Policy Control Request Triggers

The PCF provides one or more policy control request trigger(s) by including the triggers in the "policyCtrlReqTriggers" attribute(s) in the SmPolicyDecision data structure.

During the lifetime of the PDU session, the PCF updates or removes the policy control request triggers. To update the trigger, the PCF provides a new complete list of applicable policy control request triggers by including the trigger(s) in the "policyCtrlReqTriggers" attribute.

The PCF removes all previously provided triggers by providing a "policyCtrlReqTriggers" attribute set to NULL value. Upon reception of a policy control request trigger with this value, the SMF does not inform PCF of any trigger except for those triggers that are always reported and does not require provisioning from the PCF.

Whenever the PCF provisions the trigger, unless otherwise specified in the trigger's value definition, the SMF sends the corresponding currently applicable values (for example, access type, RAT type, user location information, and so on) to the PCF within the UeCampingRep data structure in the response of the HTTP POST message. In this case, the "repPolicyCtrlReqTriggers" attribute is not included.

The list of supported triggers is as follows:

TriggerDescription
RES_MO_RE

A request for resource modification has been received by the SMF. This is a mandatory trigger.

Note

This request is sent from SMF to PCF when UE/AMF requested QoS modification is triggered.

UE_IP_CHUE IP address change. This is a mandatory trigger.
DEF_QOS_CHDefault QoS Change. This is a mandatory trigger.
SE_AMBR_CHSession AMBR Change. This is a mandatory trigger.
SAREA_CHLocation Change about the Serving Area in N11 update.
SCNN_CHLocation Change about the Serving CN node. See the following section for details on how the SMF supports this trigger during the different handover scenarios.
RE_TIMEOUTIndicates that the SMF has generated the request because there has been a PCC revalidation timeout (that is, Enforced PCC rule request as defined in Table 6.1.3.5.-1 of 3GPP TS 29.503).

Support SCNN_CH Trigger in Handovers

The SMF supports the serving network change trigger in the following handovers:

  • Inter AMF Handover: If the "SCNN_CH" is provisioned, when the SMF detects a change of serving Network Function (for example, the AMF), the SMF includes the "SCNN_CH" within the "repPolicyCtrlReqTriggers" attribute and the current serving Network Function in the "servNfId" attribute. When the serving Network Function is an AMF, the SMF includes the AMF Network Function Instance Identifier within the "servNfInstId" attribute and the Globally Unique AMF Identifier within the "guami" attribute.

  • 5G to 4G handover: When the UE handed over from the 5GS to EPC/E-UTRAN, the SMF includes, if the "SCNN_CH" policy control request trigger is provisioned and met, the "servNfId" attribute including the S-GW identification within the "anGwAddr" attribute.

  • 4G to 5G handover: The SMF includes the AMF Network Function Instance Identifier within the "servNfInstId" attribute and the Globally Unique AMF Identifier within the "guami" attribute.

  • WiFi to 5G handover: The SMF includes the AMF Network Function Instance Identifier within the "servNfInstId" attribute and the Globally Unique AMF Identifier within the "guami" attribute.

  • 5G to WiFi handover: When the UE handed over from the 5GS to EPC non-3GPP access, the SMF includes, if the "SCNN_CH" policy control request trigger is provisioned and met, the ePDG identification within the "anGwAddr" attribute included in the "servNfId" attribute.