The railway community is considering a successor to GSM-R with first FRMCS trial implementations expected to start around 2020. The Future Railway Mobile Communication System (FRMCS) functional working group of the International Union of Railways (UIC) have investigated and summarised their requirements for the next generation railway communication system in the Future Railway Mobile Communication User Requirement Specification (URS) [2]. The requirements have been shared with 3GPP.

The present document identifies gaps between the FRMCS requirements and stage 2 mission critical services specifications. For those gaps that cannot be fulfilled by the existing architecture, functional architecture enhancements, new procedures and information flows are documented and suggested as candidates for normative specifications. The study takes existing 3GPP functionality and those specified for Mission Critical Communication in normative specifications TS 23.379 (MCPTT), TS 23.280 (Common functional architecture), TS 23.281 (Mission Critical Video) and TS 23.282 (Mission Critical Data) into account. Studies on migration and interconnection (TR 23.781) and interworking between LTE and non-LTE systems (TR 23.782) are considered.

The following documents contain provisions which, through reference in this text, constitute provisions of the present document.

• References are either specific (identified by date of publication, edition number, version number, etc.) or non-specific.
• For a specific reference, subsequent revisions do not apply.
• For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.