GSM 09.02 - Version 5.3.0 - Digital cellular telecommunications - ETSI

18.2.2 Procedures in the MSC
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GSM 09.02 Version 5.3.0: August 1996
The procedure is described in figure 18.2/2. These procedures make use of a number of processes and
macros not described in this subclause. The description of these can be found in the following subclauses:
Receive_Open_Cnf see subclause 21.1;
Check_Confirmation see subclause 21.2.
NOTE: If CUG Information is provided in the Initial Address Message (I_IAM) and the PLMN
does not provide a CUG capability, the call will be released if the CUG does not have
Outgoing Access. In this case the ISUP Cause indicator will be set to #87 (user not
member of CUG) and a Release message (I_REL) returned to the originating network.
If the CUG has Outgoing Access the call will be treated as an ordinary call, in this case
the CUG Information in the Initial Address Message may need to be modified. See
Annex E of CCITT Recommendation Q.767 (Approved 1990) for a description of the
procedures for a CUG call interworking with a network which does not support the
CUG facility. It has been assumed that these checks will be performed by the Gateway
MSC prior to invoking MAP procedures.
Successful Outcome
The Gateway MSC will receive an Initial Address Message (I-IAM) indicating an incoming call. To be able
to route the call toward the mobile subscriber, via the appropriate MSC, the Gateway MSC will initiate a
MAP-SEND-ROUTING-INFORMATION service request to the HLR of the MS to receive the call.
If a routing address can be provided by the HLR, it is returned to the MSC in the
MAP-SEND-ROUTING-INFORMATION service response. The routing address can take two forms: MSRN
or forwarded-to-number. If a forwarded-to-number is provided, the Gateway MSC will increment the
forwarding counter. The Gateway MSC will then construct an Initial Address Message (I-IAM) and send
this to the MSC of the area where the MS is currently located. The procedure in the Gateway MSC is then
terminated.
Data or Parameter errors
If any parameter or data errors are detected by the MSC, the procedure for this call will be terminated and
a release message (I_REL) returned to the network to release the call.
Service Provider Failure
Once the dialogue between the Gateway MSC and the HLR is established a MAP_P_ABORT service
indication may be received at any stage from the MAP Service Provider. This aborts the dialogue, see
clause 5 for a definition of the abort reasons.
The call will be released by the MSC sending a Release message (I_REL) to the Network. The procedure
in the Gateway MSC is then terminated.
Call Released by Calling Subscriber
This may occur at any stage during the call set up procedure. Call release is indicated to the MSC by a
Release Message (I_REL). The procedure in the Gateway MSC is then terminated. Any response
subsequently received from the HLR will be discarded.