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 both uplink and downlink (scheduling);

-IP header compression, 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.

The AMF hosts the following main functions (see TS 23.501):

-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.

The UPF hosts the following main functions (see TS 23.501):

-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):

-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.

In the figure yellow boxes depict the logical nodes and white boxes depict the main functions.