5.8.2.7 PDU Session and QoS Flow Policing

ARP is used for admission control (i.e. retention and pre-emption of the new QoS Flow). The value of ARP is not required to be provided to the UPF.

For every QoS Flow, the SMF shall determine the transport level packet marking value (e.g. the DSCP in the outer IP header) based on the 5QI, the Priority Level (if explicitly signalled) and optionally, the ARP priority level and provide the transport level packet marking value to the UPF.

NOTE 1: If no transport level packet marking value is provided, the UPF performs transport level packet marking based on its pre-configured logic.

For a QoS Flow with activated PDU Set based Handling, the SMF may additionally take into account the PDU Set Importance when determining the transport level packet marking values, when the network is configured to take the PDU Set Importance into account for transport level packet marking. In this case, the SMF provides a list of transport level packet marking values for the downlink direction to the UPF in the FAR corresponding to that QoS Flow, each of the transport level packet marking values corresponding to one or more PDU Set Importance values. The UPF shall then perform the transport level packet marking based on this list when it handles a PDU associated with a PDU Set Importance value.

NOTE 2: It is recommended that the PDU Set Importance based transport level packet marking values applied by the UPF only vary the drop precedence between PDUs in the transport network nodes (e.g. IP routers) on the N3/N9 interfaces. This is needed to avoid causing packet reordering in the transport network when different transport level DSCP marking values are used for a single QoS Flow.

NOTE 3: The transport level packet marking values are provided on per-QoS Flow basis and it is up to operator deployments to enforce consistency of transport level packet marking in the transport network.

When an I-SMF/I-UPF is inserted in the PDU Session and the I-SMF is notified by the SMF that transport level packet marking is being applied for the affected QoS Flow (by receiving the Transport Level Marking Indication described in TS 23.502 [3]), the I-SMF may instruct the I-UPF to derive the transport level packet marking value of the outgoing N3 downlink packet based on the transport level packet marking value of the incoming N9 downlink packet.

The SMF shall provide the Session-AMBR values of the PDU Session to the UPF so that the UPF can enforce the Session-AMBR of the PDU Session across all Non-GBR QoS Flows of the PDU Session.

SMF shall provide the GFBR and MFBR value for each GBR QoS Flow of the PDU Session to the UPF. SMF may also provide the Averaging window to the UPF, if Averaging window is not configured at the UPF or if it is different from the default value configured at the UPF.

In the case of 3GPP access, the SMF may decide to activate ECN marking for L4S by PSA UPF for the QoS Flow (see clause 5.37). In this case, the SMF shall send an ECN marking for L4S indicator to PSA UPF.