A hub is a common wiring point for star-topology networks, and is a common synonym for concentrator (though the latter generally has additional features or capabilities). Arcnet, 10BaseT Ethernet and 10BaseF Ethernet and many proprietary network topologies use hubs to connect multiple cable runs in a star-wired network topology into a single network. Token-Ring MSAUs (Multi-Station Access Units) can also be considered a type of hub, but don't let a token-ring bigot hear that. Hubs have multiple ports to attach the different cable runs. Some hubs (such as 10BaseT and active Arcnet) include electronics to regenerate and retime the signal between each hub port. Others (such as 10BaseF or passive Arcnet) simply act as signal splitters, similar to the multi-tap cable-TV splitters you might use on your home antenna coax (of course, 10BaseF uses mirrors to split the signals between cables). A Hub is basically a repeater of data packets distributed to all active connections in the network. The unfortunate downside of a HUB is the fact that is can collide.

A Collision is a condition where two devices detect that the network is idle and end up trying to send packets at exactly the same time. (within 1 round-trip delay) Since only one device can transmit at a time, both devices must back off and attempt to retransmit again. The retransmission algorithm requires each device to wait a random amount of time, so the two are very likely to retry at different times, and thus the second one will sense that the network is busy and wait until the packet is finished. If the two devices retry at the same time (or almost the same time) they will collide again, and the process repeats until either the packet finally makes it onto the network without collisions, or 16 consecutive collision occur and the packet is aborted.