AX.25 Layer 2
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AX.25 Layer 2

This web site has been established to be a concise repository for AX.25 layer 2 design activities. AX.25 is a protocol originally developed for amateur radio in the late 1970's and standardized on in 1984 with the release of the v2.0 specification. Amateur radio enthusiasts quickly developed many diverse network architectures using AX.25 as a basis. Unfortunately, AX.25 was released as a link layer protocol not a network or application layer protocol. As was common in those days, a "tower of Babel" was created with all the different network architectures. Many of the networks were also based on single frequencies causing extensive collisions between repeated packets.

When the Internet came along, amateurs quickly began to lose interest in the different AX.25 networks. While the Internet at that time was slow (14.4 kbps modems and expensive ($25 per month for local access if available), it offered worldwide connectivity and an emerging application portfolio. AX.25, on the other hand, provided limited reliability on a local level with few applications other than keyboard-to-keyboard or keyboard-to-BBS. There was some adaptation of IP over AX.25 with some success but these networks were normally UI networks without repeater coverage.

Today, there are very few applications utilizing AX.25 networks. DX clusters have significantly more users on telnet than on RF. Winlink 2000 supports packet by way of Paclink and Telpac, but primarily in point-to-point operation (repeater use requires network topology knowledge by the user). Europe has standardized on FlexNet to implement their backbone network. APRS uses specially configured digipeaters, which in the tradition of previous AX.25 networks, are not compatible with non-APRS applications. All of these networks require the end user to modify their software or hardware to use the various local environments. The prerequisite of network topology knowledge is daunting at best and leads to either disuse or misuse.

The goal of this web site and, more importantly, the AX.25 Layer 2 Special Interest Group is to define and develop a generic AX.25 layer 2 implementation that can be used by any of the above applications along with supporting layer 3 protocols without requiring prior knowledge of the local network topology by those users, applications, and protocols. Also, a generic layer 1/2 interface would be beneficial as well.
Unfortunately, TAPR has reorganized their forums and this SIG is no longer available.