History: Bridges

￿Store and forwarding according destination MAC address

￿Separated collision domains

￿Improved network performance

￿Still one broadcast domain

Three collision domains in this example !

(C) Herbert Haas 2005/03/11

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Bridges were invented for performance reasons. It seemed to be impractical that each additional station reduces the average per-station bandwidth by 1/n. On the other hand the benefit of sharing a medium for communication should be still maintained (which was expressed by Metcalfe's law).

Bridges are store and forwarding devices (introducing significant delay) that can filter traffic based on the destination MAC addresses to avoid unnecessary flooding of frames to certain segments. Thus, bridges segment the LAN into several collision domains. Broadcasts are still forwarded to allow layer 3 connectivity (ARP etc), so the bridged network is still a single broadcast domain.

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