There are three types of switching used in PSTN network. The circuit switching and message switching were explained in the section 4.7. Circuit switching was designed for voice communication. Circuit switching creates temporary (dialed) or permanent (leased) dedicated links that are well suited to this type of connection. The circuit switching also limits the flexibility and not suitable for connecting variety of digital devices. More efficient utilization of the network requires greater control channel bandwidth and increased call processing capacities in the switches. But the circuit switching not providing these capabilities. Message switching overcomes the limitations of circuits switching. This switching stores the incoming messages into a computer memory and forward it to the destination when available. This causes delay in switching. The packet switching overcomes all the limitations of message and circuit switching. Thus it is highly suitable for the data communication.
The first packet switching system Arpanet, was developed by the U.S. Defence Advanced Research Projects Agency (DARPA) in 1969. The system used PDP-8 minicomputers made by Digital Equipment Corporation as packet switches, which were connected by dedicated 50 kbps telephone lines. Since then, many private and public packet switching networks, notably the X-25 system with speeds varying from 56/64 kbps to 1.5/2 Mbps (T1/E1) have been deployed.
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