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
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 is used for all PDU Session Types. The QFI is unique within a PDU Session. The QFI may be dynamically assigned or may be equal to the 5QI
Within the 5GS, a QoS Flow is controlled by the SMF and may be preconfigured, or established via the PDU Session Establishment procedure or the PDU Session Modification procedure.
AnyQoS 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 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.
See my session on it for more understanding.