# FRMCS glossary

Canonical: https://frmcs.org/glossary
Status: editorial draft definitions — verify against the linked primary source.

## FRMCS (Future Railway Mobile Communication System)

The UIC-led successor to GSM-R for operational railway voice and data communication, built on 3GPP mobile standards (5G).

Source: [UIC FU-7100 – FRMCS User Requirements Specification v5.0.0 (19 Feb 2020)](https://img1.uic.org/IMG/pdf/fu-7100-5.0_0.pdf)

## GSM-R (Global System for Mobile Communications – Railway)

The current 2G-based digital railway radio standard used for operational voice and ETCS data, which FRMCS is intended to replace.

Source: [Commission Implementing Decision (EU) 2021/1730 – recital 1 (GSM-R obsolescence; FRMCS as successor)](https://docdb.cept.org/download/3474)

## MCX (Mission Critical Services)

The 3GPP family of mission-critical communication services (push-to-talk, video and data) that FRMCS uses for railway applications.

Source: [3GPP TS 23.280 – Common functional architecture to support mission critical services](https://www.3gpp.org/ftp/Specs/archive/23_series/23.280/)

## MCPTT (Mission Critical Push To Talk)

The 3GPP voice service within MCX providing group and private calls with priority handling.

Source: [3GPP TS 23.379 – Functional architecture and information flows to support MCPTT](https://www.3gpp.org/ftp/Specs/archive/23_series/23.379/)

## 5G NR (5G New Radio)

The 3GPP radio access technology on which the FRMCS transport stratum is based.

Source: [ETSI TS 103 765-1 V1.1.1 – FRMCS Building Blocks and Functions, Part 1: Transport Stratum](https://www.etsi.org/deliver/etsi_ts/103700_103799/10376501/01.01.01_60/ts_10376501v010101p.pdf)

## Railway frequency bands

Harmonised European spectrum for railway mobile radio in the 900 MHz and 1900 MHz ranges; 3GPP has defined corresponding bands for FRMCS use.

Source: [ECC Decision (20)02 – 874.4–880.0 / 919.4–925.0 MHz and 1900–1910 MHz for Railway Mobile Radio (amended 28 June 2024)](https://docdb.cept.org/document/16736)

## On-Board Unit (FRMCS OBU)

The on-train equipment connecting on-board applications such as ETCS and voice to the FRMCS network.

Source: [ETSI TS 103 765-3 V1.1.1 – FRMCS Building Blocks and Functions, Part 3: Train On-Board Functions and Interfaces](https://www.etsi.org/deliver/etsi_ts/103700_103799/10376503/01.01.01_60/ts_10376503v010101p.pdf)

## Gateway

A function that connects on-board or trackside applications to FRMCS communication services, decoupling applications from the radio technology.

Source: [ETSI TS 103 764 V1.1.1 – FRMCS System Architecture](https://www.etsi.org/deliver/etsi_ts/103700_103799/103764/01.01.01_60/ts_103764v010101p.pdf)

## ETCS (European Train Control System)

The European signalling and train-protection system whose data communication currently runs over GSM-R and is planned to migrate to FRMCS.

Source: [ERA – CCS TSI Appendix A: mandatory specifications (ETCS B4 R1, GSM-R B1 MR1, FRMCS B0)](https://www.era.europa.eu/era-folder/1-ccs-tsi-appendix-mandatory-specifications-etcs-b4-r1-rmr-gsm-r-b1-mr1-frmcs-b0-ato-b1)

## TSI CCS (Technical Specification for Interoperability — Control-Command and Signalling)

The EU interoperability specification that references the radio communication requirements for railways, including FRMCS.

Source: [Commission Implementing Regulation (EU) 2023/1695 – CCS TSI](https://eur-lex.europa.eu/eli/reg_impl/2023/1695/oj)

> FRMCS Atlas is a personal editorial project by Ante Samardzic (employed by Frequentis), not an official Frequentis, UIC, ETSI or ERA publication or endorsement. Claims are source-linked; review status is stated per page — database articles pass a stored quality review and human approval of the exact version, legacy static pages are marked as such.