09.023GPPMobile Application Part (MAP) specificationTS
The initiation of the process is shown in subclause 22.1.2.
Once a MAP dialogue is established, the VLR may handle the MAP_PROCESS_UNSTRUCTURED_SS_REQUEST from the MSC. This message contains information input by the user, the message may be fed to an application contained locally in the VLR or to the HLR. The rules for determining this are specified in GSM 03.90.
Message Destined for HLR
If the message is destined for the HLR then the VLR shall transfer the message transparently to the HLR.
The VLR may subsequently receive one or more MAP_UNSTRUCTURED_SS_REQUEST or MAP_UNSTRUCTURED_SS_NOTIFY indications from the HLR. These shall be sent transparently to the MSC. When a confirmation is received from the MSC this shall be returned to the HLR.
When the VLR receives a MAP_PROCESS_UNSTRUCTURED_SS_REQUEST confirmation from the HLR then it shall pass this to the MS and close the MAP provider service.
Message Destined for Local Application
If the message is destined for the local USSD application then the VLR shall transfer the message to the application.
The VLR may subsequently receive one or more requests from the application which correspond to the MAP_UNSTRUCTURED_SS_REQUEST or MAP_UNSTRUCTURED_SS_NOTIFY indications. These shall be sent transparently to the MSC. When a confirmation is received from the MSC this shall be returned to the application.
When the VLR receives the result of the original operation from the application then it shall pass this to the MSC and initiate release of the CM connection.
Both the MSC and the HLR or USSD Application may initiate release of the MAP service at any time. This is handled as shown in the diagrams.
The procedure in the VLR is shown in figures 22.9.3/1 and 22.9.3/2.
Figure 22.9.3/1 (sheet 1 of 3): Procedure MI_USSD_VLR
Figure 22.9.3/1 (sheet 2 of 3): Procedure MI_USSD_VLR
Figure 22.9.3/1 (sheet 3 of 3) : Procedure_MI_USSD_VLR
Figure 22.9.3/2: Macro Receive_Error_at_VLR