QoS Flow in 5G – 3GPP R18 Definition

I. QoS Model In 5G, the QoS Flow model supports two types of QoS flows:

• GBR QoS flows – QoS flows requiring guaranteed flow bit rate, and
• Non-GBR QoS flows – QoS flows that do not require guaranteed flow bit rate.

The QoS model in 5G also supports Reflective QoS (see Reflective QoS - TS 23.501 Clause 5.7.5).

II.QoS and PDU In a 5G system, the QoS flow is the finest granularity for distinguishing QoS within a PDU session. The QoS Flow ID (QFI) is used to identify QoS flows in the 5G system. Within a PDU session:

• user plane traffic with the same QFI will receive the same traffic forwarding processing (e.g., scheduling, admission thresholds).
• The QFI resides in the N3 (and N9) encapsulation header, meaning no changes are required to the end-to-end packet header. All PDU call types should use the QFI.
• The QFI should be unique within a PDU session.
• QFI can be dynamically allocated or equal to 5QI (see Section 5.7.2.1).

III. QoS Control In 5GS, QoS flows are controlled by the SMF and can be pre-configured or established through the PDU session establishment process (see Section 4.3.2 of TS 23.502[3]) or the PDU session modification process (Section 4.3.3 of TS 23.502[3]).

IV.QoS Flow Characteristics 5G systems have the following characteristics:

• - A QoS profile provided by the SMF to the AN via the AMF through the N2 reference point, or pre-configured in the AN;
• - One or more QoS rules, and optional QoS flow-level QoS parameters (as described in TS 24.501[47]), which can be provided by the SMF to the UE via the AMF through the N1 reference point, and/or derived by the UE through application reflective QoS control; and
• - One or more UL and DL PDRs (SMF to UPF) provided by the SMF.

V. Default QoS Flow In 5GS, a PDU session needs to establish a QoS flow associated with a default QoS rule, and this QoS flow remains established throughout the entire lifecycle of the PDU session. This QoS flow should be a non-GBR QoS flow, and the QoS flow associated with the default QoS rule provides connectivity to the UE throughout the entire lifecycle of the PDU session.Furthermore,

• the QoS flow is associated with the QoS requirements specified by QoS parameters and QoS characteristics.
• Interoperability with EPS necessitates the recommendation that this QoS flow be of the non-GBR type.