WHY DO WE TWIST THE CABLE IN CROSSOVER ?

WHY DO WE TWIST THE CABLE IN CROSSOVER ?

The  primary means of reducing crosstalk--the term crosstalk came from the ability to (overhear conversations on other lines on your phone--between the pairs in the cable, is the double helix configuration produced by twisting the wires together. This configuration produces symmetrical (identical) noise signals in each wire. Ideally, their difference, as detected at the receiver, is zero. In actuality it is much reduced.

Two wire color-code standards apply: EIA/TIA 568A and EIA/TIA 568B . The codes are commonly depicted with RJ-45 jacks as follows (the view is from the front of the jacks):

STANDARD RJ -45

Note that pins 4, 5, 7, and 8 and the blue and brown pairs are not used in either standard. Quite contrary to what you may read elsewhere, these pins and wires are not used or required to implement 100BASE-TX duplexing--they are just plain wasted.

Another way of remembering the color coding is to simply switch the Green set of wires in place with the Orange set of wires. Specifically, switch the solid Green (G) with the solid Orange, and switch the green/white with the orange/white.
that's it for now....

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