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[aprssig] ID requirements...

Robert Bruninga bruninga at usna.edu
Mon Nov 8 13:56:49 UTC 2004


>>> Ron Stordahl <ron.stordahl at digikey.com> 11/6/04 9:40:44 PM >>>
>Trying to reduce unnecessary transmissions I have 
>lengthened our many remote digi's beacon period to 
>30 minutes. 

Please do not do this.  The problem with *too*many*DIGI
beacons is due to *too*many*hops, not how often they are.

A local (direct) digi posit once every 10 minutes only makes
1 packets per 10 minutes (and none from any other 
surrounding digis either!)  Compare that to a WIDE3-3 digi
packet once every 30 minutes.   That generates 25 
copies *AND* those same other 25 digis all generate there
own, for a total of 25 more DIGI beacons heard *everywhere*
every 30 minutes (not wanted nor needed!).  

Thus, a 10 minute rate is not the problem -at-all.!  Its the LONG
paths that are *the*problem*.

We must get folks to implement the *proper* digi beacon
algorithm that generates a local (direct) packet once every
10 minutes, a 1-hop beacon every 30, and a 2 hop beacon
every hour.  The algorithm  is posted on:

http://web.usna.navy.mil/~bruninga/aprs/digi-rates.txt

Using that system (which has been THE recommended
settings for the last severaly ears), a user in an area will
only hear on average in a 10 minute period one local
DIGI beacon and about 4 or so beacons from the next
tier of digis surrounding him.  This represents less than
1% of channel capacity and is appropriate for knowing 
the status of our most important nextwork assets, our digis.

APRS is based on a *local* net-cycle time of 10 minutes
so that travlers, or new stations, or anyone just turning on their
station are updated within the assumed net cycle time of all
activity within direct range of them..

The local 10 minute position packets should be DIRECT with
no surrounding digipeats.  Then once every 30 minutes the
path can go via ONE hop for the area, and once every hour, 
it can go via 2 hops for the region.  See how to set this
up on this web page:

http://web.usna.navy.mil/~bruninga/aprs/digi-rates.txt

For areas that are very sparesely populated, there is also
an algorithm that does the above, plus a 3 hop beacon once
every 2.7  hours.

I applaud your effort to cut down on useless beacons, but
the problem is the *length*of*the*path of most digis beacons
not their rate that is the biggest problem! 

It is important APRS should be consistent and fullfil the 
documented expectations so that performance is 
consistent.


>it would appear that the minimum beacon period for 
>a remote digi must be 10 minutes, and we will have to 
>put up with the  additional transmissions this will cause.

The two GREATEST things that can be done to solve
this problem are :
1) Turn HID OFF
2) Set the 10 minute beacons to use a PATH of *NONE*

thanks, 
de WB4APR, Bob





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