2 since the physical link is a dedicated one the

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Unformatted text preview: ipment usually costs more. SWITCHING TECHNIQUES In its simplest form, data communication takes place between two devices that are directly connected by some form of transmission medium - twisted wires, coaxial cables, microwave and satellite links. Often however, it is impractical or uneconomical for two devices to be directly connected. Instead, communication is achieved by transmitting data from source to destination through a network of intermediate nodes. These nodes provide a switching facility that moves data from node to node until the destination is reached. There are three different methods of establishing communication links between the sender and receiver in a communication network, namely, circuit switching, message switching and packet switching. They are briefly described below. Circuit Switching It is the simplest method of data communication in which a dedicated physical path is established between the sending and receiving stations through the nodes of the network. This method is used to connect two subscribers for a telephone conversation. Network computers and terminals connected to a telephone network also use this method of establishing communication path among them. The method of circuit switching is illustrated in Figure 17.16. Each rectangle represents a switching node of the communication network. When a message is to be communicated, a physical path is established between the sending station and the receiving station by physically connecting the incoming and outgoing line of each of the intermediate switching nodes that fall on the path. Once a circuit is established between the two stations, it is exclusively used by the two parties and the dedicated physical link between both ends continues to exist until the call is terminated either by the sender or the receiver. As soon as the connection is terminated by one of the two stations, the dedicated resources are deallocated and can now be used by other stations also. Thus circuit switching involves three phas...
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This document was uploaded on 04/07/2014.

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