Recommendation 5 of the 19th CCTF (2012)

Development of continental-scale optical fibre time and frequency transfer networks and support to studies of improved methods for intercontinental clock comparison

The Consultative Committee for Time and Frequency (CCTF),


  • the continuing reduction in the uncertainty and instability of optical frequency standards developed in institutes around the world,
  • the need for regular comparisons between these standards, as an essential part of the preparation for a redefinition of the second and for other applications such as contributions to time scales,
  • that the stabilities of time and frequency transfer techniques currently and routinely used for comparisons around the world, i.e. for the production of International Atomic Time (TAI), are insufficient for comparisons between the best optical frequency standards,
  • the demonstrated capability of optical fibre links to realize frequency comparisons with the stability required for the best frequency standards, over distances of the order of 1000 km,
  • that optical fibre links improve the robustness of time and frequency transfer networks since they are independent of the global navigation satellite system (GNSS) and two-way satellite time and frequency transfer (TWSTFT) methods,
  • the existence of research projects concerning alternative time and frequency transfer methods with the potential to significantly improve intercontinental comparisons,

recommends that

  • national metrology institutes (NMIs), optical fibre network providers, space agencies, national governments, regional metrology organizations (RMOs), the International Committee for Weights and Measures (CIPM), International Telecommunications Union (ITU) and other relevant bodies:
    • vigorously pursue the development of continental-scale optical fibre time and frequency transfer networks,
    • actively encourage and support research aimed at significantly improving time and frequency transfer over intercontinental distances,
    • consult and coordinate with each other on access to the necessary infrastructures for new time and frequency transfer methods and on synergies with other applications of these infrastructures,
  • the BIPM participates actively in these developments, notably by making preparations for exploiting, in time scale realization, clock comparison data issued from new time and frequency transfer methods.

DOI : 10.59161/CCTF2012REC5E

The reader should note that the official version of this Resolution is the French text

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