Public Release: 

NIST's Internet Time Service serves the world

National Institute of Standards and Technology (NIST)


IMAGE: NIST delivers accurate time to your computer -- and billions around the world. To view a larger version of this infographic, visit view more

Credit: Hanacek/NIST

The Internet Time Service operated by the National Institute of Standards and Technology (NIST) serves much of the Earth, with customers from around the globe. In one month of study alone, just two of the 20 NIST servers that supply time information to Internet-connected devices received requests from 316 million unique Internet Protocol (IP) addresses, according to detailed data about the service published for the first time. This represents at least 8.5 percent of devices on the entire Internet.

"NIST should be very proud of the Internet Time Service, which is an important public resource," says NIST physicist Jeff Sherman, who collected the statistics and co-authored the new report. (The study focused on just two servers because they are local to NIST and easy to access, and they carry 25 percent of the total traffic, a statistically representative sample.)

NIST has operated the Internet Time Service since 1993. The service receives about 16 billion requests per day (as of January 2016). The 20 timeservers are located at 12 sites around the country, including NIST campuses in Gaithersburg, Md., and Boulder, Colo. The servers are linked to the NIST time scale, an ensemble of atomic clocks that maintain the U.S. version of Coordinated Universal Time. The time scale is calibrated by the NIST-F1 and NIST-F2 cesium fountain atomic clocks, the U.S. civilian time standards.

Importantly, the Internet Time Service provides a reliable source of time independent of the satellite-based Global Positioning System. Demand may increase with the growth of the Internet of Things, in which more devices will be connected to the Internet without any direct human intervention.

NIST Fellow Judah Levine came up with the original idea of distributing time over the Internet and wrote most of the software. The service is just one of the ways NIST distributes time-of-day information. Other methods include NIST radio stations, telephone call-in services, and the website


For more information, please see J.A. Sherman and J. Levine, "Usage Analysis of the NIST Internet Time Service," NIST Journal of Research, March 8, 2016. DOI: 10.6028/jres121.003.

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