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[aprssig] APRS talk in Los Alamos?

Tom Russo russo at bogodyn.org
Wed Aug 31 00:18:07 UTC 2011


On Tue, Aug 30, 2011 at 05:05:25PM -0600, we recorded a bogon-computron collision of the <ws5n at wildblue.net> flavor, containing:
> <html><head><meta name="Generator" content="PSI HTML/CSS Generator"/>

[you might want to adjust your mail program to send only plain text email to
APRSSIG --- those of us using old-fashioned text mail programs get to see
all the HTML markup, which I've hand-edited out in my reply]

>While there I hope you can monitor the APRS traffic around the city. &#160;When I drive in to Albuquerque, I start hearing "MY POS" repeats sometimes three or four times each time I beacon. &#160;I have heard it as much as 7 times! &#160;I am running WIDE1-1,WIDE2-1 in the mobile. &#160;I have my suspicions as to what is happening, but I don't have the expertise to analyze the situation and make recommendations. &#160;I'd love to hear your take on it, if you see the same behavior.

That's because all the nearby digis are ancient KPC-3 TNCs with old firmware,
with broken handling of WIDEn-N:  they fail to mark the final hop as used, 
so if WIDEn-N were implemented normally the path you are using would only
be a one-hop path:

   first transmit:  WIDE1-1,WIDE2-1
   First digipeat:  LAMOSC*,WIDE1,WIDE2-1
   First digipeat(2):  SANDIA*,WIDE1,WIDE2-1
   First digipeat(3):  CAPILA*,WIDE1,WIDE2-1
   First digipeat(4):  ELKMTN*,WIDE1,WIDE2-1
    (etc. for every digi that happens to hear you)
   End of line, because nobody will digipeat this (WIDE1 is showing as the 
    first unused digi, and nobody will do anything with that).

SO, the work-around is that all of these digis have a workaround in place:
MYALIAS is set to WIDE1-1, with all the problems that go with it --- notably, 
no dupe checking on the first hop.  So you get THIS mess instead:

   first transmit:  WIDE1-1,WIDE2-1
   First hop:  LAMOSC*,WIDE2-1
   First hop(2):  SANDIA*,WIDE2-1
   First hop(3):  CAPILA*,WIDE2-1
   First hop(4):  ELKMTN*,,WIDE2-1
and then
   Second hop:   LAMOSC*,SANDIA*,WIDE2
   Second hop:   LAMOSC*,CAPILA*,WIDE2
   Second hop:   LAMOSC*,ELKMTN*,WIDE2
   Second hop:   SANDIA*,LAMOSC*,WIDE2
   Second hop:   SANDIA*,CAPILA*,WIDE2
   Second hop:   SANDIA*,ELKMTN*,WIDE2
   and so on and so on.


That is, if you use WIDE1-1 you're no better than the Bad Old Days of 
RELAY,WIDE, thanks to outdated hardware with outdated firmware.

The KPC-3's are all donated hardware from WA5IHL who used to maintain a large
number of normal packet nodes with them, and repurposed them in the early
days of APRS.  It is not reasonable to expect that they'll all be replaced
in any sort of short order with more modern hardware/firmware, so we're stuck
with the local advice NOT to use WIDE1-1,WIDE2-1 in the central New Mexico
area --- just use WIDE2-2 so that all dupe checking is actually done properly.
With WIDE2-2, no ping-ponging is possible, you get fewer "MY POS" beeps
on your D7X0, and the channel gets less congestion.

-- 
Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
 "One man alone can be pretty dumb sometimes, but for real bona fide
 stupidity, there ain't nothin' can beat teamwork." - Edward Abbey




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