Section: 5.7.1.1 QoS Flow
Content: The 5G QoS model is based on QoS Flows. The 5G QoS model supports both QoS Flows that require guaranteed flow bit rate (GBR QoS Flows) and QoS Flows that do not require guaranteed flow bit rate (Non-GBR QoS Flows). The 5G QoS model also supports Reflective QoS (see clause 5.7.5). The QoS Flow is the finest granularity of QoS differentiation in the PDU Session. A QoS Flow ID (QFI) is used to identify a QoS Flow in the 5G System. User Plane traffic with the same QFI within a PDU Session receives the same traffic forwarding treatment (e.g. scheduling, admission threshold). The QFI is carried in an encapsulation header on N3 (and N9) i.e. without any changes to the e2e packet header. QFI shall be used for all PDU Session Types. The QFI shall be unique within a PDU Session. The QFI may be dynamically assigned or may be equal to the 5QI (see clause 5.7.2.1). Within the 5GS, a QoS Flow is controlled by the SMF and may be preconfigured, or established via the PDU Session Establishment procedure (see clause 4.3.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]), or the PDU Session Modification procedure (see clause 4.3.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]. Any QoS Flow is characterised by: - A QoS profile provided by the SMF to the AN via the AMF over the N2 reference point or preconfigured in the AN; - One or more QoS rule(s) and optionally QoS Flow level QoS parameters (as specified in TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [47]) associated with these QoS rule(s) which can be provided by the SMF to the UE via the AMF over the N1 reference point and/or derived by the UE by applying Reflective QoS control; and - One or more UL and DL PDR(s) provided by the SMF to the UPF. Within the 5GS, a QoS Flow associated with the default QoS rule is required to be established for a PDU Session and remains established throughout the lifetime of the PDU Session. This QoS Flow should be a Non-GBR QoS Flow (further details are described in clause 5.7.2.7). A QoS Flow is associated with QoS requirements as specified by QoS parameters and QoS characteristics. NOTE: The QoS Flow associated with the default QoS rule provides the UE with connectivity throughout the lifetime of the PDU Session. Possible interworking with EPS motivates the recommendation for this QoS Flow to be of type Non-GBR. A QoS Flow may be enabled with PDU Set based QoS handling as described in clause 5.37.5. For such QoS Flows, PDU Set QoS Parameters (see clause 5.7.7) are determined by the PCF and provided by SMF to the NG-RAN as part of the QoS profile.