Talk:AX.25

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I've created a separate page for AX.25 because I think there are enough things to say about it that are not directly relevant to packet radio—even though I realize there is an inexorable connection between the two topics.

My thinking is that "packet radio" should cover the history, construction, and operation of packet radio stations, while this page can delve into more of the nitty-gritty of the protocol's development, design, and use.

I'll be moving most of what is currently at packet radio over here shortly. Discussion always welcome on my talk page. Simon 15:55, 21 Jan 2005 (UTC)

Below is the text copied from packet radio. I'm placing it here instead of in the article because, to me, it sounds like a rant (even moreso before I made some edits) and is not particularly relevant. Bragging that AX.25 can operate on "multi-megabit" networks is meaningless, for instance, as these networks simply do not exist in amateur radio.

However, some of the information on acknowledgements and so forth could usefully be included in the article.

Version 2.0 and earlier of the specification had limited packet lengths, and for connected virtual circuits, could only transmit eight packets before having to wait for an acknowledgement. These limitations made sense in the context of the noisy, bandwidth-limited channels encountered in earlier packet radio implementations. While good for slower links, however, it was inefficient for faster channels. Today's AX.25, however, supports up to 128 outstanding packets before an acknowledgement is necessary, and packets with up to 8192 bytes of payload data. This makes AX.25 suitable for use on multi-megabit per second networks.

AX.25 version 2.0 and later also supports raw datagram mode of operation too. While using virtual circuits for slower links (e.g., 5 Mbit/s or slower) makes more efficient use of bandwidth and improves end-to-end throughput, the 128 packet window is a limiting factor on faster networks. Therefore, one can use AX.25 entirely in datagram mode as well, thus allowing AX.25 to rival Frame Relay and Ethernet in performance. Support for 8192 byte payloads makes AX.25 suitable for use over multi-gigabit per second networks

AX.25 has been adopted for applications outside of amateur radio as well.

Let me also add: in spite of the last paragraph above, I have never heard of AX.25 being used in a non-amateur setting. I can't imagine what benefits it would offer in a commercial environment over plain old X.25, considering that most of the differences between the two have to do with satisfying legal requirements unique to amateur radio.

Simon 18:14, 21 Jan 2005 (UTC)

Similar functional needs do exist in other applications as well. I recall having seen Geodetic GPS receivers that talk over UHF radio link to exchange ionospheric modelling data and in case of "known position reference" also "dgps" data. Having a bunch of similar devices talking to each other does need some way to identify stations. Identity in those frames is not a "call-sign", but something analogous.

Packet radio is also popular among CB enthusiasts, there are no official callsigns but everybody invents something.

Oh2mqk 11:35, 1 June 2006 (UTC)

[edit] OSI levels

Since AX25 involves some kind of routing decisions, at least in the unconnected environments used for APRS, or for connection between stations using a digipeater, wouldn't it be better to include "layer 3" in the description? The boundary between PDUs is less strict than in most other "OSI layered" protocols, but routing is conceptually layer 3. Any comment?

--Michael 21:22, 6 April 2006 (UTC)