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260 lines
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<html><head><title>
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Protocol Conformance Statement
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</title></head><body><h3>
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Protocol Conformance Statement
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</h3>
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<BR><IMG align=left SRC="pic/flatheads.gif">From <i>The
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Wizard of Oz</i>, L. Frank Baum
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<p>Say it three times and it must be right.
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<br clear=left>
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<hr>
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<p>The Network Time Protocol (NTP) is used to synchronize the time of
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a 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.
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<p>Typical NTP configurations utilize multiple redundant servers and
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diverse network paths, in order to achieve high accuracy and
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reliability. Some configurations include cryptographic authentication to
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prevent 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. General issues of the
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concepts and facilities assumed by NTP are discussed in tne <a
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href=exec.htm>Executive Summary - Computer Network Time
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Synchronization</a> page, while issues related to the NTP timescale and
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pending century are discussed in the <A HREF=y2k.htm> Network Time
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Protocol Year 2000 Conformance Statement</A> page, both of which are
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included in this document.
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<p>Note that network timekeeping technology continues to advance and may
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obsolete some of the following documents. For a current list of all
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papers, reports, briefings and other documents relevant to the NTP
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community, see the <a href=http://www.eecis.udel.edu/~mills>David L.
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Mills</a> web page.
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<P>The NTP architecture, protocol and algorithm models are described in
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<UL>
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<li>Mills, D.L. Internet time synchronization: the Network Time
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Protocol. <I>IEEE Trans. Communications COM-39, 10</I> (October 1991),
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1482-1493. <A
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HREF=http://www.eecis.udel.edu/~mills/database/papers/trans.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/papers/trans.pdf>
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PDF</a>. Also in: Yang, Z., and T.A. Marsland (Eds.). <I>Global States
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and Time in Distributed Systems</I>. IEEE Computer Society Press, Los
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Alamitos, CA, 1994, 91-102.
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</UL>
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The NTP specification and implementation has evolved over the last two
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decades to the current Version 4 of the protocol. This version includes
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significant enhancements in accuracy and reliability, as determined by
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experience in an estimated total of well over 100,000 clients and
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servers in the Internet, while retaining backward compatibility with
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previous versions.
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<P>This software distribution contains an implementation of the NTP
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Version 4 architecture, protocol and algorithms. While a formal
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specification of this version is not yet available, this version is
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fully compliant with the previous NTP Version 3 specification and
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implementation defined in
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<UL>
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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. Abstract: <A
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305a.ps>
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PostScript)</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305a.pdf>
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PDF</A>, Body: <a
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305b.ps>
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PostScript)</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305b.pdf>
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PDF</A>, Appendices: <A
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305c.ps>
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PostScript</a> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305c.pdf>
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PDF</A>.
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</UL>
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The NTP Version 4 implementation adds a number of extensions and
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refinements to the previous version, including an autonomous
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configuration and authentication capability, improved clock discipline
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algorithms capable of submicrosecond accuracy and many other
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refinements. Specific changes since the Version 3 specification was
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issued include:
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<OL>
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<p><LI>Support for precision-time kernel modifications, as described
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in</LI>
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<P>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. Abstract: <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kerna.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kerna.pdf>
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PDF</a>, Body: <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kernb.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kernb.pdf>
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PDF</a>. Major revision and update of: Network Working Group Report
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RFC-1589, University of Delaware, March 1994. 31 pp. <A
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1589.txt>ASCII</A>
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<p><LI>Support for IP Multicasting, as described in</LI>
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<P>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. Abstract: <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsa.ps>
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PostScript</A> | <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsa.pdf>
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PDF</A>, Body: <a
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HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsb.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsb.pdf>
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PDF</a>
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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</LI>
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<P>Mills, D.L. Clock discipline algorithms for the Network Time Protocol
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Version 4. Electrical Engineering Report 97-3-3, University of Delaware,
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March 1997, 35 pp. Abstract: <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/allan/securea.ps>
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PostScript</A> | <a
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/allan/securea.pdf>
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PDF</a>, Body: <A
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HREF=http://www.eecis.udel.edu/~mills/database/reports/allan/secureb.ps>
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PostScript</A> | <a
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/allan/secureb.pdf>
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PDF</a>
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<P>Mills, D.L. Improved algorithms for synchronizing computer network
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clocks. <I>IEEE/ACM Trans. Networks 3, 3</I> (June 1995), 245-254. <A
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HREF=http://www.eecis.udel.edu/~mills/database/papers/tune2.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/papers/tune2.pdf>
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PDF</a>
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<P><LI>Engineered refinements to radio clock drivers and interface code,
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as describedin:</LI>
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<P>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=http://www.eecis.udel.edu/~mills/database/papers/fine.ps>
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PostScript</A> | <A
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HREF=http://www.eecis.udel.edu/~mills/database/papers/fine.pdf>
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PDF</a>
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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.htm>Reference
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Clock Drivers </A>page.</LI>
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<P><LI>A new security model and authentication scheme based on public-
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key cryptography called <I>autokey</I>, as described in</LI>
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<P>Mills, D.L., T.S. Glassey, and M.E. McNeil. Coexistence and
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interoperability of NTP authentication schemes. Internet Draft
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draft-mills-ntp-auth-coexist-00.txt, University of Delaware and Coastek
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InfoSys, Inc., November 1997, 8 pp. <A
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HREF=http://www.eecis.udel.edu/~mills/memos/draft.txt>ASCII</A>
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<P>Mills, D.L. Authentication scheme for distributed, ubiquitous, real-
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time protocols. <I>Proc. Advanced Telecommunications/Information
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Distribution Research Program (ATIRP) Conference</I> (College Park MD,
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January 1997), 293-298. <A
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HREF=http://www.eecis.udel.edu/~mills/database/papers/atirp.ps>
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PostScript</A> | <a
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HREF=http://www.eecis.udel.edu/~mills/database/papers/atirp.pdf>
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PDF</a>
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<P>Mills, D.L. Proposed authentication enhancements for the Network Time
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Protocol version 4. Electrical Engineering Report 96-10-3, University of
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Delaware, October 1996, 36 pp. Abstract: <A
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/secure/securea.ps>
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PostScript</A> | <a
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/secure/securea.pdf>
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PDF</a>, Body: <A
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/secure/secureb.ps>
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PostScript</A> | <a
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HREF=
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http://www.eecis.udel.edu/~mills/database/reports/secure/secureb.pdf>
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PDF</a>
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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=ntpd.htm><TT>ntpd</TT> - Network Time Protocol (NTP) daemon
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</A>page.</LI>
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<P><LI>The prefer-peer scheme, as described in the <A
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HREF=prefer.htm>Mitigation Rules and the <TT>prefer</TT> Keyword
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</A>page.</LI>
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<P><LI>Specification for the Simple Network Time Protocol (SNTP), as
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described in</LI>
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<P>Mills, D.L. Simple network time protocol (SNTP) version 4 for IPv4,
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IPv6 and OSI. Network Working Group Report RFC-2030, University of
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Delaware, October 1996, 18 pp. <A
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HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc2030.txt>
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ASCII</A>. Obsoletes RFC-1769 and RFC-1361.
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<P><LI>Performance surveys for NTP Version 4 can be found in</LI>
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<p><li>Mills, D.L., A. Thyagarajan and B.C. Huffman. Internet
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timekeeping around the globe. <i>Proc. Precision Time and Time Interval
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(PTTI) Applications and Planning Meeting</i> (Long Beach CA, December
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1997), 365-371. Paper: <a
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href=http://www.eecis.udel.edu/~mills/database/papers/survey5.ps>
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PostScript</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/papers/survey5.pdf>
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PDF</a>, Slides: <a
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href=
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http://www.eecis.udel.edu/~mills/database/brief/survey/survey/index.htm>
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HTML</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/survey/survey.ps>
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PostScript</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/survey.ppt>
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PowerPoint</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/survey/survey.pdf>
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PDF</a></li>
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<p><li>Mills, D.L. The network computer as precision timekeeper.
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<i>Proc. Precision Time and Time Interval (PTTI) Applications and
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Planning Meeting</i> (Reston VA, December 1996), 96-108. Paper: <a
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href=http://www.eecis.udel.edu/~mills/database/papers/ptti.ps>
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PostScript</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/papers/ptti.pdf>
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PDF</a>, Slides: <a
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href=
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http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti/index.htm>
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HTML</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.ps>
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PostScript</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.ppt>
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PowerPoint</a> | <a
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href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.pdf>
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PDF</a></li>
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</OL>
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<hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a
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href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a>
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</address></a></body></html>
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