> I think the limit is about 18,000 feet. Then you might have trouble
>> carrying DSL over it ...
> Correct, but that's the approximate limit for the total length from
> the switch to the telephone.
Strange, isn't it, that the limit for ISDN (with an extender) is over _25,000_ ft?
In rural areas, for POTS service, 75,000+ ft of wire is not uncommon.
Beyond that, the signal is typically attenuated too much, mainly by
> cable resistance, and gets buried in noise.
Circa 18,000 ft is a general practical limit for _DSL_ circuits, only.
*NOT* due to cable "resistance", by the way -- but rather due to the cumulative effect of distributed capacitance, and the 'blurring' of high-frequency signal transitions that occurs as a result thereof.