[rescue] FDDI card

[Scott Newell]

>Ah, come on now....  you want that they should have tried too run two
>different carrier frequencies over the bloody coax now or something?

I'm kinda stupid when it comes to ethernet, so please don't come down to
hard on my ramblings here...

As I understand it, the base in 10Base-5, 10Base-2, or 10Base-T refers to
baseband, i.e., no modulated carrier, as opposed to broadband.

Forget that, and continue on with the idea of multiple carriers
frequencies.  How do you run multiple machines on shared media?  Each
machine on the shared pipe will have to talk on a different frequency, and
listen on _all_ the other frequencies at the same time.  You've also got to
assign each machine their transmit and receive frequencies.  Of course,
this assumes shared media.

Dump the shared media; you now have a bunch of point to point links, with
the ability to go full duplex just by assigning a transmit and receive
frequency at each end.  The nice thing is that you only need two, so it's
pretty simple.

Take it one step further--drop the modulation, trading off range for
bandwidth.  And since you're point to point instead of shared media, maybe
you'd add another pair of conductors to separate the transmit and receive
signals.  You could even go so far as to come up with 'straight-through'
and 'crossover' cables to swap the T/R lines around.

At this point, it's starting to sound to me like some very reasonable
engineering decisions and tradeoffs could evolve into something like where
we are today with 10Base-T.  I'm not trying to be facetious or
pedantic--this subject is interesting to me.  (Especially if we can get to
something clever that will work over rs-485...)

I'm also aware of hybrids, as used in the telco system, but I know next to
nothing about them.  There's mention in the Art of Electronics about a pair
of ECL chips that can run full duplex over coax, but I've never really dug
in and tried to figure out how they do it.


newell