[aprssig] aprs.fi duplicate packet checking

Wed May 10 09:12:42 EDT 2017

Posting Pete's answer to this same question from a different forum for
completeness.

Randy
WF5X

From: Pete Loveall AE5PL Lists <hamlists at ametx.com>
Date: Wed, May 10, 2017 at 6:13 AM
Subject: Re: [aprssig] How to Send to the APRS IS
To: "aprssig at tapr.org" <aprssig at tapr.org>

The dupe algorithm in the servers (and, I suspect, aprs.fi) is based on a
30 second -sliding- window and is individual packet-specific.  This means
that, for instance, what appears to be inconsistent in your example is
actually very consistent.  Packet #3 is a duplicate of packet #1 (29
seconds apart). Packet #2 does -not- replace packet #1 in the dupe check
algorithm.  Packets are checked based solely on the sender callsign-SSID,
the destination callsign (SSID ignored), and data without regard to later
packets with different data (each packet is consider individually because
that is how you prevent loops).  This is as designed and described at
www.aprs-is.net

73,

Pete Loveall AE5PL
pete at ae5pl dot net

On Wed, May 10, 2017 at 4:52 AM, Andrew Rich <vk4tec at internode.on.net>
wrote:

> I can’t see why aprs.fi is marking these packets as duplicate positions –
> when packets are at different positions on either side
>
>
>
> 2017-05-10 18:47:48 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.38S/15302.59E>
> 2017-05-10 18:47:53 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.39S/15302.58E> *[Duplicate
> position packet]*
> 2017-05-10 18:47:58 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.39S/15302.57E>
> 2017-05-10 18:48:03 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.40S/15302.56E>
> 2017-05-10 18:48:08 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.41S/15302.55E>
> 2017-05-10 18:48:13 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.41S/15302.54E>
> 2017-05-10 18:48:18 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.42S/15302.54E> *[Duplicate
> position packet]*
> 2017-05-10 18:48:23 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.43S/15302.53E>
> 2017-05-10 18:48:28 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.44S/15302.52E>
> 2017-05-10 18:48:33 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.45S/15302.52E>
> 2017-05-10 18:48:38 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.45S/15302.51E>
> 2017-05-10 18:48:43 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.46S/15302.51E> *[Duplicate
> position packet]*
> 2017-05-10 18:48:48 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.46S/15302.52E>
> 2017-05-10 18:48:53 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.52E>
> 2017-05-10 18:48:58 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.53E>
> 2017-05-10 18:49:03 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.54E>
> 2017-05-10 18:49:08 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.55E> *[Duplicate
> position packet]*
> 2017-05-10 18:49:13 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.56E>
> 2017-05-10 18:49:18 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.47S/15302.57E>
> 2017-05-10 18:49:23 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.58E>
> 2017-05-10 18:49:28 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.59E>
> 2017-05-10 18:49:33 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.60E> *[Duplicate
> position packet]*
> 2017-05-10 18:49:38 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.61E>
> 2017-05-10 18:49:43 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.62E>
> 2017-05-10 18:49:48 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.63E>
> 2017-05-10 18:49:53 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.48S/15302.64E>
> 2017-05-10 18:49:58 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.49S/15302.65E> *[Duplicate
> position packet]*
> 2017-05-10 18:50:03 AEST: *VK4TEC-9
> <https://aprs.fi/?c=raw&limit=&call=VK4TEC-9>*>APZ001,TCPIP*,qAS,VK4TEC
> <http://aprs.fi/?c=raw&limit=&call=VK4TEC>:!2720.49S/15302.66E>
>
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>
>
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