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<section id="general" xmlns:xi="http://www.w3.org/2001/XInclude">
    <sectioninfo>
	<revhistory>
	    <revision>
		<revnumber>$Revision$</revnumber>
		<date>$Date$</date>
	    </revision>
	</revhistory>
    </sectioninfo>
    
    <title>General Information</title>
    <section id="aboutser">
	<title>About <acronym>SIP</acronym> Express Router (<acronym>SER</acronym>)</title>
	<para>
	    SIP Express Router (<acronym>SER</acronym>) is an
	    industrial-strength, free VoIP server based on the Session
	    Initiation Protocol (<acronym>SIP</acronym>, RFC3261).  It is
	    engineered to power <acronym>IP</acronym> telephony infrastructures
	    up to large scale. The server keeps track of users, sets up VoIP
	    sessions, relays instant messages and creates space for new plug-in
	    applications.  Its proven interoperability guarantees seamless
	    integration with components from other vendors, eliminating the
	    risk of a single-vendor trap. It has successfully participated in
	    various interoperability tests in which it worked with the products
	    of other leading <acronym>SIP</acronym> vendors.
	</para>
	<para>
	    The <acronym>SIP</acronym> Express Router enables a flexible
	    plug-in model for new applications: Third parties can easily link
	    their plug-ins with the server code and provide thereby advanced
	    and customized services.  In this way, plug-ins such as RADIUS
	    accounting, SMS gateway, ENUM queries, or presence agent have
	    already been developed and are provided as advanced features. Other
	    modules are underway: firewall control, postgres and LDAP database
	    drivers and more.
	</para>
	<para>
	    Its performance and robustness allows it to serve millions of users
	    and accommodate needs of very large operators. With a $3000
	    dual-CPU PC, the <acronym>SIP</acronym> Express Router is able to
	    power <acronym>IP</acronym> telephony services in an area as large
	    as the Bay Area during peak hours. Even on an IPAQ
	    <acronym>PDA</acronym>, the server withstands 150 calls per second
	    (<acronym>CPS</acronym>)! The server has been powering our
	    iptel.org free <acronym>SIP</acronym> site withstanding heavy daily
	    load that is further increasing with the popularity of Microsoft's
	    Windows Messenger.
	</para>
	<para>
	    The <acronym>SIP</acronym> Express Router is extremely configurable
	    to allow the creation of various routing and admission policies as
	    well as setting up new and customized services. Its configurability
	    allows it to serve many roles: network security barrier,
	    application server, or <acronym>PSTN</acronym> gateway guard for
	    example.
	</para>
	<para>
	    <application>ser</application> can be also
	    used with contributed applications. Currently, 
	    <application>serweb</application>, a
	    <application>ser</application> web interface,
	    <application>SIPSak</application> diagnostic tool 
	    and 
	    <application>SEMS</application> media server
	    are available. Visit our site, 
	    <ulink url="http://www.iptel.org/">http://www.iptel.org/</ulink>, 
	    for more information on contributed packages.
	</para>
    </section> 

    <section id="aboutiptel">
	<title>About iptel.org</title>
	<para>
	    iptel.org is a know-how organization spun off from Germany's
	    national research company FhG Fokus. One of the first
	    <acronym>SIP</acronym> implementations ever, low-QoS enhancements,
	    interoperability tests and VoIP-capable firewall control concepts
	    are examples of well-known FhG's work.
	</para>
	<para>
	    iptel.org continues to keep this know-how leadership in
	    <acronym>SIP</acronym>.  The access rate of the company's site, a
	    well-known source of technological information, is a best proof of
	    interest. Thousands of hits come every day from the whole Internet.
	</para>
	<para>
	    The iptel.org site, powered by SER, offers SIP services on the public 
	    Internet. Feel free to apply for a free SIP account at
	    <ulink url="http://www.iptel.org/user/">http://www.iptel.org/user/
	    </ulink>
	</para>

	</section> <!-- iptel -->
	<section id="serfeatures">
	<title>Feature List</title>
	<para>
	    Based on the latest standards, the <acronym>SIP</acronym> Express
	    Router (<acronym>SER</acronym>) includes support for registrar,
	    proxy and redirect mode. Further it acts as an application server
	    with support for instant messaging and presence including a
	    <acronym>2G/SMS</acronym> and Jabber gateway, a call control policy
	    language, call number translation, private dial plans and
	    accounting, ENUM, authorization and authentication
	    (<acronym>AAA</acronym>) services. <application>SER</application>
	    runs on Sun/Solaris, PC/Linux, PC/BSD, IPAQ/Linux platforms and
	    supports both <acronym>IPv4</acronym> and <acronym>IPv6</acronym>.
	    Hosting multiple domains and database redundancy is supported.
	</para>
	<para>
	    <application>ser</application> has been carefully engineered with
	    the following design objectives in mind:
	    <itemizedlist>
		<listitem>
		    <para>
			<emphasis>Speed</emphasis> - With
			<application>ser</application>, thousands of calls per
			seconds are achievable even on low-cost platforms. This
			competitive capacity allows setting up networks which
			are inexpensive and easy to manage due to low number of
			devices required. The processing capacity makes dealing
			with many stress factors easier. The stress factors may
			include but are not limited to broken configurations
			and implementations, boot avalanches on power-up,
			high-traffic applications such as presence, redundancy
			replications and denial-of-service attacks.
		    </para>
		    <para> The speed has been achieved by extensive code
			optimization, use of customized code, <acronym>ANSI
			C</acronym> combined with assembly instructions and
			leveraging latest <acronym>SIP</acronym>
			improvements. When powered by a dual-CPU Linux PC,
			<application>ser</application> is able to process
			thousands of calls per second, capacity needed to serve
			call signaling demands of Bay Area population.
		    </para>
		    </listitem>
		    <listitem>
		    <para>
			<emphasis>Flexibility</emphasis> -
			<application>SER</application> allows its users to
			define its behavior.  Administrators may write textual
			scripts which determine <acronym>SIP</acronym> routing
			decisions, the main job of a proxy server. They may use
			the script to configure numerous parameters and
			introduce additional logic. For example, the scripts
			can determine for which destinations record routing
			should be performed, who will be authenticated, which
			transactions should be processed statefully, which
			requests will be proxied or redirected, etc.
		    </para>
		</listitem>
		<listitem>
		    <para>
			<emphasis>Extensibility</emphasis> -
			<application>SER</application>'s extensibility allows
			linking of new C code to ser to redefine or extend its
			logic. The new code can be developed independently on
			<application>SER</application> core and linked to it in
			run-time. The concept is similar to the module concept
			known for example in Apache Web server. Even such
			essential parts such as transaction management have
			been developed as modules to keep the
			<application>SER</application> core compact and fast.
		    </para>
		</listitem>
		<listitem>
		    <para>
			<emphasis>
			    Portability.
			</emphasis>
			<application>ser</application> has been written in ANSI
			C. It has been extensively tested on PC/Linux and
			Sun/Solaris. Ports to BSD and IPAQ/Linux exist.
		    </para>
		</listitem>
		<listitem>
		    <para>
			<emphasis>			   
			    Interoperability. 
			</emphasis>
			<application>ser</application> is based on the open
			<acronym>SIP</acronym> standard.  It has undergone
			extensive tests with products of other vendors both in
			iptel.org labs and in the SIP Interoperability Tests
			(SIPIT). <application>ser</application> powers the
			public iptel.org site 24 hours a day, 356 days a year
			serving numerous SIP implementations using this site.
		    </para>
		</listitem>
		<listitem>
		    <para>
			<emphasis>Small size.</emphasis>
			Footprint of the core is 300k, add-on modules take up to 630k.
		    </para>
		</listitem>
	    </itemizedlist>
	</para>
    </section> <!-- serfeatures -->
    
    <section id="usecases">
	<title>Use Cases</title>
	<para>
	    This section illustrates the most frequent uses of SIP. In all
	    these scenarios, the SIP Express Router (SER) can be easily
	    deployed as the glue connecting all SIP components together, be it
	    soft-phones, hard-phones, PSTN gateways or any other SIP-compliant
	    devices.
	</para>
	<section>
	    <title>Added-Value ISP Services</title>
	    <para>
		To attract customers, ISPs frequently offer applications
		bundled with IP access.  With SIP, the providers can
		conveniently offer a variety of services running on top of a
		single infrastructure. Particularly, deploying VoIP and instant
		messaging and presence services is as easy as setting up a SIP
		server and guiding customers to use Windows
		Messenger. Additionally, the ISPs may offer advanced services
		such as PSTN termination, user-driven call handling or unified
		messaging all using the same infrastructure.
	    </para>
	    <para>
		SIP Express Router has been engineered to power large scale
		networks: its capacity can deal with large number of customers
		under high load caused by modern applications. Premium
		performance allows deploying a low number of boxes while
		keeping investments and operational expenses extremely
		low. ISPs can offer SIP-based instant messaging services and
		interface them to other instant messaging systems (Jabber,
		SMS). VoIP can be easily integrated along with added-value
		services, such as voicemail.
	    </para>
	</section> <!-- Added-value ISP -->
	<section>
	    <title>PC2Phone</title>
	    <para>
		Internet Telephony Service Providers (ITSPs) offer the service
		of interconnecting Internet telephony users using PC softphone
		or appliances to PSTN. Particularly with long-distance and
		international calls, competitive pricing can be achieved by
		routing the calls over the Internet.
	    </para>
	    <para>
		SIP Express Router can be easily configured to serve pc2phone
		users, distribute calls to geographically appropriate PSTN
		gateway, act as a security barrier and keep track of charging.
	    </para>
	</section>
	<section>
	    <title>PBX Replacement</title>
	    <para>
		Replacing a traditional PBX in an enterprise can achieve
		reasonable savings. Enterprises can deploy a single
		infrastructure for both voice and data and bridge distant
		locations over the Internet. Additionally, they can benefit of
		integration of voice and data.
	    </para>
	    <para>
		The SIP Express Router scales from SOHOs to large,
		international enterprises.  Even a single installation on a
		common PC is able to serve VoIP signaling of any world's
		enterprise. Its policy-based routing language makes
		implementation of numbering plans of companies spread across
		the world very easy. ACL features allow for protection of PSTN
		gateway from unauthorized callers.
	    </para>
	    <para>
		SIP Express Router's support for programmable routing and
		accounting efficiently allows for implementation of such a
		scenario.
	    </para>
	</section>
    </section> <!-- Use Cases -->
    <section id="aboutsip">
	<title>About SIP Technology</title>
	<para>
	    The SIP protocol family is the technology which integrates
	    services.  With SIP, Internet users can easily contact each other;
	    figure out willingness to have a conversation and couple different
	    applications such as VoIP, video and instant messaging. Integration
	    with added-value services is seamless and easy. Examples include
	    integration with web (click-to-dial), E-mail (voice2email, UMS),
	    and PSTN-like services (conditional forwarding).
	</para>
	<para>
	    The core piece of the technology is the Session Initiation Protocol
	    (SIP, RFC3261) standardized by IETF.  Its main function is to
	    establish communication sessions between users connected to the
	    public Internet and identified by e-mail-like addresses. One of
	    SIP's greatest features is its transparent support for multiple
	    applications: the same infrastructure may be used for voice, video,
	    gaming or instant messaging as well as any other communication
	    application.
	</para>
	<para>
	    There are numerous scenarios in which SIP is already deployed: PBX
	    replacement allows for deployment of single inexpensive
	    infrastructure in enterprises; PC-2-phone long-distance services
	    (e.g., Deltathree) cut callers long-distance expenses; instant
	    messaging offered by public severs (e.g., iptel.org) combines voice
	    and text services with presence information.  New deployment
	    scenarios are underway: SIP is a part of UMTS networks and research
	    publications suggest the use of SIP for virtual home environments
	    or distributed network games.
	</para>
    </section> <!-- about sip -->
    <section id="serlimitations">
	<title>Known SER Limitations</title>
	<para>
	    The following items are not part of current distribution and are
	    planned for next releases:
	    <itemizedlist>
		<listitem>
		    <para>
			Script processing of multiple branches on forking
		    </para>
		    
		    <warning>
			<para>
			    <application>ser</application>'s request processing
			    language allows to make request decisions based on
			    current URI.  When a request if forked to multiple
			    destinations, only the first branch's URI is used
			    as input for script processing. This might lead to
			    unexpected results. Whenever a URI resolves to
			    multiple different next-hop URIs, only the first is
			    processed which may result in handling not
			    appropriate for the other branch. For example, a
			    URI might resolve to an IP phone SIP address and
			    PSTN gateway SIP address. If the IP phone address
			    is the first, then script execution ignores the
			    second branch. If a script includes checking
			    gateway address in request URI, the checks never
			    match. That might result in ignoring of gateway
			    admission control rules or applying them
			    unnecessarily to non-gateway destinations.
			</para>
			</warning>
		    </listitem>
	    </itemizedlist>
	</para>
	<para>
	    List of known problems is publicly available at the 
	    <application>ser</application> webpage at
	    <ulink url="http://www.iptel.org/ser/">
		http://www.iptel.org/ser/
	    </ulink>. See the "ISSUES" link.
	</para>
    </section> <!-- limitations -->
    <section id="licensing">
	<title>Licensing</title>
	<para>
	    <application>ser</application> is freely available under terms and
	    conditions of the GNU General Public License.
	</para>	
	<!-- COPYING -->
	<screen>
<xi:include href="../../COPYING" parse="text"/>
	</screen>
    </section>

    <section id="support">
	<title>Obtaining Technical Assistance</title>
	<para>
	    iptel.org offers qualified professional services. We help you to
	    plan your network, configure your server, build applications,
	    integrate SIP components with each other, and set up advanced
	    features such as redundancy, multidomain support, CLID interworking
	    and others not described in this document. Our customer alert
	    services notifies you on all new features and code fixes. We help
	    you to solve operational troubles in short time and keep you
	    updated on latest operational practices. Ask info@iptel.org for
	    information on enrollment in our support program.
	</para>
	
	<para>
	    Additionally, help may be obtained from our user forum. The
	    community of <application>SER</application> users is subscribed to
	    the serusers@iptel.org mailing list and discusses issues related to
	    <application>SER</application> operation.
	</para>
	<itemizedlist>
	    <title>Mailing List Instructions</title>
	    <listitem>
		<para>
		    Public archives and subscription form:
		    <ulink url="http://mail.iptel.org/mailman/listinfo/serusers">
			http://mail.iptel.org/mailman/listinfo/serusers
		    </ulink>
		</para>
	    </listitem>
	    <listitem>
		<para>
		    To post, send an email to serusers@iptel.org
		</para>
	    </listitem>
	    <listitem>
		<para>
		    If you think you encountered an error, please submit the
		    following information to avoid unnecessary round-trip
		    times:
		    <itemizedlist>
			<listitem>
			    <para>
				Name and version of your operating system --
				you can obtain it by calling <command>uname
				-a</command>
			    </para>
			</listitem>
			<listitem>
			    <para>
				<application>ser</application> distribution: 
				release number and package				    
			    </para>
			</listitem>
			<listitem>
			    <para>
				<application>ser</application> build -- 
				you can obtain it by calling 
				<command>ser -V</command>
			    </para>
			</listitem>
			<listitem>
			    <para>
				Your <application>ser</application> configuration file
			    </para>
			</listitem>
			<listitem>
			    <para>
				<application>ser</application> logs -- with
				default settings few logs are printed to
				<command>syslog</command> facility which
				typically dumps them to
				<filename>/var/log/messages</filename>. To
				enable detailed logs dumped to
				<filename>stderr</filename>, apply the
				following configuration options: <command>
				debug=8, log_stderror=yes, fork=no</command>.
			    </para>
			</listitem>
			<listitem>
			    <para>
				Captured SIP messages -- you can obtain them 
				using tools such as <application>ngrep</application>
				or <application>ethereal</application>.
			    </para>
			</listitem>
		    </itemizedlist>
		</para>
	    </listitem>
	</itemizedlist>
    </section>
    
    <section id="moreinfo">
	<title>More Information</title>
	<para>
	    Most up-to-date information including latest and most complete
	    version of this documentation is always available at our website,
	    <ulink
	    url="http://www.iptel.org/ser/">http://www.iptel.org/ser/</ulink>.
	    The site includes links to other important information about
	    <application>ser</application>, such as installation guidelines
	    (INSTALL), download links, development pages, programmer's manual,
	    etc.
	</para>
	<para>
	    A SIP tutorial (slide set) is available at 
	    <ulink url="http://www.iptel.org/sip/">http://www.iptel.org/sip/</ulink> .
	</para>
    </section> <!-- info -->
    
    <section>
	<title>Release Notes</title>
	<literallayout>
<xi:include href="../../NEWS" parse="text"/>
	</literallayout>
    </section> <!-- release notes -->
</section> <!-- general -->