In 5G networks, URLLC (Ultra-Reliable Low-Latency Communication) is one of the three main application scenarios, alongside enhanced Mobile Broadband (eMBB) and Massive Machine-Type Communications (mMTC). URLLC is specifically designed to deliver communication with extremely low latency and very high reliability. This makes it ideal for services that require quick, dependable responses, such as autonomous driving, smart manufacturing, remote diagnostics, and high-definition AR/VR applications.
URLLC involves end-to-end transmission across various network segments, including the core network, transport network, and radio access network (RAN). It is supported by several technologies and deployment solutions tailored to meet the needs of different industries and applications.
Application Scenarios of URLLC?
The 3GPP TS 22.261 standard outlines the communication requirements for various services. For example, services like remote shopping or education require an end-to-end latency of 10-20 milliseconds, with a jitter of 5 milliseconds and reliability of 99.9%. On the other hand, real-time control services demand much stricter parameters, such as an end-to-end latency of 1 millisecond or less, jitter of 1 microsecond, and reliability of 99.9999%. These specifications highlight the importance of URLLC in supporting critical, latency-sensitive applications in modern networks.
Table 1 – Latency requirements of various services.
| Scenario | Application | E2E Latency | Jitter | Reliability Requirement |
|---|---|---|---|---|
| Autonomous driving | Coordinated control – platooning | < 3 ms | 1 μs | 99.9999% |
| Cooperative manoeuvres (collision avoidance/lane change) | < 10 ms | 1 ms | 99.9999% | |
| Sensor information sharing | < 50 ms | 20 ms | 99.99% | |
| Remote vehicle operation | 10–30 ms | 5 ms | 99.9999% | |
| Dynamic HD map update | ~100 ms | 20 ms | 99.9% | |
| VR/AR | VR remote motion control (surgery/drone) | 10–20 ms | 5 ms | 99.9999% |
| VR 360 live event streaming | 10–20 ms | 5 ms | 99.99% | |
| VR collaborative game | 10–20 ms | 5 ms | 99.99% | |
| VR remote shopping/education | 10–20 ms | 5 ms | 99.9% | |
| AR (game/navigation) | 20 ms | 5 ms | 99.9% | |
| Smart grid | High-voltage power distribution | < 5 ms | 1 ms | 99.9999% |
| Medium-voltage power distribution | 25 ms | 5 ms | 99.9% | |
| Factory automation | Real-time motion control | ≤1 ms | 1 μs | 99.9999% |
| Discrete automation (vehicles, etc.) | 10 ms | 100 μs | 99.99% | |
| Production automation (remote control) | 50 ms | 20 ms | 99.9999% | |
| Production automation (monitoring) | 50 ms | 20 ms | 99.9% | |
| Healthcare & safety, smart city, and drone | Real-time command and control for remote surgery | 10 ms | 1 ms | 99.9999% |
| Intelligent transport systems – infrastructure backhaul | 10 ms | 5 ms | 99.9999% | |
| Time critical sensing and feedback for smart cities (such as traffic lights) | 30 ms | 5 ms | 99.99% | |
| Remote drone operation | 10–30 ms | 1 ms | 99.9999% |
Note: Several factors inherent to the network cause differences in latency for data packets that are transmitted successively using the same path on the network. The latency inconsistency between data packets is called jitter.
3GPP TR 38.913 defines target values for the communication latency and reliability on the RAN side in URLLC scenarios.
Table 2 – Target values for RAN-side latency and reliability in 5G URLLC scenarios.
| Indicator | Definition in 3GPP Specifications | Target Value |
|---|---|---|
| User-plane latency | User-plane latency refers to the time it takes to successfully deliver an application layer packet/message from the radio protocol layer 2/3 SDU ingress point to the radio protocol layer 2/3 SDU egress point via the radio interface in both uplink and downlink directions. | Downlink: 0.5 msUplink: 0.5 ms |
| Reliability | Reliability is evaluated against the probability that a specific number of bytes will be transmitted successfully within a specific delay. The delay refers to the time required for delivering a small data packet from the radio protocol layer 2/3 SDU ingress point to the radio protocol layer 2/3 SDU egress point via the radio interface at specific channel quality (for example, a coverage edge). | 99.999% (32 bytes@1 ms) |
How to Evaluate URLLC Indicators?
Evaluating URLLC indicators like latency and reliability is crucial for understanding how well the network meets the demands of ultra-reliable low-latency communication. Here’s how these indicators are typically assessed in real-world scenarios:
Latency Evaluation
Latency in the RAN (Radio Access Network) is assessed using two key metrics: One-Trip Time latency (OTT) and Round-Trip Time latency (RTT). These metrics are usually calculated by using a terminal to send “ping” requests to a server located in the core network and then recording the latency of data packets during the process.
- RAN OTT: This measures the time taken for data to travel in one direction through the RAN.
- Uplink RAN OTT: Calculated as the difference between two timestamps, (T3 – T1), where (T1) is when the packet leaves the terminal and (T3) is when it arrives at the RAN’s uplink point.
- Downlink RAN OTT: Calculated as (T6 – T4), where (T4) is when the packet leaves the RAN’s downlink point, and (T6) is when it arrives at the terminal.
- RAN RTT: This is the time taken for a packet to travel from the terminal to the server and back. It is computed as:
RAN RTT=T6−T1−(T4−T3)
RTT is generally used to observe latency because time synchronization between the terminal and the server is often not precise, making OTT measurements more challenging.
Reliability Evaluation
Reliability is assessed by examining the success rate of transmitting a specified number of data packets within a given timeframe. The process involves sending a large number of packets (e.g., 100,000 packets of 32 bytes each) and measuring the delay for each packet.
The key metric is the accuracy rate:
- If the transmission delay for 99,999 out of 100,000 packets meets the required latency threshold (e.g., within (x) milliseconds), the reliability target is considered achieved.
- In this case, if the reliability target is 99.999%, and 99,999 packets out of 100,000 are successfully transmitted within the specified time, the network meets the reliability requirements.
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