Section: 6.14.2.2 Procedure for steering of UE in VPLMN or HPLMN after registration
Content: The security procedure for the steering of UE in VPLMN after registration is described below in figure 6.14.2.2-1: Figure 6.14.2.2-1: Procedure for providing list of preferred PLMN/access technology combinations after registration 1) The UDM decides to notify the UE of the changes to the Steering of Roaming Information by the means of invoking Nudm_SDM_Notification service operation. 2-3) The UDM shall invoke Nausf_SoRProtection service operation message by including the ACK Indication and optionally the list of preferred PLMN/access technology combinations or secured packet or SoR transparent container (only if transparent container is supported by the AMF) to the AUSF to get SoR-MAC-IAUSF and CounterSoR as specified in sub-clause 14.1.3 of this document. The UDM shall select the AUSF that holds the latest KAUSF of the UE. If the HPLMN decided that the UE is to acknowledge the successful security check of the received Steering of Roaming Information, then the UDM shall set accordingly the ACK Indication included in the Nausf_SoRProtection service operation message to signal that it also needs the expected SoR-XMAC-IUE, as specified in sub-clause 14.1.3 of this document. NOTE: At reception of Nausf_SoRProtection_Protect request from the UDM, if the SoR header is not included in the request, the AUSF constructs the SOR header, as described in clause 9.11.3.51 of TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [35], based on the information received from the UDM, i.e. ACK Indication and optionally the list of preferred PLMN/access technology combinations or secured packet; otherwise, if the SoR header in contained in the request, the AUSF uses the received SoR header in the calculation of SoR-MAC-IAUSF.. The details of the CounterSoR are specified in sub-clause 6.14.2.3 of this document. The inclusion of the Steering List and the SOR header in the calculation of SoR-MAC-IAUSF allows the UE to verify that the Steering of Roaming Information received is not tampered with or removed by the VPLMN. The inclusion of these information in the calculation of the expected SoR-XMAC-IUE allows the UDM to verify that the UE received the Steering of Roaming Information. 4) The UDM shall invoke Nudm_SDM_Notification service operation, which contains the SoR transaprent container as specified in clause 6.1.6.3.2 of TS 29.503[ 5G System; Unified Data Management Services; Stage 3 ]  [93] if the VPMN AMF support SOR transparent container, or contains individual IEs including an optional the list of preferred PLMN/access technology combinations or secured packet, the ACK Indication, SoR-MAC-IAUSF, and CounterSoR within the Access and Mobility Subscription data. If the UDM requests an acknowledgement, it shall temporarily store the expected SoR-XMAC-IUE. 5) Upon receiving the Nudm_SDM_Notification message, if the SoR transparent container is included in the message, the AMF shall send a DL NAS Transport message to the served UE. including the received SoR transparent container; otherwise, the AMF shall construct the SOR transparent container (including the SOR header) as specified in clause 9.11.3.51 of 3GPP TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [35] based on the ACK Indication, the Steering List, SoR-MAC-IAUSF and CounterSoR received from the UDM, and send the constructed SoR transparent container included to the served UE in a DL NAS Transport message. 6) On receiving the DL NAS Transport message, the UE shall calculate the SoR-MAC-IAUSF in the same way as the AUSF (as specified in Annex A.17) on the received SoR transparent container, including the CounterSoR and the SoR header and verify whether it matches the SoR-MAC-IAUSF value received in the DL NAS Transport message. 7) If the UDM has requested an acknowledgement from the UE and the UE verified that the Steering Information has been provided by the HPLMN, then the UE shall send the UL NAS Transport message to the serving AMF. The UE shall generate the SoR-MAC-IUE as specified in Annex A.18 and includes the generated SoR-MAC-IUE in a SOR transparent container in the UL NAS Transport message. 8) The AMF shall send a Nudm_SDM_Info request message to the UDM. If a SOR transparent container with the SoR-MAC-IUE was received in the UL NAS Transport message, the AMF shall include the received SoR transparent container in the Nudm_SDM_Info request message if the AMF supports SoR transparent container, otherwise, the AMF shall include the SoR-MAC-IUE in the Nudm_SDM_Info request message. 9) If the HPLMN indicated that the UE is to acknowledge the successful security check of the received Steering of Roaming Information, then the UDM shall compare the received SoR-MAC-IUE with the expected SoR-XMAC-IUE that the UDM stored temporarily in step 4.