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[aprssig] Persist and Slottime for Digi?

Robert Bruninga bruninga at usna.edu
Sun Apr 3 16:09:33 UTC 2005


If anyone is doing some testing of the WIDE2-2 and
the other WIDE1-1,WIDE2-1 ideas, it is important to 
turn up the volume and LISTEN.   This is because
testing what happens under WIDEn-N is much 
different than normal digipeating.

Ideally, due to the perfect dupe-elimination algorithm in
the digis, these packets ONLY radiate outward and
never loop back.  This combined with the fratricide
concept that causes each outward tier of digis to digipeat
at the SAME time further eliminates most chances of
hearing anything beyond the first hop.

So in the old days, I could check the path between
two digis with a DIGI1,WIDE,DIGI1 path and see my
own packet come back and know what digis it got to
on the second hop.  But with WIDEn-N, you can
never hear a loop.

So if you send out a WIDE1-1,WIDE2-1 packet and 
hear only one copy, that is the expected result,  But you
MAY hear a "double" and collisiojn immediately after it
as all the surrounding digis at the second tier all respond 
at the same time.  Most of their users WILL decode it
And it will continue outward.  But you wont see them
decoded.

This fratricide lets a 2 hop path dissipate in two slot times.
Without this, then a single 2 hop packet might take 9 or 
more slot times as each digi politely waits for all the others...
This is NOT desired in the APRS RF network...

Just a thought
Bob

>>> greg at clubnet.net 4/2/05 4:50:12 PM >>>
Hassan,

You're right.  The UIDIGI configuration file states that the range of 
SLOTTIME is 1 to 255.  So 1 is the correct setting.

And yes, there is no DWAIT or UIDWAIT in UIDIGI, so using SLOTTIME and

PERSISTANCE as you have done is the best you can do.


73,
Greg
WB6ZSU


On Apr 2, 2005, at 1:36 PM, hasan schiers wrote:

> This is for UI-DIGI firmware in a TNC-2. I just set Persist for 255 
> and Slottime to 1, it would not accept a slot time of 0, the minimum

> is 1.
>
> It would not accept, (nor is there any mention in the text file for 
> programming the prom) any parameter like DWAIT, UIDWAIT.
>
> So, I'll see if the persist and slot time commands make any
difference.
>
> thanks for the tip.
>
> 73,
>
> ...hasan, N0AN


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