[aprssig] APRS-IS: frames bypassing server filter

Wojtek SP9WPN sp9wpn at gmail.com
Tue Jul 14 18:14:13 EDT 2020

W dniu 2020-07-14 o 00:12, Lynn W Deffenbaugh (Mr) wrote:
> You will receive packets generated by any station that you have gated 
> from RF to the APRS-IS for some period of time after you've last gated 
> one of their packets.  Try matching up the stations you're receiving 
> with the packets being subsequently received back from the APRS-IS.

I'm not sure about this. Most of the stations in question are not heard 
directly, but only digipeated to me. This shouldn't count, should it?

> This is done for several reasons.  One is to give you the opportunity 
> to gate a "courtesy" posit for the source of any message you may have 
> gated, but it is also so that your IGate can know if a staiton is 
> injecting packets directly to the APRS-IS so you don't gate messages 
> from the -IS to RF for addressed to a station that would have received 
> them directly on the APRS-IS.

Is this true for non-message packets, too? Because I hardly ever see 
APRS messages in the logs, just beacons and telemetry all the time. If 
APRS-IS server sends packets downstream only to stop me from uploading 
the same packets back, it sounds like a weird protocol design...

I'd agree with Andrew KA2DDO: it seems there's some "minimal data 
stream" offered to each Igate (and all IS-connected clients are 
considered Igates). It probably serves some good purpose, but is not 
well advertised.



Wojtek SP9WPN

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