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[aprssig] Digipeating behavior

scott at opentrac.org scott at opentrac.org
Sun Mar 12 05:16:22 UTC 2006

This didn't really get resolved last time, so I'm bringing it up again.  I'm
trying to nail down the exact digipeater behavior that's expected in APRS.

The AX.25 spec (version 2.2, page 13) has what I assume to be a typo in its
digipeating description - an 'or' that seems to make no sense.  Anyway,
here's what I've got so far.

1. When first digipeater field (starting after the source call) with H = 0
matches my callsign or alias:  Set H bit, retransmit frame.

Bob suggests that this should not be limited to the first H = 0 field.

2. When digipeater field matches ALIASn-n, SSID is non-zero, and
payload+address is unique in past S seconds, decrement SSID and set H = 1 if
SSID is now zero.  Optionally insert MYCALL prior to ALIASn-n.

Should this apply only to the first H = 0 field?  Preemption is also a
possibility, where position is ignored, and all fields up to the matching
one get their H bits set.

What else am I missing?


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