5G AMF UPF SMF PCF UDM DN AUSF AF functions | 5G NR Network Nodes

This page describes 5G NR Network Nodes functions. It covers 5G NR nodes or modules AMF, UPF, SMF, PCF, UDM, DN, AUSF and AF.

Introduction:
The 5G stands for 5th generation of wireless technology. It follows 3GPP road map from which LTE i.e. 4th generation wireless technology and LTE advanced have been developed.

• The figure-1 depicts 5G reference point architecture as specified in 3GPP TS 38.300 and 3GPP TS 23.501 specifications. This is non-roaming 5G architecture. The figure shows NG1 to NG15 reference points or interfaces used in the 5G NR reference point architecture.
• gNB node providing NR user plane and control plane protocol terminations towards the UE, and connected via the NG interface to the 5GC.
• ng-eNB node providing E-UTRA user plane and control plane protocol terminations towards the UE and connected via the NG interface to the 5GC.
Refer 5G basic tutorial >>.

Let us understand functions of each of the nodes shown in the figure.

5G NR AMF Functions

AMF stands for Access and Mobility Management Function. Following are the functions of 5G NR AMF node.
• Termination of RAN CP interface (N2)
• Termination of NAS (N1), NAS ciphering and integrity protection.
• Registration management.
• Connection management.
• Reachability management.
• Mobility Management.
• Lawful intercept (for AMF events and interface to LI System).
• Provide transport for SM messages between UE and SMF.
• Transparent proxy for routing SM messages.
• Access Authentication and Access Authorization
• Provide transport for SMS messages between UE and SMSF.
• Security Anchor Functionality (SEAF). It interacts with the AUSF and the UE, receives the intermediate key that was established as a result of the UE authentication process. In the case of USIM based authentication, the AMF retrieves the security material from the AUSF.
• Security Context Management (SCM). The SCM receives a key from the SEAF that it uses to derive access-network specific keys.
• Location Services management for regulatory services.
• Provide transport for Location Services messages between UE and LMF as well as between RAN and LMF.
• EPS Bearer ID allocation for interworking with EPS.
• UE mobility event notification.

In addition to the above mentioned functions, AMF also support functionalities for non 3GPP access networks.

5G NR UPF Functions

UPF stands for User plane function. Following are the functions of 5G NR UPF node.
• Anchor point for Intra-/Inter-RAT mobility (when applicable).
• External PDU Session point of interconnect to Data Network.
• Packet routing & forwarding
• Packet inspection
• User Plane part of policy rule enforcement, e.g. Gating, Redirection, Traffic steering.
• Lawful intercept (UP collection).
• Traffic usage reporting.
• QoS handling for user plane, e.g. UL/DL rate enforcement, Reflective QoS marking in DL.
• 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.
• Sending and forwarding of one or more "end marker" to the source NG-RAN node.

5G NR SMF Functions

SMF stands for Session Management Function. Following are the functions of 5G NR SMF node.
• 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.

5G NR PCF Functions

PCF stands for Policy Control Function. Following are the functions of 5G NR PCF node.
• Supports unified policy framework to govern network behaviour.
• Provides policy rules to Control Plane function(s) to enforce them.
• Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR).

5G NR UDM Functions

UDM stands for Unified Data Management. Following are the functions of 5G NR UDM node.
• Generation of 3GPP AKA Authentication Credentials.
• User Identification Handling
• Access authorization based on subscription data (e.g. roaming restrictions).
• UE's Serving NF Registration Management
• Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions.
• MT-SMS delivery support.
• Lawful Intercept Functionality
• Subscription management.
• SMS management.

5G NR DN Functions

DN stands for Data Network. Following are the functions of 5G NR DN node.
• Operator services, Internet access or other services

5G NR AUSF Functions

Following are the functions of 5G NR AUSF node.
• Supports Authentication Server Function (AUSF) as specified by SA WG3.

5G NR AF Functions

AF stands for Application Function. Following are the functions of 5G NR AF node.
• Application influence on traffic routing
• Accessing Network Exposure Function
• Interacting with the Policy framework for policy control

Reference: 3GPP specification TS 38.300, 3GPP TS 23.501