Switches: How to Create Dozens of Lanes on the
LAN
LAN switches provide the same cabling advantage that hubs do,
while providing significant performance improvements. For example, you can run a
single cable from each device to the wiring closet and connect those cables to a
switch instead of a hub. You get much better cable management.
To appreciate why switches perform better than hubs, you need
to consider the logic that a switch uses and compare it to the logic that a hub
uses. A switch allows every device on the LAN to communicate with every other
devicethe same result as when using a hubbut using different logic, which is
summarized as follows:
When receiving a frame, examine the destination Ethernet
address. Forward the frame out the one portand only that portthrough which that
address can be reached.
So, in comparison to a hub, a switch does not simply repeat the
electrical signal out all other ports. Instead, a switch forwards frames
selectivelyonly forwarding the frame where it really needs to go. Switch logic
actually examines the contents of the Ethernet frame and finds the destination
Ethernet MAC address to make an intelligent decision. Figure 6-2 illustrates the logic, with Fred sending to
Barney.
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