231 lines
9.1 KiB
HTML
231 lines
9.1 KiB
HTML
<!-- $NetBSD: biblio.html,v 1.1 1998/12/30 20:20:33 mcr Exp $ -->
|
|
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict//EN">
|
|
<html><head><title>
|
|
Further Information and Bibliography
|
|
</title></head><body><h3>
|
|
Further Information and Bibliography
|
|
</h3><hr>
|
|
|
|
<p><h4>Conformance Statement</h4>
|
|
|
|
<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. 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
|
|
|
|
<ol>
|
|
|
|
<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 = "ftp://ftp.udel.edu/pub/people/mills/papers/trans.ps">
|
|
(PostScript)</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. Condensed from: <i>Ibid</i>. Network
|
|
Working Group Report RFC-1129, University of Delaware, October 1989. <a
|
|
href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1129/rfc1129a.ps">
|
|
(Abstract: PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1129/rfc1129b.ps"> (Body:
|
|
PostScript)</a>. Also published as: Electrical Engineering Department
|
|
Report 89-9-1, University of Delaware, September 1989. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/nts/ntsa.ps"> (Abstract:
|
|
PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/nts/ntsb.ps"> (Body:
|
|
PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
<p>The NTP specification and implementation has evolved over the last
|
|
fifteen years to the current Version 3 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. The formal specification of the NTP
|
|
Version 3 protocol is contained in:
|
|
|
|
<ol>
|
|
|
|
<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. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305a.ps">
|
|
(Abstract: PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305b.ps"> (Body:
|
|
PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1305/rfc1305c.ps">
|
|
(Appendices: PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
<p>This software distribution contains a fully compliant implementation
|
|
of the NTP Version 3 protocol, including an autonomous protocol daemon
|
|
that disciplines the local host clock, as well as a set of supporting
|
|
utility programs used to debug and manage one or more NTP servers in a
|
|
network. It includes complete sources and documentation for well over
|
|
two dozen Unix-based and Microsoft NT-based workstations and file
|
|
servers. The implementation is fully compliant with RFC-1305 and, in
|
|
addition, contains certain extensions compatible with, but not defined
|
|
by, that document. These extensions include:
|
|
|
|
<ol>
|
|
|
|
<li>Support for precision-time kernel modifications, as described in
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Unix kernel modifications for precision time
|
|
synchronization. Electrical Engineering Department Report 94-10-1,
|
|
University of Delaware, October 1994, 24 pp. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/kern/kerna.ps"> (Abstract:
|
|
PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/kern/kernb.ps"> (Body:
|
|
PostScript)</a>. Major revision and update of: Network Working Group
|
|
Report RFC-1589, University of Delaware, March 1994. 31 pp. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1589.txt"> (ASCII)</a>.
|
|
|
|
</ol>
|
|
|
|
<p><li>Support for IP Multicasting, as described in
|
|
|
|
<ol>
|
|
|
|
<li>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. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/acts/actsa.ps"> (Abstract:
|
|
PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/acts/actsb.ps"> (Body:
|
|
PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
<p><li>A new hybrid phase/frequency-lock clock discipline, which
|
|
replaces the RFC-1305 local clock algorithm, as described in
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Improved algorithms for synchronizing computer network
|
|
clocks. <i>IEEE/ACM Trans. Networks</i> (June 1995), 245-254. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/papers/tune2.ps"> (PostScript)</a>.
|
|
</ol>
|
|
|
|
<p><li>Engineered refinements to radio clock drivers and interface code,
|
|
as described in:
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Precision synchronization of computer network clocks.
|
|
<i>ACM Computer Communication Review 24, 2</i> (April 1994). 28-43. <a
|
|
href = "ftp://ftp.udel.edu/pub/people/mills/papers/fine.ps">
|
|
(PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
<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.html">
|
|
Reference Clock Drivers </a> page.
|
|
<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="xntpd.html"><code>xntpd</code> - Network Time Protocol (NTP)
|
|
daemon </a> page.
|
|
|
|
<p><li>The prefer-peer scheme, as described in the <a href =
|
|
"prefer.html">Mitigation Rules and the <code>prefer</code> Keyword </a>
|
|
page.
|
|
|
|
</ol>
|
|
|
|
<p><h4>Selected Bibliography</h4>
|
|
|
|
<p>A number of articles and reports have been written on the analysis,
|
|
design, implementation and performance of NTP. A representative sample
|
|
is included here, along with a short description of each. Additional
|
|
information on NTP can be found at the web sites for <a href =
|
|
"http://www.eecis.udel.edu/~ntp"> NTP </a> and <a href =
|
|
"http://www.eecis.udel.edu/~mills"> David L. Mills </a>
|
|
|
|
<ol>
|
|
|
|
<li>A subset of NTP has been defined suitable for use where some
|
|
degradation in accuracy and reliability is acceptable, so that the
|
|
entire suite of specified algorithms need not be implemented. This
|
|
subset is defined in:
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Simple Network Time Protocol (SNTP). Network Working
|
|
Group Report RFC-1769, University of Delaware, March 1995, 14 pp. <a
|
|
href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1769.txt">
|
|
(ASCII)</a>. Major revision and update of: <i>Ibid</i>. Network Working
|
|
Group Report RFC-1361, University of Delaware, August 1992, 10 pp. <a
|
|
href = "ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1361.txt">
|
|
(ASCII)</a>.
|
|
|
|
</ol>
|
|
|
|
<p><li>An assessment of the expected accuracy of NTP operating in the
|
|
Internet is contained in the following:
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Measured performance of the Network Time Protocol in the
|
|
Internet system. Network Working Group Report RFC-1128. University of
|
|
Delaware, October 1989. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1128/rfc1128a.ps">
|
|
(Abstract: PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/rfc/rfc1128/rfc1128b.ps"> (Body:
|
|
PostScript)</a>. Also published as: Electrical Engineering Department
|
|
Report 89-9-3, University of Delaware, September 1989. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/glory/glorya.ps">
|
|
(Abstract: PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/glory/gloryb.ps"> (Body:
|
|
PostScript)</a>.
|
|
|
|
<li>Mills, D.L. On the accuracy and stability of clocks synchronized by
|
|
the Network Time Protocol in the Internet system. <i>ACM Computer
|
|
Communication Review 20, 1</i> (January 1990), 65-75. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/papers/ccr.ps"> (PostScript)</a>.
|
|
|
|
</ol>
|
|
<p><li>The following publication explores issues involved in the
|
|
development of the NTP specification, including the development of its
|
|
timescale and the treatment of leap seconds:
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. On the chronology and metrology of computer network
|
|
timescales and their application to the Network Time Protocol. <i>ACM
|
|
Computer Communications Review 21, 5</i> (October 1991), 8-17. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/papers/time.ps"> (PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
<p><li>A comprehensive analysis of the engineering model used in the NTP
|
|
algorithms is given in the following report. This includes a performance
|
|
analysis of the clock filter and selection algorithms, clock discipline
|
|
feedback loop, and error budget.
|
|
|
|
<ol>
|
|
|
|
<li>Mills, D.L. Modelling and analysis of computer network clocks.
|
|
Electrical Engineering Department Report 92-5-2, University of Delaware,
|
|
May 1992, 29 pp. <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/time/timea.ps"> (Abstract:
|
|
PostScript)</a>, <a href =
|
|
"ftp://ftp.udel.edu/pub/people/mills/reports/time/timeb.ps"> (Body:
|
|
PostScript)</a>.
|
|
|
|
</ol>
|
|
|
|
</ol>
|
|
|
|
<hr><address>David L. Mills (mills@udel.edu)</address></body></html>
|