commit d2aaa69d59d15bcc833f70e466cfcd4c7d50d2d2
Author: Stephen Wadeley <swadeley(a)redhat.com>
Date: Wed Jul 30 23:40:13 2014 +0200
Add sec- to section IDs, s1 and s2 to sec
en-US/Configuring_PTP_Using_ptp4l.xml | 38 ++++++++++++++++----------------
1 files changed, 19 insertions(+), 19 deletions(-)
---
diff --git a/en-US/Configuring_PTP_Using_ptp4l.xml
b/en-US/Configuring_PTP_Using_ptp4l.xml
index c0ac008..7288ff7 100644
--- a/en-US/Configuring_PTP_Using_ptp4l.xml
+++ b/en-US/Configuring_PTP_Using_ptp4l.xml
@@ -5,7 +5,7 @@
<chapter id="ch-Configuring_PTP_Using_ptp4l">
<title>Configuring PTP Using ptp4l</title>
- <section id="Introduction_to_PTP">
+ <section id="sec-Introduction_to_PTP">
<title>Introduction to PTP</title>
<para>
The <firstterm>Precision Time Protocol</firstterm>
(<acronym>PTP</acronym>) is a protocol used to synchronize clocks in a
network. When used in conjunction with hardware support, <systemitem
class="protocol">PTP</systemitem> is capable of sub-microsecond
accuracy, which is far better than is normally obtainable with <systemitem
class="protocol">NTP</systemitem>. <systemitem
class="protocol">PTP</systemitem> support is divided between the kernel
and user space. The kernel in <application>Fedora</application> includes
support for <systemitem class="protocol">PTP</systemitem> clocks,
which are provided by network drivers. The actual implementation of the protocol is known
as <application>linuxptp</application>, a <systemitem
class="protocol">PTPv2</systemitem> implementation according to the
IEEE standard 1588 for Linux.
@@ -13,7 +13,7 @@
<para>
The <package>linuxptp</package> package includes the
<application>ptp4l</application> and
<application>phc2sys</application> programs for clock synchronization. The
<application>ptp4l</application> program implements the <systemitem
class="protocol">PTP</systemitem> boundary clock and ordinary clock.
With hardware time stamping, it is used to synchronize the <systemitem
class="protocol">PTP</systemitem> hardware clock to the master clock,
and with software time stamping it synchronizes the system clock to the master clock. The
<application>phc2sys</application> program is needed only with hardware time
stamping, for synchronizing the system clock to the <systemitem
class="protocol">PTP</systemitem> hardware clock on the
<firstterm>network interface card</firstterm>
(<acronym>NIC</acronym>).
</para>
- <section id="Understanding_PTP">
+ <section id="sec-Understanding_PTP">
<title>Understanding PTP</title>
<para>
The clocks synchronized by <systemitem
class="protocol">PTP</systemitem> are organized in a master-slave
hierarchy. The slaves are synchronized to their masters which may be slaves to their own
masters. The hierarchy is created and updated automatically by the <firstterm>best
master clock</firstterm> (<acronym>BMC</acronym>) algorithm, which runs
on every clock. When a clock has only one port, it can be
<firstterm>master</firstterm> or <firstterm>slave</firstterm>,
such a clock is called an <firstterm>ordinary clock</firstterm>
(<acronym>OC</acronym>). A clock with multiple ports can be master on one port
and slave on another, such a clock is called a <firstterm>boundary</firstterm>
clock (<acronym>BC</acronym>). The top-level master is called the
<firstterm>grandmaster clock</firstterm>, which can be synchronized by using a
<firstterm>Global Positioning System</firstterm>
(<acronym>GPS</acronym>) time source. By using a GPS-based time source,
disparate networks can be
synchronized with a high-degree of accuracy.
@@ -32,7 +32,7 @@
</mediaobject>
</figure>
</section>
- <section id="s2-Advantages_of_PTP">
+ <section id="sec-Advantages_of_PTP">
<title>Advantages of PTP</title>
<para>
One of the main advantages that <systemitem
class="protocol">PTP</systemitem> has over the <firstterm>Network
Time Protocol</firstterm> (<acronym>NTP</acronym>) is hardware support
present in various <firstterm>network interface controllers</firstterm>
(<acronym>NIC</acronym>) and network switches. This specialized hardware
allows <systemitem class="protocol">PTP</systemitem> to account for
delays in message transfer, and greatly improves the accuracy of time synchronization.
While it is possible to use non-PTP enabled hardware components within the network, this
will often cause an increase in jitter or introduce an asymmetry in the delay resulting in
synchronization inaccuracies, which add up with multiple non-PTP aware components used in
the communication path. To achieve the best possible accuracy, it is recommended that all
networking components between <systemitem
class="protocol">PTP</systemitem> clocks are <systemitem
class="protocol">PTP</systemitem> hardware en
abled. Time synchronization in larger networks where not all of the networking hardware
supports <systemitem class="protocol">PTP</systemitem> might be
better suited for <systemitem class="protocol">NTP</systemitem>.
@@ -45,13 +45,13 @@
<!-- Topics, Tasks -->
-<section id="Using_PTP">
+<section id="sec-Using_PTP">
<title>Using PTP</title>
<para>
In order to use <systemitem class="protocol">PTP</systemitem>,
the kernel network driver for the intended interface has to support either software or
hardware time stamping capabilities.
</para>
- <section id="Checking_for_Driver_and_Hardware_Support">
+ <section id="sec-Checking_for_Driver_and_Hardware_Support">
<title>Checking for Driver and Hardware Support</title>
<para>
In addition to hardware time stamping support being present in the driver, the NIC
must also be capable of supporting this functionality in the physical hardware. The best
way to verify the time stamping capabilities of a particular driver and NIC is to use the
<application>ethtool</application> utility to query the interface as follows:
@@ -131,7 +131,7 @@ should include:
</para>
</section>
-<section id="Installing_PTP">
+<section id="sec-Installing_PTP">
<title>Installing PTP</title>
<para>
The kernel in <application>Fedora</application> includes support for
<systemitem class="protocol">PTP</systemitem>. User space support is
provided by the tools in the <application>linuxptp</application> package. To
install <application>linuxptp</application>, issue the following command as
<systemitem class="username">root</systemitem>:
@@ -139,11 +139,11 @@ should include:
This will install <application>ptp4l</application> and
<application>phc2sys</application>.
</para>
<para>
- Do not run more than one service to set the system clock's time at the same
time. If you intend to serve <systemitem
class="protocol">PTP</systemitem> time using <systemitem
class="protocol">NTP</systemitem>, see <xref
linkend="Serving_PTP_Time_with_NTP" />.
+ Do not run more than one service to set the system clock's time at the same
time. If you intend to serve <systemitem
class="protocol">PTP</systemitem> time using <systemitem
class="protocol">NTP</systemitem>, see <xref
linkend="sec-Serving_PTP_Time_with_NTP" />.
</para>
</section>
-<section id="Starting_ptp4l">
+<section id="sec-Starting_ptp4l">
<title>Starting ptp4l</title>
<para>
The <application>ptp4l</application> program tries to use hardware time
stamping by default. To use <application>ptp4l</application> with hardware
time stamping capable drivers and NICs, you must provide the network interface to use with
the <option>-i</option> option. Enter the following command as <systemitem
class="username">root</systemitem>:
@@ -179,7 +179,7 @@ By default, messages are sent to
<filename>/var/log/messages</filename>. However
<screen>~]# <command>ptp4l -i <replaceable>em3</replaceable>
-m -S</command></screen>
</para>
- <section id="Selecting_a_Delay_Mechanism">
+ <section id="sec-Selecting_a_Delay_Mechanism">
<title>Selecting a Delay Measurement Mechanism</title>
<para>
There are two different delay measurement mechanisms and they can be selected by
means of an option added to the <command>ptp4l</command> command as follows:
@@ -229,7 +229,7 @@ By default, messages are sent to
<filename>/var/log/messages</filename>. However
</section>
</section>
-<section id="Specifying_a_Configuration_File">
+<section id="sec-Specifying_a_Configuration_File">
<title>Specifying a Configuration File</title>
<para>
The command line options and other options, which cannot be set on the command line,
can be set in an optional configuration file.
@@ -249,7 +249,7 @@ time_stamping software
</para>
</section>
-<section id="Using_the_PTP_Management_Client">
+<section id="sec-Using_the_PTP_Management_Client">
<title>Using the PTP Management Client</title>
<para>
The <systemitem class="protocol">PTP</systemitem> management
client, <application>pmc</application>, can be used to obtain additional
information from <application>ptp4l</application> as follows:
@@ -312,7 +312,7 @@ if <literal>gmPresent</literal> is true, the
<systemitem class="protocol">PTP</s
</para>
</section>
-<section id="Synchronizing_the_Clocks">
+<section id="sec-Synchronizing_the_Clocks">
<title>Synchronizing the Clocks</title>
<para>
The <application>phc2sys</application> program is used to synchronize the
system clock to the <systemitem class="protocol">PTP</systemitem>
hardware clock (<acronym>PHC</acronym>) on the NIC. To start
<application>phc2sys</application>, where
<replaceable>em3</replaceable> is the interface with the <systemitem
class="protocol">PTP</systemitem> hardware clock, enter the following
command as <systemitem class="username">root</systemitem>:
@@ -335,7 +335,7 @@ When running as a service, options are specified in the
<filename>/etc/sysconfig
</para>
</section>
-<section id="Verifying_Time_Synchronization">
+<section id="sec-Verifying_Time_Synchronization">
<title>Verifying Time Synchronization</title>
<para>
When <systemitem class="protocol">PTP</systemitem> time
synchronization is working properly, new messages with offsets and frequency adjustments
will be printed periodically to the <application>ptp4l</application> and
<application>phc2sys</application> (if hardware time stamping is used)
outputs. These values will eventually converge after a short period of time. These
messages can be seen in <filename>/var/log/messages</filename> file. An
example of the output follows:
@@ -426,7 +426,7 @@ phc2sys[1060.984]: rms 266 max 675 freq -36759 ± 234 delay 2753 ±
17
</para>
</section>
-<section id="Serving_PTP_Time_with_NTP">
+<section id="sec-Serving_PTP_Time_with_NTP">
<title>Serving PTP Time with NTP</title>
<para>
The <systemitem class="daemon">ntpd</systemitem> daemon can be
configured to distribute the time from the system clock synchronized by
<application>ptp4l</application> or
<application>phc2sys</application> by using the LOCAL reference clock driver.
To prevent <systemitem class="daemon">ntpd</systemitem> from
adjusting the system clock, the <filename>ntp.conf</filename> file must not
specify any <systemitem class="protocol">NTP</systemitem> servers.
The following is a minimal example of <filename>ntp.conf</filename>:
@@ -442,7 +442,7 @@ fudge 127.127.1.0 stratum 0</screen>
</note>
</section>
-<section id="Serving_NTP_Time_with_PTP">
+<section id="sec-Serving_NTP_Time_with_PTP">
<title>Serving NTP Time with PTP</title>
<para>
<systemitem class="protocol">NTP</systemitem> to <systemitem
class="protocol">PTP</systemitem> synchronization in the opposite
direction is also possible. When <systemitem
class="daemon">ntpd</systemitem> is used to synchronize the system
clock, <application>ptp4l</application> can be configured with the
<option>priority1</option> option (or other clock options included in the best
master clock algorithm) to be the grandmaster clock and distribute the time from the
system clock via <systemitem class="protocol">PTP</systemitem>:
@@ -462,7 +462,7 @@ With hardware time stamping,
<application>phc2sys</application> needs to be used
</para>
</section>
-<section id="Improving_Accuracy">
+<section id="sec-Improving_Accuracy">
<title>Improving Accuracy</title>
<para>
Test results indicate that disabling the tickless kernel capability can significantly
improve the stability of the system clock, and thus improve the <systemitem
class="protocol">PTP</systemitem> synchronization accuracy (at the cost
of increased power consumption). The kernel tickless mode can be disabled by adding
<option>nohz=off</option> to the kernel boot option parameters.
@@ -471,12 +471,12 @@ With hardware time stamping,
<application>phc2sys</application> needs to be used
<!-- Topics, Resources -->
- <section id="s1-PTP_additional_resources">
+ <section id="sec-PTP_additional_resources">
<title>Additional Resources</title>
<para>
The following sources of information provide additional resources regarding
<systemitem class="protocol">PTP</systemitem> and the
<application>ptp4l</application> tools.
</para>
-<section id="s2-PTP-docs-inst">
+<section id="sec-PTP-docs-inst">
<title>Installed Documentation</title>
<itemizedlist>
<listitem>
@@ -498,7 +498,7 @@ With hardware time stamping,
<application>phc2sys</application> needs to be used
</itemizedlist>
</section>
-<section id="s2-PTP_useful-websites">
+<section id="sec-PTP_useful-websites">
<title>Useful Websites</title>
<para>
<variablelist>