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[aprssig] APRS W,W and W,W,W example

Robert Bruninga bruninga at usna.edu
Fri Feb 11 19:25:29 UTC 2005


>>> steve at dimse.com 2/11/05 1:27:37 PM >>>
>I understand all that, but as far as I can see, it only 
>applies to paths of order 3 and above, like 
>WIDE,WIDE,WIDE and WIDE3-3.  How can a path 
>with only two digis bounce back and forth?


Yes, if the original packet hit one and only one
initial digi.  But in many areas, most home stations
hit 2 or more digis, and each of those strings will
separately propogate through all digis as if they
were totally different packets..

Same goes for RELAY,WIDE.   In most cases,
those packets can almost always hit multple
initial RELAY's (since every digi also supports
RELAY).

And its even worse for RELAY,WIDEn-N because
now with the near perfect propogation of WIDEn-N
we have a perfect way of flooding all of the diferent
initial RELAY copies!  Talk about shooting ourselves
in the foot.

ANd I was part of the problem.  I wanted the initial
RELAY to force an identificaiton of the initial
digi, (and to help with the black holes) not realizing
how much duplication this was causing...

>Mobile transmits... If the same original packet was also heard 
>by digi B directly, then both will transmit it, and if the timing 
>works out, both will hear the other digipeat and repeat
>it

Thus generating 4 copies of the original..

> regardless of whether the path is WIDE,WIDE or WIDE2-2...

Ah, there's the catch.  Both will only digi it once and ignore
the second copy it sees.  Hence, a factor of *two*
reduction in total channel QRM...

and as you note, this initial mulitplication further 
blows up if the original packet was 3 hops and even
worse if it hit 3 digis...

Bob




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