Handling Failed QoS Flow Identifier During PDU Setup Procedure

The SMF supports handling of the failed QoS Flow Identifier (QFI) during the PDU setup procedure.

NG-RAN rejects a QoS flow due to various reasons. When the NG-RAN node reports unsuccessful establishment of a QoS flow, the SMF uses cause value to identify the reason for the unsuccessful establishment.

Handling Failed QFIs During PDU Setup
Description for Failed QFI Handling During PDU Setup
Step Description

1-7

The SMF, AMF, UDM, PCF, CHF, and UPF communicate with each other to perform the PDU setup procedure as defined in the 3GPP specification.

8

The AMF sends SM Context Update Request to the SMF. This request carries N2 payload “PDU Session Resource Setup Response Transfer”. This message includes the list of QoS flows failed to be established, if any, in the QoS Flow Failed to Setup List IE.

The SMF marks the failed PCC rules and the charging descriptors associated with them for deletion.

9

The SMF sends PFCP Session Modification message to the UPF. This message carries Remove Packet Detection Rules (PDR), Remove QoS Enforcement Rules (QER), and Remove Usage Reporting Rules (URR) for the failed PCC rules in addition to the existing Update FAR for Downlink (DL) Tunnel Endpoint Identifier (TEID) of the successful PCC rules.

10

The SMF sends the CHF Update Request message to the CHF upon receiving a termination request. The CHF sends the CHF Update Response as an acknowledgment.

11

If the PCF has subscribed for notification on failed PCC rules, the SMF sends PCF Update Request with rule report containing the failed PCC rules dropped by the NG-RAN.

12

The SMF sends the PDU Session Update Response to the AMF.

The SMF triggers internal transaction based on the failed QFI list. Then, the SMF initiates PDU UE Sync Procedure to send N1/NAS signalling.

The SMF notifies the UE about the failed QoS flows using N1 messaging, and the UPF and PCF nodes about the associated failed PCC rules.