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URL:
http://www.braddye.com/newsletters/4apr2003.html
A paging network is a collection of paging terminals,
system controllers, transmitters, receivers and data links, all carefully
engineered to make sure the paging system has optimal coverage and response
capabilities with minimal interference. Some paging systems are land-based,
while some rely on satellites for large-area coverage.
Like cellular systems, virtually all of the paging
networks involve more than one transmitter. Paging networks, especially those
that support one-way subscriber devices, rely on simulcast capability to
blanket an area. Several transmitters must send the same message over a wide
area using the same frequency. This is very different from the cell-based targeted
delivery methods used in cellular systems. Paging carriers use the same
infrastructure to support both one-way and two-way subscribers.
Not all of the paging infrastructures support single
transmitter or cell-based targeted message delivery. Paging systems are
store-and-forward systems. They accept messages for delivery to paging devices
and store them for a brief period before delivery.
Paging terminals interface to the Public Switched
Telephone Network (PSTN) to permit subscribers to dial up and send pages from
their telephones. To support alphanumeric messaging, many terminals support
access to alpha entry devices that may include PCs or other specialized
terminals and through a dial-up modem connection. With the advent of Internet
e-commerce, paging terminals also accept messages from new sources such as
email and the World Wide Web. Infrastructure suppliers and other vendors
usually develop the gateways that translate between the Internet protocols and
the paging protocols supported by the paging terminals.
In a paging system, the system controllers perform
the tasks of queuing, batching, encoding, and scheduling messages received from
paging terminals for delivery to transmitter sites. The most valuable resource
available to paging carriers is their RF (radio frequency) spectrum. Therefore,
the system controller plays a significant role in optimizing the use of this
scarce resource by implementing sophisticated scheduling algorithms, both for
inbound and outbound RF channels.
The networks used to connect paging terminals to each
other, paging terminals to system controllers, and system controllers to
transmitters and receivers can be very complex. These can be wire-line networks
that consist of digital links such as T1/E1, analog lines, and frame relay
networks. Wireless networks may also include satellite, microwave, or
radio.
Generally, paging systems are highly reliable, unless
a solar storm or electronic problem causes the satellite to fail.
Keywords:
Paging
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