Telephones, analogue to digital conversion

In the UK there are changes happening with the national telephone system that will affect all users with fixed line phone services. What is known as the Public Switched Telephone Network (PSTN) system (or sometimes just as "POTS" (Plain Old Telephone System)) is being phased out.

This is a joint program being run by all the telecomms companies, and is due to happen by the end of 2025. While is it not directly a government run program, there will still be government oversight to ensure that legislation covering telephone services in the UK keeps up with the changes.

Why the change

The current telephone system has it origins back to the late 1870's when the first phone services started to be installed in the UK. There has been vast expansion of the network since, and the continuous evolution of the technology that runs it. Much of the core of the system has long since been upgraded to modern digital technology - with multiple voice calls being handled digitally and moved via digital data networks. However there are still many parts of the existing system that are antiquated, using technology that would have been recognisable by telecomms engineers over 100 years ago. These are typically the "local loop" bits of the system, the mass of wiring, telephone poles, and street cabinets that connect individual properties to the PSTN. These parts are difficult and expensive to maintain and keep running. So there is a strong desire by the telephone companies to modernise these remaining parts of the system.

What will change

When conceived. the PSTN was a "circuit switched" communications network. This is one that requires a physical circuit to be setup between the two parties of a phone call before it can start, and then that connection needs to be disconnected after the call ends. Traditionally this was done by automated telephone exchanges that used the telephone numbers dialled to setup circuits first in the local telephone exchange, then along trunk lines between the various exchanges, and finally at the remote telephone exchange. That would ultimately connect the phone line in one property to the phone line of another.

Modern communication networks are "packet switched", where all the possible exchanges are permanently connected to each other, and calls are digitised and converted into digital packets of information that can be carried on a digital data network. These packets can then be "routed" to their destination. There is no need to setup a circuit to handle the call, or disconnect it after. This massively reduces the complexity and the overhead.

Ultimately all the remaining parts of the old PSTN will be migrated to run on modern data networks instead

How will it change

Each phone user will need a permanent data connection to their property rather than a traditional phone line. Then a telephone "adaptor" will allow telephones to be connected directly to that data connection rather than directly to a phone line.

Fortunately the vast majority of households already have this in the form of a broadband internet service.

(Ironically In many cases this internet service is still connected to the property using that very same antiquated PSTN telephone lines which have been dragged kicking and screaming from their 19th century roots, and persuaded to carry modern high speed digital data that did not even exist at the time, and that they were never designed for. This has taken many many impressive feats of engineering!)

The internet services that are currently still running over old copper phone wires, will ultimately be updated to use dedicated fibre optic "wires" that connect direct to each property. This should result in a massive increase in performance and reliability of those connections.

Common questions

What happens if I don't have an internet connection?

Telecoms companies will continue to be bound by the same regulatory obligations as they are today. So if you want a phone service on its own, you can still have it. In reality the phone line installed will actually be a digital broadband connection (but setup just to handle voice data), and the required interface equipment that will allow your normal analogue phone to work as normal.

Can I keep my existing phone number?

Yes.

Do I need to do anything?

In most cases, no. Your existing telephone service provider will contact you at an appropriate time and arrange for any changes to be made that are necessary. The change may be a simple as unplugging your phone from the phone socket on the wall, and connecting it to the phone socket on your broadband router.

What are the advantages?

Call quality and reliability should improve in many cases. Especially for rural users on the end of long phone lines. Telephone service charges should with time reduce. Capabilities should increase with better call screening, and automated rejection of scam and malicious calls. In many cases you may even be able to take you phone line with you to a new location.

So what is the bad news?

The main limitation of the new system will be that it depends on a working internet connection. This normally means that you also need mains power to run the broadband network equipment. So phone line access may no longer work during a power cut.

If you have other things connected to your phone line like a fax machine, or an alarm system, or panic button, you may need additional equipment to connect these devices to the new phone service. In some cases it may be necessary to upgrade some old equipment if it can't be made to work on the new system.

It is advised that you talk to your telecomms service provider directly if you have any concerns abut this. The independent telephone regulator Ofcom have produced guides for the telecomms industry on how they should identify and treat vulnerable customers to ensure that they have a smooth transition to the new phone service.

Let's get into the detail

For many phone users, there is no need to read further! However for technology geeks, keen DIYers, and users with special requirements, there is plenty of scope to take charge of this transition process yourself, and create a telcomms service that will bring significant new capabilities and flexibility.