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<html><head><title>
Protocol Conformance Statement
</title></head><body><h3>
Protocol Conformance Statement
</h3>
<BR><IMG align=left SRC="pic/flatheads.gif">From <i>The
Wizard of Oz</i>, L. Frank Baum
<p>Say it three times and it must be right.
<br clear=left>
<hr>
<p>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.
<p>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 <a
href=exec.htm>Executive Summary - Computer Network Time
Synchronization</a> page, while issues related to the NTP timescale and
pending century are discussed in the <A HREF=y2k.htm> Network Time
Protocol Year 2000 Conformance Statement</A> page, both of which are
included in this document.
<p>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 <a href=http://www.eecis.udel.edu/~mills>David L.
Mills</a> web page.
<P>The NTP architecture, protocol and algorithm models are described in
<UL>
<li>Mills, D.L. Internet time synchronization: the Network Time
Protocol. <I>IEEE Trans. Communications COM-39, 10</I> (October 1991),
1482-1493. <A
HREF=http://www.eecis.udel.edu/~mills/database/papers/trans.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/papers/trans.pdf>
PDF</a>. Also in: Yang, Z., and T.A. Marsland (Eds.). <I>Global States
and Time in Distributed Systems</I>. IEEE Computer Society Press, Los
Alamitos, CA, 1994, 91-102.
</UL>
The NTP specification and implementation has evolved over the last two
decades to the current Version 4 of the protocol. This version includes
significant enhancements in accuracy and reliability, as determined by
experience in an estimated total of well over 100,000 clients and
servers in the Internet, while retaining backward compatibility with
previous versions.
<P>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
<UL>
<li>Mills, D.L. Network Time Protocol (Version 3) specification,
implementation and analysis. Network Working Group Report RFC-1305,
University of Delaware, March 1992, 113 pp. Abstract: <A
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305a.ps>
PostScript)</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305a.pdf>
PDF</A>, Body: <a
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305b.ps>
PostScript)</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305b.pdf>
PDF</A>, Appendices: <A
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305c.ps>
PostScript</a> | <a
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1305/rfc1305c.pdf>
PDF</A>.
</UL>
The NTP Version 4 implementation adds a number of extensions and
refinements to the previous version, including an autonomous
configuration and authentication capability, improved clock discipline
algorithms capable of submicrosecond accuracy and many other
refinements. Specific changes since the Version 3 specification was
issued include:
<OL>
<p><LI>Support for precision-time kernel modifications, as described
in</LI>
<P>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: <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kerna.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kerna.pdf>
PDF</a>, Body: <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kernb.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/reports/kern/kernb.pdf>
PDF</a>. Major revision and update of: Network Working Group Report
RFC-1589, University of Delaware, March 1994. 31 pp. <A
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc1589.txt>ASCII</A>
<p><LI>Support for IP Multicasting, as described in</LI>
<P>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: <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsa.ps>
PostScript</A> | <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsa.pdf>
PDF</A>, Body: <a
HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsb.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/reports/acts/actsb.pdf>
PDF</a>
<p><LI>A new hybrid phase/frequency-lock clock discipline, which
replaces the RFC-1305 local clock algorithm, as described in</LI>
<P>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: <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/allan/securea.ps>
PostScript</A> | <a
HREF=
http://www.eecis.udel.edu/~mills/database/reports/allan/securea.pdf>
PDF</a>, Body: <A
HREF=http://www.eecis.udel.edu/~mills/database/reports/allan/secureb.ps>
PostScript</A> | <a
HREF=
http://www.eecis.udel.edu/~mills/database/reports/allan/secureb.pdf>
PDF</a>
<P>Mills, D.L. Improved algorithms for synchronizing computer network
clocks. <I>IEEE/ACM Trans. Networks 3, 3</I> (June 1995), 245-254. <A
HREF=http://www.eecis.udel.edu/~mills/database/papers/tune2.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/papers/tune2.pdf>
PDF</a>
<P><LI>Engineered refinements to radio clock drivers and interface code,
as describedin:</LI>
<P>Mills, D.L. Precision synchronization of computer network clocks.
<I>ACM Computer Communication Review 24, 2</I> (April 1994). 28-43. <A
HREF=http://www.eecis.udel.edu/~mills/database/papers/fine.ps>
PostScript</A> | <A
HREF=http://www.eecis.udel.edu/~mills/database/papers/fine.pdf>
PDF</a>
<P><LI>Support for over two dozen reference clock drivers for all known
national and international radio, satellite and modem standard time
services known at this time. See the <A HREF=refclock.htm>Reference
Clock Drivers </A>page.</LI>
<P><LI>A new security model and authentication scheme based on public-
key cryptography called <I>autokey</I>, as described in</LI>
<P>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. <A
HREF=http://www.eecis.udel.edu/~mills/memos/draft.txt>ASCII</A>
<P>Mills, D.L. Authentication scheme for distributed, ubiquitous, real-
time protocols. <I>Proc. Advanced Telecommunications/Information
Distribution Research Program (ATIRP) Conference</I> (College Park MD,
January 1997), 293-298. <A
HREF=http://www.eecis.udel.edu/~mills/database/papers/atirp.ps>
PostScript</A> | <a
HREF=http://www.eecis.udel.edu/~mills/database/papers/atirp.pdf>
PDF</a>
<P>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: <A
HREF=
http://www.eecis.udel.edu/~mills/database/reports/secure/securea.ps>
PostScript</A> | <a
HREF=
http://www.eecis.udel.edu/~mills/database/reports/secure/securea.pdf>
PDF</a>, Body: <A
HREF=
http://www.eecis.udel.edu/~mills/database/reports/secure/secureb.ps>
PostScript</A> | <a
HREF=
http://www.eecis.udel.edu/~mills/database/reports/secure/secureb.pdf>
PDF</a>
<P><LI> Support for the MD5 cryptographic hash algorithm, in addition to
the DES-CBC algorithm described in RFC-1305, as described in the <A
HREF=ntpd.htm><TT>ntpd</TT> - Network Time Protocol (NTP) daemon
</A>page.</LI>
<P><LI>The prefer-peer scheme, as described in the <A
HREF=prefer.htm>Mitigation Rules and the <TT>prefer</TT> Keyword
</A>page.</LI>
<P><LI>Specification for the Simple Network Time Protocol (SNTP), as
described in</LI>
<P>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. <A
HREF=http://www.eecis.udel.edu/~mills/database/rfc/rfc2030.txt>
ASCII</A>. Obsoletes RFC-1769 and RFC-1361.
<P><LI>Performance surveys for NTP Version 4 can be found in</LI>
<p><li>Mills, D.L., A. Thyagarajan and B.C. Huffman. Internet
timekeeping around the globe. <i>Proc. Precision Time and Time Interval
(PTTI) Applications and Planning Meeting</i> (Long Beach CA, December
1997), 365-371. Paper: <a
href=http://www.eecis.udel.edu/~mills/database/papers/survey5.ps>
PostScript</a> | <a
href=http://www.eecis.udel.edu/~mills/database/papers/survey5.pdf>
PDF</a>, Slides: <a
href=
http://www.eecis.udel.edu/~mills/database/brief/survey/survey/index.htm>
HTML</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/survey/survey.ps>
PostScript</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/survey.ppt>
PowerPoint</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/survey/survey.pdf>
PDF</a></li>
<p><li>Mills, D.L. The network computer as precision timekeeper.
<i>Proc. Precision Time and Time Interval (PTTI) Applications and
Planning Meeting</i> (Reston VA, December 1996), 96-108. Paper: <a
href=http://www.eecis.udel.edu/~mills/database/papers/ptti.ps>
PostScript</a> | <a
href=http://www.eecis.udel.edu/~mills/database/papers/ptti.pdf>
PDF</a>, Slides: <a
href=
http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti/index.htm>
HTML</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.ps>
PostScript</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.ppt>
PowerPoint</a> | <a
href=http://www.eecis.udel.edu/~mills/database/brief/ptti/ptti.pdf>
PDF</a></li>
</OL>
<hr><a href=index.htm><img align=left src=pic/home.gif></a><address><a
href=mailto:mills@udel.edu> David L. Mills &lt;mills@udel.edu&gt;</a>
</address></a></body></html>