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
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
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.