Section: 8.24.1 RAN TSS reporting towards the CN
Content: The signaling flow for RAN TSS reporting towards the CN is shown in Figure 8.24.1-1. This procedure is used when the TSCTSF subscribes to RAN TSS reporting at the AMF as described in TS 23.502[ Procedures for the 5G System (5GS) ]  [32]. Figure 8.24.1-1: RAN TSS reporting towards the CN 0. 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. NOTE 1: It is assumed the pre-configured thresholds in the gNB-DU are sufficient to meet UE time sync performance requirement which are configured by the operator. 1. The AMF requests RAN TSS reporting by sending the TIMING SYNCHRONISATION STATUS REQUEST message to the gNB-CU. 2. The gNB-CU requests RAN TSS reporting from at least one gNB-DU by sending the TIMING SYNCHRONISATION STATUS REQUEST message to the gNB-DU. NOTE 2: It is up to gNB-CU implementation whether to send the request to all its gNB-DUs or to a particular subset of its gNB-DUs, depending on e.g. network topology. 3. The gNB-DU replies to the gNB-CU by sending the TIMING SYNCHRONISATION STATUS RESPONSE message. 4. 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. 5. Upon sending the response to the gNB-CU, the gNB-DU provides a first RAN TSS report to the gNB-CU by sending the TIMING SYNCHRONISATION STATUS REPORT message. NOTE 3: The RAN TSS attributes included in the report is up to gNB-DU implementation. 6. 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”. 7. 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 4: Additional primary source events, if any, are up to gNB-DU implementation. 8. 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. 9. Same as step 6.