[aprssig] TT4 Config for High Altitude Balloon

[Stephen H. Smith]

On 4/8/2012 9:04 PM, John Gorkos wrote:
> I may have a fundamental misunderstanding of the WIDEN-n paradigm, then.
> I thought that a digi configured for WIDEN-n would see a WIDE2 packet as
> an undigipeated WIDE2-0, and would then digipeat it and either mark the
> WIDE2 as used (WIDE2*) or insert its own call in the digi path, and remove
> WIDE2 altogether.  Is the SSID of 1 essential to having a WIDEN-n digi
> pick it up, or is it enough that the WIDE2 with an SSID of 0 be there?  Do
> different DIGIs treat this differently (I.e. Do soft digis like APRSX and
> DigiNED act differently than KPC3?
>
> J


WIDE2 is not the same as WIDE2-n.    With WIDEn-N pathing, each digipeater 
repeats the packet and decrements the SSID by 1.

IF the path on the packet leaves the original transmitter as WIDE2-2,  the 
first digipeater will retransmit it as WIDE2-1.  The next digpeater(s) will 
retransmit this as WIDE2-0, indicating that the path is "used up" so no more 
digipeats.   WIDE2-0 is often displayed as (and treated by software as)  just 
plain WIDE2 : i.e. the path is all used up.

A starting value of WIDE2 without the SSID is equivalent to no path at all, 
since WIDE2-0 is considered dead by all digipeaters.

At altitude, the initial transmission could hit dozens of different digis in 
different directions and at different distances simultaneously, each one doing 
the WIDE2-2 -->  WIDE2-1 decrementing at the same time  Then each of these 
transmissions could be heard by a second tier of digis even farther away that 
will all do the WIDE2-1 --> WIDE2-0 decrementing at the same time.

A starting path of "WIDE2-1" by the originating transmitter is, in effect, an 
already partly "used-up" path that will yield only a single hop of digipeats in 
all directions before it becomes WIDE2-0 (i.e. WIDE2) and quits getting digipeated.


The whole story and details on WIDEn-N and digipaths in general here:

"APRS 101"  Explanation of APRS Path Selection & Digipeating
   http://wa8lmf.net/DigiPaths



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