[aprssig] Preemption Digipeating

Keith VE7GDH ve7gdh at rac.ca
Thu Oct 14 13:00:27 EDT 2010

Jason KG4WSV wrote...

> I've got one, too:  Is preemptive digipeating defined anywhere?  Or
> maybe I should say other than the T2 source code, which as far as I
> know is the only device to implement it.

Actually, the TT4 also does pre-emptive digipeating, at least with the
current firmware release.

My feelings are that everything ahead of the alias used for pre-emptive
digipeating should be marked as used. I think the only question should
be if the digi doing the pre-emptive digipeating should act immediately
or if it should wait a moment to listen and see if the generic part of the
path was used by another digi... in other words, if a station uses
WIDE1-1,WIDE2-1,SAR and the digi set up for pre-emptive digipeating
sees an asterisk ahead of the SAR, it shouldn't be digipeated. If a digi
acts on the SAR alias, I don't think it should be kicked out the door
showing the WIDE1-1,WIDE2-1 as still being available. 

Re-phrasing the above, temporary digis set up to respond to e.g. TEMP
or SAR would provide local coverage for some event, but may not be needed
if the conventional APRS network has already responded to a generic alias.

73 es cul - Keith VE7GDH
"I may be lost, but I know exactly where I am!"

73 es cul - Keith VE7GDH
"I may be lost, but I know exactly where I am!"

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