Networking: A Beginner’s Guide Fifth Edition- P14 docx

47 Chapter 4: Understanding Network Cabling of Token Ring networks are offset somewhat by the greater overhead and processing needs to handle the tokens. Overall, Token Ring networks perform about as fast as Ethernet networks with similar bandwidth. IBM invented the Token Ring network technology in the late 1960s, and the first Token Ring networks started appearing in 1986. While quite a few Token Ring LANs are installed (running at either 4 Mbps or 16 Mbps), you tend to see them predominantly in companies that have a strong IBM relationship and, perhaps, also use an IBM mainframe or minicomputer. If you’re designing a new LAN, generally your best bet is to use Ethernet in a star topology. You’ll find network equipment for this choice is readily available and inexpensive. Many qualified installers are available for 100Base-T or 1000Base-T. (There is little sense in installing 10Base-T these days; in fact, the equipment is no longer available.) As noted earlier, for new networks, you should install Cat-5E cable at a minimum, even if you’re initially going to use 100Base-T, so that you have a ready upgrade path to the faster standards. Use Token Ring if some external need is driving this choice, such as connectivity to an old IBM mainframe that doesn’t support Ethernet. Demystifying Network Cabling Network cabling can be incredibly confusing. Not only are there many different types of network cables—all with their own names and properties—but often you can select different types of cables for a single type of network. For example, Ethernet networks can use an astonishing number of cables, ranging from coaxial cable, to unshielded or shielded twisted-pair cable, to fiber-optic cable. To design or support any given network, you need to know your cable choices and how to maintain the particular type of cable you select. The focus in this section is to demystify cabling systems for you. It covers the most common types of network cable—the kinds that you’ll find in 99 percent of the networks in existence and that you’ll use for 99 percent of any new networks. When appropriate, I will make passing reference to other cable types so that you know what they are, but you should focus your attention on only a few ubiquitous cable types— primarily the ones discussed here. Overview of Basic Cable Types The most common network cable types are unshielded twisted-pair (UTP) and coaxial, followed by shielded twisted-pair (STP) and fiber optic. UTP is by far the most common type in use today. UTP cable consists of two or more pairs of plastic-insulated conductors inside a cable sheath (made from either vinyl or Teflon). For each pair, the two conductors are twisted within the cable, helping the cable resist outside electrical interference. Rigid standards exist for how this cable is made, including the proper distance between each twist of the pair. Figure 4-5 shows an example of UTP cable. 48 Networking: A Beginner’s Guide STP is similar to UTP, but STP has a braided metal shield surrounding the twisted pairs to further reduce the chance of interference from electrical sources outside the cable. Coaxial cable consists of a central copper conductor wrapped in a plastic insulation material, which is surrounded by a braided wire shield and, finally, wrapped in a plastic cable sheath. (The coaxial cable used for televisions is similar in design.) Two main types are used for networks: Thin Ethernet (10Base-2), which uses RG-58/AU or RG-58/CU cable, and Thick Ethernet (10Base-5), which uses—you guessed it—a much thicker coaxial cable called RG-8. Figure 4-6 shows an example of coaxial cable. Fiber-optic cable uses a glass strand and carries the data signals as light instead of electricity. It used to be that fiber-optic cable was required for higher-speed networks, but this is changing, and often UTP or STP can be used instead. This is good news, as fiber-optic cable is extremely expensive to purchase, install, and maintain. However, fiber-optic cable can do one thing that copper cables cannot: span extremely long distances. Fiber-optic cable can easily reach two miles at 100 Mbps. For this reason, fiber-optic cable is often used to connect together buildings in a campus-like setting. But other than when you need to span very long distances, you should avoid fiber- optic cable. Twisted-Pair Cabling: The King of Network Cables For a number of years, virtually all new networks have been built using some form of twisted-pair cabling. Usually, Cat-5 grade twisted-pair cable is used, although you may see some old networks in which Cat-3–grade cable is installed. UTP is used instead of STP in almost all cases, because it’s less expensive, easier to install and maintain, and Figure 4-5. UTP cable Twisted pairs Figure 4-6. Coaxial cable Braided metal shield Conductor Plastic 49 Chapter 4: Understanding Network Cabling not much affected by electrical interference (even without the shield). Both Ethernet and Token Ring networks use twisted-pair cabling. Note that different Ethernet types require different cables, and some higher-speed standards require STP. When a new twisted-pair network is installed, a number of wiring components form the complete run from the workstation to the hub. As shown in Figure 4-7, the cabling starts at the hub, where a patch cable (usually 6 to 10 feet long, or 2 to 3 meters) connects a port on the hub to a patch panel, using RJ-45 connectors on each end. On the other side of the patch panel, the twisted-pair cable is hard-wired to the patch panel connection, and then runs continuously to a wall jack (in an office, for instance) to which it is also hard-wired. The wall jack contains an RJ-45 connector on its other side, to which another patch cable connects, and then connects to the computer’s network interface card (NIC). The distance from the connector on the hub to the connector on the computer’s NIC cannot exceed 100 meters (328 feet) of cable length. Anywhere twisted-pair cabling isn’t hard-wired, it uses RJ-45 modular connectors. These are just like the modular connectors you see on telephones, but they are larger and can accommodate up to eight wires. 10Base-T and 100Base-T use four of those wires (two pairs: one for transmit and one for receive). 1000Base-T uses eight of those wires. Figure 4-7. A typical twisted-pair network wiring arrangement 50 Networking: A Beginner’s Guide The eight wires in the RJ-45 connector are numbered from one to eight. If you were to hold the connector in your left hand, with the pins in the connector facing up and pointed forward, pin 1 of the connector is the one farthest away from you (see Figure 4-8). Table 4-1 shows both the colors of standard Cat-5 cable that should be wired to each pin and the 10/100Base-T assignments. DCE and DTE Wiring Most communications and network devices, including those designed to use RJ-45 connectors, are either data communications equipment (DCE) or data terminal equipment (DTE). If you have DTE on one end, you need DCE on the other end. In a way, they’re just like screws and nuts. Two screws don’t go directly together, and neither do two nuts. The same principle applies here: DCE devices can’t talk directly to other DCE devices, nor can DTE devices talk directly to DTE devices. The RJ-45 jack on a hub or switch is DCE, while the RJ-45 jack on a computer’s NIC is DTE. Note that you cannot communicate between DCE and DCE devices or between DTE and DTE devices using a standard twisted-pair/RJ-45 cable that has been Figure 4-8. An RJ-45 connector Table 4-1. 10/100Base-T Wire Assignments for RJ-45 Connectors Pin Number Wire Base Color Wire Stripe Color 10/100Base-T Use 1 White Orange Transmit negative 2 Orange White Transmit positive 3 White Green Receive negative 4 Blue White Not used 5 White Blue Not used 6 Green White Receive positive 7 White Brown Not used 8 Brown White Not used 51 Chapter 4: Understanding Network Cabling wired as described in Table 4-1. For instance, you cannot use a standard twisted-pair patch cable to connect directly from a network server to a workstation, or between two workstations, because those are all DTE devices. Instead, you must purchase or prepare a crossover cable for this connection. For 10/100Base-T networks, Table 4-2 shows the wiring needed for a crossover cable. TIP You can easily purchase all the tools and parts needed to make twisted-pair/RJ-45 cables, and you should do so if you manage a network of any appreciable size (more than 50 workstations). Knowing how to use these tools and parts to make patch cables or to replace a failed cable is invaluable. This way, you can quickly make cables of any length you need. However, even though you should be able to do this, and it can get you out of a jam quickly, you’re better off purchasing premade twisted-pair/RJ-45 cables to use with your network. Professionally made cables are more reliable and should give you fewer problems than the ones that you make yourself. Make your own cables when you’re in a pinch. What’s All This About Cable Categories? Twisted-pair network cables are rated in terms of their capability to carry network traffic. These ratings are defined by the Electronic Industries Alliance (EIA) and the Telecommunications Industry Association (TIA) and are referred to as Levels 1 and 2 and Categories 3, 4, 5, and 6. The different category levels are simply called Cat-3 through Cat-6. Table 4-3 shows the rated performance for each of these levels. To achieve a particular performance rating in practice, you not only need cable certified to that performance level, but you must observe other requirements, including using connectors and patch cables that also meet that level of performance. For example, for a Cat-5 installation, you must have Cat-5 cable, connectors, patch panels, and patch cables. The entire circuit, from where the client computer connects to the hub connection at the other end, needs to be tested and certified to the performance level you need to achieve. Table 4-2. Twisted-Pair/RJ-45 Crossover Cable Wiring Cable End 1 Cable End 2 Pin Wire Base Color Wire Stripe Color Pin Wire Base Color Wire Stripe Color 1 White Orange 1 White Green 2 Orange White 2 Green White 3 White Green 3 White Orange 6 Green White 6 Orange White . inexpensive. Many qualified installers are available for 100Base-T or 1000Base-T. (There is little sense in installing 10Base-T these days; in fact, the equipment is no longer available.) As noted earlier,. cable. TIP You can easily purchase all the tools and parts needed to make twisted-pair/RJ-45 cables, and you should do so if you manage a network of any appreciable size (more than 50 workstations) twisted-pair cabling. Usually, Cat-5 grade twisted-pair cable is used, although you may see some old networks in which Cat-3–grade cable is installed. UTP is used instead of STP in almost all cases,