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[aprssig] Identifying TX Igates

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Mon Sep 19 19:25:17 UTC 2011

On 9/19/2011 3:00 PM, Bob Bruninga wrote:
> Maybe someone could write a MESSAGE CRAWLER that then watches for MESSAGE
> mobiles in one-hop range of IGates, and PINGS them with a message and then
> gathers statistics on if the mobile ACKS it. (though again, we may not know
> WHICH IGate was the TX gate0.  But that does not matter so what, since we
> would get proof that a mobile DOES get messages in that area.

I can see it now, every mobile Kenwood radio out there devolves to only 
rejecting messages because their message list is full of unviewed 
PINGs.  I'm certainly not going to put MY callsign behind such a tool!

Now, if we had a way to get a bunch of non-dupe-filtered, raw RF 
receptions from a bunch of IGates around the world (call them APRS-RF 
monitors), we'd be able to see an aggregate picture of what they're 
seeing on the RF channel, including (hopefully) digipeats of 3rd party 
-IS to RF messages gated through the same IGates.

Oh wait, I almost have that (but am fixing to remove it) in 
APRSISCE/32.  For an idea of the RF receptions being done by APRSISCE/32 
IGates around the world, see http://tinyurl.com/3gw5mqj  These are maps 
showing all RF-received packets, pre-dupe-filter, captured by 
APRSISCE/32 IGates.  Times are my local time (Eastern US).

The reason this is going to be removed is one of scale.  As APRSISCE/32 
IGate penetration rises, so does the traffic to my analysis tool.  
There's a really good reason for the dupe filter at the point of entry 
for the APRS-IS network.  It's not uncommon for the raw RF aggregate to 
see the same packet 3 or more times as digipeats make their way back to 
a single IGate.  Multiply that by the number of IGates that might hear a 
single packet as it expands circularly outward and I've seen some 
packets 10 times or more, especially WIDE3-3 pathed balloons over 5,000 

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

PS.  Red lines are direct receptions.  Green lines are digipeated 
receptions.  Black dots are digipeaters.  Red circles are the actual 
IGates.  You probably have to zoom in to see this level of detail.  And 
be patient, these plots are being served from my personal home server 
via the Coral Content Distribution Network.

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