[aprssig] ISS internet feed

Pete Loveall AE5PL Lists hamlists at ametx.com
Sun Mar 20 08:54:26 EDT 2011

There is no "winning".  When a packet is seen at a server, that server starts its dupe timer on that packet and then extends the sliding window every time the same packet is seen again until that packet is not seen within the duplicate window.  There is no administrative communication between servers.  Therefore, another server may see the same packet from a different gateway first and perform the sliding window dupe elimination based on that packet.

Don't make this more complex than it is.  A server sees a packet, does a dupe check and if not a dupe, passes the packet and starts a dupe elimination window.  If it is a dupe, the elimination window is reset to 30 seconds for that packet.  Each server works independently meaning that one server may see a packet from one gateway first while another server may see the same packet from a different gateway first.  The packet will be seen by all but which gateway "wins" is indeterminate except by which packet arrives at a server first.

 Since there are literally hundreds of servers in APRS-IS, "port of entry" for any one packet is determined by the gateways hearing the packet, the servers servicing the gateways, and the server you happen to be connected to for "listening".  You are trying to think of APRS-IS as a "system".  It is not.  It is a network of independent but interconnected servers, gateways, and clients.  Determinations are made at each individual entity and that is why you can't disable at dupe checking at one server in the network and expect dupe checking to be disabled globally.  "Independent" means just that.  For the reasons I explained previously, we do not want dupe processing disabled unless you want to go back to 2001 when we couldn't keep a server functioning for more than 24 hours with a fraction of the traffic we have today.


Pete Loveall AE5PL
pete at ae5pl dot net

> -----Original Message-----
> From: Andrew Rich
> Sent: Sunday, March 20, 2011 6:35 AM
> Peter can u talk a bit about how inter server traffic works ?
> Say two stations are gating but thru different servers and hear the same
> packet
> How does the system know which packet wins ?

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