Say it three times and it must be right.
The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides accuracies typically within a millisecond on LANs up to a few tens of milliseconds on WANs relative to Coordinated Universal Time (UTC), as provided by a Global Positioning Service (GPS) receiver, for example.
Typical NTP configurations utilize multiple redundant servers and diverse network paths, in order to achieve high accuracy and reliability. Some configurations include cryptographic authentication to prevent accidental or malicious protocol attacks. Information on the NTP architecture, protocol and algorithms can be found in the following articles and reports, which are available online. General issues of the concepts and facilities assumed by NTP are discussed in tne Executive Summary - Computer Network Time Synchronization page, while issues related to the NTP timescale and pending century are discussed in the Network Time Protocol Year 2000 Conformance Statement page, both of which are included in this document.
Note that network timekeeping technology continues to advance and may obsolete some of the following documents. For a current list of all papers, reports, briefings and other documents relevant to the NTP community, see the David L. Mills web page.
The NTP architecture, protocol and algorithm models are described in
This software distribution contains an implementation of the NTP Version 4 architecture, protocol and algorithms. While a formal specification of this version is not yet available, this version is fully compliant with the previous NTP Version 3 specification and implementation defined in
Mills, D.L. Unix kernel modifications for precision time synchronization. Electrical Engineering Department Report 94-10-1, University of Delaware, October 1994, 24 pp. Abstract: PostScript | PDF, Body: PostScript | PDF. Major revision and update of: Network Working Group Report RFC-1589, University of Delaware, March 1994. 31 pp. ASCII
Mills, D.L, and A. Thyagarajan. Network time protocol version 4 proposed changes. Electrical Engineering Department Report 94-10-2, University of Delaware, October 1994, 32 pp. Abstract: PostScript | PDF, Body: PostScript | PDF
Mills, D.L. Clock discipline algorithms for the Network Time Protocol Version 4. Electrical Engineering Report 97-3-3, University of Delaware, March 1997, 35 pp. Abstract: PostScript | PDF, Body: PostScript | PDF
Mills, D.L. Improved algorithms for synchronizing computer network clocks. IEEE/ACM Trans. Networks 3, 3 (June 1995), 245-254. PostScript | PDF
Mills, D.L. Precision synchronization of computer network clocks. ACM Computer Communication Review 24, 2 (April 1994). 28-43. PostScript | PDF
Mills, D.L., T.S. Glassey, and M.E. McNeil. Coexistence and interoperability of NTP authentication schemes. Internet Draft draft-mills-ntp-auth-coexist-00.txt, University of Delaware and Coastek InfoSys, Inc., November 1997, 8 pp. ASCII
Mills, D.L. Authentication scheme for distributed, ubiquitous, real- time protocols. Proc. Advanced Telecommunications/Information Distribution Research Program (ATIRP) Conference (College Park MD, January 1997), 293-298. PostScript | PDF
Mills, D.L. Proposed authentication enhancements for the Network Time Protocol version 4. Electrical Engineering Report 96-10-3, University of Delaware, October 1996, 36 pp. Abstract: PostScript | PDF, Body: PostScript | PDF
Mills, D.L. Simple network time protocol (SNTP) version 4 for IPv4, IPv6 and OSI. Network Working Group Report RFC-2030, University of Delaware, October 1996, 18 pp. ASCII. Obsoletes RFC-1769 and RFC-1361.