The present document specifies the technical realization of the handling of calls originated by a GSM mobile subscriber and calls directed to a GSM mobile subscriber@ up to the point where the call is established. Normal release of the call after establishment is also specified. The handling of DTMF signalling and Off-Air Call setup (OACSU) are not described in the present document. The details of the effects of GSM supplementary services on the handling of a call are described in the relevant GSM 03.8x and GSM 03.9x series of specifications. The specification of the handling of a request from the HLR for subscriber information is not part of basic call handling@ but is required for both CAMEL (GSM 03.78 [6]) and optimal routeing (GSM 03.79 [8]). The use of the Provide Subscriber Information message flow is shown in GSM 03.78 [6] and GSM 03.79 [8]. The specification of the handling of data calls rerouted to a SIWFS is described in GSM 03.54 [4]. The logical separation of the MSC and VLR (shown in clauses 4@ 5 and 7)@ and the messages transferred between them (described in clause 8) are the basis of a model used to define the externally visible behaviour of the MSC/VLR@ which is a single physical entity. They do not impose any requirement except the definition of the externally visible behaviour. If there is any conflict between the present document and the corresponding stage 3 specifications (GSM 04.08 [17]@ GSM 08.08 [19] and GSM 09.02 [20])@ the stage 3 specification shall prevail.