Precise Time Independent of GPS: CESNET Develops Technology for Time Distribution over Optical Networks

Although most people don’t give it much thought, precise time is a very important part of our lives. Whenever we make a phone call, use mobile internet, or rely on navigation, we’re depending on systems that are synchronized to a very precise time. Precise time synchronization is used not only in telecommunications, but also in the energy sector, the financial sector, defense, and research. In some cases, accuracy down to seconds or even milliseconds isn’t enough—precision is measured in microseconds and sometimes even nanoseconds.

How Networks, Power Plants, and Laboratories Synchronize

Today, satellite navigation systems such as GPS or Galileo are very commonly used to distribute precise time. In addition to determining location, they also provide highly accurate time information that serves as a reference source for a wide range of technologies. It is precisely this information that is used to synchronize mobile networks, energy systems, scientific instruments, and other infrastructure.

When GPS Alone Is Not Reliable
However, satellite navigation systems may not be reliable in all circumstances. Their signal can be jammed, intentionally distorted, or, in some situations, may be unavailable altogether. Events related to the armed conflict in Ukraine have shown that jamming of satellite navigation systems is not merely a theoretical threat. Governments and operators of vital systems are therefore actively seeking alternative ways to ensure reliable time synchronization for their critical infrastructure.

Optical fiber doesn’t just transmit data
One option is to use optical fiber, which most people associate with high-speed internet connections. These provide an independent path for distributing precise time and help reduce reliance on satellite navigation systems. For applications with high reliability requirements, they can thus serve as an important backup or supplementary infrastructure.

However, this same infrastructure can also be used to transmit highly precise time and frequency information. Thanks to the CESNET consortium, an infrastructure for distributing precise time via optical networks is being developed. The project will include approximately twenty nodes equipped with White Rabbit technology.

White Rabbit: Nanosecond-Level Accuracy
White Rabbit technology originated at CERN, where there was a need to synchronize large-scale scientific experiments with exceptionally high accuracy requirements. Compared to conventional methods, it can ensure synchronization with an accuracy better than one nanosecond and maintain it even over long distances. This makes it suitable for scientific experiments, advanced measurement systems, and the development of a robust infrastructure for time distribution.

We verified the technology’s functionality not only under laboratory conditions but also in a real-world network infrastructure. Tests conducted over routes spanning hundreds of kilometers confirmed that sub-nanosecond synchronization can be maintained even during the simultaneous operation of high-capacity data services. Building on these verified results, we are now developing an infrastructure for the distribution of precise time within the CESNET network.

This year, we presented the results of our research and practical applications at several major professional events. At the IS2 2026 conference, Vladimír Smotlacha gave a presentation on time and frequency distribution via optical networks and the modernization of the CESNET infrastructure. At the 15th White Rabbit workshop at CERN, Josef Vojtěch, together with colleagues from CERN and the Norwegian organization SIKT, presented their experiences with testing White Rabbit technology on routes hundreds of kilometers long.

The next time you make a payment, place a phone call, or open your navigation app, you probably won’t even think about the exact time. But that’s precisely a sign that it’s working exactly as it should.