It was designed specifically for the transmission of voice communication. This is a public network designed specifically for the transmission of digital data. Many countries of the world are introducing PSDN services. They can support much higher transmission rates. At the present time the world's communication systems are in a state of flux.
Public networks employ two types of switching.
Switching describes the method by which the corresponders are connected. The PSTN is a circuit switched network. The packets are then forwarded through the network, together with many other packets. These are locally distributed on arrival. The Post Office is a packet switched network.