PCF-based policy management

The Policy Control Function (PCF) is used to retrieve policy operations related to traffic forwarding, QoS, and charging. This is a pure policy-management function and does not include any authentication functionality, in contrast for example to RADIUS, where authentication and policy management (authorization) are often combined. The PCF uses the SMPolicyControl service. See Service Based Interfaces for more information.

To enable PCF communication, perform the procedure Enabling PCF communication.

When a PCF client service is configured, FWA sessions automatically attempt to contact the PCF. Use the following command to configure a dynamic policy in the ADB and bypass PCF for specific sessions.

configure mobile-gateway profile authentication-database entry dynamic-policy

You can also configure per DNN parameters using commands in the following context:

configure mobile-gateway pdn apn pcf-selection 

Options to configure include the following:

• nf-id-list and npcf-profile commands to override their equivalents in the client service instance
• dnn-format command to modify how the DNN is sent to the PCF
• exclude commands to exclude sending specific IEs to the PCF

PCF interaction is always performed after the authentication flow procedure, including any RADIUS authentication, is completed. The PCF can provide multiple policy decisions, such as an SLA profile, subscriber profile, subscriber filters, and QoS overrides. If any of these values are also provided during the authentication flow, the PCF value overrides these.

Nokia supports vendor-specific attributes in the SMPolicyDecision context, using the vendorSpecific-6527 container. The following attributes are supported:

• subscriberProfile – string indicating the subscriber profile
• slaProfile – string indicating the SLA profile
• sapTemplate – string indicating the SAP template
• groupInterfaceTemplate – string indicating the group interface template
• intermediateDestinationID – string indicating an intermediate destination ID, typically used to apply VPORT QoS
• QoSOverride – string representing specific QoS overrides, using the same format as the RADIUS Alc-Subscriber-QoS-Override attribute which can be present up to 18 times
• A subscriber filter – container that can contain the following sub-objects:
  • ingressIpv4 – string representing an IPv4 filter that is applied on ingress
  • egressIpv4 – string representing an IPv4 filter that is applied on egress
  • ingressIpv6 – string representing an IPv6 filter that is applied on ingress
  • egressIpv6 – string representing an IPv6 filter that is applied on egress

The MAG-c can retrieve an updated policy from the PCF using the Npcf_SMPolicyControl Update service call. The SMF only does this if the PCF sets triggers when providing a policy decision. The following trigger codes are supported:

• RES_MO_RE – a PDU Session Modification Request has been received from the UE to add or remove a policy and charging control (PCC) rule
• UE_IP_CH – an IP address is allocated or freed using DHCP/DHCPv6
• DEF_QOS_CH – default QoS parameters are changed via another interface; for example, because of a UDM subscription update
• SE_AMBR_CH – the Session AMBR is changed via another interface; for example, because of a UDM subscription update
• SAREA_CH – a location change was detected that changes the Serving Area
• SCNN_CH – a location change was detected that changes the Serving CN Node
• RE_TIMEOUT – the PCF provided a revalidation timer that triggered the update
• REF_QOS_IND_CH – support for reflective QoS is changed in a PDU Modification Request message
• SCELL_CH – a location change was detected that changed the Serving Cell
• CM_SES_FAIL – a credit control failure was detected; see CHF failure handling for more information

Alternatively, the PCF can directly update the policy on the MAG-c using the SmPolicyUpdateNotification callback service call. This call is executed against an explicit URI provided by the MAG-c during setup, which contains all required session context.

The Npcf_SMPolicyControl service creates a policy association for a session that can be updated or removed at any time. Each policy association has its own identifier assigned by the PCF, which may be different from MAG-c session-specific identifiers such as SUPI. The MAG-c supports the following operations of the Npcf_SMPolicyControl service, as shown in PCF Policy Control Operations:

• The Create operation is used to create the policy control association. In the request, the MAG-c sends various metadata such as SUPI, GPSI, PEI, DNN, S-NSSAI, and subscribed QoS. The MAG-c also includes a notification callback URI for the UpdateNotify operation. The PCF responds to this request with an association ID identifying the policy association, and the initial policy data.

  The Create operation is part of the initial session setup; see FWA session setup for 5G for more information.

• The Update operation that is used to inform the PCF that one or more signaled triggers have been activated. The MAG-c signals the policy association ID, applicable update trigger, and any metadata to the PCF. The PCF responds to the update with the changed policy data, if any.

• The UpdateNotify operation is used by the PCF when it requires to update a policy decision immediately. In this case it sends the request to the URI provided during the creation of the policy association, including the changed policy data. The MAG-c applies the changed policy and sends a response.

  Note: This operation does not use the association ID; the MAG-c provides any local identifier it requires as part of the callback URI.
• The Delete operation is used by the MAG-c to stop policy enforcement and remove the policy association. This operation is executed during FWA session deletion.