The ISDN Switch off is coming what you need to know

Concise | Date: July 21, 2021 | 4 minute read


ISDN technology for transmitting data and voice has been around since music cassette tapes were popular in the 1980s. If your business still uses ISDN lines for phone and data then you need to consider the impact on your business when BT finally switch it off in 2025. 


In 2025, the analogue PSTN (Public Switched Telephone Network) and ISDN (integrated services digital network) networks will be switched off and everyone will have been moved to a fully digital network. This means all telephone calls and data will be routed over IP (Internet Protocol).

In the timeline of telephony, ISDN was developed as an offshoot in the 1980s, when, in an effort to move from analogue to digital fibre-optic services, it was deemed too expensive to connect every home to use fibre optics at the time. The ISDN standard allowed voice and data to be sent down the existing copper wire by separating it into data channels. However, using the cheaper copper wire meant that the potential speed of voice and data transfer was reduced.


Its 80s technology

The ISDN standard was set in the late 1980s. During the 1980s era:

  • The world wide web was just being invented
  • Mobile telephony was just finding its feet - and still analogue
  • Urgent business documents were often sent by fax

As time moves forward the need for speedier more reliable data connections have spawned DSL (digital subscriber line) and ADSL (asymmetric digital subscriber line over copper wiring) along with many cable television providers introducing other types of internet services like on-demand television.

Since the launch of ISDN, many changes have taken place in the business world as well.

  • Remote working, flexible working and hot-desking have exploded
  • Employees use both mobile and fixed-line telephony services during the workday
  • There has been increased focus on service, efficiency, business continuity and disaster recovery
  • IP-based services are commonly used by many organisations

If your business is running on ISDN then, changing to a digital service will dramatically improve your efficiency, mitigate downtime and provide a more attractive offering to employees looking to work in a hybrid environment.


Do you drive an old car?

In many ways, still using ISDN is like driving an old car:

  • The car represented cutting-edge technology when it was launched
  • These days it’s not as efficient as its modern counterparts
  • The cost to keep the old model running is higher than a modern alternative
  • Reliability is a worry and issues can take days to resolve
  • Although a classic, sticking with the old model may no longer meet your basic needs

At this point, you’d consider upgrading to a newer model that is fit for purpose because of overall costs, speed, reliability, environmental, ease of use, gadgets, gizmos, or technology. Essentially the same applies to reasons why you may change to a digital connection.

Here’s why you should do the same if your business is still relying on ISDN:

  • ISDN lacks the agility needed to meet the needs of today’s fast-moving consumers
  • The management of multiple offices can be time consuming, maintaining consistency of service across offices is often difficult
  • Scalability is slow and often expensive
  • ISDN-based telephony systems often require substantial CapEx investment
  • Disaster Recovery is slow
  • It can’t be combined with modern technologies like Ethernet to enhance voice services


Next Generation Technology

Many organisations are now opting for ISDN replacement services in order to drive efficiencies into their business in the face of its declining popularity:

  • In 2015, 3.1 million ISDN channels were used by UK business
  • In 2018, 2.3 million ISDN channels were used by UK business

Source: Ofcom: The Communications Market 2019


What to use instead?

Connectivity is really important to consider and as an SME you may want to understand the different types of connectivity needs you have within your business and only pay for what you need. Having or doing an audit of your telecoms systems can help align what’s needed now and into the future.

One particular technology, which is fast becoming the ISDN replacement solution of choice, is SIP Trunking, as it can bring many benefits to your business if you already have an onsite PBX (Private Branch Exchange).

SIP Trunking is essentially using the data connection your business uses for the internet access to carry voice signals as VoIP. The Service provider needs to be able to handle that voice signal and your PBX is used to send and receive calls.

However, there is an alternative if you don’t already have a PBX, this is cloud-hosted telephony. The PBX is hosted in the cloud by a service provider rather than on site locally. Even if you have an onsite PBX enabling SIP technologies makes it easier to connect to services that are hosted in the cloud.

For both technologies there are similar benefits to your business:

  • Improved service features for greater efficiency gains
  • Increased flexibility to meet the changing needs of your workforce
  • Improved scalability to help drive business growth
  • Enhanced quality of service for customers
  • Improved resilience with built-in disaster recovery provisions
  • Reduced cost with significant savings to be made on call costs and line rental
  • Increased visibility of performance metrics to improve productivity and overall business performance

Technologies like SIP trunking and cloud-hosted telephony offer a more flexible, cost-effective telecoms solution for your organisation to help you achieve your business goals. That is why it’s time to add ISDN replacement to your business agenda.


  • ISDN switch off is in 2025 and will affect businesses and home users
  • Understand what uses your ISDN connection as it isn’t necessarily just voice it’s used for, door entry systems, alarms and PoS for example may also be affected
  • Carry out an audit of your telecoms system - when was the last time you looked to upgrade?
  • Find out how much your ISDN lines and on-site PBX system is costing you - how much could you save?
  • How resilient is your existing telecoms provision - how much could downtime cost your business?

Talk to Concise about your options and how best to utilise the new faster services on offer for your business phone systems and data. Call now 01606 336265 and speak to us today about a Telecoms Audit.

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