Twisted-pair wiring utp and stp cable is the most common type of LAN wiring cable in use today. It is versatile, easy to install, inexpensive, and has favorable performance characteristics. Twisted-pair cable is available with or without shielding. It comes in a variety of colors, wire gauges, insulation, twisting, and outer sheath materials.
An illustration of twisted-pair wire is shown in above Figure. A large number of pairs can be in the same cable sheath (the outer jacket). Telephone cables are commonly available in 2-pair, 4-pair, 6-pair, 25-pair, 100-pair, and even larger bundles. LAN twisted-pair cable, however, usually comes as 4-pair cable.
The 4-pair cable is a topic of several standards, including TIA/EIA-568-C. It is the cable around which most of the important LAN cable specifications and performance tests are based. Most LAN topologies actually use only two of the four pairs, however, so some installations place two LAN connections on each 4-pair cable. Telephone connections often use two pairs and may sometimes be wired in the same cable with a 2-pair LAN connection. You should be cautious in robbing pairs from the LAN cable, because some of the 100 Mbps and higher LAN schemes may use all four pairs.
Another common cable that is found in twisted-pair wire installations is the 25-pair jumper cable. This cable is preterminated in 50-pin male or female connectors (sometimes called a 50-pin telco connector). In telephone wiring, the 25-pair jumper cable is convenient for connecting between the local exchange carrier’s RJ- 21X demarcation point and the user’s punchdown blocks or private branch exchange (PBX) switching equipment. In LAN wiring, the 25-pair jumper is commonly used between connectorized punchdown blocks and patch panels. Category 3 and Category 5 grade 25-pair jumpers are available, but some caution should be used in deploying them in a Category 5 installation. Some authorities are concerned with the combination of two or more 100 Mbps signals in the same cable sheath. A 25-pair jumper would theoretically allow you to combine as many as six such signals within the same sheath (6 X4 pairs X24 pairs with one unused pair). Also, each connector introduces more untwisted wire into a circuit and some of the standards limit the amount of untwist as well as the number of connectors in a link.
UTP/STP General Construction
Twisted-pair cable consists of one or more pairs of insulated wires that are twisted together and joined in a common sheath. The main characteristics of twisted-pair cable are :
- wire gauge .
- twist pitch
- insulation type
- characteristic impedance,
- sheath material.
Each of these items may affect the suitability of a cable for a particular application.