What is pstn full form ?
The pstn stands for public switched telephone network. As pstn full form have two main things. One is public and another is switched. Public means that the pstn can be connected from any where and switched means the technique for setting up a voice channel. This a the legacy network based on SS7 switching elements . The voice and signaling have two different channels. The full form of pstn is very popular as most of the people in world at any point of time have used pstn phones. No one uses pstn full form while using pstn phones.
There is now newer telephony, called voip. This is based on internet protocols. But the pstn still is the backbone of telephony.