Guidance updated on precision timing for critical infrastructure

The International Telecommunication Union (ITU) — the United Nations agency for digital technologies — has released updated guidance to help countries maintain the precision time systems on which modern communications and critical infrastructure depend.

Precision timekeeping enables reliable operations of communications networks, navigation systems, electricity networks and financial systems. As these systems become increasingly interconnected, even small timing errors can result in service disruptions, unreliable data or operational failures.

The guidance in the 2026 edition of the Handbook on Selection and Use of Precise Frequency and Time Systems provides governments, engineers and technical specialists with an updated reference on the technologies used to generate, measure, compare and distribute precise frequency and time signals. The handbook is free to download from the ITU website.

“Global connectivity depends on technologies working together seamlessly — precision time is one of the foundations that makes this possible,” said ITU Secretary-General Doreen Bogdan-Martin. “Through international cooperation and technical expertise, ITU is helping countries strengthen the reliability and resilience of the timing systems that support communications and critical infrastructure worldwide.”

From traditional time signals to optical clocks

The digital services in our daily lives all depend on the ability to maintain and distribute precise time references, making accuracy, reliability and resilience of time synchronisation essential. The new ITU guide — updated for the first time since 1997 — covers the fundamental principles of frequency and time measurement, the operation of modern atomic clocks, and the technologies used to disseminate precise time across national and international networks.

Developed by experts from the ITU Radiocommunication Sector (ITU-R), the updated guide reflects nearly three decades of technological progress and modern society’s growing dependence on accurate, reliable time synchronisation. Key developments addressed in the 2026 edition include the following:

• Radio and satellite dissemination: The evolution of terrestrial radio time services and global navigation satellite systems (GNSS), including the continuing importance of terrestrial services as alternatives to satellite-based synchronisation.
• Optical-fibre time transfer: Advanced techniques for comparing and distributing precise frequency and time signals through optical-fibre networks.
• Optical atomic clocks: A new generation of frequency standards offering accuracy beyond conventional caesium clocks, with potential applications ranging from improved international timekeeping to measuring differences in the Earth’s gravitational potential.
• Time as a Service: Practical approaches to delivering reliable and traceable time references, including performance monitoring, system resilience and verification of traceability to Coordinated Universal Time (UTC).
   

The handbook also examines a new generation of ultra-precise clocks based on optical frequency standards that could eventually change how the world defines a second.

“We rarely think about precise time, yet modern communications, navigation and critical infrastructure depend on it every second,” said Mario Maniewicz, Director of the ITU Radiocommunication Bureau. “This handbook provides administrations and engineers with an authoritative reference for understanding the technologies behind accurate timing and for making these systems more reliable and resilient.”

Image credit: iStock.com/Kulpreya Chaichatpornsuk