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.
Established in Saint-Josse-ten-Noode in 1826 by King William I of the Netherlands under the impulse of the astronomer and mathematician Adolphe Quetelet, the observatory is home to a 100 cm (39 in) diameter aperture Zeiss reflector, one of the largest telescopes in the world at the time. The institute owns a variety of other astronomical instruments, many still on display, such as astrographs, chronographs and seismographs. Its main activities are reference systems and geodynamics, astrometry and dynamics of celestial bodies, astrophysics, and Solar physics.
In this amazing setting, across two half-days, members of the Time and Frequency community from across Europe gathered to discuss the design and deployment of Time and Frequency distribution infrastructures. The meeting brought together National Metrology Institutes, National Research and Education Networks, GÉANT, European stakeholders, industry representatives and users. The shared goal was to strengthen the community working on precise, resilient and interoperable timing across Europe.
Accurate time is often invisible. It underpins scientific research, telecommunications, energy systems, financial services, transport, navigation, digital infrastructure and emerging quantum technologies. When everything works, time is rarely noticed. But when timing is disrupted, the consequences can quickly become visible across critical services. This is why resilient Time and Frequency distribution is becoming an increasingly important topic for Europe.
The meeting took place at a moment when Europe is thinking more seriously about resilience, sovereignty and alternatives or complements to GNSS. Global Navigation Satellite Systems, including Galileo, remain essential. However, many critical sectors cannot rely on space-based timing alone. Fibre-based Time and Frequency distribution can provide an important complementary layer, supporting more resilient national and pan-European timing services.
The meeting included a presentation about the status of the GÉANT Core Time and Frequency Network, or C-TFN. The successful completion of the 2024 Pathfinder link was an important milestone, demonstrating both the technical feasibility and the value of the collaboration model between metrology institutes and research and education networks. The next step is now the build of a first international C-TFN backbone route linking France, Belgium, Germany and Poland. Fibre and equipment contracts are in place, and completion is expected by June 2027.
This first backbone route is an important step towards a European capability for Time and Frequency distribution. It will support advanced research, metrology, optical clock comparison and future sovereign infrastructure needs. It will also help position the GÉANT and NREN community as a key partner in Europe’s wider resilient timing ecosystem.
The technical discussions explored several complementary technologies. These include ultra-stable optical frequency transfer for optical atomic clocks and future work on the redefinition of the SI second, White Rabbit for Time and Frequency distribution, and ELSTAB (ELectronically STABilised time and frequency distribution) for high-performance Time and Frequency transfer.
Another important topic was Complementary Position, Navigation and Timing, or C-PNT. The European Commission Joint Research Centre is placing C-PNT as a strategic EU resilience priority, with Complementary Timing as the first focus. The proposed direction is a terrestrial UTC timing backbone that can complement Galileo and GNSS, reducing dependence on space-based timing alone.
This has direct relevance for GÉANT and the NREN community. National and international research networks are natural candidates to interconnect Time and Frequency capabilities across Europe. National Metrology Institutes provide traceable UTC generation and calibration expertise, while NRENs provide high-capacity national and cross-border fibre infrastructure. Together, they can support a neutral, trusted and high-availability timing layer for research, critical infrastructure and future services.
The discussions also highlighted the importance of governance, interoperability and sustainability. A European timing backbone must be technically excellent, but it must also be trusted, accessible and sustainable. It should involve Member States, NMIs, NRENs, GÉANT, European institutions, research infrastructures and commercial actors. It should support both public-interest infrastructure and future commercial services, while maintaining neutrality and long-term resilience.
Time and Frequency distribution is becoming a strategic infrastructure topic for Europe, connecting fundamental science with critical infrastructures, national capabilities with European collaboration, and research networks with resilience and sovereignty.
The Royal Observatory of Belgium offered an inspiring reminder that the measurement of time has always been central to science. Today, that tradition continues through fibre networks, optical clocks, metrology laboratories and cross-border collaboration. For GÉANT and the NREN community, the opportunity is to help build the trusted timing infrastructure that Europe will need for research, innovation and resilience in the years ahead.
