The purpose of this leaflet is to give the background of the radio frequency aspects and to enable railways to co-ordinate the introduction and operation of GSM-R networks in the most efficient manner. The leaflet describes: the frequencies allocated to GSM-R and Direct Mode, the method to be used in co-ordinating these frequencies at borders, the use of network colour codes, the implementation of new features and software upgrades, the use of algorithms, the use of network names, the management of network parameters.