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GSM 09.02 - Version 5.3.0 - Digital cellular telecommunications - ETSI

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Page 506<br />

<strong>GSM</strong> <strong>09.02</strong> <strong>Version</strong> <strong>5.3.0</strong>: August 1996<br />

19.6.2 Procedures in the MSC<br />

Process access request<br />

Before the Call Hold or Multi-Party supplementary services can be invoked, a CC connection must be<br />

established between the MS and the MSC as described in TS <strong>GSM</strong> 04.08 and the Call Handling procedure<br />

descriptions within this ETS.<br />

When an A_INVOKE_SS request message arrives at the MSC during a call (as described in<br />

TS <strong>GSM</strong> 04.10, 04.8x and 04.9x-series of technical specifications), then if control of subscription to the<br />

invoked supplementary service is required, the MSC initiates the process access request procedure<br />

towards the VLR as described in clause 21 of this ETS.<br />

Supplementary service invocation<br />

If the Process Access Request procedure towards the VLR is successful, the MSC shall forward a<br />

MAP_INVOKE_SS service request towards the VLR. This request shall contain the SS-Code of the<br />

supplementary service to be invoked, and possibly the Basic service code. Mapping from the<br />

A_INVOKE_SS to this service request is described in TS <strong>GSM</strong> 09.11.<br />

The MSC will receive a MAP_INVOKE_SS confirm from the VLR. If the outcome of the service is<br />

successful (i.e. the service confirm is empty), the MSC will invoke the requested supplementary service as<br />

described in <strong>GSM</strong> 02.8x-series, 03.8x and 03.9x-series of technical specifications. If the outcome of the<br />

service is unsuccessful, the MSC shall send an appropriate A_INVOKE_SS response towards the MS. The<br />

structure of this message is described in TS <strong>GSM</strong> 09.11 and 04.8x and 04.9x-series of technical<br />

specifications.<br />

Error handling<br />

If at any time during this procedure a MAP_P_ABORT, MAP_U_ABORT, MAP_NOTICE or MAP_CLOSE<br />

indication concerning the process is received from the VLR, the process is terminated. If a MAP_NOTICE<br />

indication was received from the VLR, the VLR dialogue must also be aborted by sending a<br />

MAP_U_ABORT request indicating Procedure error towards the VLR. Possible signalling to the MS is<br />

described in TS <strong>GSM</strong> 04.10.<br />

If an A_CM_RELEASE indication is received from the MS, all open transactions are released using the<br />

MAP_U_ABORT request indicating application procedure cancellation; the process terminates.<br />

The invocation procedure in the MSC is shown in figure 19.6.2/1.

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