PSTN Switch-Off: Building Management Reporting Paths

The connection decision behind PSTN migration

The Public Switched Telephone Network (PSTN), the UK’s legacy analogue telephone network, is due to be retired on 31 January 2027. In September 2026, Openreach estimated that around 350,000 business premises still had services to migrate from the legacy network (Openreach, 2026c). For a facilities team replacing the analogue line used by a building management system, the nearest digital connection may be the building occupier’s network, run by its IT team.

In brief

Choosing a replacement connection determines the route taken by a building management controller’s reports, and therefore whose network changes could interrupt them. Building management systems control heating, ventilation and other plant, typically under the responsibility of an in-house facilities team or contracted provider.

Where such equipment uses the PSTN, Openreach advises testing it for compatibility with All-IP (fully digital) networks before switching (Openreach, 2026a). Openreach runs such testing at its labs. A successful result shows that the equipment works with All-IP networks, but not how its reports will travel once installed.

Those reports, if routed through the occupier’s network, also depend on that network’s router, firewall settings and change control. The occupier’s IT team can change those settings for its own reasons, and the facilities team or contractor may not be told. Where the facilities team contracts the connection itself, responsibility for the system and its reporting path can sit within the same operational arrangement.

Replacing an analogue line also means choosing a network

Many organisations still depend on operational equipment connected to the PSTN, and building management controllers are among the systems affected (Openreach, 2026b; Openreach, 2026c). Where a controller’s reporting equipment is connected directly to a dedicated analogue line, reports reach the telephone network without relying on the occupier’s router, firewall or Wi-Fi.

Where the line is contracted independently of the occupier’s network, changes to the occupier’s router or broadband service do not automatically affect that connection. A replacement reporting path may instead use broadband or cellular connectivity managed by the facilities team, the occupier, a landlord or another provider. The migration must therefore establish who will manage the new connection and its configuration.

On the occupier’s network, a building management controller is subject to another team’s changes

In a plant room, a building management controller operates boilers and pumps and reports faults to the facilities helpdesk over whatever network the controller uses. On the occupier’s network, the fault reports cross a router and a firewall on a broadband line that the occupier’s IT team manages. That team may replace the router, tighten the firewall rules or change provider, each as part of routine IT work. Any of those changes can interrupt reporting if the controller’s connectivity requirements are not maintained through the change. A change of occupier can create a similar risk if the connection is included in services that are ceased or replaced during the handover.

If the controller continues to operate the plant locally after its reporting connection is lost, the communications failure may not be immediately apparent. Unless the reporting platform flags the controller as offline, the first visible sign could be a helpdesk call about a cold office, even though the controller has already registered the boiler fault.

An occupier’s IT policy may admit only equipment the IT team manages, and the controller then needs a connection of its own from the start. With the IT team’s approval and appropriate configuration, a controller may report successfully through the occupier’s network. The operational dependency remains for as long as that reporting path is used, even if it becomes visible only when the network configuration or service arrangement changes. Where the facilities team contracts the connection, responsibility for managing changes to the reporting arrangement instead sits with that team and its supplier.

Facilities teams can contract and manage the reporting connection

Depending on the equipment and system requirements, an individual controller may use a dedicated cellular connection, while several controllers in one plant room may share a managed broadband connection with mobile backup. In both arrangements, the reporting path runs outside the occupier’s network, so responsibility for managing the connection sits within the facilities team’s contractual arrangement.

Direct contracting therefore removes the reporting path from the occupier’s managed IT network, reducing the risk that routine changes to that network interrupt reporting. It does not remove failures within the dedicated mobile or broadband service, or dependencies elsewhere in the installed system. A second path provides protection against a failure in the first connection only where it does not share any of that connection’s failure conditions. The reporting platform needs separate protection, because a fault there stops reports arriving by any communications path.

If the occupier’s network is the only practical option, a written agreement that the IT team gives notice of network changes reduces the dependency. A second path under the facilities team’s contract reduces that dependency further.

Each controller’s entry in the facilities team’s migration plan can then record:

who contracts the connection
who can change the router and firewall settings
how a loss of reporting would be detected
whether a second path shares failure conditions with the first

CSL can provide a reporting connection outside the occupier’s IT network

CSL provides managed connectivity that allows the organisation responsible for the building management system to place the reporting connection under its own operational arrangement rather than relying on the occupier’s IT network.

CSL’s multi-network IoT SIMs connect individual controllers over mobile networks, but an active connection still depends on the core network supporting the selected mobile profile. Because a core-network fault can interrupt reporting, rSIM® provides two independent roaming mobile profiles on one SIM and can switch autonomously to its backup profile when its connectivity tests identify a loss of service. The failover decision and profile selection are made on the SIM, and the modem then re-registers using the alternative core network profile and communications path.

For a plant room, CSL Broadband provides fixed broadband with a fully managed, pre-configured router option. CSL Router configurations include single-SIM, dual-SIM and broadband with cellular backup to suit the deployment.

To discuss a managed reporting connection for building management systems, please contact sales@csl-group.com.