is carried in an encapsulation header over NG-U and serves as a pointer toward a QoS profile describing a number of QoS parameters to characterize the flow, for instance, a Guaranteed Flow Bit Rate (GFBR), Maximum Flow Bit Rate (MFBR), and Maximum Packet Loss Rate (see 3GPP TS 23.501). The QoS profile also contains a 5G QoS Identifier (5QI), which points toward QoS characteristics, for instance, the priority level, Packet Delay Budget (PDB), Packet Error Rate (PER), and Maximum Data Burst Volume (MDBV; see Section 7.3.3). This is summarized in Figure 7.2 below. The correspondence between 5QI and QoS characteristics is either fixed in the specifications or signaled to the gNB by 5GC (when the PDU session is established or later with a PDU session modification procedure). The mapping of QoS flows by the gNB onto DRBs is based on the QFI and the associ- ated QoS profiles (i.e. QoS parameters and QoS characteristics signaled from the Core Network) as depicted in Figure 7.3. The mapping of Service Data Flows (SDFs) onto QoS flows is governed by the CN. In the uplink, the mapping of QoS flows by the UE onto RBs is governed by a set of mapping rules signaled to the UE by the gNB as depicted in Figure 7.4. The mapping of SDF onto QoS flows is governed by the CN and signaled to the UE at the NAS level. QoS Profile QoS Characteristics - GFBR - priority level - PDB - etc - MDBV Figure 7.2 5G QoS parameters. ((p)) QoS information QoS flows SDF to to RBs Qos flows Internet Radio Bearer GTP Tunnel Radio Bearer Figure 7.3 Mapping of QoS flows - downlink. 7.3 SDAP Mapping Rules ((p)) QoS information SDF to QoS flows RB to QoS flows QoS flows to SDF QoS flows to RB Internet Radio Bearer GTP Tunnel Radio Bearer Figure 7.4 Mapping of QoS flows - uplink. The mapping rules are configured either explicitly via RRC signaling or implicitly via Reflective Quality of Service (RQoS). With RQoS, the UE derives the uplink mapping rules from the information available in the downlink. For instance, a QoS flow x received on DRB y in the downlin