Tuesday, January 20, 2009

Understanding Bridges

A bridge is an electronic device that is used to connects two LAN segments.Unlike a repeater,however a bridge is a digital device that uses the same network interface as a conventional computer and handles frames.The bridge listen to traffic on each segment in promiscuous mode.When it receives a frame from one segment,the bridge verifies that the frame arrived intact i.e there was no electrical interference on LAN during transmission and after that it forwards a copy of the frame to the other segment if necessary.Thus,two LAN segments behave connected by a bridge behave like a single LAN.A computer connected to either segment can send a frame to any of the other computers connected to the two segments.Because each segment supports standard network connections and uses the standard frame format that means computers do not know whether they are connected to a LAN or a bridged LAN.

When we compare bridges with LAN it is found that bridges are more useful and popular than repeaters because they help isolate problems.If two segments are connected by a repeater and lightning causes electrical interference on one of them,the repeater will propagate the interference to the other segment.In contrast if interference occurs on one of the two segments connected by a bridge,the bridge will receive an incorrectly formed frame,which the bridges simply discards the same way a conventional computer discards a frame that contains an error.Similarly,a bridge will not forward a collision from one segment to another.Thus,the bridge keeps problems on one segment from affecting the other.

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