AX.25 is a protocol for transmitting data over a radio channel.
Basic idea of the AX25 protocol
It is connection-oriented, but also allows the transmission of connectionless data. Is the transfer of data on the disturbed radio channel is repeatedly attempted to transmit the lost data again. The protocol was the X.25 protocol of ITU- T modeled and adapted to the conditions in amateur radio. There AX.25 is used in the modes Packet Radio and APRS. AX.25 defines the stage 2 of the ISO - OSI model.
Building AX25 packets
The data is divided into packets for AX.25 (frames). Each packet contains not only the data but also the necessary elements for addressing and a checksum.