The BIPM Time Department has full responsibility for the maintenance of Coordinated Universal Time (UTC) and for giving traceability to the SI second to local time scales via the key comparison CCTF-K001.UTC.
Close cooperation has been established with the International Telecommunication Union (ITU) for issues relating to the definition of UTC and to the regulation of standard time and frequency signals. The BIPM is a member of the Radiocommunication Sector of the ITU (ITU-R), and reciprocally, the ITU-R is a member of the Consultative Committee for Time and Frequency.
In its present definition, UTC is kept close to the Earth's rotation time by the insertion of leap seconds. The International Earth Rotation and Reference Systems (IERS) establishes the dates of introduction of leap seconds, thus providing relevant information to the calculation of UTC at the BIPM. The interaction with the IERS also involves the maintenance of standards and models for Earth and space referencing.
Global navigation satellite systems (GNSS) provide an essential tool for international clock comparison. For technical aspects, interaction with the International GNSS Service (IGS) grants the availability of sets of parameters involved in the computation of UTC. The BIPM Time Department has leading actions for providing the interface between GNSS and time metrology users at the Civil GPS Service Interface Committee (CGSIC), at the committees for the Galileo scientific applications, and in the most general context, at the UN International Committee for GNSS (IGS).