Ethernet hub

In addition to standard 8P8C ("RJ45") ports, some hubs may also come with a BNC or an Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments.

Hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications.

[3][4][5] A layer 1 network device such as a hub transfers data but does not manage any of the traffic coming through it.

It is aware of physical layer packets, that is it can detect their start (preamble), an idle line (interpacket gap) and sense a collision which it also propagates by sending a jam signal.

[7] For 100 Mbit/s networks, the limit is reduced to three segments between any two end stations, and even that is only allowed if the hubs are of Class II.

Hubs suffered from the problem that if there were any 10BASE-T devices connected then the whole network needed to run at 10 Mbit/s.

Class II hubs delay the signal for a maximum of 92 bit times.

This shorter delay allows the installation of two hubs in a single collision domain.

[8] Repeater hubs are defined in the standards for Gigabit Ethernet[9] but commercial products have failed to appear[10] due to the industry's transition to switching.