Public Switched Telephone Network (PSTN)

What is PSTN (Public Switched Telephone Network)?

The PSTN, short for Public Switched Telephone Network, is a global telecommunications network that enables the transmission of voice, data, and multimedia over traditional landline telephone systems. It serves as the foundation for worldwide telecommunication, allowing people to connect with each other using standard telephone lines. The PSTN is operated and maintained by telecommunications carriers, who establish the infrastructure necessary for communication to take place.

How does PSTN work?

The PSTN works through a complex network of physical connections and switching centers. When a person places a call, their voice is converted into analog signals by their telephone device. These analog signals travel over copper wires to a local exchange, where they are routed to the appropriate destination. The local exchange may connect the call to another local exchange or to a long-distance exchange.

Within the PSTN, various types of switching equipment are used to direct calls to their destinations. Initially, mechanical switches were employed, but digital switches have largely replaced them. These switches determine the most efficient path for a call based on the dialed number and establish a connection between the caller and the recipient.

What is the basic principle of PSTN?

The basic principle of the PSTN is to establish a connection between two telephone devices to enable communication. The PSTN achieves this by converting analog signals into digital format for transmission over the network. Analog signals, generated by voice or data, are converted into digital signals using codecs (coder-decoder) at the sender's end. These digital signals are then transmitted over the PSTN using various multiplexing techniques.

Once the digital signals reach the recipient's end, they are converted back into analog signals so that the receiving telephone device can understand them. This conversion is accomplished by codecs present at the receiver's end. The PSTN ensures that the entire signal conversion and transmission process occurs seamlessly, allowing people to communicate over long distances.

What is an example of a PSTN?

One example of a PSTN application is mobile communication. Although mobile networks primarily rely on wireless technology, they still interface with the PSTN for various services. When a mobile user places a call on a landline phone, the call is routed through the mobile network's base station to the nearest mobile switching center (MSC). The MSC then connects the call to the PSTN via a PSTN gateway.

The PSTN gateway acts as an interface between the mobile network and the traditional PSTN. It facilitates the conversion of signals between the two networks, allowing seamless communication between mobile and landline devices. When the call reaches the PSTN, it follows the same principles as described earlier to reach the recipient's landline phone.

In addition to voice calls, the PSTN also supports various other services such as fax transmission, data transfer, and signaling for services like caller ID and call waiting. These services rely on the robust infrastructure and extensive reach of the PSTN to ensure reliable and efficient communication.