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A hub joins multiple computers (or other network
devices) together to form a single network segment. Hubs
are actually multiport repeaters. In many cases, the
difference between the two devices is the number of
ports that each provides. While a typical repeater has
just two ports, a hub generally has from four to
twenty-four ports.
Using a hub changes the network topology from a linear
bus, where each device plugs directly into the wire, to
a star. With hubs, data arriving over the cables to a
hub port is electrically repeated on all the other ports
connected to the same network segment, except for the
port on which the data was sent.
Hubs come in three basic types:
• Passive – A passive hub serves as a physical
connection point only. It does not manipulate or view
the traffic that crosses it. It does not boost or clean
the signal. A passive hub is used only to share the
physical media. As such, the passive hub does not need
electrical power.
• Active – An active hub must be plugged into an
electrical outlet because it needs power to amplify the
incoming signal before passing it out to the other
ports.
• Intelligent – Intelligent hubs are sometimes called
smart hubs. These devices basically function as active
hubs, but also include a microprocessor chip and
diagnostic capabilities. Intelligent hubs are more
expensive than active hubs, but are useful in
troubleshooting situations.
Devices attached to a hub receive all traffic traveling
through the hub. The more devices there are attached to
the hub, the more likely there will be collisions. A
collision occurs when two or more workstations send data
over the network wire at the same time. All data is
corrupted when that occurs. Every device connected to
the same network segment is said to be a member of a
collision domain.
Sometimes hubs are called concentrators, because hubs
serve as a central connection point for an Ethernet LAN. |
