Networking: A Beginner's Guide Fifth Edition- P12

Networking: A Beginner’s Guide Fifth Edition- P12:I have run into many people over the years who have gained good evenimpressive working knowledge of PCs, operating systems, applications,and common problems and solutions. Many of these people are wizards withdesktop computers.
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Networking: A Beginner’s Guide Fifth Edition- P12Chapter 4UnderstandingNetwork Cabling 3738 Networking: A Beginner’s Guide I f you were to compare a computer network to the human body, the network cabling system would be the nerves that make up the physical manifestation of the nervous system. The network cabling system is what actually carries all the data from one point to another and determines how the network works. How a network is cabled is of supreme importance to how the network functions, how fast it functions, how reliable the network will be as a whole, and how easy it will be to expand and change the network. With any new network, your first task after assessing the needs for the network is to determine how the network should be wired; all the other components of the network are then built on that foundation. This is much like the OSI seven-layer model you learned about in Chapter 3, in that the network cabling makes up layer 1 (the physical layer), and all the upper networking layers rely on it. Many people think that network cabling is relatively simple. After all, what could be simpler than running a wire between two points? However, as you will see, the topic of network cabling encompasses more than meets the eye, and it’s an extremely important area to get right. If you make mistakes selecting or installing network cable, your network will likely be unreliable and may perform poorly. Because of the labor costs involved in wiring a network, the best time to address any potential problems in this area is well before they occur. Understanding Cable Topologies The word topology basically means shape, and the term network topology refers to the shape of a network—how all of the nodes (points) of a network are wired together. Networks may be wired in several different topologies, and the choice of a topology is often your most important decision when you plan a network. The topologies have different costs (both to install and maintain), levels of performance, and levels of reliability. DEFINE-IT! Network Segment The term network segment can mean somewhat different things depending on the topology of the network, but the concept is simplest to understand when thinking about a bus network, and is essentially the same for any topology. A segment is a single length of cable to which all the nodes in that segment are connected. In truth, a segment is not a single continuous length of cable, because it is broken at each computer connection point with a connector that lets the node connect to the network cable, but the cable is electrically one single cable. In any given segment, all the network traffic is “seen” by all the nodes on that segment. You need to take this into account when planning how many nodes you will connect to any given segment. If you have 20 computers, all fully using that segment at the same time, each computer will achieve only approximately one- twentieth of the available maximum bandwidth. This is simplified; you will learn more about how this works later in this chapter and in following chapters. Chapter 4: Understanding Network Cabling 39 The main topologies in use today are bus, star, and ring. These topologies are described in this section.Bus Topology A bus topology, more completely called a common bus multipoint topology, is a network where, basically, a single network cable is used from one end of the network to the other, with different network devices (called nodes) connected to the cable at different locations. Figure 4-1 illustrates a simple bus topology network. Different types of bus networks have different specifications, which include the following factors: How many nodes can be in a single segment How many segments can be used through the use of repeaters How close nodes can be to each other The total length of a segment Which coaxial cable type is required How the ends of the bus must be terminated Bus topology networks use coaxial cable, described later in this chapter. Each end of each segment of the network has a special cable terminator on it, without which the network will not function. Some bus topology networks, such as Thin Ethernet (10Base-2) use BNC connectors to tie all the individual pieces of cable together. Each computer is connected to the network through the use of a BNC T-connector (called that because it’s shaped like the letter T), whic ...