ETSI - TS 123 018
Digital cellular telecommunications system (Phase 2+) (GSM); Universal Mobile Telecommunications System (UMTS); LTE; Basic call handling; Technical realization
|Publication Date:||1 July 2020|
The present document specifies the technical realization of the handling of calls originated by a UMTS or GSM mobile subscriber and calls directed to a UMTS or GSM mobile subscriber, up to the point where the call is established. Normal release of the call after establishment is also specified. Trunk Originated call is also modelled.
In the present document, the term MS is used to denote a UMTS UE or GSM MS, as appropriate.
The handling of DTMF signalling and Off-Air Call set-up (OACSU) are not described in the present document.
The details of the effects of UMTS or GSM supplementary services on the handling of a call are described in the relevant 3GPP TS 23.07x, 3GPP TS 23.08x and 3GPP TS 23.09x 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 (3GPP TS 23.078 ) and optimal routeing (3GPP TS 23.079 ). The use of the Provide Subscriber Information message flow is shown in 3GPP TS 23.078  and 3GPP TS 23.079 .
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 (3GPP TS 24.008 , 3GPP TS 25.413 , 3GPP TS 48.008  and 3GPP TS 29.002 ), the stage 3 specification shall prevail.