What is a PSTN Line and What are They Used For?

Once marked as the standard for telecommunications networks, the PSTN (or Public Switched Telephone Network) is an ever-changing network of infrastructure that is slowly being replaced by next-generation alternatives.

Despite being around since the late 1800s in many countries, there is still a lot of mystery around what is a PSTN line, what is PSTN line used for and what is a PSTN line fault?

This blog will answer your most common questions and take a deep dive into all things PSTN lines.

Introduction: What is a PSTN Line?

What is a PSTN phone line? PSTN lines are an old technology used to transmit phone signals from a landline telephone to its destination. These lines are operated by telephone service providers and allow public communication.

Service providers use copper switching to transmit analogue voice data, typically between homes and small businesses.

When asking what is a PSTN phone line, people are usually referring to what most call "telephone lines" but are called many different names, including landlines, Plain Old Telephone Service (POTS), or fixed-line telephones.

Because PSTN lines are dedicated lines, customers cannot use a PSTN line for anything else while a call signal passes through it, i.e. when you're making a voice calls using your landline through a PSTN line, you cannot make another call alongside it using another phone.

PSTN phone lines are made of copper, meaning there are copper lines that connect most UK homes to street cabinets and then local exchanges to provide voice and data services. As the PSTN is being phased out by 2025, older houses might already be disconnected, or new homes might already have next-generation services such as IP (Internet Protocol).

What is a PSTN Line Used For?

PSTN lines are used to provide services that require the PSTN to function, such as:

PSTN lines are being used less and less due to their growing maintenance costs and cheaper alternatives. Line faults are often difficult to track and costly to fix - but it is inevitable when some lines are up to 100 years old.

What is a PSTN Line Fault?

A fault is generally when the connection no longer reaches its destination from its origin through the PSTN line or even when the digital signal becomes poor - this can cause problems for customers who might churn away from their service provider.

Due to the age of PSTN lines, it's common for them to become faulty over time. Whether through general degradation of its rubber casing causing copper corrosion, a line cut during construction works, or even theft, as copper has a relatively high scrap value.

To test for these faults, tests on PSTN lines can be completed for the following reasons:

One common method for testing PSTN line faults is automated copper line testing through a Test Access Switch Matrix (TASM), which allows numbers to be tested remotely via a test header. One of the most common TASM providers is UTEL, who provide rack-mounted units catering for 400 traditional circuits through just one port.

Who is Responsible for a PSTN Line Fault?

The party responsible for the PSTN line fault depends on where the fault is located, which may not be known until the above test has been carried out.

The below diagram (Source: Copper Line Testing) highlights that it will either be the customers or the service providers responsibility.

If the fault is located within the home (or past the external wall/termination box), it is the customers' responsibility as it is likely the like has been damaged as a result of someone inside the building.

If the fault is outside of the external wall/termination box (in the telephone exchange or the last mile), it will be the responsibility of telecommunication companies.

How Fast Does Data Travel Through Copper Wire (PSTN Lines)?

The speed of data transfer through PSTN lines depends upon the type of copper wire, distance to travel and some external factors.

Category 6 copper cable has a max bandwidth of 1 Gb/s, and Category 5e copper cables reach up to 100 Mb/s. However, these cables can only be up to 100m long as the high speed and strength of the signal degrade over distance.

Furthermore, due to the electromagnetic properties of copper, any external signals might also impact how fast data travels through copper wire. This is common as copper cables are often placed next to electrical cables, producing electromagnetic fields as they pass electricity.

What is a BT PSTN Line?

BT is a service provider who provides its telephone and internet services over Openreach's PSTN infrastructure, so when someone refers to a BT PSTN Line, this is a line that offers BT's services.

A PSTN line doesn't always have to be BT's - other companies can either add their own equipment and lines or use Openreach's PSTN infrastructure to provide their own services through a Local Loop unbundling process (LLU).

Before 2005, BT owned and managed the phone and broadband network provided over the PSTN. This was until Openreach was created to ensure all service providers could access the copper network fairly.

What type of Phone Line Is PSTN?

The PSTN (also known as POTS or fixed telephone lines) is a dedicated analogue phone line that can only carry a singular phone call signal. They are made from copper and can be upgraded to provide internet connection but is more often than not replaced by next-generation alternatives such as VoIP.

PSTN Replacement with VoIP

PSTN and ISDN lines are slowly being replaced as service providers switch to digital technology such as IP or VoIP (Voice over Internet Protocol). This is a cloud-based solution that moves everything online, meaning your telephone signal and internet will be transferred over next-generation VoIP connections.

With the PSTN and ISDN set to be completely switched off by 2025, all services carried over these lines need to be replaced by then, meaning all PSTN customers will be migrated to IP by 2025.

This is why you may have seen a lot in the news recently about Openreach rolling out fibre optic networks at record speeds, as this is the infrastructure that will make the PSTN redundant and available to be recovered.

To find more about Openreach's Digital Upgrade and PSTN switch-off, check out our previous blog - The Complete Guide to the UK's Digital Upgrade.

What is a PSTN Line Summary

Due to the importance of this infrastructure to society, it must be identified, removed and replaced with next-generation alternatives as fast as possible before it becomes too unreliable and expensive to maintain. Without the PSTN, many of the ways we communicate and interact with each other, keep safe and connect to the internet wouldn't be possible.

With how crucial this infrastructure is to society, it must be identified, removed and replaced with next-generation alternatives as fast as possible before it gets too unreliable and expensive to maintain. Rapid and scalable removal will certainly save customers and network operations significant time and money, while also generating additional revenues through resale.

The Complete Guide to BT Openreach Copper Switch Off and its Impact

Introduction: What is the UK BT Copper Switch off, and Why is it Happening?

By the end of 2025, the UK's analogue network (the PSTN, Public Switched Telephone Network) will be switched off. This means BT's Copper Network will be switched off.

BT copper switch off means copper phone lines that form the foundation of the nation's telecommunications infrastructure will be disconnected.

There's no need to worry about this upgrade, as it will mean faster broadband speeds and higher quality service for the nation. This blog will answer what is the UK's copper switch off, why is it happening and what you need to do to make sure you're not left behind.

BT Copper Switch Off and Openreach Digital Upgrade

Switch off means that over 16 million premises and homes will need to move to alternative technologies over the next four years.

While landline phone use is less common in the UK than ever (source), these copper lines are also responsible for connecting many essential services (covered below) as well as ISDN (Integrated Service Digital Network) internet.

Openreach has set a hard date on the BT copper switch off in line with the Government's target to give at least 85% of UK premises access to gigabit-broadband by 2025 (source).

Once enough people are connected to fibre (75% of homes and businesses connected to a particular exchange (source)), a "stop sell" is put in place. Meaning no one will be able to buy copper products or services - giving a significant incentive to move towards fibre.

Why is copper switch off happening? The UK's analogue copper network, which has been in place for over a century, is increasingly expensive to maintain. It also doesn't make sense to run an analogue and digital network simultaneously.

Once the copper is switched off, legacy equipment can be removed from telephone exchanges across the country. This will allow millions of pieces of equipment to be put into the circular economy and reused in countries that need it much more than us.

In the UK, BT's network uses around 0.6% of the UK's energy consumption, so switching off copper could have a significant downstream impact upon carbon emissions (source).

Copper Switch Off Begins

Copper switch off will occur when most customers have been migrated to next-generation technologies. Therefore, some may say the switch off process only begins when Openreach announces a "stop sell" in a region.

Stop sell is the first time a region may find out they are next to move. In August 2021, Openreach announced a further 378 regions where this will occur by August 2022 (source).

These regions are just one wave of the many more to come. Openreach is rolling out fibre at lightning speeds; with the final copper switch-off date being December 2025, expect that your region may be next. 

Be sure to keep your eyes on Openreach's news pages to keep up with the fibre rollout map and schedule to see when copper stop sell is happening in your area.

What Types of Phones and Services are Affected by BT Copper Switch Off 2025?

The types of phones affected by copper switch off include:

In addition to phones and voice services, there are many other services and equipment that you may not even realise rely on copper phone lines and the PSTN. These include:

One of the remarkable things about the copper network is that it provides backup power to all of the above - meaning they will work even during a power cut.

Once the network is switched off, unless batteries or alternative backup power is provided, they will no longer work during power cuts - potentially putting vulnerable people and CNI (Critical National Infrastructure) at risk.

Therefore, it is essential to identify anything in your business or home that will be affected before the copper network is switched off. Once identified, service providers will be able to take the necessary steps.

Preparing for the Upgrade - Openreach copper switch off FAQs.

RECOVAR attended and submitted questions to one of Openreach's Digital Upgrade Events, covering several topics, including how the UK public and businesses can prepare for the upgrade. 

Given nearly half (46%) of UK firms don't know that existing analogue phone lines will be switched off by 2025 (source), the message must be spread so that no one is left disconnected.

We have summarised some of the Digital Upgrade FAQs below, so you can know what to do next!

Will my analogue phone system work after copper switch off, and how do businesses know if their systems are reliant?

It is essential to determine if your systems are reliant as early as possible - as 2025 will be here sooner than you know it.

This should start with an audit - either yourself or a service provider should create a list of all equipment and services that could be impacted. This list will allow an expert to take the appropriate actions to test and migrate copper-reliant services or equipment onto alternatives such as fibre or mobile networks.

How will Openreach's regional approach to copper switch off impact businesses? 

As highlighted above, Openreach will be taking a region by region approach for copper switch off.

When 75% of the homes and businesses connected to an exchange can access fibre, they won't be able to buy copper products or services. This applies to new and existing customers - whether they're switching or upgrading.

In all cases, Openreach recommends businesses speak to their communications providers to understand the best course of action - particularly for multi-regional firms that may need a more complex plan.

What's the best way to stay up-to-date with the Digital Upgrade, and how can businesses with little online presence keep updated?

Openreach has a Digital phones Line webpage and the Call Waiting List subscription list so any business (or consumer) can find out more about the Digital Upgrade.

Openreach has also created specific fact sheets which focus on sectors such as:

The web pages also contain helpful information and links to the websites of the industry bodies and key stakeholders, where you can find more info beyond these sheets. 

Offline businesses must speak to their service provider as it's the company's responsibility to ensure they are ready for the move. So if you're aware of anybody that isn't aware of the Digital Upgrade, be sure you point them in the right direction to get help.

What Happens After the Upgrade? Fibre Rollout Schedule

What happens next depends upon the service you're being provided. For FTTC, you may still be due upgrade works to get you to FTTP.

FTTC is where a fibre connection goes to your local street cabinet, with a copper connection then connecting to a house or business premises (figure 1, below). 

Figure 1: ADSL, FTTC and FTTP showing where copper starts and ends

Don't worry, as even though copper goes to your home with FTTC, only E side copper is switched off in the upgrade, not D side. D side (distribution side) is between the cabinet and the premises, whereas the E side (exchange side) is between the cabinet and the exchange (as shown above).

In simple terms, FTTC will still work after Openreach's Digital Upgrade.

Premises with FTTC may get an FTTP upgrade during Openreach's fibre rollout schedule. Fibre to the premise provides a fibre optic connection from the telephone exchange to your premises, giving you the fastest connection.


While the digital upgrade might seem daunting, it's for the better. 

Fibre broadband rollout has been accelerated by Openreach putting a deadline on copper switch off, meaning faster broadband speeds will be available across the country before you know it.

Faster broadband speeds ultimately unlock economic opportunities, and Openreach only maintaining one network frees up resources to focus on exciting new projects over the coming decades.

If you have any questions, feel free to get in touch with the RECOVAR Team - if we can't answer your query, we'll certainly know someone who can.