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[aprssig] Question about APRS-IS and IS->RF igating

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Thu May 17 15:53:24 UTC 2012

On 5/17/2012 11:43 AM, Phil N6TCT wrote:
> We have a bidirectional igate, GERLCH, out in the Nevada desert.  It's 
> running aprs4r under linux.
> My question:  Why would our igate be getting this message from 
> APRS-IS?  Is it because we just gated a message to APRS-IS from this 
> station?

Yes, in my experience, if a station gates a packet from RF to -IS, the 
upstream APRS-IS server seems to put some sort of dynamic buddy filter 
on that station ID and all packets originating from that station, that 
were NOT gated via your gate, come from the APRS-IS back to your 
station.  I always expected this for messages, and maybe one posit after 
any given message (and an ack is just a message), but my KJ4ERJ-1 IGate 
keeps hearing packets from mobiles via the APRS-IS that have long since 
driven out of reception range of my gate.

> If so, that seems weird to me.  I.e., if I just gated a packet from 
> him, presumably I'm in RF range of him, so why would I need or want 
> APRS-IS to hand me a packet *from* him?  (If the packet was a message 
> addressed to him, *that* I could see...)

After any message packet, the next posit is expected to be gated as 
"free" information to the message destination station of the location of 
the message source station.

> Relatedly, is there any automated, algorithmic way that our igate 
> should be able to spot this and say, nah, we don't want to gate this?

Actually, that's what I was going to ask.  Is aprsr4 just blindly gating 
everything received from the APRS-IS feed out to the local RF channel?  
I thought IGates were supposed to have LOCAL intelligence as to which 
packets to gate from -IS to RF and not just rely on the upstream -IS 
server to only deliver gate-ready packets.

> Thanks for any light you can shed on this!

Not sure if I shed any light, but I certainly share your opinion that 
gating <IGATE packets from -IS to RF is non-helpful.  But I'm not sure 
it's the APRS-IS server's job to make that determination and believe 
that work lies with the IGate software, aprsd in your case.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

PS.  BTW, APRSIS32 runs fine under Wine and won't exhibit this 
behavior.  And it's configurable -IS to RF capabilities are set to be 
upgraded over the next 2-3 months.

> 73,
> Phil, N6TCT
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