In article ,
Mark Lloyd wrote:

They always used the center-pair for the first one.

Makes sense. For some reason, ethernet cables avoid using
the center pair.

Yeah? Well the center pins on an ethernet card (in a computer) are
shorted, for whatever THAT's worth.

Back in the dial-up days, I lost count of the times I would clear a hard
short trouble report by removing the RJ11 plug from the ethernet port in
the back of the computer and reconnect it into the nearby, internal
modem IN port.
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JR