Telemarketing can also include recorded sales pitches programmed to be played over the phone via automatic dialing. Telemarketing has come under fire in recent years, being viewed as an annoyance by many.
The public switched telephone network (PSTN) also referred to as the Plain Old Telephone Service (POTS) is the network of the world's public circuit-switched telephone networks. It is a worldwide net of telephone lines, fiberoptic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables connected by switching centers, which allows any telephone in the world to communicate with any other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core and includes mobile as well as fixed telephones.
The technical operation of the PSTN utilises standards created by the ITU-T. These standards allow different networks in different countries to interconnect seamlessly. There is also a single global address space for telephone numbers based on the E.163 and E.164 standards.
The combination of the interconnected networks and the single numbering plan make it possible for any phone in the world to dial any other phone.
A public switched data network (PSDN) is a publicly-available packet-switched network, distinct from the PSTN.
Originally this term referred only to Packet Switch Stream (PSS), an X.25-based packet-switched network, mostly used to provide leased-line connections between local area networks and the Internet using permanent virtual circuits (PVCs). Today, the term may refer not only to Frame Relay and Asynchronous Transfer Mode (ATM), both providing PVCs, but also