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Re: [amsat-bb] Re: Why FULLDUPE On is good? (Re: iss)



On Mon, 16 Apr 2001, Margaret Leber (K3XS) wrote:

> What Vince says makes sense to me...in fact, is there some reason why an earth
> station shouldn't transmit on the uplink even though the downlink is busy? I'm
> assuming here that the ARISS TNC actually can recieve and transmit at the same
> time.

Incorrect assumption.  It is just a TNC and an HT.  The HT cannot listen
and transmit at the same time...

> The uplink congestion is clearly preventing the ARISS TNC from
> *hearing* as many good packets as it could, because of collisions. 
> But am I mistaken to think that: 

> --and that while it's holding that decoded packet, waiting to digi it, it won't
> store any more? Or can there be several packets queued in the TNC waiting to
> digi outbound?   

It can probably buffer up about 16k worth of packets. So, nothing is
lost. If we were hearing bursts of MANY packets in one transmission burst,
then the FULLDUP-ON would be the problem.  But we are not, so it is
congestion (fratracide) on the uplink that is preventing RECEPTION of
good packets, and a high throughput.  Nothing to do with transmitting.

Remember with 99% collisions, every time anyone hits XMIT, they have a 99%
chance that they are only jamming someone else.  and only a lotery's
chance they they are going to get through.  But if we could get everyone
down to say one packet per 2 minutes, then there would be a 90% chance
that more than 100 people PER PASS WOULD be successful... (or so)

But now we are in the midst of a stampeed, and human nature is only
looking out for number 1, not the good of the group...  But it will come,
once everyone finally learns... 

de WB4APR, Bob

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