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[aprssig] APRS Server duplicate filtering

Jim jim at stuckinthemud.org
Wed Oct 3 21:18:32 UTC 2007

Thanks for the info, very useful background.

Point noted about the load!


-----Original Message-----
From: Steve Dimse [mailto:steve at dimse.com] 
Sent: 02 October 2007 23:07
To: jim at stuckinthemud.org; TAPR APRS Mailing List
Subject: Re: [aprssig] APRS Server duplicate filtering

On Oct 2, 2007, at 5:09 PM, Jim wrote:

> A question for the APRS Server experts!
> Do servers filter duplicate packets and, if so, what is the default 
> duplicate period?

Absolutely filtering is done, it is essential for keeping the bandwidth of
the stream within limits. The filtering is based on the payload and origin,
not the entire packet, so different digi's and iGates don't affect the
filtering. The filtering period will vary with the server's software, there
is no right answer. findU uses a mechanism based on number of packets, not
on time. The incoming packet is compared to the last 256 packets. I haven't
revisited that in a while, but since that number is now less than 10
seconds, I need to increase it.
> I'm trying to pass a couple of stations through at a 30 second 
> interval, but if stationary not all beacons are being passed out 
> again.

If they are identical packets, what reason is there for sending them at this
rate? Even for changing data, if you need it at this rate, APRS is probably
not the transport medium you should be considering.

The APRS IS is a shared resource, and those extra packets put an additional
load on dozens of servers.

Steve K4HG

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