Question: What happens when a UE performs an Initial Registration with network sharing and multiple cell-ID broadcast, but does not provide a UE-Identity that allows the DU to deduce the PLMN ID?
Option 1: The gNB-DUA sends an F1AP UE CONTEXT RELEASE REQUEST message to the gNB-CUA with a Cause set to "PLMN not served by the CU", and then initiates a new registration procedure.
Option 2: The gNB-DUB sends an F1AP INITIAL UL RRC MESSAGE to the gNB-CUB, including the NR CGI associated with PLMNB, the C-RNTI indicated by the gNB-DUA, and the RRC-Container IE and the RRC-Container-RRCSetupComplete IE.
Option 3: The gNB-CUA sends a UE CONTEXT RELEASE COMMAND message to the gNB-DU, which then releases the UE context and initiates a new registration procedure.
Option 4: The gNB-DUA and gNB-DUB initiate procedures in parallel towards their respective CUs, but do not exchange any messages with each other.
Explanation: When a UE performs an Initial Registration with network sharing and multiple cell-ID broadcast, but does not provide a UE-Identity that allows the DU to deduce the PLMN ID, the gNB-DUB sends an F1AP INITIAL UL RRC MESSAGE to the gNB-CUB. This message includes the NR CGI associated with PLMNB, the C-RNTI indicated by the gNB-DUA, and the RRC-Container IE and the RRC-Container-RRCSetupComplete IE. This allows the gNB-CUB to establish a new UE context and complete the registration procedure.