What is PSTN?
The Public Switched Telephone Network (PSTN) refers to the international telephone system that uses copper wires to carry analog voice data. It consists of a collection of individual telephones that are hardwired to a public exchange.
The Public Switched Telephone Network was formerly known simply as the public telephone network.
The original concept was that the telephone exchanges are arranged so that if a call cannot be handled in a local cluster, it is passed to one higher up for onward routing. This reduced the number of connecting trunks required between operators over long distances and also kept local traffic separate.