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[aprssig] Re: Tracker Smart Pathing: user types, alternatives

Robert Bruninga bruninga at usna.edu
Thu Mar 23 14:16:55 UTC 2006


>>> apratt at bestbits.org 03/22/06 10:22 PM >>>
>It's hard enough to reach a digi in the mountains 
>or deserts of California... With proportional pathing, 
>seven-eighths have a hop count of two or less. 
>I don't like those odds.

So this means you prefer to run 1 minute updates from  
your mobile with 3 hops all the time in California?
I think we may  have just found part of "the" problem...

>But I think a meaningful alternative has been proposed: 
>have digis rewrite hop counts to the "right" value for 
>the digi's local area.

And what is the right count?  It can change at any
minute based on who's IGate is on at any instant.  And
how many times are you willing to be -not- heard AT ALL
because some digi was set to modify your path to
only one hop, but that one IGate stopped working
yesterday, or last week, or last month?

>What hop count should such a digi write in? 

None!  Only the sender knows what he needs that
day, or that trip, or that event.  Or let Proportional
Pathing give you 1 hop every 2 minutes, 2 hops
every 4 minutes and a 3 hop once every 8 minutes.
ALl bases are covered...  and with 8 times less 
QRM to everyone else.  See the Propotional Pathing:
(3rd link down):

http://www.ew.usna.edu/~bruninga/aprs/fix14439.html

MOST of the time, you get in just fine every 2 minutes
(with 1 minute updates locally).  But even
if you occassionally need 3 hops, Proportional
Pathing will at least give you that safety net
of one position every 8 minutes if you get stuck
in a 3 hop valley.

>What about the problem of needing constant updates 
>due to changing (unreliable) IGates? Bah....
>In terms of timeliness, a digi that's updated once a year 
>would be no worse than most advice found on web
>pages.

The advice for mobiles on web pages affects only
the sender, and he can fix it instantly if is not working
for him.  A digi on the other hand, affects EVERYONE
and NO ONE but the sysop can fix it (when he gets
around to it)...

>If a digi can be programmed to TRAP high hop counts, 
>then it should be possible to bump UP the count of 
>a packet if it's unsuitably small for the area the digi 
>is in. That's all I'm suggesting.

But that is what Proportional Pathing does.  Once
every 4 minutes it bumps up your hop count by 1.
Once every 8 minutes it bumps it up again.  But
the net result is that the network sees 8 times
fewer packets.  And this is only if set to the "2"
minute rate (the rate for the 1 hop setting).  If
you set to a "1" minute rate for a special event, 
then you get a 1 minute WIDE1-1, and a 2 minute 
2 hop and a 4 minute 3 hop, though that is
excessive most of the time in dense areas.

Which is easier?  Replacing every TNC digi in the country
with new hardware and maintaining them with updates
everytime an IGate comes on the air or disappears, to do 
it your way, -or- asking new tracker designs to include the 
Proportional Pathing Option for those that see its value?

de Wb4APR






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