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[aprssig] APRS Message Idea

Wes Johnston aprs at kd4rdb.com
Fri Mar 4 20:56:36 UTC 2005


Bob's right about this one though.... the decay is the way to go.  One of the
things I thought was so cool about TCP/IP when I started playing packet was
that TCP/IP would back off exponentially when attempting to deliver a packet,
as opposed to the dumber ax.25 'fixed timing with a little randomness' method. 
When delivering packets onto a network, with TCP/IP it would start out pretty
agressive but back off quickly if the link turned out slow.  AX.25 on the other
hand could send a packet over a long link, and if set aggressivly enough, would
send the same packet again twice before the ACK got back.  Not very effecient.

Also, there's another advantage to the decay.  Let's say that I send a message
right now.  about 1 minute later, you send a message.  They collide because you
pressed enter at the same time my station resent a copy of my message.

Now in a fixed timing system where we each retry every minute, we will always
collide.

In a decay timing system, my message's next TX interval is 2 minutes from now. 
Your's is 10 seconds from now.  We don't collide again.  The point is that even
when our timings match up every once in a while, our interval to the next TX
time is different and we won't collide again for a good long while.

I wish more APRS clients used the decay model.
Wes





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