Step 1a-1b.
If the MNPF is deployed, the MNPF registers in the NRF with a new NF Type (e.g. MNPF).
Step 2.
MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in
TS 23.040.
Step 3.
The SMS-GMSC sends Nudm_UECM_SendRoutingInfoForSM to the SCP to get the serving node instance for UE from the UDM. The Nudm_UECM_SendRoutingInfoForSM contains the NF service discovery factors with the GPSI (pointing to the Number Range Holder Network) and an indicator (i.e. "target-nw-resolution") indicating that Subscription Network resolution is delegated to the SCP. The "target-nw-resolution" may also be sent by an SCP to the next hop SCP.
Step 4.
The SCP should query the NRF to find the UDM instance that manages the user subscriptions using the GPSI. The NRF receives the "target-nw-resolution" shall query the NF service consumer (MNPF) to obtain the PLMN ID of the recipient GPSI's subscription network.
Step 5.
The NRF determines the target PLMN of the recipients GPSI's subscription network using the SBI service of the MNPF i.e. the NRF invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF. As an implementation choice the NRF may determine the target PLMN by other means, e.g. local configuration of ENUM query.
Step 6.
MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.
Step 7.
NRF returns the UDM instance related to the GPSI and target PLMN Id to the SCP. For inter-PLMN discovery, the local NRF shall query the NRF in the target PLMN to find the UDM instance. If there are not NF instances available that can serve the request, the local NRF provides the discovery response indicating the consumer NF to use a legacy interface for the next operation request in the procedure.
Step 8.
SCP invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM to get the serving node instance for UE.
Step 9.
The UDM shall check the registration/reachability flags to determine the potential target nodes and responds to the SCP by sending Nudm_UECM_SendRoutingInfoForSM response, in this procedure the SMSF instance Id is included in the response message.
Step 10.
SCP forward the responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response (SMS Router address).