From GSM-R to FRMCS: a silent revolution for rail radio

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In the European rail system, radio is no longer just a communication tool: it is an essential link in traffic safety and operational performance.

It also ensures ground to board communication during traffic in ETCS (European Train Control System) level 2, transmitting movement authorizations to trains.

These functions are currently supported by the European GSM-R standard, which is reaching the end of its life (it is based on 2G transmission that is now obsolete). A new system is preparing to take over: the FRMCS.

A bit of history: solid foundations

Historically, communication between train drivers and ground operations took place through analog technologies specific to each network. In France, it was Radio Sol Train.

The first specifications of the GSM-R were created in 1993 under the impetus of the UIC (International Union of Railways), as part of the EIRENE (European Integrated Railway Radio Enhanced Network) project. A unified communication system should then make it possible to facilitate the interoperability of trains between the various countries.

The choice then falls on GSM technology, known as 2G, which is widely deployed and economically more accessible than other existing radio solutions.

These specifications are based on the European MORANE project (Mobile Radio for Railways Networks in Europe), which establishes the foundations of a common radio standard at European level.

In 2000, SNCF was a single company (EPIC). Also, the project to deploy the GSM-R ground infrastructure and embedded radios is shared, which explains why the radios are currently similar on all French-designed rolling stock.

More than twenty years later, in 2015, the UIC launched discussions on its successor: the FRMCS (Future Railway Mobile Communication System).

A first part of the specifications was published in 2023. The full version was announced in 2028 and is based on the European MORANE-2 experiment, a direct heir to the GSM-R experience.

What is the on-board radio (GSM-R) used for today?

The GSM-R is omnipresent in modern rail operations. In particular, it makes it possible to transport:

· Voice and SMS communications between train drivers and Ground Operations, in particular for the Safety Alert,

· other communications and sound systems (among others, for the information of travelers, intended for escort agents),

· the exchanges of data necessary for the operation of ETCS level 2,

· and a wide range of other messages related to the radio and the design of vehicles (for example, the alert issued in case of lack of vigilance of the driving agents).

The FRMCS: the rail radio of tomorrow

The FRMCS is expected to replace the GSM-R by 2035.

The challenge is major: GSM-R is based on 2G technology, which is now considered obsolete. Although the GSM-R is mainly based on a network dedicated to railways, its deactivation on the general public networks announces the end of production of the components necessary for its maintenance. Also, by 2035, the maintenance of the GSM-R will be hampered by the unavailability of spare parts.

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The FRMCS is based on 5G technology which, in addition to treating this obsolescence, offers:

· much higher speeds, in particular thanks to the addition of radio frequency bands,

· reduced latency,

· better reliability,

· and the ability to transmit data between the edge and the ground, open to third-party applications.

Beyond a simple technological change, the FRMCS will have to support many more flows, services and use cases than the GSM-R, in order to meet the growing needs of rail digitalization. Based on IP technology, its design should incorporate high cyber security requirements, recently reinforced by the Cyber Resilience Act. The FRMCS version 2 specifications have already been submitted to the ERA (European Union Agency for Railways). Version 3, intended for commercial use, is currently in preparation (source: UIC FRMCS, October 2025 conference).

The challenges of switching to FRMCS

For travelers, this transition must be completely transparent. For rail players, and in particular the SNCF Group, however, it is a major technical, economic and organizational challenge.

On a technical level, the migration to the FRMCS is an opportunity to design an evolving radio system, faced with the observation of a discrepancy between the lifespan of digital technologies and that of rail vehicles. This scalability should allow hardware owners to integrate future functionalities (acceleration of patch deployments, new CYBER challenges, future 6G migration and beyond) at contained costs, and without the effect of dependence on a supplier (challenge of an open architecture).

Also on the technical level, the FRMCS specifications mainly define the radio parameters (frequency bands, protocols, performances), but not the messages, nor the associated business functions. Work will therefore need to be done to define the exchanges between the shoreline and to guarantee the continuity of operation throughout the transition.

Organizationally and financially, the migration must be carried out by 2035, within the deadlines defined by infrastructure managers: a train cannot be launched into operation without functional radio. This is an unprecedented project in its scope, since it concerns all rolling stock in the European area equipped with a driver's cab. To limit the immobilization of equipment and the risks resulting from a strong tension on contributing resources, it seems necessary to design a FRMCS architecture that can be deployed in a short time and as close as possible to operation, and to anticipate project planning.

The transition from GSM-R to FRMCS marks a key stage in the evolution of European railways. Much more than a simple change in radio technology, it is a profound transformation of the communication systems that support network security, performance, and capacity.

While this transition remains invisible for travelers, it requires significant engineering efforts, the adaptation of rolling stock and coordination between actors in the rail system. The success of this project will directly condition the continuity of operation and the integration of future digital services.

The FRMCS thus paves the way for a railway that is more connected, more flexible and ready to meet the technological challenges of the coming decades.

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Sources:

https://www.youtube.com/watch?v=UPiGLzszi8U

https://en.wikipedia.org/wiki/FRMCS

https://fr.wikipedia.org/wiki/GSM-R

https://www.mermecgroup.com/signalling-br-systems/automatic-train-control/1444/radio-block-centre.php

https://uicfrmcs.org/?lang=en

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