Bridges, repeaters and gateways:

Workstations in one network often need access to computer resources in another network or another part of a WAN. For example, an office manager using a local area network might want to access an information service that is offered by a VAN over the public phone system. In order to accommodate this type of need, bridges and routers are often necessary.
Bridges: The main task of a bridge computer is to receive and pass data from one LAN to another. In order to transmit this data successfully, the bridge magnifies the data transmission signal. This means that the bridge can act as a repeater as well as a link.