Concentrators / Hubs

A concentrator is a device that provides a central connection point for cables from workstations, servers and peripherals. In star topology, twisted-pair wire is run from each workstation to a central concentrator. Hubs are multi slot concentrators into which can be plugged a number of multi-port cards to provide additional access as the network grows in size. Some concentrators are passive, that is, they allow the signal to pass from one computer to another without any change. Most concentrators are active, that is, they electrically amplify the signal as it moves from one device to another. Active concentrators are used like repeaters to extend the length of a network.
Concentrators are:

1. Usually configured with 8, 12, or 24 RJ-45 ports
2. Often used in a star or star-wired ring topology
3. Sold with specialized software for port management
4. Also called hubs
5. Usually installed in a standardized metal rack that also may store netmodems, bridges, or routers.