Insight Article: End Of The Line – UK ISDN & PSTNs To Be Retired

KEY MESSAGE – Openreach’s analogue network is to be completely switched off by the end of 2025 but, in several test sites and areas of high fibre availability, the process has already begun.


  • Withdrawal of PSTN/ISDN2/ISDN30 and ADSL.
  • Move towards FTTP and SoGEA.
  • Where available, FTTC will move to FTTP.
  • Existing sites’ analogue equipment will need to be adapted or replaced.
  • Short term – new orders will increasingly be impacted by phased withdrawal based on exchanges.

KEY ACTION – Review your estate to understand the impact and plan your response


  • Now – 220 exchanges on stop sell (no new orders) by Jan 2022
  • August 2022 – 379 exchanges on stop sell
  • September 2023 – no new orders
  • December 2025 – all analogue lines withdrawn

As with analogue mobile phones, vinyl records, and cassette tapes, the time has come to retire the analogue telephone network and to move to a fully digitised phone network. The older PSTN network has been in place for decades with the copper wiring in some places dating back to the Victorian era. Not only will a digital network offer increased reliability and more features, but it will save Openreach (and thus its customers), substantial sums of money. Furthermore, the current exchange equipment is up to 35 years old and is now reaching end of life.

Openreach’s PSTN switch off is scheduled for 2025, which for many organisations may as well be ‘just around the corner’ because, whilst at first it may appear to be a long time away, the planning some organisations may need to conduct should not be underestimated. Indeed, with pilots already underway in Salisbury and an additional 169 exchanges this year, for some the impact will be sooner. Furthermore the 2025 date is the withdrawal date, but Openreach plans includes a “stop sell” date of September 2023 at which point no new line orders, moves, or upgrades will be possible.

Given that most larger organisations have already moved to VOIP and SIP trunking-based systems, perhaps you think that this is only an area of concern for SMEs and domestic households? The truth is though, that legacy products have a habit of being retained for isolated locations and niche purposes, and this is undoubtedly still the case for many of the people reading this. As such PSTN and ISDN services persist in many businesses especially for small satellite sites, or for specific use cases.

Viewing PSTN as only a voice platform is dangerously mis-leading. Whilst PSTN and ISDN services are traditionally used to support voice, they also support many other use cases that will be affected by the switch off. Slightly more obscure examples will include alarm and lift lines – many of which are known to be reliant on PSTN phone lines. In the past there has been little or no drive to update these: they work well, are relatively cheap, and there was little functional or commercial benefit from expensive upgrading of the technology to support cellular or IP connectivity. It is particularly important to notice that these services are not always on the radar of most IT or network managers – in TNC’s experience these often live within the facilities department who may be less aware of the pending PSTN switch off and its impact upon their estate. Wherever these live, record keeping for these services is quite often poorly maintained which will add to the risk and time taken to audit these estates and to prepare for the switch off.

More concerning though may be the more well-hidden reliance a business has on PSTN/ISDN – for example, we still see PSTN, and ISDN services being used for the occasional fax machine, out-of-band management, WAN access, and IOT services. Banks and utilities often use such services to manage cashpoints or to provide telematics; this is often at such a large scale that they have working projects to address the switch off, but the smaller scale use for other organisations may be more obscure. In the past, TNC has seen small scale use of PSTN to monitor fridges that store medical supplies at certain temperatures and will alarm to prevent spoilage if the fridge malfunctions. Other examples include unmanned site access devices such as car park entry systems, customer service lines connected to payment machines, and stock control systems on vending machines. Perhaps the biggest surprise is the continued reliance on ADSL especially in smaller retail branches. ADSL is delivered over PSTN so will be impacted. Openreach’s portfolio will still contain an FTTC offering unless FTTP is available at the specific site.

One of the key topics which organisations will need to address as part of this switch off, is the likelihood of very poor-quality record keeping and lack of inventories for these services. In TNC’s experience inventory management – particularly for PSTN and ISDN services – is time consuming for both end-user organisations and telecoms providers, with little tangible benefit at an individual level, which often results in it being poorly done and over time, cumulatively results in a material drift. The result is that TNC often discovers a variance of ~10% between the assumed estate at the beginning of such a process versus the reality of the estate on the ground. Often the process of identifying these mismatches involves finding connections that are no longer required, however for the PSTN switch off the bigger concern will be in finding vital lines not being recorded and thus overlooked in this process, only to be discovered at the point of switch off with no time to remedy.

So, what should you do? The number one action TNC has identified for all organisations to undertake, is a detailed audit of your estate. The purpose of this process is to ensure your records are accurate, to engage with your suppliers and your internal customers, (they may know of lines that have long since disappeared from central view, or indeed lines that were ordered directly at site level). Once you know the scale of your exposure you can, with help from your suppliers, then determine an action plan to address this, remembering that you may have to engage not merely your telecoms suppliers, but also the hardware manufacturers for non-telecoms kit e.g., the manufacturer of the fridge, the lift, the car park entry system, the ATM, etc.

The final point is critical – organisations nearly always underestimate the time required for these activities – whether it is the planning, the data gathering, or the replacement activities etc. Furthermore, a ramping up of demand for replacement kit as the PSTN switch off approaches combined with worldwide shipping delays, a shortage of chips, and Brexit complications, means you could be facing into a perfect storm should you be reliant on kit manufacturers for replacement technology. It is also worth considering how demand will impact the capacity of Telco’s to process the necessary orders as we approach the retirement date. If everyone leaves it until the last moment, the likelihood is that suppliers will be unable to handle millions of orders in the last few months. Finally, it is worth remembering that the scale of this switch off is massive, with ~14m PSTN/ISDN lines to migrate, of which at least 3m are special cases (lifts, alarms, sensors etc) so you need to make sure you are not at the back of the queue. It is vital that if you have not started planning already, that you do so with utmost haste.

A very useful link from Openreach gives further information here: Industry (, and of course, TNC would be delighted to help you on this journey whether with a conversation, planning strategy, or by auditing your estate.


TNC’s unique market insight is underpinned by the largest independent database of network and telecoms information

Other than matters relating to The Network Collective, this research is based on current public information that we consider reliable. Opinions expressed may change without notice and may differ from views set out in other documents created by The Network Collective. The above information is provided for informational purposes only and without any obligation, whether contractual or otherwise. No warranty or representation is made as to the correctness, completeness and accuracy of the information given or the assessments made.

This research does not constitute a personal recommendation or take into account the particular investment objectives, financial situations, or needs of individual clients. Clients should consider whether any advice or recommendation in this research is suitable for their particular circumstances and, if appropriate, seek professional advice.

No part of this material may be (i) copied, photocopied or duplicated in any form by any means or (ii) redistributed without the prior written consent of The Network Collective Limited © 2022

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