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International Comparisons of Network Time Protocol Servers



Michael A. Lombardi, Judah Levine, Jose M. Lopez, Francisco Jimenez, John Bernard, Marina Gertsvolf, Harold Sanchez, Oscar G. Fallas, Liz C. Hernandez Ferero, Ricardo de Carvalho, Mario Fittipaldi, Raul Solis, Franklin Espejo


This paper describes a recently designed system that measures the time transmitted by network time protocol (NTP) servers located in North, Central, and South America. Direct measurements of the time transmitted by each server are obtained by comparing the received time stamps to the UTC(NIST) time scale at the National Institute of Standards and Technology (NIST) in Boulder, Colorado. International comparisons of the time differences between servers are obtained by utilizing UTC(NIST) as a common-view observation signal. Results of both direct and common-view measurements are published in real time via the web site of the Sistema Interamericano de Metrologia (SIM) Time and Frequency Metrology Working Group, providing verification of a given server's accuracy. The paper describes the NTP measurement system, and presents results from direct comparison and common-view measurements. It also discusses factors that contribute uncertainty to NTP measurements; in particular network asymmetry caused by inconsistent routing and/or network congestion.
Proceedings Title
Proceedings of the Precise Time and Time Interval Systems and Applications (PTTI) Meeting
Conference Dates
December 2-4, 2014
Conference Location
Boston, MA
Conference Title
Precise Time and Time Interval Systems and Applications (PTTI) Meeting


international comparisons, Network Time Protocol (NTP), time, time transfer


Lombardi, M. , Levine, J. , Lopez, J. , Jimenez, F. , Bernard, J. , Gertsvolf, M. , Sanchez, H. , Fallas, O. , Hernandez, L. , de, R. , Fittipaldi, M. , Solis, R. and Espejo, F. (2014), International Comparisons of Network Time Protocol Servers, Proceedings of the Precise Time and Time Interval Systems and Applications (PTTI) Meeting, Boston, MA, [online], (Accessed June 25, 2024)


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Created December 4, 2014, Updated February 19, 2017