All bridges are used to connect two separate network segments and do this while remaining invisible (transparent) to both sides of the bridged connection. A basic bridge listens to all frames being transmitted on each physical network, stores each frame and forwards the frame out ports connected to all LANs except the one it received it on. In this respect, a bridge in this configuration differs from a repeater or hub only in that it stores each frame before forwarding it and transmits the frame when the remote LAN is not busy. This is important in shared media networks such as Ethernet which have limits on the length of the cable. Because hubs transmit each binary bit as they receive it, connecting two Ethernet networks at extreme cable lengths would cause collisions and both networks would eventually grind to a halt. However, a bridged connection stores the whole frame and transmits the frame when the remote LAN is available avoiding the collision. Thus, a bridge can double the range of an Ethernet connection and allow two LANs to communicate. Basic bridges can also allow two different kinds of physical networks to communicate by performing protocol conversion. An Ethernet to Token Ring protocol bridge is a prime example.

 

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