PSTN

A Public Switched Telephone Network, or PSTN for short, refers to a telecommunications network which allows subscribers at different sites to communicate by voice. The term plain old telephone service (POTS) is also frequently used. The features of a PSTN are:
 

• Subscribers can be connected by entering telephone numbers
• The existing connections are primarily used to transmit speech information
• After hanging up the connection is closed and the resources used become available to other subscribers

The term public switched telephone network is primarily used for public landlines. With traditional analogue landlines speech is transmitted analogue, a ISDN network transmits speech information digitally.