This specification gives an overview of the tasks undertaken by a GSM900 or DCS1800 mobile station (MS) when in idle mode@ that is@ switched on but not having a dedicated channel allocated@ e.g.@ not making or receiving a call. It also describes the corresponding network functions. This specification outlines how the requirements of the GSM 02 series Technical Specifications (especially TS GSM 02.11) on idle mode operation shall be implemented. Further details are given in Technical Specifications GSM 04.08 and GSM 05.08. Section 2 of this specification gives a general description of the idle mode process. Section 3 outlines the main requirements and technical solutions of those requirements. Section 4 describes the processes used in idle mode. There is inevitably some overlap between these sections.