The gNB-DU is pre-configured with a threshold for each RAN TSS attribute it supports. The gNB-DU does not report RAN TSS attribute values better than the pre-configured thresholds, i.e. if a RAN TSS attribute has a value better than the pre-configured threshold, the gNB-DU reports the threshold value to the gNB-CU instead.
The gNB-CU replies to the AMF by sending the TIMING SYNCHRONISATION STATUS RESPONSE message. If the gNB-CU does not receive a successful response from at least one gNB-DU, the gNB-CU replies to the AMF by sending the TIMING SYNCHRONISATION STATUS FAILURE message and the flow stops at this step.
The gNB-CU sends the TIMING SYNCHRONISATION STATUS REPORT message to the AMF. The message contains the RAN TSS attributes received from the gNB-DU and the RAN TSS Scope IE to indicate whether the scope of the RAN TSS report is "RAN node level" or "cell list level".
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.
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").