52 Networking: A Beginner’s Guide Coaxial Cable Many older networks (those built prior to circa 1992) still have coaxial cable installed. Most of this coaxial cable is the thin variety, which is RG-58, and is used with Thin Ethernet. A few may also use the thicker RG-8 cable for Thick Ethernet, but this is rare. Thin Ethernet cabling is wired in a bus arrangement, where each network segment starts with a terminator that connects to the end of the cable, runs to each node in turn, and ends with another terminator on the other end. The terminators contain special 50-ohm resistors, and the network cable will not work unless both are installed. All the connectors in a Thin Ethernet system are BNC connectors, a quick-release bayonet-style connector, both reliable and easy to use. BNC connectors come in a variety of different styles to enable you to make just about any network connection you need along the bus. T-connectors have two female BNC connectors on each side of the crossbar of the T and a male BNC connector at the end of the shaft of the T. The two female connectors are used for the RG-58 cable coming into and out of a node, while the male connector attaches to a female BNC connector on the node’s Ethernet card. Barrel connectors have two female connectors that are used to connect two Thin Ethernet wires together. Barrel connectors are also available in different shapes, including an elbow bend and a U-shaped bend, but usually the simple straight barrel connector is used. Figure 4-2, earlier in the chapter, shows the various parts of a Thin Ethernet BNC cable system. Coaxial cable has a central conductor, which can be either a solid, single copper wire or a stranded set of wires. A white plastic material surrounds the central conductor, which is surrounded by a metal foil and then a braided wire shield. The shield is finally wrapped in a plastic cable sheath. CAUTION Cable types must not be mixed in any coaxial network. If the network uses, say, RG-58A/U, then that is what you must always use—not any other coaxial cable. Not mixing RG-58A/U and RG-58/U is also a good idea because they have ever-so-slightly different signaling characteristics. (A/U cable uses a stranded center conductor, while /U—sometimes called C/U— uses a solid center conductor.) Table 4-3. Twisted-Pair Performance Designations Level or Category Rated Performance Level 1 Not performance rated Level 2 1 Mbps Category 3 10 Mbps Category 4 16 Mbps Category 5 100 Mbps to 1 Gbps Category 6 >1 Gbps 53 Chapter 4: Understanding Network Cabling Learning to make coaxial cables with BNC connectors is fairly easy, but you need two special tools to make the job easy. First, you need a wire stripper that will cut the various parts of the cable to the right length. Many good strippers can do this for you automatically; check with your cable supplier to order one. You also need a crimper that both can crimp the central BNC pin onto the central conductor of the cable and crimp the metal sleeve that holds the entire connector onto the wire. Again, you can buy special crimpers that can easily do both jobs. The best crimpers use a ratcheting mechanism to make it easier to exert the proper amount of force for a solid, reliable connection. Plenum Versus Nonplenum Cable In a building, the area between the ceiling of the rooms and the roof of the building is called the plenum space. Most buildings use ducts (big, flexible hoses) to provide conditioned air to the rooms in the building, and they use the open plenum space for air returned from the rooms. Typically, the air returned from the rooms is partially reused by the air conditioning units to save energy because it’s already cooled or heated as appropriate. Occasionally, a building uses ducts for the return air, but the standard for office space is simply to use the plenum space. Why is this discussion of office building air handling important in a chapter about cables? Because to run network cable through the ceiling of a building that uses the plenum for return air, you must either install the cable inside special piping, called conduit piping (which is extremely expensive), or use plenum-grade cable. The difference between nonplenum cable and plenum cable is that the plastics used in plenum cable do not give off toxic fumes in case of a fire. Because most office buildings reuse the air in the plenum space, the last thing you would want to happen is to have the cables redistributing toxic fumes if a fire broke out somewhere in the building’s roof or plenum space. A fire in a very small area could cause the fumes from the burning cable to be distributed to a very large area of the building because of how these ventilation systems work—most definitely a Bad Thing. Make sure to check with your cabling contractor for details about the municipality in which you are installing network cable, but virtually all local codes in the United States require either conduit or plenum-grade cable for buildings with plenum air returns. It’s important for the cable installer to be able to handle any required wall penetrations that cross one-hour, fire-rated corridors or building fire zones. Those wall penetrations must be properly sealed to maintain the building’s fire ratings. 54 Networking: A Beginner’s Guide Installing and Maintaining Network Cabling Not only is the selection of a type of network cabling important, but the cabling must be installed correctly. A cable plant installation should include all of the following: N Proper cable and connectors for the type of network, including documentation of the components selected and used. (This is so that people adding to the network in the future can make sure to match these selections.) N Complete labeling of all parts of the network, which should include the wall plates, cables, patch panel ports, patch cables, and hub port assignments. This is important for troubleshooting. N An as-built drawing of the building showing all the cabling routes and locations. N A certification report showing that all the installed cables operate properly using a special network cable test device. CAUTION For bus-type networks, users should be made aware that they should not touch the coaxial cable for any reason whatsoever. The coaxial cable will cause all other nodes in the segment to fail if the cable is separated. Make sure that facilities personnel also know this. Making sure that a new cable plant installation is properly installed and well documented will save you time over the long run. The network will be more reliable and much easier to maintain and repair. Choosing a Cabling Contractor When building a new network, choosing a cabling contractor is extremely important. A contractor who does high-quality, well-documented work is desirable and, unfortunately, hard to find. Make sure that the contractor you choose has a lot of experience installing networks like the one you’re installing. In addition, assess the following issues as part of your selection: N How will the contractor document the cable plant? What are the contractor’s standards, and do you think those documentation standards meet your needs? (Remember that no such thing exists as too much documentation for cable plants.) N Will the contractor provide a set of as-built drawings showing how the cables were installed in the building? N How does the contractor install the cable to avoid electrical interference sources in the ceiling and walls? N Does the contractor recommend a wiring solution that combines telecommunication wiring with data wiring? Generally, keeping these two cable plants separate is best. They have different requirements and respond differently to various building conditions. What works fine for telephones may not work for network cable, and vice versa. 55 Chapter 4: Understanding Network Cabling N Has the contractor done any local installations that you can visit and view? N Does the contractor also provide speedy postinstallation support for new wiring drops? This is important, as many wiring contractors who specialize in new construction wiring are not good about returning to do the occasional single drop for new node locations. Ask for references regarding this important information. N What equipment does the contractor use to certify the cable plant? What certification documentation will the contractor provide upon completion? N Does the contractor also provide postinstallation troubleshooting services? Make sure to spend time finding the best local cable contractors available to you and compare them carefully. You may want to contact other companies like yours, or computer user group members in your area to seek recommendations and learn about their experiences with contractors. Try not to rely on only the references provided by the contractor; even firms that do sloppy work can usually put together a few good references. TIP For a large cabling job, make sure to negotiate an appropriate payment schedule. You should aim for something along the lines of 30 percent on inception; 50 percent on completion; and 20 percent on delivery of as-built drawings, certification reports, and any other final deliverables. Make sure to keep no less than 15 percent for these final deliverables to ensure that the cable contractor provides them expediently. Contractors are notorious for dragging their feet on things like this after the wiring itself is done, so you need to make sure you have a way to motivate them to get everything done. Solving Cable Problems Cable problems can be extremely hard to diagnose and repair. Many cable problems are intermittent or result in reduced network bandwidth for the affected nodes. Tracking down the source of the problem can be difficult. At times, you may not even be aware that there is a problem with the cables! Problems with network cabling typically exhibit themselves in the following ways: N Abnormally slow network performance, particularly if one node is much slower than other, similar nodes (for star networks) or if all nodes on one segment have slower network performance than nodes on other segments (for bus networks) N Sporadic disconnections from the network N Complete loss of network connectivity, which can also be an intermittent problem 56 Networking: A Beginner’s Guide Troubleshooting Star Networks Star networks are the easiest to troubleshoot. Because each node is on its own network cable leading to the hub, you can often quickly isolate the problem to several lengths of cable. If you’re having trouble with a node on a star topology network, first determine if something is wrong with the computer or the cabling. Move the computer to a different location in the building and see if the same problems occur. If they do, then it’s a sure bet the problem is in the computer, such as a failing NIC. If the computer has normal network performance in a different location, try replacing the patch cable leading from the node to the wall. These cables can often become slightly damaged as furniture or computers are moved around. Next, in the wiring closet, you can try connecting the patch panel from the node’s location to a different port on the hub using a different patch cable. While wiring closet patch panels are less likely to fail, because they aren’t moved around much, they can still have poor connections or wiring that can become problematic over time. Finally, if you have eliminated all other factors, consider replacing the cable leading from the wiring closet to the node’s location. At this point, having a qualified network cabling contractor to assist you can be extremely helpful. The contractor has equipment to test the cable in the wall and to determine if it’s bad before pulling a replacement cable through the building. For troubleshooting help, you should expect to pay around $150 for a contractor to come out and test a length of cable. If the contractor must pull a new cable all the way to the location, you’ll also need to pay for labor and materials for that work. Troubleshooting Coaxial Networks Coaxial networks can be difficult to troubleshoot because many nodes share a single segment of the network. Usually, a problem in one part of the segment affects all nodes on the segment similarly. By far, the most common problem on coaxial networks is loss of network connectivity for all the nodes in a segment. Someone disconnecting the network cable so it is not a continuous run invariably causes this loss. Find out who is moving to another office, rearranging an office, painting an office, or performing other work of this type is in the building. The chances are excellent the problem is there. If this fails, then the troubleshooting job becomes much more difficult. To track down cable breaks that aren’t obvious, you can try using a coaxial cable scanner. These are hand-held instruments that can be attached to a coaxial network cable to detect how far along the cable shorts or breaks are occurring. Keep attaching the cable scanner to the network cable in different locations until you can track down the problem. Another approach is to test with an extra terminator for the network. Disconnect the cable in a particular location and attach the terminator. See if the computers on the new, smaller segment can log in to a server. (A server must be available in the same segment; otherwise, you can use the PING command, if you’re using the TCP/IP . that is what you must always use—not any other coaxial cable. Not mixing RG-5 8A/ U and RG-58/U is also a good idea because they have ever-so-slightly different signaling characteristics. (A/ U. aware that they should not touch the coaxial cable for any reason whatsoever. The coaxial cable will cause all other nodes in the segment to fail if the cable is separated. Make sure that facilities. instruments that can be attached to a coaxial network cable to detect how far along the cable shorts or breaks are occurring. Keep attaching the cable scanner to the network cable in different locations