Railway Communications: Why Resilient Connectivity is Essential

Connectivity is no longer a support function. It is part of the operational backbone that keeps services safe, reliable and efficient. That is especially clear in modern signalling environments such as ERTMS, where ETCS Level 2 uses radio communications between the train and a Radio Block Centre to deliver movement authorities in-cab, reducing dependence on traditional lineside signalling.

In practical terms, critical connectivity in rail means communications that are predictable, resilient and secure enough to support services where downtime, latency spikes or loss of visibility carry operational consequences.

That includes signalling and control, and extends to remote asset monitoring, operational command systems, depot workflows, passenger information and connected safety systems. The National Cyber Security Centre frames OT environments explicitly around safety, uptime and operational continuity, while DfT guidance and ORR oversight underline the wider resilience and safety implications of cyber risk in rail.

When rail connectivity fails, the impact is rarely limited to IT inconvenience. It can reduce capacity, slow services, complicate incident response and undermine confidence in digital modernisation programmes. ERTMS is designed to improve interoperability, safety and line capacity, but those gains depend on robust communications. On Thameslink, the move towards 24 trains per hour through the central core relied on a broader digital operating model in which Automatic Train Operation over ETCS Level 2 played a central role, with train control dependent on continuous data exchange between train and infrastructure. Connectivity is therefore now a key enabler of operational performance in modern rail operations.

Rail organisations increasingly need to move beyond the idea that a single network can solve every problem. Critical rail connectivity is usually a layered architecture. Fibre remains essential for high-capacity backbone links. Radio systems such as GSM-R (and, over time, FRMCS as its successor) remain fundamental to operational communications. Meanwhile, cellular technologies, private wireless, satellite and edge-based processing are becoming more valuable for maintenance, monitoring, field operations and resilient backup paths. UIC describes FRMCS as a key enabler for rail digitalisation, with GSM-R coexistence expected through the mid-2030s as networks transition.

The case for connectivity in maintenance is particularly compelling. Rail operators face constant pressure to reduce delay minutes, improve asset performance and make better use of engineering windows. That pushes the industry towards connected sensors, remote condition monitoring and earlier fault prediction.

Network Rail’s Insight platform, for example, brings together measurement data, track images and remote condition monitoring to help predict faults before they disrupt passengers and freight. In each case, the underlying requirement is the same: reliable, managed rail IoT connectivity across distributed and often hard-to-reach assets.

This is familiar territory for CSL. Across telecare, fire and security, utilities and emergency services, CSL manages connectivity for more than 3.5 million devices in environments where availability is safety-critical and remote assets outnumber engineers. The same operational logic applies directly to lineside assets, depots and trackside infrastructure: autonomous failover through CSL’s rSIM, path diversity through Multi-Link routers, and centralised estate visibility through CSL’s monitoring platform. Connectivity at this level stops being a “nice to have” and becomes the mechanism that moves rail teams from reactive maintenance towards predictive decision-making.

Resilience is not just about bandwidth; it is about architecture. The NCSC’s current OT guidance stresses the importance of limiting exposure, centralising network connections, and designing connectivity so that compromise in one area does not cascade across the wider environment. In rail, that translates to practical design principles: use diverse paths where services are critical, separate operational traffic from less sensitive data flows, avoid unnecessary exposure of OT systems, and build monitoring and logging in from the start.

Multi-bearer strategies follow from the same logic. If a fibre route is cut, or cellular coverage degrades across part of a route, operations need fallback options. Combining cellular, fixed and satellite links with managed failover keeps critical services online.

For railway remote monitoring environments such as lineside assets, depots, temporary worksites and hard-to-reach locations, CSL’s DUAL-CORE multi-network architecture delivers this resilience as a managed service, maintaining simultaneous connections across independent network paths rather than relying on a single bearer.

Cybersecurity has to sit alongside resilience, not behind it. Rail has become more connected, and therefore more exposed, as control systems, operational platforms and remote access capabilities have expanded. CENELEC CLC/TS 50701 (UK implementation: PD CLC/TS 50701:2023) was developed to give the railway sector a unified framework for managing cybersecurity across communications, signalling, rolling stock and fixed installations. It aligns rail practice with broader industrial cybersecurity standards, including IEC 62443, which provides a lifecycle approach to securing industrial automation and control systems.

In the UK, the Network and Information Systems Regulations 2018 add a regulatory foundation by requiring stronger security and resilience for network and information systems that support essential services.

Rail organisations do not just need coverage; they need assurance. They need visibility of estate performance, confidence in failover behaviour, support for secure remote management, and connectivity choices that match operational criticality. CSL’s proposition is built for organisations operating in high-availability, high-accountability environments: secure and resilient connectivity, multi-network options, real-time monitoring, managed platforms and 24/7 support.

While every rail programme has its own technical and regulatory requirements, the underlying principle is the same: critical services deserve connectivity designed for continuity, not convenience.

As rail continues its shift towards digital signalling, connected maintenance and more integrated operational systems, the communications layer will only become more critical. The organisations that get this right will treat connectivity infrastructure as a strategic asset: engineered for resilience, secured by design and managed with the same rigour as any other operationally critical part of the railway. For a sector built on reliability, that is no longer optional. It is the foundation of modern rail performance.

1. ATO: Automatic Train Operation. A system that automates train driving functions such as acceleration, cruising and braking, typically operating under the supervision of ETCS movement authorities.
2. CLC/TS 50701: CENELEC Technical Specification 50701. A cybersecurity standard for railway applications covering communications, signalling, rolling stock and fixed installations. The current UK implementation is PD CLC/TS 50701:2023.
3. DUAL-CORE: CSL’s multi-network architecture that maintains simultaneous connections across independent network paths to provide resilient, always-on connectivity.
4. ERTMS: European Rail Traffic Management System. A programme to standardise rail signalling and train control across European networks, comprising ETCS and GSM-R.
5. ETCS European Train Control System. The signalling and control component of ERTMS. Level 2 uses radio-based communication to deliver movement authorities in-cab, reducing dependence on lineside signals.
6. eUICC: Embedded Universal Integrated Circuit Card. A remotely reprogrammable SIM architecture that allows network profiles to be switched over the air without physically replacing the SIM.
7. FRMCS: Future Railway Mobile Communication System. The planned successor to GSM-R, designed to support broadband data services and digitalisation across rail networks.
8. GSM-R: Global System for Mobile Communications – Railway. The dedicated mobile communications standard used for voice and data on European rail networks, now being succeeded by FRMCS.
9. IEC 62443: A series of international standards for securing industrial automation and control systems, providing a lifecycle approach to cybersecurity across operational technology environments.
10. Multi-Link CSL Routers and Outpost: CSL’s router platform supporting multiple simultaneous bearer paths across cellular, ethernet and satellite links for path diversity and resilience.
11. NCSC: National Cyber Security Centre. The UK government authority providing cybersecurity guidance and incident response, including specific guidance on operational technology environments.
12. NIS Regulations: The Network and Information Systems Regulations 2018. UK legislation requiring operators of essential services to implement appropriate security measures and report significant incidents.
13. ORR: Office of Rail and Road. The independent safety and economic regulator for Britain’s railways.
14. OT: Operational Technology. Hardware and software that monitors or controls physical equipment and processes, as distinct from information technology (IT).
15. rSIM: CSL’s resilient SIM, based on eUICC technology, providing autonomous network failover without manual intervention when a primary network degrades.
16. UIC: Union Internationale des Chemins de fer (International Union of Railways). The worldwide organisation for railway cooperation and standardisation.

1. NCSC: Operational Technology guidance: ncsc.gov.uk/collection/operational-technology
2. NCSC: Secure connectivity principles for OT (January 2026): ncsc.gov.uk/collection/operational-technology/secure-connectivity
3. ERA: European Rail Traffic Management System (ERTMS): era.europa.eu/domains/infrastructure/european-rail-traffic-management-system-ertms_en
4. UIC: Future Railway Mobile Communication System (FRMCS): uic.org/rail-system/frmcs
5. Network Rail – Intelligent Infrastructure / Insight: networkrail.co.uk/
6. BSI: PD CLC/TS 50701:2023, Railway applications – Cybersecurity: bsigroup.com (search PD CLC/TS 50701:2023)
7. ISA/IEC 62443: Security for industrial automation and control systems: isa.org/standards-and-publications/isa-standards/isa-iec-62443-series-of-standards
8. UK Government: Network and Information Systems Regulations 2018: legislation.gov.uk/uksi/2018/506
9. ORR: Cyber security and safety in rail: orr.gov.uk (search cyber security rail)