An Introduction to the ISDN/PSTN Switch off

Back in 2015, the major UK telecommunications company, BT, announced they would be switching off their PTSN and ISDN technology in 2025. This marks the biggest change to the telecoms landscape for over 30 years and represents a significant disruption to the way we communicate.

Since the 1980s, companies and consumers around the world have relied on both the PSTN and ISDN networks to communicate. However, in recent years, these solutions have become increasingly complex, unreliable, and outdated.

The ISDN/PTSN switch-off represents a universal move away from the old-fashioned communication standards in the UK, towards a more digital-focused landscape.

What are PSTN and ISDN?

ISDN and PSTN are two of the core technologies most companies will already be using to manage their everyday communications. The term “PSTN” refers to the Public Switched Telephone Network. It’s also sometimes referred to as “POTS”, or “Plain Old Telephone Service”.

The PTSN is a telecommunication network which allows subscribers at various sites to communicate by voice. The concept for this technology was first introduced in the 1800s, PSTN allows audio information to be transmitted throughout a network of copper wires.

ISDN stands for Integrated Services Digital Network. This is a group of communication standards which uses digital transmissions to allow for phone calls, video calls, and the movement of data through the circuits of the traditional PSTN environment. BT introduced ISDN to the UK in 1986, replacing old analogue landlines, and allowing for new functionality.

The ISDN/PTSN switch-off applies to the two common variants of ISDN. ISDN2 supports channels in pairs, allowing for between 2 and 8 ISDN channels. ISDN30 is intended for larger companies, which need the option for up to 30 ISDN channels on each service. A single ISDN channel can provide a customer with 1 concurrent call at any given time.

What is the IDSN/PSTN Switch Off?

The ISDN/PSTN switch-off is the roadmap outlining the decision to remove the PSTN and ISDN technologies from the UK by the end of 2025. By 2025, all phone lines in the UK will need to have moved to a fully digital network, leveraging Internet Protocol across a fibre-based service.

BT has also announced a 2023 “Stop Sell” date for the PSTN/IDSN switch-off. By September 2023, Openreach will not allow any companies to deliver a new supply of PSTN technologies like WLR (Wholesale Line Rental). There will be no new installations for ISDN or WLR by the end of 2023, and line transfers will need to be implemented.

Why are ISDN and PSTN Being Switched Off?

For decades, the PSTN environment has allowed calls to be made over traditional copper telephones as well as some fibre lines with the use of analogue signalling. Today, the technology is referred to as “traditional telephony”. In recent years, as broadband services have grown increasingly reliable and efficient, companies have begun moving away from standard PSTN solutions, in search of internet-based calling solutions through “Internet Protocol” or IP.

As a result, there’s very little requirement for traditional telephony solutions to continue to be offered in the years to come. BT and Openreach have decided to shut down these services, to instead focus on providing a high-availability fibre-first network. This also eliminates the complexity of maintaining an ageing copper wire infrastructure.

Similarly, while ISDN has improved significantly since it was first introduced, the network has remained relatively unchanged and is now considered out of date. Broadband connection speeds are now much faster than what we can achieve with ISDN, and they offer greater flexibility. The shift to cloud-based and scalable business systems makes IP technology a better choice for addressing changing company demands.

What Does the ISDN/PTSN Switch-Off Mean for You?

When the ISDN and PTSN networks are switched off, all of the services utilising the traditional copper phone line network will be affected. This means ISDN-based PBX systems in offices will become obsolete. Additionally, because PSTN supports other services like FTTC broadband via Wholesale Line Rental, companies may also need to upgrade their broadband strategy.

At some point before 2025, all organisations using PSTN, or ISDN technology will need to switch to the latest IP technology. To enable this, Openreach is working on delivering full fibre network functionality to the whole of the UK.

Companies will need to choose between two potential replacements for their ISDN and PTSN solutions: VoIP and SIP:

  • VoIP: Otherwise known as Voice over Internet Protocol, VoIP is a group of technologies which enables the delivery of multimedia and voice communications through IP networks. Data is transferred through the public internet and/or private IP networks, rather than the PSTN copper lines. VoIP drives peer-to-peer calls and Meetings within Teams or within an application such as Vonage
  • SIP: Session Initiation Protocol or SIP is a set of rules used in multimedia communications to manage and initiate data transfer between users. SIP technology creates, modifies, and terminates sessions with one or more parties in a network. SIP is what makes external calls possible or cross-application like Teams to a PBX

While VoIP allows for the set-up of an entirely new phone system, SIP allows companies to maintain their current phone system and numbers, while moving into the IP landscape.

Complete Resonate’s assessment now to see how ready your business is for ISDN switch-off.

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