommunications-system.jpg\" alt=\"Block diagram of a digital telecommunications system.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg\" data-href=\"\/media\/1\/585799\/3692\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg\" alt=\"Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/18\/4618-050-5E36758C\/signal-modulation-methods-binary-digits-amplitudes-series.jpg\" data-href=\"\/media\/1\/585799\/3693\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/4618-004-79CDE7BF\/signal-modulation-methods-binary-digits-amplitudes-series.jpg\" alt=\"digital signal modulation\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3694\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg\" alt=\"Analog multiplexing, as employed in the North American telephone systemIn frequency-division multiplexing (FDM), 12 separate voice signals, each of 4-kilohertz bandwidth, are modulated onto carrier waves in the 60\u2013108-kilohertz range. These modulated signals are combined to form a single complex group signal. Groups are further combined to form a hierarchy of increasing bandwidth and voice-carrying capacity.\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3054\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg\" alt=\"Digital multiplexing, as employed in the North American telephone systemIn time-division multiplexing (TDM), 24 digitized voice signals, each at 64 kilobits per second, are assigned successive time slots in a 1.544-megabits-per-second signal. Combined signals are further combined to form data streams of increasing bit-rate and voice-carrying capacity.\" height=\"50\" \/><\/a>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/76\/183276-138-AF2302D7\/overview-solar-flares.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"Learn how solar flares can affect satellites, rockets, telecommunications systems and activity on the surface of the Earth\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/19\/180119-138-29F20103\/Overview-invention-telephone-focus-work-Alexander-Graham.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"How the telephone was invented\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-student-links\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">For Students<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/summary\/telecommunication\"><img loading=\"lazy\" decoding=\"async\" class=\"default \" src=\"https:\/\/cdn.britannica.com\/mendel-resources\/3-131\/images\/shared\/default3.png?v=3.131.7\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/summary\/telecommunication\">telecommunication summary<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-questions\">\r\n<div class=\"text-gray-900 p-5 pb-0 font-serif font-14 font-weight-bold mx-10 mb-15\">Related Questions<\/div>\r\n<ul>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/Who-controls-the-Internet\">Who controls the Internet?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/Is-the-Internet-making-us-stupid\">Is the Internet \u201cmaking us stupid\u201d?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/Is-cancel-culture-or-callout-culture-good-for-society\">Is cancel culture (or \u201ccallout culture\u201d) good for society?<\/a><\/li>\r\n<li class=\"link-gray-900 mb-15\"><a class=\"\" href=\"https:\/\/www.britannica.com\/question\/When-was-the-telephone-patented\">When was the telephone patented?<\/a><\/li>\r\n<\/ul>\r\n<\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-invented-the-internet\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/88\/129488-131-09AB5E83\/Internet-blue-screen-blog-society-history-media-2009.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Internet http:\/\/www blue screen. 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Industrial Revolution England\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/inventors-and-inventions-of-the-industrial-revolution\">Inventors and Inventions of the Industrial Revolution<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191082-131-AD46C136\/threshold-office-Chester-A-Arthur-chromolithograph-Print-September-1881.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"&quot;On the threshold of office--what have we to expect of him?&quot; chromolithograph by Joseph Keppler, September 1881. Print shows the members of the assassinated James A. Garfield's cabinet looking at the new president, Chester Arthur. Chester A. Arthur.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\">The Surprisingly Disorderly History of the U.S. Presidential Succession Order<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/titanosaurs-8-of-the-worlds-biggest-dinosaurs\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/14\/196914-131-061D0CB0\/Patagotitan-mayorum-titanosaurs.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"illustration of the walking titanosaurus, Patagotitan mayorum\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/titanosaurs-8-of-the-worlds-biggest-dinosaurs\">Titanosaurs: 8 of the World&#8217;s Biggest Dinosaurs<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/why-does-cilantro-taste-like-soap-to-some-people\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/63\/194863-131-E49C6B35\/Coriander-leaves-cilantro-herbs-background.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Coriander leaves, fresh green cilantro on wooden background, herbs\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/why-does-cilantro-taste-like-soap-to-some-people\">Why Does Cilantro Taste Like Soap to Some People?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/73\/150373-131-DB2CFBDD\/Teton-Range-Jackson-Lake-Wyoming-Grand-National.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Jackson (Wyoming, United States). Jackson Lake (also called Jackson Hole), southern end of the Teton Range (the Grand Tetons), Grand Teton National Park, Wyoming, USA\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\">7 Wonders of America<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/189145-131-45FF672E\/Secret-Service-Agent-Earpiece.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Secret Service Agent Listens To Earpiece\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/secret-service-code-names-of-11-us-presidents\">Secret Service Code Names of 11 U.S. Presidents<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/68\/152568-131-E6B869A4\/King-cobra-world-snake.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"King Cobra snake in Malaysia. (reptile)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-of-the-worlds-deadliest-snakes\">9 of the World\u2019s Deadliest Snakes<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191982-131-D3194343\/ball.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"magic 8 ball\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/where-did-the-idea-for-the-magic-8-ball-come-from\">Where Did the Idea for the Magic 8 Ball Come From?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Technology\">Technology<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Web-Communication\">The Web &amp; Communication<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"false\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/15\/4615-004-75EA480A\/Block-diagram-telecommunications-system.jpg\" data-href=\"\/media\/1\/585799\/3691\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/15\/4615-004-75EA480A\/Block-diagram-telecommunications-system.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/15\/4615-004-75EA480A\/Block-diagram-telecommunications-system.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"Block diagram of a digital telecommunications system.\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\">Block diagram of a digital telecommunications system.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>telecommunication<\/h1>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"585799\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"caption alternate-titles\">Also known as: electronic communication<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">David E. Borth<\/span>,\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">Wayne Eric Stark<\/span><span class=\"text-gray-700 mx-5\">\u2022<\/span><a class=\"see-all border-gray-700 gtm-byline\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/additional-info#contributors\" rel=\"nofollow\">All<\/a><\/div>\r\n<div class=\"font-serif font-12 text-gray-700\"><span class=\"qa-fact-checked-by\">Fact-checked by<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link font-12 \">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-12-04T00:00:00CST\">Dec 4, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Key People:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Guglielmo-Marconi\">Guglielmo Marconi<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/money\/Carlos-Slim-Helu\">Carlos Slim Hel\u00fa<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Saad-al-Hariri\">Saad al-Hariri<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/money\/Morita-Akio\">Morita Akio<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/money\/Anousheh-Ansari\">Anousheh Ansari<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/television-technology\">television<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/broadcasting\">broadcasting<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/telephone\">telephone<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/Internet\">Internet<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/technology\/radio-technology\">radio technology<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>On the Web:<\/dt>\r\n<dd><a href=\"https:\/\/pmc.ncbi.nlm.nih.gov\/articles\/PMC4296789\/\" target=\"_blank\" rel=\"noopener\">National Center for Biotechnology Information &#8211; PubMed Central &#8211; Telecommunications and Internet Broadband Policy: Sorting Out the Pieces for Telerehabilitation<\/a>\u00a0(Dec. 04, 2024)<\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/telecommunication\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref1\" data-level=\"1\" data-has-spy=\"true\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref608159\"><\/span>telecommunication<\/strong>,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/science\" data-show-preview=\"true\">science<\/a>\u00a0and practice of transmitting information by electromagnetic means. Modern telecommunication centres on the problems involved in transmitting large volumes of information over long distances without damaging loss due to noise and interference. The basic components of a modern digital telecommunications system must be capable of transmitting voice, data, radio, and television signals.\u00a0<span id=\"ref608163\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/digital-transmission\">Digital transmission<\/a>\u00a0is employed in order to achieve high reliability and because the cost of digital\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/switching\" data-show-preview=\"true\">switching<\/a>\u00a0systems is much lower than the cost of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0systems. In order to use digital transmission, however, the analog signals that make up most voice, radio, and television\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>\u00a0must be subjected to a process of analog-to-digital conversion. (In\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data transmission<\/a>\u00a0this step is bypassed because the signals are already in digital form; most television, radio, and voice communication, however, use the analog system and must be digitized.) In many cases, the digitized signal is passed through a source encoder, which employs a number of formulas to reduce\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundant\" data-term=\"redundant\" data-type=\"MW\">redundant<\/a>\u00a0binary information. After source encoding, the digitized signal is processed in a channel encoder, which introduces redundant information that allows errors to be detected and corrected. The encoded signal is made suitable for transmission by\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/modulation-communications\" data-show-preview=\"true\">modulation<\/a>\u00a0onto a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/carrier-wave\" data-show-preview=\"true\">carrier wave<\/a>\u00a0and may be made part of a larger signal in a process known as\u00a0<span id=\"ref608166\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/multiplexing\" data-show-preview=\"true\">multiplexing<\/a>. The multiplexed signal is then sent into a multiple-access transmission channel. After transmission, the above process is reversed at the receiving end, and the information is extracted.<\/p>\r\n<p class=\"topic-paragraph\">This article describes the components of a digital telecommunications system as outlined above. For details on specific applications that utilize telecommunications systems, see the articles\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telegraph\" data-show-preview=\"true\">telegraph<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/fax\" data-show-preview=\"true\">fax<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/broadcasting\" data-show-preview=\"true\">radio<\/a>, and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/television-technology\" data-show-preview=\"true\">television<\/a>. Transmission over electric\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/wire\" data-show-preview=\"true\">wire<\/a>,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/radio-wave\" data-show-preview=\"true\">radio wave<\/a>, and optical fibre is discussed in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/telecommunications-media\" data-show-preview=\"true\">telecommunications media<\/a>. For an overview of the types of networks used in information transmission, see\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\" data-show-preview=\"true\">telecommunications network<\/a>.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76266\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\"><span id=\"ref608167\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/analogue-to-digital-conversion\">Analog-to-digital conversion<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"3692\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg\" data-href=\"\/media\/1\/585799\/3692\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg?w=300\" alt=\"Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted.\" data-width=\"280\" data-height=\"520\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/16\/4616-004-39B3985A\/steps-conversion-analog-signal-intervals-receiver-value.jpg\" data-href=\"\/media\/1\/585799\/3692\">Basic steps in analog-to-digital conversionAn analog signal is sampled at regular intervals. The amplitude at each interval is quantized, or assigned a value, and the values are mapped into a series of binary digits, or bits. The information is transmitted as a digital signal to the receiver, where it is decoded and the analog signal reconstituted.<\/a><button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In transmission of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/speech-language\" data-show-preview=\"true\">speech<\/a>, audio, or video information, the object is high fidelity\u2014that is, the best possible reproduction of the original message without the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/degradations\" data-term=\"degradations\" data-type=\"MW\">degradations<\/a>\u00a0imposed by signal\u00a0<span id=\"ref608168\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/distortion-communications\" data-show-preview=\"true\">distortion<\/a>\u00a0and\u00a0<span id=\"ref608169\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/noise-acoustics\" data-show-preview=\"true\">noise<\/a>. The basis of relatively noise-free and distortion-free telecommunication is the\u00a0<span id=\"ref608170\"><\/span>binary signal. The simplest possible signal of any kind that can be employed to transmit messages, the binary signal consists of only two possible values. These values are represented by the binary digits, or\u00a0<span id=\"ref608171\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bit-communications\" data-show-preview=\"true\">bits<\/a>, 1 and 0. Unless the noise and distortion picked up during transmission are great enough to change the binary signal from one value to another, the correct value can be determined by the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>\u00a0so that perfect reception can occur.<\/p>\r\n<p class=\"topic-paragraph\">If the information to be\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmitted\" data-term=\"transmitted\" data-type=\"EB\">transmitted<\/a>\u00a0is already in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/art\/binary-form\" data-show-preview=\"true\">binary form<\/a>\u00a0(as in data communication), there is no need for the signal to be digitally encoded. But ordinary voice communications taking place by way of a telephone are not in binary form; neither is much of the information gathered for transmission from a space probe, nor are the television or radio signals gathered for transmission through a satellite link. Such signals, which continually vary among a range of values, are said to be analog, and in digital communications systems analog signals must be converted to digital form. The process of making this signal conversion is called analog-to-digital (A\/D) conversion.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76267\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608172\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/sampling-communications\">Sampling<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Analog-to-digital\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/conversion\" data-term=\"conversion\" data-type=\"EB\">conversion<\/a>\u00a0begins with sampling, or measuring the amplitude of the analog\u00a0<span id=\"ref608173\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/wave-physics\" data-show-preview=\"true\">waveform<\/a>\u00a0at equally spaced discrete instants of time. The fact that samples of a continually varying wave may be used to represent that wave relies on the assumption that the wave is constrained in its rate of variation. Because a communications signal is actually a complex wave\u2014essentially the sum of a number of component sine waves, all of which have their own precise amplitudes and phases\u2014the rate of variation of the complex wave can be measured by the frequencies of oscillation of all its components. The difference between the maximum rate of oscillation (or highest frequency) and the minimum rate of oscillation (or lowest frequency) of the sine waves making up the signal is known as the\u00a0<span id=\"ref608174\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>\u00a0(<em>B<\/em>) of the signal.\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/Bandwidth\" data-term=\"Bandwidth\" data-type=\"EB\">Bandwidth<\/a>\u00a0thus represents the maximum\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0range occupied by a signal. In the case of a voice signal having a minimum frequency of 300 hertz and a maximum frequency of 3,300 hertz, the bandwidth is 3,000 hertz, or 3 kilohertz. Audio signals generally occupy about 20 kilohertz of bandwidth, and standard video signals occupy approximately 6 million hertz, or 6 megahertz.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">The concept of bandwidth is central to all telecommunication. In analog-to-digital conversion, there is a fundamental theorem that the analog signal may be uniquely represented by discrete samples spaced no more than one over twice the bandwidth (1\/2<em>B<\/em>) apart. This theorem is commonly referred to as the\u00a0<span id=\"ref608175\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/sampling-theorem\">sampling theorem<\/a>, and the sampling interval (1\/2<em>B<\/em>\u00a0seconds) is referred to as the\u00a0<span id=\"ref608176\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Nyquist-interval\">Nyquist interval<\/a>\u00a0(after the Swedish-born American electrical engineer\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Harry-Nyquist\" data-show-preview=\"true\">Harry Nyquist<\/a>). As an example of the Nyquist interval, in past telephone practice the bandwidth, commonly fixed at 3,000 hertz, was sampled at least every 1\/6,000 second. In current practice 8,000 samples are taken per second, in order to increase the frequency range and the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/fidelity\" data-term=\"fidelity\" data-type=\"MW\">fidelity<\/a>\u00a0of the speech representation.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76268\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608177\"><\/span>Quantization<\/h2>\r\n<p class=\"topic-paragraph\">In order for a sampled signal to be stored or transmitted in digital form, each sampled amplitude must be converted to one of a finite number of possible values, or levels. For ease in conversion to binary form, the number of levels is usually a power of 2\u2014that is, 8, 16, 32, 64, 128, 256, and so on, depending on the degree of precision required. In digital transmission of\u00a0<span id=\"ref608178\"><\/span>voice, 256 levels are commonly used because tests have shown that this provides adequate fidelity for the average telephone listener.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">The input to the quantizer is a sequence of sampled amplitudes for which there are an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/infinite\" data-term=\"infinite\" data-type=\"MW\">infinite<\/a>\u00a0number of possible values. The output of the quantizer, on the other hand, must be restricted to a finite number of levels. Assigning infinitely variable amplitudes to a limited number of levels inevitably introduces inaccuracy, and inaccuracy results in a corresponding amount of signal distortion. (For this reason quantization is often called a \u201clossy\u201d system.) The degree of inaccuracy depends on the number of output levels used by the quantizer. More quantization levels increase the accuracy of the representation, but they also increase the storage capacity or transmission speed required. Better performance with the same number of output levels can be achieved by judicious placement of the output levels and the amplitude\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/thresholds\" data-term=\"thresholds\" data-type=\"MW\">thresholds<\/a>\u00a0needed for assigning those levels. This placement in turn depends on the nature of the waveform that is being quantized. Generally, an optimal quantizer places more levels in amplitude ranges where the signal is more likely to occur and fewer levels where the signal is less likely. This technique is known as\u00a0<span id=\"ref608179\"><\/span>nonlinear quantization. Nonlinear quantization can also be accomplished by passing the signal through a compressor circuit, which amplifies the signal\u2019s weak components and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/attenuates\" data-term=\"attenuates\" data-type=\"MW\">attenuates<\/a>\u00a0its strong components. The compressed signal, now occupying a narrower\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamic\" data-term=\"dynamic\" data-type=\"MW\">dynamic<\/a>\u00a0range, can be quantized with a uniform, or linear, spacing of thresholds and output levels. In the case of the telephone signal, the compressed signal is uniformly quantized at 256 levels, each level being represented by a sequence of eight bits. At the receiving end, the reconstituted signal is expanded to its original range of amplitudes. This sequence of compression and expansion, known as\u00a0<span id=\"ref608180\"><\/span>companding, can yield an effective dynamic range equivalent to 13 bits.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<div data-page-index=\"18\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76269\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\"><span id=\"ref608181\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bit-mapping\">Bit mapping<\/a><\/h1>\r\n<p class=\"topic-paragraph\">In the next step in the digitization process, the output of the quantizer is mapped into a binary sequence. An\u00a0<span id=\"ref608182\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/encoding\">encoding<\/a>\u00a0table that might be used to generate the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/binary\" data-term=\"binary\" data-type=\"EB\">binary<\/a>\u00a0sequence is shown below:<span class=\"md-formula\"><span id=\"ref-14213\"><\/span><img decoding=\"async\" class=\"inline-image-baseline\" src=\"https:\/\/cdn.britannica.com\/13\/14213-004-A165FB67\/Encoding-table.jpg\" alt=\"Encoding table.\" \/><\/span>It is apparent that 8 levels require three binary digits, or bits; 16 levels require four bits; and 256 levels require eight bits. In general 2<sup><em>n<\/em><\/sup>\u00a0levels require\u00a0<em>n<\/em>\u00a0bits.<\/p>\r\n<p class=\"topic-paragraph\">In the case of 256-level voice quantization, where each level is represented by a sequence of 8 bits, the overall rate of transmission is 8,000 samples per second times 8 bits per sample, or 64,000 bits per second. All 8 bits must be transmitted before the next sample appears. In order to use more levels, more binary samples would have to be squeezed into the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/allotted\" data-term=\"allotted\" data-type=\"EB\">allotted<\/a>\u00a0time slot between successive signal samples. The circuitry would become more costly, and the bandwidth of the system would become correspondingly greater. Some transmission\u00a0<span id=\"ref608183\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/channel-communications\">channels<\/a>\u00a0(telephone wires are one example) may not have the bandwidth capability required for the increased number of binary samples and would distort the digital signals. Thus, although the accuracy required determines the number of quantization levels used, the resultant binary sequence must still be transmitted within the bandwidth tolerance allowed.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76270\" data-level=\"1\" data-has-spy=\"true\">\r\n<h2 class=\"h1\"><span id=\"ref608165\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/source-encoding\">Source encoding<\/a><\/h2>\r\n<p class=\"topic-paragraph\">As is pointed out in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication#ref76266\" data-show-preview=\"true\">analog-to-digital conversion<\/a>, any available\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/telecommunications-media\" data-show-preview=\"true\">telecommunications medium<\/a>\u00a0has a limited capacity for\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data transmission<\/a>. This capacity is commonly measured by the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/parameter\" data-term=\"parameter\" data-type=\"MW\">parameter<\/a>\u00a0called\u00a0<span id=\"ref608184\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>. Since the bandwidth of a signal increases with the number of bits to be transmitted each second, an important function of a digital communications system is to represent the digitized signal by as few bits as possible\u2014that is, to reduce\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundancy\" data-term=\"redundancy\" data-type=\"MW\">redundancy<\/a>.\u00a0<span id=\"ref608185\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/source-encoding\">Redundancy reduction<\/a>\u00a0is accomplished by a source encoder, which often operates in conjunction with the analog-to-digital converter.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76271\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608186\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/Huffman-encoding\">Huffman codes<\/a><\/h2>\r\n<p class=\"topic-paragraph\">In general, fewer bits on the average will be needed if the source encoder takes into account the probabilities at which different quantization levels are likely to occur. A simple example will illustrate this concept. Assume a quantizing scale of only four levels: 1, 2, 3, and 4. Following the usual standard of binary encoding, each of the four levels would be mapped by a two-bit code word. But also assume that level 1 occurs 50 percent of the time, that level 2 occurs 25 percent of the time, and that levels 3 and 4 each occur 12.5 percent of the time. Using variable-bit code words might cause more efficient mapping of these levels to be achieved. The variable-bit encoding rule would use only one bit 50 percent of the time, two bits 25 percent of the time, and three bits 25 percent of the time. On average it would use 1.75 bits per sample rather than the 2 bits per sample used in the standard code.<\/p>\r\n<p class=\"topic-paragraph\">Thus, for any given set of levels and associated probabilities, there is an optimal\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/encoding\" data-term=\"encoding\" data-type=\"EB\">encoding<\/a>\u00a0rule that minimizes the number of bits needed to represent the source. This encoding rule is known as the Huffman code, after the American\u00a0<span id=\"ref608187\"><\/span>D.A. Huffman, who created it in 1952. Even more efficient encoding is possible by grouping sequences of levels together and applying the Huffman code to these sequences.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76272\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">The\u00a0<span id=\"ref608188\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Lempel-Ziv-algorithm\">Lempel-Ziv algorithm<\/a><\/h2>\r\n<p class=\"topic-paragraph\">The design and performance of the Huffman code depends on the designers\u2019 knowing the probabilities of different levels and sequences of levels. In many cases, however, it is desirable to have an encoding system that can adapt to the unknown probabilities of a source. A very efficient technique for encoding sources without needing to know their probable occurrence was developed in the 1970s by the Israelis\u00a0<span id=\"ref608189\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Abraham-Lempel\">Abraham Lempel<\/a>\u00a0and\u00a0<span id=\"ref608190\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Jacob-Ziv\">Jacob Ziv<\/a>. The Lempel-Ziv\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/algorithm\" data-term=\"algorithm\" data-type=\"MW\">algorithm<\/a>\u00a0works by constructing a codebook out of sequences encountered previously. For example, the codebook might begin with a set of four 12-bit code words representing four possible signal levels. If two of those levels arrived in sequence, the encoder, rather than transmitting two full code words (of length 24), would transmit the code word for the first level (12 bits) and then an extra two bits to indicate the second level. The encoder would then construct a new code word of 12 bits for the sequence of two levels, so that even fewer bits would be used thereafter to represent that particular combination of levels. The encoder would continue to read quantization levels until another sequence arrived for which there was no code word. In this case the sequence without the last level would be in the codebook, but not the whole sequence of levels. Again, the encoder would transmit the code word for the initial sequence of levels and then an extra two bits for the last level. The process would continue until all 4,096 possible 12-bit combinations had been assigned as code words.<\/p>\r\n<p class=\"topic-paragraph\">In practice, standard\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/algorithms\" data-term=\"algorithms\" data-type=\"MW\">algorithms<\/a>\u00a0for compressing binary files use code words of 12 bits and transmit 1 extra bit to indicate a new sequence. Using such a code, the Lempel-Ziv algorithm can compress transmissions of English text by about 55 percent, whereas the Huffman code compresses the transmission by only 43 percent.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76273\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608191\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/run-length-encoding\">Run-length codes<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Certain signal sources are known to produce \u201cruns,\u201d or long sequences of only 1s or 0s. In these cases it is more efficient to transmit a code for the length of the run rather than all the bits that represent the run itself. One source of long runs is the\u00a0<span id=\"ref608192\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/facsimile-machine\">fax machine<\/a>. A fax machine works by scanning a document and mapping very small areas of the document into either a black pixel (picture element) or a white pixel. The document is divided into a number of lines (approximately 100 per inch), with 1,728 pixels in each line (at standard resolution). If all black pixels were mapped into 1s and all white pixels into 0s, then the scanned document would be represented by 1,857,600 bits (for a standard American 11-inch page). At older\u00a0<span id=\"ref608193\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modem\" data-show-preview=\"true\">modem<\/a>\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmission\" data-term=\"transmission\" data-type=\"EB\">transmission<\/a>\u00a0speeds of 4,800 bits per second, it would take 6 minutes 27 seconds to send a single page. If, however, the sequence of 0s and 1s were compressed using a run-length code, significant reductions in transmission time would be made.<\/p>\r\n<p class=\"topic-paragraph\">The code for fax machines is actually a combination of a run-length code and a Huffman code; it can be explained as follows: A run-length code maps run lengths into code words, and the codebook is partitioned into two parts. The first part contains symbols for runs of lengths that are a multiple of 64; the second part is made up of runs from 0 to 63 pixels. Any run length would then be represented as a multiple of 64 plus some remainder. For example, a run of 205 pixels would be sent using the code word for a run of length 192 (3 \u00d7 64) plus the code word for a run of length 13. In this way the number of bits needed to represent the run is decreased significantly. In addition, certain runs that are known to have a higher probability of occurrence are\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/encoded\" data-term=\"encoded\" data-type=\"EB\">encoded<\/a>\u00a0into code words of short length, further reducing the number of bits that need to be transmitted. Using this type of encoding, typical compressions for facsimile transmission range between 4 to 1 and 8 to 1. Coupled to higher modem speeds, these compressions reduce the transmission time of a single page to between 48 seconds and 1 minute 37 seconds.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"19\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76274\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\"><span id=\"ref608194\"><\/span>Channel encoding<\/h1>\r\n<p class=\"topic-paragraph\">As described in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Bit-mapping#ref76269\" data-show-preview=\"true\">Source encoding<\/a>, one purpose of the source encoder is to eliminate\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundant\" data-term=\"redundant\" data-type=\"MW\">redundant<\/a>\u00a0binary digits from the digitized signal. The strategy of the channel encoder, on the other hand, is to add\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundancy\" data-term=\"redundancy\" data-type=\"MW\">redundancy<\/a>\u00a0to the transmitted signal\u2014in this case so that errors caused by noise during transmission can be corrected at the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>. The process of encoding for protection against channel errors is called\u00a0<span id=\"ref608195\"><\/span>error-control coding. Error-control codes are used in a variety of applications, including\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/satellite-communication\" data-show-preview=\"true\">satellite communication<\/a>, deep-space\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/communication\" data-show-preview=\"true\">communication<\/a>, mobile\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/radio\" data-show-preview=\"true\">radio<\/a>\u00a0communication, and computer networking.<\/p>\r\n<p class=\"topic-paragraph\">There are two commonly employed methods for protecting electronically transmitted information from errors. One method is called\u00a0<span id=\"ref608196\"><\/span>forward error control (FEC). In this method information bits are protected against errors by the transmitting of extra redundant bits, so that if errors occur during transmission the redundant bits can be used by the\u00a0<span id=\"ref608197\"><\/span>decoder to determine where the errors have occurred and how to correct them. The second method of error control is called\u00a0<span id=\"ref608198\"><\/span>automatic repeat request (ARQ). In this method redundant bits are added to the transmitted information and are used by the receiver to detect errors. The receiver then signals a request for a repeat transmission. Generally, the number of extra bits needed simply to detect an error, as in the ARQ system, is much smaller than the number of redundant bits needed both to detect and to correct an error, as in the FEC system.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76275\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608199\"><\/span>Repetition codes<\/h2>\r\n<p class=\"topic-paragraph\">One simple, but not usually\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/implemented\" data-term=\"implemented\" data-type=\"MW\">implemented<\/a>, FEC method is to send each data bit three times. The receiver examines the three transmissions and decides by majority vote whether a 0 or 1 represents a sample of the original signal. In this coded system, called a repetition code of block-length three and rate one-third, three times as many bits per second are used to transmit the same signal as are used by an uncoded system; hence, for a fixed available\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>\u00a0only one-third as many signals can be conveyed with the coded system as compared with the uncoded system. The gain is that now at least two of the three coded bits must be in error before a reception error occurs.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76276\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">The\u00a0<span id=\"ref608200\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/Hamming-code\">Hamming code<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Another simple example of an FEC code is known as the Hamming code. This code is able to protect a four-bit information signal from a single error on the channel by adding three\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/redundant\" data-term=\"redundant\" data-type=\"EB\">redundant<\/a>\u00a0bits to the signal. Each sequence of seven bits (four information bits plus three redundant bits) is called a code word. The first redundant bit is chosen so that the sum of ones in the first three information bits plus the first redundant bit amounts to an even number. (This calculation is called a\u00a0<span id=\"ref608201\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/parity-check\">parity check<\/a>, and the redundant bit is called a parity bit.) The second parity bit is chosen so that the sum of the ones in the last three information bits plus the second parity bit is even, and the third parity bit is chosen so that the sum of ones in the first, second, and fourth information bits and the last parity bit is even. This code can correct a single channel error by recomputing the parity checks. A parity check that fails indicates an error in one of the positions checked, and the two\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/subsequent\" data-term=\"subsequent\" data-type=\"EB\">subsequent<\/a>\u00a0parity checks, by process of elimination, determine the precise location of the error. The Hamming code thus can correct any single error that occurs in any of the seven positions. If a double error occurs, however, the decoder will choose the wrong code word.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76277\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608203\"><\/span>Convolutional encoding<\/h2>\r\n<p class=\"topic-paragraph\">The Hamming code is called a\u00a0<span id=\"ref608202\"><\/span>block code because information is blocked into bit sequences of finite length to which a number of redundant bits are added. When\u00a0<em>k<\/em>\u00a0information bits are provided to a block encoder,\u00a0<em>n<\/em>\u00a0\u2212\u00a0<em>k<\/em>\u00a0redundancy bits are appended to the information bits to form a transmitted code word of\u00a0<em>n<\/em>\u00a0bits. The entire code word of length\u00a0<em>n<\/em>\u00a0is thus completely determined by one block of\u00a0<em>k<\/em>\u00a0information bits. In another channel-<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/encoding\" data-term=\"encoding\" data-type=\"EB\">encoding<\/a>\u00a0scheme, known as convolutional encoding, the encoder output is not naturally segmented into blocks but is instead an unending stream of bits. In convolutional encoding, memory is incorporated into the encoding process, so that the preceding\u00a0<em>M<\/em>\u00a0blocks of\u00a0<em>k<\/em>\u00a0information bits, together with the current block of\u00a0<em>k<\/em>\u00a0information bits, determine the encoder output. The encoder accomplishes this by shifting among a finite number of \u201cstates,\u201d or \u201cnodes.\u201d There are several variations of convolutional encoding, but the simplest example may be seen in what is known as the (<em>n<\/em>,1) encoder, in which the current block of\u00a0<em>k<\/em>\u00a0information bits consists of only one bit. At each given state of the (<em>n<\/em>,1) encoder, when the information bit (a 0 or a 1) is received, the encoder\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmits\" data-term=\"transmits\" data-type=\"EB\">transmits<\/a>\u00a0a sequence of\u00a0<em>n<\/em>\u00a0bits assigned to represent that bit when the encoder is at that current state. At the same time, the encoder shifts to one of only two possible successor states, depending on whether the information bit was a 0 or a 1. At this successor state, in turn, the next information bit is represented by a specific sequence of\u00a0<em>n<\/em>\u00a0bits, and the encoder is again shifted to one of two possible successor states. In this way, the sequence of information bits stored in the encoder\u2019s memory determines both the state of the encoder and its output, which is modulated and transmitted across the channel. At the receiver, the demodulated bit sequence is compared to the possible bit sequences that can be produced by the encoder. The receiver determines the bit sequence that is most likely to have been transmitted, often by using an efficient decoding\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/algorithm\" data-term=\"algorithm\" data-type=\"MW\">algorithm<\/a>\u00a0called\u00a0<span id=\"ref608204\"><\/span>Viterbi decoding (after its inventor, A.J. Viterbi). In general, the greater the memory (i.e., the more states) used by the encoder, the better the error-correcting performance of the code\u2014but only at the cost of a more complex decoding algorithm. In addition, the larger the number of bits (<em>n<\/em>) used to transmit information, the better the performance\u2014at the cost of a decreased data rate or larger bandwidth.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Coding and decoding processes similar to those described above are employed in\u00a0<span id=\"ref608205\"><\/span>trellis coding, a coding scheme used in high-speed\u00a0<span id=\"ref608206\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modem\" data-show-preview=\"true\">modems<\/a>. However, instead of the sequence of bits that is produced by a convolutional encoder, a trellis encoder produces a sequence of modulation symbols. At the transmitter, the channel-encoding process is coupled with the modulation process, producing a system known as\u00a0<span id=\"ref608207\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/trellis-coded-modulation\">trellis-coded modulation<\/a>. At the receiver,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/decoding\" data-term=\"decoding\" data-type=\"EB\">decoding<\/a>\u00a0and demodulating are performed jointly in order to optimize the performance of the error-correcting algorithm.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"20\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76278\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\"><span id=\"ref608208\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modulation-communications\" data-show-preview=\"true\">Modulation<\/a><\/h1>\r\n<p class=\"topic-paragraph\">In many telecommunications systems, it is necessary to represent an information-bearing signal with a waveform that can pass accurately through a transmission medium. This assigning of a suitable waveform is accomplished by\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/modulation-communications\" data-show-preview=\"true\">modulation<\/a>, which is the process by which some characteristic of a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/carrier-wave\" data-show-preview=\"true\">carrier wave<\/a>\u00a0is varied in accordance with an information signal, or modulating wave. The modulated signal is then transmitted over a channel, after which the original information-bearing signal is recovered through a process of demodulation.<\/p>\r\n<p class=\"topic-paragraph\">Modulation is applied to information signals for a number of reasons, some of which are outlined below.<\/p>\r\n<ol>\r\n<li>\r\n<div>Many transmission channels are characterized by limited passbands\u2014that is, they will pass only certain ranges of frequencies without seriously\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/attenuating\" data-term=\"attenuating\" data-type=\"MW\">attenuating<\/a>\u00a0them (reducing their amplitude). Modulation methods must therefore be applied to the information signals in order to \u201cfrequency translate\u201d the signals into the range of frequencies that are permitted by the channel. Examples of channels that exhibit passband characteristics include alternating-current-coupled coaxial cables, which pass signals only in the range of 60 kilohertz to several hundred megahertz, and fibre-optic cables, which pass light signals only within a given wavelength range without significant attenuation. In these instances\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0translation is used to \u201cfit\u201d the information signal to the communications channel.<\/div>\r\n<\/li>\r\n<li>\r\n<div>In many instances a communications channel is shared by multiple users. In order to prevent mutual interference, each user\u2019s information signal is modulated onto an assigned carrier of a specific frequency. When the frequency assignment and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/subsequent\" data-term=\"subsequent\" data-type=\"EB\">subsequent<\/a>\u00a0combining is done at a central point, the resulting combination is a\u00a0<span id=\"ref608209\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-division-multiplexing\">frequency-division<\/a>\u00a0multiplexed signal, as is discussed in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Multiplexing#ref76285\" data-show-preview=\"true\">Multiplexing<\/a>. Frequently there is no central combining point, and the communications channel itself acts as a distributed combine. An example of the latter situation is the broadcast\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/radio\" data-show-preview=\"true\">radio<\/a>\u00a0bands (from 540 kilohertz to 600 megahertz), which permit simultaneous transmission of multiple AM radio, FM radio, and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/television-technology\" data-show-preview=\"true\">television<\/a>\u00a0signals without mutual interference as long as each signal is assigned to a different frequency band.<\/div>\r\n<\/li>\r\n<li>\r\n<div>Even when the communications channel can support direct transmission of the information-bearing signal, there are often practical reasons why this is undesirable. A simple example is the transmission of a three-kilohertz (i.e., voiceband) signal via\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/radio-wave\" data-show-preview=\"true\">radio wave<\/a>. In free space the wavelength of a three-kilohertz signal is 100 kilometres (60 miles). Since an effective radio\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/antenna-electronics\" data-show-preview=\"true\">antenna<\/a>\u00a0is typically as large as half the wavelength of the signal, a three-kilohertz radio wave might require an antenna up to 50 kilometres in length. In this case translation of the voice frequency to a higher frequency would allow the use of a much smaller antenna.<\/div>\r\n<\/li>\r\n<\/ol>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76279\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608211\"><\/span>Analog modulation<\/h2>\r\n<p class=\"topic-paragraph\">As is noted in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication#ref76266\" data-show-preview=\"true\">analog-to-digital conversion<\/a>, voice signals, as well as audio and video signals, are inherently\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0in form. In most modern systems these signals are digitized prior to transmission, but in some systems the\u00a0<span id=\"ref608210\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/analog-signal\">analog signals<\/a>\u00a0are still transmitted directly without converting them to digital form. There are two commonly used methods of modulating analog signals. One technique, called\u00a0<span id=\"ref608213\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/amplitude-modulation\" data-show-preview=\"true\">amplitude modulation<\/a>, varies the amplitude of a fixed-frequency carrier wave in proportion to the information\u00a0<span id=\"ref1047195\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/signal\">signal<\/a>. The other technique, called\u00a0<span id=\"ref608214\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-modulation\" data-show-preview=\"true\">frequency modulation<\/a>, varies the frequency of a fixed-amplitude carrier wave in proportion to the information signal.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76280\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608216\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/digital-signal-modulation\">Digital modulation<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"3693\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/18\/4618-050-5E36758C\/signal-modulation-methods-binary-digits-amplitudes-series.jpg\" data-href=\"\/media\/1\/585799\/3693\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/18\/4618-050-5E36758C\/signal-modulation-methods-binary-digits-amplitudes-series.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/18\/4618-050-5E36758C\/signal-modulation-methods-binary-digits-amplitudes-series.jpg?w=300\" alt=\"digital signal modulation\" data-width=\"1600\" data-height=\"1127\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/18\/4618-050-5E36758C\/signal-modulation-methods-binary-digits-amplitudes-series.jpg\" data-href=\"\/media\/1\/585799\/3693\">digital signal modulation<\/a>A digital signal, representing the binary digits 0 and 1 by a series of on and off amplitudes, is impressed onto an analog carrier wave of constant amplitude and frequency. In amplitude-shift keying (ASK), the modulated wave represents the series of bits by shifting abruptly between high and low amplitude. In frequency-shift keying (FSK), the bit stream is represented by shifts between two frequencies. In phase-shift keying (PSK), amplitude and frequency remain constant, and the bit stream is represented by shifts in the phase of the modulated signal.<button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In order to transmit computer\u00a0<span id=\"ref608217\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/data-transmission\" data-show-preview=\"true\">data<\/a>\u00a0and other digitized information over a communications channel, an analog carrier wave can be modulated to reflect the binary nature of the digital baseband signal. The\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/parameters\" data-term=\"parameters\" data-type=\"MW\">parameters<\/a>\u00a0of the carrier that can be modified are the amplitude, the frequency, and the phase.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76281\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref608218\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/amplitude-shift-keying\">Amplitude-shift keying<\/a><\/h2>\r\n<p class=\"topic-paragraph\">If amplitude is the only\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/parameter\" data-term=\"parameter\" data-type=\"MW\">parameter<\/a>\u00a0of the carrier wave to be altered by the information signal, the modulating method is called amplitude-shift keying (ASK). ASK can be considered a digital version of analog amplitude modulation. In its simplest form, a burst of radio frequency is transmitted only when a binary 1 appears and is stopped when a 0 appears. In another variation, the 0 and 1 are represented in the modulated signal by a shift between two preselected amplitudes.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-read-more-module\" href=\"https:\/\/www.britannica.com\/technology\/materials-science\/Materials-for-computers-and-communications#ref406224\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/76\/105676-050-81373A43\/Movement-electron-hole-crystal-lattice.jpg\" alt=\"electron hole: movement\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-navy-dark\">More From Britannica<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">materials science: Materials for computers and communications<\/div>\r\n<\/div>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76282\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref608219\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-shift-keying\">Frequency-shift keying<\/a><\/h2>\r\n<p class=\"topic-paragraph\">If frequency is the parameter chosen to be a function of the information signal, the modulation method is called frequency-shift keying (FSK). In the simplest form of FSK signaling, digital\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>\u00a0is transmitted using one of two frequencies, whereby one frequency is used to transmit a 1 and the other frequency to transmit a 0. Such a scheme was used in the Bell 103 voiceband\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/modem\" data-show-preview=\"true\">modem<\/a>, introduced in 1962, to transmit information at rates up to 300 bits per second over the public switched\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0network. In the Bell 103 modem, frequencies of 1,080 +\/- 100 hertz and 1,750 +\/- 100 hertz were used to send binary data in both directions.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76283\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref608220\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/phase-shift-keying\">Phase-shift keying<\/a><\/h2>\r\n<p class=\"topic-paragraph\">When phase is the parameter altered by the information signal, the method is called phase-shift keying (PSK). In the simplest form of PSK a single radio frequency carrier is sent with a fixed phase to represent a 0 and with a 180\u00b0 phase shift\u2014that is, with the opposite polarity\u2014to represent a 1. PSK was employed in the Bell 212 modem, which was introduced about 1980 to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmit\" data-term=\"transmit\" data-type=\"EB\">transmit<\/a>\u00a0information at rates up to 1,200 bits per second over the public switched telephone network.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76284\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Advanced methods<\/h2>\r\n<p class=\"topic-paragraph\">In addition to the elementary forms of digital modulation described above, there exist more advanced methods that result from a superposition of multiple modulating signals. An example of the latter form of modulation is\u00a0<span id=\"ref608221\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/quadrature-amplitude-modulation\">quadrature amplitude modulation<\/a>\u00a0(QAM). QAM signals actually transmit two amplitude-modulated signals in phase quadrature (i.e., 90\u00b0 apart), so that four or more bits are represented by each shift of the combined signal. Communications systems that employ QAM include digital cellular systems in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>\u00a0and Japan as well as most voiceband modems transmitting above 2,400 bits per second.<\/p>\r\n<p class=\"topic-paragraph\">A form of modulation that\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/combines\" data-term=\"combines\" data-type=\"EB\">combines<\/a>\u00a0convolutional codes with QAM is known as\u00a0<span id=\"ref608222\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/trellis-coded-modulation\">trellis-coded modulation<\/a>\u00a0(TCM), which is described in\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\/Channel-encoding#ref76274\" data-show-preview=\"true\">Channel encoding<\/a>. Trellis-coded modulation forms an essential part of most of the modern voiceband modems operating at data rates of 9,600 bits per second and above, including V.32 and V.34 modems.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"21\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76285\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\"><span id=\"ref608223\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/multiplexing\" data-show-preview=\"true\">Multiplexing<\/a><\/h1>\r\n<p class=\"topic-paragraph\">Because of the installation cost of a communications channel, such as a microwave link or a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/coaxial-cable\" data-show-preview=\"true\">coaxial cable<\/a>\u00a0link, it is desirable to share the channel among multiple users. Provided that the channel\u2019s data capacity exceeds that required to support a single user, the channel may be shared through the use of multiplexing methods. Multiplexing is the sharing of a communications channel through local\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/combining\" data-term=\"combining\" data-type=\"EB\">combining<\/a>\u00a0of signals at a common point. Two types of multiplexing are commonly employed: frequency-division multiplexing and time-division multiplexing.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76286\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608224\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/frequency-division-multiplexing\">Frequency-division multiplexing<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"3694\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3694\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg?w=300\" alt=\"Analog multiplexing, as employed in the North American telephone systemIn frequency-division multiplexing (FDM), 12 separate voice signals, each of 4-kilohertz bandwidth, are modulated onto carrier waves in the 60\u2013108-kilohertz range. These modulated signals are combined to form a single complex group signal. Groups are further combined to form a hierarchy of increasing bandwidth and voice-carrying capacity.\" data-width=\"590\" data-height=\"370\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/19\/4619-004-41851F3A\/multiplexing-North-American-frequency-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3694\">Analog multiplexing, as employed in the North American telephone systemIn frequency-division multiplexing (FDM), 12 separate voice signals, each of 4-kilohertz bandwidth, are modulated onto carrier waves in the 60\u2013108-kilohertz range. These modulated signals are combined to form a single complex group signal. Groups are further combined to form a hierarchy of increasing bandwidth and voice-carrying capacity.<\/a><button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In frequency-division multiplexing (FDM), the available\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>\u00a0of a communications channel is shared among multiple users by\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0translating, or modulating, each of the individual users onto a different carrier frequency. Assuming sufficient frequency separation of the carrier frequencies that the modulated signals do not overlap, recovery of each of the FDM signals is possible at the receiving end. In order to prevent overlap of the signals and to simplify filtering, each of the modulated signals is separated by a\u00a0<span id=\"ref608225\"><\/span>guard band, which consists of an unused portion of the available frequency spectrum. Each user is assigned a given frequency band for all time.<\/p>\r\n<p class=\"topic-paragraph\">While each user\u2019s information signal may be either\u00a0<span id=\"ref608227\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/analog-signal\">analog<\/a>\u00a0or digital, the combined FDM signal is inherently an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0waveform. Therefore, an FDM signal must be transmitted over an analog channel. Examples of FDM are found in some of the old long-distance\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0transmission systems, including the American N- and\u00a0<span id=\"ref608230\"><\/span>L-carrier coaxial cable systems and analog\u00a0<span id=\"ref608228\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/point-to-point-microwave-transmission\">point-to-point microwave<\/a>\u00a0systems. In the L-carrier system a hierarchical combining structure is employed in which 12 voiceband signals are frequency-division multiplexed to form a group signal in the frequency range of 60 to 108 kilohertz. Five group signals are multiplexed to form a supergroup signal in the frequency range of 312 to 552 kilohertz, corresponding to 60 voiceband signals, and 10 supergroup signals are multiplexed to form a master group signal. In the L1 carrier system,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/deployed\" data-term=\"deployed\" data-type=\"MW\">deployed<\/a>\u00a0in the 1940s, the master group was transmitted directly over coaxial cable. For microwave systems, it was frequency modulated onto a microwave carrier frequency for point-to-point transmission. In the\u00a0<span id=\"ref608231\"><\/span>L4 system, developed in the 1960s, six master groups were combined to form a jumbo group signal of 3,600 voiceband signals.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76287\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608232\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/time-division-multiplexing\">Time-division multiplexing<\/a><\/h2>\r\n<div class=\"assemblies\">\r\n<div class=\"w-100\">\r\n<figure class=\"md-assembly m-0 mb-md-0 card card-borderless print-false\" data-assembly-id=\"3054\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media\" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3054\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg?w=300\" alt=\"Digital multiplexing, as employed in the North American telephone systemIn time-division multiplexing (TDM), 24 digitized voice signals, each at 64 kilobits per second, are assigned successive time slots in a 1.544-megabits-per-second signal. Combined signals are further combined to form data streams of increasing bit-rate and voice-carrying capacity.\" data-width=\"430\" data-height=\"300\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/25\/4625-004-7A5370CF\/multiplexing-North-American-time-division-telephone-system-voice.jpg\" data-href=\"\/media\/1\/585799\/3054\">Digital multiplexing, as employed in the North American telephone systemIn time-division multiplexing (TDM), 24 digitized voice signals, each at 64 kilobits per second, are assigned successive time slots in a 1.544-megabits-per-second signal. Combined signals are further combined to form data streams of increasing bit-rate and voice-carrying capacity.<\/a><button class=\"js-more-btn btn btn-unstyled font-12 bg-white js-content\" aria-label=\"Toggle more\/less fact data\"><span class=\"link-blue\">(more)<\/span><\/button><\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Multiplexing also may be conducted through the interleaving of time segments from different signals onto a single transmission path\u2014a process known as time-division multiplexing (TDM). Time-division multiplexing of multiple signals is possible only when the available\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/data\" data-term=\"data\" data-type=\"EB\">data<\/a>\u00a0rate of the channel exceeds the data rate of the total number of users. While TDM may be applied to either digital or analog signals, in practice it is applied almost always to digital signals. The resulting composite signal is thus also a digital signal.<\/p>\r\n<p class=\"topic-paragraph\">In a representative TDM system, data from multiple users are presented to a time-division multiplexer. A scanning switch then selects data from each of the users in sequence to form a composite TDM signal consisting of the interleaved data signals. Each user\u2019s data path is assumed to be time-aligned or synchronized to each of the other users\u2019 data paths and to the scanning mechanism. If only one bit were selected from each of the data sources, then the scanning mechanism would select the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/value\" data-term=\"value\" data-type=\"EB\">value<\/a>\u00a0of the arriving bit from each of the multiple data sources. In practice, however, the scanning mechanism usually selects a slot of data consisting of multiple bits of each user\u2019s data; the scanner switch is then advanced to the next user to select another slot, and so on. Each user is assigned a given time slot for all time.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Most modern telecommunications systems employ some form of TDM for transmission over long-distance routes. The multiplexed signal may be sent directly over cable systems, or it may be modulated onto a carrier signal for transmission via\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/radio-wave\" data-show-preview=\"true\">radio wave<\/a>. Examples of such systems include the North American T carriers as well as digital point-to-point microwave systems. In\u00a0<span id=\"ref608233\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/T1\" data-show-preview=\"true\">T1 systems<\/a>, introduced in 1962, 24 voiceband signals (or the digital equivalent) are time-division multiplexed together. The voiceband signal is a 64-kilobit-per-second data stream consisting of 8-bit symbols transmitted at a rate of 8,000 symbols per second. The TDM process interleaves 24 8-bit time slots together, along with a single frame-synchronization bit, to form a 193-bit frame. The 193-bit frames are formed at the rate of 8,000 frames per second, resulting in an overall data rate of 1.544 megabits per second. For transmission over more recent T-carrier systems, T1 signals are often further multiplexed to form higher-data-rate signals\u2014again using a hierarchical scheme.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"22\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 grey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76288\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\"><span id=\"ref608234\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/multiple-access\">Multiple access<\/a><\/h1>\r\n<p class=\"topic-paragraph\">Multiplexing is defined as the sharing of a communications channel through local combining at a common point. In many cases, however, the communications channel must be efficiently shared among many users that are geographically distributed and that sporadically attempt to communicate at random points in time. Three schemes have been\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/devised\" data-term=\"devised\" data-type=\"EB\">devised<\/a>\u00a0for efficient sharing of a single channel under these conditions; they are called frequency-division multiple access (FDMA), time-division multiple access (TDMA), and code-division multiple access (CDMA). These techniques can be used alone or together in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/telephone\" data-show-preview=\"true\">telephone<\/a>\u00a0systems, and they are well illustrated by the most advanced mobile cellular systems.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76289\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608235\"><\/span>Frequency-division multiple access<\/h2>\r\n<p class=\"topic-paragraph\">In FDMA the goal is to divide the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/frequency-physics\" data-show-preview=\"true\">frequency<\/a>\u00a0spectrum into slots and then to separate the signals of different users by placing them in separate frequency slots. The difficulty is that the frequency spectrum is limited and that there are typically many more potential communicators than there are available frequency slots. In order to make efficient use of the communications channel, a system must be devised for managing the available slots. In the\u00a0<span id=\"ref608236\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/advanced-mobile-phone-system\">advanced mobile phone system<\/a>\u00a0(AMPS), the\u00a0<span id=\"ref608237\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/cell-phone\" data-show-preview=\"true\">cellular<\/a>\u00a0system employed in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>, different callers use separate frequency slots via FDMA. When one telephone call is completed, a network-managing computer at the cellular base station reassigns the released frequency slot to a new caller. A key goal of the AMPS system is to reuse frequency slots whenever possible in order to accommodate as many callers as possible. Locally within a cell, frequency slots can be reused when corresponding calls are terminated. In addition, frequency slots can be used simultaneously by multiple callers located in separate cells. The cells must be far enough apart geographically that the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/radio\" data-show-preview=\"true\">radio<\/a>\u00a0signals from one cell are sufficiently\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/attenuated\" data-term=\"attenuated\" data-type=\"MW\">attenuated<\/a>\u00a0at the location of the other cell using the same frequency slot.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76290\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608238\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/time-division-multiple-access\">Time-division multiple access<\/a><\/h2>\r\n<p class=\"topic-paragraph\">In TDMA the goal is to divide time into slots and separate the signals of different users by placing the signals in separate time slots. The difficulty is that requests to use a single communications channel occur randomly, so that on occasion the number of requests for time slots is greater than the number of available slots. In this case information must be buffered, or stored in memory, until time slots become available for transmitting the data. The buffering introduces delay into the system. In the\u00a0<span id=\"ref608239\"><\/span>IS54 cellular system, three digital signals are interleaved using TDMA and then transmitted in a 30-kilohertz frequency slot that would be occupied by one\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analog\" data-term=\"analog\" data-type=\"MW\">analog<\/a>\u00a0signal in AMPS. Buffering digital signals and interleaving them in time causes some extra delay, but the delay is so brief that it is not ordinarily noticed during a call. The IS54 system uses aspects of both TDMA and FDMA.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref76291\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\"><span id=\"ref608240\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/code-division-multiple-access\">Code-division multiple access<\/a><\/h2>\r\n<p class=\"topic-paragraph\">In CDMA, signals are sent at the same time in the same frequency band. Signals are either selected or rejected at the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>\u00a0by recognition of a user-specific signature waveform, which is constructed from an assigned spreading code. The\u00a0<span id=\"ref608241\"><\/span>IS95 cellular system employs the CDMA technique. In IS95 an analog\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/speech-language\" data-show-preview=\"true\">speech<\/a>\u00a0signal that is to be sent to a cell site is first quantized and then organized into one of a number of digital frame structures. In one frame structure, a frame of 20 milliseconds\u2019 duration consists of 192 bits. Of these 192 bits, 172 represent the speech signal itself, 12 form a cyclic\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundancy\" data-term=\"redundancy\" data-type=\"MW\">redundancy<\/a>\u00a0check that can be used for error\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/detection\" data-show-preview=\"true\">detection<\/a>, and 8 form an encoder \u201ctail\u201d that allows the decoder to work properly. These bits are formed into an encoded data stream. After interleaving of the encoded data stream, bits are organized into groups of six. Each group of six bits indicates which of 64 possible waveforms to transmit. Each of the waveforms to be transmitted has a particular pattern of alternating polarities and occupies a certain portion of the radio-frequency spectrum. Before one of the waveforms is transmitted, however, it is multiplied by a code sequence of polarities that\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/alternate\" data-term=\"alternate\" data-type=\"EB\">alternate<\/a>\u00a0at a rate of 1.2288 megahertz, spreading the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/bandwidth\" data-show-preview=\"true\">bandwidth<\/a>\u00a0occupied by the signal and causing it to occupy (after filtering at the transmitter) about 1.23 megahertz of the radio-frequency spectrum. At the cell site one user can be selected from multiple users of the same 1.23-megahertz bandwidth by its assigned code sequence.<\/p>\r\n<p class=\"topic-paragraph\">CDMA is sometimes referred to as\u00a0<span id=\"ref608242\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/spread-spectrum-multiple-access\">spread-spectrum multiple access<\/a>\u00a0(SSMA), because the process of multiplying the signal by the code sequence causes the power of the transmitted signal to be spread over a larger bandwidth. Frequency management, a necessary feature of FDMA, is eliminated in CDMA. When another user wishes to use the communications channel, it is assigned a code and immediately\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmits\" data-term=\"transmits\" data-type=\"EB\">transmits<\/a>\u00a0instead of being stored until a frequency slot opens.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/James-S-Lehnert\/4193\">James S. Lehnert<\/a><\/span><span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/Wayne-Eric-Stark\/4216\">Wayne Eric Stark<\/a><\/span><span class=\"md-signature\"><a href=\"https:\/\/www.britannica.com\/contributor\/David-E-Borth\/4163\">David E. Borth<\/a><\/span><\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>\r\n<div data-page-index=\"23\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<article class=\"article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded\" data-topic-id=\"129024\">\r\n<div class=\"grid gx-0\">\r\n<div class=\"col-auto\">\r\n<div class=\"topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open\">\r\n<div class=\"drawer d-flex flex-column open\">\r\n<div class=\"left-rail-section-content\">\r\n<div class=\"topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center\">\r\n<div class=\"tlr-title px-20 py-15 text-left\"><a class=\"font-serif font-weight-bold text-black link-blue\" href=\"https:\/\/www.britannica.com\/topic\/communication\">communication<\/a><\/div>\r\n<\/div>\r\n<div class=\"section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 \">\r\n<div class=\"toc mb-20\">\r\n<div class=\"font-serif font-14 font-weight-bold mx-15 mb-15 mt-20\">Table of Contents<\/div>\r\n<ul class=\"list-unstyled my-0\" data-level=\"h1\">\r\n<li class=\"\" data-target=\"#ref1\">\r\n<div class=\"pl-25\"><a class=\"link-gray-900 w-100\" href=\"https:\/\/www.britannica.com\/topic\/communication\">Introduction<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref21920\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/topic\/communication\/Models-of-communication\">Models of communication<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-parent\" data-target=\"#ref21926\">\r\n<div class=\"d-flex align-items-center\"><button class=\"h1-link-drawer-button btn btn-xs btn-circle d-flex rounded\" type=\"button\" aria-label=\"Toggle Heading\"><\/button><a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/topic\/communication\/Types-of-communication\">Types of communication<\/a><\/div>\r\n<\/li>\r\n<li class=\"spy-active\" data-target=\"#ref21941\">\r\n<div class=\"d-flex align-items-center\">\r\n<div class=\"ml-25\">\u00a0<\/div>\r\n<a class=\"w-100 link-gray-900\" href=\"https:\/\/www.britannica.com\/topic\/communication\/The-psychology-of-communication\">The psychology of communication<\/a><\/div>\r\n<\/li>\r\n<\/ul>\r\n<a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/topic\/communication\/additional-info\">References &amp; Edit History<\/a><a class=\"toc-extra-link link-gray-900\" href=\"https:\/\/www.britannica.com\/facts\/communication\">Related Topics<\/a><\/div>\r\n<div class=\"tlr-media-slider pb-10 mb-30\"><a class=\"section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10\" href=\"https:\/\/www.britannica.com\/topic\/communication\/images-videos\">Images &amp; Videos<\/a>\r\n<div class=\"slider js-slider position-relative d-inline-flex align-items-center mw-100 \">\r\n<div class=\"slider-container js-slider-container overflow-hidden d-flex text-nowrap ml-15 rw-slider rw-prev-disabled\">\r\n<div class=\"rw-track\"><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/45\/119545-050-B033BE31\/Operator-telephone-switchboard-1900.jpg\" data-href=\"\/media\/1\/129024\/121144\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/119545-004-BF0400C5\/Operator-telephone-switchboard-1900.jpg\" alt=\"communication\" height=\"50\" \/><\/a><a class=\"media-overlay-link d-inline-block mr-5 rw-slide\" href=\"https:\/\/cdn.britannica.com\/75\/61775-004-AC154AAC\/signal-telephone-receiver-communication-model-conversation-Shannon.jpg\" data-href=\"\/media\/1\/129024\/52075\"><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/75\/61775-004-AC154AAC\/signal-telephone-receiver-communication-model-conversation-Shannon.jpg\" alt=\"Shannon's communication model\" height=\"50\" \/><\/a>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/65\/186265-138-9D70B009\/Australian-Sign-Language.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"See the efforts of the University of Melbourne in providing intensive classes to teach Australian sign language, commonly known as Auslan taught wholly by deaf teachers\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/32\/186432-138-95D37698\/Internet-effect-communication.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"Discover how internet English affects the spoken English language\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/19\/180119-138-29F20103\/Overview-invention-telephone-focus-work-Alexander-Graham.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"How the telephone was invented\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/80\/179580-138-C9006071\/laughter-health-benefits.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"Explore the health benefits of laughter and how contagious it can be\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<div class=\"position-relative --aspect-ratio: 16\/9\"><img decoding=\"async\" class=\"col-100\" src=\"https:\/\/cdn.britannica.com\/64\/180164-138-AE845BB7\/brain-language.jpg?w=400&amp;h=225&amp;c=crop\" alt=\"How does the human brain process language?\" \/>\r\n<div class=\"btn btn-sm btn-white btn-circle position-absolute shadow\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"prev-button js-prev-button position-absolute btn btn-circle shadow btn-blue rw-disabled\" disabled=\"disabled\" aria-label=\"Previous\"><\/button><button class=\"next-button js-next-button position-absolute btn btn-circle shadow  btn-blue \" aria-label=\"Next\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-related-quizzes\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Quizzes<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/are-you-an-idiom-savant-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/57\/256457-131-76CA8488\/young-boy-1980s-retro-thinking-cap.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"A young boy dressed in retro 1980s attire, with bow tie and eyeglasses, wears a light bulb idea invention machine to help him think of the next big idea. (nerd, nerdy, thinker) SEE CONTENT NOTES.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/are-you-an-idiom-savant-quiz\">Are You An Idiom Savant? Quiz<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/word-nerd-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/09\/157609-131-5D5D9424\/Hand-with-pencil-writing-on-page.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Hand with pencil writing on page. (handwriting; write)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/word-nerd-quiz\">Word Nerd Quiz<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/quiz\/communications-firsts-quiz\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/95\/151195-131-77ACB0EC\/Jack-Brown-movie-stars-Lauren-Bacall-Humphrey.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Armed Forces Radio Services broadcaster Jack Brown interviews Humphrey Bogart and Lauren Bacall for broadcast to troops overseas during World War II.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/quiz\/communications-firsts-quiz\">Communications Firsts Quiz<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-read-next\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Read Next<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-everyday-english-idioms-and-where-they-come-from\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/72\/195572-131-75DF4873\/flying-pig.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Happy, smiling, flying pig\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-everyday-english-idioms-and-where-they-come-from\">7 Everyday English Idioms and Where They Come From<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/the-worlds-5-most-commonly-used-writing-systems\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/52\/220252-131-120630CC\/Chinese-pictograph-calligraphy-Huang-Tingjian.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Chinese pictograph, calligraphy tablet of Huang Tingjian, a famous calligrapher in Ancient Song Dynasty. The background of Chinese cultural elements.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/the-worlds-5-most-commonly-used-writing-systems\">The World\u2019s 5 Most Commonly Used Writing Systems<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/citizen-journalists\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/65\/221365-131-7DE55193\/newspapers.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"close up of newspapers\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/citizen-journalists\">Citizen Journalists<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/why-do-languages-die\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/63\/133063-131-B83DD391\/Aleppo-Codex-Portion-language-ce-Hebrew-Bible.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Portion of the Aleppo Codex, a manuscript of the Hebrew Bible written in the Hebrew language in the 10th century CE; in the Shrine of the Book, Israel Museum, Jerusalem.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/why-do-languages-die\">Why Do Languages Die?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"mb-30 tlr-discover\">\r\n<div class=\"text-gray-900 p-5 font-serif font-14 font-weight-bold mx-10 mb-10\">Discover<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/17-questions-about-health-and-wellness-answered\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/20\/167120-131-5791618D\/Hand-washing-hand-spread-mouth-disease-foot.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Hand washing. Healthcare worker washing hands in hospital sink under running water. contagious diseases wash hands, handwashing hygiene, virus, human health\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/17-questions-about-health-and-wellness-answered\">17 Questions About Health and Wellness Answered<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/9-mind-altering-plants\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/39\/123539-131-B5711E3A\/Hemp.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Hemp (Cannabis sativa).\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/9-mind-altering-plants\">9 Mind-Altering Plants<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/11\/113311-131-8848D08B\/Victoria-Woodhull-woman-suffrage-US-House-of-1871.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Judiciary Committee of the U.S. House of Representatives receiving a deputation of female suffragists, January 11, 1871, a lady delegate (identified as Victoria Woodhull) reading her argument (cont'd)\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/who-was-the-first-woman-to-run-for-president-of-the-united-states\">Who Was the First Woman to Run for President of the United States?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/73\/150373-131-DB2CFBDD\/Teton-Range-Jackson-Lake-Wyoming-Grand-National.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Jackson (Wyoming, United States). Jackson Lake (also called Jackson Hole), southern end of the Teton Range (the Grand Tetons), Grand Teton National Park, Wyoming, USA\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/list\/7-wonders-of-america\">7 Wonders of America<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/82\/191082-131-AD46C136\/threshold-office-Chester-A-Arthur-chromolithograph-Print-September-1881.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"&quot;On the threshold of office--what have we to expect of him?&quot; chromolithograph by Joseph Keppler, September 1881. Print shows the members of the assassinated James A. Garfield's cabinet looking at the new president, Chester Arthur. Chester A. Arthur.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/the-surprisingly-disorderly-history-of-the-us-presidential-succession-order\">The Surprisingly Disorderly History of the U.S. Presidential Succession Order<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/which-religion-is-the-oldest\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/91\/223091-131-A986B08A\/relief-Zoroastrian-god-Ahura-Mazda-Persepolis-Iran.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"Ahura Mazda - relief of the Zoroastrian god Ahura Mazda at the ancient ruins of Persepolis in Iran. Also known as Ormazd Zoroastrianism,\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/which-religion-is-the-oldest\">Which Religion Is the Oldest?<\/a><\/div>\r\n<\/div>\r\n<div class=\"imagelink-with-image-on-the-side card card-horizontal tlr-img-with-side-link ml-15 link-gray-900 mb-10\">\r\n<div class=\"position-relative card-media\"><a class=\"ilf-image position-relative\" href=\"https:\/\/www.britannica.com\/story\/whats-the-difference-between-modern-and-contemporary-art\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/16\/191216-131-B288FFB5\/Tulips-sculpture-group-colour-coating-stainless-steel-2004.jpg?w=200&amp;h=200&amp;c=crop\" alt=\"The Jeff Koons tulips sculputure outside the Guggenheim Museums in Bilbao, Spain, Basque Country.\" width=\"200\" height=\"200\" \/><\/a><\/div>\r\n<div class=\"card-body ilf-content\"><a class=\"font-weight-semi-bold d-block mb-5 font-16 ilf-title\" href=\"https:\/\/www.britannica.com\/story\/whats-the-difference-between-modern-and-contemporary-art\">What\u2019s the Difference Between Modern and Contemporary Art?<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<button class=\"drawerToggle btn position-sticky border btn-xs btn-white btn-circle rounded-sm d-none d-lg-flex \" type=\"button\" aria-label=\"Toggle Drawer\"><\/button><\/div>\r\n<\/div>\r\n<div class=\"col\">\r\n<div class=\"h-100 ml-0 \">\r\n<div class=\"h-100 grid gx-0 \">\r\n<div class=\"h-100 col-sm\">\r\n<div class=\"h-100 infinite-pagination-container d-flex flex-column position-relative\">\r\n<div class=\"position-absolute top-0 h-100 w-100\">\r\n<div class=\"toc-sticky-header bg-gray-50 px-10 px-sm-30 position-sticky w-100\">\r\n<div class=\"toc-sticky-header-inner-container align-items-center d-flex mx-auto h-100 w-100\"><button class=\"ai-ask-button btn border-2 js-header-ai-ask-button btn-sm btn-outline-red-400 border-red-400 mr-0 mr-lg-10 ml-5 ml-sm-10 ml-lg-0 p-10\">Ask the Chatbot a Question<\/button>\r\n<div class=\"header-ai-summarize-button-placeholder\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"grey-box w-100 grey-box-top\">\r\n<div class=\"grey-box-content mx-auto w-100\"><nav class=\"breadcrumb mt-20\"><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Health-Medicine\">Health &amp; Medicine<\/a><\/span><span class=\"breadcrumb-item \"><a class=\"link-gray-600\" href=\"https:\/\/www.britannica.com\/browse\/Psychology-Mental-Health\">Psychology &amp; Mental Health<\/a><\/span><\/nav>\r\n<div class=\"page2ref-true topic-content topic-type-REGULAR\" data-student-article=\"true\">\r\n<div class=\"reading-channel\">\r\n<div class=\"desktop-header-image module-spacing\">\r\n<figure class=\"md-assembly m-0 mb-20 mb-md-0 card card-borderless print-false\" data-assembly-id=\"13684\" data-asm-type=\"image\">\r\n<div class=\"md-assembly-wrapper card-media \" data-type=\"image\"><a class=\"gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media\" href=\"https:\/\/cdn.britannica.com\/45\/119545-050-B033BE31\/Operator-telephone-switchboard-1900.jpg\" data-href=\"\/media\/1\/129024\/121144\"><picture><source srcset=\"https:\/\/cdn.britannica.com\/45\/119545-050-B033BE31\/Operator-telephone-switchboard-1900.jpg?w=300\" media=\"(min-width: 680px)\" \/><img decoding=\"async\" src=\"https:\/\/cdn.britannica.com\/45\/119545-050-B033BE31\/Operator-telephone-switchboard-1900.jpg?w=400&amp;h=300&amp;c=crop\" alt=\"communication\" \/><\/picture><button class=\"magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10\" aria-label=\"Zoom in\"><\/button><\/a><\/div>\r\n<figcaption class=\"card-body\">\r\n<div class=\"md-assembly-caption text-muted font-14 font-serif line-clamp\"><a class=\"gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link\" href=\"https:\/\/cdn.britannica.com\/45\/119545-050-B033BE31\/Operator-telephone-switchboard-1900.jpg\" data-href=\"\/media\/1\/129024\/121144\">communication<\/a>\u00a0Operator at a telephone switchboard,\u00a0<em>c.<\/em>\u00a01900.<\/div>\r\n<\/figcaption>\r\n<\/figure>\r\n<\/div>\r\n<div class=\"topic-header\">\r\n<div class=\"d-flex align-items-top justify-content-between\">\r\n<div class=\"d-flex flex-column\">\r\n<div>\r\n<div>\r\n<h1>communication<\/h1>\r\n<\/div>\r\n<\/div>\r\n<div class=\"topic-identifier font-16 font-md-20\">social behavior<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"d-none d-sm-flex flex-row\">\r\n<div class=\"mr-10 mb-15\"><button class=\"ai-ask-button btn border-2 btn-sm js-inline-ai-ask-button btn-outline-red-400 border-red-400\">Ask the Chatbot a Question<\/button><\/div>\r\n<div class=\"d-block md-topic-tools qa-action-buttons mb-15\" data-topic-id=\"129024\"><button class=\"js-tooltip btn btn-sm btn-outline-blue border pr-10 border-2 text-nowrap\">More Actions<\/button>\r\n<div class=\"md-more-popover popover popover-sm p-0 font-14 z-1\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<div>\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"toc-header-marker\">\u00a0<\/div>\r\n<div class=\"md-byline module-spacing \">\r\n<div class=\"font-serif font-12\"><span class=\"written-by text-gray-700\">Written by\u00a0<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 clamp-description text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline\">George N. Gordon<\/span><\/div>\r\n<div class=\"font-serif font-12 text-gray-700\"><span class=\"qa-fact-checked-by\">Fact-checked by<\/span>\r\n<div class=\"editor-popover popover p-0\" data-popper-placement=\"top-start\" data-popper-reference-hidden=\"\" data-popper-escaped=\"\">\r\n<div class=\"editor-title font-16 font-weight-bold\">\u00a0<\/div>\r\n<div class=\"editor-description font-12 font-serif mt-5 text-black\">\u00a0<\/div>\r\n<div data-popper-arrow=\"\">\u00a0<\/div>\r\n<\/div>\r\n<span class=\"btn btn-link editor-link p-0 qa-byline-link font-12 \">The Editors of Encyclopaedia Britannica<\/span><\/div>\r\n<div class=\"last-updated font-12 font-serif\"><span class=\"text-gray-700\">Last Updated:\u00a0<time datetime=\"2024-12-09T00:00:00CST\">Dec 9, 2024<\/time>\u00a0\u2022<\/span>\u00a0<a class=\"byline-edit-history\" href=\"https:\/\/www.britannica.com\/topic\/communication\/additional-info#history\" rel=\"nofollow\">Article History<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded\">\r\n<div class=\"facts-list mt-10\">\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Key People:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Ernest-G-Bormann\">Ernest G. Bormann<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/money\/Jean-Marie-Messier\">Jean-Marie Messier<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Maxwell-McCombs\">Maxwell McCombs<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Wilbur-Schramm\">Wilbur Schramm<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/biography\/Jurgen-Habermas\">J\u00fcrgen Habermas<\/a><\/dd>\r\n<\/dl>\r\n<button class=\"js-more-btn btn btn-unstyled font-12 bg-gray-50\" aria-label=\"Toggle more\/less fact data\"><em class=\"js-content link-blue\">(Show\u00a0more)<\/em><\/button><\/div>\r\n<\/div>\r\n<div class=\"\">\r\n<div class=\"js-fact mb-10 line-clamp clamp-3\">\r\n<dl>\r\n<dt>Related Topics:<\/dt>\r\n<dd><a href=\"https:\/\/www.britannica.com\/topic\/language\">language<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/topic\/public-opinion\">public opinion<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/science\/animal-communication\">animal communication<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/science\/information-theory\">information theory<\/a><\/dd>\r\n<dd><a href=\"https:\/\/www.britannica.com\/topic\/body-language-communications\">body language<\/a><\/dd>\r\n<\/dl>\r\n<\/div>\r\n<div class=\"text-center\"><a class=\"btn btn-sm btn-link p-0\" href=\"https:\/\/www.britannica.com\/facts\/communication\">See all related content<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref1\" data-level=\"1\" data-has-spy=\"true\">\r\n<p class=\"topic-paragraph\"><strong><span id=\"ref383991\"><\/span>communication<\/strong>, the exchange of\u00a0<span id=\"ref383992\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/meaning\" data-show-preview=\"true\">meanings<\/a>\u00a0between individuals through a common system of symbols.<\/p>\r\n<p class=\"topic-paragraph\">This article treats the functions, types, and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/psychology\" data-show-preview=\"true\">psychology<\/a>\u00a0of communication. For a treatment of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/animal-communication\" data-show-preview=\"true\">animal communication<\/a>,\u00a0<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/animal-behavior\" data-show-preview=\"true\">animal behaviour<\/a>. For further treatment of the basic components and techniques of human communication,\u00a0<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/language\" data-show-preview=\"true\">language<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/speech-language\" data-show-preview=\"true\">speech<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/writing\" data-show-preview=\"true\">writing<\/a>. For technological aspects, including communications devices and information systems,\u00a0<em>see<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/broadcasting\" data-show-preview=\"true\">broadcasting<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/dictionary\" data-show-preview=\"true\">dictionary<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/encyclopaedia\" data-show-preview=\"true\">encyclopaedia<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/information-processing\" data-show-preview=\"true\">information processing<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/information-theory\" data-show-preview=\"true\">information theory<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/library\" data-show-preview=\"true\">library<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/printing-publishing\" data-show-preview=\"true\">printing<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/publishing\" data-show-preview=\"true\">publishing, history of<\/a>;<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/telecommunications-media\" data-show-preview=\"true\">\u00a0telecommunications media<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunications-network\" data-show-preview=\"true\">telecommunications network<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\" data-show-preview=\"true\">telecommunications system<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">The subject of communication has concerned scholars since the time of ancient\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/place\/Greece\" data-show-preview=\"true\">Greece<\/a>. Until modern times, however, the topic was usually subsumed under other\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/disciplines\" data-term=\"disciplines\" data-type=\"MW\">disciplines<\/a>\u00a0and taken for granted as a natural process\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/inherent\" data-term=\"inherent\" data-type=\"MW\">inherent<\/a>\u00a0to each. In 1928 the English literary critic and author\u00a0<span id=\"ref383993\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/I-A-Richards\" data-show-preview=\"true\">I.A. Richards<\/a>\u00a0offered one of the first\u2014and in some ways still the best\u2014definitions of communication as a discrete aspect of human enterprise:<\/p>\r\n<blockquote>Communication takes place when one\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/mind\" data-show-preview=\"true\">mind<\/a>\u00a0so acts upon its\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environment\" data-term=\"environment\" data-type=\"MW\">environment<\/a>\u00a0that another mind is influenced, and in that other mind an experience occurs which is like the experience in the first mind, and is caused in part by that experience.<\/blockquote>\r\n<p class=\"topic-paragraph\">Richards\u2019s\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/definition\" data-show-preview=\"true\">definition<\/a>\u00a0is both general and rough, but its application to nearly all kinds of communication\u2014including those between humans and animals (but excluding machines)\u2014separated the contents of messages from the processes in human affairs by which these messages are transmitted. More recently, questions have been raised concerning the adequacy of any single definition of the term\u00a0<em>communication<\/em>\u00a0as it is currently employed. The American psychiatrist and scholar\u00a0<span id=\"ref383994\"><\/span>Jurgen Ruesch identified 40 varieties of disciplinary approaches to the subject, including architectural, anthropological, psychological, political, and many other interpretations of the apparently simple interaction described by Richards. In total, if such informal communications as sexual attraction and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/play-behavior\" data-show-preview=\"true\">play<\/a>\u00a0behaviour are included, there exist at least 50 modes of interpersonal communication that draw upon dozens of discrete\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/intellectual\" data-term=\"intellectual\" data-type=\"MW\">intellectual<\/a>\u00a0disciplines and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analytic\" data-term=\"analytic\" data-type=\"MW\">analytic<\/a>\u00a0approaches. Communication may therefore be analyzed in at least 50 different ways.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/are-you-an-idiom-savant-quiz\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/57\/256457-131-76CA8488\/young-boy-1980s-retro-thinking-cap.jpg\" alt=\"A young boy dressed in retro 1980s attire, with bow tie and eyeglasses, wears a light bulb idea invention machine to help him think of the next big idea. (nerd, nerdy, thinker) SEE CONTENT NOTES.\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Are You An Idiom Savant? Quiz<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">Interest in communication has been stimulated by advances in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/science\" data-show-preview=\"true\">science<\/a>\u00a0and technology, which, by their nature, have called attention to humans as communicating creatures. Among the first and most dramatic examples of the inventions resulting from technological ingenuity were the telegraph and telephone, followed by others like wireless radio and telephoto devices. The development of popular newspapers and periodicals, broadcasting, motion pictures, and television led to institutional and cultural\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/innovations\" data-term=\"innovations\" data-type=\"MW\">innovations<\/a>\u00a0that permitted efficient and rapid communication between a few individuals and large populations; these media have been responsible for the rise and social power of the new phenomenon of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/mass-communication\" data-show-preview=\"true\">mass communication<\/a>. (<em>See also<\/em>\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/information-theory\" data-show-preview=\"true\">information theory<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/information-processing\" data-show-preview=\"true\">information processing<\/a>;\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/telecommunication\" data-show-preview=\"true\">telecommunication system<\/a>.)<\/p>\r\n<p class=\"topic-paragraph\">Since roughly 1920 the growth and apparent influence of communications technology have attracted the attention of many specialists who have attempted to isolate communication as a specific facet of their particular interest.\u00a0<span id=\"ref383995\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/social-science\" data-show-preview=\"true\">Psychologists<\/a>, in their studies of behaviour and mind, have evolved concepts of communication useful to their investigations as well as to certain forms of therapy. Social scientists have identified various forms of communication by which\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/myths\" data-term=\"myths\" data-type=\"MW\">myths<\/a>, styles of living, mores, and traditions are passed either from generation to generation or from one segment of society to another. Political scientists and economists have recognized that communication of many types lies at the heart of the regularities in the social order. Under the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/impetus\" data-term=\"impetus\" data-type=\"MW\">impetus<\/a>\u00a0of new technology\u2014particularly high-speed computers\u2014mathematicians and engineers have tried to quantify and measure components of communicated information and to develop methods for translating various types of messages into quantities or amounts\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/amenable\" data-term=\"amenable\" data-type=\"MW\">amenable<\/a>\u00a0to both their procedures and instruments. Numerous and differently phrased questions have been posed by artists, architects, artisans, writers, and others concerning the overall influences of various types of communication. Many researchers, working within the relevant concerns of their disciplines, have also sought possible theories or laws of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/causation\" data-show-preview=\"true\">cause and effect<\/a>\u00a0to explain the ways in which human\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dispositions\" data-term=\"dispositions\" data-type=\"MW\">dispositions<\/a>\u00a0are affected by certain kinds of communication under certain circumstances, and the reasons for the change.<\/p>\r\n<div class=\"module-spacing\">\r\n<div class=\"marketing-INLINE_SUBSCRIPTION marketing-content\" data-marketing-id=\"INLINE_SUBSCRIPTION\">\r\n<div class=\"student-promo-banner-wrapper\">\r\n<div class=\"student-promo-banner d-flex flex-column align-items-center bg-blue rounded p-20\">\r\n<div class=\"student-promo-banner-img-wrapper mb-20 mr-0 d-flex justify-content-center\"><img decoding=\"async\" class=\"rounded\" src=\"https:\/\/cdn.britannica.com\/marketing\/BlueThistle.webp\" \/><\/div>\r\n<div class=\"student-promo-banner-text-wrapper ml-0 mb-10 text-center text-white\">\r\n<div class=\"h2 mb-10\">Get Unlimited Access<\/div>\r\n<div class=\"h4 font-weight-semi-bold\">Try Britannica Premium for free and discover more.<\/div>\r\n<\/div>\r\n<div class=\"student-promo-banner-button-wrapper d-flex justify-content-center align-items-center ml-auto mr-auto\"><a class=\"btn btn-m btn-orange\" href=\"https:\/\/premium.britannica.com\/premium-membership\/?utm_source=premium&amp;utm_medium=inline-cta&amp;utm_campaign=august-2024\">Subscribe<\/a><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">In the 1960s a Canadian educator,\u00a0<span id=\"ref383996\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Marshall-McLuhan\" data-show-preview=\"true\">Marshall McLuhan<\/a>, drew the threads of interest in the field of communication into a view that associated many contemporary psychological and sociological phenomena with the media employed in modern\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/culture\" data-term=\"culture\" data-type=\"MW\">culture<\/a>. McLuhan\u2019s often repeated idea, \u201cthe medium is the message,\u201d stimulated numerous filmmakers, photographers, artists, and others, who adopted McLuhan\u2019s view that contemporary society had moved (or was moving) from a \u201cprint\u201d culture to a \u201cvisual\u201d one. The particular forms of greatest interest to McLuhan and his followers were those associated with the sophisticated technological instruments for which young people in particular display enthusiasm\u2014namely, motion pictures, television, and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/sound-physics\" data-show-preview=\"true\">sound<\/a>\u00a0recordings.<\/p>\r\n<p class=\"topic-paragraph\">In the late 20th century the main focus of interest in communication drifted away from McLuhanism and began to centre on (1) the mass communication industries, the people who run them, and the effects they have upon their audiences, (2) persuasive communication and the use of technology to influence dispositions, (3) processes of interpersonal communication as mediators of information, (4)\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamics\" data-term=\"dynamics\" data-type=\"MW\">dynamics<\/a>\u00a0of verbal and nonverbal (and perhaps extrasensory) communication between individuals, (5)\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/perception\" data-show-preview=\"true\">perception<\/a>\u00a0of different kinds of communications, (6) uses of communication technology for social and artistic purposes, including education in and out of school, and (7) development of relevant\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/criticism\" data-term=\"criticism\" data-type=\"MW\">criticism<\/a>\u00a0for artistic endeavours employing modern communications technology.<\/p>\r\n<div class=\"one-good-fact-module\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">In short, a communication expert may be oriented to any of a number of disciplines in a field of inquiry that has, as yet, neither drawn for itself a conclusive roster of subject matter nor agreed upon specific\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/methodologies\" data-term=\"methodologies\" data-type=\"MW\">methodologies<\/a>\u00a0of analysis.<\/p>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div class=\"ai-dialog-placeholder\">\u00a0<\/div>\r\n<div data-page-index=\"24\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21920\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\">Models of communication<\/h1>\r\n<p class=\"topic-paragraph\">Fragmentation and problems of interdisciplinary outlook have generated a wide range of discussion concerning the ways in which communication occurs and the processes it entails. Most speculation on these matters admits, in one way or another, that the communication theorist\u2019s task is to answer as clearly as possible the question, \u201c<em>Who<\/em>\u00a0says\u00a0<em>what<\/em>\u00a0to\u00a0<em>whom<\/em>\u00a0with\u00a0<em>what effect<\/em>?\u201d (This query was originally posed by the U.S. political scientist\u00a0<span id=\"ref383997\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Harold-Lasswell\" data-show-preview=\"true\">Harold D. Lasswell<\/a>.) Obviously, all the critical elements in this question may be interpreted differently by scholars and writers in different\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/disciplines\" data-term=\"disciplines\" data-type=\"MW\">disciplines<\/a>.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21921\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Linear models<\/h2>\r\n<p class=\"topic-paragraph\">One of the most productive schematic models of a communications system that has been proposed as an answer to Lasswell\u2019s question emerged in the late 1940s, largely from the speculations of two American mathematicians,\u00a0<span id=\"ref383998\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Claude-Shannon\" data-show-preview=\"true\">Claude Shannon<\/a>\u00a0and\u00a0<span id=\"ref383999\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Warren-Weaver\" data-show-preview=\"true\">Warren Weaver<\/a>. The simplicity of their model, its clarity, and its surface generality proved attractive to many students of communication in a number of disciplines, although it is neither the only model of the communication process\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/extant\" data-term=\"extant\" data-type=\"MW\">extant<\/a>\u00a0nor is it universally accepted. As originally conceived, the model contained five elements\u2014an information source, a\u00a0<span id=\"ref384000\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/transmitter\">transmitter<\/a>, a\u00a0<span id=\"ref384001\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/channel-communications\">channel<\/a>\u00a0of transmission, a\u00a0<span id=\"ref384002\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/receiver\" data-show-preview=\"true\">receiver<\/a>, and a destination\u2014all arranged in linear order.\u00a0<span id=\"ref384003\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/message-information-theory\">Messages<\/a>\u00a0(electronic messages, initially) were supposed to travel along this path, to be changed into electric energy by the transmitter, and to be reconstituted into intelligible\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/language\" data-show-preview=\"true\">language<\/a>\u00a0by the receiver. In time, the five elements of the model were renamed so as to specify components for other types of communication transmitted in various manners. The information source was split into its components (both source and message) to provide a wider range of applicability. The six\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/constituents\" data-term=\"constituents\" data-type=\"MW\">constituents<\/a>\u00a0of the revised model are (1) a source, (2) an\u00a0<span id=\"ref384004\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/encoding\">encoder<\/a>, (3) a message, (4) a channel, (5) a decoder, and (6) a receiver. For some communication systems, the components are as simple to specify as, for instance, (1) a person on a landline telephone, (2) the mouthpiece of the telephone, (3) the words spoken, (4) the electrical wires along which the words (now electrical impulses) travel, (5) the earpiece of another telephone, and (6) the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/mind\" data-show-preview=\"true\">mind<\/a>\u00a0of the listener. In other communication systems, the components are more difficult to isolate\u2014e.g., the communication of the emotions of a fine artist by means of a painting to people who may respond to the message long after the artist\u2019s death.<\/p>\r\n<p class=\"topic-paragraph\">Begging a multitude of psychological,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/aesthetic\" data-term=\"aesthetic\" data-type=\"MW\">aesthetic<\/a>, and sociological questions concerning the exact nature of each component, the linear model appeared, from the commonsense perspective, at least, to explain in general terms the ways in which certain classes of communication occurred. It did not indicate the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/reason\" data-show-preview=\"true\">reason<\/a>\u00a0for the inability of certain communications\u2014obvious in daily life\u2014to fit its neat\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/paradigm\" data-term=\"paradigm\" data-type=\"MW\">paradigm<\/a>.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21922\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384005\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/entropy-information-theory\">Entropy<\/a>, negative entropy, and redundancy<\/h2>\r\n<p class=\"topic-paragraph\">Another concept, first called by Shannon a\u00a0<em>noise source<\/em>\u00a0but later associated with the notion of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/entropy\" data-term=\"entropy\" data-type=\"MW\">entropy<\/a>\u00a0(a principle derived from physics), was imposed upon the communication model. Entropy is\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analogous\" data-term=\"analogous\" data-type=\"MW\">analogous<\/a>\u00a0in most communication to audio or visual static\u2014that is, to outside influences that diminish the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/integrity\" data-term=\"integrity\" data-type=\"MW\">integrity<\/a>\u00a0of the communication and, possibly, distort the message for the receiver.\u00a0<span id=\"ref384006\"><\/span>Negative entropy may also occur in instances in which incomplete or blurred messages are nevertheless received intact, either because of the ability of the receiver to fill in missing details or to recognize, despite\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/distortion-communications\" data-show-preview=\"true\">distortion<\/a>\u00a0or a paucity of information, both the intent and content of the communication.<\/p>\r\n<p class=\"topic-paragraph\">Although rarely shown on diagrammatic models of this version of the communication process,\u00a0<span id=\"ref384007\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/redundancy\">redundancy<\/a>\u2014the repetition of elements within a message that prevents the failure of communication of information\u2014is the greatest\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/antidote\" data-term=\"antidote\" data-type=\"MW\">antidote<\/a>\u00a0to entropy. Most written and spoken languages, for example, are roughly half-redundant. If 50 percent of the words of this article were taken away at random, there would still remain an intelligible\u2014although somewhat peculiar\u2014essay. Similarly, if one-half of the words of a radio news commentator are heard, the broadcast can usually be understood.\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/Redundancy\" data-term=\"Redundancy\" data-type=\"MW\">Redundancy<\/a>\u00a0is apparently involved in most human activities, and, because it helps to overcome the various forms of entropy that tend to turn intelligible messages into unintelligible ones (including psychological entropy on the part of the receiver), it is an indispensable element for effective communication.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">Messages are therefore susceptible to considerable modification and mediation. Entropy distorts, while negative entropy and redundancy clarify; as each occurs differentially in the communication process, the chances of the message being received and correctly understood vary. Still, the process (and the model of it) remains conceptually static, because it is fundamentally concerned with messages sent from point to point and not with their results or possible influences upon sender and receiver.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21923\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384008\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/feedback-control-biology\">Feedback<\/a><\/h2>\r\n<p class=\"topic-paragraph\">To correct this flaw, the principle of feedback was added to the model and provided a closer approximation of interpersonal human interaction than was known theretofore. This construct was\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/derived\" data-term=\"derived\" data-type=\"EB\">derived<\/a>\u00a0from the studies of\u00a0<span id=\"ref384009\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Norbert-Wiener\" data-show-preview=\"true\">Norbert Wiener<\/a>, the so-called father of the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/science\" data-show-preview=\"true\">science<\/a>\u00a0of\u00a0<span id=\"ref384010\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/cybernetics\" data-show-preview=\"true\">cybernetics<\/a>. Wiener\u2019s cybernetic models, some of which provide the basis for current computer technology, were designed to be responsive to their own behaviour; that is, they audited their own performances mathematically or electronically in order to avoid errors of entropy, unnecessary redundancy, or other simple hazards.<\/p>\r\n<p class=\"topic-paragraph\">Certain types of common communications\u2014holiday greeting cards, for instance\u2014usually require little feedback. Others, particularly interactions between human beings in conversation, cannot function without the ability of the message sender to weigh and calculate the apparent effect of his words on his listener. It is largely the aspect of feedback that provides for this model the qualities of a process, because each instance of feedback conditions or alters the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/subsequent\" data-term=\"subsequent\" data-type=\"EB\">subsequent<\/a>\u00a0messages.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"25\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21924\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\">Dynamic models<\/h1>\r\n<p class=\"topic-paragraph\">Other models of communication processes have been constructed to meet the needs of students of communication whose interests differ from those of quantitatively oriented theorists like Shannon, Weaver, and Wiener. While the model described above displays some generality and shows simplicity, it lacks some of the predictive, descriptive, and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analytic\" data-term=\"analytic\" data-type=\"MW\">analytic<\/a>\u00a0powers found in other approaches. A psychologist,\u00a0<span id=\"ref384011\"><\/span>Theodore M. Newcomb, for example, has\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/articulated\" data-term=\"articulated\" data-type=\"MW\">articulated<\/a>\u00a0a more fluid system of dimensions to represent the individual interacting in his\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environment\" data-term=\"environment\" data-type=\"MW\">environment<\/a>. Newcomb\u2019s model and others similar to it are not as precisely mathematical (quantitative) as Shannon\u2019s and thus permit more flexible accounts of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/human-behavior\" data-show-preview=\"true\">human behaviour<\/a>\u00a0and its variable relationships. They do not deny the relevance of linear models to Shannon and Weaver\u2019s main concerns\u2014quanta of information and the delivery of messages under controlled conditions\u2014but they question their completeness and utility in describing\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/cognitive\" data-term=\"cognitive\" data-type=\"MW\">cognitive<\/a>, emotional, and artistic aspects of communication as they occur in sociocultural matrices.<\/p>\r\n<p class=\"topic-paragraph\">Students concerned mainly with persuasive and artistic communication often centre attention upon different kinds, or modes, of communication (i.e., narrative, pictorial, and dramatic) and theorize that the messages they contain, including messages of emotional quality and artistic content, are communicated in various manners to and from different sorts of people. For them the stability and function of the channel or medium are more variable and less mechanistically related to the process than they are for followers of Shannon and Weaver and psychologists like Newcomb. (McLuhan, indeed, asserts that the channel actually dictates, or severely influences, the message\u2014both as sent and received.) Many analysts of communication, linguistic philosophers, and others are concerned with the nature of messages, particularly their compatibility with sense and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/emotion\" data-show-preview=\"true\">emotion<\/a>, their style, and the intentions behind them. They find both linear and geometric models of process of little interest to their concerns, although considerations related to these models, particularly those of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/entropy\" data-term=\"entropy\" data-type=\"MW\">entropy<\/a>,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/redundancy\" data-term=\"redundancy\" data-type=\"MW\">redundancy<\/a>, and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/feedback-biology\" data-show-preview=\"true\">feedback<\/a>, have provided significant and productive concepts for most students of communication.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21925\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Applications of formal logic and mathematics<\/h2>\r\n<p class=\"topic-paragraph\">Despite the numerous types of communication or\u00a0<span id=\"ref384012\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/information-theory\" data-show-preview=\"true\">information theory<\/a>\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/extant\" data-term=\"extant\" data-type=\"MW\">extant<\/a>\u00a0today\u2014and those likely to be formulated tomorrow\u2014the most rationally and experimentally consistent approaches to communication theory so far developed follow the constructions of Shannon and others described above. Such approaches tend to employ the structural rigours of\u00a0<span id=\"ref384013\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/formal-logic\" data-show-preview=\"true\">logic<\/a>\u00a0rather than the\u00a0<span id=\"ref384014\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/applied-logic\" data-show-preview=\"true\">looser<\/a>\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/syntaxes\" data-term=\"syntaxes\" data-type=\"MW\">syntaxes<\/a>, grammars, and vocabularies of common languages, with their symbolic, poetic, and inferential aspects of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/meaning\" data-show-preview=\"true\">meaning<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">Cybernetic theory and\u00a0<span id=\"ref384015\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/computer\" data-show-preview=\"true\">computer<\/a>\u00a0technology require rigorous but straightforward\u00a0<span id=\"ref384016\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/information-processing\" data-show-preview=\"true\">languages<\/a>\u00a0to permit translation into nonambiguous, special symbols that can be stored and utilized for statistical manipulations. The closed system of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/formal-logic\" data-show-preview=\"true\">formal logic<\/a>\u00a0proved ideal for this need.\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/Premises\" data-term=\"Premises\" data-type=\"MW\">Premises<\/a>\u00a0and conclusions drawn from syllogisms according to logical rules may be easily tested in a consistent, scientific manner, as long as all parties communicating share the rational premises employed by the particular system.<\/p>\r\n<p class=\"topic-paragraph\">That this logical mode of communication drew its frame of discourse from the logic of the ancient Greeks was inevitable. Translated into an Aristotelian manner of discourse, meaningful interactions between individuals could be transferred to an equally rational closed system of mathematics: an arithmetic for simple transactions, an algebra for solving certain well-delimited puzzles, a calculus to simulate changes, rates and flows, and a geometry for purposes of illustration and model construction. This progression has proved quite useful for handling those limited classes of communications that arise out of certain structured, rational operations, like those in economics, inductively oriented sociology,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/experimental-psychology\" data-show-preview=\"true\">experimental psychology<\/a>, and other behavioral and social sciences, as well as in most of the natural sciences.<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-quiz-module\" href=\"https:\/\/www.britannica.com\/quiz\/are-you-an-idiom-savant-quiz\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/57\/256457-131-76CA8488\/young-boy-1980s-retro-thinking-cap.jpg\" alt=\"A young boy dressed in retro 1980s attire, with bow tie and eyeglasses, wears a light bulb idea invention machine to help him think of the next big idea. (nerd, nerdy, thinker) SEE CONTENT NOTES.\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-green\">Britannica Quiz<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">Are You An Idiom Savant? Quiz<\/div>\r\n<\/div>\r\n<p class=\"topic-paragraph\">The basic theorem of information theory rests, first, upon the assumption that the message\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/transmitted\" data-term=\"transmitted\" data-type=\"EB\">transmitted<\/a>\u00a0is well organized, consistent, and characterized by relatively low and determinable degrees of entropy and redundancy. (Otherwise, the mathematical structure might yield only probability statements approaching random scatters, of little use to anyone.) Under these circumstances, by devising proper coding procedures for the transmitter, it becomes possible to transmit symbols over a channel at an average rate that is nearly the capacity of units per second of the channel (symbolized by C) as a function of the units per second from an information source (H)\u2014but never at rates in excess of capacity divided by units per second (C\/H), no matter how expertly the symbols are coded. As simple as this notion seems, upon determining the capacity of the channel and by cleverly coding the information involved, precise mathematical models of information transactions (similar to electronic frequencies of energy transmissions) may be evolved and employed for complex analyses within the strictures of formal logic. They must, of course, take into account as precisely as possible levels of entropy and redundancy as well as other known variables.<\/p>\r\n<p class=\"topic-paragraph\">The internal\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/capacities\" data-term=\"capacities\" data-type=\"EB\">capacities<\/a>\u00a0of the channel studied and the sophistication of the coding procedures that handle the information limit the usefulness of the theorem presented above. At present such procedures, while they may theoretically offer broad prospects, are restricted by formal encoding procedures that depend upon the capacities of the instruments in which they are stored. Although such devices can handle quickly the logic of vast amounts of relatively simple information, they cannot match the flexibility and complexity of the human brain, still the prime instrument for managing the subtleties of most human communication.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"26\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21926\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\">Types of communication<\/h1>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21927\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Nonvocal communication<\/h2>\r\n<p class=\"topic-paragraph\">Signals, signs, and symbols, three related components of communication processes found in all known\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/cultures\" data-term=\"cultures\" data-type=\"MW\">cultures<\/a>, have attracted considerable scholarly attention because they do not relate primarily to the usual\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/conception\" data-term=\"conception\" data-type=\"MW\">conception<\/a>\u00a0of words or\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/language\" data-show-preview=\"true\">language<\/a>. Each is apparently an increasingly more complex modification of the former, and each was probably developed in the depths of prehistory before, or at the start of, early human experiments with vocal language.<\/p>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21928\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384017\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/signal\">Signals<\/a><\/h2>\r\n<p class=\"topic-paragraph\">A signal may be considered as an interruption in a field of constant\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/energy-transfer\" data-show-preview=\"true\">energy transfer<\/a>. An example is the dots and dashes that open and close the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/electromagnetic-field\" data-show-preview=\"true\">electromagnetic field<\/a>\u00a0of a telegraph circuit. Such interruptions do not require the construction of a man-made field; interruptions in nature (e.g., the tapping of a pencil in a silent room, or puffs of smoke rising from a mountaintop) may produce the same result. The basic function of such signals is to provide the change of a single environmental factor in order to attract attention and to transfer\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/meaning\" data-show-preview=\"true\">meaning<\/a>. A\u00a0<span id=\"ref384018\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/code-communications\" data-show-preview=\"true\">code<\/a>\u00a0system that refers interruptions to some form of meaningful language may easily be developed with a crude\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/vocabulary\" data-show-preview=\"true\">vocabulary<\/a>\u00a0of dots, dashes, or other elemental audio and visual articulations. Taken by themselves, the interruptions have a potential breadth of meaning that seems extremely small; they may indicate the presence of an individual in a room, an impatience, agreement, or disagreement with some aspect of the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environment\" data-term=\"environment\" data-type=\"MW\">environment<\/a>, or, in the case of a scream for help, a critical situation demanding attention. Coded to refer to spoken or written language, their potential to communicate language is extremely great.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21929\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384019\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/sign-communications\">Signs<\/a><\/h2>\r\n<p class=\"topic-paragraph\">While signs are usually less germane to the development of words than signals, most of them contain greater amounts of meaning of and by themselves.\u00a0<span id=\"ref384020\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Ashley-Montagu\" data-show-preview=\"true\">Ashley Montagu<\/a>, an anthropologist, has defined a sign as a \u201cconcrete denoter\u201d possessing an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/inherent\" data-term=\"inherent\" data-type=\"MW\">inherent<\/a>\u00a0specific meaning, roughly\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analogous\" data-term=\"analogous\" data-type=\"MW\">analogous<\/a>\u00a0to the sentence \u201cThis is it; do something about it!\u201d The most common signs encountered in daily life are pictures or drawings, although a human posture like a clenched fist, an outstretched arm, or a hand posed in a \u201cstop\u201d gesture may also serve as signs. The main difference between a sign and a signal is that a sign (like a policeman\u2019s badge) contains meanings of an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/intrinsic\" data-term=\"intrinsic\" data-type=\"MW\">intrinsic<\/a>\u00a0nature; a signal (like a scream for help) is merely a device by which one is able to formulate extrinsic meanings. Their difference is illustrated by the observation that many types of animals respond to signals while only a few intelligent and trained animals (usually dogs and apes) are competent to respond to even simple signs.<\/p>\r\n<p class=\"topic-paragraph\">All known cultures utilize signs to convey relatively simple messages swiftly and conveniently. The meaning of signs may depend on their form, setting, colour, or location. In the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>, traffic signs, uniforms, badges, and barber poles are frequently encountered signs. Taken en masse, any society\u2019s\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/lexicon\" data-term=\"lexicon\" data-type=\"EB\">lexicon<\/a>\u00a0of signs makes up a rich vocabulary of colourful communications.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21930\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384021\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/symbol\" data-show-preview=\"true\">Symbols<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Symbols are more difficult than signs to understand and to define, because, unlike signs and signals, they are intricately woven into an individual\u2019s ongoing perceptions of the world. They appear to contain a dimly understood capacity that (as one of their functions), in fact, defines the very reality of that world. The\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/symbol\" data-show-preview=\"true\">symbol<\/a>\u00a0has been defined as any device with which an\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/abstraction\" data-show-preview=\"true\">abstraction<\/a>\u00a0can be made. Although far from being a precise construction, it leads in a profitable direction. The abstractions of the values that people imbue in other people and in things they own and use lie at the heart of symbolism. Here is a process, according to the British philosopher\u00a0<span id=\"ref384022\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Alfred-North-Whitehead\" data-show-preview=\"true\">Alfred North Whitehead<\/a>, whereby<\/p>\r\n<a class=\"link-module shadow-sm d-block qa-read-more-module\" href=\"https:\/\/www.britannica.com\/place\/United-Kingdom\/British-society-by-the-mid-18th-century#ref483291\" data-link-module-iframe-link=\"\"><img decoding=\"async\" class=\"rounded-sm mr-15\" src=\"https:\/\/cdn.britannica.com\/25\/4825-050-977D8C5E\/Flag-United-Kingdom.jpg\" alt=\"United Kingdom\" width=\"70\" \/><\/a>\r\n<div class=\"line-clamp clamp-5\">\r\n<div class=\"module-title bg-navy-dark\">More From Britannica<\/div>\r\n<div class=\"font-weight-semi-bold mt-5\">United Kingdom: The revolution in communications<\/div>\r\n<\/div>\r\n<blockquote>some components of [the mind\u2019s] experience elicit\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/consciousness\" data-term=\"consciousness\" data-type=\"MW\">consciousness<\/a>, beliefs, emotions, and usages respecting other components of experience.<\/blockquote>\r\n<p class=\"topic-paragraph\">In Whitehead\u2019s opinion, symbols are\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/analogues\" data-term=\"analogues\" data-type=\"MW\">analogues<\/a>\u00a0or\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/metaphors\" data-term=\"metaphors\" data-type=\"MW\">metaphors<\/a>\u00a0(that may include written and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/speech-language\" data-show-preview=\"true\">spoken language<\/a>\u00a0as well as visual objects) standing for some quality of reality that is\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/enhanced\" data-term=\"enhanced\" data-type=\"MW\">enhanced<\/a>\u00a0in importance or value by the process of symbolization itself.<\/p>\r\n<p class=\"topic-paragraph\">Almost every society has evolved a symbol system whereby, at first glance, strange objects and odd types of behaviour appear to the outside observer to have irrational meanings and seem to evoke odd, unwarranted cognitions and emotions. Upon examination, each symbol system reflects a specific cultural logic, and every symbol functions to communicate information between members of the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/culture\" data-term=\"culture\" data-type=\"MW\">culture<\/a>\u00a0in much the same way as, but in a more subtle manner than, conventional language. Although a symbol may take the form of as discrete an object as a wedding ring or a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/art\/totem-pole\" data-show-preview=\"true\">totem pole<\/a>, symbols tend to appear in clusters and depend upon one another for their accretion of meaning and value. They are not a language of and by themselves; rather they are devices by which ideas too difficult, dangerous, or inconvenient to\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/articulate\" data-term=\"articulate\" data-type=\"MW\">articulate<\/a>\u00a0in common language are transmitted between people who have acculturated in common ways. It does not appear possible to compile discrete vocabularies of symbols, because they lack the precision and regularities present in natural language that are necessary for\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/explicit\" data-show-preview=\"true\">explicit<\/a>\u00a0definitions.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21931\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384023\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/icon-semiotics\">Icons<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Rich clusters of related and unrelated symbols are usually regarded as icons. They are actually groups of interactive symbols, like the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/White-House-Washington-DC\" data-show-preview=\"true\">White House<\/a>\u00a0in Washington, D.C., a funeral ceremony, or an Impressionist painting. Although, in examples such as these, there is a tendency to isolate icons and individual symbols for examination, symbolic communication is so closely allied to all forms of human activity that it is generally and nonconsciously used and treated by most people as the most important aspect of communication in society. With the recognition that spoken and written words and numbers themselves\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/constitute\" data-term=\"constitute\" data-type=\"MW\">constitute<\/a>\u00a0symbolic metaphors, their critical roles in the worlds of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/science\" data-show-preview=\"true\">science<\/a>, mathematics, literature, and art can be understood. In addition, with these symbols, an individual is able to define his own identity.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"27\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"2\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21932\" data-level=\"3\" data-has-spy=\"true\">\r\n<h1 class=\"h3\"><span id=\"ref384024\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/gesture\">Gestures<\/a><\/h1>\r\n<p class=\"topic-paragraph\">Professional actors and dancers have known since antiquity that body gestures may also generate a\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/vocabulary\" data-show-preview=\"true\">vocabulary<\/a>\u00a0of communication more or less unique to each\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/culture\" data-term=\"culture\" data-type=\"MW\">culture<\/a>. Some American scholars have tried to develop a vocabulary of body language, called\u00a0<span id=\"ref384025\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/kinesics\">kinesics<\/a>. The results of their investigations, both amusing and potentially practical, may eventually produce a genuine lexicon of American gestures similar to one prepared in detail by\u00a0<span id=\"ref384026\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Francois-Delsarte\">Fran\u00e7ois Delsarte<\/a>, a 19th-century French teacher of pantomime and gymnastics who described the ingenious and complex language of contemporary face and body positions for theatrical purposes.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21933\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384027\"><\/span>Proxemics<\/h2>\r\n<p class=\"topic-paragraph\">Of more general, cross-cultural significance are the theories involved in the study of proxemics developed by an American anthropologist,\u00a0<span id=\"ref384028\"><\/span>Edward Hall. Proxemics involves the ways in which people in various\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/cultures\" data-term=\"cultures\" data-type=\"MW\">cultures<\/a>\u00a0utilize both time and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/space-physics-and-metaphysics\" data-show-preview=\"true\">space<\/a>\u00a0as well as body positions and other factors for purposes of communication. Hall\u2019s \u201csilent language\u201d of\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/nonverbal-communication\" data-show-preview=\"true\">nonverbal communications<\/a>\u00a0consists of such culturally determined interactions as the physical distance or closeness maintained between individuals, the body heat they give off, odours they perceive in social situations, angles of vision they maintain while talking, the pace of their behaviour, and the sense of time appropriate for communicating under differing conditions. By comparing matters like these in the behaviour of different social classes (and in varying relationships), Hall elaborated and codified a number of sophisticated general principles that demonstrate how certain kinds of nonverbal communication occur. Although Hall\u2019s most impressive arguments are almost entirely\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/empirical\" data-term=\"empirical\" data-type=\"MW\">empirical<\/a>\u00a0and many of them are open to question, the study of proxemics does succeed in calling attention to major features of communication\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamics\" data-term=\"dynamics\" data-type=\"MW\">dynamics<\/a>\u00a0rarely considered by linguists and symbologists. Students of words have been more interested in objective formal vocabularies than in the more subtle means of discourse unknowingly acquired by the members of a culture.<\/p>\r\n<\/section>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21934\" data-level=\"2\" data-has-spy=\"true\">\r\n<h2 class=\"h2\">Vocal communication<\/h2>\r\n<p class=\"topic-paragraph\">Significant differences between nonvocal and vocal communication are matters more of degree than of kind. Signs, signals, symbols, and possibly icons may, at times, be easily verbalized, although most people tend to think of them as visual means of expression. Kinesics and proxemics may also, in certain instances, involve vocalizations as accompaniments to nonverbal phenomena or as somehow\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/integral\" data-term=\"integral\" data-type=\"MW\">integral<\/a>\u00a0to them. Be they grunts, words, or sentences, their function is to help in forwarding a communication that is fundamentally nonverbal.<\/p>\r\n<p class=\"topic-paragraph\">Although there is no shortage of speculation on the issue, the origins of human\u00a0<span id=\"ref384029\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/speech-language\" data-show-preview=\"true\">speech<\/a>\u00a0remain obscure at present. It is plausible that man is born with an instinct for speech. A phenomenon supporting this belief is the presence of unlearned cries and gurgles of infants operating as crude vocal signs directed to others the baby cannot possibly be aware of. Some anthropologists claim that within the vocabularies of kinesics and proxemics are the virtual building blocks of spoken language; they postulate that primitive humans made various and ingenious inventions (including speech) as a result of their need to communicate with others in order to pool their\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/intellectual\" data-term=\"intellectual\" data-type=\"MW\">intellectual<\/a>\u00a0and physical resources. Other observers suggest similar origins of speech, including the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/science\/vocalization\" data-show-preview=\"true\">vocalization<\/a>\u00a0of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/physical-activity\" data-show-preview=\"true\">physical activity<\/a>, imitation of the sounds of nature, and sheer\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/serendipity\" data-term=\"serendipity\" data-type=\"MW\">serendipity<\/a>. Scientific proof of any of these speculations is at present impossible.<\/p>\r\n<p class=\"topic-paragraph\">Not only is the origin of speech disputed among experts, but the precise reasons for the existence of the numerous languages of the world are also far from clear. In the 1920s an American linguistic anthropologist,\u00a0<span id=\"ref384030\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Edward-Sapir\" data-show-preview=\"true\">Edward Sapir<\/a>, and later\u00a0<span id=\"ref384031\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Benjamin-Lee-Whorf\" data-show-preview=\"true\">Benjamin Lee Whorf<\/a>, centred attention upon the various methods of expression found in different cultures. Drawing their evidence primarily from the languages of primitive societies, they made some very significant observations concerning spoken (and probably written) language. First, human language reflects in subtle ways those matters of greatest relevance and importance to the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/value\" data-term=\"value\" data-type=\"EB\">value<\/a>\u00a0system of each particular culture. Thus, language may be said to reflect culture, or, in other words, people seem to find ways of saying what they need to say. A familiar illustration is the many words (or variations of words) that Eskimos use to describe whale blubber in its various states\u2014e.g., on the whale, ready to eat, raw, cooked, rancid. Another example is the observation that\u00a0<em>drunk<\/em>\u00a0possesses more synonyms than any other term in the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/English-language\" data-show-preview=\"true\">English language<\/a>. Apparently, this is the result of a psychological necessity to euphemize a somewhat nasty, uncomfortable, or taboo matter, a device also employed for other words that describe seemingly important but improper behaviour or facets of culture.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21935\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Adaptability of\u00a0<span id=\"ref384032\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/language\" data-show-preview=\"true\">language<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Other observations involve the discovery that any known language may be employed, without major modification, to say almost anything that may be said in any other language. A high degree of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/circumlocution\" data-term=\"circumlocution\" data-type=\"MW\">circumlocution<\/a>\u00a0and some nonverbal vocalization may be required to accomplish this end, but, no matter how alien the concept to the original language, it may be expressed clearly in the language of another culture. Students of linguistic anthropology have been able to describe adequately in English the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/esoteric\" data-term=\"esoteric\" data-type=\"MW\">esoteric<\/a>\u00a0linguistic propositions of primitive societies, just as it has been possible for anthropologists to describe details of Western technology to persons in remote cultures. Understood as an\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/artifact\" data-term=\"artifact\" data-type=\"MW\">artifact<\/a>\u00a0of culture, spoken language may therefore be considered as a universal channel of communication into which various societies dip differentially in order to expedite and specify the numerous points of contact between individuals.<\/p>\r\n<p class=\"topic-paragraph\">Language remains, however, a still partially understood phenomenon used to transact several types of discourse. Language has been classified on the basis of several\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/criteria\" data-term=\"criteria\" data-type=\"MW\">criteria<\/a>. One scheme established four categories on the basis of informative,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamic\" data-term=\"dynamic\" data-type=\"MW\">dynamic<\/a>, emotive, and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/aesthetic\" data-term=\"aesthetic\" data-type=\"MW\">aesthetic<\/a>\u00a0functions. Informative communication deals largely with narrative aspects of meaning; dynamic discourse concerns the transaction of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dispositions\" data-term=\"dispositions\" data-type=\"MW\">dispositions<\/a>\u00a0such as opinions and attitudes; the emotive employment of language involves the evocation of feeling states in others in order to impel them to action; and aesthetic discourse, usually regarded as a poetic quality in speech, conveys stylistic aspects of expression.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21936\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\"><span id=\"ref384033\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/laughter\">Laughter<\/a><\/h2>\r\n<p class=\"topic-paragraph\">Although most vocal sounds other than words are usually considered prelinguistic language, the phenomenon of laughter as a form of communication is in a category by itself, with its closest relative being its apparent opposite, crying. Twentieth-century ethnologists, like\u00a0<span id=\"ref384034\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Konrad-Lorenz\" data-show-preview=\"true\">Konrad Lorenz<\/a>, attempted to associate laughter with\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/animal-social-behaviour\" data-show-preview=\"true\">group behaviour<\/a>\u00a0among animals in instances in which aggression is thwarted and laughlike phenomena seem to result among herds. Lorenz\u2019s\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/metaphors\" data-term=\"metaphors\" data-type=\"MW\">metaphors<\/a>, while apparently reasonable, cannot be verified inductively. They seem less reasonable to many than the more common notions of the Austrian neurologist\u00a0<span id=\"ref384035\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Sigmund-Freud\" data-show-preview=\"true\">Sigmund Freud<\/a>\u00a0and others that laughter either results from or is related to the nonconscious reduction of tensions or inhibitions. Developed as a form of self-generated pleasure in the infant and rewarded both physically and psychologically by feelings of gratification, laughter provides a highly effective, useful, and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/contagious\" data-term=\"contagious\" data-type=\"MW\">contagious<\/a>\u00a0means of vocal communication. It deals with a wide range of cultural problems, often more effectively than speech, in much the same manner that crying, an infantile and probably instinctive reaction to discomfort, communicates an unmistakable emotional state to others.<\/p>\r\n<p class=\"topic-paragraph\">The reasons for laughter in complex social situations is another question and is answered differently by philosophers and psychologists. The English novelist\u00a0<span id=\"ref384036\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/George-Meredith\" data-show-preview=\"true\">George Meredith<\/a>\u00a0proposed a theory, resulting from his analysis of 18th-century French court comedies, that laughter serves as an enjoyable social corrective. The two best-known modern theories of the social wellsprings of laughter are the philosopher\u00a0<span id=\"ref384037\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Henri-Bergson\" data-show-preview=\"true\">Henri Bergson<\/a>\u2019s\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/hypothesis\" data-term=\"hypothesis\" data-type=\"MW\">hypothesis<\/a>\u00a0that laughter is a form of rebellion against the mechanization of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/human-behavior\" data-show-preview=\"true\">human behaviour<\/a>\u00a0and nature and Freud\u2019s concept of laughter as repressed sexual feeling. The writer\u00a0<span id=\"ref384038\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/biography\/Arthur-Koestler\" data-show-preview=\"true\">Arthur Koestler<\/a>\u00a0regarded laughter as a means of individual enlightenment, revelation, and subsequent freedom from confusion or misunderstanding concerning some part of the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environment\" data-term=\"environment\" data-type=\"MW\">environment<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">The human vocal instrument as a device of communication represents an apex of physical and intellectual evolution. It can express the most basic instinctual demands as well as a range of highly intellectual processes, including the possible mastery of numerous complex languages, each with an enormous vocabulary. Because of the imitative capacity of the vocal mechanism (including its cortical directors), suitably talented individuals can simulate the sounds of nature in song, can communicate in simple ways with animals, and can indulge in such tricks as\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/art\/ventriloquism\" data-show-preview=\"true\">ventriloquism<\/a>\u00a0and the mimicry of other voices. Recent\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/tape-recording\" data-show-preview=\"true\">tape recording<\/a>\u00a0techniques have even extended this flexibility into new\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/domains\" data-term=\"domains\" data-type=\"EB\">domains<\/a>, allowing singers to accompany their own voices in different keys to produce effects of duets or choruses composed electronically from one person\u2019s\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/voice-grammar\" data-show-preview=\"true\">voice<\/a>.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"28\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 \">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<section data-level=\"1\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21937\" data-level=\"2\" data-has-spy=\"true\">\r\n<h1 class=\"h2\">Mass and public communication<\/h1>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21938\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Prerequisites for\u00a0<span id=\"ref384039\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/mass-media\" data-show-preview=\"true\">mass communication<\/a><\/h2>\r\n<p class=\"topic-paragraph\">The technology of modern\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/mass-communication\" data-show-preview=\"true\">mass communication<\/a>\u00a0results from the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/confluence\" data-term=\"confluence\" data-type=\"MW\">confluence<\/a>\u00a0of many types of inventions and discoveries, some of which (the printing press, for instance) actually preceded the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/event\/Industrial-Revolution\" data-show-preview=\"true\">Industrial Revolution<\/a>. Technological ingenuity of the 19th and 20th centuries developed the newer means of mass communication, particularly\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/broadcasting\" data-show-preview=\"true\">broadcasting<\/a>, without which the present near-global\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/diffusion\" data-term=\"diffusion\" data-type=\"MW\">diffusion<\/a>\u00a0of printed words, pictures, and sounds would have been impossible. The steam\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/printing-press\" data-show-preview=\"true\">printing press<\/a>,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/radio\" data-show-preview=\"true\">radio<\/a>, motion pictures,\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/television-technology\" data-show-preview=\"true\">television<\/a>, and\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/technology\/sound-recording\" data-show-preview=\"true\">sound recording<\/a>\u2014as well as systems of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/technology\/mass-production\" data-show-preview=\"true\">mass production<\/a>\u00a0and distribution\u2014were necessary before public communication in its present form might occur.<\/p>\r\n<p class=\"topic-paragraph\">Technology was not, however, the only prerequisite for the development of mass communication in the West. A large public of literate citizens was necessary before giant publishing and\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/newspaper\" data-show-preview=\"true\">newspaper<\/a>\u00a0empires might employ\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/extant\" data-term=\"extant\" data-type=\"MW\">extant<\/a>\u00a0communications technology to satisfy widespread desires or needs for popular reading materials. Affluence and interest were (and are) prerequisites for the maintenance of the radio, television, cinema, and recording industries, institutions that are most highly developed in wealthy, industrial nations. Even in countries in which public communication is employed largely for government\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/propaganda\" data-show-preview=\"true\">propaganda<\/a>, certain minimal economic and educational standards must be achieved before this persuasion is accepted by the general public.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21939\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Control of mass communication<\/h2>\r\n<p class=\"topic-paragraph\">Over the years, control of the instruments of mass communication has fallen into the hands of relatively small (some claim diminishing) numbers of professional communicators who seem, as populations expand and interest widens, to reach ever-increasing numbers of people. In the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/place\/United-States\" data-show-preview=\"true\">United States<\/a>, for example, far fewer\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/newspaper\" data-show-preview=\"true\">newspapers<\/a>\u00a0currently serve more readers than ever before, and a handful of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/book-publication\" data-show-preview=\"true\">book<\/a>\u00a0publishers produce the majority of the best sellers.<\/p>\r\n<p class=\"topic-paragraph\">Public communicators are not entirely free to follow their own whims in serving the masses, however. As is the case of any market, consumer satisfaction (or the lack of it) limits the nature and quantity of the material produced and circulated. Mass communicators are also restricted in some measure by laws governing libel,\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/slander\" data-term=\"slander\" data-type=\"MW\">slander<\/a>, and invasion of privacy and, in most countries, by traditions of professionalism that entail obligations of those who maintain access to the public\u2019s eyes and ears. In almost every modern nation, privileges to use broadcasting frequencies are circumscribed either loosely or rigidly by government regulations. In some countries, national agencies exercise absolute control of all broadcasting, and in certain areas print and film media operate under strict government control. Written and film communications may be subject to local legal restraints in regard to\u00a0<span id=\"ref384040\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/censorship\" data-show-preview=\"true\">censorship<\/a>\u00a0and have restrictions similar to those of other private businesses. Traditions of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/decorum\" data-term=\"decorum\" data-type=\"MW\">decorum<\/a>\u00a0and self-censorship, however, apply variably to publishers and filmmakers, depending usually upon the particular markets to which their fare is directed.<\/p>\r\n<\/section>\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21940\" data-level=\"3\" data-has-spy=\"true\">\r\n<h2 class=\"h3\">Effects of mass communication<\/h2>\r\n<p class=\"topic-paragraph\">Lively controversy centres on the effect of public communication upon audiences, not only in matters concerning\u00a0<span id=\"ref384041\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/public-opinion\" data-show-preview=\"true\">public opinion<\/a>\u00a0on political issues but in matters of personal lifestyles and tastes, consumer behaviour, the sensibilities and\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dispositions\" data-term=\"dispositions\" data-type=\"MW\">dispositions<\/a>\u00a0of children, and possible inducements to violence. Feelings regarding these matters vary greatly. Some people construe the overall effects of mass communication as generally harmless to both young and old. Many sociologists follow the theory that mass communication seems to influence\u00a0<span id=\"ref384042\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/attitude-psychology\" data-show-preview=\"true\">attitudes<\/a>\u00a0and behaviour only insofar as it confirms the status quo\u2014i.e., it influences values already accepted and operating in the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/culture\" data-term=\"culture\" data-type=\"MW\">culture<\/a>. Numerous other analysts, usually oriented to psychological or psychiatric\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/disciplines\" data-term=\"disciplines\" data-type=\"MW\">disciplines<\/a>, believe that mass communications provide potent sources of informal education and\u00a0<span id=\"ref384043\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/persuasion-psychology\" data-show-preview=\"true\">persuasion<\/a>. Their conclusions are drawn largely from observations that many, or most, people in technological societies form their personal views of the social realities beyond their immediate experience from messages presented to them through public communication.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">To assume that public communication is predominantly reflective of current values,\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/morality\" data-show-preview=\"true\">morals<\/a>, and attitudes denies much common experience. Fashions, fads, and small talk are too obviously and directly influenced by material in the press, in films, and in television to support this view. The success of public communication as an instrument of commercial\u00a0<span id=\"ref384044\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/money\/advertising\" data-show-preview=\"true\">advertising<\/a>\u00a0has also been constant and noticeable. Present evidence indicates that various instruments of mass communication produce varying effects upon different segments of the audience. These effects seem too numerous and short-lived to be measured effectively with currently available instruments. Much of the enormous output on television and radio and in print is probably simply regarded as \u201cplay\u201d and of little\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off eb\" href=\"https:\/\/www.britannica.com\/dictionary\/consequence\" data-term=\"consequence\" data-type=\"EB\">consequence<\/a>\u00a0in affecting adult dispositions, although many psychologists believe that the nature of children\u2019s\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/play-behavior\" data-show-preview=\"true\">play<\/a>\u00a0experiences is critical to their maturation.<\/p>\r\n<p class=\"topic-paragraph\">The role of newspapers, periodicals, and television in influencing political opinion is fairly well established in the voting behaviour of the so-called undecided\u00a0<span id=\"ref384045\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/election-political-science\" data-show-preview=\"true\">voters<\/a>. Numerous studies have shown that, while the majority of citizens in the United States cast their votes along party lines and according to social, educational, and economic determinants, middle-of-the-road voters often hold the\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/balance-of-power\" data-show-preview=\"true\">balance of power<\/a>\u00a0that determines the outcomes of elections. Politicians have become sensitive to their\u00a0<span id=\"ref384046\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/television-broadcasting\">television<\/a>\u00a0images and have devised much of their campaign strategy with the television audience in\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/mind\" data-show-preview=\"true\">mind<\/a>. Advertising agencies familiar with television techniques have been brought into the political arena to plan campaigns and develop their clients\u2019 images. The effectiveness of television campaigning cannot yet be determined reliably.<\/p>\r\n<p class=\"topic-paragraph\">Public communication is a near-ubiquitous condition of modernity. Most reliable surveys show that the majority of the people of the world (including those of totalitarian countries) are usually satisfied with the kind of mass communication available to them. Lacking\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/alternatives\" data-term=\"alternatives\" data-type=\"MW\">alternatives<\/a>\u00a0to the communication that they easily and conveniently receive, most people seem to accept what they are given without complaint. Mass communication is but one facet of life for most individuals, whose main preoccupations centre on the home and on daily employment. Public communication is an inexpensive\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/addendum\" data-term=\"addendum\" data-type=\"MW\">addendum<\/a>\u00a0to living, usually directed to low common denominators of taste, interest, and refinement of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/perception\" data-show-preview=\"true\">perception<\/a>. Although mass communication places enormous potential power in the hands of relatively few people, traditional requirements for popular approval and assent generally have prevented its use for overt subversion of culturally sanctioned institutions. Fear of such subversion is sometimes expressed by critics.<\/p>\r\n<\/section>\r\n<\/section>\r\n<\/section>\r\n<\/div>\r\n<div id=\"chatbot-root\">\u00a0<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<div data-page-index=\"29\">\u00a0<\/div>\r\n<div class=\"loaded-infinite-scroll-container qa-infinite-scroll-container\">\r\n<div class=\"grey-box w-100 grey-box-bottom\">\r\n<div class=\"grey-box-content mx-auto w-100\">\r\n<div class=\"page2ref-false topic-content topic-type-REGULAR\">\r\n<div class=\"reading-channel\">\r\n<div class=\"md-sentinel--spy-target\">\u00a0<\/div>\r\n<section id=\"ref21941\" data-level=\"1\" data-has-spy=\"true\">\r\n<h1 class=\"h1\">The psychology of communication<\/h1>\r\n<p class=\"topic-paragraph\">Contemporary psychologists have, since\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/event\/World-War-II\" data-show-preview=\"true\">World War II<\/a>, shown considerable interest in the ways in which communications occur.\u00a0<span id=\"ref384047\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/behaviourism-psychology\" data-show-preview=\"true\">Behaviourists<\/a>\u00a0have been prone to view communication in terms of stimulus-response relationships between sources of communications and individuals or groups that receive them. Those who subscribe to Freud\u2019s analysis of group psychology and ego theory tend to regard interactions in communication as reverberations of family group\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dynamics\" data-term=\"dynamics\" data-type=\"MW\">dynamics<\/a>\u00a0experienced early in life.<\/p>\r\n<p class=\"topic-paragraph\">By the mid-1950s, psychological interest settled largely on the persuasive aspects of various types of messages. Psychologists have attempted to discover whether a general factor of\u00a0<a class=\"md-crosslink autoxref \" href=\"https:\/\/www.britannica.com\/topic\/personality\" data-show-preview=\"true\">personality<\/a>\u00a0called \u201cpersuasibility\u201d might be identified in people at large. It would appear, though with qualifications, that individuals are indeed variably persuasible and that, at times, factors of personality are related to this quality.<\/p>\r\n<p class=\"topic-paragraph\">Other psychologists have studied the recipients of communication, evolving concepts of \u201cselective\u00a0<span id=\"ref384048\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/topic\/perception\" data-show-preview=\"true\">perception<\/a>,\u201d \u201cselective attention,\u201d and \u201cselective retention\u201d in order to explain not only the ways in which communication changed attitudes but also the reasons for resistance to change. Among their interests were the dynamics of the communication of rumours, the effects of \u201cscare messages,\u201d the degree of credulity that sources of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/prestige\" data-term=\"prestige\" data-type=\"MW\">prestige<\/a>\u00a0value provide, and the pressure of group\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/consensus\" data-term=\"consensus\" data-type=\"MW\">consensus<\/a>\u00a0upon individual perceptions of communications.<\/p>\r\n<p class=\"topic-paragraph\">Some of the suggestions that emerged from the work of certain modern psychologists may be subsumed under a theory of what is called \u201c<span id=\"ref384049\"><\/span><a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/cognitive-dissonance\" data-show-preview=\"true\">cognitive dissonance<\/a>,\u201d which is based upon the observation that most people cannot tolerate more than a specific degree of inconsistency in the\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/environments\" data-term=\"environments\" data-type=\"MW\">environments<\/a>\u00a0they perceive. An example of\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/cognitive\" data-term=\"cognitive\" data-type=\"MW\">cognitive<\/a>\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/dissonance\" data-term=\"dissonance\" data-type=\"MW\">dissonance<\/a>\u00a0may involve a person who considers himself a superb bowler but who on one occasion earns an extremely low score. The dissonant or inconsistent elements include the bowler\u2019s knowledge of his skill and the fact of his poor score. This produces tension. To reduce this tension\u2014dissonance\u2014the bowler may change his behaviour or misinterpret or reinterpret the dissonant elements in order to lessen the difference between the facts. For example, he may blame his performance on the\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/sports\/bowling\" data-show-preview=\"true\">bowling<\/a>\u00a0ball, the alley, or the temperature of the room. Thus he seeks a psychological\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/equilibrium\" data-term=\"equilibrium\" data-type=\"MW\">equilibrium<\/a>.<\/p>\r\n<p class=\"topic-paragraph\">This modification of an individual\u2019s perception of reality is of fundamental interest to the psychologist of communications. Because the agreement or disagreement of a communication with an individual\u2019s cognitive structure affects not only behaviour but perception as well, the major\u00a0<a class=\"md-dictionary-link md-dictionary-tt-off mw\" href=\"https:\/\/www.merriam-webster.com\/dictionary\/criterion\" data-term=\"criterion\" data-type=\"MW\">criterion<\/a>\u00a0for the psychological analysis of communication is neither the message nor the medium but the expectation of the person receiving the message.<\/p>\r\n<div class=\"module-spacing\">\u00a0<\/div>\r\n<p class=\"topic-paragraph\">It must not be assumed that any of the theories of audience\u00a0<a class=\"md-crosslink \" href=\"https:\/\/www.britannica.com\/science\/psychology\" data-show-preview=\"true\">psychology<\/a>\u00a0offered to date (including those of Gestaltists, Freudians, behaviourists, and others) lack relevance to an understanding of communication processes. None, however, seems to account fully for all the effects of communications upon people. The many facets of communication offer substantial problems for future psychological experimentation and theorizing.<\/p>\r\n<h3>Disclaimer<\/h3>This content has been reposted from <a href=\"https:\/\/www.britannica.com\/topic\/communication\/The-psychology-of-communication\" target=\"_blank\" rel=\"noreferrer noopener\">Britannica.com<\/a> for informational purposes only.<\/section>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article>\r\n<\/div>","protected":false},"excerpt":{"rendered":"<p>\u00a0 How the telephone was inventedOverview of the invention of the telephone, with a focus on the work by Alexander [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":3083,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_bbp_topic_count":0,"_bbp_reply_count":0,"_bbp_total_topic_count":0,"_bbp_total_reply_count":0,"_bbp_voice_count":0,"_bbp_anonymous_reply_count":0,"_bbp_topic_count_hidden":0,"_bbp_reply_count_hidden":0,"_bbp_forum_subforum_count":0,"footnotes":""},"categories":[120,118,119,109],"tags":[193,194,195,192],"class_list":["post-499","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-communication","category-history","category-innovation-inventions","category-technology","tag-communication","tag-landline-phones","tag-telecommunication-devices","tag-telephone-history"],"_links":{"self":[{"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/posts\/499","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/comments?post=499"}],"version-history":[{"count":3,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/posts\/499\/revisions"}],"predecessor-version":[{"id":1450,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/posts\/499\/revisions\/1450"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/media\/3083"}],"wp:attachment":[{"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/media?parent=499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/categories?post=499"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demo.geekybot.com\/index.php\/wp-json\/wp\/v2\/tags?post=499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}