"Andy Wade" wrote in message
...

[1] The ADSL modem in my roota usually claims an SNR margin of around 30
dB, so clearly there is a lot of margin in the system.

Getting up to 8Mbps through the system with 30dB noise margin took years of
design effort and years arguing in standards forums about what the best
method was. If you think of it another way, with 0dB margin it is
difficult to get much through at all.