🚀 go-pugleaf

In message <19960615.123038.30@axis.demon.co.uk> Nick Craig-Wood wrote:

> Peter Chambers (peter@hightown.demon.co.uk) wrote:
> 
> > If your line was digital between a codec directly connected to modems
> > at both ends this might be made to work. But it isn't. You have all
> > of that analogue wiring as well.
> 
> Ask yourself what the bandwidth of the bit of copper going from my house to
> the exchange is?  Very large isn't it?  (In fact I have two pieces of
> identical copper leaving my house, one of which carries analogue phone
> calls, and the other ISDN at 160 kbits/s.)  The copper wire doesn't go
> though any multiplexers, it just goes straight to the codec at the exchange.
> 
> What may be a problem are the filters on the codec limiting the bandwidth,
> but this isn't a function of a piece of copper :-)
> 
> > Ben Formesyn is right. You are limited by the Shannon Channel Capacity of
> > real telecom lines. This seems to be little more than 33,000 bps according
> > to results in the trade press.
> 
> If you substitute 'codec filters' for 'lines' in the above then you may well
> be right.
> 

The 'copper' and all of the bits (collectively called the 'local loop') can
indeed be a problem. It can act as a filter. Modems and like equipment must
be designed to work with 'typical' local loops to be saleable.

Things like ISDN, 10-baseT and the quasi-balanced system (ADSL ?) developed
of Video-On-Demand rely on heavyweight equalisers to operate. Before the cheap,
integrated equalisers we have now they said that 64Kbps, 10Mbps could not go
through copper. Even voice was equalised on long analogue lines. Now the data-
stream with the PCM u-Law/A-law on it is equalised to keep Inter Symbol Interference
down and the Bit Error Rate at acceptable levels.

Another factor is that the voice line is going to be converted back and forth
between standards by the Telcos. This is going to ruin the "64K artefacts" that
were mentioned in the original post.

I think that you have already done the best option. ISDN. I can't justify
that for my use, yet. V.34 is my most cost effective option for a while.

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