22.7 Invocation procedure

09.023GPPMobile Application Part (MAP) specificationTS

22.7.1 General

The invocation procedure is used to check subscription data in the VLR for certain supplementary services which are invoked after the call set-up phase is finished. For invocation of supplementary services which are invoked during the call set-up phase, please refer to the Call Handling procedure descriptions.

The invocation procedure is shown in figure 22.7.1/1. Note that some optional services may be invoked in connection with this procedure, as described in the subclause below.

The following services are used:

MAP_PROCESS_ACCESS_REQUEST (defined in clauses 8 and 25);

MAP_TRACE_SUBSCRIBER_ACTIVITY (defined in clauses 9 and 25);

MAP_PROVIDE_IMSI (defined in clauses 8 and 25);

MAP_FORWARD_NEW_TMSI (defined in clauses 8 and 25);

MAP_AUTHENTICATE (defined in clauses 8 and 25);

MAP_SET_CIPHERING_MODE (defined in clauses 8 and 25);

MAP_CHECK_IMEI (defined in clauses 8 and 25);

MAP_READY_FOR_SM (defined in clauses 12 and 25);

MAP_INVOKE_SS (defined in clause 11).

+—-+ +—-+ B +—-+
ª MS ª————-ªMSC ª——+——-ªVLR ª
+—-+ +—-+ +—-+
ª A_CM_SERV_REQ ª ª ß
ª—————–>ªMAP_PROCESS_ACC_REQ ª ß
ª (note 1) ª——————->
ª ª (note 2) ª ß
ª A_INVOKE_SS ª ª ß
ª—————–>ª MAP_INVOKE_SS ª ß
ª (note 3) ª——————->ª ß
ª ª ª ß
ª A_INVOKE_SS ª MAP_INVOKE_SS ª ß
ª<—————–ª<——————-ª ß

NOTE 1: For details of the procedure on the radio path, see GSM 04.08, 04.10, 04.8x and 04.9x. Services shown in dotted lines indicate the trigger provided by the signalling on the radio path, and the signalling triggered on the radio path.

NOTE 2: For details on the Process Access Request procedure, please refer to clause 25 in the present document.

NOTE 3: A_INVOKESS is a generic message to illustrate any supplementary service invocation request message on the air interface, e.g. BuildMPTY, see GSM 04.80.

Figure 22.7.1/1: Interfaces and services for supplementary service invocation

22.7.2 Procedures in the MSC

Process access request

Before the Call Hold or Multi-Party supplementary services can be invoked, a CC connection must be established between the MS and the MSC as described in GSM 04.08 and the Call Handling procedure descriptions within the present document.

When an A_INVOKE_SS request message arrives at the MSC during a call (as described in GSM 04.10, 04.8x and 04.9x-series of technical specifications), then if control of subscription to the invoked supplementary service is required, the MSC initiates the process access request procedure towards the VLR as described in clause 25 of the present document.

Supplementary service invocation

If the Process Access Request procedure towards the VLR is successful, the MSC shall forward a MAP_INVOKE_SS service request towards the VLR. This request shall contain the SS-Code of the supplementary service to be invoked, and possibly the Basic service code. Mapping from the A_INVOKE_SS to this service request is described in GSM 09.11.

The MSC will receive a MAP_INVOKE_SS confirm from the VLR. If the outcome of the service is successful (i.e. the service confirm is empty), the MSC will invoke the requested supplementary service as described in GSM 02.8x-series, 03.8x and 03.9x-series of technical specifications. If the outcome of the service is unsuccessful, the MSC shall send an appropriate A_INVOKE_SS response towards the MS. The structure of this message is described in GSM 09.11 and 04.8x and 04.9x-series of technical specifications.

Error handling

If at any time during this procedure a MAP_P_ABORT, MAP_U_ABORT, MAP_NOTICE or MAP_CLOSE indication concerning the process is received from the VLR, the process is terminated. If a MAP_NOTICE indication was received from the VLR, the VLR dialogue must also be aborted by sending a MAP_U_ABORT request indicating Procedure error towards the VLR. Possible signalling to the MS is described in GSM 04.10.

If an A_CM_RELEASE indication is received from the MS, all open transactions are released using the MAP_U_ABORT request indicating application procedure cancellation; the process terminates.

The invocation procedure in the MSC is shown in figure 22.7.2/1.

Figure 22.7.2/1 (sheet 1 of 2): Procedure Invoke_SS_MSC

Figure 22.7.2/1 (sheet 2 of 2): Procedure Invoke_SS_MSC

22.7.3 Procedures in the VLR

Process Access Request

When receiving the MAP_PROCESS_ACCESS_REQUEST indication, the VLR acts as described in clause 25 of the present document.

Supplementary service invocation

When receiving the MAP_INVOKE_SS indication, the MAP user acts as follows:

– if the operator has barred the subscriber from access to supplementary services, the error "Call Barred" is returned to the MSC. The parameter "operatorBarring" shall be included with the error;

– if any irrelevant information elements (according to the service description) or invalid information element values are present in the service request, then the unexpected data value error is returned to the MSC in the MAP_INVOKE_SS response;

– if the VLR does not support the invoked supplementary service then the VLR shall respond with the SS Not Available error;

– if the requested supplementary service cannot be invoked by subscriber actions, then the VLR shall respond with the Illegal SS Operation error;

– if the subscriber is not provided with (i.e. subscribed to) the requested supplementary service, then the SS error status error (possibly including the SS-Status as parameter) is returned to the MSC in the MAP_INVOKE_SS response.

If all checks are passed the VLR returns an empty MAP_INVOKE_SS response to the MSC, thus indicating that the invocation request was accepted.

If at any time during this procedure a MAP_P_ABORT, MAP_U_ABORT, MAP_NOTICE or unexpected MAP_CLOSE indication concerning the process is received from the MSC, the process terminates. If a MAP_NOTICE indication was received from the MSC, that dialogue must be aborted by sending a MAP_U_ABORT request indicating Procedure error towards the MSC. The process terminates.

The invocation procedure in the VLR is shown in figure 22.7.3/1.

Figure 22.7.3/1: Procedure Invoke_SS_VLR