On the Accuracy and Stablility of Clocks Synchronized by the Network Time Protocol in the Internet System

Abstract

This paper describes a series of experiments involving over 100,000 hosts of the Internet system and located in the U.S., Europe and the Pacific. The experiments are designed to evaluate the availability, accuracy and reliability of international standard time distribution using the Internet and the Network Time Protocol (NTP), which has been designated an Internet Standard protocol. NTP is designed specifically for use in a large, diverse internet system operating at speeds from mundane to lightwave. In NTP a distributed subnet of time servers operating in a self-organizing, hierarchical, master-slave configuration exchange precision timestamps in order to synchronize host clocks to each other and national time standards via wire or radio.The experiments are designed to locate Internet hosts and gateways that provide time by one of three time distribution protocols and evaluate the accuracy of their indications. For those hosts that support NTP, the experiments determine the distribution of errors and other statistics over paths spanning major portions of the globe. Finally, the experiments evaluate the accuracy and reliability of precision timekeeping using NTP and typical Internet paths involving ARPANET, NSFNET and regional networks. The experiments demonstrate that timekeeping throughout most portions of the Internet can be maintained to an accuracy of a few tens of milliseconds and a stability of a few milliseconds per day, even in cases of failure or disruption of clocks, time servers or networks.