[aprssig] A few additional clarifications for APRS presentation, Please
Stephen H. Smith
wa8lmf2 at aol.com
Sat May 24 23:59:41 EDT 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
JavAPRS Filter Port 14580 Guide
http://wa8lmf.net/aprs/JAVaprsFilters.htm
"APRS 101" Explanation of APRS Path Selection & Digipeating
http://wa8lmf.net/DigiPaths
Updated "Rev H" APRS http://wa8lmf.net/aprs
Symbols Set for UI-View,
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