A hub is an element of hardware for centralising network traffic coming from multiple hosts, and to propagate the signal. The hub has a certain number of ports (it has enough ports to link machines to one another, usually 4, 8, 16 or 32). Its only goal is to recover binary data coming into a port and send it to all the other ports. As with a repeater, a hub operates on layer 1 of the OSI model, which is why it is sometimes called a multiport repeater.
The hub connects several machines together, sometimes arranged in a star shape, which gives it its name, due to the fact that all communication coming from the machines on the network passes through it.
Types of hubs
There are several categories of hubs:
"Active" hubs: They are connected to an electrical power source and are used to refresh the signal being sent to the ports.
"Passive" ports: They simply send the signal to all the connected hosts, without amplifying it.
Connecting multiple hubs
It is possible to connect several hubs together in order to centralise a larger number of machines; this is sometimes called a daisy chain. To do this, all that is needed is to connect the hubs using crossover cable, a kind of cable which links the in/out ports on one end to those on the other.
Hubs generally have a special port called an "uplink" for connecting two hubs together using a patch cable. There are also hubs which can cross or uncross their ports automatically depending on whether they are connected to a host or a hub.
Up to three hubs can be chained.
If you want to connect multiple machines to your Internet connection, a hub is not enough. You'll either need to have a router or a switch, or to leave the computer connected directly as a gateway (it will stay on constantly for as long as the other computers on the network want to access the Internet.)
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