Question: what are hub,switch and repeaters? 

Answer: A hub links multiple systems via ethernet into a single network. Anything which is sent to the hub is sent back out to all the other machines on the network.\n\nA switch is a smarter hub. It keeps a record of the network addresses of the machines and other networks connected to it. When data comes in, the switch sends it out only to the machine or network that it needs to be sent to, rather than to everyone. This improves network efficiency.\n\nA router is a smarter switch. As well as doing what a switch does, it can also implement complex rules like "To get to address X, send to address Y and that machine will forward it", or "If you receive data for address A, re-write it to say it's for address B, and send to machine C."\n\nA repeater takes the incoming signal, decodes it to digital data, and then sends the same signal back out as a clean copy.
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