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

Robert Bruninga bruninga at usna.edu
Fri Feb 11 19:36:24 UTC 2005


>>> Steve Dimse <steve at dimse.com> 2/11/05 1:31:11 PM >>>
On 2/11/05 at 1:17 PM Robert Bruninga <bruninga at usna.edu> sent:

>Whereas the WIDEn-N algorithm does not depend on
>callsign substitution ,but does dupe elimination by
>exact comparison to the full packet (with a CRC check).

That'w what I didn't know, I was under the impression that all TNC dup
suppression was path based. You know this for a fact? And all TNC's
that do n-n
do this?

Yes.  That is the parameter "30" in the UIFLOOD and UITRACE
parameters of the KPC3 and all others that do WIDEn-N.
That is the depth of the buffer (in seconds) for keeping old packets
for
comparison.  I think they only keep a CRC, and not the actual
copy of each packet..  That CRC is based only on the DATA part 
of the packet and ignore the path...

So WIDEn-N brought us both efficient FLOODING and
efficient dupe elimination.  When I recently went on my crusade
to conquer the FLOODING problem  that has gotten totally 
out of hand with large values of N,  I initially overlooked
the tremendous value of the dupe elimination and ended
up almost throwing the baby out with the washwater...

So now we are stickign with WIDEn-N now for its
great dupe-elimination, and conquering the large N
problem with TRAPS.

And that was also a new discovery.  That by adding
WIDE7-7 to the ALIAS list in a KPC-3 digi, that
that will force a callsign substitution at that digi
and so that packet cannot go any farther.  Thus
we now have a way to ENFORCE a limit on big
N's at every digi and using the hardware that is
already there.

Thus a NEW Paradigm.  Becuase we can have our
cake and eat it too (with the network enforcing 
limits on big N's where needed.).

Bob






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