A bridge carries out three main functions:
It improves performance by keeping local traffic within a limited part of the LAN.
It makes it possible to build a mixed-speed LAN. For example, traffic must be bridged between a 10Mbps Ethernet segment and a 100Mbps segment, or a 100Mbps segment and a 1000Mbps segment. Note that a 10/100Mbps or 100/1000Mbps "hub" contains a hidden bridge.
It extends the area covered by a LAN. The size of a collision domain is limited by rules that restrict cable lengths and the number of repeatersin a path. The scope of these rules ends when a frame reaches a bridge port. The frame makes a fresh start when it is transmitted out another bridge port.
For example, in Figure 12.1 most of the ...