What’s a PSTN?

The PSTN, which stands for the Public Switched Telephone Network, is the collection of circuit-switch public telephone networks. Through the PSTN, homes and businesses are provided landline phone service, also known as Plain Old Telephone Service (POTS).

The PSTN connects all telephone lines through its switching centers, sometimes referred to as a central office (CO) or wire centers. This connection allows phone lines to reach one another through the transfer of voice signals.


A history of the Public Switched Telephone Network

In the late 1800s, before the PSTN, telephones were paired together over individual copper wires. In order to speak with someone, you each needed a connected pair of telephones. There was no ring or signal when one wanted to communicate with the other – one had to whistle or yell loudly simply to grab the other’s attention.

As telephones rapidly increased in popularity, the demand for the Public Switched Telephone Network arrived. Telephones then were connected to a local telephone exchange via a copper wire.

Eventually, this worldwide telephone network was as widespread as the telegraph network once was. Today, we have an international landline phone service network.


What happens when a call is made over the Public Switched Telephone Network?

POTS, which is carried over the PSTN, remains a popular form of communication for both homes and businesses. When a call is made over landline, the PSTN network carries analog voice data over copper wires. The voice data is eventually converted into electrical signals. These signals are then routed through the switching centers, which allow for connection and, ultimately, communication.

The PSTN allows for both local and long distance calls. Communication is bidirectional over phone lines, meaning one caller can both speak and be heard by the other caller, and vice versa. Service is available for any subscriber, making landline phone service a very accessible form of communication.