[aprssig] ISS internet feed
vk4tec at tech-software.net
Sun Mar 20 10:26:55 CDT 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.
> 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
>> How does the system know which packet wins ?
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