Montblack wrote:

Now I'm confused. Is my DSL running at higher frequencies, over the same
(single) wire strand that my voice is running on? Or is it running on the
second wire strand, in my standard household wire - which contains 2 wire
strands? Or is it using both strands?

It depends. Read on.

Newps replied:

It takes two wires to have a voice line. There are typically 4 wires in a
residential phone line; red, green, yellow and black. Normally the first
phone number uses the red and green wires. The other two will be for your
second phone number, should you get one. The DSL uses the same two wires as
your first phone number, with a filter to keep the two things separate.

Many houses with DSL are wired as Newps writes, but not all. DSL operates at
frequencies that are unused by "plain old telephone system" (POTS); like 20KHz
and up. Therefore the phone company can provide DSL without stringing new
copper from the central office to the home (which would be a *huge* cost),
provided the quality of the line is up to the task (this is the physics behind
the "X,000 ft rule", where "X" is 18 or 20 or so). Putting the DSL signal on
the voice pair usually requires a high frequency attentuator be placed at each
phone, however.

Some neighborhoods, like mine, are wired with optical fiber to the pedestal (in
the alley, shared by several homes), and then copper from the pedestal to the
outlet. Since I only have one landline (red-green), the telephone company
opted to use the second copper pair (yellow-black) as the DSL line. This saved
me the hassle of having the DSL filters (high freqency attenuators) at each
phone.

Russell Kent