Description
The Quality of Service Class Identifier (QCI) is a fundamental mechanism within the 3GPP Evolved Packet System (EPS) for managing and enforcing Quality of Service (QoS). It is a standardized integer value, ranging from 1 to 9 in its initial definition and later extended, that maps to a pre-configured set of QoS characteristics. These characteristics are not signaled on a per-bearer basis but are instead node-specific parameters that are pre-provisioned within network elements like the eNodeB, Serving Gateway (S-GW), and Packet Data Network Gateway (P-GW). When a bearer is established or modified, it is associated with a specific QCI. This QCI value acts as a reference pointer, instructing each network node on how to handle the packets belonging to that bearer.
Each QCI value is linked to a specific resource type (Guaranteed Bit Rate - GBR or Non-GBR), priority level, Packet Delay Budget (PDB), and Packet Error Loss Rate (PELR). The priority is an integer where a lower value indicates a higher priority for scheduling. The PDB defines an upper bound for the time a packet may be delayed between the UE and the P-GW (or UE and the RAN node in 5G). The PELR defines an upper bound for a rate of non-congestion related packet losses. For GBR bearers, the QCI also implies the need for admission control based on the guaranteed bit rate. The network uses these parameters to make scheduling, queue management, and link layer configuration decisions to meet the service requirements.
Architecturally, QCI is a core part of the EPS bearer model. It is used in the S5/S8 interface between the S-GW and P-GW, the S1 interface between the eNodeB and the MME/S-GW, and over the radio Uu interface. In the control plane, the MME receives the authorized QCI for a bearer from the P-GW (via the S-GW) and communicates it to the eNodeB during bearer setup. The eNodeB then uses this QCI, along with its locally configured mapping tables, to apply the appropriate radio resource scheduling (e.g., in the MAC layer). In 5G, the QoS model evolved with the 5G QoS Identifier (5QI), which is a direct conceptual successor to QCI, though with an expanded range of standardized values and more flexible parameters for new service types.
Purpose & Motivation
QCI was introduced to solve the critical problem of traffic differentiation and guaranteed service performance in all-IP mobile networks. Prior to 3GPP Release 8 and the EPS, circuit-switched and packet-switched domains were separate, with QoS often tied to specific, rigid bearer services. The move to a flat IP architecture required a new, scalable, and efficient method to manage diverse traffic—from voice and video streaming to web browsing and background file downloads—over a shared infrastructure. QCI provides this by standardizing a limited set of well-understood QoS profiles, enabling multi-vendor interoperability and simplifying network configuration and policy management.
Its creation was motivated by the need to support IMS-based services like Voice over LTE (VoLTE) which demand low latency and guaranteed bandwidth, alongside best-effort internet traffic. Without a mechanism like QCI, all packets would be treated equally, leading to poor user experience for real-time applications. QCI allows operators to create a virtual 'pipe' (the bearer) with specific characteristics for a service or application, ensuring that network resources are allocated appropriately. It abstracts complex per-flow QoS parameters into a simple integer, reducing signaling overhead and enabling fast, consistent policy enforcement across the entire network path from the core to the radio interface.
Classification
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (24 CRs across 6 releases). Complements the general historical overview above with the evidence-based evolution of this function.
Studied in Rel-8, normative work from Rel-15.
In Release 15, the QCI function was enhanced with the introduction of a new QCI specifically for MCVideo services. Furthermore, packet handling began to consider the ARP priority level in addition to the QCI for more granular QoS control. These changes were part of broader updates that included new application identifiers for Service Data Streams (SDSs).
- Introduction of SDS application type identifiers TS 23.282CR0079
- New QCI for MCVideo TS 24.301CR3080
- Use of ARP priority level in addition to QCI for packet handling TS 23.401CR3359
- Adding application identifier in media plane SDSs TS 23.282CR0089
- Handling of extended EPS quality of service IE and extended APN-AMBR IE TS 24.301CR2919
- Correction of Extended EPS quality of service IE naming TS 24.301CR2949
+ 4 more changes
In Release 16, the QCI function was updated with a correction to the QCI value assigned for Mission Critical services and the addition of a missing mapping between QCI and the 5G QoS parameter CAPC (5QI to QoS Flow Mapping). These changes ensured proper alignment for critical service prioritization and resolved a mapping gap in the QoS framework.
- Inclusion of Version Identifier in PLMN assigned ID TS 23.401CR3561
- Correct qci for Mission critical extension TS 29.116CR0046
- Missing QCI to CAPC mapping TS 36.300CR1240
- Alignment of the 5G ciphering and integrity algorithm identifiers TS 24.301CR3221
- Correction of connected en-gNB Identifier TS 36.300CR1289
In Release 17, the primary update to the QCI function was a clarification on the QCI setting for video services, as prompted by an ETSI Plugtest request. This clarification aimed to provide more precise guidance on applying the appropriate QoS parameters for video traffic, which falls under the broader service category of interactive services. The change sought to ensure consistent implementation of the performance parameters defining this service class across networks.
- Clarification on video QCI setting requested by ETSI Plugtest TS 24.281CR0175
In Release 18, a new Quality of Service Class Identifier, QCI 10, was introduced specifically for QoS control for satellite access. This addition, defined as a new QCI for satellite access – Category A, expands the QoS framework to accommodate the distinct performance characteristics of non-terrestrial networks. The release also included work on floor control signalling over the existing QCI 69 and QCI 65.
- Identifier availability for Lawful Interception during Inter-MME/ MME-5GS handover TS 23.401CR3720
- Floor control signalling over QCI 69 and QCI 65 TS 23.379CR0314
- Clarification of satellite identifiers TS 36.300CR1430
- Clarification of satellite identifiers TS 36.331CR5152
- New QCI 10 for QoS control for satellite access – Cat A TS 24.301CR3829
In Release 19, there were no new functional changes or additions specified for the QCI (Quality of Service Class Identifier) function itself. The provided Change Request titles and grounding context contain no modifications or enhancements related to QoS classes, bearers, or the QCI parameter. The technical details within the release materials pertain to other areas, such as message classification corrections and general terminology definitions.
- Correction to the classification of EMM TRANSPORT message as partially ciphered TS 24.301CR4541
In Release 20, the QCI function was extended to authorize specific quality of connection requests for new service clients, namely MCData and MCPTT. This introduced authorization procedures for these mission-critical services as a new class of elementary procedures within the system. These procedures govern the successful or unsuccessful establishment of the requested QoS for these client types.
Explore further
Broader topics and technologies where QCI plays a role.
Defining Specifications
3GPP specifications that define or reference QCI, with the latest known release. Sourced from the 3GPP document catalog — see methodology.
| Specification | Title | Release |
|---|---|---|
| TR 21.905 vj00 | 3GPP Technical Terms and Definitions | Rel-19 |
| TS 23.203 vj20 | Policy and charging control architecture | Rel-19 |
| TS 23.282 vk00 | MCData Functional Architecture & Info Flows | Rel-20 |
| TS 23.379 vk00 | MCPTT Functional Architecture | Rel-20 |
| TS 23.401 vj50 | Evolved Packet System (EPS) Stage 2 Description | Rel-19 |
| TS 23.468 vj00 | Group Communication System Enablers for LTE | Rel-19 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 23.795 vg10 | V2X Application Architecture Study | Rel-16 |
| TS 24.229 vj50 | IMS call control protocol based on SIP and SDP | Rel-19 |
| TS 24.281 vj40 | MCVideo Signalling Control Specification | Rel-19 |
| TS 24.282 vj50 | MCData Signalling Control Protocols | Rel-19 |
| TS 24.301 vj60 | NAS protocol for Evolved Packet System | Rel-19 |
| TS 24.379 vj50 | Mission Critical Push To Talk (MCPTT) call control | Rel-19 |
| TS 26.114 vj10 | IMS Multimedia Telephony Media Handling | Rel-19 |
| TS 26.348 vj00 | xMB Interface Specification | Rel-19 |
| TR 26.928 vj00 | Study on eXtended Reality (XR) in 5G | Rel-19 |
| TS 29.061 vj00 | Packet Domain Interworking for PLMN | Rel-19 |
| TS 29.116 vj00 | REST-based protocol for xMB reference point | Rel-19 |
| TS 29.213 vj20 | PCC Signalling Flows and QoS Mapping | Rel-19 |
| TS 29.866 vj00 | IMS Disaster Prevention & Restoration Enhancement | Rel-19 |
| TS 32.130 vj20 | Network Sharing OAM&P Requirements | Rel-19 |
| TS 32.251 vj00 | PS Domain Charging Management | Rel-19 |
| TS 36.300 vj00 | E-UTRAN Radio Interface Protocol Architecture Overview | Rel-19 |
| TS 36.314 vj00 | E-UTRA Radio Measurements Specification | Rel-19 |
| TS 36.331 vj00 | LTE RRC Protocol Specification | Rel-19 |
| TS 36.579 | 3GPP TR 36.579 | Rel-8 |
| TS 36.880 vd00 | MDT Enhancements Study for E-UTRAN | Rel-13 |
| TS 37.320 vj00 | Minimization of Drive Tests (MDT) Overview | Rel-19 |
| TS 37.579 vi40 | Mission Critical services conformance testing | Rel-18 |
| TR 37.901 vf10 | UE Application Layer Data Throughput Performance | Rel-15 |
| TR 38.835 vi01 | Technical Report on XR Enhancements for NR | Rel-18 |