2. Circuit switching

The telephone system in the UK used to use a technique called 'circuit switching' to let two telephones (or computers) connect across the national network.

Circuit switching enables you to send digital messages across a network by setting up a physical path between the sender and receiver. This is done using wires or fibre optic cable and is set up prior to transmission of the message. The path remains open throughout the communication and is only released for use by others once the message is complete.

• Very inefficient - once the connection is made, the line is tied up and no one else can use them, even if no data is passing between them.
• Difficult to scale up the network to deal with millions of devices.
• Every connection would have to be capable of supporting the maximum bandwidth required. This was no problem for voice calls as a voice call needs a very low bandwidth (3KHz), but not when bandwidths of 100Mbps + are needed.