through the Xn interface. NG-RAN and 5G-NR The data is transmitted to the ng-eNB entity via one of the following options (Figure 1.4): - from the master node gNB, which performs the split bearer (option 4, MN terminated split bearer); - from the 5GC network (option 4a, SCG bearer). Option 4 Option 4a Figure 1.4. NE-DC architecture - option 4 1.1.3. Option 7 Option 7 relies on the 5G core (5GC). The ng-eNB acts as an MN; it supports signaling (MCG signaling bearer) with the 5GC core network's transport plane through the NG-C interface and exchanges data to the 5G core network's user plane through the NG-U interface. The gNB base station acts as an SN. It is controlled by the ng-eNB base station via the Xn-C interface. The ng-eNB (4G base station) controls the gNB through the Xn interface. The data is transmitted to the gNB entity via one of the following options (Figure 1.5): - from the ng-eNB base station, which performs a split bearer. This is option 7 (MN terminated split bearer); - from the 5G core network. This is option 7a (SCG bearer). NG-RAN Network - Functional Architecture Option 7 Option 7a Figure 1.5. NE-DC architecture - option 7 1.2. Description of the NG-RAN network The NG-RAN provides both NR and LTE radio access. An NG-RAN node is either a gNB (5G base station), providing NR user plane and control plane services, or an ng-eNB (new generation 4G base station) providing the LTE/E-UTRAN services towards the UE (control plane and user plane). The NG-RAN ensures the connection of mobiles and the reservation of radio resources between: - the mobile and the ng-eNB base station on a single 4G carrier (LTE) or on several 4G frequency carriers (LTE-Advanced); - the mobile and the gNB base station on one or more 5G frequency bands (5G-NR). The gNBs and ng-eNBs are interconnected through the Xn interface. The gNBs and ng-eNBs are also connected, via NG interfaces, to the 5G core (5GC). The NG interface is the point of reference between the NG-RAN and the 5G core network: - the NG-C interface is the interface 