A repeater is a network device that is used to regenerate or replicate signals that are weakened or distorted by transmission over long distances and through areas with high levels of electromagnetic interference (EMI).
The purpose of a repeater is to extend the LAN segment beyond its physical limits (e.g. Ethernet is 500m for 10Base5).
It is a simple hardware device that moves all packets from one local area network segment to another. The main purpose of a repeater is to extend the length of the network transmission medium beyond the normal maximum cable lengths.
Typically, repeaters are used to connect two physically close buildings together (when they are too far apart to just extend the segment). They can be used to connect floors of a building that would normally surpass the maximum allowable segment length.
Repeaters operate at the physical layer, i.e., the bottom layer of the seven-layer OSI reference model. They can only operate on the same type of physical layer, i.e., tthernet-to-tthernet, or token ring-to-token ring. They can connect 10Base5 to 10BaseT because they both use the same 802.3 MAC layer.
Because repeaters provide no isolation between segments, and the repeater is transparent to both sides of the segment, both sides of the repeater appear as one long network segment.
Analog repeaters frequently can only amplify signals. Digital repeaters can additionally reconstruct signals to close to their original quality.
In a data network, a repeater can relay messages between subnetworks that use different protocols or cable types. Hubs can operate as repeaters by relaying messages to all connected computers. A repeater cannot perform the intelligent routing performed by bridges and routers, because it only repeats the signals without understanding the packets, including their sources and destinations.
Unlike bridges and switches, repeaters do not have physical addresses on the network.
It is not permitted to create a loop between two network segments by using two repeaters.
Repeaters provide a simple way to solve the Ethernet distance limitations, but they have some disadvantages. For example, if numerous collisions are occurring in one part of the network, they will be forwarded to other parts of the network.
A hub is essentially a repeater that has multiple ports (i.e., connection points) and can connect more than two network segments.
Created October 4, 2005.