| Ethernet LANs that use a bridge for segmenting the LAN
provide more bandwidth per user because there are fewer users on the segments than there
are when compared to the entire LAN. The bridge allows only those frames
that have destinations outside the segment to pass through. Bridges
learn a network’s segmentation by building address tables that
contain the physical address of each network device, as well as the
port to use to reach the device. Bridges differ from routers because
they are Layer 2 devices, and are, therefore, independent of Layer 3 protocols. Bridges
pass on data frames, regardless of which Layer 3 protocol is used, and are transparent to
the other devices on the network. Bridges increase
the latency (delay) in a network by 10-30%. This latency is due to the decision
making that is required of the bridge, or bridges, when transmitting data to the correct
segment. A bridge is considered a store-and-forward device because it must receive the entire frame and compute the cyclic redundancy check (CRC) before forwarding can take
place. The time it takes to perform these tasks can slow network
transmissions, thus causing delay.
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