For UL packet classification, SMF provides QoS rules to the UE. Or the UE implicitly derives the rules from downlink packets. This latter case is called Reflective QoS.
Both reflective and non-reflective QoS can coexist within the same PDU session. Reflective QoS applies to IP PDU session and Ethernet PDU session. UE indicates to SMF if it supports Reflective QoS during PDU Session Establishment. UE may change its support and indicate this via PDU Session Modification. UE-derived QoS rule would include UL packet filter, QFI and precedence value.
Reflective QoS is controlled per packet. SMF signals the use of Reflective QoS Indication (RQI) marking to UPF. SMF signals Reflective QoS Attribute (RQA) to the Access Network(AN) via N2 interface. Subsequently, UPF includes RQI for every DL packet of an SDF that’s using Reflective QoS. AN indicates the RQI to the UE.
When UE receives a DL packet with RQI, it creates or updates the QoS rule for UL traffic. It also starts the Reflective QoS Timer. There’s one timer per UE-derived rule. The timer is restarted when a matching DL packet is received. Rule is discarded when timer expires.
