The public telephone network managed by the local telco and long-distance carriers. The Public Switched Telephone Network (PSTN) consists of a digital backbone of switched circuits together with the analog local loop wiring still found in many residences. The PSTN is also known as the Plain Old Telephone Service (POTS), although that term specifically relates to the older, nondigital portion of the PSTN.
The PSTN provides the most popular basis for creating wide area networks (WANs) through both leased lines and dial-up lines between local and remote networks.
PSTN is often used in wide area networking because of its ubiquitous nature - local loop connections exist almost everywhere in the world.