5G System QoS Key Parameters

In the 5G (NR) system, QoS is the finest granularity unit for differentiating QoS (Quality of Service) in a terminal (UE)'s PDU session. Each QoS flow is identified by a unique identifier called QFI (QoS Flow ID), which is also unique within the PDU session. QoS typically includes the following parameters:

1. GFBR (Guaranteed Flow Bit Rate)

• Application: Applicable only to GBR and delay-critical GBR QoS flows.
• Function: Defines the minimum bit rate that the QoS flow can achieve when measured over an averaging window.
• Uplink and Downlink: Specifies the GFBR for the uplink and downlink separately.

2. MFBR (Maximum Flow Bit Rate)

• Application: Applicable only to GBR and delay-critical GBR QoS flows.
• Function: Defines the maximum bit rate that the QoS flow can achieve when measured over an averaging window.
• Uplink and Downlink: Specifies the MFBR for the uplink and downlink separately.

3. Session Maximum Allowed Bit Rate (Session-AMBR)

• Function: Defines the sum of the maximum allowed bit rates of all Non-GBR QoS flows in a specific PDU session.
• Execution: Managed by the User Plane Function (UPF) of the relevant PDU session.

4. Terminal (UE) Maximum Allowed Bit Rate (UE-AMBR)

• Function: Defines the sum of the maximum allowed bit rates of all non-GBR QoS flows of a specific UE.
• Execution: Managed by the serving base station.

5. Maximum Packet Loss Rate

• Application: Applicable only to GBR and delay-critical GBR QoS flows, and only for voice media in 3GPP specification Release 15.
• Function: Defines the maximum tolerable packet loss rate in the uplink and downlink.

6. Notification Control

• Function: Indicates whether the base station should notify the SMF if the QoS flow fails to meet its GFBR.
• Behavior: If the GFBR is not met, the base station will continue to try while notifying the SMF, which may reconfigure or release the QoS flow.

7. Reflective QoS Attribute (RQA)

• Function: Indicates whether packets in the QoS flow require the UE application to use reflective QoS, which involves learning uplink rules from the downlink pattern.
• Scope of application: Used for PDU sessions of IP or Ethernet data packets (not applicable to unstructured data packets).