Figure 5.1.7.3.4-1 shows the procedure for Direct Communication with Delegated Discovery, the SCP is the service consumer of the GPSI-to-Subscription-Network resolution service in MNPF and routes an SBI message based on GPSI when direct routing of MNPF is implemented.
The SMS-GMSC sends Nudm_UECM_SendRoutingInfoForSM to the SCP to get the serving node instance for UE from the UDM. As specified in the Indirect Communication with Delegated Discovery model, the Nudm_UECM_SendRoutingInfoForSM shall contain the discovery factors containing the GPSI (pointing to the Number Range Holder Network) and an indicator that Subscription Network resolution is delegated to the SCP.
The SCP determines the target PLMN of the recipients GPSI's subscription network using the SBI service of the MNPF i.e. the SCP invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF.
SCP shall query the NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6. For step 7b-8b, if the target PLMN ID is not the originating network, the local NRF forwards the discovery request to the NRF of the target PLMN.
SCP invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM of the target PLMN to get the serving node instance for UE. 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.