Tech Insight : ISDN To be Switched Off

With BT Openreach officially setting the timeframe for switching off PSTN/ISDN, we look at what this means for businesses.


Integrated Services Digital Network (ISDN), which really came into being in the 1990s, is a set of communication standards that are used for simultaneous digital transmission of voice, video, data, and other network services over the digitised circuits of the Public Switched Telephone Network (PSTN). The PSTN is a broad term for the world’s collection of interconnected, circuit-switched, voice-oriented, public telephone networks that (whether operated by national, regional, or local telephony operators) make up the infrastructure and services for public telecommunication.

Originally, ISDN offered the chance for digital services to operate through the same copper wire as the normal telephone system.  It became popular with businesses because it offered a faster Internet connection than dial-up. Fast-forwarding through different attempts to upgrade includes B-ISDN, transmitting data over fibre optic cable, and ISDN BRI (improving voice services), and the building of modern internet protocol (IP) based networks which can support both broadband and landline telephone services, and ISDN now seems to be only of real use for internet access in areas which haven’t yet been reached by broadband.

Also, as noted by Ofcom, the old PSTN is reaching the end of its life and is becoming increasingly difficult and costly to maintain, which is another reason why a switch-over to a better alternative is necessary.

What’s Happening With the Switch-Off?

BT Openreach have announced that starting from the end of this year and finishing in 2025, it will be “switching off the UK telephone network as we know it” by moving 15 million lines to a VoIP (Voice over Internet Protocol) based replacement telephone service. In essence, this means that the Internet (broadband) will be used to carry telephone calls rather than traditional copper wires.  Since ISDN used the copper wire phone network, this change marks the ISDN switch-off.

The Alternatives

With the now inevitable switch-off of ISDN, the main alternatives for businesses are:

– SIP, which uses virtual, cloud-based phone lines rather than physical lines. This may be more suitable for businesses with an on-premise phone system. Many existing phone systems are already compatible with SIP.

– Hosted VoIP/ a Hosted IP phone system may suit businesses that don’t want to commit or retain an on-premise phone system.  As this option uses the business’s internet lines, it essentially means that the business rents a phone system.

What Are The Advantages?

Broadly speaking, the switch to VoIP should bring many advantages, such as:

– A greater breadth of capabilities.

– Cost savings and fewer system failures and outages.

– Scalability and portability (VoIP phone systems can go wherever the company goes).

– Greater communications mobility, flexibility, and increased productivity and collaboration. The importance of this has been particularly well-illustrated with the need to use remote, cloud-based communications and collaborative working platforms during the pandemic.

– Better security that’s continuously updated.

– Greater reliability.

– Improved customer experiences.

– Clearer calls, making it easier to keep existing numbers, and the choice to have broadband provided separately from the telephone service.

– Better identification and prevention of nuisance calls, thereby saving businesses time and money and potentially protecting against scammers.

What Are The Disadvantages?

Some disadvantages of switching to VoIP could be:

– Potential problems with latency.

– Vulnerability to phone systems going down if there’s a broadband outage or if the electricity supply is interrupted.

Possible Impact Downstream

Both Ofcom and Openreach have acknowledged that the area of concern, if preparations are not made sufficiently in advance of the switch-over, is downstream services such as security and fire alarms, telecare devices, retail payment terminals, and equipment for monitoring and controlling networks.  These rely on some attributes of the PSTN that may not be fully replicated in VoIP-based platforms, hence the importance of adequate preparation.  This will require service providers to test their equipment to see if it will continue to function over IP and then replace, upgrade, or reconfigure it as appropriate. These service provider businesses will also need to ensure that customers (from residential users to large commercial and public sector entities) are made aware of the issue well in advance so that necessary steps can be taken to maintain service(s).

Ofcom has stated that the government will work with the sectors that use these downstream services (e.g. health, energy, transport, and business) so that they are aware of the change and can prepare in time.

What Does This Mean For Your Business?

Although the move is industry-led, there is little doubt that analogue and old, expensive to maintain copper wire phone systems will not be able to provide the scope, flexibility, speed, capacity, and economies of the digital alternative as businesses now rely heavily on the Internet. The switch-over will be spread over four years. Provided that there is adequate information and support given by the regulator and BT Openreach, and coordination among communications service providers (CSPs), and adequate advice and help for downstream providers, then change should be manageable, and disruption should be minimised.

Particular attention clearly needs to be paid to those sectors and organisations (many of which are vital to UK business and infrastructure) that still rely on some attributes of the PSTN that may not yet look as though they can be fully replicated in VoIP-based platforms. With this already being acknowledged and working groups already planned to tackle the issue, a smooth transition looks more likely.

The pandemic has increased the digital transformation of many businesses and the advantages of the switch to VoIP and digital appear to be in-keeping with this, and look likely to benefit businesses going forward. 

More information about the switch and what to do about the migration can be found here:  Also, Ofcom provides some useful information about its plans for the switch-over here:

Leave a Comment

Your email address will not be published. Required fields are marked *