How it Works

The SMF integrates the CHF and PCF functions based on the following information:

  • Policy control request triggers, which are received in the SM policy decision during PDU session establishment or PCF or UE-initiated modification.

  • Session-level or rating-group-level charging triggers, which are received during PDU session establishment or in response to SMF-initiated Charging Update Request or CHF-initiated Charging Update Notify Request.

The SMF supports the following access-side information to detect the PCF and CHF triggers. The SMF sends the trigger information to the CHF and PCF during the N2-based handover.

Access-Side Information for PCF and CHF Triggers

Access Side Information

CHF Triggers

PCF Triggers

UserLocation

USER_LOCATION_CHANGE

SAREA_CH

UeTimeZone

UE_TIMEZONE_CHANGE

SAREA_CH

ServingNetwork

PLMN_CHANGE

PLMN_CH

TargetServingNfId

SERVING_NODE_CHANGE

For a change in the subscriber location, the SMF sends USER_LOCATION_CHANGE trigger towards CHF and SAREA_CH trigger towards PCF.

The SMF generates the usage report whenever a change in the subscriber location is detected in the following messages:

  • Delete Bearer Command

  • Delete Bearer Response

  • Modify Bearer Request

For example, when a Delete Bearer Command is received with a new ULI, a CDR event is triggered with new ULI. If PCF or CHF has armed notification for ULI modifications, the SMF sends a notification to the PCF and CHF respectively.

This feature is compliant with the 3GPP TS 32.291, version 15.4.0.