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[aprssig] Definitive digipeater specification?

Robert Bruninga bruninga at usna.edu
Tue Feb 28 01:57:45 UTC 2006


>I'd like to see that, too.
>>Is there any 'official' explanation of exactly how 
>a modern APRS digipeater is supposed to function?

Here is my first cut?

1) Callsign substitution of the ALIAS list:
Any digi field that equals any of the digi aliases are
digipeated and the field is replaced with the tnc MYCALL
and has-been-digipeated bit set

AND these substitutions take priority over any of the
next processes.

2) UIFLOOD:
If UIFLOOD is set to XXXX then any field that
looks like XXXXn-n and has a non-zero SSID
AND does not match the FROM-TO and DATA
field of any previous packet in the last S seconds
will have the SSID decremented once.  If the
decrement results in -0, then the has-been-
digipeated bit is set.

If ID is set to ON, then MYCALL is inserted
in front of the XXXXn-N field.

3) UITRACE:  Same as UIFLOOD (as defined above)
but ID IS ALWAYS ON.  So the path builds as
the packet proceeds.

4) It is also NICE to have a n-N  hop limit that
will NOT do further digipeating of a pcket if the
n-N value is greater than this limit.  If the limit
is exceeded, then the packet IS digipeated AND
is DECREMENTED but the has-been-digipeated
bit is set.

5) Pre-EMPTIVE digipeating:  (not many TNC's have
done this, but I have always wanted it)...

If PREEMPT callsign is ZZZZZ
(including ZZZZZn-N) and a match occurs
in any field that has NOT been digipeated, then
- THe packet is digipeated
- all previous digi hops up to an includeing this one
  are marked with the has-been-digipeted bit set.
- This digi inserts its MYCALL in front of the ZZZZZ field.

I wonder if that covers it all?

de WB4APR, Bob





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