Architecture model and concepts 5G NR

Non-Roaming 5G System Architecture in reference point representation

Network Function and entities:

1) Authentication Server Function (AUSF)
2) Access and Mobility Management Function (AMF)
3) Data Network (DN)
4) Unstructured Data Storage Function (UDSF)
5) Network Exposure Function (NEF)
6) Network Repository Function (NRF)
7) Network Slice Selection Function (NSSF)
8) Policy Control Function (PCF)
9) Session Management Function (SMF)
10) Unified Data Management (UDM)
11) Unified Data Repository (UDR)
12) User Plane Function (UPF)
12) Application Function (AF)
13) User Equipment (UE)
14) (Radio) Access Network (RAN)
15) 5G - Equipment Identity Register (5G-EIR)
16) Network Data Analytic Function (NWDAF)
17) Charging Function (CHF)
18) Service Communication Proxy (SCP)
19) Security Edge Protection Proxy (SEPP)
20) Non-3GPP Interworking Function (N3IWF)
21) Wireline Access Gateway Function (W-AGF)


Network Function Functional Description 

AMF: 

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.

Access Authorization.

Provide transport for SMS messages between UE and SMSF.

Security Anchor Functionality (SEAF) as specified in TS 33.501.

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.

Support for Control Plane CIoT 5GS Optimisation.

Provisioning of external parameters (Expected UE Behaviour parameters or Network Configuration parameters).

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.

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.

Support of authentication of UEs connected over N3IWF.

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.

A co-ordinated RM management context valid over 3GPP and Non 3GPP accesses.

Dedicated CM management contexts for the UE for connectivity over non-3GPP access.

SMF

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

UE IP address allocation & management (including optional Authorization). The UE IP address may be received from a UPF or from an external data network.

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

Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information 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.

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.

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).

Charging data collection and support of charging interfaces.

Control and coordination of charging data collection at UPF.

Termination of SM parts of NAS messages.

Downlink Data Notification.

Initiator of AN specific SM information, sent via AMF over N2 to AN.

Determine SSC mode of a session.

Support for Control Plane CIoT 5GS Optimisation.

Support of header compression.

Act as I-SMF in deployments where I-SMF can be inserted, removed and relocated.

Provisioning of external parameters (Expected UE Behaviour parameters or Network Configuration parameters).

Roaming functionality.

UPF

• Anchor point for Intra-/Inter-RAT mobility (when applicable).
• Allocation of UE IP address/prefix (if supported) in response to SMF request.
• 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.
• Functionality to respond to Address Resolution Protocol (ARP) requests and / or IPv6 Neighbour Solicitation requests based on local cache information 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.
• Packet duplication in downlink direction and elimination in uplink direction in GTP-U layer.
• TSN Translator functionality to hold and forward user plane packets for de-jittering when 5G System is integrated as a bridge with the TSN network.

PCF

• 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).

NEF

• 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).

• 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 Behaviour, 5GLAN group information and service specific information. In that case the NEF may authenticate and authorize and assist in throttling the Application Functions.

• 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.

• 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 "re-exposed" by the NEF to other network functions and Application Functions, and used for other purposes such as analytics.
• 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 NEF may also support a 5GLAN Group Management Function: The 5GLAN Group Management Function in the NEF may store the 5GLAN group information in the UDR via UDM as described in.
• Exposure of analytics:

NWDAF analytics may be securely exposed by NEF for external party

• Retrieval of data from external party by NWDAF:

Data provided by the external party may be collected by NWDAF via NEF for analytics generation purpose. NEF handles and forwards requests and notifications between NWDAF and AF.

NRF

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

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

    -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 priority information.

-NF Set ID.

-NF Service Set ID of the NF service instance.

-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.

-Other service parameter, e.g., DNN, notification endpoint for each type of notification that the NF service is interested in receiving.

-Location information for the NF instance.

-TAI(s).

-Routing Indicator, for UDM and AUSF.

-One or more GUAMI(s), in case of AMF.

-SMF area identity(ies) in case of UPF.

-UDM Group ID, range(s) of SUPIs, range(s) of GPSIs, range(s) of external group identifiers for UDM.

-UDR Group ID, range(s) of SUPIs, range(s) of GPSIs, range(s) of external group identifiers for UDR.

-AUSF Group ID, range(s) of SUPIs for AUSF.

-Analytics ID, in case of NWDAF.

-PLMN level (the NRF is configured with information for the whole PLMN),

-shared-slice level (the NRF is configured with information belonging to a set of Network Slices),

-slice-specific level (the NRF is configured with information belonging to an S-NSSAI).

-the NRF(s) in the Visited PLMN (known as the vNRF) configured with information for the visited PLMN.

-the NRF(s) in the Home PLMN (known as the hNRF) configured with information for the home PLMN, referenced by the vNRF via the N27 interface.

UDM

• Generation of 3GPP AKA Authentication Credentials. 
• User Identification Handling (e.g. storage and management of SUPI for each subscriber in the 5G system). 
• Support of de-concealment of privacy-protected subscription identifier (SUCI).  
• Access authorization based on subscription data (e.g. roaming restrictions).
• UE's Serving NF Registration Management (e.g. storing serving AMF for UE, storing serving SMF for UE's PDU Session).
• Support to service/session continuity e.g. by keeping SMF/DNN assignment of ongoing sessions.
• MT-SMS delivery support.
• Lawful Intercept Functionality (especially in outbound roaming case where UDM is the only point of contact for LI).
• Subscription management.
• SMS management.
• 5GLAN group management handling.
• Support of external parameter provisioning (Expected UE Behaviour parameters or Network Configuration parameters).

AUSF

• Supports authentication for 3GPP access and untrusted non-3GPP access.

N3IWF

• Support of IPsec tunnel establishment with the UE: The N3IWF terminates the IKEv2/IPsec protocols with the UE over NWu and relays over N2 the information needed to authenticate the UE and authorize its access to the 5G Core Network.
• Termination of N2 and N3 interfaces to 5G Core Network for control - plane and user-plane respectively.
• Relaying uplink and downlink control-plane NAS (N1) signalling between the UE and AMF.
• Handling of N2 signalling from SMF (relayed by AMF) related to PDU Sessions and QoS.
• Establishment of IPsec Security Association (IPsec SA) to support PDU Session traffic.
• Relaying uplink and downlink user-plane packets between the UE and UPF. This involves:
• De-capsulation/ encapsulation of packets for IPSec and N3 tunnelling
• Enforcing QoS corresponding to N3 packet marking, taking into account QoS requirements associated to such marking received over N2
• N3 user-plane packet marking in the uplink.
• Local mobility anchor within untrusted non-3GPP access networks using MOBIKE per IETF RFC 4555.
• Supporting AMF selection.

TNGF

• Terminates the N2 and N3 interfaces.
• Terminates the EAP-5G signalling and behaves as authenticator when the UE attempts to register to 5GC via the TNAN.
• Implements the AMF selection procedure.
• Transparently relays NAS messages between the UE and the AMF, via the NWt connection.
• Handles N2 signalling with SMF (relayed by AMF) for supporting PDU sessions and QoS.
• Transparently relays PDU data units between the UE and a UPF in 5GC.
• Implements a local mobility anchor within the TNAN.

AF

• Application influence on traffic routing;
• Accessing Network Exposure Function;
• Interacting with the Policy framework for policy control.

     Based on operator deployment, Application Functions considered to be trusted by the operator can be allowed to interact directly with relevant Network Functions.

    Application Functions not allowed by the operator to access directly the Network Functions shall use the external exposure framework via the NEF to interact with relevant Network Functions.

    The functionality and purpose of Application Functions are only defined in this specification with respect to their interaction with the 3GPP Core Network.

UDR

• Storage and retrieval of subscription data by the UDM.
• Storage and retrieval of policy data by the PCF.
• Storage and retrieval of structured data for exposure.
• Application data (including Packet Flow Descriptions (PFDs) for application detection, AF request information for multiple UEs, 5GLAN group information for 5GLAN management).

UDSF

• Storage and retrieval of information as unstructured data by any NF.

SMSF

• SMS management subscription data checking and conducting SMS delivery accordingly.
• SM-RP/SM-CP with the UE.
• Relay the SM from UE toward SMS-GMSC/IWMSC/SMS-Router.
• Relay the SM from SMS-GMSC/IWMSC/SMS-Router toward the UE.
• SMS related CDR.
• Lawful Interception.
• Interaction with AMF and SMS-GMSC for notification procedure that the UE is unavailable for SMS transfer (i.e, notifies SMS-GMSC to inform UDM when UE is unavailable for SMS).

NSSF

• Selecting the set of Network Slice instances serving the UE;
• Determining the Allowed NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
• Determining the Configured NSSAI and, if needed, the mapping to the Subscribed S-NSSAIs;
• 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.

5G-EIR

• Check the status of PEI (e.g. to check that it has not been blacklisted).

SEPP

• Message filtering and policing on inter-PLMN control plane interfaces.
• Topology hiding.

Network Data Analytics Function (NWDAF)

• Support data collection from NFs and AFs;
• Support data collection from OAM;
• NWDAF service registration and metadata exposure to NFs/AFs;
• Support analytics information provisioning to NFs, AF.

SCP

• Indirect Communication.
• Delegated Discovery.
• Message forwarding and routing to destination NF/NF service.
• Communication security (e.g. authorization of the NF Service Consumer to access the NF Service Producer API), load balancing, monitoring, overload control, etc.
• Ability to discover and select one or more UDM(s), AUSF(s), UDR(s), PCF(s) with access to subscription data stored in the UDR based on UE's SUPI, SUCI or GPSI.

[1] 3GPP TS 23.501 System Architecture for the 5G System v16.0.2