4.1 Service Description

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

4.1.1 Overview

The Npcf_PolicyAuthorization Service, as defined in 3GPP TS 23.502 [3] and in 3GPP TS 23.503 [4], is provided by the Policy Control Function (PCF).

The Npcf_PolicyAuthorization service authorises a NF service consumer request and creates policies as requested by the authorised NF service consumer for the PDU session to which the AF session is bound to. This service also allows the NF service consumer to subscribe/unsubscribe to notifications on events (e.g. access type change, PLMN change, usage report, access network information report).

4.1.2 Service Architecture

The 5G System Architecture is defined in 3GPP TS 23.501 [2]. The Policy and Charging control related 5G architecture is also described in 3GPP TS 23.503 [4] and 3GPP TS 29.513 [7].

The only known NF service consumers of the Npcf_PolicyAuthorization service are the Application Function (AF), the Network Exposure Function (NEF), the Time Sensitive Communication and Time Synchronization Function (TSCTSF) and the Policy Control Function for the UE (PCF for the UE).

The Npcf_PolicyAuthorization service is provided by the PCF and consumed by the AF, the NEF, the TSCTSF and, when the PCF for the PDU session and the PCF for the UE are different, the PCF for the UE, as shown in figure 4.1.2-1 for the SBI representation model and in figure 4.1.2-2 for the reference point representation model.

Figure 4.1.2-1: Npcf_PolicyAuthorization service Architecture, SBI representation

Figure 4.1.2-2: Npcf_PolicyAuthorization service Architecture, reference point representation

NOTE: When the N43 reference point exists, i.e. when the PCF is a NF service consumer of the Npcf_PolicyAuthorization service, the PCF for the UE interacts with the PCF for the PDU session.

The AF trusted by the operator interacts with the PCF via the N5 reference point. In the case of an untrusted AF, the AF interacts with the PCF via the NEF. The NEF interacts with the PCF via the N30 reference point in the same way that the AF interacts with the PCF via the N5 reference point.

4.1.3 Network Functions

4.1.3.1 Policy Control Function (PCF)

The PCF (Policy Control Function) performs policy and charging control for the PDU session and/or the flows indicated by the NF service consumer and according to the service requirements provided by the NF service consumer.

The policy and charging control for service data flows enable the PCF to provide network control regarding the service data flow detection, gating, QoS and flow based charging (except credit management) towards the SMF/UPF.

The PCF receives session and media related information from the Npcf_PolicyAuthorization service consumers and notifies them of subscribed traffic plane events.

The PCF may receive from the NF service consumers the request to monitor the requested service and media information and notifies them of the UL/DL/round-trip delay of the requested flows.

The PCF may receive service routing requirements and the indication of receiving notifications about user plane path changes from the Npcf_PolicyAuthorization service consumers.

The PCF may receive from the NF service consumers the specific required QoS and a prioritized list of alternative QoS profiles and notifies them about the QoS target the access network guarantees.

The PCF checks that the service information provided by the NF service consumer is consistent with the operator defined policy rules before storing the service information.

The PCF uses the received service information and the subscription information when it applies as basis for the policy and charging control decisions.

The PCF derives PCC rules and provisions them to the SMF via the Npcf_SMPolicyControl service and subscribes to traffic plane events via policy control request triggers as described in 3GPP TS 29.512 [8].

In 5GS interworking with external time sensitive networks (e.g.TSN network), the PCF:

– notifies the NF service consumer (i.e. TSN AF or TSCTSF) about the TSC user plane node and DS-TT port information corresponding to a PDU session;

– enables the NF service consumer (i.e. TSN AF or TSCTSF) configures the TSC user plane node and ports by forwarding TSC user plane node management containers and port management containers to the SMF as described in 3GPP TS 29.512 [8];

– notifies the NF service consumer (i.e. TSN AF or TSCTSF) about updated TSC user plane node configuration and port configuration by forwarding TSC user plane node management containers and port management containers received from the SMF; and

– uses the received QoS and TSC assistance information to derive the policy information delivered in the PCC rule to the SMF as described in 3GPP TS 29.512 [8].

4.1.3.2 NF Service Consumers

The known NF service consumers are the AF, the NEF, the TSCTSF and the PCF (for a UE), as defined in 3GPP TS 23.502 [3].

The AF is an element offering control to applications that require the policy and charging control of traffic plane resources; specific user plane paths for the requested traffic, the monitoring of the required service QoS, and/or specific QoS and alternative QoS profiles. The AF uses the Npcf_PolicyAuthorization service to provide service information to the PCF.

In 5GS interworking with TSN networks, the TSN AF is an element offering to TSC control functions an interface to 5GS to forward TSC user plane node and port management configuration, and to set the QoS policy required to forward the TSC traffic making use of the 5GS traffic plane resources.

The AFs can be deployed by the same operator offering the access services or can be provided by external third-party service provider. If the AF is not allowed by the operator to access directly the PCF, the AF uses the external exposure framework via NEF to interact with the PCF, as described in clause 5.20 of 3GPP TS 23.501 [2].

The Network Exposure Function (NEF) supports external exposure of capabilities of network functions.

The AF trusted by the operator or the NEF can use the TSCTSF to interface with PCF to support time sensitive communication and time synchronization. The TSCTSF is an element offering, to internal and/or external time sensitive AF (via NEF), control to handle from/towards the PCF the required TSC user plane node and port management configuration, and to set in the PCF the QoS policy required to forward TSC traffic.

The PCF providing session management policy control for a UE (i.e. PCF for a PDU session) and the PCF providing UE policy control and/or access and mobility control for this same UE (i.e. PCF for a UE) may be different PCFs. When access and mobility policies depend on traffic plane events (as e.g. application detection control), the PCF for a UE may act as an NF service consumer of the PCF for the PDU session by subscribing to such events.