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ZL3AI > APRDIG 17.02.07 08:01l 48 Lines 1865 Bytes #999 (0) @ WW
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Subj: [APRSSIG] Vol 32 #16, 2/2
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From: ZL3AI@ZL2BAU.#79.NZL.OC
To : APRDIG@WW
Message: 7
Date: Thu, 15 Feb 2007 09:54:46 -0500
From: "Robert Bruninga" <bruninga_at_usna.edu>
Subject: RE: [aprssig] Routing
>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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