[aprssig] RE: Delayed packets

Robbie, wa9inf mwrobertson at comcast.net
Wed Jun 7 13:13:17 CDT 2006

Curt, WE7U wrote:

>On Wed, 7 Jun 2006 mconner at aer.com wrote:
>>I really think any internet user of the APRS-IS, whether it's
>>FindU users, IGates, or whatever, should be concerned about this.
>>If an duplicate report is the last one received, FindU reports
>>that old position as the "latest" one.  Similarly, APRS clients
>>who use the APRS-IS for their data will also display an old
>>position.  This has happened to me relatively frequently where I
>>check FindU for a mobile station and have to go to the "raw data"
>>display to make sure what I'm seeing is truly the latest position
>>sent out by that mobile.
>Well, _most_ APRS clients might have that problem, but at least one
>of them has dupe-filtering capability of it's own and will prevent
>these sorts of things from occurring on the map screen if it's
>Xastir:  File->Configure->Defaults->Disable Posit Dupe-Checks
>I'll give you just one guess why it was added way back when...  ;-)
>Curt, WE7U.   APRS Client Comparisons: http://www.eskimo.com/~archer
>"Lotto:    A tax on people who are bad at math." -- unknown
>"Windows:  Microsoft's tax on computer illiterates." -- WE7U
>"The world DOES revolve around me:  I picked the coordinate system!"
I downloaded the raw Findu data of the friend I was tracking. The "play 
back" of the logs confirm that the I-Gate in question IS the one only 
I-Gate around the area that inserts a delayed position report of 
significant time delay. The mobile definitely jumps backwards past one 
or two earlier position reports by other I-Gates as evidenced by the one 
or two grayed out plots..

This I-Gate is at least 60 to 80 miles from the mobile when this started 
happening until the mobile destinated. To me, this was obviously an 
issue of some kind of RF digipeating hold off somewhere getting the 
packet out to it..

Anyone who cares to, can set up a client, use a filter for a mobile from 
one of the tier2 servers, disable RF input, and turn on your logging. 
after a reasonable amount of time, play back the track and see if any of 
the packets from the APRS-IS actually jump backwards, then look at the 
q-construct identified I-Gate. Chances are it will be the same I-Gate 
causing this on most all the tests you run...

I will start doing this on the mobiles in my area as time permits, :-)  
As I am retired, free time is hard to come by...


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