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[aprssig] Routing

Robert Bruninga bruninga at usna.edu
Thu Feb 15 14:54:46 UTC 2007


> I seem to be missing something with regard to WIDEn-N routing 
> and have been doing lots of reasearch to defuddle my brain. I 
> understand how the SSID is decremented after each hop, but 
> what yardstick is used to determine the initial numbers used 
> for n and N?

All APRS client software should display what is called your
ALOHA circle that it computes from the on-air traffic.  The
algorithm is simple, yet works in the highest of density of
areas with hundreds of stations in one city to very sparse areas
where thousands of square miles are involved.  The ALOHA circle
is simply that part of the APRS network surrounding -your-
station, that represents 100% channel loading of the 1200 baud
channel.

Your "N" should be chosen as to noot send yoru packets outside
of that area.  All across the USA, it seems that N is 2 or less
in almost all populated areas, and no more than 3 in the very
sparse areas.  The ALOHA algorithm is well documented and there
is an add-on for Uiview to display it.

See: http://www.ew.usna.edu/~bruninga/aprs/ALOHAcir.txt

To see some graphical examples, see the ALOHA paragraphs about
30% down the New-N Paradigm Page:
http://www.ew.usna.edu/~bruninga/aprs/fix14439.html

We need to make sure that everyone on APRS gets a good
understanding of these concepts of channel capacity and loading.
1200 Buad is a slow, but robust channel.  But it works if not
overloaded.  And "works" does not mean -range- but means
*individiual*reliability* for users at the local level.


Bob, Wb4APR





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