, requirements, and interfaces 45 NG-eNB NG-eNB FIGURE 2-2 NG-RAN (copied from 3GPP 38.300). NG-RAN, Next-Generation Radio Access Network User Plane Control Plane User-Plane PDUs Xn-AP/NG-AP GTP-U Data Link Layer Data Link Layer Physical Layer Physical Layer FIGURE 2-3 User plane (left hand side) and control plane/signaling plane traffic. 46 Open Radio Access Network (O-RAN) Systems Architecture and Design User Plane Control Plane SDAP Layer SDAP Layer NAS Layer NAS Layer PDCP Layer PDCP Layer RRC Layer RRC Layer RLC Layer RLC Layer PDCP Layer PDCP Layer MAC Layer MAC Layer RLC Layer RLC Layer Physical Layer Physical Layer MAC Layer MAC Layer Physical Layer Physical Layer FIGURE 2-4 User plane (left) and control plane (right) 5G protocol stacks. Other Network Service Function Based Interfaces CP IF CP IF UP IF UP IF UP IF Internet to (IP) Data Gateway Network Non-Wireless Network Non-3GPP wireless (WiFi) N3IWF FIGURE 2-5 CP/UP Split in 5G network components. CP, control plane; UP, user plane. and is an anchor point for intra- and inter-radio access technology mobility. The UPF is explicitly design to support multiple access networks including wireline and other wireless interfaces, targeting fixed-mobile convergence. Chapter 2 System components, requirements, and interfaces 47 CP functions are implemented in the following components: Access and Mobility Management Function (AMF). Termination of Non Access Stratum (NAS) signaling, NAS ciphering and integrity, registration/connection/mobility management, including roaming, access authentication and authorization, and security context management. This function terminates the CP protocol to the UE as we showed before. Session Management Function. Session management (establishment, modification, and release), UE IP address allocation and management, Dynamic Host Configuration Protocol (DHCP), termination of NAS signaling related to session management, DL data notification, and traffic steering configuration for UPF for proper traffic routing. Policy Control Function (