[aprssig] ISS internet feed

Andrew Rich vk4tec at tech-software.net
Sun Mar 20 11:26:55 EDT 2011

So please correct me if I am wrong

+ The same packet is cut down by a sliding window so only one copy exists.
+ A different packet will be let through because it is not the same.
+ The APRS-IS does not look at any timestamps ?

Or does a time stamp simply make a packet "different"

How does the APRS-IS server build a list of packets to check against ? RAM 
or database ?

- Andrew -

----- Original Message ----- 
From: "Pete Loveall AE5PL Lists" <hamlists at ametx.com>
To: "TAPR APRS Mailing List" <aprssig at tapr.org>
Sent: Sunday, March 20, 2011 10:54 PM
Subject: Re: [aprssig] ISS internet feed

> 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.
> 73,
> 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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