ty decisions are taken by a gNB-CU, the source gNB-DU sends an Uplink RRC Transfer message to the gNB-CU to convey the received Measurement Report. 3. If the gNB-CU decides to handover the UE, it sends an UE Context Setup Request message to the target gNB-DU to create an UE context and setup one or more bearers. This step assumes intra-gNB-CU mobility. 4 NG-RAN Architecture Source Target gNB-CU gNB-DU gNB-DU Downlink user data Uplink user data 1. Measurement Report 2. Uplink RRC Transfer (Measurement Report) 3. UE Context Setup Request 4. UE Context Setup Response 5. UE Context Modification Request (RRCConnectionReconfiguration) 6. RRCConnectionReconfiguration Downlink Data Delivery Status 7. UE Context Modification Response 8. Random Access Procedure Downlink Data Delivery Status 9. RRCConnectionReconfigurationComplete Downlink User Data 10. Uplink RRC Transfer Downlink user data (RRCConnectionReconfigurationComplete) Uplink user data 11. UE Context Release Command 12. UE Context Release Complete Figure 4.2.5 Inter-gNB-DU mobility for intra-NR. (Source: Reproduced by permission of © 3GPP). 4. If the target gNB-DU accepts the request, it responds to the gNB-CU with an UE Context Setup Response message. 5. The gNB-CU sends an UE Context Modification Request message to the source gNB-DU, which includes a generated RRCConnectionReconfiguration message and indicates to stop the data transmission for the UE. 6. The source gNB-DU forwards the received RRCConnectionReconfiguration message to the UE. The source gNB-DU also sends a Downlink Data Delivery Status frame to inform the gNB-CU about the unsuccessfully transmitted downlink data to the UE. 7. The source gNB-DU responds to the gNB-CU with the UE Context Modification Response message to complete the context modification procedure. 8. The UE performs a Random Access procedure toward the target. The target gNB-DU sends a Downlink Data Delivery Status frame to inform the gNB-CU. Downlink packets, which may include PDCP PDUs not successfully delivered through the sourc