CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [403]
CAT Levels UTP cables come in categories that define the maximum speed at which data can be transferred (also called bandwidth). The major categories (CATs) are as follows:
The CAT level should be clearly marked on the cable, as Figure 23-7 shows.
Figure 23-7 Cable markings for CAT level
The Telecommunication Industry Association/Electronics Industries Alliance (TIA/EIA) establishes the UTP categories, which fall under the TIA/EIA 568 specification. Currently, most installers use CAT 5e or CAT 6 cable. Although many networks run at 10 Mbps, the industry standard has shifted to networks designed to run at 100 Mbps and faster. Because only CAT 5 or better handles these speeds, just about everyone is installing the higher rated cabling, even if they are running at speeds that CAT 3 or CAT 4 would do. Consequently, it is becoming more difficult to get anything but CAT 5, CAT 5e, or CAT 6 cables.
Shielded Twisted Pair
Shielded twisted pair (STP), as its name implies, consists of twisted pairs of wires surrounded by shielding to protect them from EMI, or electromagnetic interference. STP is pretty rare, primarily because there’s so little need for STP’s shielding; it only really matters in locations with excessive electronic noise, such as a shop floor area with lots of lights, electric motors, or other machinery that could cause problems for other cables.
Implementing 10/100/1000BaseT
The 10BaseT, 100BaseT, and 1000BaseT cabling standards require two pairs of wires: a pair for sending and a pair for receiving. 10BaseT runs on CAT 3, CAT 4, or CAT 5 cable. 100BaseT requires at least CAT 5 to run. 1000BaseT is a special case because it needs all four pairs of wires in a CAT 5e or CAT 6 cable. These cables use a connector called an RJ-45 connector. The RJ (registered jack) designation was invented by Ma Bell (the phone company, for you youngsters) years ago and is still used today. Currently only two types of RJ connectors are used for networking: RJ-11 and RJ-45 (Figure 23-8). RJ-11 is the connector that hooks your telephone to the telephone jack. It supports up to two pairs of wires, though most phone lines use only one pair. The other pair is used to support a second phone line. RJ-11 connectors are primarily used for dial-up networking (see Chapter 25, “The Internet”) and are not used in any common LAN installation, although a few weird (and out of business) “network in a box” companies used them. RJ-45 is the standard for UTP connectors. RJ-45 has connections for up to four pairs and is visibly much wider than RJ-11. Figure 23-9 shows the position of the #1 and #8 pins on an RJ-45 jack.
Figure 23-8 RJ-11 and RJ-45
The TIA/EIA has two standards for connecting the RJ-45 connector to the UTP cable: the TIA/EIA 568A and the TIA/EIA 568B. Both are acceptable. You do not have to follow any standard as long as you use the same pairings on each end of the cable; however, you will make your life simpler if you choose a standard. Make sure that all of your cabling uses the same standard and you will save a great deal of work in the end. Most importantly, keep records !
Like all wires, the wires in UTP are numbered. However, a number does not appear on each wire. Instead, each wire has a standardized color. Table 23-1 shows the official TIA/EIA Standard Color Chart for UTP.
Figure 23-9 RJ-45 pin numbers
Table 23-1 UTP Cabling Color Chart
Plenum versus PVC Cabling Most workplace installations of network cable go up above the ceiling and then drop down through the walls to present a nice port in the wall. The space in the ceiling, under the floors, and in the walls through which cable runs is called the plenum space. The potential problem with this cabling running through the plenum space is that the protective sheathing for networking cables, called the jacket, is made from plastic, and if