Unshielded twisted-pair cable (UTP) is a four-pair wire medium that is used
in a variety of networks
. The eight
individual copper wires in the UTP cable are each covered by insulating
material. Two wires are twisted around each other to form pairs. This type of
cable relies on the cancellation effect, produced by the twisted-wire pairs, to
limit signal degradation caused by crosstalk and external EMI and RFI. To
further reduce crosstalk between pairs in the UTP cable, the number of twists
in the wire pairs is increased. Like STP cable, UTP cable must follow precise
specifications as to how many twists there are for every 30 cm (1 ft) of cable.
The four pairs used in UTP cable for networking are usually 22 or 24
American Wire Gauge (AWG) copper wire. This differentiates it from the
twisted-pair cable used for telephone wiring, which is typically 19, 22, 24, or
26 AWG. Because UTP has an external diameter of approximately 0.64 cm (0.25
inches), 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.
UTP cable has many advantages. It is easy to install and
is less expensive than other types of networking media. Since it has a small
external diameter, UTP does not fill up wiring ducts as rapidly as other types
of cable, with the exception of fiber-optic cable, which costs more to purchase
and install. This can be an extremely important factor to consider,
particularly when installing a network in an older building. Another advantage
of UTP is related to the hub-based or switch-based star topology that is used
on UTP-based Ethernet LANs
. This
topology is considered much easier to troubleshoot than the bus topology of
coaxial-based LANs.
There are also disadvantages to using UTP cabling.
UTP cable is more prone to electrical noise and interference than other types
of networking media, and the distance between signal boosts is shorter for UTP
than it is for coaxial and fiber-optic cables.
UTP was once considered
to be slower at transmitting data than other types of cable. UTP can currently
reach transmission rates up to 1000 Mbps (1 Gbps). A 10-Gbps standard is being
considered.