5.7.5.1 General

Reflective QoS enables the UE to map UL User Plane traffic to QoS Flows without SMF provided QoS rules and it applies for IP PDU Session and Ethernet PDU Session. This is achieved by creating UE derived QoS rules in the UE based on the received DL traffic. It shall be possible to apply Reflective QoS and non-Reflective QoS concurrently within the same PDU Session.

For a UE supporting Reflective QoS functionality, the UE shall create a UE derived QoS rule for the uplink traffic based on the received DL traffic if Reflective QoS function is used by the 5GC for some traffic flows. The UE shall use the UE derived QoS rules to determine mapping of UL traffic to QoS Flows.

If the 3GPP UE supports Reflective QoS functionality, the UE should indicate support of Reflective QoS to the network (i.e. SMF) for every PDU Session. For PDU Sessions established in EPS and PDU Sessions transferred from EPS without N26 interface, the UE indicates Reflective QoS support using the PDU Session Establishment procedure. After the first inter-system change from EPS to 5GS for PDU Sessions established in EPS and transferred from EPS with N26 interface, the UE indicates Reflective QoS support using the PDU Session Modification procedure as described in clause 5.17.2.2.2. The UE as well as the network shall apply the information whether or not the UE indicated support of Reflective QoS throughout the lifetime of the PDU Session.

NOTE: The logic driving a supporting UE under exceptional circumstances to not indicate support of Reflective QoS for a PDU Session is implementation dependent.

Under exceptional circumstances, which are UE implementation dependent, the UE may decide to revoke previously indicated support for Reflective QoS using the PDU Session Modification procedure. In such a case, the UE shall delete all derived QoS rules for this PDU Session and the network shall stop any user plane enforcement actions related to Reflective QoS for this PDU Session. In addition, the network may provide signalled QoS rules for the SDFs for which Reflective QoS was used before. The UE shall not indicate support for Reflective QoS for this PDU Session for the remaining lifetime of the PDU Session.

If under the same exceptional circumstances mentioned above and while NAS level MM or SM congestion control timer is running, the UE needs to revoke a previously indicated support for Reflective QoS, the UE performs PDU Session Release procedure that is exempt from MM and SM congestion control as defined in clause 5.19.7.