PSTN is an acronym for Public Switched telephone network and is the global collection of interconnected voice-oriented public telephone networks, both government-owned and commercial. PSTN is also called the Plain Old Telephone Service (POTS). It is the aggregation of circuit-switching telephone networks.
Except for the final link from the central-local telephone office to the user, PSTN is almost digital in technology today. For free and easy communication within businesses.