[aprssig] odd siting in these here parts

Heikki Hannikainen hessu at hes.iki.fi
Mon Sep 15 01:19:31 CDT 2014


On Sun, 14 Sep 2014, Steve Dimse wrote:

>> Hessu - are you watching this? Could this be happening at aprs.fi,
>> or is it happening back at the R Pi IGate? I suspect the latter,
>> but perhaps you could come up with an answer.
>
> It is not unusual to see merged packets like this on the APRS Internet 
> System. This particular packet also appears on findU, so it is not a 
> problem in aprs.fi

Right, it's really very common, and the phenomenon has been there as long 
as I've been around. At one point I ran a second APRS-IS packet log 
collector client (netcat), which was completely different and independent 
of aprs.fi code, just to log the APRS-IS stream to a file with as little 
and as simple code as possible, to make sure the merged packets are coming 
from the IS and not in my code.

I have a little bit of code on aprs.fi that tries to catch some of these 
(looks for double Q constructs and other parts of the packet headers 
appearing twice), but with some luck the merging happens so nicely that 
it's not possible detect reliably.

Maybe I should at some point try to add some code in aprsc to detect and 
count these (but probably not drop), and try to triangulate which clients 
they're coming from.

   - Hessu


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