Pager
From Wikipedia, the free encyclopedia
A pager is an electronic device used to contact people via a paging network. It pre-dates mobile phone technology, being most popular during the 1980s and 1990s, but similarly uses radio transmissions to communicate between a control/call center and the recipient. Many of today's pagers use the FLEX on-air protocol. The slower POCSAG on-air protocol is still used for some pagers in the United States and likely in other countries.
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[edit] Uses
Pagers remain in use to notify emergency personnel. For example, they are required to be used by UK lifeboat men and retained firefighters. In this use, they can be thought of as a modern equivalent of maroon rockets. A common type of pager used to alert emergency personnel is the Motorola MINITOR pager. On a smaller scale, pagers are mostly carried by staff in medical establishments, allowing them to be summoned to emergencies.
Pagers are also widely used in the IT world, especially in cases where on-call technicians cannot rely on more modern cellular telephone systems. A good example would be in a cellular telephone company, where a service interruption in the cellular network would also mean that it would not be possible to notify a technician due to the outage in the network. Therefore, in these companies, engineers are usually equipped with a pager that uses another telco's mobile network to ensure reachability in case of emergency.
Most modern paging systems use simulcast delivery, by satellite controlled networks. This type of distributed system makes them inherently more reliable than terrestial based cellular networks for message delivery. Many paging transmitters may overlap a coverage area, where in contrast cellular systems are built to fill the holes. When terrestial networks go down in an emergency, satellite systems continue to perform. Because of superior building penetration and availability of service in disaster situations pagers are primarily used by life saving first responders.
Pager subscriptions have been on the decline since the widespread availability of mobile phones and their ability to send and receive text messages based on short message service (SMS is used in large hospital complexes, where cellular coverage is often weak or nonexistent, and where radio transmitters may interfere with sensitive medical equipment.
Pagers also have privacy advantages compared with cellular phones. Since a one-way pager is a passive receiver only (it sends no information back to the base station), its location cannot be tracked. But this can also be disadvantageous, as a message sent to a pager must be broadcast from every paging transmitter in the pager's service area. Thus, if a pager has nationwide service, a message sent to it could be intercepted by criminals or law enforcement agencies anywhere within the nationwide service area.
Pagers have the benefit of distributing text information to a large number of recipients simultaneously by using group call features. This ability coupled with delivery times of less than 20 seconds makes them well-suited for trauma notifications in emergency rooms.
Pager technology is now used in hospitals, irrigation control systems, and traffic signals.
[edit] Functionality
Early pagers only provided an audio notification, such as a series of bleeps, to indicate reception of a page. The paged party then had to telephone the control/call centre to collect the message either from an operator or an early voice mail device.
Some early models included an analog audio receiver and speaker; upon receiving a page the speaker would activate, and the user would hear a human voice reciting their message. Later pagers used digital messages, first numeric and later alphanumeric, to provide the recipient with more information.
Even more recent models included the ability to send messages in a two-way fashion and even included the ability to send and receive email. Many paging operators also support WCTP for sending and receiving messages from 1.5, 1.7 and two-way pagers. This is called two-way paging.
Many paging network operators now allow numeric and textual pages to be submitted to the paging networks via email. This is convenient for many users, due to the widespread adoption of email; but email-based message submission methods do not usually provide any way to ensure that messages have been received by the paging network. This can result in pager messages being delayed or lost. Older forms of message submission using the Telocator Alphanumeric input Protocol protocol involve modem connections directly to a paging network, and are less subject to these delays. For this reason, older forms of message submission retain their usefulness for disseminating highly-important alerts to users such as emergency services personnel.
Pagers usually have very simple ring tones and some include a vibrating alert. Note that the idiomatic sound heard in popular media (movies and television programs) as "pager going off" (a series of two short beeps interrupted by a slightly longer pause) is actually the "pager power-up verification beep" sequence, perhaps because it was easier to generate that tone on demand (simply flip the power switch on).
Common paging protocols include Telocator Alphanumeric input Protocol (TAP), FLEX, ReFLEX, POCSAG, Golay, ERMES and NTT. Past paging protocols include Two-tone and 5/6-tone.
In the United States, pagers typically receive signals using the FLEX protocol in the 900 MHz band. Commercial paging transmitters typically radiate 1000 watts of effective power, resulting in a much wider coverage area per tower than a mobile phone transmitter, which typically radiates in the neighborhood of 0.6 Watt per channel.
Although 900 MHz FLEX paging networks tend to have stronger in-building coverage than mobile phone networks, commercial paging service providers will work with large institutions to install repeater equipment in the event that service is not available in needed areas of the subscribing institution's buildings. This is especially critical in hospital settings where emergency staff must be able to reliably receive pages in order to respond to patient needs.
Other radio bands used for pagers include the 400 MHz band, the VHF band, and the FM commercial broadcast band (88-108 MHz). Other paging protocols used in the VHF, 400 MHz UHF, and 900 MHz bands include POCSAG and ERMES. Pagers using the commercial FM band receive a subcarrier, called the Subsidiary Communications Authority, of a broadcast station.
