Public Switched Telephone Network

Public Switched Telephone Network (PSTN) is an agglomeration of an interconnected network of telephone lines owned by both governments as well as commercial organizations.

It is also known as Plain Old Telephone Service (POTS)
It has evolved from the invention of telephone by Alexander Graham Bell.
The individual networks can be owned by national government, regional government or private telephone operators.
Its main objective is to transmit human voice in a recognizable form.
It is an aggregation of circuit-switched networks of the world.
Originally, it was an entirely analog network laid with copper cables and switches.
Presently, most part of PSTN networks is digitized and comprises of a wide variety communicating devices.
The present PSTNs comprises of copper telephone lines, fibre optic cables, communication satellites, microwave transmission links and undersea telephone lines. It is also linked to the cellular networks.
The interconnection between the different parts of the telephone system is done by switching centres. This allows multiple telephone and cellular networks to communicate with each other.
Present telephone systems are tightly coupled with WANs (wide area networks) and are used for both data and voice communications.
The operation of PSTN networks follows the ITU-T standards.