5.7.5.3 Reflective QoS Control

Reflective QoS is controlled on per-packet basis by using the Reflective QoS Indication (RQI) in the encapsulation header on N3 (and N9) reference point together with the QFI and together with a Reflective QoS Timer (RQ Timer) value that is either signalled to the UE upon PDU Session Establishment (or upon PDU Session Modification as described in clause 5.17.2.2.2) or set to a default value. The RQ Timer value provided by the core network is at the granularity of PDU Session (the details are specified in TS 24.501 [47]).

When the 5GC determines that Reflective QoS has to be used for a specific SDF belonging to a QoS Flow, the SMF shall provide the RQA (Reflective QoS Attribute) within the QoS Flow's QoS profile to the NG-RAN on N2 reference point unless it has been done so before. When the RQA has been provided to the NG-RAN for a QoS Flow and the 5GC determines that the QoS Flow carries no more SDF for which Reflective QoS has to be used, the SMF should signal the removal of the RQA (Reflective QoS Attribute) from the QoS Flow's QoS profile to the NG-RAN on N2 reference point.

NOTE 1: The SMF could have a timer to delay the sending of the removal of the RQA. This would avoid signalling to the RAN in the case of new SDFs subject to Reflective QoS are bound to this QoS Flow in the meantime.

When the 5GC determines to use Reflective QoS for a specific SDF, the SMF shall ensure that the UPF applies the RQI marking (e.g. by setting the indication to use Reflective QoS in the QER associated with the DL PDR if not already set) for this SDF. The SMF shall also ensure that the uplink packets for this SDF can be received by the UPF from the QoS Flow to which the DL PDR of the SDF is associated with as specified in TS 29.244 [65], e.g. by generating a new UL PDR for this SDF for that QoS Flow and providing it to the UPF.

When the UPF is instructed by the SMF to apply RQI marking, the UPF shall set the RQI in the encapsulation header on the N3 (or N9) reference point for every DL packet corresponding to this SDF.

When an RQI is received by (R)AN in a DL packet on N3 reference point, the (R)AN shall indicate to the UE the QFI and the RQI of that DL packet.

Upon reception of a DL packet with RQI:

• if a UE derived QoS rule with a Packet Filter corresponding to the DL packet does not already exist,
• the UE shall create a new UE derived QoS rule with a Packet Filter corresponding to the DL packet (as described in clause 5.7.5.2); and
• the UE shall start, for this UE derived QoS rule, a timer set to the RQ Timer value.
• otherwise,
• the UE shall restart the timer associated to this UE derived QoS rule; and
• if the QFI associated with the downlink packet is different from the QFI associated with the UE derived QoS rule, the UE shall update this UE derived QoS rule with the new QFI.

NOTE 2: Non-3GPP ANs does not need N2 signalling to enable Reflective QoS. Non 3GPP accesses are expected to send transparently the QFI and RQI to the UE. If the UPF does not include the RQI, no UE derived QoS rule will be generated. If RQI is included to assist the UE to trigger an update of the UE derived QoS rule, the reception of PDU for a QFI restarts the RQ Timer.

Upon timer expiry associated with a UE derived QoS rule the UE deletes the corresponding UE derived QoS rule.

When the 5GC determines not to use Reflective QoS for a specific SDF any longer:

• The SMF shall ensure that the UPF stops applying RQI marking as specified in TS 29.244 [65] (e.g. by removing the indication to use Reflective QoS from the QER associated with the DL PDR) for this SDF.
• When the UPF receives this instruction to stop applying RQI marking, the UPF shall no longer set the RQI in the encapsulation header on the N3 (or N9) reference point DL packets corresponding to this SDF.
• The SMF shall also ensure that, after an operator configurable time, the uplink packets for this SDF will not be accepted by the UPF over the QoS Flow on which Reflective QoS was applied for this SDF as specified in TS 29.244 [65], e.g. by removing the UL PDR for this SDF from that QoS Flow.

NOTE 3: The operator configurable time has to be at least as long as the RQ Timer value to ensure that no UL packet would be dropped until the UE derived QoS rule is deleted by the UE.

When the 5GC determines to change the binding of the SDF while Reflective QoS is used for this SDF, the SMF shall ensure that the uplink packets for this SDF are accepted over the newly bound QoS Flow and, for an operator configurable time, over the previously bound QoS Flow.