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Re: Why FULLDUPE On is good? (Re: iss)



On Mon, 16 Apr 2001, Vince Fiscus, KB7ADL wrote:

> I know Bob APR disagrees, but the TNC on the ISS won't transmit until the 
> uplink frequency is clear....  The result of all of [setting FULDUP ON] 
> is that we get more packets from the ISS.

Yes I agree that FULLDUP on for ISS is the desired state,  but what I 
disagree with is the conclusion that it would make any difference in what
we are now hearing: 

1) I think the ISS packet system uses DCD, and so the channel can be
totally saturated with uplink mush, but only a GOOD VALID packet will
trigger DCD.  This is how most new TNC's work with open squelch...

2) CHANNEL-BUSY is having no effect on the downlink because I have not
heard, and no one has ever reported even a dual frame packet, much less a
bundle.  CHANNEL-BUSY would only be a "cause" of the problem if we were
hearing multiple bundles of packets of lots of frames in each packet.
We are not hearing these...

So although FULLDUP is/or will be ON in the ultimate arrangement, it has
nothing to do with the lack of packets we are now seeing.  That is totally
caused by the congestion on the uplink which prevents ISS from "receiving"
any valid packets.

Until someone comes up with another number, I'm assumning there are
somewhere between 1000 to 10,000 people trying to hit ISS at the same
time..  If even two of these collide, then no one gets through in that
second.

Hope that helps...
 WB4APR@amsat.org, Bob


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