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[aprssig] Fundamental APRS capacity

Robert Bruninga bruninga at usna.edu
Mon Oct 4 22:42:42 UTC 2004


>>> rtg at aapsc.com 10/4/04 2:54:39 PM >>>
>>Using the example before, it will be revealing
>> then as everyone converges on a HAMfest with their
>> 1 minute mobiles how the usable range of APRS shrinks
>> to the size of the parking lot!
>
> So if I'm hearing you correctly, you're advocating that the 
>mobiles then respond by removing all digipeater paths 
>from their trackers, right?  So how is a TT3 or Pocketracker 
>user supposed to do that, short of running
>home and plugging it into the computer for reprogramming?
>What is the expected response of the home stations in 
>the vicinity?

Like anything else, it requires the application of common sense.
The purpose of re-computing and showing the actual ALOHA
circle on the map is to ALERT the operator to what is happening
on the channel, with an easy visual clue...

If he can do something about it, thats good.  If he cant, then
thats that.  But at least he can see with a repeatable metric
what the conditions are in the area with respect to reliability
or over congestion on the channel..

>Just how closely are we to watch the channel activity 
>and how often are we to reset our beacon frequency 
>and/or UNPROTO path?

That is up to you.  Its all up to the individual.  If there is an
alt-freq receiver at the site (there should be an alt-channel
input at any major Ham venu in my opinion to help the
congestion away from 144.39)...  We are hams.  We are
supposed to know how to optimize our radios to the situation
at hand.  Any known planned event should plan an APRS
infroastructure to match.  Just assuming that the network
will operate in Dayton with 150 APRS mobiles the same
way it did last week with 6, is not good amateur radio thinking...


>  In an earlier message, a ham reported that findu reports some
stations
>within his closest 40 to be on the other side of a mountain, with no
RF
>path or linking digi available.  I understand your algorithm only
pertains
>to RF-heard packets, so I imagine that considering terrain and
>use/population densities, the ALOHA range will be anything but a
circle.
>In the case cited, the ALOHA group for that station will extend a
much
>greater distance away from the mountain.

Yes, and see how easy that was to draw that conclusion?  We
assume here that operators are aware of their environment.
The ALOHA circle just gives them a measure of channel capacity
in a consistent manner.  The human brain then needs to
then draw the logical conclusions... 

>Possibly the map implementors would draw a polygon 
>around the the most distant stations within the ALOHA group, 
>rather than assuming it's a circle at the radius of the farthest 
>station heard.

Trying to throw a computer at common sense is what makes
most computer solutions often just dead wrong.   If you start
trying to bring in all the common-sense attributes that the
human brain processes easily, will guarnatee yuou a wrong
solution unless you can guarantee that you have covered
every possible nuance.  You cant.  Therefore it is better
to draw the circle and let the human decide than trying to
dray a polygon which "implies better accuracy" but is completely
missleading because it isnt...

>I still think the place for this algorithm is in the smart
digipeater,
>which simply drops any packets that originate outside the 
>defined ALOHA region.

I strongly oppose any such solution.  Only the ORIGINATOR 
of a packet knows its immediate need.  He should be able
to use whatever path he needs for the immediate requirement
and not be blocked by the network.  But the network should
ADVISE him of what is routinely best and should caution him
when he exceeds that.  That is what I call network stewardship.

It has been in APRSdos since day one. to encourage people
to do the right thing and to be a nuisance if they try to do the
wrong thing.  But it only warns them, it doesnt prevent them.
But it warns then on every single packet every time it is  sent
if it exceeds those recommendations...

Bob

-- 
Rick Green

"They that can give up essential liberty to obtain a little
 temporary safety, deserve neither liberty nor safety."
                                  -Benjamin Franklin


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