Twisted-pair cabling is a form of copper cabling that consists of one to four pairs of color-coded insulated stranded copper wires that are twisted together in pairs and enclosed in a protective outer sheath.
Twisted-pair cabling is terminated with RJ-11 connectors and was originally developed for the telephone system. It is now also the cabling of choice for networking workgroups and departmental local area networks (LANs). Twisted-pair cabling for networking purposes has RJ-45 connectors at each end.
In computer networking environments that use twisted-pair cabling, one pair of wires is typically used for transmitting data while another pair receives data. The twists in the cabling reduce the effects of crosstalk and make the cabling more resistant to electromagnetic interference (EMI), which helps maintain a high signal-to-noise ratio for reliable network communication. Twisted-pair cabling used in Ethernet networking is usually unshielded twisted-pair (UTP) cabling, while shielded twisted-pair (STP) cabling is typically used in Token Ring networks. UTP cabling comes in different grades for different purposes, the most common of which is category 5 cabling.
In a telephone environment, one pair is sufficient for phone communication to take place. Most customer premises wiring established by telcos uses two-pair wiring in case a second phone line is later needed for fax or modem use.