Improved Algorithms for Synchronizing Computer Network Clocks Manuscript received December 6, 1994; approved by IEEE/ACM Transactions on Networking Editor R. Guerin. This work was supported by the Advanced Research Projects Agency under NASA Ames Research Center Contract NAG 2-638, the National Science Foundation under Grant NCR-93-01002, and the U.S. Navy Surface Weapons Center under Northeastern Center for Engineering Education Contract A30327-93.IEEE Log Number 9412272
Readings in Multimedia Computing and Networking
The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementations. Most of the estimated deployment of 100,000 NTP servers and clients enjoy synchronization to within a few tens of milliseconds in the Internet of today. This paper describes
... cific improvements developed for NTP Version 3 which have resulted in increased accuracy, stability and reliability in both local-area and wide-area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well as to select the best ensemble from among a set of peer clocks and combine their differences to produce a clock accuracy better than any in the ensemble. This paper also describes engineered refinements of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined oscillator. The refinements provide automatic adjustment of message-exchange intervals in order to minimize network traffic between clients and busy servers while maintaining the best accuracy. Finally, this paper describes certain enhancements to the Unix operating system software in order to realize submillisecond accuracies with fast workstations and networks.