Switzerland’s rail communications landscape has taken a major leap forward. Faced with the imminent shutdown of 3G services by Swisscom, Ericsson was commissioned by SBB to introduce new technology that enables GSM-R railway voice services to operate securely and reliably over the public 4G network – a world first in live operation.
The project not only secures mission-critical communication functions in rail transport, but also sets new standards for the digitization of railways. This modernization ensures uninterrupted voice and data services, allowing essential railway features – including emergency calls, group calls, and functional numbering – to work seamlessly between the existing GSM-R network and roaming in 4G.
To learn more about this technological first, we spoke with Carsten Beier, Delivery Manager Rail and Business Communication at SBB, who co-led the project’s implementation with Miltiadis Samlidis. His insights shed light on the motivations, challenges, and benefits of this ambitious undertaking.
Q: Can you explain what has been implemented in this project, and how does the solution work?
A: GSM-R in Switzerland is operated by SBB Infrastructure and covers approximately 3,100 km –about 95% of the standard-gauge railnet. It forms the backbone for both train radio and ETCS cab signalling.
Until now, some smaller branch lines without GSM-R coverage relied on national public roaming – using 3G for voice and 3G/4G for data. In view of the imminent shutdown of 3G, we have decided to enable roaming to VoLTE (Voice over LTE/4G), thereby connecting the GSM-R world with the IP/IMS domain.
We built a converged fixed/mobile IMS solution with a VoLTE application server, integrated directly with the existing GSM-R system. Around 1,000 trains at SBB and partner railways needed to be 4G-enabled – many already have compatible modems installed, and train migrations are underway. In addition, we needed to upgrade around 10,000 smartphones for train crews and devices for shunting which will also run on 4G.
Q: Why was SBB compelled to act now? What were the limitations of the previous system?
A: Swisscom announced in 2020 that it would shut down its 3G network by the end of 2025. This would have affected parts of our network where we relied on 3G voice via public roaming and overall Roaming. We had two options: expand GSM-R or move to 4G/5G.
We chose modernization. In addition, SBB was phasing out its legacy corporate telephony systems (BTA/Dispatcher Telephony). The new IMS-based architecture enables a unified and future-proof communication environment for both railway operations and corporate users.
Q: What benefits does the new system offer in terms of performance, reliability and longevity?
A: Our top priority was to ensure seamless service continuity – uninterrupted voice communication over 4G/VoLTE while maintaining full GSM-R compatibility. All rail-specific features – emergency calls, group calls, public address announcements – continue through interworking between the two systems.
With 4G/5G readiness, we are not only avoiding service interruptions caused by the shutdown of 3G, but also enabling further possibilities such as the establishment of operational telephony (dispatcher terminals) (BTA) on IMS. The new IMS/VoLTE platform is already in operation, and the migration process for trains and user devices is running smoothly.
Q: What were the major challenges during development and installation?
A: Ensuring reliable interworking between GSM-R core and the new IMS platform was key – especially maintaining safety-critical functions like the emergency stop feature, but also improving GSM-R numbering over 4G. Our goal was to migrate all functions “without limitations” – for Cabin Telephony (CAB-Radio) this was also required by law to obtain safety approvals.
Delivering the world’s first VoLTE-to-GSM-R call with functional numbering required intensive collaboration, rigorous testing and innovation. During the system roll-out, we upgraded the GSM-R core and IP transport network without a single minute of downtime – a huge achievement.
The project involved multiple suppliers and followed an agile delivery model with regular planning intervals. Extensive field testing was carried out to verify network coverage and performance under real operational conditions.
Q: Is the system performing as expected so far?
A: The IMS/VoLTE system is live and both train and smartphone migrations are progressing according to plan. Our operations teams have been fully trained on the new technology and processes.
Q: What are the major lessons from this project that could guide future railway digitization efforts?
A: Early involvement of all stakeholders – especially across multiple vendors – was crucial. Integrating the railway-specific GSM-R features into a standardized IMS/VoLTE telecom environment is complex and requires deep expertise across telecom and railway domains.
These learnings will strongly influence how we design contracts, plan projects and manage supplier collaboration for railway telecommunication upgrades – including a future migration toward 5G-based FRMCS.
Read the full case study to see how the project came together: SBB rail GSM-R integration with LTE - Ericsson
