Unshielded Twisted-Pair (UTP) Cable

Unshielded Twisted-Pair (UTP) Cable

Unshielded twisted-pair cable doesn’t incorporate a braided shield into its structure. However, the characteristics of UTP are similar in many ways to STP, differing primarily in attenuation and EMI. As shown in Figure 3.15, several twisted-pairs can be bundled together in a single cable. These pairs typically are color coded to distinguish them.

Telephone systems commonly use UTP cabling. Network engineers can sometimes use existing UTP telephone cabling (if it is new enough and of a high enough quality to support network communications) for network cabling.

UTP cable is a latecomer to high-performance LANs because engineers only recently solved the problems of managing radiated noise and susceptibility to EMI. Now, however, a clear trend toward UTP is in operation, and all new copper-based cabling schemes are based on UTP.

UTP cable is available in the following five grades, or categories:

Categories 1 and 2. These voice-grade cables are suitable only for voice and for low data rates (below 4 Mbps). Cate-gory 1 was once the standard voice-grade cable for telephone systems. The growing need for data-ready cabling systems, however, has caused Categories 1 and 2 cable to be supplanted by Category 3 for new installations.
Category 3. As the lowest data-grade cable, this type of cable generally is suited for data rates up to 10 Mbps. Some innovative schemes, however, enable the cable to support data rates up to 100 Mbps. Category 3, which uses four twisted-pairs with three twists per foot, is now the standard cable used for most telephone installations.
Category 4. This data-grade cable, which consists of four twisted-pairs, is suitable for data rates up to 16 Mbps.
Category 5. This data-grade cable, which also consists of four twisted-pairs, is suitable for data rates up to 100 Mbps. Most new cabling systems for 100 Mbps data rates are designed around Category 5 cable.

In a UTP cabling system, the cable is only one component of the system. All connecting devices also are graded, and the overall cabling system supports only the data rates permitted by the lowest-grade component in the system. In other words, if you require a Category 5 cabling system, all connectors and connecting devices must be designed for Category 5 operation.

Category 5 cable also requires more stringent installation procedures than the lower cable categories. Installers of Cate-gory 5 cable require special training and skills to understand these more rigorous requirements.

UTP cable offers an excellent balance of cost and performance characteristics, as discussed in the following sections.

Further Information