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[aprssig] APRS Server duplicate filtering

Steve Dimse steve at dimse.com
Tue Oct 2 22:07:22 UTC 2007

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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