231 lines
9.1 KiB
HTML
231 lines
9.1 KiB
HTML
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<!-- $NetBSD: biblio.html,v 1.1 1998/12/30 20:20:33 mcr Exp $ -->
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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict//EN">
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<html><head><title>
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Further Information and Bibliography
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</title></head><body><h3>
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Further Information and Bibliography
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</h3><hr>
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<p><h4>Conformance Statement</h4>
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<p>The Network Time Protocol (NTP) is used to synchronize the time of a
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computer client or server to another server or reference time source,
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such as a radio or satellite receiver or modem. It provides accuracies
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typically within a millisecond on LANs up to a few tens of milliseconds
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on WANs relative to Coordinated Universal Time (UTC), as provided by a
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Global Positioning Service (GPS) receiver, for example. Typical NTP
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configurations utilize multiple redundant servers and diverse network
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paths, in order to achieve high accuracy and reliability. Some
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configurations include cryptographic authentication to prevent
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accidental or malicious protocol attacks. Information on the NTP
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architecture, protocol and algorithms can be found in the following
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articles and reports, which are available online
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<ol>
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<li>Mills, D.L. Internet time synchronization: the Network Time Protocol.
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<i>IEEE Trans. Communications COM-39, 10</i> (October 1991), 1482-1493.
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<a href = "ftp://ftp.udel.edu/pub/people/mills/papers/trans.ps">
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(PostScript)</a>. Also in: Yang, Z., and T.A. Marsland (Eds.). <i>Global
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States and Time in Distributed Systems</i>. IEEE Computer Society Press,
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Los Alamitos, CA, 1994, 91-102. Condensed from: <i>Ibid</i>. Network
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Working Group Report RFC-1129, University of Delaware, October 1989. <a
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href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1129/rfc1129a.ps">
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(Abstract: PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1129/rfc1129b.ps"> (Body:
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PostScript)</a>. Also published as: Electrical Engineering Department
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Report 89-9-1, University of Delaware, September 1989. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/nts/ntsa.ps"> (Abstract:
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PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/nts/ntsb.ps"> (Body:
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PostScript)</a>.
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</ol>
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<p>The NTP specification and implementation has evolved over the last
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fifteen years to the current Version 3 of the protocol. This version
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includes significant enhancements in accuracy and reliability, as
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determined by experience in an estimated total of well over 100,000
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clients and servers in the Internet, while retaining backward
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compatibility with previous versions. The formal specification of the NTP
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Version 3 protocol is contained in:
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<ol>
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<li>Mills, D.L. Network Time Protocol (Version 3) specification,
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implementation and analysis. Network Working Group Report RFC-1305,
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University of Delaware, March 1992, 113 pp. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305a.ps">
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(Abstract: PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305b.ps"> (Body:
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PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305c.ps">
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(Appendices: PostScript)</a>.
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</ol>
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<p>This software distribution contains a fully compliant implementation
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of the NTP Version 3 protocol, including an autonomous protocol daemon
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that disciplines the local host clock, as well as a set of supporting
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utility programs used to debug and manage one or more NTP servers in a
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network. It includes complete sources and documentation for well over
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two dozen Unix-based and Microsoft NT-based workstations and file
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servers. The implementation is fully compliant with RFC-1305 and, in
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addition, contains certain extensions compatible with, but not defined
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by, that document. These extensions include:
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<ol>
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<li>Support for precision-time kernel modifications, as described in
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<ol>
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<li>Mills, D.L. Unix kernel modifications for precision time
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synchronization. Electrical Engineering Department Report 94-10-1,
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University of Delaware, October 1994, 24 pp. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/kern/kerna.ps"> (Abstract:
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PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/kern/kernb.ps"> (Body:
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PostScript)</a>. Major revision and update of: Network Working Group
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Report RFC-1589, University of Delaware, March 1994. 31 pp. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1589.txt"> (ASCII)</a>.
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</ol>
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<p><li>Support for IP Multicasting, as described in
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<ol>
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<li>Mills, D.L, and A. Thyagarajan. Network time protocol version 4
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proposed changes. Electrical Engineering Department Report 94-10-2,
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University of Delaware, October 1994, 32 pp. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/acts/actsa.ps"> (Abstract:
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PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/acts/actsb.ps"> (Body:
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PostScript)</a>.
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</ol>
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<p><li>A new hybrid phase/frequency-lock clock discipline, which
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replaces the RFC-1305 local clock algorithm, as described in
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<ol>
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<li>Mills, D.L. Improved algorithms for synchronizing computer network
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clocks. <i>IEEE/ACM Trans. Networks</i> (June 1995), 245-254. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/papers/tune2.ps"> (PostScript)</a>.
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</ol>
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<p><li>Engineered refinements to radio clock drivers and interface code,
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as described in:
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<ol>
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<li>Mills, D.L. Precision synchronization of computer network clocks.
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<i>ACM Computer Communication Review 24, 2</i> (April 1994). 28-43. <a
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href = "ftp://ftp.udel.edu/pub/people/mills/papers/fine.ps">
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(PostScript)</a>.
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</ol>
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<p><li>Support for over two dozen reference clock drivers for all known
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national and international radio, satellite and modem standard time
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services known at this time. See the <a href = "refclock.html">
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Reference Clock Drivers </a> page.
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<p><li>Support for the MD5 cryptographic hash algorithm, in addition to
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the DES-CBC algorithm described in RFC-1305, as described in the <a
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href="xntpd.html"><code>xntpd</code> - Network Time Protocol (NTP)
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daemon </a> page.
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<p><li>The prefer-peer scheme, as described in the <a href =
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"prefer.html">Mitigation Rules and the <code>prefer</code> Keyword </a>
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page.
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</ol>
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<p><h4>Selected Bibliography</h4>
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<p>A number of articles and reports have been written on the analysis,
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design, implementation and performance of NTP. A representative sample
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is included here, along with a short description of each. Additional
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information on NTP can be found at the web sites for <a href =
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"http://www.eecis.udel.edu/~ntp"> NTP </a> and <a href =
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"http://www.eecis.udel.edu/~mills"> David L. Mills </a>
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<ol>
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<li>A subset of NTP has been defined suitable for use where some
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degradation in accuracy and reliability is acceptable, so that the
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entire suite of specified algorithms need not be implemented. This
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subset is defined in:
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<ol>
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<li>Mills, D.L. Simple Network Time Protocol (SNTP). Network Working
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Group Report RFC-1769, University of Delaware, March 1995, 14 pp. <a
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href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1769.txt">
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(ASCII)</a>. Major revision and update of: <i>Ibid</i>. Network Working
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Group Report RFC-1361, University of Delaware, August 1992, 10 pp. <a
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href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1361.txt">
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(ASCII)</a>.
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</ol>
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<p><li>An assessment of the expected accuracy of NTP operating in the
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Internet is contained in the following:
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<ol>
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<li>Mills, D.L. Measured performance of the Network Time Protocol in the
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Internet system. Network Working Group Report RFC-1128. University of
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Delaware, October 1989. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1128/rfc1128a.ps">
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(Abstract: PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1128/rfc1128b.ps"> (Body:
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PostScript)</a>. Also published as: Electrical Engineering Department
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Report 89-9-3, University of Delaware, September 1989. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/glory/glorya.ps">
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(Abstract: PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/glory/gloryb.ps"> (Body:
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PostScript)</a>.
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<li>Mills, D.L. On the accuracy and stability of clocks synchronized by
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the Network Time Protocol in the Internet system. <i>ACM Computer
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Communication Review 20, 1</i> (January 1990), 65-75. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/papers/ccr.ps"> (PostScript)</a>.
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</ol>
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<p><li>The following publication explores issues involved in the
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development of the NTP specification, including the development of its
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timescale and the treatment of leap seconds:
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<ol>
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<li>Mills, D.L. On the chronology and metrology of computer network
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timescales and their application to the Network Time Protocol. <i>ACM
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Computer Communications Review 21, 5</i> (October 1991), 8-17. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/papers/time.ps"> (PostScript)</a>.
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</ol>
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<p><li>A comprehensive analysis of the engineering model used in the NTP
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algorithms is given in the following report. This includes a performance
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analysis of the clock filter and selection algorithms, clock discipline
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feedback loop, and error budget.
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<ol>
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<li>Mills, D.L. Modelling and analysis of computer network clocks.
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Electrical Engineering Department Report 92-5-2, University of Delaware,
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May 1992, 29 pp. <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/time/timea.ps"> (Abstract:
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PostScript)</a>, <a href =
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"ftp://ftp.udel.edu/pub/people/mills/reports/time/timeb.ps"> (Body:
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PostScript)</a>.
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</ol>
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</ol>
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<hr><address>David L. Mills (mills@udel.edu)</address></body></html>
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