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Explain me the difference between a repeater, bridge and router? Relate this to the OSI model.
Brenton 16-September-2007 06:03:23 PM


Router - 5.5. Repeater - 5.6. Difference between a hub and a switch - 5.7. ... They thus work on level 1, 2 and 3 of OSI model
more details
www.ybet.be/en-hardware-2-05/hub-switch.htm - 38k -
Posted by waqasahmad

Repeaters, bridges, and routers are devices used to link individual LANs together to form larger internet works. Each one operates within a specific layer of the OSI model.
Repeaters operate at the Physical Layer of the OSI model. They simply listen to all network traffic on one port and send it back out through one or more ports, extending smaller networks into a larger, single network. A repeater simply receives frames, regenerates them, and passes them along. It performs no processing of the frames or the data they contain.
Relation to OSI Layer Functions
Because repeaters operate at the Physical Layer, they do not need any addressing data from the frame. Repeaters do not even look at the frames they are forwarding, passing along even damaged frames. This can be especially problematic if one segment malfunctions and begins a broadcast storm. All those erroneous broadcasts are forwarded faithfully by the repeater!
Bridges operate at the Data Link Layer. They use the Data Link Layer and its physical addressing to join several networks into a single network efficiently.
Bridges join two or more network segments together, forming a larger individual network. They function similarly to a repeater, except a bridge looks to see whether data it receives is destined for the same segment or another connected segment. If the data is destined for a computer on the same segment, the bridge does not pass it along. If that data is going to a computer on another segment, the bridge sends it along.
Bridges use a routing table to determine whether data is destined for the local network or not. On a bridge, the routing table contains MAC addresses. Each time the bridge receives data, it looks in its routing table to see whether or not the data is destined for a node on the local network. If it belongs to the local network, it does not forward the data. If it is not destined for the local network, it looks in the routing table to determine which physical network the destination address resides on, and sends the data out onto that network.
Bridges can not join dissimilar networks. If you have an Ethernet network and a Token Ring network, you cannot use a bridge; you must use a router. However, a bridge can join networks that use the same frame type but different media, just like a repeater.
Relation to OSI Layer Functions
Bridges work with the MAC sublayer of the Data Link Layer. Remember that the Data Link Layer is concerned with communicating on the local network only. Bridges use information from the MAC sublayer to make decisions on whether a packet is destined for the same network or another network. The MAC address is used by bridges to determine first if the destination is local or not, then to choose which connected network it must go to.

The Network Layer is concerned with network addressing for larger networks that consist of many physical networks, often with multiple paths between them. Routers operate at the Network Layer. They use the addressing information provided at the network level to join the many networks together to form an internetwork.
Routers divide larger networks into logically designed networks. Routers may seem a lot like bridges, but they are much smarter. Bridges cannot evaluate possible paths to the destination to determine the best route. This can result in inefficient use of network resources. Bridges also cannot use redundant paths. While two bridges can connect two networks, they risk sending packets in an endless loop between the two networks. This behavior eventually saturates the network, rendering it unusable.
The drawback to a routerís inherent intelligence is their speed. Because they process so much information, routers tend to be slower than bridges.
Relation to OSI Layer Functions
Routers operate at the Network Layer of the OSI model. The Network Layer provides addressing for internetworks, and routers use this addressing information to determine how to pass along packets of data. Because routers operate at the Network Layer, they can link different physical network topologies.

Posted by henry

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