5G Stuff: NG-RAN Architecture elements

The below figure shows NG-RAN (NextGen - RAN) architecture. It consists of

          - NG-RAN consists of gNBs, providing both control and user data plane terminations towards UE.
                   - Here gNBs are interconnected with Xn interface

          - NGC (NextGen Core) consists of AMF/UPF
                   - Here gNBs and AMF/UPF are interconnected with NG-CU interface

gNB has similar functionalities, like eNB in LTE. They are below (as per 3GPP TR 38.804 V14.0, sec 5.1)
       - Radio Resource Management
       - IP header compression and encryption of user plane data
       - selection of AMF during UE attachment when no routing to an AMF can be determined from the information provided by the UE
       - Routing of User plane data to UPF
       - Scheduling and transmission of paging messages, System Broadcast Infos 
       - Measurement and Measurement reporting config

AMF Functionality can be as follows
      - 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);

      - Tracking Area list management (for UE in idle and active mode);

      - AMF selection for handovers with AMF change;

      - Access Authentication;

      - Access Authorization including check of roaming rights.

UPF:

-     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);

-     Transport level packet marking in the uplink and downlink;

-     Downlink packet buffering and downlink data notification triggering.

SMF:

-      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.