[nos-bbs] AX.25 status reporting

wa7nwp at jnos.org wa7nwp at jnos.org
Mon Sep 25 19:12:29 EDT 2006

>> everyone told us that 'datagram' was good (simply
>> because it reduced channel traffic by eliminating the AX.25 I-frame
>> acknowledgements).  Unfortunately, that was a lie.  The fact is, an
>> underlying 'datagram' AX.25 "system" is probably not performing very
>> well at all with carrying IP content.  For every IP frame that gets
>> lost due to hidden terminals and collisions, the TCP/IP system relies
>> on the TCP retry parameters that are set at each end of the TCP
>> transport circuit and these will normally back off to much greater
>> amounts than an AX.25 t1 (retry) timer will.  This is why it is
>> *good* to use 'virtual circuit' mode on channels which are carrying
>> IP.  And you will also see your AX.25 "stats" that way...

It depends on the circuit...

With a "packet repeater" where there are (essentially) no collisions, then
DG mode works well.  In a typical ad-hoc senario, VC would make for more
robust data circuits and faster retries.

At one time I used a mountain top node in mixed mode.  I would send to it
in VC mode since there were collisions and retries.   I had it set to send
to me as Datagrams because it was 110% loud and clean into my location.

Fun stuff eh?  Really nice to be able to tune it for the situation at hand.

Bill - WA7NWP

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