PSTN = Public Switched Telephone Network.

Refers to the international telephone system based on copper wires carrying analog voice data (the standard telephone service used when making telephone calls). Technically, it is a collection of interconnected systems operated by various telephone companies and administrations around the world. The main distinctions between PSTN and non-PSTN services are speed and bandwidth. PSTN generally delivers about 52 Kbps (52,000 bits per second).

Non-PSTN services (such as ISDN) are much quicker and involve features that make them preferable for accessing the Internet. (For example, with ISDN or DSL you can use one line for both voice and data versus having to get a second phone line for your Internet connection.)

It started with human-operated, analogue, circuit-switching systems (called plugboards) and has evolved into electromechanical switches so that the transmission is completely digital-except for the final connection to the subscriber (the "last mile") which is why Internet users are opting for DSL, an always-on connection with better speed.

Telephone service carried by the PSTN is often called plain old telephone service (POTS).