Electricity flows near the speed of light, not not quite. It's not much to do with why ADSL is slower than optic broadband though, that is more about the poor connections in the old copper cable and the systems on each end. Think about how old the telephone line system is in the UK, much like the rail system it is a bit worn out.
I think a dedicated strip of optic was put down in the US for stock exchange stuff though, blowing trough mountains and such that were in the way to take the shortest path. It gave some stupid nano-second advantage in trading times. A couple of years later that has apparently been beaten by microwave transmission towers or something.
Hardly even that. Domestic telephone relies on a twisted-pair of wires designed only to transmit analogue audio in a 3khz bandwidth the last mile or so to the subscriber (the local exchanges are all very, very much more hi-tech)
Pushing multiplexed signals and 50Mhz+ of bandwidth through that archaic wire pair is a real technical achievement! It requires some very clever phase modulation/demultiplexing and also takes a lot of power to overcome the inevitable losses in the last mile given the HF energy required. It's what DSL drivers starting with the AD815 were invented for - also why they are capable of 1W+ in class A and MHZ bandwidths...
Optical provides a route with a much higher-bandwidth potential in the first place.
Thanks for the explanations guys.So it's basically a question of getting enough current through the old copper system to drive the bits at each end of the cable.
I would have replied sooner but my system is so fast now that I didn't want my reply to arrive before you answered the question.
All the best to everyone for a healthy and happy new year.
