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Packet Radio

Packet radio is a form of digital data transmission used to link computers. The most common use of PKT is in amateur radio, to construct wireless computer networks.

Its name is a reference to the use of packet switching between network nodes, which allows multiple virtual circuits to coexist on a single radio channel. Packet radio networks use the AX.25 data link layer protocol, derived from the X.25 protocol suite and adapted for amateur radio use.

Note that while the term "packet radio" also was used for early version of mobile ad hoc networks, this technology has little in common with the description below. Station configuration

A basic packet radio station consists of a computer, a modem, and a transceiver with an antenna. Traditionally, the computer and modem are combined in one unit, the terminal node controller (TNC), with a dumb terminal (or terminal emulator) used to input and display data. Increasingly, however, personal computers are taking over the functions of the TNC, with the modem either a standalone unit or implemented entirely in software. Alternatively, multiple manufacturers (including Kenwood and Alinco) now market handheld or mobile radios with built-in TNCs, allowing connection directly to the serial port of a computer or terminal with no other equipment required.

The computer is responsible for managing network connections, formatting data as AX.25 packets, and controlling the radio channel. Frequently it provides other functionality as well, such as a simple bulletin board system to accept messages while the operator is away.

Data link layer: AX.25
Packet radio networks rely on the AX.25 data link layer protocol, derived from the X.25 protocol suite and intended specifically for amateur radio use. Despite its name, AX.25 defines both the physical and data link layers of the OSI model. (It also defines a network layer protocol, though this is seldom used.)

Network layer
Packet radio has most often been used for direct, keyboard-to-keyboard connections between stations, either between two live operators or between an operator and a bulletin board system. No network services above the data link layer are required for these applications.

To provide automated routing of data between stations (important for the delivery of electronic mail), several network layer protocols have been developed for use with AX.25. Most prominent among these are NET/ROM, ROSE, and TexNet.

In principle, any network layer protocol may be used, including the ubiquitous Internet protocol.

 TCP/IP

TCP/IP stands for Transmission Control Protocol/Internet Protocol. TCP/IP is commonly used over the Internet wired computer network. The TCP/IP suite contains different transmission facilities such as FTP (File Transfer Protocol), SMTP (Simple Mail Transport Protocol), Telnet (Remote terminal protocol), and NNTP (Net News Transfer Protocol) The KA9Q NOS program (also called NET) is the most commonly used version of TCP/IP in packet radio. NOS originally was written for the PC compatible. However, NOS has been ported to many different computers such as the Amiga, Macintosh, Unix, and others. Smaller computers like the Commodore 64 and the Timex-Sinclar do not currently have versions of NOS available. TCP/IP based amateur networks are becoming more common each day.

 

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