The Full Form of GSTN is‍ General Switched Telephone Network.

The general switched telephone network (GSTN) is the international public telephone networks which comprise the national Public Switched Telephone Networks (PSTNs) and all the technologies and facilities that interconnect them.

The GSTN is an encompassing name for the various types of telephony networks being used around the world. It includes Asynchronous Transfer Mode (ATM), Public Switched Telephone Networks (PSTN), Integrated Services Digital Networks (ISDN), and all wireless networks and private networks.

It also includes all of the interconnecting facilities that connect these networks. The term is rarely used outside of ITU-T papers, with PSTN being the term widely used to refer to telephony networks. Even as the term gained wide usage, it was still used to refer to the US PSTNs, instead of referring to the international connectivity of these networks.

Since GSTN refers to generally all of telecommunication networks, some of its sections are used for VoIP, Digital Subscriber Line (DSL), and many other internet-based networking infrastructure and technologies as well as being directly connected to most IP networks.