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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.
Computer Networks 233

