AX.25 is a data link layer protocol derived from the X.25 protocol suite and designed for use by amateur radio operators. It is used extensively on amateur packet radio networks.
AX.25 occupies the first and second layers of the OSI networking model, and is responsible for transferring data (encapsulated in packets) between nodes and detecting errors introduced by the communications channel. It is thus comparable to Ethernet in the services it provides.
AX.25 supports both connected and connectionless modes of operation, the latter used to great effect by the Automatic Position Reporting System.