A switch forwards data only to the intended recipient computer.
Switches offer the following additional benefits over hubs:
• Because of the one-to-one link allowed by a switch, computers linked by a switch can communicate using full duplex, which further increases throughput, particularly when two computers exchange data in both directions.
• The one-to-one link established by a switch lets two computers communicate at their fastest possible speed, even when that speed is faster than is supported by other computers attached to the switch. Hubs, by contrast, force all computers to run at the slowest supported speed. For instance, suppose madison in Figures 17.9 and 17.10 has a 10Mbps NIC, but all the other computers have 100Mbps NICs. In this case, polk and pierce can only transfer data at 10Mbps when a hub is used, whereas they can transfer data at 100Mbps when a switch is used.
• Because Ethernet frames normally go only to the recipient computer, switches make setting up a sniffer on one computer ineffective at retrieving data from other computers on the network. This feature is a major security benefit on networks on which individual computers might be compromised in one way or another. On the other hand, it can be a minus if you want to perform network diagnostics.
All in all, then, switches are superior devices. Why would anybody buy a hub? In a word, cost. Hubs have traditionally cost less than switches. Since 1998, though, the costs of hubs and switches have equalized somewhat. Hubs still cost less than switches, but the difference is less than it used to be.
If you have a small network (say, fewer than half a dozen computers) and don't require the absolute best in speed, a hub can be an acceptable device. If you need the best performance possible, though, or if your network is large or hosts a lot of traffic, a switch is a better choice.
Some devices have some hub-like and some switch-like characteristics. For instance, there are hubs that include two banks of connections, with switch-like communication between the two banks. Such devices can be very useful in reducing network traffic or supporting networks with a mix of 10- and 100Mbps NICs, without going for full switches. Such devices blur the line between hubs and switches, which complicates buying. You should be sure you get a full switch if that's what you want, and not a hybrid device.
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