The SOR-AF to the UDM: Nudm_ParameterProvision_Update request is sent to the UDM to trigger the update of the UE with the new list of preferred PLMN/access technology combinations or a secured packet for a UE identified by SUPI.

The UDM to the AMF: The UDM notifies the changes of the user profile to the affected AMF by the means of invoking Nudm_SDM_Notification service operation. The Nudm_SDM_Notification service operation contains the steering of roaming information that needs to be delivered transparently to the UE over NAS within the Access and Mobility Subscription data. If the HPLMN or subscribed SNPN decided that the UE is to acknowledge successful security check of the received steering of roaming information, the Nudm_SDM_Notification service operation also contains an indication that the UDM requests an acknowledgement from the UE as part of the steering of roaming information.

The AMF to the UE: the AMF sends a DL NAS TRANSPORT message to the served UE. The AMF includes in the DL NAS TRANSPORT message the steering of roaming information received from the UDM.

Upon receiving the steering of roaming information, the UE shall perform a security check on the steering of roaming information included in the DL NAS TRANSPORT message to verify that the steering of roaming information is provided by HPLMN, and:

1. if the security check is successful:
   • if the steering of roaming information contains a secured packet (see TS 31.115) and the service "data download via SMS Point-to-point" is allocated and activated in the USIM Service Table (see TS 31.102), the ME shall upload the secured packet to the USIM using procedures in TS 31.111; and
   • if the steering of roaming information contains the list of preferred PLMN/access technology combinations, the ME shall replace the highest priority entries in the "Operator Controlled PLMN Selector with Access Technology" list stored in the ME with the received list of preferred PLMN/access technology combinations, and delete the PLMNs identified by the list of preferred PLMN/access technology combinations from the Forbidden PLMN list and from the Forbidden PLMNs for GPRS service list, if they are present in these lists.
   If the UDM has requested an acknowledgement from the UE in the DL NAS TRANSPORT message, the UE sends an UL NAS TRANSPORT message to the serving AMF with an SOR transparent container including the UE acknowledgement and the UE shall set the "ME support of SOR-SNPN-SI" indicator to "supported".
   If the UDM has not requested an acknowledgement from the UE then step 5 is skipped; and
2. if the security check is not successful and the UE is in automatic network selection mode, then:
   • if the UE has a stored SOR-CMCI, then:
     • if there are ongoing PDU sessions or services, the current SNPN is considered as lowest priority and the UE shall apply the actions in clause C.4.2;
     • if there are no ongoing PDU sessions or services, the UE shall release the current N1 NAS signalling connection locally and attempt to obtain service on a higher priority SNPN as specified in clause 4.9.3, with an exception that the current SNPN is considered as lowest priority;
   • if the UE does not have a SOR-CMCI stored in the non-volatile memory of the ME, then:
     • if there are ongoing PDU sessions or services, the UE shall wait until it moves to idle mode or 5GMM-CONNECTED mode with RRC inactive indication (see TS 24.501) before attempting to obtain service on a higher priority SNPN as specified in clause 4.9.3, with an exception that the current SNPN is considered as lowest priority. If the UE has an established emergency PDU session then the UE shall attempt to perform the SNPN selection after the emergency PDU session is released and after the UE enters idle mode or 5GMM-CONNECTED mode with RRC inactive indication (see TS 24.501); or
     • if there are no ongoing PDU sessions or services, the UE shall release the current N1 NAS signalling connection locally and attempt to obtain service on a higher priority SNPN as specified in clause 4.9.3, with an exception that the current SNPN is considered as lowest priority.
   Step 5 is skipped;

The AMF to the UDM: If the UL NAS TRANSPORT message with an SOR transparent container is received, the AMF uses the Nudm_SDM_Info service operation to provide the received SOR transparent container to the UDM. If the HPLMN decided that the UE is to acknowledge successful security check of the received steering of roaming information in step 2, the UDM verifies that the acknowledgement is provided by the UE. The UDM shall store the "ME support of SOR-SNPN-SI" indicator except if the UE supports equivalent SNPNs, the ME does not support SOR-SNPN-SI and the UE is in an equivalent SNPN of the subscribed SNPN. If the present flow was invoked by the UDM after receiving from the SOR-AF a list of preferred PLMN/access technology combinations or a secured packet for a UE identified by SUPI using an Nudm_ParameterProvision_Update request, and the UDM verification of the UE acknowledgement is successful, then the UDM informs the SOR-AF about successful delivery of the steering of roaming information using Nsoraf_SoR_Info (SUPI of the UE, successful delivery); and

The UDM to the SOR-AF: Nsoraf_SoR_Info (SUPI of the UE, successful delivery, "ME support of SOR-SNPN-SI" indicator, if any). If the HPLMN policy for the SOR-AF invocation is present and the HPLMN UDM received and verified the UE acknowledgement in step 5, then the UDM informs the SOR-AF about successful delivery of the steering of roaming information to the UE. If the "ME support of SOR-SNPN-SI" indicator is stored for the UE, the UDM shall include the "ME support of SOR-SNPN-SI" indicator.