When connecting network cables, many people find it hard to tell which of the eight copper conductors inside the cable are the ones that keep network transmission working properly.
First, you need to understand the overall role of the eight copper conductors. They exist to reduce mutual electromagnetic interference, with every two conductors twisted together at a set density. This way, the radio waves radiated by each conductor during electrical signal transmission cancel each other out, effectively eliminating interference. The name “twisted pair” is derived from exactly this construction.
Twisted pair cable was first used to carry telephone signals, and only later was it gradually introduced into digital signal transmission. Today the most widely used types are Cat5e and Cat6 twisted pair, with bandwidths of up to 1000 Mbps. The only drawback of twisted pair is its short transmission distance, limited to 100 meters.
Cat5 and Cat5e twisted pair normally require four pairs, that is, all eight conductors. Below 100M, four conductors are typically used: 1, 2, 3 and 6.
Straight-through cable (standard 568B): both ends use the same wiring order, namely orange-white, orange, green-white, blue, blue-white, green, brown, brown-white. Crossover cable (568A): one end uses the straight-through order, while the other end is green, green, orange-white, blue, blue-white, orange, brown-white, brown. There is no need to memorize the 568A order: first, this wiring order is no longer used today; second, it can be obtained simply by swapping 1-3 and 2-6 on the basis of B.
Why exactly are conductors 1, 2, 3 and 6 used? That requires understanding what each conductor does: 1 Output data (+) 2 Output data (-) 3 Input data (+) 4 Reserved for telephone use 5 Reserved for telephone use 6 Input data (-) 7 Reserved for telephone use 8 Reserved for telephone use. This shows that although twisted pair has eight conductors, in the 100 Mbps networks widely used today only four of them are actually used, namely the 1st, 2nd, 3rd and 6th, which handle the receiving and sending of signals respectively. 4, 5, 7 and 8 are bidirectional lines, reserved for use.
However, on networks running above 100M, all eight conductors are usually used. For example, Cat6 and Cat6a cables use not only 1, 3, 2, 6 but all eight conductors; otherwise network operation becomes unstable. If we strip the cable, we can see that the four twisted pairs are not twisted at the same density: the orange and green pairs used for data transmission are twisted noticeably more tightly than the brown and blue pairs used for grounding and other common purposes. We therefore recommend that when making patch cords you strictly follow the 568B order. People often say: “I like to use my own habitual order when making cables — doesn’t that work too?” At home you can do as you please, but in a project you should be rigorous and follow the wiring order. Otherwise the twisted pair loses its purpose: data transmission attenuation becomes severe and the transmission distance drops sharply. Here we want to stress that if you insist on arranging the wiring order your own way, you must place conductors 1 and 3 on the same twisted pair, and conductors 2 and 6 on the same twisted pair.
