<P> 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 . </P> <P> 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 . This resilience has led public safety agencies to adopt pagers over cellular and other commercial services for critical messaging . </P> <P> Pagers themselves vary from very cheap and simple beepers, to more complex personal communications equipment, falling into eight main categories . </P> <Dl> <Dt> Beepers or tone - only pagers </Dt> <Dd> Beepers or tone - only pagers are the simplest and least expensive 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 They were named beepers because they originally made a beeping noise, but current pagers in this category use other forms of alert as well .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 . </Dd> <Dt> Voice / tone </Dt> <Dd> Voice / Tone pagers enable pager users to listen to a recorded voice message when an alert is received . </Dd> <Dt> Numeric </Dt> <Dd> 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 . </Dd> <Dt> Alphanumeric </Dt> <Dd> 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 . The sender must enter a message, either numeric and push #or, text & push #or a verbal message . The pager does not automatically record the sender's number; the pager will beep but no message can be seen or heard if none has been entered . </Dd> <Dt> Response </Dt> <Dd> 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 . </Dd> <Dt> Two - way </Dt> <Dd> Two - way pagers are response pagers with built - in QWERTY keyboards . These pagers allow the user to reply to messages, originate messages, and forward messages using free - form text as well as "canned" responses . </Dd> <Dt> One - way modems </Dt> <Dd> One - way modems are controllers with integrated paging receivers, which are capable of taking local action based on messages and data they receive . </Dd> <Dt> Two - way modems </Dt> <Dd> Two - way modems have capabilities similar to one - way modems . They can also confirm messages and transmit their own messages and data . </Dd> </Dl>

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