3Com 3CR990SVR95, 3CR990-TX-97, 3CR990-TX-95, 3CR990SVR97 manual 10BASE-T Operation, Category Use

Cabling Requirements 155

The EIA/TIA defines five categories of unshielded twisted-pair cable.

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 characteristics include:

■A data rate of 10 Mbps.

■A broadcast architecture.

■A specific media-access control (MAC) scheme.

The 10BASE-T name indicates a signaling speed of 10 Mbps and twisted-pair wiring. Base stands for baseband, which denotes a technique for transmitting signals as direct-current pulses rather than modulating them onto separate carrier frequencies.

A wiring topology using 10BASE-T specifies a wiring

hub, cable arranged in a star configuration, and unshielded twisted-pair cable. Each node has a separate cable run that must not exceed 100 meters (328 ft) from the node to the hub.