What is ISDN and how does it work? 

What is ISDN and how does it work?  

Integrated Services Digital Network (ISDN) is the communications infrastructure that has kept the UK connected since 1986. BT brought it in to improve the UK’s existing public switched telephone network (PTSN), which was unreliable and analogue.  

ISDN brought the UK into the twenty-first century with communications, helping usher in the digital age. It’s been an integral part of the communication landscape, but that is changing. 

How does ISDN work? 

ISDN separates the traditional copper telephone line that underpins the communication system into several digital channels. This allows multiple phones and internet connections to utilise a single line, essentially creating a digital version of the existing analogue PSTN.  

As game-changing as ISDN was, BT announced in 2017 that they were phasing the technology out. 2025 is the year when the ISDN and the PSTN it connects to will finally be switched off in the UK. 

Why is ISDN ending? 

The ISDN switch-off is coming because while it undoubtedly improved connectivity, the ageing technology has now served its purpose. It’s reliant on copper wiring, which is less flexible than the alternatives, which have rocketed in usage in recent years, particularly post-pandemic. 

On top of that, it restricts phone numbers to be in both a specific location and welded to an often expensive hardware solution. Fully digital and cloud-based solutions offer a greater level of features and flexibility, a leap accelerated by the onset of working from home during the early days of Covid-19. ISDN bridged the gap between the digital and analogue ages, but it’s now time to take over a completely digital solution. 

What will replace it? 

Fibre optic will take the place of the old copper lines, which are considerably more connective and versatile. This has enabled newer and nimbler internet-based technologies to replace ISDN, which work by themselves or dovetail with each other to offer your business a raft of connectivity choices.  

The core of these is voice over internet protocol (VoIP). The key ISDN replacement, VoIP enables you to make calls over an internet connection instead of a telephone line. VoIP converts your voice into a digital signal, compresses it then transmits it across the intent to its destination. At the other end, it’s uncompressed and relayed to the receiver, all in rapid fashion. 

VoIP runs through the cloud, meaning there’s no need to house your phone system through a complex on-site system. It connects through a session initiation protocol (SIP), with a SIP trunk the virtual version of your traditional phone line using an internet connection. This improves both the reliability of the connection and the costs, with internet usage considerably cheaper than landline charges. 

Businesses can also do much more with their private branch exchange (PBX). A PBX is essentially a phone system designed for business use. It can incorporate commercially beneficial features such as managing multiple inbound and outbound calls and offering individual extensions.  

PBX isn’t a modern technology or an ISDN replacement; it can and has been working through ISDN connections for some time. But it’s much more powerful when utilising VoIP as its core channel, particularly cloud-based PBX systems. 

How we can help 

Dealing with the ISDN switch-off is something every business needs to make. If you’re unsure about when is the right time to make that transition, our experts are on hand to talk you through your options. 

We can help you create strategies for getting the most from your ISDN systems while they are still a part of your activity, alongside planning when it is right to make the switch. 

Want more information on how we can help? Request a callback and a specialist will give contact you to discuss your options.