5 Architecture model and reference points

23.5033GPPPolicy and charging control framework for the 5G System (5GS)Release 18Stage 2TS

5.1 General

This specification describes the policy and charging control framework for the 5G system. The interaction between network functions is represented in two ways:

– A service-based representation, where network functions enable other authorized network functions to access their services. This representation also includes point-to-point reference points where necessary;

– A reference point representation, which shows that interactions exist between those network functions for which a reference point is depicted between them.

5.2 Reference architecture

5.2.1 Non-roaming architecture

The reference architecture of policy and charging control framework for the 5G System is comprised by the functions of the Policy Control Function (PCF), the Session Management Function (SMF), the User Plane Function (UPF), the Access and Mobility Management Function (AMF), the Network Exposure Functionality (NEF), the Network Data Analytics Function (NWDAF), the Charging Function (CHF), the Application Function (AF) and UDR (Unified Data Repository).

Figure 5.2.1-1 shows the service based representation and Figure 5.2.1-1a shows the reference point representation of the reference architecture of policy and charging control framework for the 5G System.

Figure 5.2.1-1: Overall non-roaming reference architecture of policy and charging control framework for the 5G System (service based representation)

Figure 5.2.1-1a: Overall non-roaming reference architecture of policy and charging control framework for the 5G System (reference point representation)

NOTE 1: The N4 reference point is not part of the 5G Policy Framework architecture but shown in the figures for completeness. See TS 23.501 [2] for N4 reference point definition.

NOTE 2: How the PCF/NEF stores/retrieves information related with policy subscription data or with application data is defined in TS 23.501 [2].

NOTE 3: The 5G DDNMF to PCF reference point is not depicted in the point-to-point reference architecture diagrams and the 5G DDNMF is not shown in the service-based architecture diagrams. The 5G DDNMF is included in the ProSe architecture depicted in TS 23.304 [34].

NOTE 4: For clarity, the DCCF and its connections with PCF are not depicted in the point-to-point and service-based architecture diagrams. For more information on network data analytics architecture using DCCF refer to TS 23.288 [24].

The Nchf service for online and offline charging consumed by the SMF is defined in TS 32.240 [8].

The Nchf service for Spending Limit Control consumed by the PCF is defined in TS 23.502 [3].

The PCF providing session management policy control for a UE (i.e. PCF for the PDU Session) and the PCF providing non-session management policy control for that UE (i.e. PCF for the UE) may be different PCF instances. For the case that there are different PCF instances, the PCF for the PDU Session does not support the N15 reference point while the PCF for the UE does not support the N7 reference point. The N43 reference point enables communication between the PCF for a UE and the PCF for the PDU Session.

5.2.2 Roaming architecture

Figure 5.2.2-1 shows the local breakout roaming policy framework architecture in 5G:

Figure 5.2.2-1: Overall roaming reference architecture of policy and charging control framework for the 5G System – local breakout scenario

Figure 5.2.2-1a: Overall roaming reference architecture of policy and charging control framework for the 5G System – local breakout scenario (reference point representation)

NOTE 1: In the LBO architecture, the PCF in the VPLMN may interact with the AF in order to generate PCC Rules for services delivered via the VPLMN. The PCF in the VPLMN uses locally configured policies according to the roaming agreement with the HPLMN operator as input for PCC Rule generation. The PCF in VPLMN has no access to subscriber policy information from the HPLMN for PCC Rule generation.

NOTE 2: In the LBO architecture, N24 can be used to deliver UE policy information from the PCF in the HPLMN to the PCF in the VPLMN. The PCF in the VPLMN can provide access and motility policy information without contacting the PCF in the HPLMN.

NOTE 3: In the LBO architecture, AF requests providing routing information for roamers targeting a DNN and S-NSSAI (targeting all roamers) or an External-Group-Identifier (identifying a group of roamers) are stored as Application Data in the UDR(in the VPLMN) by the NEF (in the VPLMN).

NOTE 4: For the sake of clarity, SEPPs are not depicted in the roaming reference point architecture figures.

Figure 5.2.2-2 shows the roaming policy framework architecture (home routed scenario) in 5G:

Figure 5.2.2-2: Overall roaming reference architecture of policy and charging control framework for the 5G System – home routed scenario

Figure 5.2.2-2a: Overall roaming reference architecture of policy and charging control framework for the 5G System – home routed scenario (reference point representation)

NOTE 5: All functional entities as described in Figure 5.2.1-1 non-roaming scenario, except NWDAF, applies also to the HPLMN in the home routed scenario above.

NOTE 6: For the sake of clarity, SEPPs are not depicted in the roaming reference point architecture figures.

5.2.3 Void

5.3 Service-based interfaces and reference points

5.3.1 Interactions between PCF and AF

Npcf and Naf enable transport of application level session information and Ethernet port management information from AF to PCF. Such information includes, but is not limited to:

– IP filter information or Ethernet packet filter information to identify the service data flow for policy control and/or differentiated charging;

– media/application bandwidth requirements for QoS control;

– In addition, for sponsored data connectivity:

– the sponsor’s identification;

– optionally, a usage threshold and whether the PCF reports these events to the AF;

– information identifying the application service provider and application (e.g. SDFs, application identifier, etc.);

– information required to enable Application Function influence on traffic routing as defined in clause 5.6.7 of TS 23.501 [2];

– information required to enable setting up an AF session with required QoS as defined in clause 6.1.3.22;

– information required to enable setting up an AF session with support for Time Sensitive Networking (TSN) as defined in clause 6.1.3.23.

Npcf also enables the AF to request to influence Access and Mobility related policies for a UE and enables the AF to provide guidance for UE URSP rule determination. Npcf and Naf enable the AF subscription to notifications on PDU Session events, i.e. the events requested by the AF as described in clause 6.1.3.18 and the change of DNAI as defined in clause 5.6.7 of TS 23.501 [2].

The N5 reference point is defined for the interactions between PCF and AF in the reference point representation.

5.3.2 Interactions between PCF and SMF

Npcf and Nsmf enable the PCF to have dynamic control over the policy and charging behaviour at a SMF.

Npcf and Nsmf enable the signalling of policy and charging control decisions and support the following functionality:

– Creation of a SM Policy Association as defined in clause 4.16 of TS 23.502 [3];

– Request for policy and charging control decision from the SMF to the PCF when a Policy Control Request Trigger related to Session Management has been met;

– Provision of policy and charging control decision from the PCF to the SMF;

– Deletion of a SM Policy Association as defined in clause 4.16 of TS 23.502 [3].

The N7 reference point is defined for the interactions between PCF and SMF in the reference point representation.

5.3.3 Interactions between PCF and AMF

Npcf and Namf enable the PCF to provide Access and Mobility related policy information to the AMF as well as to provide UE policy information to the UE via the AMF and support the following functionality:

– Creation and Deletion of an AM Policy Association as defined in clause 4.16 of TS 23.502 [3];

– Creation and Deletion of an UE Policy Association as defined in clause 4.16 of TS 23.502 [3];

– Request for access and mobility related policy information from the AMF to the PCF when a Policy Control Request Trigger related to Access and Mobility Management, UE access selection or PDU Session selection has been met as defined in clause 6.1.2.5;

– Provision of access and mobility management related policy information from the PCF to the AMF as defined in clause 6.5;

– Handling of transparent delivery of UE policy information from the PCF to the UE via the AMF.

The N15 reference point is defined for the interactions between PCF and AMF in the reference point representation.

5.3.4 Interactions between V-PCF and H-PCF

For roaming scenario, the interactions between V-PCF and H-PCF through Npcf enables:

– Creation of an UE Policy Association as defined in clause 4.16 of TS 23.502 [3];

– Relay of notification of changes from the V-PCF in the VPLMN to the H-PCF as defined in clause 4.16 of TS 23.502 [3];

– Provision of UE policy information to the V-PCF in the VPLMN;

– Deletion of an UE Policy Association as defined in clause 4.16 of TS 23.502 [3].

The N24 reference point is defined for the interactions between V-PCF and H-PCF in the reference point representation.

5.3.5 Interactions between PCF and UDR

The Nudr enables the PCF to access policy control related subscription information and application specific information stored in the UDR. The Nudr interface supports the following functions:

– request for policy control related subscription information and application specific information from the UDR;

– provisioning of policy control related subscription information and application specific information to the UDR;

– notifications from the UDR on changes in the policy control related subscription information;

– subscription to the UDR for the AF requests targeting a DNN and S-NSSAI or a group of UEs (roaming UEs for LBO case) identified by an Internal Group Identifier;

– notifications from the UDR on the update of AF requests targeting a DNN and S-NSSAI or a group of UEs (roaming UEs for LBO case) identified by an Internal Group Identifier.

The N36 reference point is defined for the interactions between PCF and UDR in the reference point representation.

5.3.6 Interactions between SMF and CHF

The interactions between SMF and CHF enable online and offline charging.

The N40 reference point is defined for the interactions between SMF and CHF in the reference point representation.

Since the N40 reference point resides between the SMF and CHF in the HPLMN, home routed roaming and non-roaming scenarios are supported in the same manner.

NOTE: The functionality of this interface/reference point is defined in TS 32.240 [8].

5.3.7 Void

5.3.8 Interactions between PCF and CHF

The Nchf enables the PCF to access policy counter status information relating to subscriber spending from CHF and support the following functionality:

– Request for reporting of policy counter status information from PCF to CHF and subscribe to or unsubscribe from spending limit reports (i.e. notifications of policy counter status changes);

– Report of policy counter status information upon a PCF request from CHF to PCF;

– Notification of spending limit reports from CHF to PCF;

– Cancellation of spending limit reporting from PCF to CHF.

The N28 reference point is defined for the interactions between PCF and CHF in the reference point representation.

Since the N28 reference point resides between the PCF and CHF in the HPLMN, home routed roaming and non-roaming scenarios are supported in the same manner.

NOTE: In this Release of the specification, there is no support by the Nchf_SpendingLimitControl service between the PCF in VPLMN and the CHF in the HPLMN.

5.3.9 Interactions between SMF and NEF

Nsmf and Nnef enable transport of PFDs from the NEF (PFDF) to the SMF for a particular application identifier or for a set of application identifiers. It is achieved with the support of the following functionality:

– Creation, updating and removal of individual or the whole set of PFDs from the NEF (PFDF) to the SMF;

– Confirmation of creation, updating and removal of PFDs from the SMF to the NEF (PFDF).

NOTE: The interactions between the SMF and the NEF (PFDF) for transporting PFDs are not related to any PDU Session.

The N29 reference point is defined for the interactions between SMF and NEF (PFDF) in the reference point representation.

5.3.10 Interactions between NEF and PCF

Npcf and Nnef enable the negotiation of policy and charging control behaviour between PCF and NEF by supporting the following functionality:

– service specific policy and charging control;

– sponsor data connectivity including usage monitoring;

– AF-influenced traffic steering authorization;

– subscription and reporting of events for the event exposure;

– negotiations for future background data transfer;

– negotiation of planned data transfer with QoS requirements.

The N30 reference point is defined for the interactions between PCF and NEF in the reference point representation.

5.3.11 Interactions between NWDAF and PCF

The Nnwdaf enables the PCF to request or subscribe to and be notified on the following analytics as specified in clause 6 of TS 23.288 [24]:

– Slice Load Level.

– Service Experience.

– Network Performance.

– Abnormal Behaviour.

– UE Mobility.

– UE Communication.

– User Data Congestion.

– Data or Transaction Dispersion.

– WLAN performance.

– DN Performance.

– Session Management Congestion Control Experience.

NOTE: How these analytics can be used by the PCF is described in clause 6.1.1.3.

The N23 reference point is defined for the interactions between NWDAF and PCF in the reference point representation.

5.3.12 Interactions between PCF for a UE and PCF for a PDU Session

Npcf services enable reporting of PDU Session related events detected by the PCF for a PDU Session to the PCF for a UE. Such events are reporting the start and stop of application traffic detection.

5.3.13 Interactions between PCF and TSCTSF

Npcf enables transport of application level session information from TSCTSF to PCF and Ethernet port management information between PCF and TSCTSF. Such information includes, but is not limited to:

– information required to enable setting up an AF session with support for Time Sensitive Communication and Time Synchronization as defined in clause 6.1.3.23a.

Npcf enables the TSCTSF subscription to notifications on PDU Session events, i.e. the events requested by the TSCTSF as described in clause 6.1.3.18.

The N84 reference point is defined for the interactions between PCF and TSCTSF in the reference point representation.

5.3.14 Interactions between NWDAF and NEF (PFDF)

The Nnwdaf enables the NEF (PFDF) to request or to subscribe and to be notified with the PFD Determination analytics as specified in TS 23.288 [24].

NOTE: How Application Detection analytics can be used by the NEF (PFDF) is described in clause 6.1.2.3.1.