Network Topologies

The arrangement of cables between computers cannot be random; it must follow specific rules. These rules are determined by the network technology, and the result is referred to as the network topology. Three topologies are in common use on small networks today:

• Bus A bus topology links each computer to two others, except for the computers at the ends of the bus. The result is a chain of computers, as depicted in Figure 17.3. The coaxial Ethernet technologies and LocalTalk use bus topologies.

Figure 17.3

The bus of a bus topology links all the computers in a line.

Figure 17.3

The bus of a bus topology links all the computers in a line.

• Ring A ring is much like a bus topology, except that the bus loops back on itself. The result is depicted in Figure 17.2. The ring portion of Token Ring derives from the fact that Token Ring uses this topology in its hubs.

• Star A star topology links all the computers to a central point, as shown in Figure 17.4. This central point is a networking device known as either a hub or a switch in Ethernet networks. (The differences between hubs and switches are discussed later in the chapter.) Twisted-pair Ethernet networks use the star topology. Token Ring networks are wired in the same way; the ring of these networks is implemented internally to the Token Ring hub.

If you examine Table 17.1, you might think that the star topology twisted-pair networks suffer relative to their coaxial cable counterparts in terms of the size of the network that's supported. This isn't usually the case, however. The cable length limit for the coaxial technologies refers to the entire length of the bus, whereas the cable length limit for twisted-pair Ethernet refers to the length of the cable from one device to the hub. Therefore, unless the computers are strung out in a straight line, the star topology and twisted-pair cabling actually allow you to connect computers over a wider area than do the coaxial technologies. In fact, even in a straight line, twisted-pair wins over thin coaxial, because if you place a hub at the midpoint of the line, cables can extend from the hub 328 feet in each direction, for a total linear extent of 656 feet, which is slightly greater than the 607-foot limit of thin coaxial cabling.

Chapter 17

Figure 17.4

All network traffic passes through the central device in a star topology network.

Figure 17.4

All network traffic passes through the central device in a star topology network.

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