The present document provides a system wide view of the operation of discontinuous reception on the GSM system. The support of DRX is mandatory in GSM PLMNs. The detailed coding and procedural details are defined in the relevant Technical Specifications dealing with the specific interfaces that are involved@ for instance GSM 08.08 and GSM 04.08. Reference is also made to the framing on the air interface which is defined in Technical Specification GSM 05.02. The present document gives an overview of the implementation of discontinuous reception DRX within the GSM system@ the actions required at MSC@ BSS@ and MS@ the support of the facility via the air interface@ and some operational aspects of the facility.