Section: 8.22.1 Inter-DU direct path addition on top of indirect path
Content: The signalling flow for inter-DU direct path addition is shown in Figure 8.22.1-1. This procedure is only applicable to the MP Remote UE using PC5 link. Figure 8.22.1-1: Signalling procedure of inter-DU direct path addition on top of indirect path 1. The Uu measurement configuration and measurement report signalling are performed between MP Remote UE and the gNB-CU to evaluate both relay link measurement and Uu link measurement. The MP Remote UE may report Uu measurement results of neighboring cells and one or multiple candidate MP Relay UE(s). 2. The gNB-CU decides to add the direct path to MP Remote UE under a different gNB-DU (i.e., gNB-DU1). NOTE: Mode 1 resource configuration cannot be configured for MP Remote UE in inter-gNB-DU multi-path relay in this release. 3. The gNB-CU sends the UE CONTEXT SETUP REQUEST message for the MP Remote UE to the gNB-DU1, which contains at least the direct path configuration. 4. The gNB-DU1 responds to the gNB-CU with a UE CONTEXT SETUP RESPONSE message. 5. The gNB-CU sends an RRCReconfiguration message to the MP Relay UE to update the indirect path configuration if necessary. 6. The gNB-CU sends the UE CONTEXT MODIFICATION REQUEST message for MP Remote UE by including the direct path addition information and the RRCReconfiguration message to the gNB-DU2. The gNB-DU2 may update the stored UE context for MP Remote UE. The contents in the RRCReconfiguration message may include at least direct path addition configuration, RLC channel configuration, bearer mapping and the associated radio bearer(s). 7. The gNB-DU2 sends the RRCReconfiguration message to the MP Remote UE. 8. The gNB-DU2 sends the UE CONTEXT MODIFICATION RESPONSE message to the gNB-CU. 9. The MP Remote UE performs random access procedure at the gNB-DU1. 10. The MP Remote UE sends the RRCReconfigurationComplete message to the gNB-DU1 via direct path in order to complete the direct path addition procedure. 10a. In case the SRB1 with duplication is configured, the MP Remote UE also sends the RRCReconfigurationComplete message to the gNB-DU2 via indirect path. 11. The gNB-DU1 sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message received in step 10. 11a. In case the SRB1 with duplication is configured, the gNB-DU2 also sends the UL RRC MESSAGE TRANSFER message to gNB-CU by including the RRCReconfigurationComplete message received in step 10a.