>SDSL uses the same data rate in and out causing the ability to cancel
>out(depending on how they do it) on the medium(copper) therefore getting a
>longer range and less errors.

It's not really true to say that crosstalk cancellation is related to
whether the data rates up and down are the same, at least not in the way
you imply it. Twisted pair cabling relies on equal and opposite currents
flowing in each twisted pair at every given instant of the waveform that is
being sent to achieve cancellation of the magnetic and electromagnetic
fields, thus minimizing radiation of the signal. (It also minimizes
_reception_ of spurious nearby signals too, since the currents of the same
direction are induced instead of differential signals - eg common mode
signals)

You're confusing direction of information flow with direction of current
flow. The current flow is what matters for cancellation, not the direction
the information is going. Whether you're sending a "signal" in one
direction only, or the other, or both at once, if the cables are driven and
terminated properly there will be equal and opposite currents flowing in
the twisted pair.

Regards,
Simon

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Received on Fri Mar 23 09:28:30 2001