wireshark/docbook/wsdg_src/WSDG_chapter_works.xml

<!-- WSDG Chapter Works -->
<!-- $Id$ -->

<chapter id="ChapterWorks">
  <title>How Wireshark Works</title>
  
  <section id="ChWorksIntro">
	<title>Introduction</title>
	<para>
	This chapter will give you a short overview of how Wireshark works.
	</para>
  </section>

  <section id="ChWorksOverview">
	<title>Overview</title>
	<para>
	The following will give you a simplified overview of Wireshark's function blocks:
	<figure id="ChWorksFigOverview">
	  <title>
	    <application>Wireshark</application> function blocks.
	  </title>
	  <graphic entityref="WiresharkFunctionBlocks" format="PNG"/>
	</figure>
	</para>
	<para>
	The function blocks in more detail:
	<variablelist>
	  <varlistentry><term><command>GTK+ 2</command></term>
	    <listitem>
	      <para>
		  Handling of all user input/output (all windows, dialogs and such). 
		  Source code can be found in the <filename>gtk</filename> directory.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry><term><command>Core</command></term>
	    <listitem>
	      <para>
		  Main "glue code" that holds the other blocks together. Source 
		  code can be found in the root directory.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry><term><command>Epan</command></term>
	    <listitem>
	      <para>
		  Ethereal Packet ANalyzer - the packet analyzing engine.
		  Source code can be found in the <filename>epan</filename> directory.
	      </para>
	  <itemizedlist>
	    <listitem>
	      <para>
		  Protocol-Tree - Keep data of the capture file protocol information.
	      </para>
	    </listitem>
	    <listitem>
	      <para>
		  Dissectors - The various protocol dissectors in 
		  <filename>epan/dissectors</filename>.
	      </para>
	    </listitem>
	    <listitem>
	      <para>
		  Dissector-Plugins - Some of the protocol dissectors are implemented
		  as plugins. Source code can be found in <filename>plugins</filename>.
	      </para>
	    </listitem>
	    <listitem>
	      <para>
		  Display-Filters - the display filter engine at 
		  <filename>epan/dfilter</filename>.
	      </para>
	    </listitem>
	  </itemizedlist>
	    </listitem>
	  </varlistentry>
	  <varlistentry><term><command>Wiretap</command></term>
	    <listitem>
	      <para>
		  The wiretap library is used to read/write capture files in libpcap
		  and a lot of other file formats. Source code in the
		  <filename>wiretap</filename> directory.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry><term><command>Capture</command></term>
	    <listitem>
	      <para>
		  The interface with the capture engine. Source code in the
		  root directory.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry><term><command>Dumpcap</command></term>
	    <listitem>
	      <para>
		  The capture engine itself. This is the only part that is to execute
		  with elevated privileges. Source code in the root directory.
	      </para>
	    </listitem>
	  </varlistentry>
	  <varlistentry>
	  <term><command>WinPcap / libpcap (not part of the Wireshark package)</command></term>
	    <listitem>
	      <para>
		  The platform dependent packet capture library, including the capture 
		  filter engine. That's the reason why we still have different display 
		  and capture filter syntax, as two different filtering engines are used.
	      </para>
	    </listitem>
	  </varlistentry>
	</variablelist>
	</para>
  </section>

	<section id="ChWorksCapturePackets">
	<title>Capturing packets</title>
	<para>
	Capturing will take packets from a network adapter, and save them to a file 
	on your harddisk. 
	</para>
	<para>
	Since raw network adapter access requires elevated privileges these functions
	are isolated into the dumpcap program. It's only this program that needs these
	privileges, allowing the main part of the code (dissectors, user interface,
	etc) to run as normal user program.
	</para>
	<para>
	To hide all the lowlevel machine dependent details from 
	Wireshark, the libpcap/WinPcap (see <xref linkend="ChLibsPcap"/>) library 
	is used. This library provides a general purpose interface to capture 
	packets from a lot of different network interface types (Ethernet, 
	Token Ring, ...). 
	</para>
	</section>

	<section id="ChWorksCaptureFiles">
	<title>Capture Files</title>
	<para>
	Wireshark can read and write capture files in its natural file format, the 
	libpcap format, which is used by many other network capturing tools, 
	e.g. tcpdump. In addition to this, as one of its strengths,
	Wireshark can read/write files in many different file formats of other 
	network capturing tools. The wiretap library, developed together with 
	Wireshark, provides a general purpose interface to read/write all the file 
	formats. If you need to add another capture file format, this is the place 
	to start.	
	</para>
	</section>

	<section id="ChWorksDissectPackets">
	<title>Dissect packets</title>
	<para>
	While Wireshark is loading packets from a file, each packet is dissected. 
	Wireshark tries to detect the packet type and gets as much 
	information from the packet as possible. In this run though, only the information shown 
	in the packet list pane is needed. 
	</para>
	<para>
	As the user selects a specific packet in the packet list pane, this packet
	will be dissected again. This time, Wireshark tries to 
	get every single piece of information and put it into 
	the packet details pane.
	</para>
	</section>

</chapter>
<!-- End of WSDG Chapter Works -->