5.1 | Cabling the LAN | |||
5.1.7 | Hubs |
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.
Hubs are most commonly used in Ethernet 10BASE-T or
100BASE-T networks, although there are other network architectures
that use them as well.
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:
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.
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