[GLLUG] Internet Data Rate

Chris Bell chrisbell at chrisbell.org.uk
Wed May 13 16:33:42 UTC 2020

On Wednesday, 13 May 2020 13:21:50 BST Marco van Beek via GLLUG wrote:
> With so few people having / using POTS telephones these days, it is
> really hard to explain to people that the quality of the line affected
> the quality of the data. Most of the time when I turn up to fault-find a
> xDSL line, I start by plugging a £10 handset into the line, and then
> have to tell them it is a voice fault and we need to report it to the
> telephone company, not the broadband company. They usually just don't
> get it.
In the days when telephones had to make the best of sometimes poor quality 
copper connections, the line quality was often tweaked to get an improved 
voice quality, but we had a much more complex "fairy fingers box" to extract 
the best possible result for broadcast use, and we had to remove any pre-
equalisation first.
Neither would be much use for broadband data because equalisation could 
increase higher audio frequencies, then produce a hard cut just above.
On the other hand, engineering control lines were often random pairs strung 
together without amplification, so you really had to shout if you were trying 
to speak over very long distances.
The best music quality lines used a "phantom" connection with each leg of the 
pair sitting on the transformer centre tap of an ordinary telephone pair.

Chris Bell
Website http://chrisbell.org.uk

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