The Public Switched Telephone Network (PSTN) has been the backbone of global telecommunication infrastructure for over a century. It was the first means of connecting people over long distances and paved the way for today’s advanced communication systems.

From the first switchboards to fibre optic cables, this history of PSTN has seen several key milestones and technological advancements. However, as technology and communication evolves, PSTN is scheduled to be turned off in 2025. In this blog we take a look at the fascinating history of this iconic communication network, what is planned to replace it and what happens next in the UC environment.

Learn everything you need to know about the switch-off and how it will affect your business by watching our informative video guide now. Don’t miss out on staying ahead of the communication evolution.



When was the PSTN copper wire system invented?

The history of PSTN begins in 1875, when Alexander Graham Bell created the American Bell Telephone Company. The following year, in March 1976, he patented the next generation of telegraphy, or telephone. Using this device, he called his associate, Thomas A. Watson over a 2 mile distance between Cambridge – Boston  Massachusetts.

The first voice transmission was carried out using a ring-down circuit. The transmission didn’t have the facility to dial numbers, but a single wire was connected between two local devices. To communicate with another person, the user had to blow a whistle to draw the person’s attention at the other side.

Later, Alexander Graham Bell introduced a calling bell system, which made signalling for a call much easier for the recipient. It’s rumoured that this is where the phrase ‘give me a bell ‘originated.

These hardwired copper lines connected individual phone lines to the telephone exchange and in some instances, the same copper connections have been in place since the introduction of PSTN in 1875.


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How and why was the telephone exchange invented?

Before the invention of the telephone exchange switchboard, early telephones were hardwired to and communicated with only a single other phone. The telephone exchange system provides telephone service to a limited geographic area by connecting subscriber lines to allow calls to be made between them. This setup has replaced the previous method, where individual small telephone systems were connected directly to each subscriber station.

The telephone exchange was based on the ideas of Puskás, originally pitched in 1877, and built by the Bell Telephone Company in the same year.


When did the first transcontinental and international call take place?

In January 1915, Alexander Graham Bell made the first coast-to-coast call. He phoned Thomas A Watson, who lived in San Francisco, from New York.

The copper wire stretched 14,000 miles and used 130,000 telephone poles to link the East Coast to the West Coast. This connection was 1,700 times longer than their first, and compared to their first phone call over 30 years prior, the pair heard each other much more distinctly. 

In January 1927, the first telephone service from the U.S. to the U.K. was set up. Radio phones were the first phones used for this connection, but there was interference. At the time this cutting edge technology enabled a three-minute phone call to take place and this cost £10, which is the equivalent of almost £800 today.


How the world wars affected communication

During the First World War, governments needed modern technologies to give them an advantage on the battlefield.  During this time, telecommunications advanced rapidly in order to exchange information faster and more efficiently.

One of the major players in the innovation of telecommunications were The Engineering Department of the General Post Office, who later were to become British Telecom (BT).

They worked tirelessly to improve existing telecommunication equipment, including modified cavalry field radios into field communication devices for gun spotters, creating instantaneous communication.

On the home front, the female workforce was taking on new responsibilities including manually operating the switchboard to connected telephones. These calls were not number operated, but audible; you’d tell them who you wanted to talk to, and the operator would manually connect you.

The development of armoured teams in the second world war meant split-second communication was vital. As they were unable to communicate with standard PSTN lines, every tank had at least one adapted radio, which transmitted the user’s voice to a switchboard and allowed soldiers to cross communicate. To achieve this, multi-conductor cables were invented, these long range cables enabled up to four conversations to take place simultaneously through the use of a carrier telephony. 


VoIP (Voice over Internet Protocol) is soon to replace PSTN services. Learn everything you need to know about the PSTN switch off by downloading your copy of ‘PSTN Switch Off: Information Hub’.

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This history of PSTN: How did the network develop post-war?

Bundles of wires, more commonly called ‘trunks’, were run between exchanges, forming proto networks. All of these networks were connected together until they connected countries across the world.

As telephones become more common and cheaper to make they become more accessible, meaning direct home-to-home connections evolved into home to central switch connections.

Yet as technology advanced, analogue switchboards could no longer keep up, and the Repeater was invented.

A Repeater directly copies whatever binary data it receives, and transfers it via radio signals. For example, if the repeater received 101010, it passed on 101010. This digital voice meant clearer, cleaner sound quality could be transmitted over longer distances, accelerating the history of the PSTN as it could release new features faster, including call forwarding and conference calling.


How did the invention of the internet impact the PSTN network?

The dawn of the internet created a new data transport format that changed the history of PSTN forever; packets.  Digital information is transmitted as IP (Internet Protocol) packets over a packet-switched network, replacing the PSTN model. These networks have formed the foundation of Voice over IP (VoIP) that we use today.

With communication rapidly evolving, we’re migrating away from traditional lines, and towards a digitalised network. This is due to the change in technology and the way we want to communicate. Rapidly evolving mobile technologies have meant that now we are used to communicating via a plethora of channels including video conferencing, instant messaging and email.

Because of this, traditional phone lines became obsolete, with homeowners choosing not to have a traditional ‘home phone’ as their parents would have a generation before. But whilst our communication style has evolved, the fundamental structure of PSTN has not, rendering it obsolete in modern society.


Are you ready for the future? PSTN is being turned off in 2025. Make sure your business is ready by learning everything you need to know in your guide ‘ PSTN Switch-Off: Information Hub’. 

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The history of PSTN: What’s next?

While the PSTN network has served us well for almost 150 years, it’s time for it to retire in 2025. BT came to this decision in 2016 based on a variety of factors, including:

  • Outdated infrastructure. People are switching to mobile and internet communications, meaning the original purpose for the copper lines is becoming redundant.
  • Costly repairs. Due to the size and age of the network, it’s becoming increasingly difficult and expensive to fix. 

With VoIP and communication rapidly evolving, it’s vital you don’t get caught up in history. The PSTN network is starting to retire in 2023. It’s important to ensure your business has a head start, and you begin outlining a post-PSTN migration plan now. 


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In 2025 the PSTN network is being switched off forever, and internet enabled networks will take their place. Learn everything you need to know about the switch-off and how it will affect your business by downloading your guide.

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