The 5G network architecture consist of the Radio access Network (RAN) and the core network (NG-Core). The NG-Core stands for Next Generation Core and it consists of the following network functions:

 

1- AMF The Access and Mobility Management function (AMF)

2- SMF The Session Management function (SMF) 

3- UPF The User plane function (UPF) 

4- PCF The Policy Control Function (PCF) 

5- NEF The Network Exposure Function (NEF)

6- NRF The Network Repository Function (NRF)

7- UDM The Unified Data Management (UDM)

8- AUSF The Authentication Server Function (AUSF) 

9- AF The Application Function (AF) 

10- NSSF: The Network Slice Selection Function (NSSF)

 

 

The functionality and services of the Next Generation Core (NG-Core) network functions:

AMF The Access and Mobility Management function (AMF) includes the following functionality. Some or all of the AMF functionalities may be supported in a single instance of an AMF: 

1- Termination of RAN CP interface (N2). 

2- Termination of NAS (N1), NAS ciphering and integrity protection. 

3- Registration management. 

4- Connection management. 

5- Reachability management. 

6- Mobility Management. 

7- Lawful intercept (for AMF events and interface to LI System).

8- Provide transport for SM messages between UE and SMF. 

9- Transparent proxy for routing SM messages. 

10- Access Authentication. 

11- Access Authorization. 

12- Provide transport for SMS messages between UE and SMSF.

 13- Security Anchor Functionality

14- Location Services management for regulatory services.

 15- Provide transport for Location Services messages between UE and LMF as well as between RAN and LMF.

16- EPS Bearer ID allocation for interworking with EPS. 

17- UE mobility event notification. 

In addition to the functionalities of the AMF described above, the AMF may include the following functionality to support non-3GPP access networks: 

1- Support of N2 interface with N3IWF. Over this interface, some information (e.g. 3GPP Cell Identification) and procedures (e.g. Handover related) defined over 3GPP access may not apply, and non-3GPP access specific information may be applied that do not apply to 3GPP accesses.

2- Support of NAS signalling with a UE over N3IWF. Some procedures supported by NAS signalling over 3GPP access may be not applicable to untrusted non-3GPP (e.g. Paging) access. 

3- Support of authentication of UEs connected over N3IWF. 

4- Management of mobility, authentication, and separate security context state(s) of a UE connected via non-3GPP access or connected via 3GPP and non-3GPP accesses simultaneously. 

5- Support as  a co-ordinated RM management context valid over 3GPP and Non 3GPP accesses. 

6- Support dedicated CM management contexts for the UE for connectivity over non3GPP access. 

 

SMF The Session Management function (SMF) includes the following functionality. Some or all of the SMF functionalities may be supported in a single instance of a SMF:

1- Session Management e.g. Session Establishment, modify and release, including tunnel maintain between UPF and AN node. 

2- UE IP address allocation & management (including optional Authorization). 

3- DHCPv4 (server and client) and DHCPv6 (server and client) functions. 

4- ARP proxying and / or IPv6 Neighbour Solicitation Proxying  functionality for the Ethernet PDUs. The SMF responds to the ARP and / or the IPv6 Neighbour Solicitation Request by providing the MAC address corresponding to the IP address sent in the request. 

5- Selection and control of UP function, including controlling the UPF to proxy ARP or IPv6 Neighbour Discovery, or to forward all ARP/IPv6 Neighbour Solicitation traffic to the SMF, for Ethernet PDU Sessions. 

6- Configures traffic steering at UPF to route traffic to proper destination. – Termination of interfaces towards Policy control functions. – Lawful intercept (for SM events and interface to LI System).

7- Charging data collection and support of charging interfaces. 

8- Control and coordination of charging data collection at UPF. 

9- Termination of SM parts of NAS messages. – Downlink Data Notification. – Initiator of AN specific SM information, sent via AMF over N2 to AN.

8- Determine SSC mode of a session. 

9- Roaming functionality: 

– Handle local enforcement to apply QoS SLAs (VPLMN).

– Charging data collection and charging interface (VPLMN). 

– Lawful intercept (in VPLMN for SM events and interface to LI System).

– Support for interaction with external DN for transport of signalling for PDU Session authorization/authentication by external DN. 

 

UPF The User plane function (UPF) includes the following functionality. Some or all of the UPF functionalities may be supported in a single instance of a UPF: 

– Anchor point for Intra-/Inter-RAT mobility (when applicable). 

– External PDU Session point of interconnect to Data Network.

 – Packet routing & forwarding (e.g. support of Uplink classifier to route traffic flows to an instance of a data network, support of Branching point to support multi-homed PDU Session). 

– Packet inspection (e.g. Application detection based on service data flow template and the optional PFDs received from the SMF in addition).

 – 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. 

– ARP proxying  and / or IPv6 Neighbour Solicitation Proxying  functionality for the Ethernet PDUs. The UPF responds to the ARP and / or the IPv6 Neighbour Solicitation Request by providing the MAC address corresponding to the IP address sent in the request. 

 

PCF The Policy Control Function (PCF) includes the following functionality: 

1- Supports unified policy framework to govern network behaviour.

 2- Provides policy rules to Control Plane function(s) to enforce them. 

3- Accesses subscription information relevant for policy decisions in a Unified Data Repository (UDR). 

 

 NEF The Network Exposure Function (NEF) supports the following independent functionality:

1- Exposure of capabilities and events: 

NF capabilities and events may be securely exposed by NEF for e.g. 3rd party, Application Functions, Edge Computing 

NEF stores/retrieves information as structured data using a standardized interface (Nudr) to the Unified Data Repository (UDR). 

2- Secure provision of information from external application to 3GPP network: 

It provides a means for the Application Functions to securely provide information to 3GPP network, e.g. Expected UE Behavior. In that case the NEF may authenticate and authorize and assist in throttling the Application Functions.

3- Translation of internal-external information:

 It translates between information exchanged with the AF and information exchanged with the internal network function. For example, it translates between an AF-Service-Identifier and internal 5G Core information such as DNN, S-NSSAI. 

In particular, NEF handles masking of network and user sensitive information to external AF’s according to the network policy.

4- The Network Exposure Function receives information from other network functions (based on exposed capabilities of other network functions). NEF stores the received information as structured data using a standardized interface to a Unified Data Repository (UDR). The stored information can be accessed and “reexposed” by the NEF to other network functions and Application Functions, and used for other purposes such as analytics. 

5- A NEF may also support a PFD Function: The PFD Function in the NEF may store and retrieve PFD(s) in the UDR and shall provide PFD(s) to the SMF on the request of SMF (pull mode) or on the request of PFD management from NEF (push mode). 

A specific NEF instance may support one or more of the functionalities described above and consequently an individual NEF may support a subset of the APIs specified for capability exposure. 

 

 NRF The Network Repository Function (NRF) supports the following functionality:

1- Supports service discovery function. Receive NF Discovery Request from NF instance, and provides the information of the discovered NF instances (be discovered) to the NF instance.

2 – Maintains the NF profile of available NF instances and their supported services. 

NF profile of NF instance maintained in an NRF includes the following information: 

– NF instance ID.

– NF type. 

– PLMN ID. 

– Network Slice related Identifier(s) e.g. S-NSSAI, NSI ID. 

– FQDN or IP address of NF. 

– NF capacity information. 

– NF Specific Service authorization information.

 – if applicable, Names of supported services. 

– Endpoint Address(es) of instance(s) of each supported service. 

– Identification of stored data/information. 

 

UDM The Unified Data Management (UDM) includes support for the following functionality:

1- Generation of 3GPP AKA Authentication Credentials.

2- User Identification Handling (e.g. storage and management of SUPI for each subscriber in the 5G system). 

3- Support of de-concealment of privacy-protected subscription identifier (SUCI). 

4- Access authorization based on subscription data (e.g. roaming restrictions). 

5- UE’s Serving NF Registration Management (e.g. storing serving AMF for UE, storing serving SMF for UE’s PDU Session).

6- Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions. 

7- MT-SMS delivery support.

8- Lawful Intercept Functionality (especially in outbound roaming case where UDM is the only point of contact for LI). 

9- Subscription management.

10- SMS management. 

 

AUSF The Authentication Server Function (AUSF) supports the following functionality:

 1- Supports authentication for 3GPP access and untrusted non-3GPP access 

 

AF The Application Function (AF) interacts with the 3GPP Core Network in order to provide services, for example to support the following: 

1- Application influence on traffic routing

2- Accessing Network Exposure Function

3- Interacting with the Policy framework for policy control, 

 

NSSF: The Network Slice Selection Function (NSSF) supports the following functionality:

1 – Selecting the set of Network Slice instances serving the UE, 

2- Determining the Allowed NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs,

 3- Determining the Configured NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs, 

4- Determining the AMF Set to be used to serve the UE, or, based on configuration, a list of candidate AMF(s), possibly by querying the NRF. 

 

The 5G System Architecture contains the following reference points: 

N1: Reference point between the UE and the AMF.

N2: Reference point between the (R)AN and the AMF. 

N3: Reference point between the (R)AN and the UPF. 

N4: Reference point between the SMF and the UPF. 

N5: Reference point between the PCF and an AF.

N6: Reference point between the UPF and a Data Network. 

N7: Reference point between the SMF and the PCF. 

N8: Reference point between the UDM and the AMF.

N9: Reference point between two UPFs. 

N10: Reference point between the UDM and the SMF. 

N11: Reference point between the AMF and the SMF. 

N12: Reference point between AMF and AUSF.

N13: Reference point between the UDM and Authentication Server function the AUSF. 

N14: Reference point between two AMFs. 

N15: Reference point between the PCF and the AMF in the case of non-roaming scenario, PCF in the visited network and AMF in the case of roaming scenario.

N16: Reference point between two SMFs, (in roaming case between SMF in the visited network and the SMF in the home network). 

N17: Reference point between AMF and 5G-EIR. 

N18: Reference point between any NF and UDSF. 

N22: Reference point between AMF and NSSF.

N23: Reference point between PCF and NWDAF. 

N24: Reference point between the PCF in the visited network and the PCF in the home network.

 N27: Reference point between NRF in the visited network and the NRF in the home network. 

N31: Reference point between the NSSF in the visited network and the NSSF in the home network.