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.

What will phone lines look like in the future?

If you order a new phone line in the post PSTN era, you will still get something that looks and behaves like a phone line. The difference is that the line installed will be a broadband connection, and there will be a "box" (in reality an internet router with a VoIP port on it) into which you can connect your phone. You pick up the phone, get a dialling tone, and dial away. The call will connect just like before.

The difference is what is going on under the hood. The phone line is a broadband connection. If you don't also want broadband they might just install limited bandwidth broadband connection - designed to be enough throughput for a good quality phone call rather than streaming Netflix! However in reality there is a fair chance that even if you don't order broadband you will still get some internet connectivity into the deal even if you don't use it.

The box supplied by your phone line provider will have one side designed to look (from the electrical point of view) like a PSTN phone socket into which you can plug you normal analogue phone (or wire up to other extension sockets in the house).

However the internet facing side will probably use a communications protocol called SIP (session initiation protocol) to setup and stop the logical connections for calls as required using a SIP service (probably run by your telecomms company).

So what options do I have?

If you have a good broadband connection, you don't actually need a "phone line" installed - and you don't have to use the phone capability included in the router that that came with your broadband connection (which in the interests of keeping you tied into their eco system may not play nice with standard SIP kit). You can instead shop around for SIP providers to provide a telephone service for you that is independent of your broadband provider. You can port your PSTN telephone number to is as well so you keep you number. You can then provide your own hardware for talking to this SIP service.

What can I use with my SIP service?

Because SIP is a defined standard, lots of kit will play nicely with it, assuming your 'broadband voice' provider uses standard SIP and other protocols.

• You could follow the same approach as the off the shelf options - buy a VoIP interface box, plug your existing analogue phone in one side, and connect the other to your broadband.
• You could buy your own router with built in VoIP capabilities, configure that to talk to you SIP service, and plug the phone into the router.
• You could ignore add on boxes and routers altogether, and buy a IP Phone with SIP capability built in. That will look and feel like (and advanced) phone handset, but connect (typically) to Ethernet rather than a phone line. That now basically means that you can take you phone handset anywhere there is a broadband service with an Ethernet connection available (i.e. pretty much all of them), and make and receive calls on your "home" line regardless of where the phone actually is.
• You could configure your mobile to place calls over VoIP using SIP, and you now have an IP phone that runs from batteries and can be used anywhere there is data coverage.
• You can install a "softphone" application on your computer and make calls directly from that - copy and past in a number and hit the dial button. Add a decent set of headphones with a microphone built in and you now have a really good hands free phone (wireless as well if you want)

What new stuff can I do?

Now you have advanced VoIP technology, you can:

• Make and receive calls,
• Do conference calls.
• Divert on busy, or on no answer.
• Route your calls (at no extra expensed) to you mobile.
• If your SIP account allows it you might have the option of using multiple "lines" at once - handy in busy households or running a small business.

What about more advanced features?

Another option is to have your own P(A)BX (Private (Automated) Branch eXchange). Once the domain of business customers (and a few dedicated DIYers!) you can run your own PBX. Instead of this being a physical box of tricks that needs to be wired up to the building's phone sockets, this can now be just software (hosted on your own equipment, or cloud based). You can now have multiple extensions connected to different rooms - call room to room. The "rooms" don't even need to be in the same physical building. In this modern "Work From Home" work pattern, different staff can be in their own space, but all joined to the same PBX system. Calling a colleague is then as easy as clicking on their name on the internal phone book.

Self hosted PBX

Setting up you own PBX running locally is a bit more complicated, but there are number of preconfigured setups that run on things like the humble Raspberry Pi computer. (just to add a bit of confusion - the system that runs your private PBX is often called a Session Boarder Controller or "SBC" for short. Raspberry Pi is an example of a cheap Single Bard Computer... also a SBC!)

Cloud based PBX

There are loads of these, a google search will find them. Big names include 3CX, Vonage, RingCentral and many more. Many have free or low cost options for customers with only a small number of users.

What happens in a power cut?

Starting position is you have no phone service in a power cut. You can keep a service by providing battery backup for the box fitted for the new line. But that alone will only work with a wired phone plugged into it. Anything beyond that needs further backup supplies for routers etc. This may be an opportunity to take stock of UPSs.

What about emergency services?

A big issue for some people is they call 999 etc in a power cut. (Often people who have only DECT phones for their landline!) Ofcom's guidance for providers [1] requires them to make sure customers can call emergency services during a power cut. For many this may be just their current mobile phone. But providers must provide a solution free of charge if necessary.

Home alarms etc

Ofcom advise anyone with a home alarm, call or fall pendant, telecare etc [2] to tell their provider before they are moved to the new service. Ofcom don't require providers to meet any and all costs but they do require providers to take special care with disabled and vulnerable customers.