+2001-05-22 Harlan Stenn <stenn@whimsy.udel.edu>
+
+ * html/release.htm:
+ * html/ntpd.htm:
+ * html/miscopt.htm:
+ From: Dave Mills: Updates.
+
2001-05-21 Harlan Stenn <stenn@whimsy.udel.edu>
* configure.in: 4.0.99k38
href="refclock.htm">Reference Clock Drivers</a> page for further
information. The default for this flag is <tt>enable</tt>.</dd>
-<dt><tt>pps</tt></dt>
-
-<dd>Enables the precision-time kernel support for the
-pulse-per-second (PPS) signal generated by some radio clocks and
-laboratory equipment. See the <a href="pps.htm">Pulse-per-second
-(PPS) Signal Interfacing Monitoring Options</a> . The default for
-this flag is <tt>enable</tt>.</dd>
-
<dt><tt>stats</tt></dt>
<dd>Enables the statistics facility. See the <a href="monopt.htm">
<dt><tt>allan <i>allan</i></tt></dt>
-<dd>The argument becomes the new value for the minimum Allan intercept, which is a parameter of the PLL/FLL clock discipline algorithm. The value defaults to 1024 s, which is also lower limit 1024 s.</dd>
+<dd>The argument becomes the new value for the minimum Allan
+intercept, which is a parameter of the PLL/FLL clock discipline
+algorithm. The value defaults to 1024 s, which is also the lower
+limit.</dd>
+
+<dt><tt>huffpuff <i>huffpuff</i></tt></dt>
+
+<dd>The argument becomes the new value for the experimental
+huff-n'-puff filter span, which determines the most recent interval
+the algorithm will search for a minimum delay. The lower limit is
+900 s (15 m), but a more reasonable value is 7200 (2 hours). There
+is no default, since the filter is not enabled unless this command
+is given.</dd>
</dl>
</dd>
updated once per hour and is available to initialize the frequency
on subsequent daemon restarts.</p>
+<h4>The huff-n'-puff filter</h4>
+
+<p>In scenarios where a considerable amount of data are to be
+downloaded or uploaded over telephone modems, timekeeping quality
+can be seriously degraded. This occurs because the differential
+delays on the two directions of transmission can be quite large. In
+many cases the apparent time errors are so large as to exceed the
+step threshold and a step correction can occur during and after the
+data transfer is in progress.</p>
+
+<p>The huff-n'-puff filter is designed to correct the apparent time
+offset in these cases. It depends on knowledge of the propagation
+delay when no other traffic is present. In common scenarios this
+occurs during other than work hours. The filter maintains a shift
+register that remembers the minimum delay over the most recent
+interval measured usually in hours. Under conditions of severe
+delay, the filter corrects the apparent offset using the sign of
+the offset and the difference between the apparent delay and
+minimum delay. The name of the filter reflects the negative (huff)
+and positive (puff) correction, which depends on the sign of the
+offset.</p>
+
+<p>The filter is activated by the <tt>tinker</tt> command and <tt>
+huffpuff</tt> keyword, as described in the <a href="miscopt.htm">
+Miscellaneous Options</a> page.</p>
+
<h4>Notes</h4>
<p>If NetInfo support is built into <tt>ntpd</tt>, then <tt>
<h4>NTP Version 4 Release Notes</h4>
-<p>This release of the NTP Version 4 (NTPv4) daemon for Unix and
-Windows (NT4 and 2000) incorporates new features and refinements to
-the NTP Version 3 (NTPv3) algorithms. However, it continues the
-tradition of retaining backwards compatibility with older versions.
-The NTPv4 version has been under development for quite a while and
-isn't finished yet. In fact, quite a number of NTPv4 features have
-already been retrofitted in the current NTPv3, although this
-version is not actively maintained by the NTPv4 developer's
-group.</p>
+<p>This release of the NTP Version 4 (NTPv4) daemon for Unix, VMS
+and Windows (NT4 and 2000) incorporates new features and
+refinements to the NTP Version 3 (NTPv3) algorithms. However, it
+continues the tradition of retaining backwards compatibility with
+older versions, except for symmetric mode in NTPv1. Client/server
+mode continues to be supported in NTPv1. The NTPv4 version has been
+under development for quite a while and isn't finished yet. In
+fact, quite a number of NTPv4 features have already been
+retrofitted in the current NTPv3, although this version is not
+actively maintained by the NTPv4 developer's group.</p>
<p>The primary purpose of this release is to verify the remaining
new code compiles and runs in the various architectures, operating
<h4>Nasty Surprises</h4>
-There are a few things different about this release that have
+<p>There are a few things different about this release that have
changed since the latest NTP Version 3 release. Following are a few
-things to worry about:
+things to worry about:</p>
<ol>
<li>
<li>
<p>The enable and disable commands have a few changes in their
arguments see the <tt>ntpd</tt> <a href="confopt.htm">Configuration
-Options</a> page for details.</p>
+Options</a> page for details. Note that the <tt>authenticate</tt>
+command has been removed.</p>
</li>
<li>
<a href="accopt.htm">Authentication Options</a> page for further
information.</p>
</li>
+
+<li>
+<p>An experimental filter algorithm called huff-n'-puff has been
+implemented to reduce errors under conditions of severe assymetric
+delays characteristic of <tt>ppp</tt> connections with telephone
+modems and downloading or uploading considerable traffic. See the
+<a href="ntpd.htm">ntpd - Network Time Protocol (NTP) daemon</a>
+page for further information.</p>
+</li>
</ol>
<h4>Caveats</h4>
-This release has been compiled and tested on several systems,
+<p>This release has been compiled and tested on several systems,
including SunOS 4.1.3, Solaris 2.5.1-2.8, Alpha 4.0, Ultrix 4.4,
Linux, FreeBSD and HP-UX 10.02. It has been compiled and tested on
Windows NT, but not yet on any other Windows version or for VMS. We
are relying on the NTP volunteer corps to do that. Known problems
-are summarized below:
+are summarized below:</p>
<ol>
<li>
projects / thirdparty / ntp.git / commitdiff
