Editing Packet radio (section)

{{Short description|Form of amateur radio data communications using the AX25 protocol}}
[[File:Tnc2400-stardado.JPG|thumb|Terminal Node Controller 2400 baud packet radio modem]]

In [[digital radio]], '''packet radio''' is the application of [[packet switching]] techniques to digital radio communications. Packet radio uses a [[packet switching]] [[Communication protocol|protocol]] as opposed to [[circuit switching]] or [[message switching]] protocols to transmit digital data via a [[radio]] [[communication link]].

Packet radio is frequently used by [[amateur radio]] operators. The [[AX.25]] (Amateur X.25) protocol was derived from the [[X.25]] [[data link layer]] protocol and adapted for amateur radio use. Every AX.25 packet includes the sender's amateur radio callsign, which satisfies the US FCC requirements for amateur radio station identification. AX.25 allows other stations to automatically repeat packets to extend the range of transmissions. It is possible for any packet station to act as a [[digipeater]], linking distant stations with each other through [[ad hoc network]]s. This makes packet radio especially useful for emergency communications.

Packet radio can be used in [[mobile communications]]. Some mobile packet radio stations transmit their location periodically using the [[Automatic Packet Reporting System]] (APRS). If the APRS packet is received by an "i-gate" station, position reports and other messages can be routed to an internet server, and made accessible on a public web page. This allows amateur radio operators to track the locations of vehicles, hikers, high-altitude balloons, etc., along with telemetry and other messages around the world.

Some packet radio implementations also use dedicated point-to-point links such as TARPN. In cases such as this, new protocols have emerged such as [[Improved Layer 2 Protocol]] (IL2P) supporting [[forward error correction]] for noisy and weak signal links.