[aprssig] Preemption Digipeating

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Thu Oct 14 11:32:26 EDT 2010

A question about Preemptive Digipeating:

If a station transmits a packet with a path of WIDE1-1,WIDE2-1,SAR and 
the SAR-1digipeater is configured to preemptively digipeat on SAR, what 
will/should the digipeated packet path be A, B, or C?

A) - WIDE1-1,WIDE2-1,SAR-1,SAR*

B) - SAR-1*,WIDE1-1,WIDE2-1

C) - SAR-1,SAR*,WIDE1-1,WIDE2-1

I tried this with a T2-135/OT2m and got D) WIDE1-1,WIDE2-1,SAR-1* which 
is basically A with callsign substitution instead of insertion.

I personally find B or C more useful as it preserves the original 
desired path rather than preemptively removing the path by jumping the 
Used flag to the end of the path.  I realize that an original 
WIDE1-1,WIDE2-1,SAR,WIDE1-1,WIDE2-1 could accomplish the same thing, but 
I think we'd all agree that is a bit extreme.

I'm looking for both how preemption is handled in existing devices 
and/or software and also if it would be considered safe and/or 
acceptible to support C in a new software implementation.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

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