|  | 5.1 | Most Common LAN Media
| 5.1.2 | UTP
Unshielded twisted-pair cable (UTP) is a four-pair wire medium - composed of pairs of wires - used in a variety of networks. Each pair of wires is insulated from the others. This type of cable relies solely on the cancellation effect, produced by the twisted wire pairs, to limit signal degradation caused by EMI and RFI. To further reduce crosstalk between the pairs in UTP cable, the number of twists in the wire pairs varies. Like STP cable, UTP cable must follow precise specifications as to how many twists or braids are permitted per foot of cable. When used as a networking medium, UTP cable has four pairs of either 22 or 24 gauge copper wire. UTP used as a networking medium has an impedance of 100 ohms. This differentiates it from other types of twisted-pair wiring such as that used for telephone wiring. Because UTP has an external diameter of approximately .43 cm, its small size can be advantageous during installation. Since UTP can be used with most of the major networking architectures, it continues to grow in popularity. Unshielded twisted-pair cable has many advantages. It is easy to install and is less expensive than other types of networking media. In fact, UTP costs less per meter than any other type of LAN cabling, however its real advantage is its size. Since it has such a small external diameter, UTP does not fill up wiring ducts as rapidly as other types of cable. This can be an extremely important factor to consider, particularly when installing a network in an older building. Also, when UTP cable is installed using an RJ connector, potential sources of network noise are greatly reduced, and a good solid connection is practically guaranteed. There are, however, a number of disadvantages in using twisted-pair cabling. UTP cable is more prone to electrical noise and interference than other types of networking media. Also, UTP was once considered slower at transmitting data than other types of cable. However, this is no longer true. In fact, today, UTP is considered the fastest copper-based media. The distance between signal boosts is shorter for UTP than it is for coaxial cable.
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