4.2 Functional Split

38.3003GPPNRNR and NG-RAN Overall descriptionRelease 17Stage 2TS

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 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 [3] (ng-eNB only).

NOTE 1: BL UE or UE in enhanced coverage is only supported by ng-eNB, see TS 36.300 [2].

NOTE 2: NB-IoT UE is only supported by ng-eNB, see TS 36.300 [2].

The AMF hosts the following main functions (see TS 23.501 [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 [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 [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