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[aprssig] WIDEn-N 'Decay Sequence'

Robert Bruninga bruninga at usna.edu
Wed Jun 21 21:39:16 UTC 2006


> APRS is not a "set-it-and-forget it" operating mode of 
> amateur radio.  Amateur radio has no "set-it-and-forget-it" 
>operating modes.

Actually, the original APRS was designed with this issue in mind!

So that the user did not have to make ANY changes between
routine 24/7 monitoring, and immediate emergency requiremnts.
THus, there was not supposed to be any such thing as wrong
settings.  The fundamental principles that made the original APRS so
flexible are:

1) Decay rate timing.  It updates as rapidly as 16 seconds when
you make a change in any parameter, but every packt then decays
by double to the next retry until 30 minutes is reached.  Thus,
someone with instant information gets as many as  6 retries in 
the first 5 minutes, but as many as 4 in the first 2 minutes.
Messages FLY this way.

2) The default of 30 minutes maximum decay is automatically 
determined based on the number of hops in the path.  If the
user sets only 1 hop, then his default net-cycle time changes
to 10 minutes.

3) Also it remains at 10 minutes as long as the operator is
active.  (THis assumes he is actually DOING something on APRS).
When he stops doing anything, it goes back to the 30 minute
rate.

REPLY-ACKS.  The original APRS does reply-acks, so that it embeds
ACKS in outgoing messages so that message really fly in a diaolg 
with only as much as 8 seconds between initial retries (sue to the
decay algorithm).

Both of these systems guarantee the fastest rates when you 
need them, and yet network conservation when you dont.
ANd the user does not have to change anything.  In fact,
he cant.  There is nothing to change!  APRS was just supposed
to just work.  And the software was supposed to warn users
of network abusive settings.  etc...

I consider the fixed rates to be an anathma to APRS.
1) they almost guarantee that people may be using the 
wrong rates at the wrong times, set abusinve high
rates and forget about it, or be in a crisis with a low
rate and not be able to communicate.
2) THey make messaging over a collision channel
frustratinly slow, or abusively fast.
etc
etc...

Bob
Just for what its worth.
Bob, WB4APR







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