Twisted-pair cable consists of copper wires surrounded by an
insulator. Two wires are twisted together (the twisting prevents interference
problems) to form a pair, and the pair forms a circuit that can transmit data. A
cable is a bundle of one or more twisted pairs surrounded by an insulator.
Unshielded twisted pair (UTP) is the most commonly used type of twisted-pair cable.
Shielded twisted pair (STP) provides protection against crosstalk. Twisted-pair cable is now commonly used in Ethernet, Fast Ethernet, and other network topologies.
The EIA/TIA defines five categories of unshielded twisted-pair cable.
1 Traditional telephone cable.
2 Data transmission up to 4 MHz.
3 Voice and data transmission up to 25 MHz. The cable typically has four pairs of wires. Category 3 is the most common type of installed cable found in older corporate wiring schemes.
4 Voice and data transmission up to 33 MHz. The cable normally has four pairs of wire. This grade of UTP is not common.
5 Voice and data transmission up to 125 MHz. The cable normally has four pairs of copper wire and three twists per foot. Category 5 UTP is the most popular cable used in new installations today.
RJ-45 Connector Pin Assignments