5.33.3.2 Per QoS Flow per UE QoS Measurement

SMF may activate the end to end UL/DL packet delay measurement between UE and PSA UPF for a QoS Flow during the PDU Session Establishment or Modification procedure.

The SMF sends a QoS Monitoring request to the PSA UPF via N4 and NG-RAN via N2 signalling to request the QoS monitoring between PSA UPF and NG-RAN. The QoS Monitoring request may contain monitoring parameters determined by SMF based on the authorized QoS Monitoring policy received from the PCF and/or local configuration.

The NG-RAN initiates the RAN part of UL/DL packet delay measurement based on the QoS Monitoring request from SMF. NG-RAN reports the RAN part of UL/DL packet delay result to the PSA UPF in the UL data packet or dummy UL packet.

If the NG-RAN and PSA UPF are time synchronised, the one way packet delay monitoring between NG-RAN and PSA UPF is supported.

If the NG-RAN and PSA UPF are not time synchronised, it is assumed that the UL packet delay and the DL packet delay between NG-RAN and PSA UPF are the same.

For both time synchronised and not time synchronised between NG-RAN and PSA UPF, the PSA UPF creates and sends the monitoring packets to the RAN in a measurement frequency, decided by the PSA UPF, taking the Reporting frequency for QoS Monitoring received from the SMF into account:

• The PSA UPF encapsulates in the GTP-U header with QFI, QoS Monitoring Packet (QMP) indicator (which indicates the packet is used for UL/DL packet delay measurement) and the local time T1 when the PSA UPF sends out the DL monitoring packets.
• The NG-RAN records the local time T1 received in the GTP-U header and the local time T2 at the reception of the DL monitoring packets.
• When receiving an UL packet from UE for that QFI or when the NG-RAN sends a dummy UL packet as monitoring response (in case there is no UL service packet for UL packet delay monitoring), the NG-RAN encapsulates QMP indicator, the RAN part of UL/DL packet delay result, the time T1 received in the GTP-U header, the local time T2 at the reception of the DL monitoring packet and the local time T3 when NG-RAN sends out this monitoring response packet to the UPF via N3 interface, in the GTP-U header of the monitoring response packet.

NOTE 1: When the NG-RAN sends the dummy UL packet as monitoring response to PSA UPF depends on NG-RAN's implementation.

• The PSA UPF records the local time T4 when receiving the monitoring response packets and calculates the round trip (if not time synchronized) or UL/DL packet delay (if time synchronized) between NG-RAN and anchor PSA UPF based on the time information contained in the GTP-U header of the received monitoring response packet. If the NG-RAN and PSA UPF are not time synchronised, the PSA UPF calculates the UL/DL packet delay between the NG-RAN and the PSA UPF based on the (T2-T1+T4-T3)/2. If the NG-RAN and PSA UPF are time synchronised, the PSA UPF calculates the UL packet delay and DL packet delay between the NG-RAN and the PSA UPF based on (T4-T3) and (T2-T1), respectively. The PSA UPF calculates the UL/DL packet delay between UE and PSA UPF based on the received RAN part of UL/DL packet delay result and the calculated UL/DL packet delay between RAN and PSA UPF.

NOTE 2: If the NG-RAN and PSA UPF are not time synchronised, it can cause inaccurate result of UL/DL packet delay.

• The PSA UPF reports the QoS Monitoring results as described in clause 5.8.2.18.

If the redundant transmission on N3/N9 interfaces is activated, the UPF and NG-RAN performs QoS monitoring for both UP paths. The UPF reports the packet delays of the two UP paths independently to the SMF.