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■    Bus

■    Ring

■    Star

■    Mesh

■    Wireless


In a bus topology, all computers are attached to a single continuous cable that is terminated at both ends, which is the simplest way to create a physical network. Originally, computers were attached to the cable with wire taps. This did not prove practical, so drop cables are now used to attach computers to the main cable. Figure 1.5 shows an example of a bus network. Notice how the cable runs from computer to computer with several bends and twists.

FIGURE 1.5 An example of a physical bus topology

When communicating on a network that uses a bus topology, all computers see the data on the wire. This does not create chaos, though, because the only computer that actually accepts the data is the one to which it is addressed. You can think of a bus network as a small party. David is already there, along with 10 other people. David would like to tell Joe something. David yells out, “Joe! Will you grab me a cup of coffee, please?” Everyone in the party can hear David, but only Joe will respond. A star network with a hub, which you’ll read about later in this section, also operates in this manner.

Real World Scenario

A bus sounds good, but . . .

Despite the simplicity of the bus topology, there are some inherent disadvantages to this design. For example, what happens if the wire breaks or is disconnected? Neither side can communicate with the other, and signal bounce occurs on both sides. The result is that the entire network is down. For this reason, bus topologies are considered to have very little fault tolerance.

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