The third SIG-TFN (Special Interest Group on Time and Frequency Network) meeting took place in Brussels, kindly hosted by the Royal Observatory of Belgium.
The meeting brought together the National Research and Education Network (NREN) and National Metrology Institute (NMI) communities, alongside GÉANT, European stakeholders, industry representatives and users, to discuss the development of resilient Time and Frequency infrastructures across Europe.
Over two half-days, with 40 on-site participants and 50 remote, the meeting focused on threats to positioning, navigation, timing and how terrestrial fibre networks can improve resiliency. The community shared updates on the current status of Time and Frequency network development, discussed emerging threats to Global Navigation Satellite Systems (GNSS), and explored future applications for a European terrestrial Time and Frequency network.
Why accurate time matters
Accurate time is often invisible, but it underpins many of the systems that modern society depends on, including scientific research, telecommunications, energy systems, financial services, transport, navigation, digital infrastructure and emerging quantum technologies. As dependence on precise timing grows, ensuring that these services remain available, resilient and trustworthy is becoming an increasingly important strategic priority for Europe.
The meeting took place at a moment when Europe is increasingly considering resilience, sovereignty and alternatives or complements to GNSS-based timing. While systems such as Galileo remain essential, many critical applications require additional layers of resilience. Terrestrial fibre-based Time and Frequency distribution can provide such a complementary capability, strengthening national and cross-border infrastructure.
Resilience, GNSS threats and Complementary PNT
A major focus of the meeting was the growing need to address vulnerabilities in Positioning, Navigation and Timing (PNT). Participants discussed how terrestrial networks can improve resilience and reduce dependence on space-based timing alone by providing highly accurate, traceable and reliable timing distribution.
Matteo Paonni, Deputy Head of the Unit for Space, Connectivity and Economic Security at the European Commission’s Joint Research Centre (JRC), joined the meeting to outline a strategic shift towards a Coordinated Position, Navigation and Timing (C-PNT) “system of systems”. This approach aims to strengthen infrastructure resilience against emerging vulnerabilities, expand European technical capabilities and support the development of future expertise and talent.
The upcoming Multiannual Financial Framework (MFF) reflects this growing strategic interest in establishing a terrestrial time backbone. The JRC encouraged the Time and Frequency community to use its extensive technical and practical experience to help shape an upcoming technical study, which will operate under a highly compressed study and implementation timetable.
The JRC also highlighted its commitment to supporting the community throughout this process — acting as both a strategic bridge to the European Commission and a practical enabler. This includes offering access to laboratory facilities, encouraging technical knowledge exchange and supporting coordination between European stakeholders.
GÉANT Core Time and Frequency Network (C-TFN)
The meeting included an update on the status of the GÉANT Core Time and Frequency Network (C-TFN). The successful completion of the 2024 Pathfinder link demonstrated the technical feasibility of the approach and the value of collaboration between metrology institutes and research and education networks.
The next major step is the construction of the first international C-TFN backbone route connecting France, Belgium, Germany and Poland. Fibre and equipment contracts are in place, with completion expected by June 2027.
This first backbone route represents an important milestone towards a European capability for Time and Frequency distribution. It will support advanced research, optical clock comparisons, metrology activities and future sovereign infrastructure needs, while demonstrating the role of GÉANT and NRENs as key contributors to Europe’s resilient timing ecosystem.
Participants also congratulated Christian Chardonnet (Refimeve) following the announcement that the FOREST (Fiber-based Optical netwoRk for European Science and Technology) concept had been accepted onto the ESFRI Roadmap 2026. This recognition further highlights the strategic importance of fibre-based optical networks for European scientific and technological capabilities.
National implementations and future applications
The second day of the meeting included a deep dive into the Belgian Time and Frequency network implementation, presented jointly by Belnet and the Royal Observatory of Belgium. The session demonstrated the value of close collaboration between an NREN and an NMI, combining national fibre infrastructure expertise with precision timing and metrology capabilities.
Participants also explored future applications for Time and Frequency networks, including the potential for terrestrial networks to improve the resilience and accuracy of Coordinated Universal Time (UTC) calculations. Discussions also covered how terrestrial sensing capabilities could be deployed alongside Time and Frequency distribution infrastructure, creating new opportunities for scientific and critical infrastructure applications.
The technical discussions further explored complementary technologies, including ultra-stable optical frequency transfer for optical atomic clocks and future work related to the redefinition of the SI second, White Rabbit for Time and Frequency distribution, and ELSTAB (ELectronically STABilised time and frequency distribution) for high-performance transfer.
Looking ahead
The discussions highlighted a clear shared ambition: building resilient, trusted and interoperable Time and Frequency infrastructure across Europe. Achieving this will require continued cooperation between NMIs, NRENs, GÉANT, European institutions, research infrastructures and industry.
The meeting demonstrated how terrestrial national and cross-border fibre networks can strengthen Europe’s PNT resilience and sovereignty, while showing the progress of GÉANT’s cross-border Time and Frequency network and the benefits of collaboration between technical communities.
A European timing backbone must not only be technically excellent, but also trusted, accessible and sustainable. By combining the expertise of NMIs with the connectivity capabilities of NRENs, Europe can develop a robust timing ecosystem supporting research, innovation, critical infrastructure and future digital services.
Hosted at the Royal Observatory of Belgium, a place with a long tradition of precision measurement and scientific discovery, the meeting provided a fitting setting for discussions about the future of time. Today, that future is being shaped through optical clocks, fibre networks, metrology expertise and European collaboration.
