4 - The public switched telephone network (PSTN)

Abstract

This chapter discusses the concept of the public switched telephone network (PSTN). The PSTN provides the communications infrastructure to carry voice and data locally, nationally or internationally throughout the world. It has evolved from being an analog, voice-only, communications network to a sophisticated high-speed digital network capable of carrying any form of data communications, including digitized speech. The PSTN is made up of local networks connected by a long-distance network. The PSTN is used to provide connections between end-users. The local network comprises the end users and circuits connecting them to local switching points called “nodes.” The nodes switch the communications traffic from the originating local network to the destination local network by means of trunks. PSTN circuits are increasingly used to carry data, particularly for Internet access. Some technologies enable all or part of the PSTN to be bypassed. These include private networks operated by private service providers or utilities, such as railway or power companies and satellite systems enabling direct customer-to-customer communication.