The present document applies to the next generation radio communication system for railway operations@ intended to replace GSM-R@ and hereafter referred to as Future Railway Mobile Communication System (FRMCS)@which may require a change of the present frequency designation within CEPT and of the present regulatory framework for the proposed band(s). The preferred regulatory approach for FRMCS is to reuse the same frequency bands that are currently designated for railway operations@ within the 873 - 880 MHz paired with 918 - 925 MHz frequency band. The present document@ in particular: ? gives a GSM-R market overview; ? provides some technical information; ? investigates the harmonised UIC frequency band currently used for GSM-R@ 876 - 880 MHz UL / 921 - 925 MHz DL@ as well as the E-UIC frequency band@ 873 - 880 MHz UL / 918 - 925 MHz DL for critical railways communications; ? notes the regulatory issues in order to ensure a smooth introduction of FRMCS as well as an efficient use of spectrum. The FRMCS is used for communication between trains@ portable UE and trackside communication entities@ for applications directly related to railway operation. Passenger connectivity is out-of-scope of the present document.