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[aprssig] A few additional clarifications for APRS presentation, Please

Stephen H. Smith wa8lmf2 at aol.com
Sun May 25 03:59:41 UTC 2008


Steve Noskowicz wrote:
>  
>
>    Well, actually it is; as I *meant it* (note the quotes).  You describe
> precisely my understanding of the RF network.  What I meant was that whatever
> digis hear my packet and/or the digipeated version thereof  (up to the
> originator's WIDEn-N limit) determine(s) where the packet "winds up".  This is
> an ad-hoc determination – intended, yes, but not a specified, linear route as
> in regular Packet.  



This is a huge difference between APRS and classic packet. The classic 
case is of a linear route through specific designated digipeaters. The 
APRS case is an AREA transmission that spreads outward in an 
ever-widening circle in EVERY direction at once, as transmissions 
relayed by one digipeater are heard (and retransmitted) by ALL other 
digis within earshot in every direction. (Assuming of course that 
digipeaters exist in every direction from your original transmitting 
location). In turn, even more digis within earshot of the first tier 
around the original station retransmit the next hop. This geometric 
spreading outwards every which way is sometimes referred to as 
"UI-Flooding".

Before the "New Paradigm" efforts to control excessive retransmitting of 
packets, users would set paths like WIDE3-3 or WIDE4-4 or even WIDE7-7 
into their hardware or software with the results that beacons would 
flood, via dozens of digipeaters, hundreds (or even thousands) of miles 
in every direction from the source. With digipeaters here in the west 
routinely THOUSANDS of feet up in the mountains above the cities they 
serve, we would routinely hear packets from San Francisco (400 miles to 
the north), Las Vegas (250 miles to the NE) and Phoenix, AZ (300 miles 
to the east), Once in a while, we would hear packets from Portland, WA 
(1000 miles to the north), Salt Lake City, UT (600 miles to the NE) and 
Abuquerqe, NM (750 miles to the east).

Here in the greater Los Angeles, CA basin even the local activity nearly 
saturates 144.39 in this metro area of 18+ million people. There is 
almost NEVER a quiet period of more that 3-5 seconds on 144.39, even at 
3:00 AM. Our near-saturation activity in Southern Cal was being heard in 
all these places at once due to the all-directions-at-once UI-flooding, 
helped by the fact that the very first digi hop was normally from one of 
the 5000 foot mountain tops ringing the Los Angeles area. [Today the 
LA-area digis chop off any path beyond the first hop, no matter what you 
set.]





--

Stephen H. Smith wa8lmf (at) aol.com
EchoLink Node: 14400 [Think bottom of the 2M band]
Home Page: http://wa8lmf.com --OR-- http://wa8lmf.net

NEW! World Digipeater Map
http://wa8lmf.net/APRSmaps

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http://wa8lmf.net/aprs/JAVaprsFilters.htm

"APRS 101" Explanation of APRS Path Selection & Digipeating
http://wa8lmf.net/DigiPaths

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