ewhat loosely defined to allow sufficient freedom of implementation and generally include: UE admission control over the radio interface; UE radio interface connection setup and release; Radio resource management, including UE radio bearer control, and uplink and down- link scheduling for a UE; UE mobility control in connected state (i.e. handover) and in inactive state; UE measurements, including measurement configuration and processing of UE mea- surement reports; Routing of user-plane and control-plane packets toward UPF and AMF, respectively; UE QoS flow management and mapping to radio bearers; Slicing; Tight interworking between NR and LTE, including multiple dual connectivity options (between these technologies); RAN sharing between multiple operators. As mentioned above, some of the NG-RAN functions, for example the air interface or the NG interface protocol stacks, are well defined in the corresponding specifications and are described in the present book; some other functions (e.g. scheduling, resource isolation for slicing, radio resource management, and others) are intentionally left unspecified, in order to allow for implementation flexibility and differentiation. 3.3 NG Radio Access Network The following key enhancements have been introduced in NG-RAN compared with E-UTRAN. Multiple air interfaces: in contrast to E-UTRAN, NG-RAN supports two air interfaces; gNB supports the NR air interface and ng-eNB supports the LTE air interface. Both gNB and ng-eNB are considered NG-RAN network nodes. Split architectures: in addition to the "flat" architecture with a monolithic gNB, which is similar to E-UTRAN, NG-RAN supports an architecture with a gNB split into two (high-level and low-level referred to CU and DU, respectively) logical nodes, with a standardized F1 interface between them. Furthermore, the central unit of a gNB, which implements the higher layers of the split, can be deployed as separate control-plane and user-plane logical network nodes with a standardized E1 interface between them. More- over, 