The Protocol : AX25
AX.25 (Amateur X.25) is the communications protocol used for packet radio. AX.25 was developed in the 1970's and based on the wired network protocol X.25. Because of the difference in the transport medium (radios vs wires) and because of different addressing schemes, X.25 was modified. AX.25 includes a digipeater field to allow other stations to automatically repeat packets to extend the range of transmitters. One advantage of AX.25 is that every packet sent contains the sender's and recipient's radio callsign, thus providing station identification with every transmission.
Often, special packet radio protocols (TCP/IP) are encapsulated within AX.25 packet frames.