Description
Ultra Reliable Low Latency Communication (URLLC) is a foundational service category within the 5G system architecture, defined to support applications with stringent requirements for end-to-end latency, reliability, and availability. Unlike enhanced Mobile Broadband (eMBB) which focuses on high data rates, URLLC prioritizes deterministic performance, often targeting latencies as low as 1 millisecond for the radio interface and reliability levels up to 1-10^-5 or 1-10^-6 (99.999% to 99.9999% success probability). The architecture supporting URLLC permeates both the Radio Access Network (RAN) and the Core Network (5GC), requiring coordinated enhancements in scheduling, transmission schemes, and network resource management.
At the physical and MAC layer, URLLC employs several key techniques to achieve low latency. These include grant-free or configured grant uplink transmissions, which allow a User Equipment (UE) to transmit data immediately without waiting for a scheduling grant, drastically reducing signaling delay. Short Transmission Time Intervals (TTIs), such as mini-slots, enable faster packet encoding and decoding. For reliability, robust modulation and coding schemes (MCS), along with techniques like repetition coding, frequency diversity, and multi-connectivity (where a UE is simultaneously connected to multiple gNBs or cells), are utilized. Packet duplication over multiple paths, managed by the Packet Data Convergence Protocol (PDCP) layer, is a critical feature where identical data packets are sent via different radio links or carriers to increase the chance of successful delivery.
In the Core Network, URLLC support involves network functions like the Access and Mobility Management Function (AMF) and Session Management Function (SMF) being aware of URLLC Quality of Service (QoS) profiles. The 5G QoS Identifier (5QI) includes standardized values specifically for URLLC flows, which map to precise packet delay budget, packet error rate, and default priority levels. The core network ensures that user plane functions (UPF) are deployed appropriately, potentially using edge computing (via Multi-access Edge Computing - MEC) to localize traffic processing and further reduce latency. Network slicing is intrinsically linked with URLLC, allowing the creation of dedicated, logically isolated network slices with reserved resources and tailored configurations to guarantee the required performance independently from other service types.
Purpose & Motivation
URLLC was created to address the growing demand for wireless connectivity in industrial and mission-critical applications that cannot tolerate the variable latency and reliability of traditional mobile broadband services. Prior to 5G, cellular networks (2G, 3G, 4G) were optimized for human-centric communication—voice and mobile internet—where delays of tens or hundreds of milliseconds were acceptable. The advent of Industry 4.0, autonomous systems, and remote real-time control exposed the limitations of these networks for applications like factory automation, smart grids, and tele-surgery, where a missed deadline or a lost packet could lead to catastrophic failure, safety hazards, or significant economic loss.
The motivation for standardizing URLLC within 3GPP, starting from Release 14 as a study item and evolving through subsequent releases, was to transform cellular technology into a universal connectivity fabric capable of supporting both human and machine-type communication with guaranteed performance. It solves the problem of providing 'deterministic' wireless communication over a shared, statistical multiplexing medium. By defining clear targets and standardizing the enabling mechanisms across the entire protocol stack, URLLC allows diverse vertical industries to rely on 5G as a replacement for or complement to wired fieldbus systems (like PROFINET, EtherCAT) and proprietary wireless solutions, enabling greater flexibility, mobility, and scalability in automated environments.
Detected Changes Across Releases
from 3GPP Change RequestsSpecific changes extracted from the „Change history“ tables of 3GPP specifications (104 CRs across 6 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, foundational URLLC enhancements were introduced, including specific 5G QoS fixes for attributes like Packet Delay Budget (PDB) and Packet Error Rate (PER) to define guaranteed service performance. The release also standardized the use of TCP for reliable NAS transport to the N3IWF and refined channel quality indicators (CQI) and modulation and coding schemes (MCS) tailored for ultra-reliable low latency communication.
In Release 16, key URLLC enhancements included the introduction of QoS monitoring to assist the URLLC service and the provision for "Always on Control for the GBR QoS Flow" to ensure highly reliable performance. Furthermore, the release specified enhancements to QoS handling for V2X communication over the Uu reference point and introduced new architectural support for indirect communication between Network Functions with related service discovery and selection schemas.
- High Latency Overall Description TS 23.501CR0751
- Introduction to Reliable Data Service TS 23.501CR0825
- New clause for URLLC supporting TS 23.501CR0810
- Introduction of indirect communication between NF services and implicit discovery TS 23.501CR0736
- eSBA communication schemas related to general discovery and selection TS 23.501CR0799
- eSBA communication schemas related to UDM and UDR discovery and selection TS 23.501CR0800
+ 43 more changes
In Release 17, key URLLC enhancements included the introduction of architectures for Time Sensitive Communication (TSC) and Time Synchronization, as well as support for TSC beyond just TSN. The release also added the use of Redundant Transmission Experience analytics for URLLC service assurance and introduced a new Service and Session Continuity (SST) value for High-Performance Machine-Type Communications (HMTC).
- CR for group communication in 5G system TS 22.261CR0403
- Introduction of the architectures for Time Sensing Communication other than TSN. TS 23.501CR2573
- Adding the usage of Redundant Transmission Experience analytics for URLLC service TS 23.501CR2581
- Introduction of architecture for AF requested support of Time Sensitive Communication and Time Synchronization TS 23.501CR2833
- Support Time Sensing Communication other than TSN TS 29.512CR0760
- Remove the editor's note for AF preference for the user plane latency TS 29.512CR0845
+ 6 more changes
In Release 18, URLLC enhancements specifically introduced new features for PDU set handling and real-time latency control, alongside explicit support for uplink and downlink transmission coordination to meet round-trip latency requirements. The release also added definitions and procedures for PIN communication and CN-based Mobile-Terminated communication handling for UEs in RRC_INACTIVE state. Furthermore, it introduced Timing Resiliency and periodicity feedback for Time Sensitive Communications to improve reliability and synchronization.
- TACMM CR Introduction of text for Tactile and multi-modal communication service TS 22.261CR0611
- PIN communication configuration TS 23.501CR3897
- CN based MT communication capability indication TS 23.501CR4081
- KI#4 implementation of cross-SMF VN group communication TS 23.501CR4313
- Support of Uplink Downlink transmission coordination to meet RT latency requirement TS 29.512CR1073
- Introduction of new features for PDU set handle and RT latency TS 29.512CR1132
+ 14 more changes
In Release 19, URLLC enhancements focused on expanding mission-critical connectivity through new UE-to-UE multi-hop relay requirements and the support of UE-Satellite-UE communications, including procedures for when the serving satellite changes. Furthermore, it introduced policy-based procedures for establishing and deleting SEALDD-enabled URLLC transmission connections, utilizing protocols like HTTP and CoAP.
- UE-to-UE Multi-hop relay requirements for mission critical communications TS 22.261CR0681
- Support of UE-Satellite-UE communication TS 23.501CR5583
- Support of UE-satellite-UE communications when serving satellite changes TS 23.501CR5518
- Update for support of UE-Satellite-UE communication TS 23.501CR6144
- SEALDD enabled URLLC transmission connection deletion based on policy procedure based on HTTP TS 24.543CR0015
- SEALDD enabled URLLC transmission connection establishment based on policy procedure based on HTTP TS 24.543CR0012
+ 11 more changes
In Release 20, URLLC enhancements specifically addressed satellite-based communication by introducing support for UE-to-UE communication for non-IMS services via satellite. This release also included necessary corrections to the technical specifications for calculating end-to-end latency in satellite scenarios, ensuring the performance criteria for guaranteed and predictive service models are accurately defined.
Explore further
Broader topics and technologies where URLLC plays a role.
Defining Specifications
3GPP specifications that define or reference URLLC, 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 22.261 vk30 | 5G System Service Requirements | Rel-20 |
| TS 22.830 vg10 | Business Role Models for Network Slicing | Rel-16 |
| TS 23.501 vk00 | 5G System Architecture Stage 2 | Rel-20 |
| TS 23.700 vk00 | XR Services Application Enablement Layer | Rel-20 |
| TS 23.725 vg20 | Study on URLLC Architecture Enhancements | Rel-16 |
| TR 23.745 vh00 | Study on App Layer Support for Factories of the Future in 5G | Rel-17 |
| TS 24.543 vj50 | SEAL Data Delivery Management Protocol | Rel-19 |
| TR 26.806 vi00 | Technical Report on Smartly Tethering AR Glasses | Rel-18 |
| TS 29.512 vj40 | 5G Session Management Policy Control Service | Rel-19 |
| TS 29.892 vg00 | Study on User Plane Protocol in 5GC | Rel-16 |
| TS 33.501 vk00 | 5G Security Architecture and Procedures | Rel-20 |
| TS 33.825 vg01 | Security for 5G URLLC Services | Rel-16 |
| TR 37.910 vj00 | 5G SRIT and NR RIT Self-Evaluation Report | Rel-19 |
| TS 38.300 vj00 | NG-RAN Overall Description | Rel-19 |
| TR 38.802 ve20 | Study on New Radio Access Technology Physical Layer Aspects | Rel-14 |
| TR 38.804 ve00 | Study on New Radio Access Technology; Radio Interface Protocol Aspects | Rel-14 |
| TS 38.811 vf40 | Study on NR Support for Non-Terrestrial Networks | Rel-15 |
| TR 38.812 vg00 | Study on NOMA for NR | Rel-16 |
| TR 38.825 vg00 | Study on NR Industrial IoT | Rel-16 |
| TR 38.890 vh00 | NR QoE Management and Optimization | Rel-17 |
| TR 38.912 vj00 | Study on New Radio Access Technology | Rel-19 |
| TR 38.913 vj00 | Next Gen Access Tech Scenarios & Requirements | Rel-19 |