[aprssig] Delayed Delivery Dupllcate Packets

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Sat Jul 18 05:47:57 CDT 2009

(and copying to the aprssig group to confirm my statements)

Actually, there's not supposed to be two copies of each even if they do 
reach two IGates.  There's actually a problem in your area, it seems, of 
some extreme DELAYS in your packets between the source and the IGate.  
If you look at the aprs.fi timestamp and compare it to the timestamp 
generated by the tracker (thank you for using the hhmmss format and not 
the ddhhmm), you see this:

 2009-07-18 03:34:44 UTC: ...qAR,K6MJW-10...033442h
 2009-07-18 03:35:44 UTC: ...qAS,KE6O-15:/033442h - Duplicate 60
 2009-07-18 03:39:16 UTC: ...qAR,W6YX-5:/033914h
 2009-07-18 03:39:47 UTC: ...qAR,KE6ZBX-10:/033914h - Duplicate 31
 2009-07-18 03:42:42 UTC: ...qAR,K6MJW-10:/034240h
 2009-07-18 03:43:23 UTC: ...qAS,KE6O-15:/034240h - Duplicate 41

Most default configured IGates only consider a packet to be a duplicate 
for 30 seconds.  it seems that youre environment delivered the first 
packet with a 60 second delay, the second packet with a 31 second delay 
and the third packet with a 41 second delay.  If you had actually been 
mobile and beaconing every 30 seconds (admittedly extreme), you would 
see your path ping-ponging back and forth along your route.

If you ever look at a path that seems to play leap-frog with itself, or 
have APRS.FI complain that you're moving too fast, it's because of these 
delayed delivery packets.

Sometimes I wonder if we (IGate operators) should be increasing the 
duplicate delay detection to 60 seconds instead of 30....It should only 
suppress these delayed packets but continue to accept packets that are 
different in content.

Lynn (D) - KJ4ERJ

PS.  I'm trying to visualize and then implement a tool to detect and 
report this effect by scanning the APRS-IS stream, so the more of us 
that beacon the hhmmss format, the better for me!  The ddhhmm doesn't 
have sufficient resolution for me to make assumptions about duplicates 
vs fast beaconers.

Lynn (D) - KJ4ERJ

John Rabold wrote:
> --- In tinytrak4 at yahoogroups.com, Byon Garrabrant <byonics.byon at ...> wrote:
>>> Can you try a different computer and see if accepts the symbol? That's sounding pretty strange. Maybe try turning off the timestamp, too. <<
> Instead, I prowled around inside TT4TrackerConfig 4.07 for a while, and happened upon the Secondary tab. There was some strange data in some of the fields on that (unused) tab, including in the Symbol and Table/Overlay fields. I cleaned that out and set the Auto Transmit Rate and Manual Transmit Rate fields to zero. Then everything seemed fine with the Symbol field back on the Primary tab. I could use Save and Write and the chosen ">" symbol remained there. And then my packets were accepted by aprs.fi, even with the timestamp. Here are three of them (there are two copies of each because each reached two igates). 
>  2009-07-18 03:34:44 UTC: KS6M-4>APT407,WA6AFT-3*,qAR,K6MJW-10:/033442h3749.50N/12211.20W>360/000/A=001440
>  2009-07-18 03:35:44 UTC: KS6M-4>APT407,WA6AFT-3*,qAS,KE6O-15:/033442h3749.50N/12211.20W>360/000/A=001440
>  2009-07-18 03:39:16 UTC: KS6M-4>APT407,N6ZX-3,WIDE1*,qAR,W6YX-5:/033914h3749.50N/12211.20W>360/000/A=001440
>  2009-07-18 03:39:47 UTC: KS6M-4>APT407,N6ZX-3,WIDE1*,qAR,KE6ZBX-10:/033914h3749.50N/12211.20W>360/000/A=001440
>  2009-07-18 03:42:42 UTC: KS6M-4>APT407,N6ZX-3,WIDE1*,qAR,K6MJW-10:/034240h3749.50N/12211.20W>360/000/A=001440/TinyTrak4
>  2009-07-18 03:43:23 UTC: KS6M-4>APT407,N6ZX-3,WIDE1*,qAS,KE6O-15:/034240h3749.50N/12211.20W>360/000/A=001440/TinyTrak4
> So now I think I'm all happy until either I get a more modern GPS unit or you release the next Alpha build. Thank you! 
> John KS6M
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