Pager

For terminal pagers, see [[:more (Unix) or less (Unix)]].

A pager (sometimes called a beeper) is a simple personal telecommunications device for short messages. A one-way numeric pager can only receive a message consisting of a few digits, typically a phone number that the user is then expected to call. Alphanumeric pagers are also available, and two-way ones can send email or SMS messages as well as receiving.

Until the popular adoption of mobile phones in the late 1990s, pagers fulfilled the role of common personal and mobile communications. As of 2007, pagers have fallen into obsolescence and are preserved only by niche markets consisting largely of emergency service personnel, medical personnel, and information technology support staff.

History

Paging was invented by Multitone Electronics in 1956 at St Thomas' Hospital in London to alert doctors attending emergencies. Since then, paging has evolved in sophistication. Today, millions of messages are transmitted to people needing fast, reliable messaging communications.

In the world of paging there are two distinct categories of system in operation. There are on-site paging systems that are used in hospitals to convey the same urgent information as when they were invented in 1956. The other type is wide area paging, which offers similar features as on-site paging, but provides the radio coverage across a city, region or country rather than in just one hospital building.

Originally operating on AM radio frequencies, paging moved to FM schemes prior to becoming a ubiquitous form of communications around the developed and developing world. In some cases, before the advent of cellular phone systems the pager was used as a replacement for a lack of cheap local or international phone services.

Function and operation

The front end of a numeric pager

A Motorola alphanumeric pager used in Brazil in the 1990s, operated by Teletrim

Paging is a subscription service offered in a variety of plans and options to meet the needs of a subscriber and the type of device used. In general, all pagers are given unique phone numbers while alphanumeric pagers are given an email address, usually consisting of the phone number.

Upon calling a phone number assigned to a pager, the calling party reaches a recorded greeting asking the caller to enter a numeric message, and sometimes giving the caller an option to leave voice mail. Usually, within a few minutes, the paged person will receive an alert from the pager with the phone number to return the call and/or a pager code. In the case of email paging, the text is displayed.

• Numeric pagers are the simplest of the type of devices offering only a numeric display of the phone number to be called and pager codes
• Alphanumeric pagers are essentially modified versions of numeric pagers with sophisticated display to accommodate text. These devices are usually given an email address to receive text messages.
• Two-way Alphanumeric pagers are alphanumeric pagers with the ability to send text messages typed in with a small keyboard.

Most modern paging systems use simulcast delivery by satellite controlled networks. This type of distributed system makes them inherently more reliable than terrestrial based cellular networks for message delivery. Many paging transmitters may overlap a coverage area, while cellular systems are built to fill holes in existing networks. When terrestrial 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 often used by first responders in emergencies.

Pager use in the 21st century

A Skyper pager that is in use for HAM Radio

A pager that is in use for emergency services

File:AvontDelfA.jpg

A mid '90s opaque black Avont pager model

Pagers are still in use today in places where mobile phones typically cannot reach users, and also in places where the operation of the radio transmitters contained in mobile phones is problematic or prohibited. One such type of location is a large hospital complex, where cellular coverage is often weak or nonexistent, where radio transmitters are suggested to interfere with sensitive medical equipment and where there is a greater need of assurance for a timely delivery of a message.

Some common environments in which pagers are still used are:

• Pagers remain in use to notify emergency personnel. For example, they are required to be used by UK lifeboat men and retained firefighters.
• 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. Pagers are also frequently used by non-telco IT departments.

Additionally, some irrigation control systems and traffic signals are now controlled by messages sent via paging networks. Due to energy concerns in the United States and other countries, 2Way paging networks are being used for power company meter reading and control.

Security

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. However, 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.

Technical information

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.

Common paging protocols include 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 around 0.6 Watts 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.

Unlike mobile phones, most one-way pagers do not display any information about whether a signal is being received or about the strength of the received signal. Since one-way pagers do not contain transmitters, one-way paging networks have no way to track whether a message has been successfully delivered to a pager. Because of this, if a one-way pager is turned off or is not receiving a usable signal at the time a message is transmitted, the message will never be received and the sender of the message will not be notified of this fact.

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.

See also

• Alfred J. Gross
• Plectron
• Motorola Minitor Voice Pager
• Wireless Communications Transfer Protocol (WCTP)
• Simple Network Paging Protocol (SNPP)

External links

• MULTITONE ELECTRONICS Inventors & manufacturers of paging systems
• BBC news reports closure of UK domestic pager systems in 2001
• POCSAG and FLeX pager gallery
• NotePage technical support - Technical information on protocols, carriers, etc.