on ID), there are one or more DRB To Setup Items, each of which contains a list of QFIs to indicate the mapping between QoS flows and DRBs. The flow mapping information shall be included only in the messages sent by the gNB-CU-CP, because the gNB-CU-CP is in charge of mapping. 4.4.3.1.3 Full UE Initial Access Procedure (with Focus on E1) A comprehensive call flow that incorporates E1 Bearer Context Management and F1 UE Context Management during UE initial access is illustrated in Figure 4.4.6. In this call flow we focus on E1 procedures, which are explained in detail, while other messages exchanged (e.g. over the F1 interface) are provided for context. 1. When the UE needs to establish a connection with the network (e.g. to send uplink data), it sends an RRC Connection Request message to the gNB-DU. 12 In other words, a split bearer is terminated in two gNB-DUs. 13 The elementary connectivity between a UE and a UPF is a PDU session, which associates the UE and the data network to provide a PDU connectivity service. 4 NG-RAN Architecture gNB-DU gNB-CU-CP gNB-CU-UP 1. RRC Connection Request 2. Initial UL RRC message 3. DL RRC message transfer 4. ARC Connection Setup 5. RRC Connection Setup Complete 6. UL RRC Message Transfer 7. Initial UE message 8. Initial UE Context Setup request 9. Bearer Context Setup Request 10. Bearer Context Setup Request 11. UE Context Setup Request 12. RRC Security Mode Command 13. UE Context Setup Response 14. Bearer Context Modification Request 15. Bearer Context Modification Response 16. RRC Security Mode Complete 17. UL RRC Message Transfer 18. DL RRC Message Transfer 19. RRC Connection Reconfiguration 20. RISC Connection Reconfiguration Complete 21. UL RRC Message Transfer 22. Initial UE Context Setup Response Figure 4.4.6 UE initial access procedure involving E1 and F1. (Source: Reproduced by permission of © 3GPP). 2. If the gNB-DU decides to admit the UE, it forwards the RRC message received from the UE to the gNB-CU in the F1AP Initial UL RRC Message Transfer message, together with