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<span>Architecture</span> </div> </a> <button aria-controls="toc-Architecture-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Architecture subsection</span> </button> <ul id="toc-Architecture-sublist" class="vector-toc-list"> <li id="toc-Access_network" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Access_network"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Access network</span> </div> </a> <ul id="toc-Access_network-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Core_network" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Core_network"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>Core network</span> </div> </a> <ul id="toc-Core_network-sublist" class="vector-toc-list"> <li id="toc-Call_Session_Control_Function_(CSCF)" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Call_Session_Control_Function_(CSCF)"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.1</span> <span>Call Session Control Function (CSCF)</span> </div> </a> <ul id="toc-Call_Session_Control_Function_(CSCF)-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Application_servers" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Application_servers"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.2</span> <span>Application servers</span> </div> </a> <ul id="toc-Application_servers-sublist" class="vector-toc-list"> <li id="toc-Functional_model" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Functional_model"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.2.1</span> <span>Functional model</span> </div> </a> <ul id="toc-Functional_model-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Public_Service_Identity" class="vector-toc-list-item vector-toc-level-4"> <a class="vector-toc-link" href="#Public_Service_Identity"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.2.2</span> <span>Public Service Identity</span> </div> </a> <ul id="toc-Public_Service_Identity-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Media_servers" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Media_servers"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.3</span> <span>Media servers</span> </div> </a> <ul id="toc-Media_servers-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Breakout_gateway" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Breakout_gateway"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.4</span> <span>Breakout gateway</span> </div> </a> <ul id="toc-Breakout_gateway-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-PSTN_gateways" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#PSTN_gateways"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.5</span> <span>PSTN gateways</span> </div> </a> <ul id="toc-PSTN_gateways-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Media_resources" class="vector-toc-list-item vector-toc-level-3"> <a class="vector-toc-link" href="#Media_resources"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2.6</span> <span>Media resources</span> </div> </a> <ul id="toc-Media_resources-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-NGN_interconnection" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#NGN_interconnection"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>NGN interconnection</span> </div> </a> <ul id="toc-NGN_interconnection-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Charging" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Charging"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.4</span> <span>Charging</span> </div> </a> <ul id="toc-Charging-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-IMS-based_PES_architecture" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#IMS-based_PES_architecture"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.5</span> <span>IMS-based PES architecture</span> </div> </a> <ul id="toc-IMS-based_PES_architecture-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Interfaces_description" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Interfaces_description"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.6</span> <span>Interfaces description</span> </div> </a> <ul id="toc-Interfaces_description-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Session_handling" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Session_handling"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Session handling</span> </div> </a> <button aria-controls="toc-Session_handling-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Session handling subsection</span> </button> <ul id="toc-Session_handling-sublist" class="vector-toc-list"> <li id="toc-Initial_filter_criteria" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Initial_filter_criteria"> <div class="vector-toc-text"> <span class="vector-toc-numb">3.1</span> <span>Initial filter criteria</span> </div> </a> <ul id="toc-Initial_filter_criteria-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Security_aspects_of_early_IMS_and_non-3GPP_systems" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Security_aspects_of_early_IMS_and_non-3GPP_systems"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Security aspects of early IMS and non-3GPP systems</span> </div> </a> <ul id="toc-Security_aspects_of_early_IMS_and_non-3GPP_systems-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-See_also" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#See_also"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>See also</span> </div> </a> <ul id="toc-See_also-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-References" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#References"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>References</span> </div> </a> <ul id="toc-References-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Further_reading" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Further_reading"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Further reading</span> </div> </a> <ul id="toc-Further_reading-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-External_links" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#External_links"> <div class="vector-toc-text"> <span class="vector-toc-numb">8</span> <span>External links</span> </div> </a> <ul id="toc-External_links-sublist" class="vector-toc-list"> </ul> </li> </ul> </div> </div> </nav> </div> </div> <div class="mw-content-container"> <main id="content" class="mw-body"> <header class="mw-body-header vector-page-titlebar"> <nav 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id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">IP Multimedia Subsystem</span></h1> <div id="p-lang-btn" class="vector-dropdown mw-portlet mw-portlet-lang" > <input type="checkbox" id="p-lang-btn-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-p-lang-btn" class="vector-dropdown-checkbox mw-interlanguage-selector" aria-label="Go to an article in another language. Available in 20 languages" > <label id="p-lang-btn-label" for="p-lang-btn-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--action-progressive mw-portlet-lang-heading-20" aria-hidden="true" ><span class="vector-icon mw-ui-icon-language-progressive mw-ui-icon-wikimedia-language-progressive"></span> <span class="vector-dropdown-label-text">20 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/IMS" title="IMS – Azerbaijani" lang="az" hreflang="az" data-title="IMS" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/Subsistema_Multim%C3%A8dia_IP" title="Subsistema Multimèdia IP – Catalan" lang="ca" hreflang="ca" data-title="Subsistema Multimèdia IP" data-language-autonym="Català" data-language-local-name="Catalan" class="interlanguage-link-target"><span>Català</span></a></li><li class="interlanguage-link interwiki-cs mw-list-item"><a href="https://cs.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Czech" lang="cs" hreflang="cs" data-title="IP Multimedia Subsystem" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – German" lang="de" hreflang="de" data-title="IP Multimedia Subsystem" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Subsistema_Multimedia_IP" title="Subsistema Multimedia IP – Spanish" lang="es" hreflang="es" data-title="Subsistema Multimedia IP" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%B2%DB%8C%D8%B1%D8%B3%D8%A7%D9%85%D8%A7%D9%86%D9%87_%DA%86%D9%86%D8%AF%D8%B1%D8%B3%D8%A7%D9%86%D9%87%E2%80%8C%D8%A7%DB%8C_%D8%A2%DB%8C%E2%80%8C%D9%BE%DB%8C" title="زیرسامانه چندرسانه‌ای آی‌پی – Persian" lang="fa" hreflang="fa" data-title="زیرسامانه چندرسانه‌ای آی‌پی" data-language-autonym="فارسی" data-language-local-name="Persian" class="interlanguage-link-target"><span>فارسی</span></a></li><li class="interlanguage-link interwiki-fr mw-list-item"><a href="https://fr.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – French" lang="fr" hreflang="fr" data-title="IP Multimedia Subsystem" data-language-autonym="Français" data-language-local-name="French" class="interlanguage-link-target"><span>Français</span></a></li><li class="interlanguage-link interwiki-ko mw-list-item"><a href="https://ko.wikipedia.org/wiki/IP_%EB%A9%80%ED%8B%B0%EB%AF%B8%EB%94%94%EC%96%B4_%EC%84%9C%EB%B8%8C%EC%8B%9C%EC%8A%A4%ED%85%9C" title="IP 멀티미디어 서브시스템 – Korean" lang="ko" hreflang="ko" data-title="IP 멀티미디어 서브시스템" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Italian" lang="it" hreflang="it" data-title="IP Multimedia Subsystem" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Dutch" lang="nl" hreflang="nl" data-title="IP Multimedia Subsystem" data-language-autonym="Nederlands" data-language-local-name="Dutch" class="interlanguage-link-target"><span>Nederlands</span></a></li><li class="interlanguage-link interwiki-ja mw-list-item"><a href="https://ja.wikipedia.org/wiki/IP%E3%83%9E%E3%83%AB%E3%83%81%E3%83%A1%E3%83%87%E3%82%A3%E3%82%A2%E3%82%B5%E3%83%96%E3%82%B7%E3%82%B9%E3%83%86%E3%83%A0" title="IPマルチメディアサブシステム – Japanese" lang="ja" hreflang="ja" data-title="IPマルチメディアサブシステム" data-language-autonym="日本語" data-language-local-name="Japanese" class="interlanguage-link-target"><span>日本語</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Polish" lang="pl" hreflang="pl" data-title="IP Multimedia Subsystem" data-language-autonym="Polski" data-language-local-name="Polish" class="interlanguage-link-target"><span>Polski</span></a></li><li class="interlanguage-link interwiki-pt mw-list-item"><a href="https://pt.wikipedia.org/wiki/Sistema_Interactivo_Multim%C3%A9dia" title="Sistema Interactivo Multimédia – Portuguese" lang="pt" hreflang="pt" data-title="Sistema Interactivo Multimédia" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ro mw-list-item"><a href="https://ro.wikipedia.org/wiki/Subsistem_multimedia_IP" title="Subsistem multimedia IP – Romanian" lang="ro" hreflang="ro" data-title="Subsistem multimedia IP" data-language-autonym="Română" data-language-local-name="Romanian" class="interlanguage-link-target"><span>Română</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/IMS_(%D1%8D%D0%BB%D0%B5%D0%BA%D1%82%D1%80%D0%BE%D1%81%D0%B2%D1%8F%D0%B7%D1%8C)" title="IMS (электросвязь) – Russian" lang="ru" hreflang="ru" data-title="IMS (электросвязь)" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sk mw-list-item"><a href="https://sk.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Slovak" lang="sk" hreflang="sk" data-title="IP Multimedia Subsystem" data-language-autonym="Slovenčina" data-language-local-name="Slovak" class="interlanguage-link-target"><span>Slovenčina</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Finnish" lang="fi" hreflang="fi" data-title="IP Multimedia Subsystem" data-language-autonym="Suomi" data-language-local-name="Finnish" class="interlanguage-link-target"><span>Suomi</span></a></li><li class="interlanguage-link interwiki-sv mw-list-item"><a href="https://sv.wikipedia.org/wiki/IP_Multimedia_Subsystem" title="IP Multimedia Subsystem – Swedish" lang="sv" hreflang="sv" data-title="IP Multimedia Subsystem" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/IMS" title="IMS – Ukrainian" lang="uk" hreflang="uk" data-title="IMS" data-language-autonym="Українська" data-language-local-name="Ukrainian" class="interlanguage-link-target"><span>Українська</span></a></li><li class="interlanguage-link interwiki-zh mw-list-item"><a href="https://zh.wikipedia.org/wiki/IP%E5%A4%9A%E5%AA%92%E4%BD%93%E5%AD%90%E7%B3%BB%E7%BB%9F" title="IP多媒体子系统 – Chinese" lang="zh" hreflang="zh" data-title="IP多媒体子系统" data-language-autonym="中文" data-language-local-name="Chinese" class="interlanguage-link-target"><span>中文</span></a></li> </ul> <div class="after-portlet after-portlet-lang"><span class="wb-langlinks-edit wb-langlinks-link"><a href="https://www.wikidata.org/wiki/Special:EntityPage/Q1140664#sitelinks-wikipedia" title="Edit interlanguage links" class="wbc-editpage">Edit links</a></span></div> </div> </div> </div> </header> <div class="vector-page-toolbar"> <div class="vector-page-toolbar-container"> <div id="left-navigation"> <nav aria-label="Namespaces"> <div id="p-associated-pages" class="vector-menu vector-menu-tabs mw-portlet mw-portlet-associated-pages" > <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li id="ca-nstab-main" class="selected vector-tab-noicon mw-list-item"><a href="/wiki/IP_Multimedia_Subsystem" title="View the content page [c]" accesskey="c"><span>Article</span></a></li><li id="ca-talk" class="vector-tab-noicon mw-list-item"><a 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role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/40px-Ambox_important.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/60px-Ambox_important.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/b/b4/Ambox_important.svg/80px-Ambox_important.svg.png 2x" data-file-width="40" data-file-height="40" /></span></span></div></td><td class="mbox-text"><div class="mbox-text-span"><div class="multiple-issues-text mw-collapsible"><b>This article has multiple issues.</b> Please help <b><a href="/wiki/Special:EditPage/IP_Multimedia_Subsystem" title="Special:EditPage/IP Multimedia Subsystem">improve it</a></b> or discuss these issues on the <b><a href="/wiki/Talk:IP_Multimedia_Subsystem" title="Talk:IP Multimedia Subsystem">talk page</a></b>. <small><i>(<a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove these messages</a>)</i></small> <div class="mw-collapsible-content"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-Technical plainlinks metadata ambox ambox-style ambox-technical" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/f/f2/Edit-clear.svg/40px-Edit-clear.svg.png" decoding="async" width="40" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/f/f2/Edit-clear.svg/60px-Edit-clear.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/f/f2/Edit-clear.svg/80px-Edit-clear.svg.png 2x" data-file-width="48" data-file-height="48" /></span></span></div></td><td class="mbox-text"><div class="mbox-text-span">This article <b>may be too technical for most readers to understand</b>.<span class="hide-when-compact"> Please <a class="external text" href="https://en.wikipedia.org/w/index.php?title=IP_Multimedia_Subsystem&action=edit">help improve it</a> to <a href="/wiki/Wikipedia:Make_technical_articles_understandable" title="Wikipedia:Make technical articles understandable">make it understandable to non-experts</a>, without removing the technical details.</span> <span class="date-container"><i>(<span class="date">December 2010</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1251242444"><table class="box-Abbreviations plainlinks metadata ambox ambox-style" role="presentation"><tbody><tr><td class="mbox-image"><div class="mbox-image-div"><span typeof="mw:File"><span><img alt="" 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Multimedia Subsystem">talk page</a>.</span> <span class="date-container"><i>(<span class="date">May 2011</span>)</i></span><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> </div> </div><span class="hide-when-compact"><i> (<small><a href="/wiki/Help:Maintenance_template_removal" title="Help:Maintenance template removal">Learn how and when to remove this message</a></small>)</i></span></div></td></tr></tbody></table> <p>The <b>IP Multimedia Subsystem</b> or <b>IP Multimedia Core Network Subsystem</b> (<b>IMS</b>) is a standardised <a href="/wiki/Architectural_Framework" class="mw-redirect" title="Architectural Framework">architectural framework</a> for delivering IP <a href="/wiki/Multimedia" title="Multimedia">multimedia</a> services. Historically, mobile phones have provided voice call services over a <a href="/wiki/Circuit_switching" title="Circuit switching">circuit-switched</a>-style network, rather than strictly over an IP <a href="/wiki/Packet_switching" title="Packet switching">packet-switched</a> network. Various <a href="/wiki/Voice_over_IP" title="Voice over IP">voice over IP</a> technologies are available on smartphones; IMS provides a standard protocol across vendors. </p><p>IMS was originally designed by the wireless <a href="/wiki/Standardization" title="Standardization">standards</a> body <a href="/wiki/3rd_Generation_Partnership_Project" class="mw-redirect" title="3rd Generation Partnership Project">3rd Generation Partnership Project</a> (3GPP), as a part of the vision for evolving mobile networks beyond <a href="/wiki/GSM" title="GSM">GSM</a>. Its original formulation (3GPP Rel-5) represented an approach for delivering Internet services over <a href="/wiki/GPRS" class="mw-redirect" title="GPRS">GPRS</a>. This vision was later updated by 3GPP, <a href="/wiki/3GPP2" class="mw-redirect" title="3GPP2">3GPP2</a> and <a href="/wiki/European_Telecommunications_Standards_Institute" title="European Telecommunications Standards Institute">ETSI</a> <a href="/wiki/TISPAN" class="mw-redirect" title="TISPAN">TISPAN</a> by requiring support of networks other than <a href="/wiki/GPRS" class="mw-redirect" title="GPRS">GPRS</a>, such as <a href="/wiki/Wireless_LAN" title="Wireless LAN">Wireless LAN</a>, <a href="/wiki/CDMA2000" title="CDMA2000">CDMA2000</a> and fixed lines. </p><p>IMS uses <a href="/wiki/IETF" class="mw-redirect" title="IETF">IETF</a> protocols wherever possible, e.g., the <a href="/wiki/Session_Initiation_Protocol" title="Session Initiation Protocol">Session Initiation Protocol</a> (SIP). According to the 3GPP, IMS is not intended to standardize applications, but rather to aid the access of multimedia and voice applications from wireless and wireline terminals, i.e., to create a form of <a href="/wiki/Fixed%E2%80%93mobile_convergence" title="Fixed–mobile convergence">fixed-mobile convergence</a> (FMC).<sup id="cite_ref-23.228_1-0" class="reference"><a href="#cite_note-23.228-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> This is done by having a horizontal control layer that isolates the access network from the <a href="/wiki/Service_layer" title="Service layer">service layer</a>. From a logical architecture perspective, services need not have their own control functions, as the control layer is a common horizontal layer. However, in implementation this does not necessarily map into greater reduced cost and complexity. </p><p>Alternative and overlapping technologies for access and provisioning of services across wired and wireless networks include combinations of <a href="/wiki/Generic_Access_Network" class="mw-redirect" title="Generic Access Network">Generic Access Network</a>, <a href="/wiki/Softswitch" title="Softswitch">softswitches</a> and "naked" SIP. </p><p>Since it is becoming increasingly easier to access content and contacts using mechanisms outside the control of traditional wireless/fixed operators, the interest of IMS is being challenged.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> </p><p>Examples of global standards based on IMS are <a href="/wiki/Multimedia_telephony" title="Multimedia telephony">MMTel</a> which is the basis for Voice over LTE (<a href="/wiki/VoLTE" class="mw-redirect" title="VoLTE">VoLTE</a>), <a href="/wiki/Generic_Access_Network" class="mw-redirect" title="Generic Access Network">Wi-Fi Calling</a> (VoWIFI), <a href="/wiki/Video_over_LTE" title="Video over LTE">Video over LTE</a> (ViLTE), SMS/MMS over WiFi and LTE, <a href="/wiki/USSD" class="mw-redirect" title="USSD">Unstructured Supplementary Service Data</a> (USSD) over LTE, and <a href="/wiki/Rich_Communication_Services" title="Rich Communication Services">Rich Communication Services</a> (RCS), which is also known as joyn or Advanced Messaging, and now RCS is operator's implementation. RCS also further added Presence/EAB (enhanced address book) functionality.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li>IMS was defined by an industry forum called 3G.IP, formed in 1999. 3G.IP developed the initial IMS architecture, which was brought to the 3rd Generation Partnership Project (<a href="/wiki/3GPP" title="3GPP">3GPP</a>), as part of their standardization work for <a href="/wiki/3G" title="3G">3G</a> mobile phone systems in <a href="/wiki/Universal_Mobile_Telecommunications_System" class="mw-redirect" title="Universal Mobile Telecommunications System">UMTS</a> networks. It first appeared in Release 5 (<a href="/wiki/Evolution_to_3G" class="mw-redirect" title="Evolution to 3G">evolution from 2G to 3G networks</a>), when SIP-based multimedia was added. Support for the older <a href="/wiki/GSM" title="GSM">GSM</a> and <a href="/wiki/GPRS" class="mw-redirect" title="GPRS">GPRS</a> networks was also provided.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup></li> <li><a href="/wiki/3rd_Generation_Partnership_Project_2" title="3rd Generation Partnership Project 2">3GPP2</a> (a different organization from 3GPP) based their CDMA2000 Multimedia Domain (MMD) on 3GPP IMS, adding support for <a href="/wiki/CDMA2000" title="CDMA2000">CDMA2000</a>.</li> <li>3GPP release 6 added interworking with <a href="/wiki/Wireless_LAN" title="Wireless LAN">WLAN</a>, inter-operability between IMS using different IP-connectivity networks, routing group identities, multiple registration and forking, presence, speech recognition and speech-enabled services (<a href="/wiki/Push_to_talk" class="mw-redirect" title="Push to talk">Push to talk</a>).</li> <li>3GPP release 7 added support for <a href="/wiki/Fixed_phone" class="mw-redirect" title="Fixed phone">fixed</a> networks by working together with <a href="/wiki/TISPAN" class="mw-redirect" title="TISPAN">TISPAN</a> release R1.1, the function of AGCF (access gateway control function) and PES (<a href="/wiki/Public_switched_telephone_network" title="Public switched telephone network">PSTN</a> emulation service) are introduced to the wire-line network for the sake of inheritance of services which can be provided in PSTN network. AGCF works as a bridge interconnecting the IMS networks and the Megaco/H.248 networks. Megaco/H.248 networks offers the possibility to connect terminals of the old legacy networks to the new generation of networks based on IP networks. AGCF acts a SIP User agent towards the IMS and performs the role of P-CSCF. SIP User Agent functionality is included in the AGCF, and not on the customer device but in the network itself. Also added voice call continuity between circuit switching and packet switching domain (<a href="/wiki/Voice_call_continuity" title="Voice call continuity">VCC</a>), fixed broadband connection to the IMS, interworking with non-IMS networks, policy and charging control (<a href="/w/index.php?title=Policy_and_charging_control&action=edit&redlink=1" class="new" title="Policy and charging control (page does not exist)">PCC</a>), emergency sessions. It also added SMS over IP.<sup id="cite_ref-:0_5-0" class="reference"><a href="#cite_note-:0-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup></li> <li>3GPP release 8 added support for <a href="/wiki/3GPP_long-term_evolution" class="mw-redirect" title="3GPP long-term evolution">LTE</a> / <a href="/wiki/System_architecture_evolution" class="mw-redirect" title="System architecture evolution">SAE</a>, multimedia session continuity, enhanced emergency sessions, SMS over SGs<sup id="cite_ref-:0_5-1" class="reference"><a href="#cite_note-:0-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and IMS centralized services.</li> <li>3GPP release 9 added support for IMS emergency calls over <a href="/wiki/GPRS" class="mw-redirect" title="GPRS">GPRS</a> and <a href="/wiki/Evolved_Packet_System" class="mw-redirect" title="Evolved Packet System">EPS</a>, enhancements to <a href="/wiki/Multimedia_telephony" title="Multimedia telephony">multimedia telephony</a>, IMS <a href="/w/index.php?title=Media_plane&action=edit&redlink=1" class="new" title="Media plane (page does not exist)">media plane</a> security, enhancements to services centralization and continuity.</li> <li>3GPP release 10 added support for inter device transfer, enhancements to the single radio voice call continuity (SRVCC), enhancements to IMS emergency sessions.</li> <li>3GPP release 11 added <a href="/wiki/Unstructured_Supplementary_Service_Data" title="Unstructured Supplementary Service Data">USSD</a> simulation service, network-provided location information for IMS, <a href="/wiki/SMS" title="SMS">SMS</a> submit and delivery without MSISDN in IMS, and overload control.</li></ul> <p>Some operators opposed IMS because it was seen as complex and expensive. In response, a cut-down version of IMS—enough of IMS to support voice and SMS over the LTE network—was defined and standardized in 2010 as <a href="/wiki/Voice_over_LTE" title="Voice over LTE">Voice over LTE</a> (VoLTE).<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Architecture">Architecture</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=2" title="Edit section: Architecture"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-center" typeof="mw:File/Frame"><a href="/wiki/File:Ims_overview.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/6/60/Ims_overview.png" decoding="async" width="720" height="540" class="mw-file-element" data-file-width="720" data-file-height="540" /></a><figcaption>3GPP / TISPAN IMS architectural overview</figcaption></figure> <figure class="mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Ims_overview-2.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Ims_overview-2.png/550px-Ims_overview-2.png" decoding="async" width="550" height="515" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/83/Ims_overview-2.png/825px-Ims_overview-2.png 1.5x, //upload.wikimedia.org/wikipedia/commons/8/83/Ims_overview-2.png 2x" data-file-width="972" data-file-height="910" /></a><figcaption>3GPP / TISPAN IMS architectural overview – HSS in IMS layer (as by standard)</figcaption></figure> <p>Each of the functions in the diagram is explained below. </p><p>The IP multimedia core network subsystem is a collection of different functions, linked by standardized interfaces, which grouped form one IMS administrative network.<sup id="cite_ref-29.228_7-0" class="reference"><a href="#cite_note-29.228-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> A function is not a node (hardware box): An implementer is free to combine two functions in one node, or to split a single function into two or more nodes. Each node can also be present multiple times in a single network, for dimensioning, load balancing or organizational issues. </p> <div class="mw-heading mw-heading3"><h3 id="Access_network">Access network</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=3" title="Edit section: Access network"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The user can connect to IMS in various ways, most of which use the standard IP. IMS terminals (such as <a href="/wiki/Mobile_phone" title="Mobile phone">mobile phones</a>, <a href="/wiki/Personal_digital_assistant" title="Personal digital assistant">personal digital assistants</a> (PDAs) and computers) can register directly on IMS, even when they are <a href="/wiki/Roaming" title="Roaming">roaming</a> in another network or country (the visited network). The only requirement is that they can use IP and run SIP user agents. Fixed access (e.g., <a href="/wiki/Digital_subscriber_line" title="Digital subscriber line">digital subscriber line</a> (DSL), <a href="/wiki/Cable_modem" title="Cable modem">cable modems</a>, <a href="/wiki/Ethernet" title="Ethernet">Ethernet</a>, <a href="/wiki/Fiber_to_the_x" title="Fiber to the x">FTTx</a>), mobile access (e.g. <a href="/wiki/5G_NR" title="5G NR">5G NR</a>, <a href="/wiki/LTE_(telecommunication)" title="LTE (telecommunication)">LTE</a>, <a href="/wiki/W-CDMA" class="mw-redirect" title="W-CDMA">W-CDMA</a>, <a href="/wiki/CDMA2000" title="CDMA2000">CDMA2000</a>, <a href="/wiki/GSM" title="GSM">GSM</a>, <a href="/wiki/GPRS" class="mw-redirect" title="GPRS">GPRS</a>) and wireless access (e.g., <a href="/wiki/Wireless_LAN" title="Wireless LAN">WLAN</a>, <a href="/wiki/WiMAX" title="WiMAX">WiMAX</a>) are all supported. Other phone systems like <a href="/wiki/Plain_old_telephone_service" title="Plain old telephone service">plain old telephone service</a> (POTS—the old analogue telephones), <a href="/wiki/H.323" title="H.323">H.323</a> and non IMS-compatible systems, are supported through <a href="/wiki/VoIP_gateway" class="mw-redirect" title="VoIP gateway">gateways</a>. </p> <div class="mw-heading mw-heading3"><h3 id="Core_network">Core network</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=4" title="Edit section: Core network"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><b>HSS – Home subscriber server:</b><br /> The <i>home subscriber server</i> (HSS), or <i>user profile server function</i> (UPSF), is a master user database that supports the IMS network entities that actually handle <a href="/wiki/Telecommunication" class="mw-redirect" title="Telecommunication">calls</a>. It contains the subscription-related information (subscriber <a href="/wiki/User_profile" title="User profile">profiles</a>), performs <a href="/wiki/Authentication" title="Authentication">authentication</a> and <a href="/wiki/Authorization" title="Authorization">authorization</a> of the user, and can provide information about the subscriber's location and IP information. It is similar to the GSM <a href="/wiki/Network_Switching_Subsystem#Home_location_register_(HLR)" class="mw-redirect" title="Network Switching Subsystem">home location register</a> (HLR) and <a href="/wiki/Network_Switching_Subsystem#Authentication_centre_(AUC)" class="mw-redirect" title="Network Switching Subsystem">Authentication centre</a> (AuC). </p><p>A <i><a href="/wiki/Subscriber_location_function" title="Subscriber location function">subscriber location function</a></i> (SLF) is needed to map user addresses when multiple HSSs are used. </p><p><b>User identities:</b><br /> Various identities may be associated with IMS: IP multimedia private identity (IMPI), IP multimedia public identity (IMPU), globally routable user agent URI (GRUU), wildcarded public user identity. Both IMPI and IMPU are not phone numbers or other series of digits, but <a href="/wiki/Uniform_resource_identifier" class="mw-redirect" title="Uniform resource identifier">uniform resource identifier</a> (URIs), that can be digits (a Tel URI, such as <i><a rel="nofollow" class="external free" href="tel:+1-555-123-4567">tel:+1-555-123-4567</a></i>) or alphanumeric identifiers (a SIP URI, such as <i><a rel="nofollow" class="external free" href="sip:john.doe@example.com">sip:john.doe@example.com</a>" ).</i> </p><p><b>IP Multimedia Private Identity:</b><br /> The <i>IP Multimedia Private Identity</i> (IMPI) is a unique permanently allocated global identity assigned by the home network operator. It has the form of a Network Access Identifier(NAI) i.e. user.name@domain, and is used, for example, for Registration, Authorization, Administration, and Accounting purposes. Every IMS user shall have one IMPI. </p><p><b>IP Multimedia Public Identity:</b><br /> The <i>IP Multimedia Public Identity</i> (IMPU) is used by any user for requesting communications to other users (e.g. this might be included on a <a href="/wiki/Business_card" title="Business card">business card</a>). Also known as Address of Record (AOR). There can be multiple IMPU per IMPI. The IMPU can also be shared with another phone, so that both can be reached with the same identity (for example, a single phone-number for an entire family). </p><p><b>Globally Routable User Agent URI:</b><br /> <i>Globally Routable User Agent URI</i> (GRUU) is an identity that identifies a unique combination of IMPU and <a href="/wiki/User_equipment" title="User equipment">UE</a> instance. There are two types of GRUU: Public-GRUU (P-GRUU) and Temporary GRUU (T-GRUU). </p> <ul><li>P-GRUU reveal the IMPU and are very long lived.</li> <li>T-GRUU do not reveal the IMPU and are valid until the contact is explicitly de-registered or the current registration expires</li></ul> <p><b>Wildcarded Public User Identity:</b><br /> A <i>wildcarded Public User Identity</i> expresses a set of IMPU grouped together. </p><p>The HSS subscriber database contains the IMPU, IMPI, <a href="/wiki/International_Mobile_Subscriber_Identity" class="mw-redirect" title="International Mobile Subscriber Identity">IMSI</a>, <a href="/wiki/MSISDN" title="MSISDN">MSISDN</a>, subscriber service profiles, service triggers, and other information. </p> <div class="mw-heading mw-heading4"><h4 id="Call_Session_Control_Function_(CSCF)"><span id="Call_Session_Control_Function_.28CSCF.29"></span>Call Session Control Function (CSCF)</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=5" title="Edit section: Call Session Control Function (CSCF)"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Several roles of SIP servers or proxies, collectively called Call Session Control Function (CSCF), are used to process SIP signaling packets in the IMS. </p> <ul><li>A <i>Proxy-CSCF</i> (P-CSCF) is a <a href="/wiki/SIP_proxy" class="mw-redirect" title="SIP proxy">SIP proxy</a> that is the first point of contact for the IMS terminal. It can be located either in the visited network (in full IMS networks) or in the home network (when the visited network is not IMS compliant yet). Some networks may use a <a href="/wiki/Session_Border_Controller" class="mw-redirect" title="Session Border Controller">Session Border Controller</a> (SBC) for this function. The P-CSCF is at its core a specialized SBC for the <a href="/wiki/User%E2%80%93network_interface" title="User–network interface">User–network interface</a> which not only protects the network, but also the IMS terminal. The use of an additional SBC between the IMS terminal and the P-CSCF is unnecessary and infeasible due to the signaling being encrypted on this leg. The terminal discovers its P-CSCF with either <a href="/wiki/Dynamic_Host_Configuration_Protocol" title="Dynamic Host Configuration Protocol">DHCP</a>, or it may be configured (e.g. during initial provisioning or via a 3GPP IMS Management Object (MO)) or in the <a href="/wiki/IP_Multimedia_Services_Identity_Module" title="IP Multimedia Services Identity Module">ISIM</a> or assigned in the <a href="/wiki/PDP_Context" class="mw-redirect" title="PDP Context">PDP Context</a> (in <a href="/wiki/General_Packet_Radio_Service" title="General Packet Radio Service">General Packet Radio Service</a> (GPRS)). <ul><li>It is assigned to an IMS terminal before registration, and does not change for the duration of the registration.</li> <li>It sits on the path of all signaling, and can inspect every signal; the IMS terminal must ignore any other unencrypted signaling.</li> <li>It provides subscriber authentication and may establish an <a href="/wiki/IPsec" title="IPsec">IPsec</a> or <a href="/wiki/Transport_Layer_Security" title="Transport Layer Security">TLS</a> security association with the IMS terminal. This prevents <a href="/wiki/Spoofing_attack" title="Spoofing attack">spoofing attacks</a> and <a href="/wiki/Replay_attack" title="Replay attack">replay attacks</a> and protects the privacy of the subscriber.</li> <li>It inspects the signaling and ensures that the IMS terminals do not misbehave (e.g. change normal signaling routes, disobey home network's routing policy).</li> <li>It can compress and decompress SIP messages using <a href="/wiki/SigComp" class="mw-redirect" title="SigComp">SigComp</a>, which reduces the round-trip over slow radio links.</li> <li>It may include a Policy Decision Function (PDF), which authorizes media plane resources e.g., <a href="/wiki/Quality_of_service" title="Quality of service">quality of service</a> (QoS) over the media plane. It is used for policy control, bandwidth management, etc. The PDF can also be a separate function.</li> <li>It also generates charging records.</li></ul></li> <li>An <i>Interrogating-CSCF</i> (I-CSCF) is another SIP function located at the edge of an administrative domain. Its IP address is published in the <a href="/wiki/Domain_Name_System" title="Domain Name System">Domain Name System</a> (DNS) of the domain (using <a href="/wiki/NAPTR" class="mw-redirect" title="NAPTR">NAPTR</a> and <a href="/wiki/SRV_record" title="SRV record">SRV</a> type of DNS records), so that remote servers can find it, and use it as a forwarding point (e.g., registering) for SIP packets to this domain. <ul><li>it queries the HSS to retrieve the address of the S-CSCF and assign it to a user performing SIP registration</li> <li>it also forwards SIP request or response to the S-CSCF</li> <li>Up to Release 6 it can also be used to hide the internal network from the outside world (encrypting parts of the SIP message), in which case it's called a <i>Topology Hiding Inter-network Gateway</i> (THIG). From Release 7 onwards this "entry point" function is removed from the I-CSCF and is now part of the <i>Interconnection Border Control Function</i> (IBCF). The IBCF is used as gateway to external networks, and provides <a href="/wiki/Network_address_translation" title="Network address translation">NAT</a> and <a href="/wiki/Firewall_(networking)" class="mw-redirect" title="Firewall (networking)">firewall</a> functions (<a href="/wiki/Firewall_pinhole" title="Firewall pinhole">pinholing</a>). The IBCF is a <a href="/wiki/Session_border_controller" title="Session border controller">session border controller</a> specialized for the <a href="/wiki/Network-to-network_interface" title="Network-to-network interface">network-to-network interface</a> (NNI).</li></ul></li> <li>A <i>Serving-CSCF</i> (S-CSCF) is the central node of the signaling plane. It is a SIP server, but performs session control too. It is always located in the home network. It uses Diameter Cx and Dx interfaces to the HSS to download user profiles and upload user-to-S-CSCF associations (the user profile is only cached locally for processing reasons and is not changed). All necessary subscriber profile information is loaded from the HSS. <ul><li>it handles SIP registrations, which allows it to bind the user location (e.g., the <a href="/wiki/IP_address" title="IP address">IP address</a> of the terminal) and the SIP address</li> <li>it sits on the path of all signaling messages of the locally registered users, and can inspect every message</li> <li>it decides to which application server(s) the SIP message will be forwarded, in order to provide their services</li> <li>it provides routing services, typically using <a href="/wiki/Electronic_Numbering" class="mw-redirect" title="Electronic Numbering">Electronic Numbering</a> (ENUM) lookups</li> <li>it enforces the policy of the network operator</li> <li>there can be multiple S-CSCFs in the network for <a href="/wiki/Load_distribution" class="mw-redirect" title="Load distribution">load distribution</a> and <a href="/wiki/High_availability" title="High availability">high availability</a> reasons. It's the HSS that assigns the S-CSCF to a user, when it's queried by the I-CSCF. There are multiple options for this purpose, including a mandatory/optional capabilities to be matched between subscribers and S-CSCFs.</li></ul></li></ul> <div class="mw-heading mw-heading4"><h4 id="Application_servers">Application servers</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=6" title="Edit section: Application servers"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">See also: <a href="/wiki/Next_generation_network_services" class="mw-redirect" title="Next generation network services">Next generation network services</a></div> <p>SIP <a href="/wiki/Application_server" title="Application server">Application servers</a> (AS) host and execute <a href="/wiki/Service_(systems_architecture)" title="Service (systems architecture)">services</a>, and interface with the S-CSCF using SIP. An example of an application server that is being developed in 3GPP is the <a href="/wiki/Voice_call_continuity" title="Voice call continuity">Voice call continuity</a> Function (VCC Server). Depending on the actual service, the AS can operate in SIP proxy mode, SIP UA (<a href="/wiki/User_agent" title="User agent">user agent</a>) mode or SIP <a href="/wiki/B2BUA" class="mw-redirect" title="B2BUA">B2BUA</a> mode. An AS can be located in the home network or in an external third-party network. If located in the home network, it can query the HSS with the Diameter Sh or Si interfaces (for a SIP-AS). </p> <ul><li>SIP AS: Host and execute IMS specific services</li> <li><i>IP Multimedia Service Switching Function</i> (IM-SSF): Interfaces SIP to <a href="/wiki/Camel_Application_Part" class="mw-redirect" title="Camel Application Part">CAP</a> to communicate with <a href="/wiki/Customized_Applications_for_Mobile_networks_Enhanced_Logic" title="Customized Applications for Mobile networks Enhanced Logic">CAMEL</a> Application Servers</li> <li><a href="/wiki/Open_Services_Access" title="Open Services Access">OSA</a> service capability server (OSA SCS): Interfaces SIP to the OSA framework;</li></ul> <div class="mw-heading mw-heading5"><h5 id="Functional_model">Functional model</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=7" title="Edit section: Functional model"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The AS-ILCM (Application Server - Incoming Leg Control Model) and AS-OLCM (Application Server - Outgoing Leg Control Model) store transaction state, and may optionally store session state depending on the specific service being executed. The AS-ILCM interfaces to the S-CSCF (ILCM) for an incoming leg and the AS-OLCM interfaces to the S-CSCF (OLCM) for an outgoing leg. Application Logic provides the service(s) and interacts between the AS-ILCM and AS-OLCM. </p> <div class="mw-heading mw-heading5"><h5 id="Public_Service_Identity">Public Service Identity</h5><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=8" title="Edit section: Public Service Identity"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Public Service Identities (PSI) are identities that identify services, which are hosted by application servers. As user identities, PSI takes the form of either a SIP or Tel URI. PSIs are stored in the HSS either as a distinct PSI or as a wildcarded PSI: </p> <ul><li>a distinct PSI contains the PSI that is used in routing</li> <li>a wildcarded PSI represents a collection of PSIs.</li></ul> <div class="mw-heading mw-heading4"><h4 id="Media_servers">Media servers</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=9" title="Edit section: Media servers"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The <i>Media Resource Function</i> (MRF) provides media related functions such as <a href="/wiki/Media_manipulation" title="Media manipulation">media manipulation</a> (e.g. voice stream mixing) and playing of tones and announcements. </p><p>Each MRF is further divided into a <i>media resource function controller</i> (MRFC) and a <i>media resource function processor</i> (MRFP). </p> <ul><li>The MRFC is a signalling plane node that interprets information coming from an AS and S-CSCF to control the MRFP</li> <li>The MRFP is a media plane node used to mix, source or process media streams. It can also manage access right to shared resources.</li></ul> <p>The <i>Media Resource Broker</i> (MRB) is a functional entity that is responsible for both collection of appropriate published MRF information and supplying of appropriate MRF information to consuming entities such as the AS. MRB can be used in two modes: </p> <ul><li>Query mode: AS queries the MRB for media and sets up the call using the response of MRB</li> <li>In-Line Mode: AS sends a SIP INVITE to the MRB. The MRB sets up the call</li></ul> <div class="mw-heading mw-heading4"><h4 id="Breakout_gateway">Breakout gateway</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=10" title="Edit section: Breakout gateway"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A <i>Breakout Gateway Control Function</i> (BGCF) is a SIP proxy which processes requests for routing from an S-CSCF when the S-CSCF has determined that the session cannot be routed using DNS or ENUM/DNS. It includes routing functionality based on telephone numbers. </p> <div class="mw-heading mw-heading4"><h4 id="PSTN_gateways">PSTN gateways</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=11" title="Edit section: PSTN gateways"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>A PSTN/CS gateway interfaces with <a href="/wiki/PSTN" class="mw-redirect" title="PSTN">PSTN</a> <a href="/wiki/Circuit_switching" title="Circuit switching">circuit switched</a> (CS) networks. For signalling, CS networks use <a href="/wiki/ISDN_User_Part" title="ISDN User Part">ISDN User Part</a> (ISUP) (or <a href="/wiki/Bearer_Independent_Call_Control" class="mw-redirect" title="Bearer Independent Call Control">BICC</a>) over <a href="/wiki/Message_Transfer_Part" title="Message Transfer Part">Message Transfer Part</a> (MTP), while IMS uses SIP over IP. For media, CS networks use <a href="/wiki/Pulse-code_modulation" title="Pulse-code modulation">Pulse-code modulation</a> (PCM), while IMS uses <a href="/wiki/Real-time_Transport_Protocol" title="Real-time Transport Protocol">Real-time Transport Protocol</a> (RTP). </p> <ul><li>A signalling gateway (SGW) interfaces with the signalling plane of the CS. It transforms lower layer protocols as <a href="/wiki/Stream_Control_Transmission_Protocol" title="Stream Control Transmission Protocol">Stream Control Transmission Protocol</a> (SCTP, an IP protocol) into <a href="/wiki/Message_Transfer_Part" title="Message Transfer Part">Message Transfer Part</a> (MTP, a <a href="/wiki/Signalling_System_7" class="mw-redirect" title="Signalling System 7">Signalling System 7</a> (SS7) protocol), to pass <a href="/wiki/ISDN_User_Part" title="ISDN User Part">ISDN User Part</a> (ISUP) from the MGCF to the CS network. The SGW does call control protocol conversion between SIP and ISUP/BICC under the control of the MGCF.</li> <li>A <i>media gateway controller function</i> (MGCF) is a SIP endpoint that interfaces with the SGW over SCTP. It also controls the resources in a <i><a href="/wiki/Media_Gateway" class="mw-redirect" title="Media Gateway">Media Gateway</a></i> (MGW) across an <a href="/wiki/Gateway_Control_Protocol" class="mw-redirect" title="Gateway Control Protocol">H.248</a> interface.</li> <li>A <i><a href="/wiki/Media_gateway" title="Media gateway">media gateway</a></i> (MGW) interfaces with the media plane of the CS network, by converting between <a href="/wiki/Real-time_Transport_Protocol" title="Real-time Transport Protocol">RTP</a> and <a href="/wiki/PCM" class="mw-redirect" title="PCM">PCM</a>. It can also transcode when the <a href="/wiki/Codec" title="Codec">codecs</a> don't match (e.g., IMS might use <a href="/wiki/Adaptive_Multi-Rate" class="mw-redirect" title="Adaptive Multi-Rate">AMR</a>, PSTN might use <a href="/wiki/G.711" title="G.711">G.711</a>).</li></ul> <div class="mw-heading mw-heading4"><h4 id="Media_resources">Media resources</h4><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=12" title="Edit section: Media resources"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Media Resources are those components that operate on the media plane and are under the control of IMS core functions. Specifically, <i><a href="/wiki/Media_Server" class="mw-redirect" title="Media Server">Media Server</a></i> (MS) and <i><a href="/wiki/Media_gateway" title="Media gateway">Media gateway</a></i> (MGW) </p> <div class="mw-heading mw-heading3"><h3 id="NGN_interconnection">NGN interconnection <span class="anchor" id="SoIx"></span><span class="anchor" id="CoIx"></span></h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=13" title="Edit section: NGN interconnection"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are two types of <a href="/wiki/Next_Generation_Networking" class="mw-redirect" title="Next Generation Networking">next-generation networking</a> interconnection: </p> <ul><li><b>Service-oriented interconnection</b> (SoIx): The physical and logical linking of NGN domains that allows carriers and service providers to offer services over NGN (i.e., IMS and PES) platforms with control, signalling (i.e., session based), which provides defined levels of interoperability. For instance, this is the case of "carrier grade" voice and/or multimedia services over IP interconnection. "Defined levels of interoperability" are dependent upon the service or the QoS or the Security, etc.</li> <li><b>Connectivity-oriented interconnection</b> (CoIx): The physical and logical linking of carriers and service providers based on simple IP connectivity irrespective of the levels of interoperability. For example, an IP interconnection of this type is not aware of the specific end to end service and, as a consequence, service specific network performance, QoS and security requirements are not necessarily assured. This definition does not exclude that some services may provide a defined level of interoperability. However, only SoIx fully satisfies NGN interoperability requirements.</li></ul> <p>An NGN interconnection mode can be direct or indirect. Direct interconnection refers to the interconnection between two network domains without any intermediate network domain. Indirect interconnection at one layer refers to the interconnection between two network domains with one or more intermediate network domain(s) acting as <a href="/w/index.php?title=Transit_network&action=edit&redlink=1" class="new" title="Transit network (page does not exist)">transit networks</a>. The intermediate network domain(s) provide(s) transit functionality to the two other network domains. Different interconnection modes may be used for carrying <a href="/wiki/Service_layer" title="Service layer">service layer</a> signalling and media traffic. </p> <div class="mw-heading mw-heading3"><h3 id="Charging">Charging</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=14" title="Edit section: Charging"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Offline charging is applied to users who pay for their services periodically (e.g., at the end of the month). <a href="/wiki/Online_charging_system" title="Online charging system">Online charging</a>, also known as credit-based charging, is used for <a href="/wiki/Prepayment_for_service" title="Prepayment for service">prepaid</a> services, or real-time credit control of postpaid services. Both may be applied to the same session. </p><p><i>Charging function addresses</i> are addresses distributed to each IMS entities and provide a common location for each entity to send charging information. <i>charging data function</i> (CDF) addresses are used for offline billing and <i>Online Charging Function</i> (OCF) for online billing. </p> <ul><li>Offline Charging : All the SIP network entities (P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS) involved in the session use the <a href="/wiki/Diameter_(protocol)" title="Diameter (protocol)">Diameter</a> Rf interface to send accounting information to a CDF located in the same domain. The CDF will collect all this information, and build a <i>call detail record</i> (CDR), which is sent to the billing system of the domain.<br />Each session carries an <i>IMS Charging Identifier</i> (ICID) as a unique identifier generated by the first IMS entity involved in a SIP transaction and used for the correlation with CDRs. <i>Inter Operator Identifier</i> (IOI) is a globally unique identifier shared between sending and receiving networks. Each domain has its own charging network. Billing systems in different domains will also exchange information, so that <a href="/wiki/Roaming" title="Roaming">roaming</a> charges can be applied.</li> <li>Online charging : The S-CSCF talks to a <i>IMS gateway function</i> (IMS-GWF) which looks like a regular SIP application server. The IMS-GWF can signal the S-CSCF to terminate the session when the user runs out of credits during a session. The AS and MRFC use the <a href="/wiki/Diameter_(protocol)" title="Diameter (protocol)">Diameter</a> Ro interface towards an OCF. <ul><li>When <i>immediate event charging</i> (IEC) is used, a number of credit units is immediately deducted from the user's account by the ECF and the MRFC or AS is then authorized to provide the service. The service is not authorized when not enough credit units are available.</li> <li>When <i>event charging with unit reservation</i> (ECUR) is used, the ECF (event charging function) first reserves a number of credit units in the user's account and then authorizes the MRFC or the AS. After the service is over, the number of spent credit units is reported and deducted from the account; the reserved credit units are then cleared.</li></ul></li></ul> <div class="mw-heading mw-heading3"><h3 id="IMS-based_PES_architecture">IMS-based PES architecture</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=15" title="Edit section: IMS-based PES architecture"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>IMS-based PES (PSTN Emulation System) provides IP networks services to analog devices. IMS-based PES allows non-IMS devices to appear to IMS as normal SIP users. Analog terminal using standard analog interfaces can connect to IMS-based PES in two ways: </p> <ul><li>Via A-MGW (Access Media Gateway) that is linked and controlled by AGCF. AGCF is placed within the Operators network and controls multiple A-MGW. A-MGW and AGCF communicate using <a href="/wiki/H.248" title="H.248">H.248</a>.1 (<a href="/wiki/Megaco" class="mw-redirect" title="Megaco">Megaco</a>) over the P1 reference point. POTS phone connect to A-MGW over the z interface. The signalling is converted to H.248 in the A-MGW and passed to AGCF. AGCF interprets the H.248 signal and other inputs from the A-MGW to format H.248 messages into appropriate SIP messages. AGCF presents itself as P-CSCF to the S-CSCF and passes generated SIP messages to S-CSCF or to IP border via IBCF (Interconnection Border Control Function). Service presented to S-CSCF in SIP messages trigger PES AS. AGCF has also certain service independent logic, for example on receipt of off-hook event from A-MGW, the AGCF requests the A-MGW to play dial tone.</li> <li>Via VGW (VoIP-Gateway) or SIP Gateway/Adapter on customer premises. POTS phones via VOIP Gateway connect to P-CSCF directly. Operators mostly use <a href="/wiki/Session_border_controller" title="Session border controller">session border controllers</a> between VoIP gateways and P-CSCFs for security and to hide network topology. VoIP gateway link to IMS using <a href="/wiki/Session_Initiation_Protocol" title="Session Initiation Protocol">SIP</a> over Gm reference point. The conversion from POTS service over the z interface to SIP occurs in the customer premises VoIP gateway. POTS signaling is converted to SIP and passed on to P-CSCF. VGW acts as SIP user agent and appears to P-CSCF as SIP terminal.</li></ul> <p>Both A-MGW and VGW are unaware of the services. They only relay call control signalling to and from the PSTN terminal. Session control and handling is done by IMS components. </p> <div class="mw-heading mw-heading3"><h3 id="Interfaces_description">Interfaces description</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=16" title="Edit section: Interfaces description"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:TISPAN_IMS_Reference_Architecture.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/en/thumb/9/9c/TISPAN_IMS_Reference_Architecture.png/650px-TISPAN_IMS_Reference_Architecture.png" decoding="async" width="650" height="488" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/9/9c/TISPAN_IMS_Reference_Architecture.png 1.5x" data-file-width="960" data-file-height="720" /></a><figcaption> TISPAN IMS architecture with interfaces</figcaption></figure> <table class="wikitable"> <tbody><tr> <th>Interface name </th> <th>IMS entities </th> <th>Description </th> <th>Protocol </th> <th>Technical specification </th></tr> <tr> <td>Cr </td> <td>MRFC, AS </td> <td>Used by MRFC to fetch documents (e.g. scripts, announcement files, and other resources) from an AS. Also used for media control related commands. </td> <td>TCP/SCTP channels </td></tr> <tr> <td>Cx </td> <td>(I-CSCF, S-CSCF), HSS </td> <td>Used to send subscriber data to the S-CSCF; including filter criteria and their priority. Also used to furnish CDF and/or OCF addresses. </td> <td>Diameter </td> <td>TS29.229, TS29.212 </td></tr> <tr> <td>Dh </td> <td>AS (SIP AS, OSA, IM-SSF) <-> SLF </td> <td>Used by AS to find the HSS holding the user profile information in a multi-HSS environment. DH_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name. </td> <td>Diameter </td></tr> <tr> <td>Dx </td> <td>(I-CSCF or S-CSCF) <-> SLF </td> <td>Used by I-CSCF or S-CSCF to find a correct HSS in a multi-HSS environment. DX_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name. </td> <td>Diameter </td> <td>TS29.229, TS29.212 </td></tr> <tr> <td>Gm </td> <td>UE, P-CSCF </td> <td>Used to exchange messages between SIP user equipment (UE) or Voip gateway and P-CSCF </td> <td>SIP </td></tr> <tr> <td>Go </td> <td>PDF, GGSN </td> <td>Allows operators to control QoS in a user plane and exchange charging correlation information between IMS and GPRS network </td> <td>COPS (Rel5), diameter (Rel6+) </td></tr> <tr> <td>Gq </td> <td>P-CSCF, PDF </td> <td>Used to exchange policy decisions-related information between P-CSCF and PDF </td> <td>Diameter </td></tr> <tr> <td>Gx </td> <td>PCEF, PCRF </td> <td>Used to exchange policy decisions-related information between PCEF and PCRF </td> <td>Diameter </td> <td>TS29.211, TS29.212 </td></tr> <tr> <td>Gy </td> <td>PCEF, OCS </td> <td>Used for online flow-based bearer charging. Functionally equivalent to Ro interface </td> <td>Diameter </td> <td>TS23.203, TS32.299 </td></tr> <tr> <td>ISC </td> <td>S-CSCF <-> AS </td> <td>Reference point between S-CSCF and AS. Main functions are to : <ul><li>Notify the AS of the registered IMPU, registration state and UE capabilities</li> <li>Supply the AS with information to allow it to execute multiple services</li> <li>Convey charging function addresses</li></ul> </td> <td>SIP </td></tr> <tr> <td>Ici </td> <td>IBCFs </td> <td>Used to exchange messages between an IBCF and another IBCF belonging to a different IMS network. </td> <td>SIP </td></tr> <tr> <td>Izi </td> <td>TrGWs </td> <td>Used to forward media streams from a TrGW to another TrGW belonging to a different IMS network. </td> <td>RTP </td></tr> <tr> <td>Ma </td> <td>I-CSCF <-> AS </td> <td>Main functions are to: <ul><li>Forward SIP requests which are destined to a public service identity hosted by the AS</li> <li>Originate a session on behalf of a user or public service identity, if the AS has no knowledge of a S-CSCF assigned to that user or public service identity</li> <li>Convey charging function addresses</li></ul> </td> <td>SIP </td></tr> <tr> <td>Mg </td> <td>MGCF -> I,S-CSCF </td> <td>ISUP signalling to SIP signalling and forwards SIP signalling to I-CSCF </td> <td>SIP </td></tr> <tr> <td>Mi </td> <td>S-CSCF -> BGCF </td> <td>Used to exchange messages between S-CSCF and BGCF </td> <td>SIP </td></tr> <tr> <td>Mj </td> <td>BGCF -> MGCF </td> <td>Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in the same IMS network to send SIP message from BGCF to MGCF </td> <td>SIP </td></tr> <tr> <td>Mk </td> <td>BGCF -> BGCF </td> <td>Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in another IMS network to send SIP message from BGCF to the BGCF in the other network </td> <td>SIP </td></tr> <tr> <td>Mm </td> <td>I-CSCF, S-CSCF, external IP network </td> <td>Used for exchanging messages between IMS and external IP networks </td> <td>SIP </td></tr> <tr> <td>Mn </td> <td>MGCF, IM-MGW </td> <td>Allows control of user-plane resources </td> <td>H.248 </td></tr> <tr> <td>Mp </td> <td>MRFC, MRFP </td> <td>Allows an MRFC to control media stream resources provided by an MRFP. </td> <td>H.248 </td></tr> <tr> <td>Mr<br />Mr' </td> <td>S-CSCF, MRFC<br />AS, MRFC </td> <td>Used to exchange information between S-CSCF and MRFC<br />Used to exchange session controls between AS and MRFC </td> <td>Application server sends SIP message to MRFC to play tone and announcement. This SIP message contains sufficient information to play tone and announcement or provide information to MRFC, so that it can ask more information from application server through Cr Interface. </td> <td>SIP </td></tr> <tr> <td>Mw </td> <td>P-CSCF, I-CSCF, S-CSCF, AGCF </td> <td>Used to exchange messages between CSCFs. AGCF appears as a P-CSCF to the other CSCFs </td> <td>SIP </td></tr> <tr> <td>Mx </td> <td>BGCF/CSCF, IBCF </td> <td>Used for the interworking with another IMS network, when the BGCF has determined that a breakout should occur in the other IMS network to send SIP message from BGCF to the IBCF in the other network </td> <td>SIP </td></tr> <tr> <td>P1 </td> <td>AGCF, A-MGW </td> <td>Used for call control services by AGCF to control H.248 A-MGW and residential gateways </td> <td>H.248 </td></tr> <tr> <td>P2 </td> <td>AGCF, CSCF </td> <td>Reference point between AGCF and CSCF. </td> <td>SIP </td></tr> <tr> <td>Rc </td> <td>MRB, AS </td> <td>Used by the AS to request that media resources be assigned to a call when using MRB in-line mode or in query mode </td> <td>SIP, in query mode (not specified) </td></tr> <tr> <td>Rf </td> <td>P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS </td> <td>Used to exchange offline charging information with CDF </td> <td>Diameter </td> <td>TS32.299 </td></tr> <tr> <td>Ro </td> <td>AS, MRFC, S-CSCF </td> <td>Used to exchange online charging information with OCF </td> <td>Diameter </td> <td>TS32.299 </td></tr> <tr> <td>Rx </td> <td>P-CSCF, PCRF </td> <td>Used to exchange policy and charging related information between P-CSCF and PCRF <p>Replacement for the Gq reference point. </p> </td> <td>Diameter </td> <td>TS29.214 </td></tr> <tr> <td>Sh </td> <td>AS (SIP AS, OSA SCS), HSS </td> <td>Used to exchange User Profile information (e.g., user-related data, group lists, user-service-related information or user location information or charging function addresses (used when the AS has not received the third-party REGISTER for a user)) between an AS (SIP AS or OSA SCS) and HSS. Also allow AS to activate/deactivate filter criteria stored in the HSS on a per-subscriber basis </td> <td>Diameter </td></tr> <tr> <td>Si </td> <td>IM-SSF, HSS </td> <td>Transports CAMEL subscription information, including triggers for use by CAMEL-based application services information. </td> <td>MAP </td></tr> <tr> <td>Sr </td> <td>MRFC, AS </td> <td>Used by MRFC to fetch documents (scripts and other resources) from an AS </td> <td>HTTP </td></tr> <tr> <td>Ut </td> <td>UE and SIP AS (SIP AS, OSA SCS, IM-SSF) PES AS and AGCF </td> <td>Facilitates the management of subscriber information related to services and settings </td> <td>HTTP(s), XCAP </td></tr> <tr> <td>z </td> <td>POTS, Analog phones and VoIP gateways </td> <td>Conversion of POTS services to SIP messages </td> <td> </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Session_handling">Session handling</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=17" title="Edit section: Session handling"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>One of the most important features of IMS, that of allowing for a SIP application to be dynamically and differentially (based on the user's profile) triggered, is implemented as a filter-and-redirect signalling mechanism in the S-CSCF. </p><p>The S-CSCF might apply filter criteria to determine the need to forward SIP requests to AS. It is important to note that services for the originating party will be applied in the originating network, while the services for the terminating party will be applied in the terminating network, all in the respective S-CSCFs. </p> <div class="mw-heading mw-heading3"><h3 id="Initial_filter_criteria">Initial filter criteria</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=18" title="Edit section: Initial filter criteria"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>An <b>initial filter criteria</b> (iFC) is an <a href="/wiki/XML" title="XML">XML</a>-based format used for describing control logic. iFCs represent a provisioned subscription of a user to an application. They are stored in the HSS as part of the IMS Subscription Profile and are downloaded to the S-CSCF upon user registration (for registered users) or on processing demand (for services, acting as unregistered users). iFCs are valid throughout the registration lifetime or until the User Profile is changed.<sup id="cite_ref-29.228_7-1" class="reference"><a href="#cite_note-29.228-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> </p><p>The iFC is composed of: </p> <ul><li>Priority - determines the order of checking the trigger.</li> <li>Trigger point - logical condition(s) which is verified against initial dialog creating SIP requests or stand-alone SIP requests.</li> <li>Application server URI - specifies the application server to be forwarded to when the trigger point matches.</li></ul> <p>There are two types of iFCs: </p> <ul><li>Shared - When provisioning, only a reference number (the shared iFC number) is assigned to the subscriber. During registration, only the number is sent to the CSCF, not the entire XML description. The complete XML will have previously been stored on the CSCF.</li> <li>Non-shared - when provisioning, the entire XML description of the iFC is assigned to the subscriber. During registration, the entire XML description is sent to the CSCF.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Security_aspects_of_early_IMS_and_non-3GPP_systems">Security aspects of early IMS and non-3GPP systems</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=19" title="Edit section: Security aspects of early IMS and non-3GPP systems"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>It is envisaged that security defined in TS 33.203 may not be available for a while especially because of the lack of <a href="/wiki/Universal_Subscriber_Identity_Module" class="mw-redirect" title="Universal Subscriber Identity Module">USIM</a>/<a href="/wiki/IP_Multimedia_Services_Identity_Module" title="IP Multimedia Services Identity Module">ISIM</a> interfaces and prevalence of devices that support <a href="/wiki/IPv4" title="IPv4">IPv4</a>. For this situation, to provide some protection against the most significant threats, 3GPP defines some security mechanisms, which are informally known as "early IMS security," in TR33.978. This mechanism relies on the authentication performed during the network attachment procedures, which binds between the user's profile and its IP address. This mechanism is also weak because the signaling is not protected on the <a href="/wiki/User%E2%80%93network_interface" title="User–network interface">user–network interface</a>. </p><p><a href="/wiki/CableLabs" title="CableLabs">CableLabs</a> in <a href="/wiki/PacketCable#PacketCable_2.0" title="PacketCable">PacketCable 2.0</a>, which adopted also the IMS architecture but has no USIM/ISIM capabilities in their terminals, published deltas to the 3GPP specifications where the Digest-MD5 is a valid authentication option. Later on, <a href="/wiki/TISPAN" class="mw-redirect" title="TISPAN">TISPAN</a> also did a similar effort given their fixed networks scopes, although the procedures are different. To compensate for the lack of IPsec capabilities, TLS has been added as an option for securing the Gm interface. Later 3GPP Releases have included the Digest-MD5 method, towards a Common-IMS platform, yet in its own and again different approach. Although all 3 variants of Digest-MD5 authentication have the same functionality and are the same from the IMS terminal's perspective, the implementations on the Cx interface between the S-CSCF and the HSS are different. </p> <div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=20" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/4G" title="4G">4G</a></li> <li><a href="/wiki/Generic_Access_Network" class="mw-redirect" title="Generic Access Network">Generic Access Network</a></li> <li><a href="/wiki/Image_share" class="mw-redirect" title="Image share">Image share</a></li> <li><a href="/wiki/OMA_Instant_Messaging_and_Presence_Service" title="OMA Instant Messaging and Presence Service">OMA Instant Messaging and Presence Service</a></li> <li><a href="/wiki/IP_connectivity_access_network" title="IP connectivity access network">IP connectivity access network</a></li> <li><a href="/wiki/Mobile_broadband" title="Mobile broadband">Mobile broadband</a></li> <li><a href="/wiki/Mobile_VoIP" title="Mobile VoIP">Mobile VoIP</a></li> <li><a href="/wiki/Peer-to-peer_video_sharing" title="Peer-to-peer video sharing">Peer-to-peer video sharing</a></li> <li><a href="/wiki/Service_capability_interaction_manager" title="Service capability interaction manager">Service capability interaction manager</a></li> <li><a href="/wiki/System_Architecture_Evolution" title="System Architecture Evolution">System Architecture Evolution</a></li> <li><a href="/wiki/SIMPLE_(instant_messaging_protocol)" title="SIMPLE (instant messaging protocol)">SIMPLE</a></li> <li><a href="/wiki/SIP_extensions_for_the_IP_multimedia_subsystem" class="mw-redirect" title="SIP extensions for the IP multimedia subsystem">SIP extensions for the IP multimedia subsystem</a></li> <li><a href="/wiki/Text_over_IP" title="Text over IP">Text over IP</a></li> <li><a href="/wiki/Ultra_Mobile_Broadband" class="mw-redirect" title="Ultra Mobile Broadband">Ultra Mobile Broadband</a></li> <li><a href="/wiki/Video_share" class="mw-redirect" title="Video share">Video share</a></li> <li><a href="/wiki/Voice_call_continuity" title="Voice call continuity">Voice call continuity</a></li></ul> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=21" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist 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data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px 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.cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFTechnical_Specification_Group_Services_and_System_Aspects2006" class="citation cs2">Technical Specification Group Services and System Aspects (2006), <i>IP Multimedia Subsystem (IMS), Stage 2, TS 23.228</i>, 3rd Generation Partnership Project</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IP+Multimedia+Subsystem+%28IMS%29%2C+Stage+2%2C+TS+23.228&rft.pub=3rd+Generation+Partnership+Project&rft.date=2006&rft.au=Technical+Specification+Group+Services+and+System+Aspects&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAlexander_Harrowell,_Staff_Writer2006" class="citation cs2">Alexander Harrowell, Staff Writer (October 2006), <a rel="nofollow" class="external text" href="https://web.archive.org/web/20100918042052/http://www.allbusiness.com/primary-metal-manufacturing/foundries-nonferrous/4104136-1.html"><i>A Pointless Multimedia Subsystem?</i></a>, Mobile Communications International, archived from <a rel="nofollow" class="external text" href="http://www.allbusiness.com/primary-metal-manufacturing/foundries-nonferrous/4104136-1.html">the original</a> on 2010-09-18</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+Pointless+Multimedia+Subsystem%3F&rft.pub=Mobile+Communications+International&rft.date=2006-10&rft.au=Alexander+Harrowell%2C+Staff+Writer&rft_id=http%3A%2F%2Fwww.allbusiness.com%2Fprimary-metal-manufacturing%2Ffoundries-nonferrous%2F4104136-1.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFZhaoWeiXiaZeng2012" class="citation cs2">Zhao, Peng; Wei, Qun; Xia, Hailun; Zeng, Zhimin (2012), Tan, Honghua (ed.), <span class="id-lock-subscription" title="Paid subscription required"><a rel="nofollow" class="external text" href="https://doi.org/10.1007/978-3-642-27708-5_33">"A New Mechanism of EAB in RCS"</a></span>, <i>Knowledge Discovery and Data Mining</i>, Advances in Intelligent and Soft Computing, Berlin, Heidelberg: Springer, pp. <span class="nowrap">247–</span>254, <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-642-27708-5_33">10.1007/978-3-642-27708-5_33</a>, <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-3-642-27708-5" title="Special:BookSources/978-3-642-27708-5"><bdi>978-3-642-27708-5</bdi></a><span class="reference-accessdate">, retrieved <span class="nowrap">2021-04-08</span></span></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Knowledge+Discovery+and+Data+Mining&rft.atitle=A+New+Mechanism+of+EAB+in+RCS&rft.pages=%3Cspan+class%3D%22nowrap%22%3E247-%3C%2Fspan%3E254&rft.date=2012&rft_id=info%3Adoi%2F10.1007%2F978-3-642-27708-5_33&rft.isbn=978-3-642-27708-5&rft.aulast=Zhao&rft.aufirst=Peng&rft.au=Wei%2C+Qun&rft.au=Xia%2C+Hailun&rft.au=Zeng%2C+Zhimin&rft_id=https%3A%2F%2Fdoi.org%2F10.1007%2F978-3-642-27708-5_33&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> <li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.3gpp.org/ftp/Information/WORK_PLAN/Description_Releases/">"3GPP Release Descriptions"</a>. <i>3GPP</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=3GPP&rft.atitle=3GPP+Release+Descriptions&rft_id=http%3A%2F%2Fwww.3gpp.org%2Fftp%2FInformation%2FWORK_PLAN%2FDescription_Releases%2F&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> <li id="cite_note-:0-5"><span class="mw-cite-backlink">^ <a href="#cite_ref-:0_5-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:0_5-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.3gpp.org/news-events/1268-Dispelling-LTE-Myths">"Dispelling LTE Myths"</a>. <i>www.3gpp.org</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2021-04-08</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.3gpp.org&rft.atitle=Dispelling+LTE+Myths&rft_id=https%3A%2F%2Fwww.3gpp.org%2Fnews-events%2F1268-Dispelling-LTE-Myths&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> <li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"> Ian Poole, editor. <a rel="nofollow" class="external text" href="https://www.electronics-notes.com/articles/connectivity/4g-lte-long-term-evolution/volte-voice-over-lte.php">"What is Voice over LTE, VoLTE"</a>.</span> </li> <li id="cite_note-29.228-7"><span class="mw-cite-backlink">^ <a href="#cite_ref-29.228_7-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-29.228_7-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.3gpp.org/ftp/Specs/html-info/23228.htm">"3GPP Stage 2 Specifications"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=3GPP+Stage+2+Specifications&rft_id=http%3A%2F%2Fwww.3gpp.org%2Fftp%2FSpecs%2Fhtml-info%2F23228.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></span> </li> </ol></div></div> <div class="mw-heading mw-heading2"><h2 id="Further_reading">Further reading</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=22" title="Edit section: Further reading"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCamarilloGarcía-Martín2007" class="citation book cs1">Camarillo, Gonzalo; García-Martín, Miguel A. (2007). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/3gipmultimediasu0000cama"><i>The 3G IP multimedia subsystem (IMS) : Merging the Internet and the Cellular Worlds</i></a></span> (2 ed.). Chichester [u.a.]: Wiley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-470-01818-7" title="Special:BookSources/978-0-470-01818-7"><bdi>978-0-470-01818-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+3G+IP+multimedia+subsystem+%28IMS%29+%3A+Merging+the+Internet+and+the+Cellular+Worlds&rft.place=Chichester+%5Bu.a.%5D&rft.edition=2&rft.pub=Wiley&rft.date=2007&rft.isbn=978-0-470-01818-7&rft.aulast=Camarillo&rft.aufirst=Gonzalo&rft.au=Garc%C3%ADa-Mart%C3%ADn%2C+Miguel+A.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2F3gipmultimediasu0000cama&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFPoikselkä2007" class="citation book cs1">Poikselkä, Miikka (2007). <i>The IMS : IP multimedia concepts and services</i> (2 ed.). Chichester [u.a.]: Wiley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-470-01906-1" title="Special:BookSources/978-0-470-01906-1"><bdi>978-0-470-01906-1</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+IMS+%3A+IP+multimedia+concepts+and+services&rft.place=Chichester+%5Bu.a.%5D&rft.edition=2&rft.pub=Wiley&rft.date=2007&rft.isbn=978-0-470-01906-1&rft.aulast=Poikselk%C3%A4&rft.aufirst=Miikka&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFSyed_A._Ahson,_Mohammed_Ilyas2009" class="citation book cs1">Syed A. Ahson, Mohammed Ilyas, ed. (2009). <i>IP multimedia subsystem (IMS) handbook</i>. Boca Raton: CRC Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-4200-6459-9" title="Special:BookSources/978-1-4200-6459-9"><bdi>978-1-4200-6459-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IP+multimedia+subsystem+%28IMS%29+handbook&rft.place=Boca+Raton&rft.pub=CRC+Press&rft.date=2009&rft.isbn=978-1-4200-6459-9&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWuthnowStaffordShih2010" class="citation book cs1">Wuthnow, Mark; Stafford, Matthew; Shih, Jerry (2010). <i>IMS : A New Model for Blending Applications</i>. Boca Raton: CRC Press. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1-4200-9285-1" title="Special:BookSources/978-1-4200-9285-1"><bdi>978-1-4200-9285-1</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=IMS+%3A+A+New+Model+for+Blending+Applications&rft.place=Boca+Raton&rft.pub=CRC+Press&rft.date=2010&rft.isbn=978-1-4200-9285-1&rft.aulast=Wuthnow&rft.aufirst=Mark&rft.au=Stafford%2C+Matthew&rft.au=Shih%2C+Jerry&rfr_id=info%3Asid%2Fen.wikipedia.org%3AIP+Multimedia+Subsystem" class="Z3988"></span></li></ul> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=IP_Multimedia_Subsystem&action=edit&section=23" title="Edit section: External links"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a rel="nofollow" class="external text" href="http://www.tele.pw.edu.pl/~mareks/eims/IMS_an_overview-1.pdf">A decent IMS tutorial</a></li> <li><a rel="nofollow" class="external text" href="http://www.eventhelix.com/ims/">IMS Call Flows</a></li></ul> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:IMS_call_flow.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/IMS_call_flow.png/220px-IMS_call_flow.png" decoding="async" width="220" height="205" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/d/df/IMS_call_flow.png/330px-IMS_call_flow.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/d/df/IMS_call_flow.png/440px-IMS_call_flow.png 2x" data-file-width="936" data-file-height="872" /></a><figcaption>IMS call flow with SIP messages</figcaption></figure>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?useformat=desktop&type=1x1&usesul3=0" alt="" width="1" height="1" style="border: none; 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