Section: 8.24.2 RAN TSS reporting towards the UE
Content: The signaling flow for RAN TSS reporting towards the UE in RRC_CONNECTED state is shown in Figure 8.24.2-1. Figure 8.24.2-1: RAN TSS reporting towards the UE in RRC_CONNECTED state NOTE 1: In this signalling flow, it is assumed that RAN TSS reporting is already enabled at the gNB-DU. 1. The AMF sends the INITIAL CONTEXT SETUP REQUEST message to the gNB-CU, containing the Clock Quality Reporting Control Information IE within the Time Synchronization Assistance Information IE. The clock quality reporting control information indicates the clock quality detail level to provide to the UE, i.e. “metrics” or “acceptable/not acceptable indication”. If clock quality detail level equals “acceptable/not acceptable indication”, the clock quality reporting control information also contains the clock quality acceptance criteria. NOTE 2: The clock quality reporting control information can also be provided in the UE CONTEXT MODIFICATION REQUEST, HANDOVER REQUEST, or PATH SWITCH REQUEST ACKNOWLEDGE messages. 2. The gNB-CU replies to the AMF by sending the INITIAL CONTEXT SETUP RESPONSE message. 3. The gNB-CU sends the latest clock quality information to the UE by sending the DLInformationTransfer message. The clock quality information provided to the UE depends on the clock quality detail level received in step 1 (i.e., “metrics” or “acceptable/not acceptable indication”). 4. Later, the gNB-DU detects a primary source event: a) a RAN TSS attribute cannot meet a pre-configured threshold (i.e. status is degraded); b) a RAN TSS attribute meets the pre-configured threshold again (i.e. status is no longer degraded); c) event a) occurred and b) has not yet been reached, the gNB-DU performs periodic reporting or a previously reported RAN TSS attribute value can no longer be met. NOTE 3: Additional primary source events, if any, are up to gNB-DU implementation. 5. Upon detecting the primary source event, the gNB-DU provides an updated RAN TSS report to the gNB-CU by sending a TIMING SYNCHRONISATION STATUS REPORT message. 6. Same as step 3.