A-2APPENDIX A: SPECIFICATIONS AND CABLING REQUIREMENTS
Twisted-Pair Cable
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 (see Table A-1).
Table A-1Unshielded Twisted-pair Cable Categories
Category Use
1Traditional telephone cable.
2Data transmissions up to 4 MHz.
3Voice 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.
4Voice and data transmission up to 33 MHz. The cable normally has four pairs of wire. This grade of UTP is not common.
5Voice 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.
10BASE-T Operation
10BASE-T is the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard for Ethernet signaling over unshielded twisted-pair wire at 10 Mbps.
Ethernet, as the most widely used network protocol, uses 10BASE-T as its primary cabling scheme. Ethernet’s characteristics include:
■A data rate of 10 Mbps
■A broadcast architecture
■A specific media-access control (MAC) scheme
