Time constant of the information upon which the

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Unformatted text preview: l. Packet Switching This method works in a similar fashion as message switching. However, it overcomes the disadvantages of message switching technique because in this method routing is done on 'packet' basis and not on 'message' basis. A message is split up into 'packets' of a fixed size (of the order of one or few thousand bits). Besides the block of data (part of a message) to be sent, a packet has a header that contains the destination and source addresses, control information, message number, number of current and last packet, synchronization bits, acknowledgement and error checking bytes, etc. Like message switching, the packets may be routed from the sender node to the destination node either by store-and-forward method or by broadcast method. In the store-and-forward method, the packets are stored temporarily at the intermediate nodes for error recovery purposes and are routed to the next node based on an available free channel. The actual path taken by the packet to its destination is dynamic as the path is established as it travels along. Thus, it is possible that different packets of the same message can be routed across different paths leading to the same destination depending upon line availability and congestion. Packet switching is used in the X.25 public packet network and the Internet. Advantages 1. Unlike messages, packets are of small and fixed size. Hence the storage requirement for buffering the packets at intermediate nodes is minimal. 2. Since the routing is done on packet basis, the intermediate nodes do not have to wait for the entire message, hence the transmission is very fast. 3. The method is fast enough for interactive/real-time applications. 4. It is most suitable for "bursty" computer-to-computer communication and is widely used in wide area networks. Disadvantages 1. Due to the need to buffer each packet at every intermediate node and to reassemble the packets at the destination node, the overhead incurred per packet is large. 2. There is no guarantee of how long it takes a message to go from its source node to its destina...
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This document was uploaded on 04/07/2014.

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