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[aprssig] ISS internet feed

Pete Loveall AE5PL Lists hamlists at ametx.com
Sun Mar 20 15:56:15 UTC 2011


Andrew, I am not going to get into how a server works internally as it is immaterial and varies between software.  A packet is considered a duplicate if the station of origin, destination callsign ("To call" sans SSID) , and I field (all data) are the same.  How a server determines that, maintains its dupe list, etc. varies between server software and is not germane to this discussion.  The destination callsign is included because it can represent data in Mic-E format packets.  Paths are ignored as they do not alter packet content.

Hope this clears it up for you.  Per your original question and hopefully to put this thread to rest, it is not possible to create a "special" feed containing duplicate packets within the current APRS-IS architecture.

73,

Pete Loveall AE5PL
pete at ae5pl dot net

> -----Original Message-----
> From: Andrew Rich
> Sent: Sunday, March 20, 2011 10:27 AM
> 
> So please correct me if I am wrong
> 
> + The same packet is cut down by a sliding window so only one copy exists.

At any one server.  Since there are hundreds of servers, different "copies" may exist in a network.

> + A different packet will be let through because it is not the same.

The definition of not being a duplicate.

> + The APRS-IS does not look at any timestamps ?

Time stamps, if they exist, are part of the packet data (I field) and therefore are used to differentiate between packets (see explanation above).

> 
> 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 ?


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