oS identifier (5QI) and an ARP. In case of a GBR QoS flow, the QoS parameters are guaranteed flow bit rate (GFBR) and maximum flow bit rate (MFBR) for uplink and downlink. In case of non-GBR, the QoS parameters include the newly defined reflective QoS attribute (RQA). The RQA, when included, indicates that some and not necessarily all traffic carried on this QoS flow is subject to reflective QoS at NAS level. At AS level, the DRB defines the packet treat- ment on the radio interface. A DRB serves packets with the same packet forwarding treat- ment. Separate DRBs may be established for QoS flows requiring different packet 176 Chapter 1 forwarding treatments. In the downlink, the NG-RAN maps QoS flows to DRBs based on NG-U marking (QFI) and the associated QoS profiles. In the uplink, the UE marks uplink packets over the radio interface with the QFI for the purposes of marking forwarded packets to the core network. When reflective QoS is used, a 5G UE can create a QoS rule for the uplink traffic based on the received downlink traffic without generating control-plane sig- naling overhead, as shown in Fig. 1.87 [16]. In the uplink, the NG-RAN may control the mapping of QoS flows to DRB in two different ways. Reflective mapping where for each DRB the UE monitors the QFI(s) of the downlink packets and applies the same mapping in the uplink, that is, for a DRB, the UE maps the uplink packets belonging to the QoS flows(s) corresponding to the QFI(s) and PDU session observed in the downlink packets for that DRB. To enable reflective mapping, the NG- RAN marks downlink packets over the air interface with QFI. In addition to the reflective mapping, the NG-RAN may configure an uplink QoS flow to DRB mapping via RRC sig- naling. The UE always applies the latest update of the mapping rules regardless of whether it is performed via reflective mapping or explicit configuration. For each PDU session, a default DRB is configured. If an incoming uplink packet matches neither an RRC config- ured nor a reflective QoS flow ID to DRB ma