🚀 go-pugleaf

Richard Morrell wrote:
> 
> In article <Pine.SUN.3.95.970220121654.24605B-100000@tardis.tardis.ed.ac.uk>, Alastair B Roberts <abr@tardis.ed.ac.uk> writes:
> >
> > For a *telecommunications* company, who are trying to move into the
> > so-called information age by introducing cable networks, internet access,
> > cable-modems, etc, etc, etc, it is quite ironic that these people fail to
> > understand the technology involved. If anybody should understand these
> > things, it should be Telewest!
> 
> Sorry for asking a quick spoddy question on what is a rather good rant-thread, but:
> 
> Speaking of cable modems and the like, I was wondering if anyone could explain
> 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?

64kbps is not a magic physical limit for copper cables: it is the
quantum of digitisation inside the phone network. I.e. when you
call is converted to digital at the central office, it is done
at 64kbps, hence any attempt to drive signals faster than 64k
through the switched network will fail.

Copper can support much faster than 64k using xDSL technologies,
as can coax networks. The details differ (e.g. cable modems
modulate the digital signal onto a broadband carrier), but the
principles are similar: use the local cabling to carry a
high speed digital signal directly to an IP router bypassing
the switched phone network altogether.

Martin

P.S. It can get more confusing if you try to think about
the digital transmission network (SDH or PDH), as often
the same wires/fibres might be carrying the IP traffic
and the switched voice traffic!
-- 
Martin Baines - Telecommunications Market Consultant
Silicon Graphics, Arlington Business Park, Reading, RG7 4SB, UK

email:  martinb@reading.sgi.com     SGI vmail:  6-788-7842
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