[aprssig] Tracker Smart Pathing

John Ronan jronan at tssg.org
Tue Mar 21 15:29:09 CST 2006

On 21 Mar 2006, at 20:47, Robert Bruninga wrote:

>> The problem is defining channel load....
>> ...  The easy metric is packets-per-minute.
> Which is also perfectlly the -wrong- method, because as
> the channel gets loaded more and more above about
> 18% of capacity, the actual number of packets decoded
> begins to go down.  On a 100% collisions channel,
> the throughput is close to zero packets per minute,
> similar to a totally clear channel.  And the TNC cannot
> tell the difference.
ok, I'll defer to your knowledge here.

>> Or possibly percentage of time that the squelch is
>> open or tones are present - that'd count collisions
>> as well.
> Yes, that is the only way to measure channel load.
> -but- you cannot even use the DCD light in a true
> CD TNC, beacuse the "true CD" (designed for use
> with open squelch) is also only looking for valid
> AX.25 structure and it also does not detect a
> collision in most cases.
> So the only way to measure channel"load" is with
> an RF carrier squelch circuit.  Which by definition is
> a big step backwards in adding additional time delays
> to every packet and also making the network
> vulnerable to any old computer birdie that can
> completely shut down the digipeater.
Would that not happen now anyway?
> So again, we need to be very careful about the smart digi
> bandwagon which looks good on paper but has so many
> pitfalls in implementation and human maintenance, as
> to become a nightmare... in many cases.
Absolutely, I suppose thats why we're discussing it.
> Remember the KISS principle...

John Ronan <jronan at tssg.org>, +353-51-302938
Telecommunications Software &  Systems Group,  http://www.tssg.org

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