[aprssig] Airborne Digis

[Stephen H. Smith]

Gregory A. Carter wrote:
> Hi Keith,
>
> I hadn't thought of using: WIDE1-1,WIDE2-1,SAR1-1,WIDE2-1
>
> The only down side to that I can think of would be this scenario:
>
> Tracker TXs: Packet A
> Airborne Digi Sees SAR1-1, retransmits using up 
> WIDE1-1*,WIDE2-1*,SAR1-1* leaving WIDE2-1: Packet B
> Mountain Digi Sees original (packet A), digis on first WIDE2-1
> Mountain Digi Sees last unused WIDE2-1 from Airborne digi (packet B) 
> and Digis a second time.
>
> I am assuming that dup checking on the mountain digi should catch that 
> last one right?
>

NO. 

Before "Mtn digi sees original (packet A)", either home fill-ins or 
other Mtn digis have to process WIDE1-1 first. 

No matter what the SARn-N digi does, "normal" digis will process the 
first two hops independently and simultaneously.  All digis including 
home fill-ins will respond to the "WIDE1-1" part and then the big guns 
only will respond to the "WIDE2-1" part.   

Remember, the home digis are primarily using "dumb" non-APRS-aware 
classic clunker hand-me-down TNCs (like PK-232s and TNC2 clones like 
MFJ-127x) that blindly respond to the fixed alias WIDE1-1 and *DON'T DO 
*dupe checking.  (Dupe checking is an APRS-specific feature only present 
in KPC3s and the new-generation APRS-centric TNCs like Tracker2s, TT4s, 
TNC-X, etc. or in TNCs under  control of KISS-mode APRS software like 
UIview.)


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Stephen H. Smith    wa8lmf (at) aol.com
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