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[aprssig] Delayed packets (yet again)

AE5PL Lists HamLists at ametx.com
Sat Aug 26 16:31:03 UTC 2006

>From: john b. leonard, jr.
>Posted At: Saturday, August 26, 2006 9:14 AM
>Subject: RE: [aprssig] Delayed packets (yet again)
>It occurs to me that it may be a combination of things, all
contributing to a built-in delay, which may be characteristic of the IS

The delays are not caused by a "characteristic" of the IS system (see
>The delay may be caused by the time lag between a packet going out at
1200 baud, going from the TNC to the computer at 9600 baud, being picked
up by an RF-Internet gateway, going to the server at much higher b/s
rates, crammed into the server's buffer, then sent out on the Internet
to each station connected, some of which are not range-filtered, and
finally sent from the computer at whatever rate the client NIC/computer
sends it to the screen.  

We are talking less than 5 seconds total of which 95% is taken up in the
transmission/reception on RF.  The servers do a 30 second dupe check to
eliminate these dupes caused by multiple IGates seeing and gating the
same packet to APRS-IS.  Internet delays are normally under 100 ms with
peaks towards 1 second when bandwidth shapers are in use.

So what does cause these excessively delayed packets (over 30 seconds)?
As has been discussed:

1: Malfunctioning/misconfigured digipeater causing excessive RF delays.
2: IGate connected to a full APRS-IS feed but unable to keep up.
3: Malfunctioning serial port or driver (this includes USB-serial ports,
improperly configured AX.25 drivers, etc.).
4: Malfunctioning IGate or server software causing packets to be either
delayed or duplicated inside of the software.
5: Someone playing log files while connected to RF or APRS-IS.
6: And more.

I would venture to say the first three are significantly more prevalent
than the others.  None are a "characteristic" of APRS-IS but they are
anomalies of improperly configured APRS software and hardware.  The
other comments made in this thread are good hints for finding the cause
of why that specific IGate is exhibiting issues.  These types of delays
should not be ignored because they are generating anomalies in the
packets on APRS-IS and they are signs of either improper configuration
or operation.


Pete Loveall AE5PL
mailto:pete at ae5pl.net 

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