PCF-initiated Modification Call Flow

This section explains the processing of PCF-initiated dedicated bearer modification call flow when the procedure SLA timer expires.

Procedure SLA handling explained in this section include other flavors of dedicated bearer procedure started by internal transactions due to the following triggers:

  • PCF-initiated triggers: Piggy-back Dedicated Bearer Procedure, PCF Update/Notify Response triggered Dedicated Bearer Procedure, NIntSelfTxnExpPcfUpdNotifyReq, and so on.

  • Other triggers: Clear Sub, Revalidation Timeout, N4 Session Report, Internal Txn to restart dedicated bearer procedure upon collision-abort.

Note

The SMF uses procedure SLA configuration for the N7 interface for handling the dedicated bearer procedure failures.

The following figure depicts the dedicated bearer modification call flow initiated by the N7 Policy Notify Request from PCF.

PCF-initiated Modification Call Flow

The following table describes the processing performed at each stage when the procedure SLA timer expires:

Processing of PCF-initiated Modification During SLA Timer Expiry

Timeline or Slice availability

Request or Event

Stage - Failure

Timeout due to SLA

Procedure SLA as configured

N7 PCF Notify Request

PCF Notify

Respond to N7 PCF Notify with the HTTP status code "504 Gateway Timeout" and the protocol error as "TIMED_OUT_REQUEST".

Procedure SLA as configured

First N4 Modification Request

For newly added flows:

Async N4 Modification to remove N4 tunnels for the new flows.

Send Async PCF update with rule reports based on triggers.

For deleted flows:

Async Delete Bearer Request (DBR)

Sync N4 to remove tunnels for deleted rules. Perform sync procedure to avoid loss of usage reports which the UPF sends in N4 modification response for the deleted flows.

Async PCF update with rule reports based on triggers.

Procedure SLA as configured

Delete Bearer Request

Sync N4 to remove tunnels for the deleted rules. Perform sync procedure to avoid loss of usage reports which the UPF sends in N4 modification response for deleted flows.

Async PCF update with rule reports based on triggers.

Procedure SLA as configured

Update Bearer Request

Not supported currently

Procedure SLA as configured

Create Bearer Request

Async N4 Modification to remove N4 tunnels for the deleted and new flows.

Send PCF update with rule reports based on triggers.

Procedure SLA as configured

Second N4 Modify Request

For added flows:

Perform async DBR and async N4 Modification. Send Async Failure Rule report to PCF.

For deleted flows:

Send Async Success Rule report to PCF. Then, update PDU context.

Procedure SLA as configured

Charging Update Request

Last leg, treat as procedure success.

Send PCF update with success rule reports based on triggers. Then, update PDU context.

Last Leg – lenient approach no SLA

PCF Update Request

Mark modification complete.