air, or UTP, is a form of cabling that uses pair
s of wire
s that are twisted together to reduce crosstalk. Refer to twisted-pair
to understand the background for twisted-pair usage.
UTP is just a set of twisted-wire pairs enclosed in a plastic jacket. There is no foil or braid shielding to reduce electromagnetic interference (EMI) or signal bleeding.
UTP is mostly used in data and voice communications cabling. There are several categories of UTP, and the category determines the use of the cable. These categories were introduced by the Electrical Industries Association (EIA).
The categories are:
Category Rate Use
CAT1,2 4Mbps Originally used for voice
old phone lines.
CAT3 10Mbps Suitable for most computer networks.
Most newer phone systems now use
CAT4 20Mbps Not as common, allows a higher
data rate. Most people opt for the
benefits of CAT5 cable instead
CAT5 100Mbps+ Supports Fast Ethernet systems, but
requires more expensive 100Mbps
equipment to take advantage of the
higher data rate. The wiring is of a
higher quality, including better
insulation, more twists per linear
foot and better outer jackets.
Most businesses now install CAT5
when running cable due to the
expandability. It is cheaper to run
CAT5 now than install CAT3 and
replace it later with CAT5, but
running CAT5 requires a more
CAT3, 4 and 5 UTP cable use copper conductors. Because copper attenuates signals over distances, the length of one cable is limited to approximately 100 meters. UTP only supports two nodes or devices per cable, one at each end. Ethernet is basically equipment connected by patch cords.
The wires in UTP are grouped in pairs. Most data cables (CAT 3, 4, 5) have four wires or 8 wires. THe 4-wire cable is called two-pair, and the 8 conductor version four-pair. Networking using UTP requires at least a two-pair cable.
The connectors for Ethernet 4-pair UTP are called RJ-45 modular phone connectors. They look very similar to the phone connectors on many telephones, especially in the United States. The two-pair UTP cables can use RJ-11 connectors, which are smaller versions of the RJ-45.