Policy paper

PSTN: Critical National Infrastructure Charter

Published 18 November 2024

Background

The telecoms industry’s planned replacement of copper line rental services, including the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) with digital landline telephony is a critical change to the UK’s digital infrastructure. While necessary to secure connectivity for the future, this transition will have effects beyond residential landline telephony, particularly for Critical National Infrastructure (CNI).

Retaining connectivity for CNI assets and mitigating the risks associated with retiring legacy telecoms networks will only be possible with effective collaboration between Communications Providers and CNI customers, with the support of government where necessary.

The Department for Science, Innovation and Technology (DSIT) therefore expects those organisations that own and manage CNI assets to engage actively and in good faith with their Communication Provider(s) to identify and address their dependencies on the PSTN and ISDN at the earliest opportunity. Failure to engage with this process may risk connectivity losses, as the withdrawal of these network services is not an optional process. Those that own and manage CNI assets may also wish to consider their supply chain and seek assurance that any upstream or downstream PSTN/ISDN dependencies are also addressed.

In turn, the following voluntary charter of commitments outlines the core safeguards that Communication Providers (CPs) and, where relevant, Network Operators (NOs), will put in place to support customers with CNI assets that rely on the PSTN or ISDN.

Charter commitments

We the signatories recognise the vital role of CNI assets across the UK and the risks that connectivity loss can pose. In turn, we commit to:

1. Establish a process for identifying CNI customers that we have a direct relationship with (including via self-identification) or, where possible, CNI circuits, and take all reasonable steps to inform these customers of plans to retire the PSTN and ISDN.

2. Provide clear dedicated points of contact to liaise on matters relating to the PSTN/ISDN migration for known CNI customers or circuits where we have a direct customer relationship; support these customers to identify their use of these legacy networks, notwithstanding that devices and services that are not provided by us are the responsibility of CNI asset managers and their equipment vendors and manufacturers; and work with known CNI customers to identify alternative connectivity options.

3. Actively support known CNI customers (as well as their equipment manufacturers and vendors) to enable them to test their equipment to ensure functionality over the digital network or, where applicable, transitional products.

4. Not cease PSTN or ISDN services to known CNI assets before providing them with prior notice, and only cease such services without explicit consent after having exhausted all avenues of engagement, including up to the highest levels of seniority.

a. If a CNI customer does not engage or consent, we will alert DSIT to this issue and allow time to escalate engagement across government before undertaking a non-voluntary migration. DSIT will work with Communication Providers and Network Operators as necessary to establish a defined process with clear timelines for escalating issues across government and responding to the relevant Communication Provider or Network Operator (NO).

5. Where requested by CNI customers, clearly outline our approach to providing network resilience in the event of a power outage (with particular reference to service constraints) and discuss any options to improve resilience with them. While we are responsible for managing the resilience of the network, individual CNI customers are responsible for providing and maintain power to devices they rely on.

Notes

• Communication Provider signatories have committed to all clauses of the charter. Noting that Network Operators do not have direct customer relationships, Network Operator signatories have committed to clauses 3, 4 and 5.

• The reference to non-voluntary migrations in clause 4 includes instances in which a contract for a CNI circuits ceases with no alternative product organised.

• The UK government’s official definition of Critical National Infrastructure is as follows:

  • ‘Those critical elements of infrastructure (namely assets, facilities, systems, networks or processes and the essential workers that operate and facilitate them), the loss or compromise of which could result in:

a) Major detrimental impact on the availability, integrity or delivery of essential services - including those services whose integrity, if compromised, could result in significant loss of life or casualties - taking into account significant economic or social impacts; and/or

b) Significant impact on national security, national defence, or the functioning of the state.’

• This charter applies specifically to assets and services for which the loss of PSTN/ISDN connectivity could result in loss of life or casualties. This includes, but is not limited to, assets and services that rely on PSTN/ISDN connectivity to supply key functions in areas such as defence; health; transport; water provision and power/electricity provision. However, DSIT strongly encourages signatories to apply the principles to all assets that meet the government’s official definition of critical national infrastructure.

• Not everything within a CNI sector is judged to be ‘critical’ – for example, routine phone lines where there are wider back ups - and in turn, not all PSTN and ISDN lines used by CNI sites will support ‘critical’ functions. DSIT does not intend to specify an exhaustive list of assets and services that it considers to be constitute CNI for the purposes of withdrawing the PSTN and ISDN. Rather, DSIT expects CNI customers to alert their Communication Providers to use cases that they deem to fall within the definition of CNI, and for Communication Providers to provide support to customers in CNI sectors to identify potential CNI use cases.

• DSIT is working closely with other government departments to support awareness of changes to the PSTN and ISDN and identify dependencies on these networks. Where Communication Providers’ efforts to engage with CNI customers are unsuccessful (for example due to a lack of responsiveness), DSIT will escalate this to the relevant government department and support outreach at senior levels to prompt engagement.

Signatories

Communication Providers:

• BT
• KCOM
• Virgin Media O2
• Vodafone

Network Operators:

• KCOM
• Openreach