ding of RMSI and the gNB-CU is responsible for encoding of other SI messages. The gNB-DU and gNB-CU measurement reporting functions are used to report the measurements of gNB-DU and gNB-CU, respectively. The gNB-DU is further responsible for transmitting paging information according to the scheduling parameters. The gNB-CU provides paging information to enable gNB-DU to cal- culate the exact paging occasion and paging frame. The gNB-CU is responsible for calculat- ing paging area. The gNB-DU combines the paging records for a particular paging occasion, frame, and area and further encodes the RRC message and broadcasts the paging message. The F1 UE context management function supports the establishment and modifi- cation of the necessary overall initial UE context. The mapping between QoS flows and radio bearers is performed by gNB-CU where the granularity of bearer related management over F1 is at radio-bearer level. To support PDCP duplication for intra-DU carrier aggrega- tion, one DRB should be configured with two GTP-U tunnels between gNB-CU and gNB-DU. 1.2.1.1.3 E1 Control-Plane Functions and Procedures As we discussed earlier, the disaggregated gNB model was introduced to enable separation of control-plane and user-plane functions in addition to the functional split of the protocol stack in gNB which facilitates design and development of new-generation gNBs based on the SDN/NFV concepts. As such, a new interface between the gNB-CU-CP and gNB-CU- UP components has been defined by 3GPP to support exchange of signaling information between these entities (see Fig. 1.52). E1 is an open interface which would allow multi- vendor implementation of the control-plane and data-plane components of the CU. E1 estab- lishes a logical point-to-point interface between a gNB-CU-CP and a gNB-CU-UP even in the absence of a direct physical connection between the endpoints. The E1 interface sepa- rates radio network and TNLs and enables exchange of UE associated/non-UE associated information. The E1 interface is a control inter