5.18 Enhanced PFCP Association Release

29.2443GPPInterface between the Control Plane and the User Plane nodesRelease 17TS

5.18.1 General

To ensure no loss of usage reports and signalling efficiency, during a PFCP Association Release procedure, which is either initiated by CP function, or upon request from the UP function, the CP function and UP function may support the Enhanced PFCP Association Release feature (EPFAR) as described below.

When both the CP function and the UP function support the EPFAR feature, and when the CP (or UP) function determines that the PFCP association is to be released, the CP (or UP) function shall send a PFCP Association Update Request message with a "PFCP Association Release Preparation Start" flag to inform the peer UP (or CP) function that the PFCP Association is going to be released and the final non-zero usage reports are to be collected for these PFCP sessions which will be affected by PFCP association release.

The CP function should stop establishing new PFCP sessions in the UP function after receiving or sending a PFCP Association Release Preparation Start indication. The CP(or UP) function shall send a PFCP Association Update Response with a successful cause value to the peer.

Then the UP function shall initiate the PFCP Session Release procedure as specified in clause 5.18.2 by sending one or more PFCP Session Report Request messages for the PFCP sessions affected by the release of the PFCP association and that have non-zero usage reports to be reported. In the PFCP Session Report Request message, the UP function shall:

– set the Usage Report Trigger to TEBUR (Termination By UP function Report) for the usage reports being reported; and

– set the PSDBU (PFCP Session Deleted By the UP function) flag to "1" to indicate to the CP function that the PFCP Session is being deleted in the UP function and the usage reports included in the message are the final usage reports for the given PFCP Session, if this is the last PFCP Session Report Request message sent for the PFCP session.

When the UP function has sent all the non-zero usage reports for the PFCP sessions affected by the release of the PFCP Association, the UP function shall send a PFCP Association Update Request with the flag URSS (non-zero Usage Reports for the affected PFCP Sessions Sent) set to "1" to indicate to the CP function that all non-zero usage reports for the affected PFCP sessions have been sent to the CP function and the corresponding PFCP sessions in the UP function have been locally deleted. The CP function shall then send a PFCP Association Update Response with a successful cause to the peer to indicate the PFCP Association Update Request is handled successfully.

The CP function shall then send a PFCP Association Release Request to release the PFCP Association as specified in clause 6.2.8.

5.18.2 UP Function Initiated PFCP Session Release

When the UP function needs delete a PFCP sesssion, e.g. during the Enhanced PFCP Association Release as described in clause 5.18.1 or when it detects an error or partial failure, the UP function shall:

– send one or more PFCP Session Report Request messages for this PFCP session;

– set the Report Type to "USAR" (Usage Report) if there is non-zero usage report for the PFCP session, or set the Report Type to "UISR" if there is no usage report to send (e.g. for a session without an URR provisioned or with an URR provisioned but with only null usage measurements);

– set the Usage Report Trigger to "TEBUR" for non-zero usage report(s), if usage reports are included in the PFCP Session Report Request message(s); and

– set the PSDBU flag to "1" to indicate to the CP function that the PFCP session is being deleted, in the last PFCP Session Report Request message sent for that PFCP session.

NOTE: The UP Function can release one or more PFCP Sessions (without tearing down the entire PFCP Association) when there is a partial failure in the UP Function.