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[aprssig] APRS Message Idea

Robert Bruninga bruninga at usna.edu
Sat Mar 5 01:21:26 UTC 2005


John Kraus wrote:
>> Get on a quiet channel and try UI-View, APRSDOS, APRS+, 
>> xastir side by side.... measure the length  of time and 
>> number of packets ... to get the message through.  

Actually, in the absence of QRM on a quiet channel every 
system will workperfectly with instant deilvery, no collisions
and no retries...

>> Then get on 144.39 and do the same test.   

Yes, that is where the difference comes in.  The decay
algorithm is all about doing the retries efficiently *and*
farily, but with channel stewardship in mind.  Similarly, 
smart-acking also works to improve the odds in the 
presence of collisions...

>>> ad6nh at arrl.net 3/4/05 6:20:36 PM >>>
>I have done this very test, and I have found that [UIview]
>works quite well.  I guess I know how to use the program 
>in a way that others do not.  

It all depends on the channel.  On a private QRM free
channel everything works well.   Also one can always get
good "performance" by setting max rates and max hops
for digi saturation from all directions with multiple copies
and stepping on everyone else to get one's own messages 
through.  But it kills the channel for everyone else..  

Remember, without network stewardship, anyone can
make settings to force their stuff through at the expense
of everyone else.  But I dont call that "good performance".
Yes good for one person but bad for everyone else.

That is why APRS was fundamentally designed around the
decay algorithm.   No one can abuse it, yet everyone gets
almost instant retries (8 seconds) on new fresh data, but
then falls off to share the channel almost as fast if the
packet is not getting through...  Everyone wins, and no one
loses beacuse of other peoples "agressive" user settings.

Its common gaming theory and human nature.  Any system
that *depends* on fair play to work, yet gives individuals the
tools to improve their own odds at the expense of everyone
else will always fail.  Because everyone thinks, "well, ill
just crank  up my probabilities a little bit to beat the others"
but everyone else does the same thing to compensate 
and the result is no one wins.

See the movie "Its a beautiful mind" or whatever it was...

Bob, WB4APR





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