A repeater (or re generator) is an electronic device that
operates on only the physical layer of the OSI model. Signals that carry
information within a network can travel a fixed distance before attenuation (weakening
of the signal due to friction) or interference from noise endangers the integrity
of the data. A repeater installed on a link receives the signal before it
becomes too weak or corrupted.Regenerates the original bit pattern.and puts the refreshed
copy back onto the link. In effect, the signal with the corruption removed, is
transmitted a second time from a location closer to the destination.
A repeater allows us to extend only the physical length of a
network. The repeater does not change the functionality of the network in any
way.The two sections connected by the repeater in the following figure :
In really one network,if station A sends a frame to station B,all stations(including C and D) will receive the frame.Just as they would without the repeater. The repeater does not have the intelligence to keep the frame from passing to the right side when it is meant for a station on the left.The difference is that with the repeater,stations C and D receive a truer copy of the frame than would otherwise have been possible.
Not and amplifier
It is tempting to compare a repeater to an amplifier,but the comparison is inaccurate.An amplifier cannot discriminate between the intended signal and noise: it amplifies equally everything fed into it.A repeater does not amplify the signal, it regenerates it.When it receives a weakened or corrupted signal.It creates a copy bit for bit at the original strength.
A repeater is a regenerator not an amplifier.
The location of a repeater on a link is vital.A repeater must be placed so that a signal reaches it before any noise changes the meaning of any of its bits.A little noise can alter the precision of a bit's voltage without destroying its identity.If the corrupted bit travels much farther.However,accumulated noise can change its meaning completely.At that point the original voltage becomes unrecoverable and the error can be corrected only by retransmission. A repeater placed on the line before the legibility of the signal becomes lost can still read the signal well enough to determine the intended voltages and replicate them in their original form.
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