Repeaters are needed when copper wire communication is takes place. According to the fact that electrical signal goes weaker while travelling over copper lines. A repeater is used to gain the signal strength. It amplifies the weakening signal received from one packet and then retransmits onto another packet. It is given in the figure below:
One repeater doubles, two repeaters triple the highest cable length limitation.
Devices attached to different code segments communicate as if they are connected to the similar cable.
It is to be noticed that we cannot increase the maximum cable length as several times as we wish by just including repeaters. The reason for this is that each repeater produce a delay and the access function such as CSMA/CD does not work with long time delays.
Ethernet standard specifies that any two stations may not be distinguish by more than four repeaters.
The diagram displays repeaters using the vertical code segment. We see that only two repeaters differ any two stations in this function.
DISADVANTAGES OF REPEATERS:
Repeaters do not known frame formats, they just retransmit and amplify the electrical signal. If a error or collision happens in one segment, repeaters retransmit and amplify also the error onto the other code segments.