The International Telecommunication Union (ITU) 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.
"Global connectivity depends on technologies working together seamlessly - precision time is one of the foundations that makes this possible," said Doreen Bogdan-Martin, ITU Secretary-General. "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
Precision timekeepng is an essential, largely invisible component of critical infrastructure.
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 synchronization essential.
The new ITU guide is the first update since 1997. It 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:
- 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 synchronization.
- 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."
International timekeeping enters a new phase
The publication comes at a significant moment for international timekeeping.
At its 28th meeting in October 2026, the General Conference on Weights and Measures (CGPM) adopted resolutions advancing preparations for a future redefinition of the second and establishing a continuous Coordinated Universal Time (UTC) from 20 May 2027, ending the insertion of leap seconds.
The move towards continuous UTC is intended to reduce the risk of disruptions in digital systems and critical infrastructure caused by adjustments to the international time scale.
In its decision, the CGPM recognized the close cooperation between the International Bureau of Weights and Measures (BIPM) and ITU-R, including work undertaken through ITU-R.
The new Handbook provides technical background for understanding these developments and the technologies that support internationally coordinated timekeeping.
An international reference for administrations
The work was developed by ITU-R Working Party 7A, chaired by Dr Joseph Achkar (France), through a correspondence group led by Felicitas Arias (France) and Andreas Bauch (Germany).
Experts contributing to the work came from administrations, national metrology institutes, research organizations and universities, including the Observatoire de Paris, Physikalisch-Technische Bundesanstalt (PTB), the United Kingdom's National Physical Laboratory (NPL), Japan's National Institute of Information and Communications Technology (NICT), the University of Colorado, Centre national d'études spatiales (CNES), Franche-Comté Électronique Mécanique Thermique et Optique - Sciences et Technologies (FEMTO-ST), BIPM and the European Laboratory for Particle Physics (CERN).
