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A pager (also known as a beeper) is a wireless telecommunications device that receives and displays numeric and/or receives and announces voice messages. ''One-way pagers'' can only receive messages, while ''response pagers'' and ''two-way pagers'' can also acknowledge, reply to, and originate messages using an internal transmitter.〔http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci212739,00.html〕 Pagers operate as part of a paging system which includes one or more fixed transmitters (or in the case of response pagers and two-way pagers, one or more base stations), as well as a number of pagers carried by mobile users. These systems can range from a restaurant system with a single low-power transmitter, to a nationwide system with thousands of high-power base stations. One of the first practical paging services was launched in 1950 for physicians in the New York City area. Physicians paid $12 per month for the service and carried a 6 oz () pager that would receive phone messages within 25 mi () of a single transmitter tower. The system was manufactured by the Reevesound Company and operated by Telanswerphone.〔(''Pocket Radio Pages Doctors Night Or Day'', January 1951, Popular Science )〕 In 1960, John Francis Mitchell combined elements of Motorola's walkie-talkie and automobile radio technologies to create the first transistorized pager,〔(John F. Mitchell Biography )〕〔(The Top Giants in Telephony )〕〔(Who invented the cell phone? )〕 and from that time, paging technology continued to advance, and pager adoption continued to expand, until the early 1990s. However, by the mid-1990s, as cellular technologies became cheaper and more widely available, advanced services began to displace paging as a commercial product. Today, pagers exist largely as niche products, finding preferential use in applications such as hospitals, public safety,〔(''Use of Pagers in Crisis Situations'' ) ((Archive ))〕 and retail〔(''Shoppers Drug Mart Pharmacy Services'' )〕 locations where their simplicity, high reliability, and low cost represent significant advantages. == Function and operation == Paging systems are operated by commercial carriers, often as a subscription service, and they are also operated directly by end users as private systems. Commercial carrier systems tend to cover a larger geographical area than private systems, while private systems tend to cover their limited area more thoroughly and deliver messages faster than commercial systems. In all systems, clients send messages to pagers, an activity commonly referred to as ''paging''. System operators often assign unique phone numbers or email addresses to pagers (and pre-defined groups of pagers), enabling clients to page by telephone call, e-mail, and SMS. Paging systems also support various types of direct connection protocols, which sacrifice global addressing and accessibility for a dedicated communications link. Automated monitoring and escalation software clients, often used in hospitals, IT departments, and alarm companies, tend to prefer direct connections because of the increased reliability. Small paging systems, such as those used in restaurant and retail establishments, often integrate a keyboard and paging system into a single box, reducing both cost and complexity. Paging systems support several popular direct connection protocols, including TAP, TNPP, SNPP, and WCTP, as well as proprietary modem- and socket-based protocols. Additionally, organizations often integrate paging systems with their Voice-mail and PBX systems, conceptually attaching pagers to a telephone extensions, and they set up web portals to integrate pagers into other parts of their enterprise. A paging system alerts a pager (or group of pagers) by transmitting information over an RF channel, including an address and message information. This information is formatted using a paging protocol, such as 2-tone, 5/6-tone, GOLAY, POCSAG, FLEX, ERMES, or NTT. Two-way pagers and response pagers typically use the ReFLEX protocol. Pagers themselves vary from very cheap and simple beepers, to more complex personal communications equipment, falling into eight main categories: * Beepers or Tone-only Pagers are the simplest form of paging. They were named beepers because they originally made a beeping noise, but current pagers in this category use other forms of alert as well. Some use audio signals, others light up and some vibrate, often used in combination. The majority of restaurant pagers fall into this category.〔 〕 * Voice/Tone pagers provide the ability to listen to a recorded voice message when an alert is received. * Numeric Pagers contain a numeric LCD display capable of displaying the calling phone number or other numeric information generally up to 10 digits. The display can also convey pager codes, a set of number codes corresponding to mutually understood pre-defined messages. * Alphanumeric Pagers contain a more sophisticated LCD capable of displaying text and icons. These devices receive text messages, often through email or direct connection to the paging system. * Response Pagers are alphanumeric pagers equipped with built-in transmitters, with the ability to acknowledge/confirm messages. They also allow the user to reply to messages by way of a multiple-choice response list, and to initiate canned messages from pre-programmed address and message lists. These devices are sometimes called "1.5-way pagers" or "1.7-way pagers" depending on capabilities. * Two-way Pagers are response pagers with built-in QWERTY keyboards. These pagers allow the user reply to messages, originate messages, and forward messages using free-form text as well as canned responses. * One-way Modems are controllers with integrated paging receivers, which are capable of taking local action based on messages and data they receive. * Two-way Modems have capabilities similar to one-way modems, and can also confirm messages and transmit their own messages and data. Modern paging systems typically use multiple base transmitters to modulate the same signal on the same RF channel, a design approach called ''simulcast''. This type of design enables pagers to select the strongest signal from several candidate transmitters using FM capture, thereby improving overall system performance. Simulcast systems often use satellite to distribute identical information to multiple transmitters, and GPS at each transmitter to precisely time its modulation relative to other transmitters. The coverage overlap, combined with use of satellite communications, can make paging systems more reliable than terrestrial based cellular networks in some cases, including during natural and man-made disaster.〔US. FCC. Report and Recommendations to the Federal Communications Commission. FCC, 12 June 2006, pg 24. Web. 14 Apr. 2013. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pager」の詳細全文を読む スポンサード リンク
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