Public switched telephone network

The public switched telephone network (PSTN) is the network of the world's public circuit-switched telephone networks, in much the same way that the Internet is the network of the world's public Internet protocol-based, packet-switched networks. Originally a network of fixed-line, analog telephone systems, the PSTN is now almost entirely digital, and now includes mobile as well as fixed telephones.

The PSTN is largely governed by technical standards created by the ITU-T, and uses E.164 addresses (known more commonly as telephone numbers) for addressing.