5.2.4 Mobile Terminating Roaming Forwarding Call during Retrieval of Routeing Information

23.0183GPPBasic call handlingRelease 17Technical realizationTS

The information flow for mobile terminating roaming forwarding (MTRF) call during retrieval of routeing information is shown in figure 4d. It applies to a mobile terminating call while the called mobile is simultaneously moving from an old to a new MSC, if the old and the new terminating MSC/VLRs support the MT Roaming Forwarding procedure. The HLR should also support the Mobile Terminating Roaming Forwarding procedure in order to ensure that roaming forwarding can be offered in all scenarios (e.g. in case of IMSI in the LAU Request from UE); an HLR that supports Optimal Routeing shall support the requirements defined in this clause to ensure that charging requirements for optimal routeing are never contravened. The procedure may e.g. apply during pre-paging if the GMSC, HLR and old MSC/VLR support pre-paging.

The principles and requirements specified for MT Roaming Forwarding Call after successful Retrieval of Routeing Information (see clause 5.2.3) shall also apply for MT Roaming Forwarding Call during Retrieval of Routeing Information with the following modifications or clarifications.

When an MSRN is retrieved successfully from the new MSC/VLR, the old MSC/VLR shall return the received MSRN within the MAP Provide Roaming Number response to the HLR, which allows the call to be routed from the GMSC to the new MSC.

Figure 4d: Information flow for a mobile terminating roaming forwarding call during Retrieval of Routeing Information

The sequence follows the normal MT terminating call with the following differences:

1-2. Same as steps 1 and step 2 in figure 4c.

3. Same as step 3 in figure 4c, with the addition that the HLR shall not authorise MTRF between the old and the new MSCs if routing the call between the GMSC and the new MSC contravenes charging requirements if Optimal Routeing is supported (see 3GPP TS 23.079[13]).

4. Same as step 4 in figure 4c, where the old MSC/VLR stops pre-paging.

5. Same as step 5 in figure 4c.

6. Same as step 6 in figure 4c. If the OR interrogation indicator is received in the PRN request, the new VLR shall return a PRN negative response if it does not support Optimal Routeing (see 3GPP TS 23.079 [13]).

7. Same as step 7 in figure 4c.

8. The new MSC/VLR returns to the old VLR a MAP Providing Roaming Number response including the MSRN, the new VMSC Address, and if the new MSC/VLR supports the MAP Release Resource procedure, the ReleaseResourcesSupported flag.

9. Upon receipt of the MSRN from the new VLR, the old VLR returns the PRN Ack to the HLR including the MSRN and the VMSC Address received from the new VLR, and the ReleaseResourcesSupported flag if received from the new MSC/VLR.

10. If the HLR needs to return the VMSC Address to the GMSC (as per the conditions specified in 3GPP TS 29.002 [29]), and if a VMSC Address was received with an MSRN in the PRN Ack, the HLR shall pass in the SRI ack to the GMSC the MSRN and the VMSC Address received in the PRN ack.
Receipt of the MSRN from the HLR enables the GMSC to relay the call towards the new MSC.

11. Same as step 10 in figure 4c.