c02architecture.xml

<chapter id="c02arch">
	<title>&kamailio; Architecture</title>
	<para>
		&kamailio; has a modular architecture. As a big picture, there are two main categories:
	</para>
	<itemizedlist>
		<listitem>
			<para>
				<emphasis>the core</emphasis> - it is the component that provides the low-level
				functionalities for &kamailio;.
			</para>
			<para>
				Starting with version 3.0.0, &kamailio; core includes so called
				<emphasis>internal libraries</emphasis>. They collect code shared by several modules
				but which does not have a general purpose to be part of main core.
			</para>
		</listitem>
		<listitem>
			<para>
				<emphasis>the modules</emphasis> - are the components that provides the most
				of the functionalities that make &kamailio; powerful in real world deployments.
			</para>
		</listitem>
	</itemizedlist>
	<para>
		The architecture for &kamailio; v1.5.x (or older) is shown in the next figure.
	</para>
	<figure>
		<title>&kamailio; 1.x Architecture</title>
		<mediaobject>
			<imageobject>
				<imagedata fileref="./obj/kamailio_architecture_old.png"/>
			</imageobject>
		</mediaobject>
	</figure>
	<para>
		The architecture for &kamailio; v3.0.x (or newer) was refactored, permitting 
		to have code shared by several modules stored in internal libraries. Some of
		the core components in v1.x being relocated as an internal library. The new
		architecture for v3.0.x compared with the one from v1.x is shown in the next figure.
	</para>
	<figure>
		<title>&kamailio; 3.x Architecture</title>
		<mediaobject>
			<imageobject>
				<imagedata fileref="./obj/kamailio_architecture_new.png"/>
			</imageobject>
		</mediaobject>
	</figure>


	<section>
		<title>&kamailio; Core</title>
		<para>
			The core includes:
		</para>
		<itemizedlist>
			<listitem>
				<para>
					memory manager
				</para>
			</listitem>
			<listitem>
				<para>
					SIP message parser
				</para>
			</listitem>
			<listitem>
				<para>
					locking system
				</para>
			</listitem>
			<listitem>
				<para>
					DNS and transport layer management (UDP, TCP, TLS, SCTP)
				</para>
			</listitem>
			<listitem>
				<para>
					configuration file parser and interpreter
				</para>
			</listitem>
			<listitem>
				<para>
					stateless forwarding
				</para>
			</listitem>
			<listitem>
				<para>
					pseudo-variables and transformations engines
				</para>
			</listitem>
			<listitem>
				<para>
					RPC control interface API
				</para>
			</listitem>
			<listitem>
				<para>
					timer API
				</para>
			</listitem>
		</itemizedlist>
		<para>
			The internal libraries include:
		</para>
		<itemizedlist>
			<listitem>
				<para>
					some components from old Kamailio v1.5.x core
				</para>
			</listitem>
			<listitem>
				<para>
					database abstraction layers (DB API v1 and v2)
				</para>
			</listitem>
			<listitem>
				<para>
					management interface (MI) API
				</para>
			</listitem>
			<listitem>
				<para>
					statistics engine
				</para>
			</listitem>
		</itemizedlist>

	</section>

	<section>
		<title>&kamailio; Modules</title>
		<para>
			There are over 150 modules in the repository at this moment. By loading modules,
			you can get functionalities such as:
		</para>
		<itemizedlist>
			<listitem>
				<para>
					registrar and user location management
				</para>
			</listitem>
			<listitem>
				<para>
					accounting, authorization and authentication
				</para>
			</listitem>
			<listitem>
				<para>
					text and regular expression operations
				</para>
			</listitem>
			<listitem>
				<para>
					stateless replying
				</para>
			</listitem>
			<listitem>
				<para>
					stateful processing - SIP transaction management
				</para>
			</listitem>
			<listitem>
				<para>
					SIP dialogs tracking - active calls management
				</para>
			</listitem>
			<listitem>
				<para>
					instant messaging and presence extensions
				</para>
			</listitem>
			<listitem>
				<para>
					RADIUS and LDAP support
				</para>
			</listitem>
			<listitem>
				<para>
					SQL and no-SQL database connectors
				</para>
			</listitem>
			<listitem>
				<para>
					MI and RPC transports
				</para>
			</listitem>
			<listitem>
				<para>
					Enum, GeoIP API and CPL interpreter
				</para>
			</listitem>
			<listitem>
				<para>
					topology hiding and NAT traversal
				</para>
			</listitem>
			<listitem>
				<para>
					load balancing and least cost routing
				</para>
			</listitem>
			<listitem>
				<para>
					asynchronous SIP request processing
				</para>
			</listitem>
			<listitem>
				<para>
					interactive configuration file debugger
				</para>
			</listitem>
			<listitem>
				<para>
					Lua, Perl, Python and Java SIP Servlet extensions
				</para>
			</listitem>
		</itemizedlist>
	</section>
	<section id="c02message_processing">
		<title>SIP Message Processing</title>
		<para>
			The execution of &kamailio; configuration file is triggered when receiving a SIP message from
			the network. The processing flow is different for a SIP request or a SIP reply.
		</para>

		<figure>
		<title>SIP Request Processing</title>
		<mediaobject>
			<imageobject>
				<imagedata fileref="./obj/kamailio_request_processing.png"/>
			</imageobject>
		</mediaobject>
		</figure>
		<figure>
		<title>SIP Reply Processing</title>
		<mediaobject>
			<imageobject>
				<imagedata fileref="./obj/kamailio_reply_processing.png"/>
			</imageobject>
		</mediaobject>
		</figure>

		<para>
			The document contains a chapter dedicated to <emphasis role="strong">Configuration File</emphasis> that
			explains its structure and the types of routing blocks.
		</para>
	</section>
</chapter>