 it in the F1AP UE Context Setup Request message to the gNB-DU. The message may also include SRB ID(s) and DRB ID(s) to be set up, and 4.2 High-Level gNB-CU/DU Split gNB-DU gNB-CU 2. Paging 1. FIAP: Paging 3. RRC Resume Request 4. FIAP: INITIAL UL RRC MESSAGE TRANSFER 5. FIAP: UE CONTEXT SETUP REQUEST 6. FIAP: UE CONTEXT SETUP RESPONSE 8. RRC Resume/Reject/Setup/Release 7. FIAP: DL RRC MESSAGE TRANSFER 9. RRC Resume/Setup Complete 10. FIAP: UL RRC MESSAGE TRANSFER Figure 4.2.6 RRC inactive to other RRC states transition procedure. (Source: Reproduced by permission of © 3GPP). CellGroupConfig stored in gNB-CU or retrieved from the old NG-RAN node, which are used by the gNB-DU to communicate with the UE. 6. If the procedure succeeds, the gNB-DU responds with the F1AP UE Context Setup Response message carrying the gNB-DU UE F1AP ID that it has allocated - this com- pletes the establishment of the F1 connection for that UE. The messages also contains a list of successfully established SRBs and DRBs, along with their RLC/MAC/PHY con- figuration, the list of bearers the gNB-DU failed to establish, and other UE-related infor- mation, which is handled by the gNB-DU but must be known to the gNB-CU as well. 7. Using the information received in step 6 from the gNB-DU, the gNB-CU generates the RRC Resume message for the UE. The RRC message is encapsulated in the F1AP DL RRC Message Transfer message together with the corresponding SRB ID and sent to the gNB-DU. 8. The gNB-DU forwards the RRC message received in step 7 to the UE either over SRBO or SRB1 as indicated by the SRB ID. 9. The UE sends the RRC Resume Complete message to the gNB-DU. 10. The gNB-DU encapsulates the received RRC message in the F1AP UL RRC Message Transfer message and sends it to the gNB-CU, which completes the RRC state transition procedure. 4 NG-RAN Architecture The paging procedure explained above illustrates why some RRC functions involve both gNB-DU and gNB-CU. For example, a paging message can arrive at a gNB-CU either from core network (i.e. AMF)