Ericsson leads Europe’s first major IMS/VoLTE integration for future-proof railway communications

Ericsson and Swiss national rail operator SBB (Schweizerische Bundesbahnen) have successfully delivered Europe’s first live integration of the legacy railway communications system GSM-R with an advanced IP Multimedia Subsystem (IMS) platform with Voice over LTE (VoLTE) service.

This major infrastructure upgrade ensures uninterrupted, nationwide railway communication for Switzerland’s 3,100km rail network ahead of the planned decommissioning of Swisscom’s 3G services by the end of 2025. Furthermore, onboard 4G service upgrades have been implemented for about 1,000 trains, redefining connectivity and reliability for SBB’s railway operations.

For years, voice roaming for Swiss rail communication relied on Swisscom’s public 3G network in areas where GSM-R coverage was not available. With Swisscom’s decision to decommission its 3G services, Swiss railway operators faced an urgent need to modernize. Expanding the old GSM-R system was one option, but SBB engaged Ericsson to deliver a future-ready solution based on IMS and VoLTE, bridging GSM-R rail specific functions with modern mobile and fixed telephony systems.

Ericsson successfully designed and deployed the solution, integrating multiple vendor technologies into a converged IMS Core. Demonstrating resilience and forward-thinking innovation, the new system now ensures continuous end-to-end rail communication, setting benchmarks for railway operators across Europe facing legacy telecom shutdowns.

Ericsson’s deployment strategy prioritized zero service interruptions and robust safety compliance. Key features of the IMS implementation included IMS-GSM-R interworking, GSM-R numbering adaptation, and mandatory safety-critical functions like emergency stop calls. Starting in June 2023, the IMS/VoLTE integration progressed through rigorous testing phases:

• June 2023: Platform deployment initiated
• Early 2024: First end-to-end VoLTE-to-GSM-R calls successfully completed
• January 2025: Extensive field tests across pilot trains, certified by Switzerland’s Federal Authority Office of Transport
• April 2025: nationwide go-live of the system ahead of schedule.

Now in December 2025, the new infrastructure is in operation with approximately 450 trains and 1,000 operational devices using VoLTE technology with zero downtime.

The live IMS/VoLTE platform guarantees high-performance rail communication with scalable, modernized dispatcher telephony, reducing risks and limitations of the legacy infrastructure. Key rail-specific functions—including EIRENE functional numbering (European Integrated Radio Enhanced Network), emergency stop calls, group calls, and onboard announcements—are seamlessly preserved. By enabling 4G/5G, Switzerland’s railway network avoids service interruptions from the 3G shutdown while laying the groundwork for upcoming 5G-based Future Railway Mobile Communication System (FRMCS) innovations. So far, migrations have proceeded smoothly, supported by extensive training provided to SBB’s operational teams.

Nicolas Segond, Head of Mission Critical Communications for Railways in Europe, Middle East and Africa, Ericsson says: “Our work with SBB demonstrates our capability to deliver complex digital transformations under tight timelines. We look forward to setting benchmarks in railway communication innovation and supporting the transition to FRMCS in the coming years.&rdquo

While the full migration of train fleet communications and smartphone operations continues toward its December 2025 completion, the collaboration has paved the way for future enhancements. Valuable insights gained during this project will guide improvements in strategies for similar railway transformations globally.

Case Story

Ericsson– Integrating GSM-R with IMS/VoLTE for Swiss railways

Further reading

Smart railways with mission-critical 4G and 5G (Ericsson)

Mission Critical Communications (Ericsson)

5G Rail Corridors & FRMCS: Transforming Railways (Ericsson)

VoLTE: The sound of voice, driving the future of communication (Ericsson)

Bahnfunk (SBB / in German)