On Monday, November 14, 2016 at 1:15:54 AM UTC-5, Michael Terrell wrote:
DoN. Nichols wrote:

Well ... 25-pair cables *are* 50 wires, and the dots on solid
uniquely marked each wire in that count. (Aside from that, the two wires
in a pair were also twisted -- to minimize crosstalk to adjacent pairs.)
The twisting helps keep them together so you don't have to search
through 49 other wires to find the other half of a pair. :-)


Not only re he pairs twisted, but the twist rate varies from pair to
pair to reduce the crosstalk even further.

Those phone company guys are pretty smart. I remember reading, in the very early 1980s, an article that explained in great detail why it was physically impossible to squeeze more than 1200 bits per second over a voice-grade phone wire. Then in the early 2000s, I spent a couple of months at Bell Labs, working up test procedures for DSLAM installations.

In each corner of each floor of the building, there was a seating area with a large whiteboard. The boards were covered with math that is far, far beyond what I could understand. It looked almost cartoonish - like they were making fun of math nerds.

But these were the guys who figured out how to cram millions of bits per second over that 1200 bit maximum twisted pair. On the other hand, they needed ME to come in and show them how to, basically, determine whether one end of a wire was connected to the other. only a very small percentage of those guys had a clue which end of a soldering iron to pick up.