ISDN Switch Off Date - Why it Matters for Northern Ireland Business?

Thanks for taking your time to read our information on the importance of the ISDN switch off date for businesses in Northern Ireland.

BT announced as far back as 2015-16 that they were going to switch off ISDN services in 2025.


Initially BT said they would not take new orders for ISDN in 2020. That has now been revised, and ISDN orders can still be placed until September 2023. 

There will then be a forced migration phase between April and December 2025. We will keep you posted if this information changes.

What is the ISDN Switch off?

A huge part of the telephone infrastructure in Northern Ireland are cables that are underground. For years these cables have provided telephone lines to consumers and businesses throughout N.Ireland.

These lines are referred to as Analogue lines and Digital telephone lines.

Analogue Lines

In the telecommunications industry Analogues lines are also known as Public Switched Telephone Network (PSTN). These are the normal lines that go into homes and business premises throughout N.Ireland

Digital Lines

Digital telephone lines are also known as Integrated Services Digital Network (ISDN). A digital line is used by many business customers who also needed to use data as well as voice. ISDN was first introduced to the UK on June 25th 1985.

For years now, these 2 types of telephone lines have been the core of the telephone network. They relied on copper cables in the ground and in overhead cables.

isdn switch off

What is Changing for ISDN?

The telephone network has been undergoing massive changes in the last ten years. The copper cables are being replaced with fibre optic cables.

A fibre optic cable is an advanced type of network cable, offering significantly improved performance in terms of bandwidth and data when compared to traditional metal conductor cables.

Optical fibre cabling transfers information via pulses of light, which pass along transparent glass or plastic pipes, which are slightly bigger than an average hair.

These small pipes are then protected by various sheaths that protect the cable.

Fibre cable simply improves the amount of data that can be sent and also greatly improves the speed at which it can be sent and received.

Most consumers and businesses already benefit from this type of cable as it is mainly used for Broadband services.

Fibre is being rolled out across Northern Ireland and this takes a lot of money and it takes time to replace the existing network.

At present Ofcom estimates (May 2019 data) that 95% of N.Ireland can access a 10Mbps (USO) capable broadband network, which falls to 90% for speeds of 30Mbps+, 48% for ultrafast speeds (300Mbps+) and 25% for Gigabit-capable “full fibre” (FTTP) infrastructure.

changeover to fibre in northern ireland

Fibre Optic Cable

Areas with Fibre

If fibre exists in an area of N.Ireland, then businesses can now change to a fibre broadband connection. That also means they can change from ISDN to what are called SIP lines, which we explain just below.

Areas without Fibre

If fibre does not yet exist in an area of N.Ireland, then businesses will have to wait until fibre has been rolled out, before changing out their ISDN. This is an ongoing process that should be completed by 2023.

What is Replacing ISDN?

ISDN is being replaced by Session Initiation Protocol usually referred to as SIP. SIP can be used for telephone calls, to set up video and audio multicast meetings, or instant messaging conferences.

It is a form of Voice over Internet Protocol (VoIP) where calls can be routed over a broadband connection.

ISDN lines will be replaced by what are called SIP Channels, also referred to as SIP Trunks.

SIP trunks are a modern alternative to ISDN lines that most organisations use to make phone calls.

Difference between ISDN & SIP

For many years the most common way for a business to connect to the Telephone Network was through a PBX (phone system). This allowed a company to allocate phone lines and numbers.

SIP trunking lets you do the same thing but it is cheaper and more efficient.

SIP trunks route voice calls and data over the Internet. That means you don’t have to maintain two separate networks, one for data and another one for phone calls.

Benefits of Moving from ISDN to SIP

Eventually businesses will be forced to migrate at some stage when BT finally close down their ISDN network in 2025

Why wait though?

  • SIP trunks and SIP calls are much cheaper than ISDN lines and calls
  • Calls made between employees in your company are free and it doesn’t matter if they’re located in different offices or one of them is working from home
  • Long-distance calls become much cheaper since the call travels over the PSTN for a short distance
  • You can save on maintenance costs as your business can send video, instant messages and voice calls through the same system instead of using different software for each
  • You can integrate services such as digital faxing, voicemail, IVR etc in one neat package
  • Easy to integrate with other systems such as CRM and ERP systems, greatly improving productivity

Upgrading to SIP trunks can be one of the smartest decisions you can make for your business today.

Call Us for More Information on how to make a smooth move from ISDN to SIP

Are BT Getting Rid of Phone Lines?

These dates of 2025 are not set in stone and things could change. Those are aspirational dates set by BT.

However, ast some point in time, all ISDN and PSTN telephone lines will be phased out. We will continue to keep you updated as this progresses.



Why Pick Fenix Solutions?

  • Experienced communication's company with years of experience
  • Based in Belfast with a team of fully accredited and trained engineers
  • Northern Ireland billing and support teams at the end of the phone
  • Partnered with the leading providers in all communication fields
  • Communication specialists in Fibre Broadband, Leased Lines, VoIP, ISDN, SIP trunks and call bundles
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