Public switched telephone network

The public switched telephone network (PSTN) is the concatenation of the world's circuit-switched? telephone networks, in much the same way that the Internet is the concatenation of the world's public IP-based packet-switched? networks. Originally a network of analog telephone systems, the PSTN is now almost entirely digital.

The PSTN is largely governed by technical standards created by the ITU-T, and uses E.163/E.164? addresses (known more commonly as telephone numbers) for addressing.

The backbone of the PSTN uses synchronous optical transmission (SONET and SDH?) technology, designed to carry multiples of the basic unit of a 64-kilobit-per-second basic channel, originally designed by Bell Labs as the basis for digital telephony.

Many observers believe that the long term future of the PSTN is to be just one application of the Internet - however, the Internet has some way to go before this transition can be made.

The PSTN was the earliest example of traffic engineering to deliver Quality of Service guarantees. (See the work of A.K. Erlang for some history on this).

Sometimes PSTN is reffered to as POTS, Plain Old Telephony System.