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

Ericsson's project with SBB broke new ground with Europe's first live use of GSM-R railway-specific functions via IMS/VoLTE. SBB is one of Switzerland's national railway operators and operates the mobile network for all Swiss railways on the standard gauge network. The new solution bridges the GSM R world with the IP world and ensures seamless railway communication beyond GSM-R even with the shutdown of 3G in Switzerland.

SBB, Switzerland’s national railway operator, relied on 3G networks from public telecom operators to maintain railway communications when outside GSM-R coverage. 

Swisscom announced the decommissioning of its 3G network by the end of 2025, which meant SBB’s existing GSM-R roaming over 3G would no longer function. 
To address this, SBB decided to migrate to a future-proof solution based on VoLTE (Voice over LTE) using the IP Multimedia Subsystem (IMS) architecture within a tight two-year timeline.

The project was highly complex due to the need to interwork legacy GSM-R railway communication standards (such as EIRENE) with modern IMS systems. This required adapting railway-specific number formats and protocols to fit the 3GPP IMS framework. 

Managing coordination among numerous stakeholders and vendors from the railway domain was critical to meet strict deadlines. 

Additionally, regulatory certification by the Swiss Federal Transport Authority (BAV) involved executing around 800 rigorous tests on CABRadios, followed by extensive field testing.

In May 2023, SBB selected Ericsson to deliver an IMS platform integrated with VoLTE service, working alongside other vendors to ensure interoperability with GSM-R. The solution was designed to ensure “Continuous Rail Service,” meaning the transition would be seamless without any disruption despite Swisscom’s 3G shutdown.

From mid-2023, Ericsson deployed and integrated the IMS/VoLTE platform with existing GSM-R networks, CABRadios, BTA Dispatcher software, and internal operational systems. 

Early 2024 saw successful end-to-end VoLTE to GSM-R calls in SBB labs, validating the architecture. The tests culminated in August 2024 with a proof of compliance for 4G CABRadios and regulatory approval by the Transport Authority BAV. Field tests commenced on about 20 trains in January 2025, with the full rollout starting in April 2025. 

By September 2025, approximately 450 trains and 1,000 field staff devices were using VoLTE technology.

The deployed solution integrates:

• Swisscom’s network
• SBB’s GSM-R network
• VoLTE & GSM-R CABRadios
• BTA Dispatcher and RACO devices for shunting communication
• SBB’s GEMS (GSM-R Expandable Mapping Services) and operational support systems

Ericsson implemented the project with end-to-end responsibility, operating under demanding timelines, demonstrating strong multi-vendor coordination and adherence to agile methods.

Markus Elmer, Head of SBB’s Operations Center Technology, explained, “Key challenges included executing the phased transition with zero downtime in a 24/7 environment, ensuring interoperability with existing systems, and conducting rigorous end-to-end testing. To date, Ericsson has performed well overall. Their technical expertise and responsiveness supported a stable start of operations. While there were the usual integration issues, these were resolved within the agreed change windows and without operational impact. Based on our experience so far, Ericsson’s expertise and ability to translate operational requirements into the solution—together with the efforts of our own teams and partners—have contributed to the outcome.”

Carsten Beier, Delivery Manager Rail and Business Communication at SBB, commented, “The implementation of a project of this scale and complexity requires technical precision, cross-functional coordination, and a strong partnership. Thanks to collaboration with Ericsson, our internal teams, and other suppliers, we delivered a future-proof communications solution on schedule and rolled it out without any impact on day-to-day operations.

“Agile collaboration with PI planning on a 10 week cadence, along with the close involvement of the Ericsson teams, helped us meet the ambitious timeline and keep all stakeholders consistently focused on shared delivery outcomes.”

SBB is on track to complete the migration ahead of the 3G shutdown deadline, including trains from partner operators BLS and SOB.

April 2025 go-live target was achieved well before the shutdown, fulfilling SBB’s strategic objectives. The comprehensive testing and certification phases have ensured operational reliability and compliance. SBB has expressed high satisfaction with Ericsson’s leadership, delivery, and project execution.

Looking forward, the project will conclude field tests and complete migration of trains, phones, and dispatch stations through to the end of 2025.

This project marks Europe’s pioneering live migration from 3G GSM-R to IMS/VoLTE, exemplifying digital transformation in railway operations and setting a benchmark for future telecom transitions in critical infrastructure.

Thomas Henzmann, Head of Telecom at SBB, commented, “Digitalizing our railway communications is a central step toward the rail system of the future. A key driver for introducing IMS/VoLTE was the planned 3G sunset in Switzerland. To ensure reliable voice and data communications under national roaming going forward, we needed a future‑proof, IP‑based solution with high availability.

“It was especially important to guarantee seamless operations with no impact on day‑to‑day services. Implementation and migration had to be executed in a way that avoided any disruption to the live railway operation.

“SBB is pleased with Ericsson’s performance. They delivered what they promised—with strong technical expertise in IMS/VoLTE, a solid understanding of rail‑specific requirements, and a professional, collaborative way of working. Quality, stability, and on‑time delivery were all in place; milestones were met and the solution is running reliably. Ericsson is a dependable partner for long‑term innovation in rail digitalization.”