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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.
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.
- Spring '14