[aprssig] IGATE delays

Wes Johnston aprs at kd4rdb.com
Wed Jun 8 08:44:51 CDT 2005

I've looked into the APRS IS dupe problem a little more... none of this
is set in stone, just my ramblings.

I wrote a little script this morning to pull data from findu, and check
each packet from my station against the following 50 packets for dupes. 
I chose my car because the position is usually unique since it's moving
all the time and seldom left on when parked.

The minimum delay is 98 seconds, max "real" delay was 454 seconds.

A frequency analysis of the delays revealed that most of the delayed
packets are between 101 and 274 seconds late.  There is another band at
389 to 454 seconds, but I have reason to believe those are occasions
when I did leave my tracker running while parked.  I hope this inline
GIF image shows up in the list.... the y axis is the number of dupes, x
axis is the delay in seconds.

These two packets are interesting to me because the 2nd is nearly 600
miles from my location.  Could it take 98 seconds for a packet to travel
3 hops?  doubt it.

I have seen packets delivered ontime by qAR kc4pl-2,qAo W4HNK-1,qAR
WA4SAS-11,qaO w1gre, and many others.

I have seen packet delivered late by qAo,WW6JC-2, qAR KG4YZY-11

If anyone else has seen these problems, I'm glad to analyze your
tracker.... just send me the callsign.

ww6jc-2 is connected to montana.aprs.net:14580. 

Anyone have any clues about this?  I'm gunna guess this is a aprs-is
tier problem, but really haven't a clue.


Wes Johnston wrote:

> I spoke with ww6jc last night on the phone (super nice guy, just
> getting started in aprs), and he said his copy of uiview is connected
> to montana.aprs.net:14580.  Could it be that Curt's problem station,
> and the one mentioned from canada are both connected to this same
> hub?   I asked ww6jc to connect to a different aprs server (kc4pl's
> server that is local to South Carolina) for the time being to help
> diagnose this problem.
> Wes
> Curt, WE7U wrote:
>>On Tue, 7 Jun 2005, Keith - VE7GDH wrote:
>>>Wes KD4RDB wrote on 07/06/2005
>>>>Guys, try to follow me on this one.... last night I noticed that my
>>>>track from driving home seemed to "ratchet" back and forth.
>>>I have observed this for stations just east of Vancouver BC. When
>>>I get a chance will look at some log files I had and one that was
>>>sent to me and try and pin down which of several IGates it could
>>>be. I suspected it could be the time being off at one of the
>>>IGates but haven't had a chance to spend look at it properly yet.
>>>I am one of the IGates involved, but my computer time is within a
>>One of the reasons I backed my path for my mobile down was that
>>there were igates up there that were putting my packet into the
>>internet delayed, which combined with the igating down near Seattle
>>made my path all screwy.  By shortening my path I avoided a lot of
>>It shouldn't be a time-setting on the computer that's the problem,
>>as Xastir (what I was monitoring with via an internet connection)
>>and findu.com ignore the timestamps.  It's a delay in feeding the
>>packet to the internet.  Whether that's an RF delay or a computer
>>processing delay, I can't tell.
>>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!"
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