GSM-R & migration

GSM-R (Global System for Mobile Communications – Railway) is the dedicated wireless communications standard deployed across European railway networks as the radio bearer for ETCS and for operational voice communication between train drivers and control centres.

GSM-R operates on reserved railway frequency bands — 876–880 MHz uplink and 921–925 MHz downlink — and on extended bands 873–876 MHz / 918–921 MHz (E-GSM-R). The system is based on 2G GSM technology enhanced with railway-specific features.

These include the Railway Emergency Call (REC), a one-button broadcast from a driver’s cab that reaches all trains in the affected geographic area in under two seconds and overrides all other calls on the network.

The enhanced Multi-Level Precedence and Pre-emption (eMLPP) protocol ensures safety-critical calls are not blocked by lower-priority traffic. Maximum data throughput is 9.6 kbps on the ETCS data channel.

GSM-R is deployed on approximately 130,000 km of track across Europe and more than 200,000 km worldwide. In Europe, it is a mandatory requirement under the CCS Technical Specification for Interoperability, meaning it cannot be operated as an optional layer.

Role in ETCS Level 2

ETCS Level 2 uses GSM-R as the radio data bearer between the train’s on-board unit and the Radio Block Centre (RBC). The RBC calculates movement authorities and transmits them to trains via the GSM-R data channel; the train unit reports position and speed in return.

This continuous bidirectional data exchange requires reliable connectivity throughout the train’s journey, including in tunnels and cuttings where base station spacing and coverage engineering must guarantee connection without gaps. ETCS Level 2 also uses Eurobalises at fixed locations for position calibration and odometry reference, but the movement authority communication itself is GSM-R-dependent.

Migration drivers and constraints

GSM-R rests on 2G technology whose commercial lifecycle has ended. Equipment suppliers have committed to supporting the system until approximately 2030, with some contracts extended toward 2035, but sourcing components and retaining specialist engineering skills becomes progressively more difficult as the 2G ecosystem contracts.

At the same time, the bandwidth limitations of GSM-R are becoming operationally constraining: increased ETCS Level 2 traffic density, the introduction of ATO, and the desire to transmit CCTV and maintenance data over a single radio bearer all require more capacity than GSM-R can provide.

Migration to FRMCS will require replacement of GSM-R base stations at trackside, installation of new onboard cab radios and antenna systems compatible with the FRMCS 1900 MHz band, and recertification of the ETCS data communication link over the new bearer.

Because a train cannot operate without a functional radio connection, the transition requires a dual-mode phase during which GSM-R and FRMCS operate in parallel until all rolling stock and infrastructure on a given line have migrated. SNCF and DB estimated at the ERTMS 2024 Conference that approximately 10,000 vehicles per year would need to be equipped across Europe to meet a 2035 transition deadline.