General Features of Metallic Cabling

The term cable refers to a combination of plastics, metal wires, optical fibers, possibly rubber, and other materials molded into a cord of varying lengths. Well, that's at least a formal definition. People see cables every day. The power cords that go from the electrical wall socket to each of your electrically powered appliances and lamps at home are all cables. There are cables protruding from the back of your PC. And for networking, the phone cord stretching from the wall outlet to your phone is actually a networking cable.

Most networking cables use either copper wires inside the cable to transfer an electrical signal, or glass fiber inside the cable to transfer optical light signals. So, many people refer to cabling as wiring just because the vast majority of networking cables are actually copper wire cables. The wire cables also sometimes are called copper cabling, just because the most popular metal to use in the cable is copper.

When sending an electrical signal over a cable, the signal introduces a magnetic field and also introduces radio frequency interference. Translation: When the cable is in use, it emits radiation that can interfere with other signals in other wires or signals that pass through the air. When one wire affects another in this manner, it is commonly referred to as crosstalk. So, the various national governments tend to regulate how much of these unwanted physics effects are allowed. These metallic wire cables are designed to reduce the effects of the radiation and interference.

The wires can be affected by outside interference as well. Nearby cables can interfere with the transmission on the cable, actually changing the electrical signal and causing bit errors. So, electrical cables create their own emissions and are susceptible to problems from the emissions from other sources, particularly nearby cables.

The most popular way today to reduce the effects of emissions is to transmit over a pair of wires and twist those two wires together. By using an opposite current on each wire, each wire produces an identical magnetic field, but in an opposite direction. It's sort of like having two equal-power magnets of the same polarity, both trying to pull things toward them. If you put a paper clip between them at equal distances, with equal strength for the magnets, the paper clip should not move. If only one magnet were there, it would attract the paper clip. Essntially, twisting the wires has a similar effect—the two magnetic fields cancel each other out.

Twisted-pair wiring is used in today's most popular electrical (wire) networking cables.

The other popular way to reduce the emissions of copper cabling is to shield the wires. That means that the wires have some material placed around them, using a material that blocks most of the electromagnetic radiation. The concept is similar to when you need to get an x-ray, and the person taking the x-ray leaves the room or stands behind a screen made of lead— the x-rays (which are a form of electromagnetic raditaion) do not pass through the lead screen. Similarly, by shielding the cables, the cables emit less raditation.

Unfortunately, shielding the wires makes the cable more expensive and less flexible. The need to add more materials to a cable to shield the cable increases materials and manufacturing costs for the cables. You need a lot of cables to build a typical enterprise network, so the extra cost does add up. If the cable does not bend easily, you might not be able to run it in tight spaces behind walls, in ceilings, into where the wall plate sits behind the wall, and so on. So, inflexible cabling could require you to open walls in the building to make a new space for the cables to run—costing time and money.

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