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CompTIA A+ Certification All-in-One Exam Guide

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Figure 18-9 A switch

Hubs and switches look pretty much identical and they perform the same

basic job: taking the signal from one host and then repeating the signal out to

other hosts. Even though they look the same and do functionally the same

job, they do the job differently. Basically, hubs were stupid repeaters:

anything sent in one port automatically went out all the other connected ports.

Switches are smart repeaters: they memorize the MAC addresses of all the

connected devices and only send out repeated signals to the correct host. This

makes switched networks much faster than hubbed networks.

A simple example demonstrates the difference between hubs and switches.

Let’s say you have a network of 32 machines, all using 100-Mbps NICs

attached to a 100-Mbps hub or switch. We would say the network’s

bandwidth is 100 Mbps. If you put the 32 systems on a 32-port 100-Mbps

hub, you would have 32 computers sharing the 100 Mbps of bandwidth. A

switch addresses this problem by making each port its own separate network.

Each system gets to use the full bandwidth. The bottom line? Once switches

became affordable, hubs went away.

The connection between a computer and a switch is called a segment.

With most cable types, Ethernet segments are limited to 100 meters or less.

You cannot use a splitter to split a single segment into two or more

connections with an Ethernet network that uses this star bus topology. Doing

so prevents the switch from recognizing which host is sending or receiving a

signal, and no hosts connected to a split segment will be able to

communicate. Splitters negatively affect signal quality.

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