On 29 January 2026, Vrije Universiteit Amsterdam hosted the launch of the the Dutch Time and Frequency Network at the Department of Physics and Astronomy, bringing together researchers, network engineers, and metrologists to celebrate the development of precision timing over Dutch research and education networks made possible by SURF and their research partners across the Netherlands
SURF have announced Time and Frequency as a new addition to their portfolio, offering a specialised service for research and education institutions, delivering accurate and precise time and frequency signals over fibre to connected organisations [https://www.surf.nl/en/services/network-connectivity/surf-timefrequency]. In order to deliver these services, SURF have reused existing fibres where possible and deployed dedicated White Rabbit equipment to build a stable backbone, with a 24/7 monitoring of both synchronisation status and link behaviour. These services have their origins in the SuperGPS project, which aimed to develop a terrestrial positioning and timing system independent of satellite navigation.
SuperGPS combined reference atomic clocks, fibre-based time transfer, and wireless time-difference-of-arrival techniques to demonstrate decimetre-level positioning using ground-based infrastructure. The project adopted White Rabbit to distribute time with sub-nanosecond accuracy, which also paved the way to a much wider range of applications.
The demand for accurate time
There is a steady increase in demand from timing-critical experiments and geographically distributed research groups, which made ad hoc provisioning increasingly impractical and drove the demand for an integrated service platform. For example, in 2019, White Rabbit was deployed over live SURFnet8 production links to synchronise the Dwingeloo and Westerbork telescopes as part of the ASTERICS (Astronomy ESFRI and Research Infrastructure Cluster) project, demonstrating that high-precision timing could be maintained on shared research network infrastructure. Jeroen Koelemeij, who is Group leader and expert in White Rabbit time and frequency distribution networks from the hosting institution, VU Amsterdam, described how this work expanded through collaboration with the Dutch radio astronomy community, particularly JIVE and ASTRON, where precise timing was required for coherent interferometric observations.
These deployments showed that fibre networks originally designed for data transport could also serve as metrology-grade timing channels when supported by appropriate hardware and calibration procedures.
With clock performance continuing to improve, the ability to distribute their output without degrading stability becomes more and more important. Fibre-based methods such as White Rabbit currently offer the only practical means of transferring optical-clock-level performance over national distances.
Jeroen also presented two key examples of how accurate clock and timing services are essential for science. The first concerned the development of robust network clocks based on ensembles of atomic clocks connected by White Rabbit links, forming a distributed “atomic flywheel” that improves stability and resilience through continuous intercomparison.
The second focused on high-precision spectroscopy of simple atoms and molecules, where ultra-stable lasers are used to excite trapped ions and measure transition frequencies with extreme accuracy. These techniques enabled VU researchers to measure the proton–electron mass ratio with 21 parts-per-trillion precision in 2020.
Such experiments rely on long-term frequency stability and traceability to national standards, which the fibre network provides.
National Timekeeping by the Dutch National Metrology Institute
VSL, the Dutch National Metrology Institute, presented at the event and focused on the relationship between fibre-based distribution and national timekeeping. VSL outlined its work on integrating advanced frequency standards and optical clocks into the realisation of UTC, including the development of an optical clock at the University of Amsterdam.
The Dutch time and frequency infrastructure emerged through a long-term collaboration among navigation research, radio astronomy, metrology, and network engineering communities. Beginning with SuperGPS field trials and continuing through SURFnet8 deployments and national backbone development, the network becomes a crucial tool to ensure time and frequency distribution.
Working together with SURF, VSL provides the reference frequency that is then distributed across the SURF fibre network to ensure the White Rabbit switches can synchronise their reference time.
Timekeeping across Europe
Accurate timekeeping is not a purely national requirement. As Amanda Díez Fernández, coordinator of the White Rabbit Collaboration at CERN explained. She emphasised the growing role of White Rabbit as a long-distance complementary PNT technology and its inclusion in European resilience strategies.
Amanda reported that White Rabbit is used within the Galileo ground segment for synchronising critical infrastructure and is deployed nationally in several European countries [https://white-rabbit.web.cern.ch]. She also referred to its role in European PNT resilience monitoring and assessment frameworks. These developments align with the findings of the European Commission’s Joint Research Centre, which identifies fibre-based timing as a mature component of a complementary PNT “system of systems”.
Time and Frequency across GÉANT
This need for a pan-European facility is driving developments across the wider GÉANT environment, this trajectory follows similar developments in other countries where NRENs increasingly support precision timing, quantum networking, and resilient infrastructure. Research and education networks are gradually evolving into components of Europe’s shared timing ecosystem.
A natural extension of this shift appeared in April 2025, when GÉANT launched its Long-Haul White Rabbit Time Distribution Incubator. The initiative explores how precise time transfer can operate over DWDM infrastructure at a continental scale, positioning the pan-European network as a foundation for an eventual EU-wide timing and navigation backbone. In doing so, it complements GNSS, bolsters safety-critical services, and contributes to Europe’s broader ambitions for digital sovereignty.
GÉANT is also ensuring that European engineers and researchers are supported in learning about how to implement, develop and use advanced time and frequency services through its Time and Frequency Network Training program (https://wiki.geant.org/spaces/NETDEV/pages/905379919/Time+and+Frequency+Networks+Training) that aims to ensure that Europe continues to be at the forefront of T&F technologies.
