Hubs/repeaters are used to connect together 2 or more Ethernet segments of Amy media type.In larger designs,signal quality begins to deteriorate as segments exceed their maximum length. Hubs provide signal amplification required to allow a segment to be extended a greater distance. A hub takes any incoming signal and repeats it out -all ports.
Ethernet hubs are necessary in star topologies as IOBaseT.A very important fact to note about hub us that they only allow users to share Ethernet.
Hubs are mandatory in IOBaseT twisted pair Ethernet as well as Token Ring n/ws.They are also used to replace the daisy chain cabling in 10Base 5 and 10Base2 coaxial Ethernets in order to improve n/w management.
In Token Rings,the hub is called a MAU(multi-station Access Unit).
There are 3 types of hubs:
Passive hub: simply combines the signals of n/w segments. There is no signal processing of regeneration.
Active hub: are like passive hub except that they have electronic components that regenerate or amplify signals.
Intelligent hub: In addition to signal regeneration, intelligent hubs perform some n/w management and intelligent path selection.