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[aprssig] Object Timestamps and 111111

Heikki Hannikainen hessu at hes.iki.fi
Tue Dec 14 12:50:51 UTC 2010


On Tue, 14 Dec 2010, Al Wolfe wrote:

>   What about just turning off timestamps? It would make for shorter packets. 
> About 80 to 90 percent of the timestamps that I see are wrong. It seems that 
> most APRS users using timestamps don't know what day it is or haven't 
> mastered GMT offsets.

They're often incorrect, right, also in timestamped position packets (not 
objects/items). But in those, even incorrect timestamps can be useful, at 
least if they change in every packet. They can be used to detect duplicate 
packets in the receiving end, even if the duplicate packet would have some 
sort of corruption elsewhere.

It would be very useful if the protocol had some sort of sequence number 
in the transmitted position packets, so that the receiver could detect and 
reorder packets which arrive in the wrong order, or when duplicates 
appear. That happens a lot for a number of reasons, causing cars to jump 
back and forth to old positions. The timestamp can be used in place of a 
sequence number, although it takes up more space.

   - Hessu




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