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Sometimes, because a cable is inside a wall, you cannot physically see a break. To determine if a break has occurred, you can use a tool known as a Time Domain Reflectometer, or TDR (also called a cable tester). This device sends out a signal and measures how much time it takes to return. Programmed with the specifications of the cable being tested, it determines where the fault lies with a high degree of accuracy. We’ll discuss cable testers in Chapter 6, «Network Installation and Upgrades.»

As with most things, there are pros and cons to a bus topology. On the pro side, a bus topology:

■    Is simple to install

■    Is relatively inexpensive

■    Uses less cable than other topologies On the con side, a bus topology:

■    Is difficult to move and change

■    Has little fault tolerance (a single fault can bring down the entire network)

■    Is difficult to troubleshoot


Unlike those in a bus topology, each computer in a star topology is connected to a central point by a separate cable. The central point is a device known as a hub. Although this setup uses more cable than a bus, a star topology is much more fault tolerant than a bus topology. This means that if a failure occurs along one of the cables connecting to the hub, only that portion of the network is affected, not the entire network. It also means that you can add new stations just by running a single new cable. Figure 1.6 shows a typical star topology.

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