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[aprssig] AX.25 'H' flag

Curt, WE7U archer at eskimo.com
Mon Nov 14 21:18:58 UTC 2005


On Mon, 14 Nov 2005, Wes Johnston wrote:

> Just to be sure.... I am talking about the KISS frames I captured by
> monitoring the transmission of packets on air.

Yep.  Can't get much closer to the on-the-air format than that.
Well, you can, but I wouldn't recommend it (6803 at 0.79 MHz,
Assembly language, XR-2211 into an interrupt pin).


> In the end, we can say how it's *supposed* to be in the spec all we want
> ( and I agree that each digipeater should set each bit in sequence), but
> I just wanted to make sure that Scott knows that not all TNC's meet the
> spec, and he'll have to work around them.
>
> kc4pl has my pk88 TNC on loan... maybe I need to dig it out to recreate
> this h flag problem again??  I'll have to see if I can dig out the
> source code for my kiss mode digi, maybe this is in the comments....

Probably not worth it at this point, but if you could prove that
they did that it'd be good to send a bug report to the vendor on it.
Perhaps newer firmware versions were fixed though and it was an old
bug.

If they were doing pre-emptive digipeating I could see finding a
matching callsign further down the string, but even in that case
you'd want to set all of the 'H' bits to one up to and including
that callsign when you re-transmitted the packet.  Having any zeroes
in between the one bits just isn't right.  It has to be one of
these orders for the 'H' bits:

  All 0's (no digi's used yet)
  All 1's (all digi's in the path used up)
  1's followed by 0's (some digi's used at the start of path)

Anything else is not per spec.

--
Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
"Lotto:    A tax on people who are bad at math." -- unknown
"Windows:  Microsoft's tax on computer illiterates." -- WE7U
"The world DOES revolve around me:  I picked the coordinate system!"




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