- The system now covers some 450 trains and about 1,000 devices on VoLTE, with “zero downtime” since going live.
- The upgrade preserves essential railway-specific communications (emergency/stopping calls, dispatching, numbering standards) while future-proofing for forthcoming 4G/5G-based communications standards such as FRMCS.
What happened: Switzerland’s national railway operator SBB, in collaboration with Ericsson, has deployed a landmark upgrade
Switzerland’s national railway operator SBB, in collaboration with Ericsson, has deployed a landmark upgrade: interworking the legacy railway communication standard GSM-R with a modern IP Multimedia Subsystem (IMS) platform offering Voice over LTE (VoLTE).
Originally reliant on GSM-R for rail-specific communications and on Swisscom’s public 3G network for roaming when GSM-R coverage was lacking, SBB faced a hard deadline — Swisscom intends to fully shut down its 3G services by the end of 2025.
To prevent any disruption, SBB chose not simply to expand the old GSM-R infrastructure but to build a converged IMS/VoLTE solution that preserves all safety-critical and rail-specific functions (such as emergency stop calls, EIRENE numbering adaptation, dispatcher communications and group calls) while migrating voice services to 4G.
Deployment began in mid-2023, followed by internal tests, lab validation, and field tests with pilot trains starting in January 2025. By April 2025 the system was rolled out nationwide. As of December 2025, around 450 trains and 1,000 operational devices use VoLTE with zero downtime.
Ericsson describes the integration as Europe’s first live example of GSM-R/IMS interworking at this scale and says it demonstrates the viability of a path to future railway communication systems.
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Why it’s important
The move by SBB and Ericsson addresses several critical challenges associated with the impending 3G shutdown: it ensures uninterrupted, safety-critical voice and data communications for the rail network, avoids reliance on a soon-to-be-decommissioned network, and establishes a model that other rail operators across Europe may follow.
By preserving all the railway-specific features of GSM-R via the IMS/VoLTE solution — emergency stop calls, specific numbering, dispatcher and group calls — the upgrade demonstrates that rail-grade communications can be migrated to IP-based networks without sacrificing safety or reliability.
Furthermore, the project lays the groundwork for future adoption of the FRMCS standard, which is expected to rely on 5G. Early success in such a migration may encourage wider acceptance of similar transitions elsewhere.
However, the initiative also raises questions. For instance:
- Can VoLTE/IMS infrastructures maintain the same resilience and safety levels as purpose-built GSM-R, especially in extreme conditions or under heavy load?
- Will the migration process be as smooth for other railway operators with larger or more complex networks?
- Might there be unintended dependencies on commercial mobile-network operators — potentially reintroducing vulnerabilities that dedicated rail systems aimed to avoid?
Given that this is reportedly the first such integration in Europe, only time will tell whether VoLTE-over-IMS will become the de facto standard or a stop-gap on the road to full FRMCS adoption.
