The AX.25 protocol offers both connected and connectionless modes of operation, and is used either by itself for point-point links, or to carry other protocols such as TCP/IP and NetRom.
It is similar to X.25 level 2 in structure, with some extensions to make it more useful in the amateur radio environment.
The NetRom protocol is an attempt at a full network protocol and uses AX.25 at its lowest layer as a datalink protocol. It provides a network layer that is an adapted form of AX.25.
Alan Cox developed some early kernel based AX.25 software support for Linux.
Jonathon Naylor <g4klx@g4klx.demon.co.uk> has taken up ongoing
development of the code, has added NetRom support and is now the developer
of the AX.25 related kernel code and utilities. DAMA support was developed by
Joerg, DL1BKE, jreuter@lykos.tng.oche.de. Finally Baycom support was
added by Thomas Sailer, <sailer@ife.ee.ethz.ch>.
The Linux code supports KISS based TNC's (Terminal Node Controllers), the Ottawa PI card, the Gracilis PacketTwin card and other Z8530 SCC based cards with the generic SCC driver and both the Parallel and Serial port Baycom modems.
The User programs contain a simple PMS (Personal Message System), a beacon facility, a line mode connect program, `listen' an example of how to capture all AX.25 frames at raw interface level and programs to configure the NetRom protocol. Included also are an AX.25 server style program to handle and despatch incoming AX.25 connections and a NetRom daemon which does most of the hard work for NetRom support.