🚀 go-pugleaf

In message <19960613.161905.06@unthank.demon.co.uk> Robert P.North wrote:

> In article <19960611.233455.39@axis.demon.co.uk>,
>           ncw@axis.demon.co.uk (Nick Craig-Wood) wrote:
> 
> > Ben Formesyn (formesbc@boat.bt.com) wrote:
> > 
> > > IIR the theoretical limit is around 38000bps, limited by the SNR of the 
> > > connection and the bandwidth of the connection. Shannon's Theorum has all the 
> > > gory details if you're really interested(!)
> 
> Now, if you find patterns in the noise, you could say that it is no longer
> noise! 
> ... of course, that's what Nick talks about below...
> 
> > 
> > This is correct for a line of a given signal to noise ratio.  However an
> > analogue telephone line is immediately digitised at the exchange to 64k
> > (8000 samples per second to 8 bits logarithmic).
> > 
> > If you were very clever and could get in sync with the digitisers (maybe by
> > looking at artifacts on the incoming channel) then you could certainly do
> > better than 38k, say 56k (storing 7 bits in each 8 bit sample).
> 
> Now that's clever... if someone can pull it off
> 
>  ... might call it ISDN for hackers!
> 

This is a "nice *but*" idea.

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. 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.

And if you had digits & codecs in your house...then you would have ISDN anyway! 

-- 
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