The present document is an 800 series Technical Report (TR) written by 3GPP TSG SA WG1 (SA1). Such a TR is not normative, i.e. cannot be used for implementation directly and cannot be referred to by other 3GPP specifications. It was primarily written by SA1 to summarise the high-level communication needs of the railway community and to identify the corresponding requirements, which, in another step have been introduced into normative Technical Specifications (TS) of 3GPP. An 800 series TR will not be updated when in the process of introduction of the requirements to TS changes are made to those requirements, i.e. the text of the requirements listed here in this TR will not be aligned with the requirements in the TS. Due to the fact that most of the requirements identified in this document were introduced in already existing Mission Critical Communication (MCX) TS, an alignment with the MCX terminology and functionality was made resulting in most of the requirements in here being reworded in the TS. Also, TS requirements changes due to future work affecting requirements stemming from this TR will not result in updates of this TR. However, the columns "Comments" of the requirements tables listed below were updated to indicate the disposition of the requirement in the TS and most of the time summarising deviations and decisions taken when introducing those requirement into normative TS. By following these references into the normative TS the functionality provided by 3GPP for railway communication can be derived by the reader. FRMCS will adapt 3GPP transport to provide communication to railway users. It eventually will resemble GSM-R and will additionally provide communication capabilities beyond what GSM-R has been able to. It will provide higher data rates, lower data latencies, multimedia communication, and improved communication reliability. FRMCS considers end-to-end use cases and also provides requirements that might or might not be in scope of 3GPP existing specifications. To facilitate smooth migration from legacy communication systems (e.g. GSM) to FRMCS, interworking requirements between legacy communication systems and FRMCS are provided. FRMCS Equipment shall connect to application domain through 3GPP radio access or other access. It provides emergency group communication, low latency and high reliable data and video service in high speed train environment. Amongst others it has the following important features:

• Prioritized emergency group communication, train control data and video service
• Seamless connectivity in high speed railway moving environments
• Low latency and high reliable data and video service
• Real time train monitoring and management for safe train operation
• Reliable location tracking including in tunnel tracking
• Legacy railway communication interworking to GSM-R system

Basically, railway communication services [5] can be categorized into

• Train control services
• Maintenance services
• Railway specific services (such as Railway Emergency Call, functional addressing, and location-based addressing)
• Other services (providing train crews or train Drivers with information of train operation and interworking with the existing railway communication systems)

This study categorizes all the use cases by considering inherent characteristics of railway applications. Specifically, the following categories of use cases are considered.

• Basic functionality
• Critical communication applications
• Performance communication applications
• Business communication applications
• Critical support applications
• Performance support applications
• Business support applications
• FRMCS System principles
  The categories can be depicted conceptually as follows: