Re: Cable Modems (was Re: Telewest Communications FIASCO)

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From: David Fraser
Date: Mon, 17 Mar 1997 00:00

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<Pine.SUN.3.95.970220121654.24605B-100000@tardis.tardis.ed.ac.uk>,
Alastair B Roberts <abr@tardis.ed.ac.uk> writes:
>
> ...something to me.  I have heard that the telewest cable network is not completely
> fibre optic (i.e. parts of it are made up of copper wire).  Now if parts of the
> network are made of copper, how do Telewest plan to offer faster access speeds than
> 64kbps which is the theoretical maximum throughput on a copper wire?

I think what you don't understand is that this limit assumes a simple
keyed digital signal.  Modern modems split the bandwidth into a
collection of channels with different combinations of amplitude and
phase differences, and the signal is sent down these channels in
parallel, and each channel can be filtered out at the other end.  This
enables them to transmit at much higher bit rates than your 'theoretical
maximum'.

Dave.

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From: David Fraser <djf@dcs.ed.ac.uk>
Subject: Re: Cable Modems (was Re: Telewest Communications FIASCO)
Date: 1997/03/17
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