A-2 APPENDIX 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).
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
Table A-1 Unshielded Twisted-pair Cable Categories
Category Use
1 Traditional telephone cable.
2 Data transmissions 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.
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.