gNB-CU and gNB-DU as follows: gNB-CU determines what is sent in a paging message and gNB-DU determines how the message is sent over the air interface. This is because the information about which UEs to page in which cells is received at a gNB-CU (either from core network or from another NG-RAN node); however, gNB-CU cannot determine by itself scheduling-related parameters - only gNB-DU is aware of these. Therefore, the gNB-CU sends to the gNB-DU either a core network or RAN UE paging identity, paging priority, and a list of cells to page the UE using the F1AP Paging message. The gNB-DU determines a Paging Occasion (PO) and a Paging Frame (PF), and eventually sends the paging message to the UE over the air. All the F1AP messages for RRC message transfer are specified in 3GPP TS 38.473, clause 9.2.3, and Paging messages in 3GPP TS 38.473, clause 9.2.6. 4.2.3.2 User-Plane Protocol The F1-U user-plane protocol design also follows the same principles as many other user-plane protocols used on various RAN interfaces. It is based on GTP-U, with the protocol stack described in Section 3.3. A GTP-U tunnel is mapped to an NG-RAN bearer one-to-one and a single F1-U GTP-U PDU carries a single PDCP PDU. Furthermore, the NR user-plane protocol is applicable for the Xn interface (3GPP TS 38.425) as well, hence sequence numbering, retransmissions (if needed), and flow control are supported for PDCP PDUs carried over the NG-RAN user-plane interfaces. More details about the F1-U protocol are can be found in 3GPP TS 38.425. 4.2.3.3 OAM Aspects As mentioned above, both gNB-DU and gNB-CU need to have certain information pre- configured before they establish the F1 interface between them - this is performed via OAM. It is generally assumed that a gNB-CU and a gNB-DU have independent manage- ment interfaces and are managed by the OAM separately. In particular, this means that certain information needed for NG-RAN to operate is preconfigured via OAM in a gNB-CU and a gNB-DU and the peer nodes are not necessarily aware of each other's co