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Repeater                            Repeater



















                                                        Figure 6.17 Repeater

            6.5.4 Hub

            A hub comprises several ports, each of which connects to a single cable. A hub transmits the data arriving on any
            incoming line to all the connected lines. A hub is used for communication up to  200 meters. A hub may be categorised
            as passive and active. A passive hub copies a signal on the outgoing lines as it is received. An active hub intensifies
            the incoming signals before forwarding them. A hub may support 8, 12, or 24 RJ-45 connections. If the two nodes
            connected to a hub attempt to send a message simultaneously, a collision is said to occur. However, it is easy to
            resolve the problem of collisions. Each node waits for a randomly chosen amount of time and communicates again
            so that a collision is improbable to follow another. Figure 6.18 illustrates the use of a hub in a network that uses star
            topology. Node D sends a message (addressed to node B) to the hub. On receiving the message from node D, the
            hub forwards it to all the connected nodes. As the message is intended for node B,  node B accepts it, while all other
            nodes discard it.



                                                                 Hub







                      Discarded                                                                     Source
                                            Destination       Discarded






                                                                                                  D
                                A                     B                      C
                                                          Figure 6.18 Hub

            6.5.5 Bridge

            A bridge is a multiport device that connects two or more Local Area Networks (LANs)  to form an extensive network.
            Thus, the devices on one LAN segment can communicate with the devices on another segment. Unlike a hub, a bridge
            is an intelligent device that exercises discretion while forwarding data. When a bridge receives a frame from a LAN
            segment, it examines the destination address of the incoming frame and forwards it to the appropriate LAN segment.
            Before transmitting a frame to the outgoing line, it regenerates the signal. Different LAN segments may operate at
            different speeds.



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