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<book id="uid_domain" xmlns:xi="http://www.w3.org/2001/XInclude">
	<bookinfo>
		<title>UID Domain Module</title>
		<authorgroup>
			<author>
				<firstname>Juha</firstname>
				<surname>Heinanen</surname>
				<email>jh@tutpro.com</email>
			</author>
		</authorgroup>
		<copyright>
			<year>2002-2010</year>
			<holder>Juha Heinanen</holder>
		</copyright>
	</bookinfo>
	<toc></toc>
	<chapter>
		<title>Admin Guide</title>
	<section id="uid_domain.overview">
		<title>Overview</title>
		<para>Domain modules, as the name suggests, implements support for
		multiple independent virtual domains hosted on one SIP server. This is
		often useful if you have multiple domain names and you want to make
		them all work and appear as one. Alternatively you might find the
		module useful if you want to run a shared SIP service for multiple
		independent customers. The module stores all supported domains and
		associated configuration in a database table. Most of the information
		can be cached in memory for performance reasons.</para>

		<section>
			<title>Virtual Domains</title>
			<para>The domain module adds support for so-called virtual
			domains. A virtual domain is just a collection of domain names and
			associated configuration information identified by a unique
			identifier. We refer to the domain identifier as DID elsewhere in
			the documentation. DID stands for "Domain IDentifier". In
			traditional POST world the term DID has a different meaning
			though. Please be aware that this is just pure coincidence.</para>
			
			<para>All domain names that belong to one virtual domain are
			interchangeable. From SIP server's perspective there is no
			difference between them. They can be used in SIP URIs
			interchangeably and the behavior of the SIP server will not be
			affected. This is called "domain name normalization" and it is one
			of the steps performed early during SIP message processing.</para>

			<para>The DID identifier can be anything. To the SIP server DIDs
			are just opaque strings and what format you choose depends on your
			requirements and the type of the setup. You can use numbers in
			smaller setups if the size of the data is a concern. You can set
			the DID to the canonical domain name of the domain. You can use
			RFC 4122 style UUIDs if your setup is large and distributed. You
			can use anything as long as it can be represented as string. The
			only requirement is that the identifier of each virtual domain
			must be unique.</para>
		
			<para>The following example illustrates how one virtual domain can
			be represented. The iptel.org domain runs a public SIP
			service. The users of the service can use SIP URIs of form
			sip:username@iptel.org. The SIP service is distributed, there is a
			number of SIP servers. The SIP servers are also available through
			a number of other domain names, such as sip.iptel.org,
			proxy.iptel.org and so on. We created one virtual domain in the
			domain module and added all such domain names to the virtual
			domain:</para>

			<example>
				<title>Virtual Domain iptel.org</title>
				<programlisting>
iptel
  |
  +---iptel.org
  +---sip.iptel.org
  +---proxy.iptel.org
  +---213.192.59.75
				</programlisting>
			</example>
			
			<para>In the example above, we chose "iptel" as the unique
			identifier for the virtual domain. This identifier is
			permanent. It never changes. Over time we may change domain names
			assigned to this virtual domain, but this identifier never
			changes. The main reason why virtual domain identifiers must never
			change is that because they are referenced from other tables, for
			example the accounting table. The data in the accounting table is
			long-lived, usually archived, and this ensures that the data will
			still reference correct virtual domain, no matter what domain
			names are assigned to it.</para>

			<para>The virtual domain described above will be stored in the
			domain table in the database:</para>
			<example>
				<title>Database Representation of Virtual Domain</title>
				<programlisting>
+-------+-----------------+-------+
| did   | domain          | flags |
+-------+-----------------+-------+
| iptel | iptel.org       |    33 | 
| iptel | sip.iptel.org   |    33 | 
| iptel | proxy.iptel.org |    33 | 
| iptel | 213.192.59.75   |    33 | 
+-------+-----------------+-------+
				</programlisting>
			</example>

			<para>Because all domain names that belong to one particular
			virtual domain are equal, it does not matter which domain name is
			used in the host part of the SIP URI. Thus an imaginary user joe
			with SIP URI sip:joe@iptel.org will also be reachable as
			sip:joe@sip.iptel.org, sip:joe@proxy.iptel.org, and
			sip:joe@213.192.59.75. If we add a new domain name to this virtual
			domain then joe will also be able to use the new domain name in
			his SIP URI, without the need to change anything.</para>
		</section>
		
		<section>
			<title>Domain-level Configuration Attributes</title>
			<para>In addition to a number of domain names, each virtual domain
			can also have extra configuration information associated with
			it. The possibility to configure the SIP server sightly
			differently in each virtual domain is, in fact, the main reason
			why we introduced the concept of virtual domains. We wanted to
			have one SIP server which will provide SIP service to multiple
			different customers and each of the customers may have slightly
			different configuration requirements. That's how domain-level
			configuration attributes were born.</para>
		
			<para>Because the administrator of the SIP server seldom knows
			configuration requirements in advance, we decided to implement a
			generic solution and store all configuration options in named
			attributes. Named attributes are just like variables, they have a
			name and they have a value. Attributes are accessible from the
			configuration script of the SIP server. Domain-level attributes
			are attributes that are associated with a particular virtual
			domain. They can be used to store additional configuration for the
			entire virtual domain, that is all users that belong (or have SIP
			URI) in that particular virtual domain. Domain-level attributes
			can be overridden be user-level attributes with the same name
			configured for a particular user. In other words a domain level
			attribute will only be effective if no user-level attribute with
			the same name exists.</para>
			
			<para>Domain-level attributes are stored in a separate table. The
			name of the table is domain_attrs and it is defined as follows:
			</para>

			<example>
				<title>Table domain_attrs</title>
				<programlisting>
+-------+------------------+------+-----+---------+-------+
| Field | Type             | Null | Key | Default | Extra |
+-------+------------------+------+-----+---------+-------+
| did   | varchar(64)      | YES  | MUL | NULL    |       | 
| name  | varchar(32)      | NO   |     | NULL    |       | 
| type  | int(11)          | NO   |     | 0       |       | 
| value | varchar(255)     | YES  |     | NULL    |       | 
| flags | int(10) unsigned | NO   |     | 0       |       | 
+-------+------------------+------+-----+---------+-------+
				</programlisting>
			</example>

			<para>Each attribute has name, type and value. A single attribute
			can have multiple values and in that case it will occupy more rows
			in the table. Each attribute is associated with a particular
			virtual domain using the DID identifier. Domain-level attributes
			can contain just about anything. It is a generic configuration
			mechanism and it is up to you to define a list of attribute that
			are meaningful in your setup and use those attributes in the
			routing part of the configuration file.
			</para>

			<para>Attributes for a particular virtual-domain are made
			available to script function by the lookup_domain function. This
			is the function that is used to map domain names to DIDs. One of
			the side-effects of the function is that it makes domain-level
			attributes available to script function if a matching virtual
			domain is found.
			</para>

			<para>When caching is enabled, all attributes from domain_attrs
			table are cached in memory, just like virtual domain
			themselves. If you disable caching then the domain module will
			attempt to load attributes from the database each time you call
			lookup_domain. Attributes cached in memory can be realoaded with
			the domain.reload management function.</para>
		</section>

		<section>
			<title>Caching</title>

			<para>Domain module operates in caching or non-caching mode
			depending on value of module parameter
			<parameter>db_mode</parameter>. In caching mode domain module
			reads the contents of domain table into cache memory when the
			module is loaded.  After that domain table is re-read only when
			module is given domain_reload fifo command.  Any changes in domain
			table must thus be followed by domain_reload command in order to
			reflect them in module behavior. In non-caching mode domain module
			always queries domain table in the database.</para>

			<para>Caching is implemented using a hash table. The size of the
			hash table is given by HASH_SIZE constant defined in
			domain_mod.h. Its "factory default" value is 128. Caching mode is
			highly recommended if you want to use domain-level
			attributes.</para>
		</section>
	</section>
	
	<section id="uid_domain.dep">
		<title>Dependencies</title>
		<para>
			The module depends on the following modules (in the other words
			the listed modules must be loaded before this module):
			<itemizedlist>
				<listitem>
					<para><emphasis>database</emphasis> - Any database module</para>
				</listitem>
	    </itemizedlist>
		</para>
	</section>
	
	<section id="uid_domain.known_limitations">
		<title>Known Limitations</title>
		<para>
			There is an unlikely race condition on domain list update.  If a process uses a table,
			which is reloaded at the same time twice through <acronym>FIFO</acronym>, the second
			reload will delete the original table still in use by the process.
		</para>
	</section>
	
	<xi:include href="params.xml"/>
	<xi:include href="functions.xml"/>
	<xi:include href="fifo.xml"/>
	<xi:include href="domain_api.xml"/>
	</chapter>
</book>
