AX.25 [data link layer protocol for packet radio networks]

For packet radio networks, the AX.25 data link layer protocol is most often used. However, TCP/IP (Transport Control Protocol/Internet Protocol) is also popular. The AX.25 protocol is a variant of the international X.25 protocol applied to wireless communication and packet radio. Most networks are composed of copper or fiber optic cable and provide reliable communication between hosts. The wireless medium is vastly different. It is less reliable and suffers from phenomena that are not present in conventional wired networks. For example, in a cable network all hosts on a network can hear each other. This makes "carrier sense" protocols such as Ethernet easy to implement. Before any host seizes the network, it first listens to help avoid collisions. Wireless networks also support carrier sense. However, hosts on the network cannot always hear each other for numerous reasons. Buildings and the local terrain are two important factors that determine the ability to receive information. We concentrate on the analysis of AX.25 packet radio networks operating in the 144-148 MHz band. Understanding and studying a network is a com analyzers, sometimes called "sniffers," are available to aid the packet user in understanding how a network operates. XNET, a network analyzer developed specifically to examine AX.25 networks, is described.