Section: 4.2 Functional Split
Content: The gNB and ng-eNB host the following functions: - Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in uplink, downlink and sidelink (scheduling); - IP and Ethernet header compression, uplink data decompression, encryption and integrity protection of data; - Selection of an AMF at UE attachment when no routing to an AMF can be determined from the information provided by the UE; - Routing of User Plane data towards UPF(s); - Routing of Control Plane information towards AMF; - Connection setup and release; - Scheduling and transmission of paging messages; - Scheduling and transmission of system broadcast information (originated from the AMF or OAM); - Measurement and measurement reporting configuration for mobility and scheduling; - Transport level packet marking in the uplink; - Session Management; - Support of Network Slicing; - QoS Flow management and mapping to data radio bearers; - Support of UEs in RRC_INACTIVE state; - Distribution function for NAS messages; - Radio access network sharing; - Dual Connectivity; - Tight interworking between NR and E-UTRA; - Maintain security and radio configuration for User Plane CIoT 5GS Optimisation, as defined in TS 23.501[ System architecture for the 5G System (5GS) ]  [3] (ng-eNB only). NOTE 1: BL UE or UE in enhanced coverage is only supported by ng-eNB, see TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [2]. NOTE 2: NB-IoT UE is only supported by ng-eNB, see TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [2]. The AMF hosts the following main functions (see TS 23.501[ System architecture for the 5G System (5GS) ]  [3]): - NAS signalling termination; - NAS signalling security; - AS Security control; - Inter CN node signalling for mobility between 3GPP access networks; - Idle mode UE Reachability (including control and execution of paging retransmission); - Registration Area management; - Support of intra-system and inter-system mobility; - Access Authentication; - Access Authorization including check of roaming rights; - Mobility management control (subscription and policies); - Support of Network Slicing; - SMF selection. - Selection of CIoT 5GS optimisations; The UPF hosts the following main functions (see TS 23.501[ System architecture for the 5G System (5GS) ]  [3]): - Anchor point for Intra-/Inter-RAT mobility (when applicable); - External PDU session point of interconnect to Data Network; - Packet routing & forwarding; - Packet inspection and User plane part of Policy rule enforcement; - Traffic usage reporting; - Uplink classifier to support routing traffic flows to a data network; - Branching point to support multi-homed PDU session; - QoS handling for user plane, e.g. packet filtering, gating, UL/DL rate enforcement; - Uplink Traffic verification (SDF to QoS flow mapping); - Downlink packet buffering and downlink data notification triggering. The Session Management function (SMF) hosts the following main functions (see TS 23.501[ System architecture for the 5G System (5GS) ]  [3]): - Session Management; - UE IP address allocation and management; - Selection and control of UP function; - Configures traffic steering at UPF to route traffic to proper destination; - Control part of policy enforcement and QoS; - Downlink Data Notification. This is summarized on the figure below where yellow boxes depict the logical nodes and white boxes depict the main functions. Figure 4.2-1: Functional Split between NG-RAN and 5GC