le. The NG-AP application layer protocol enables the exchange of control data between the NG-RAN radio access and the AMF function, via the N2 logical interface. The NG-AP protocol is extended to the on-3GPP radio access network between the N3IWF (Non-3GPP InterWorking Function) and the AMF function. The main functions associated with the mobile established through NG-AP messages concern: - management of mobile attachment and monitoring its mobility (N1-NAS MM); - management of the bearers established between the NG-RAN access node and the 5G core network (N1-NAS SM). NAS signaling messages exchanged between the mobile and the AMF function are secured using an encryption key and an integrity key. NG-RAN and 5G-NR The N2 control plan separates the functions related to the AMF entity and the functions related to the SMF entity. For session request (SM) exchanges, the AMF transparently transfers the NG-AP messages to the SMF. 2.1.4.1. NG-C interface The NG-C control plane interface is the interface between an NG-RAN node (gNB, ng-eNB) and the AMF function. The protocol stack is defined on the N2 interface (Figure 2.10). From a user point of view, the functions on the NG-C control plane interface allow: - management of the NG interface; - UE context management (the UE context management functionality between the NG-RAN access and the 5G core network), including the context of the PDU session, the security key exchange, the mobility restriction list, the radio capacities and the security capacities of the mobile. Context management includes creating, modifying and deleting the context; - management of UE mobility in connected mode (handover); - notification of the RRC_INACTIVE state of the mobile to the AMF function; - NAS message transport; - NAS request routing (e.g. when registering on the dedicated network slice); - session notification (paging); - the management of PDU sessions for the establishment and deletion of PDU sessions, as well as for the transfer of a PDU session between two NG-RAN nodes via the core ne