Bridges operate in both the physical and the data link layers of the OSI model. A single bridge connects different types of networks together and promotes interconnectivity between networks together and promotes interconnectivily between networks. Bridges divide a large network into smaller segments. Unlike repeaters, bridges contain logic that allows them to keep separate the traffic for each segment. Bridges are smart enough to relay a frame towards the intended recipient so that traffic can be filtered. In fact, this filtering operation makes bridges useful for controlling congestion, isolating problem links and promoting security through this partitioning of traffic.

A bridge can access the physical addresses of all stations connected to it. When a frame enters a bridge, the bridge not only regenrates the signal but also checks the address belongs. When a bridge ecounters a packet, it reads the address contained in the frame and compares that address with a table of all the stations on both segments. When it finds a match, it discovers to which segment the station belongs and relays the packet to that segment only.


Example :
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When you want to connect the two or more MAN ( metropolytent Area Network), you need bridge. Bridge has decision making logic programs and circuit. It also regenerates the signals and make them strong as the repeater do.