QoS Enforcement Rule

Description

The QoS Enforcement Rule (QER) is a core element of the 5G Policy and Charging Control (PCC) architecture, specified in 3GPP TS 29.244 (PFCP protocol) and TS 26.804 (codec-specific aspects). A QER is a container of instructions that dictates how the User Plane Function (UPF) should handle packets belonging to a specific Protocol Data Unit (PDU) Session or QoS Flow. It is created, modified, or removed by the Session Management Function (SMF) based on policies received from the Policy Control Function (PCF) using the N7 reference point.

Each QER contains several key information elements that define its enforcement behavior. This includes a QER Identifier, the QoS Flow Identifier (QFI) to which it applies, and a set of enforcement actions. The primary actions are Gate Status (open/close), which controls whether packets are allowed to pass, and QoS Enforcement parameters. The QoS parameters typically include the Guaranteed Flow Bit Rate (GFBR), Maximum Flow Bit Rate (MFBR), and optionally, an Aggregate Bit Rate (ABR) for the flow. The UPF uses these parameters to perform policing, marking, and scheduling of packets to ensure the contracted QoS is delivered.

Operationally, QERs are installed in the UPF via the Packet Forwarding Control Protocol (PFCP) Session Modification procedure. The SMF sends a PFCP Session Modification Request containing one or more QERs to be applied. The UPF then installs these rules in its fast-path data plane, where they are matched against incoming packets based on filters like the QFI. Enforcement involves metering the traffic against the configured bit rates, dropping or marking (e.g., setting Drop Eligibility Indicator) packets that exceed limits, and ensuring minimum guaranteed rates are sustained. This mechanism allows for highly dynamic and service-specific QoS treatment, which is central to 5G's network slicing and service-based architecture.

Purpose & Motivation

QoS Enforcement Rules (QERs) were introduced in 3GPP Release 14, initially for LTE Advanced Pro, and became central to the 5G Core (5GC) defined in Release 15. Their creation was driven by the need for more flexible, dynamic, and granular QoS enforcement beyond the static QoS Class Identifier (QCI) and Allocation and Retention Priority (ARP) mechanisms of 4G EPS. Previous systems lacked the ability to dynamically adjust bit rate guarantees and enforcement policies on a per-flow basis during an active session, which limited support for novel services with highly variable bandwidth demands.

The primary problem QERs solve is enabling network-slicing and service-specific QoS guarantees. In 5G, a single PDU Session can contain multiple QoS Flows with different requirements (e.g., one for enhanced mobile broadband and another for ultra-reliable low-latency communication). QERs provide the tool for the PCF and SMF to instruct the UPF on how to police and shape each flow independently and in real-time. This is crucial for meeting Service Level Agreements (SLAs) for diverse use cases like industrial IoT, autonomous vehicles, and augmented reality.

Furthermore, QERs facilitate the separation of control and user plane in 5G. By defining a standardized rule format communicated via PFCP, they allow a centralized PCF/SMF to control distributed UPFs efficiently. This architectural shift supports cloud-native deployment and scalability. QERs thus represent a key evolution towards software-defined, policy-driven QoS management that can adapt to rapidly changing application needs and network conditions.

Key Features

• Defines enforceable QoS parameters per QoS Flow, including GFBR, MFBR, and Aggregate Bit Rate
• Contains Gate Status control to dynamically allow or block packet forwarding for a flow
• Provisioned dynamically by PCF via SMF and installed in UPF using PFCP protocol
• Enables per-flow policing, marking, and scheduling in the 5G user plane
• Supports dynamic policy changes during an active PDU Session
• Fundamental for realizing network slicing and service-specific QoS guarantees

Evolution Across Releases

Defining Specifications