What Is PSTN?

PSTN is the network of the familiar, but vanishing, landline phone

The Public Switched Telephone Network (PSTN), also known as POTS (Plain Old Telephone System), is used for the landline telephone system. PSTN was created primarily for analog voice communication over cables that covered countries and continents and was an improvement over the basic telephone system of Alexander Graham Bell. It brought better management and helped turn telephone communications into a lucrative and revolutionary industry.

The PSTN and Other Communication Systems

Mobile telephony has emerged as the first alternative to PSTN in voice communication, overcoming PSTN's inability to make and receive calls without being physically connected to a landline.

Person using a smartphone with a house with a landline

Lifewire / Evan Polenghi

Until relatively recently, PSTN was the default for most people. Most homes and businesses had landlines. Plus, the PSTN was the main carrier for internet connectivity in some parts of the world. Even using alternative means of communication such as VoIP and other OTT technologies often required a PSTN line for internet connectivity.

All this has changed, however. Most people carry cellphones now, and internet access is no longer analog in most areas.


VoIP was a serious competitor to PSTN because it allowed people to communicate locally and worldwide for free or at a low cost. Think of Skype, WhatsApp, and the other VoIP services and apps, some of which were banned in some countries to protect the local or government-owned telephone companies.

Skype online with the Calls button highlighted

How the PSTN Works 

In the early days of telephony, establishing voice communication between two parties required stretching wires between them. Longer distances meant higher costs. The PSTN leveled the cost despite the distance.

Switches and Circuits

The PSTN consists of switches at centralized points on the networks. These switches act as nodes for communication between two points on the network. This way, one person can talk to another on the other side of the network by being on the end of a circuit that consists of a number of switches between them.

Circuit and Packet Switching

This circuit is dedicated to the two corresponding parties throughout the length of the call. This type of switching is called circuit switching. IP networks, such as the internet, brought about packet switching, which uses the same underlying network but without reserving any portion of the line.

The voice and data messages are split into small parcels called packets, which are disseminated through the switches independently of each other and reassembled on the other end. This resulted in free voice communications on the internet through VoIP.

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