The Physics of Network Cabling
Copper (Twisted Pair) Cables
Twisted pair cables emerged in the 1990's, according to Bradley Mitchell, "as the leading cabling standard for Ethernet." They are often the first thing that comes to mind when the average person thinks of a network cable, as we are used to seeing them everyday.
Twisted pair cables commonly consist of 4 twisted pairs of sheathed copper wire (8 wires total). There are two different types of twisted pair cables, Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP). UTP is the most popular of the two, as it is the cheaper yet still very reliable option, and comes it currently seven different categories ranging from telephone wire to Gigabit Ethernet.
| Category | Speed | Use |
|---|---|---|
| 1 | 1 Mbps | Voice Only (Telephone Wire) |
| 2 | 4 Mbps | LocalTalk & Telephone (Rarely used) |
| 3 | 16 Mbps | 10BaseT Ethernet |
| 4 | 20 Mbps | Token Ring (Rarely used) |
| 5 | 100 Mbps (2 pair) | 100BaseT Ethernet |
| 100 Mbps (4 pair) | Gigabit Ethernet | |
| 5e | 1 Gbps | Gigabit Ethernet |
| 6 | 10 Gbps | Gigabit Ethernet |
The standard connector for UTP cables is (Registered Jack) RJ-45 connector. This plastic connector looks like a larger version of the RJ-11 connector that is used on telephone wire. The slot on it allows it to be inserted into an interface only one way. Registered Jack implies that the connector follows a standard "borrowed from the telephone industry," which designates which wires correspond to which pins inside the connector. Most twisted pair cables will follow the T568B standard pinout configuration, but there are some very rare (meaning proprietary) situations where the T568A pinout configuration will be used.
Although UTP cables are the cheapest, they are susceptible to attenuation (loss) due to radio and electrical interference and as such should be kept away from motors, lights, even power cords. If twisted pair cables must be placed in this kind of environment, STP may be the solution and can also give some extra distance if need be. STP cables are available in three different configurations: each pair of wires is individually wrapped with foil, there is a foil or braid shield inside the jacket covering all wires, and there is a shield around each individual pair and around the group (known as double shielded twisted pair).
It is extremely important the twisted pair cables have all four pairs of the cables twisted; at low frequencies it is not a big deal, but at high frequencies you run into noise (extraneous inductance, capacitance, and electromagnetic signals from the outside) and crosstalk (tiny electromagnetic signals that work their way into the adject wire) cancellation. When the wires are twisted together, the electromagnetic polarity of the unwanted signals become skewed. Thus, the more twists the better the cancellation effect.