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[aprssig] Local Event using RELAY?

Robert Bruninga bruninga at usna.edu
Thu Mar 31 15:27:15 UTC 2005


You're both right...

>>> HamLists at ametx.com 3/31/05 7:19:54 AM >>>
> As to your statements above, they are incorrect.  That 
>station with the low HAAT is most definitely running CSMA 
>to over 90% [or 99%] of the packets being generated...

Just to help clarify.  Yes this is true, that the low-HAAT-station
that can't hear anyone else direct (except the digi) and he
DOES avoid collisions with 99% of the traffic he hears by
using CSMA.  But ALL that he hears (that 99%) is from the 
single DIGI *only*.  Thus the only station he is avoiding a 
collision with via CSMA is the high-power-high-HAAT digi.

THus his 99% use of CSMA only helps himself, and is of
zero benefit to any other collisions with anyone else that
he cannot hear:  There are two cases:

1) If he transmits while the digi is transmitting it is only
himsellf that loses.  It impacts no one else because
no one else can hear him direct.

2) If he waits to transmit until the digi stops and he then
hears silence and then he transmits, then he is in a pure
hidden-transmitter-random-probability of collision (which
some are calling ALOHA) and again, his use of CSMA
does absolutely nothing to help him avoid a collision
with another user of the digi outside of his earshot.  

In fact, you could argue that CSMA increases his probabiliy 
of a collision with another low-HAAT user, because they 
are both waiting for the same silient peirod.

So Both Pete's 90 or 99% CSMA assessment and others
almost-pure-hidden transmiter assessment are both right.
But it just depends on how you count the apples and 
the oranges..

de Wb4APR, Bob





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