Repeaters

Network repeaters regenerate incoming signals. On physical media like Ethernet data transmissions can only span a limited distance because the quality of the signal degrades. Repeaters attempt to preserve signal integrity and extend the distance over which data can safely travel.
The actual network devices that serve as repeaters are usually referred to by another name.
Active hubs for example are sometimes called 'multiport repeaters' but usually these are simply referred to as hubs.
Not all hubs are repeaters though.
So called passive hubs retransmit signals but do not regenerate them thus they do not perform the service of a repeater.
Higher-level devices in the OSI model like switches and routers generally do not incorporate the functions of a repeater.
Technically a repeater is a physical layer device.
Suppose data is traveling over a cable.
When the length of the cable keeps on increasing the signal keeps on decreasing.
This happens due to the process of attenuation.
The amount of attenuation depends on the type of media.
A repeater is hence used to amplify the signal and extend the maximum permissible distance for a particular media.
For example the maximum length of an Ethernet cable is 202 yards.
Connecting a repeater at one end would allow the network to be extended by another 202 yards.
Repeaters can be bifurcated into two categories.
Amplifiers
Signal regenerators
Amplifiers simply amplify the signal.
This includes amplification of any noise (disturbances).
Signal regenerators strip out the original signal which has weakened.
After that they build a new signal of the original strength and condition.
Therefore signal regenerators are preferred.
However they are more complicated devices and are slower because of that.
Features of repeaters are described under as follows:
Repeaters work at the physical layer of the OSI model.
Repeaters can connect different types of cable provided they use the same access method.
For example a repeater can connect a 10Base2 Ethernet segment using a thin cable to a 10BaseF Ethernet using a fibre optic cable.
Modular repeaters allow different modules to be selected depending on the types of media to be connected.
A repeater has no packet conversion ability.
Hence we cannot combine Ethernet and token Ring segments using a repeater.
Repeaters are intranetwork connectivity devices and so segments connected by a repeater are treated as belonging to the same network.
A repeater is the cheapest way of expanding a network but it has the least intelligence
They will amplify or rebuild any and every signal passed on to them.
They don't have ability to distinguish between erroneous packets and collisions.
They also have no ability to filter or translate packets.
Repeaters can also be used for emergency standby purposes.
One can add repeaters just so that they are sure that the signal will not weaken at any point.