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Node A (Computer)                                                   Node B (Computer)
                                            Modem                              Modem
                                                           Telephone line



                                  Digital signal                                     Digital signal
                                                            Analog signal
                                                        Figure 6.21 MODEM

            6.5.8 Router
            Routers are used for connecting various networks. A router may be used to interconnect several networks, possibly
            having different topologies. Also, a router may be used to connect several nodes (computers, mobile phones,
            tablets, etc.) to the Internet. For example, a WiFi router is often used in  homes to connect to the Internet. Each
            router has a routing table that it consults for forwarding an incoming packet to an outgoing line. It examines the
            destination address (IP address) of  a received packet and sends the packet to the appropriate network, keeping
            in view the current information about the network. Figure 6.22 shows a router that is connected to two switches.
            In Figure 6.23, we see several nodes, connected to a router. On receiving a packet from a node, it passes it on to
            the Internet.
                                                              Router


                                                  Switch 1             Switch 2


                                                           Hub




                                                         Figure 6.22 Router


                                        Node 1




                                        Node 1                 Router        to the Internet
                                           a
                                           b
                                           c
                                        Node n

                                                      Figure 6.23 Use of Router

            6.5.9 Gateway

            A gateway is a hardware device that operates as a "gate" between networks. A gateway connects the networks that
            use different protocols. Thus, a gateway may be thought of as a router with protocol conversion software. The data
            from a network that uses a specific protocol is transformed to make it compatible with the outgoing line’s protocol.
            Figure 6.24 shows a switch that acts as a gateway for the data flowing from the server to any node (A-E) or vice versa.
            Also, data from a node (say D) to a node (say A) will flow via the gateway. Figure 6.25 shows two different networks
            connected via a router. Here, the router acts as another gateway. If node B wants to send data to node G, the data will
            flow from node B to its server (gateway), passing through the router (gateway). Subsequently, the router will pass the
            data to the server of the second network, which will pass it on to node G.

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