Description
The 5G QoS Identifier (5QI) is a fundamental mechanism in 5G System (5GS) architecture for managing Quality of Service. It's a scalar value ranging from 1 to 255, where standardized values (1-89) have predefined QoS characteristics defined in 3GPP specifications, while dynamic values (90-254) can be assigned with operator-specific QoS parameters. Each 5QI value maps to a specific QoS profile containing five key parameters: Resource Type (GBR, Delay Critical GBR, or Non-GBR), Priority Level, Packet Delay Budget (PDB), Packet Error Rate (PER), and Averaging Window (for GBR flows only).
When a Protocol Data Unit (PDU) Session is established, the 5G Core Network (5GC) assigns one or more QoS Flows identified by their 5QI values. The Access and Mobility Management Function (AMF) communicates these QoS requirements to the Radio Access Network (RAN) via the N2 interface. The RAN then maps each QoS Flow to appropriate Data Radio Bearers (DRBs) using QoS Flow to DRB mapping rules. This hierarchical approach separates QoS control (in 5GC) from bearer management (in RAN), providing flexibility and scalability.
The 5QI mechanism works through standardized signaling procedures. During PDU Session Establishment or Modification, the Session Management Function (SMF) determines the appropriate 5QI based on the service requirements and subscriber profile. The SMF sends this information to the User Plane Function (UPF) for packet marking and to the RAN via the AMF. In the user plane, packets are marked with QoS Flow Identifiers (QFIs) derived from 5QI values, enabling consistent QoS treatment across network nodes. The RAN uses these markings to apply appropriate scheduling, admission control, and link layer configurations.
Key architectural components involved in 5QI implementation include the Policy Control Function (PCF), which provides policy rules containing 5QI assignments; the SMF, which enforces these policies; the UPF, which performs packet marking and rate policing; and the gNB, which implements radio resource scheduling based on 5QI parameters. The system supports both reflective QoS, where the UE can derive QoS rules from downlink traffic, and explicit QoS signaling via NAS and RRC protocols.
5QI plays a critical role in enabling network slicing and service differentiation. Different network slices can use different 5QI values to achieve their specific performance requirements. The standardized 5QI values cover a wide range of services including conversational voice, live streaming, autonomous driving, industrial automation, and massive IoT applications. This standardized approach ensures interoperability between different vendors' equipment and consistent QoS experience for end users.
Purpose & Motivation
5QI was created to address the limitations of previous QoS mechanisms in 4G/LTE networks, particularly the QCI (QoS Class Identifier). While QCI served well for 4G services, it lacked the granularity and flexibility needed for 5G's diverse use cases including ultra-reliable low-latency communications (URLLC), enhanced mobile broadband (eMBB), and massive machine-type communications (mMTC). The 4G system's bearer-based QoS model was too rigid for 5G's service-based architecture and network slicing requirements.
5QI solves several key problems: First, it provides finer granularity for delay-critical services with specific values for industrial automation, intelligent transport systems, and remote control applications. Second, it introduces the Delay Critical GBR resource type specifically for URLLC services requiring both guaranteed bitrate and strict latency bounds. Third, 5QI enables more efficient resource utilization through improved priority handling and the separation of QoS control from bearer management.
The historical context for 5QI development includes the need to support vertical industry requirements identified in 3GPP Study Items like TR 22.891 and TR 22.804. These studies revealed that previous QoS mechanisms couldn't adequately support services with conflicting requirements operating simultaneously on the same device, such as augmented reality (requiring high bandwidth) and vehicle-to-everything communication (requiring ultra-low latency). 5QI provides the foundation for meeting these diverse requirements through standardized yet flexible QoS profiles.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (141 CRs across 5 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-14, normative work from Rel-15.
In Release 15, the 5G QoS Identifier (5QI) function was formally standardized, introducing a consistent description and a completed characteristics table for standardized 5QI values. Key clarifications and corrections were made, including the alignment of 5QI with 4G QCI, fixes for URLLC service attributes like Packet Delay Budget (PDB) and Packet Error Rate (PER), and the definition of priority levels. The release also specified the use of a preconfigured 5QI for the QoS Flow associated with the default QoS rule.
- Use of identifiers for mobility between GERAN/UTRAN and 5GS TS 23.501CR0017
- 5G QoS fixes for URLLC services related attributes - PDB, PER, MDB, 5QI TS 23.501CR0087
- Partitioning of Identifier space to ensure success of Context retrieval for EPS Interworking TS 23.501CR0090
- Subscription Permanent Identifier TS 23.501CR0189
- Changed length and mapping of 5GS Temporary Identifiers TS 23.501CR0206
- Clarification to the usage of Internal-Group Identifier TS 23.501CR0262
+ 22 more changes
In Release 16, the 5QI function was enhanced to support Ultra-Reliable Low Latency Communications (URLLC) through the introduction of QoS monitoring and end-to-end delay measurement procedures. The standardized 5QI to QoS characteristics mapping table was also extended to accommodate enhanced Vehicle-to-Everything (V2X) requirements, including the specific introduction of 5QI 86. Furthermore, clarifications and optimizations were added for handling URLLC traffic over redundant PDU sessions and for Time-Sensitive Networking (TSN) 5QI usage.
- New clause for URLLC supporting TS 23.501CR0810
- Introduction of QoS Monitoring to assist URLLC Service TS 23.501CR0990
- Extension of standardized 5QI to QoS characteristics mapping table to accommodate enhanced V2X requirements TS 23.501CR1735
- 5QI 86 introduction TS 24.501CR1697
- Retrieval of BDT policy data for a set of BDT reference identifiers TS 29.513CR0086
- Subscription to Notification of change of PLMN Identifier at initial IMS Registration TS 29.513CR0133
+ 38 more changes
In Release 17, the 5G QoS Identifier (5QI) function was extended with new standardized 5QI values to support Advanced Interactive Services (AIS). Furthermore, specific 5QI considerations and mappings were introduced to support services carried over satellite access, accounting for the unique characteristics of GEO, MEO, or LEO satellite links. This enables the system to select communication links providing the best 5QI with respect to metrics like jitter or required bit rates for satellite access.
- Adding the usage of Redundant Transmission Experience analytics for URLLC service TS 23.501CR2581
- New 5QI values to support Advance Interactive Services (AIS) in 5G TS 23.501CR2701
- New standardized 5QI values for Advanced Interactive Services TS 23.501CR2740
- 5QI for satellite access TS 24.501CR3143
- 5QI value for services carried over satellite access/backhaul TS 29.513CR0284
- Introduction of Rel-17 IIoT/URLLC to TS 38.300 TS 38.300CR0416
+ 12 more changes
In Release 18, the 5G QoS Identifier (5QI) function was enhanced to define new standardized 5QIs for services delivered via Multicast/Broadcast Service (MBS), specifically for V2X and A2X message delivery. Furthermore, support was introduced for a 5QI Priority Level within QoS constraints, and new 5QIs were defined to cater to AIML (AI/ML) services. The release also included relaxations to 5QI delay requirements for first packets in RRC-INACTIVE mode and for other best-effort 5QIs.
- 5QI for V2X message delivery via MBS TS 23.501CR3881
- 5QI for A2X message delivery via MBS TS 23.501CR4249
- PIN identifiers TS 23.501CR4287
- Protecting the N3IWF/TNGF identifier information in the REGISTRATION REJECT message TS 24.501CR5932
- Resolving the EN related to N3IWF selection based on N3IWF identifier information in the REGISTRATION REJECT message TS 24.502CR0230
- Prefixed OI/TAI Identifier FQDN for N3IWF selection TS 24.502CR0223
+ 22 more changes
In Release 19, key enhancements for the 5QI function focused on enabling QoS differentiation for Non-3GPP Device Identifiers, including support for multiple identifiers, suspension procedures, and clarifications for roaming and session management. Additionally, the release provided specific clarifications on applying 5QI values and QoS characteristics for satellite access networks, ensuring the system can select communication links offering the best 5QI with respect to jitter or required bit rates. These updates expanded 5G QoS support to more efficiently manage devices connecting behind a UE or 5G-RG over various access types.
- UDR enhancement supporting Device Identifier of non-3GPP Devices connecting behind a UE/5G-RG TS 23.501CR5547
- Definition of identifiers of N3GPP device behind UE/5G-RG TS 23.501CR5749
- Support of reject QoS differentiation for non-3GPP device identifier(s) TS 24.501CR6926
- Procedure update for QoS differentiation of non-3GPP device identifiers TS 24.501CR6994
- Support of satellite identifier report at call set-up TS 29.513CR0602
- Add new identifiers in Namf_AIoT_MessageDelivery service operation TS 29.518CR1248
+ 17 more changes
Explore further
Broader topics and technologies where 5QI plays a role.
Defining Specifications
3GPP specifications that define or reference 5QI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TS 22.822 vg00 | Satellite Access in 5G Study | Rel-16 |
| TR 22.832 vh40 | Study on cyber-physical control in vertical domains | Rel-17 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TR 23.764 vh10 | Study on V2X Application Layer Enhancements | Rel-17 |
| TS 24.501 vj50 | 5G NAS Protocols Specification | Rel-19 |
| TS 24.502 vj20 | 5G Core Access via Non-3GPP Networks; Stage 3 | Rel-19 |
| TS 24.890 vg00 | 5G NAS Protocol for 5GS Stage 3 | Rel-16 |
| TS 26.502 vj30 | 5G Multicast-Broadcast User Services Architecture | Rel-19 |
| TR 26.928 vj00 | Study on eXtended Reality (XR) in 5G | Rel-19 |
| TS 28.802 vf00 | Management Study for 5G Network Architecture | Rel-15 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.513 vj40 | 5G PCC Signalling Flows & QoS Mapping | Rel-19 |
| TS 29.518 vj50 | AMF Service Based Interface Protocol | Rel-19 |
| TS 29.520 vj40 | 5G Network Data Analytics Services Stage 3 | Rel-19 |
| TS 29.543 vj20 | 5G Data Transfer Policy Control Services Stage 3 | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 29.890 vg00 | CT3 5G System Technical Report | Rel-16 |
| TS 37.473 vj00 | W1 Application Protocol (W1AP) Specification | Rel-19 |
| TS 37.483 vj10 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TS 38.413 vj10 | NG Application Protocol (NGAP) | Rel-19 |
| TS 38.414 vj00 | NG Interface User Plane Protocol | Rel-19 |
| TS 38.423 vj10 | Xn Application Protocol (XnAP) specification | Rel-19 |
| TS 38.463 vj00 | E1 Application Protocol (E1AP) | Rel-19 |
| TS 38.473 vj10 | 5G F1 Application Protocol (F1AP) | Rel-19 |