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<li id="toc-How_the_CCITT_standardized_virtual_circuits" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#How_the_CCITT_standardized_virtual_circuits"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.1</span> <span>How the CCITT standardized virtual circuits</span> </div> </a> <ul id="toc-How_the_CCITT_standardized_virtual_circuits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Worldwide_public_data_networks" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Worldwide_public_data_networks"> <div class="vector-toc-text"> <span class="vector-toc-numb">1.2</span> <span>Worldwide public data networks</span> </div> </a> <ul id="toc-Worldwide_public_data_networks-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Architecture" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Architecture"> <div class="vector-toc-text"> <span class="vector-toc-numb">2</span> <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-Relation_to_the_OSI_Reference_Model" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Relation_to_the_OSI_Reference_Model"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.1</span> <span>Relation to the OSI Reference Model</span> </div> </a> <ul id="toc-Relation_to_the_OSI_Reference_Model-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-User_device_support" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#User_device_support"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.2</span> <span>User device support</span> </div> </a> <ul id="toc-User_device_support-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Error_control" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Error_control"> <div class="vector-toc-text"> <span class="vector-toc-numb">2.3</span> <span>Error control</span> </div> </a> <ul id="toc-Error_control-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Addressing_and_virtual_circuits" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Addressing_and_virtual_circuits"> <div class="vector-toc-text"> <span class="vector-toc-numb">3</span> <span>Addressing and virtual circuits</span> </div> </a> <ul id="toc-Addressing_and_virtual_circuits-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Billing" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Billing"> <div class="vector-toc-text"> <span class="vector-toc-numb">4</span> <span>Billing</span> </div> </a> <ul id="toc-Billing-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-X.25_packet_types" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#X.25_packet_types"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>X.25 packet types</span> </div> </a> <ul id="toc-X.25_packet_types-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-X.25_details" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#X.25_details"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>X.25 details</span> </div> </a> <button aria-controls="toc-X.25_details-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 X.25 details subsection</span> </button> <ul id="toc-X.25_details-sublist" class="vector-toc-list"> <li id="toc-X.25_facilities" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#X.25_facilities"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.1</span> <span>X.25 facilities</span> </div> </a> <ul id="toc-X.25_facilities-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-X.25_protocol_versions" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#X.25_protocol_versions"> <div class="vector-toc-text"> <span class="vector-toc-numb">6.2</span> <span>X.25 protocol versions</span> </div> </a> <ul id="toc-X.25_protocol_versions-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Legacy" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Legacy"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Legacy</span> </div> </a> <ul id="toc-Legacy-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">8</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">9</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">10</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">11</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 aria-label="Contents" class="vector-toc-landmark"> <div id="vector-page-titlebar-toc" class="vector-dropdown vector-page-titlebar-toc vector-button-flush-left" title="Table of Contents" > <input type="checkbox" id="vector-page-titlebar-toc-checkbox" role="button" aria-haspopup="true" data-event-name="ui.dropdown-vector-page-titlebar-toc" class="vector-dropdown-checkbox " aria-label="Toggle the table of contents" > <label id="vector-page-titlebar-toc-label" for="vector-page-titlebar-toc-checkbox" class="vector-dropdown-label cdx-button cdx-button--fake-button cdx-button--fake-button--enabled cdx-button--weight-quiet cdx-button--icon-only " aria-hidden="true" ><span class="vector-icon mw-ui-icon-listBullet mw-ui-icon-wikimedia-listBullet"></span> <span class="vector-dropdown-label-text">Toggle the table of contents</span> </label> <div class="vector-dropdown-content"> <div id="vector-page-titlebar-toc-unpinned-container" class="vector-unpinned-container"> </div> </div> </div> </nav> <h1 id="firstHeading" class="firstHeading mw-first-heading"><span class="mw-page-title-main">X.25</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 32 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-32" 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">32 languages</span> </label> <div class="vector-dropdown-content"> <div class="vector-menu-content"> <ul class="vector-menu-content-list"> <li class="interlanguage-link interwiki-ar mw-list-item"><a href="https://ar.wikipedia.org/wiki/%D8%AD%D8%B2%D9%85%D8%A9_%D8%A8%D8%B1%D9%88%D8%AA%D9%88%D9%83%D9%88%D9%84%D8%A7%D8%AA_%D8%A5%D9%83%D8%B3_25" title="حزمة بروتوكولات إكس 25 – Arabic" lang="ar" hreflang="ar" data-title="حزمة بروتوكولات إكس 25" data-language-autonym="العربية" data-language-local-name="Arabic" class="interlanguage-link-target"><span>العربية</span></a></li><li class="interlanguage-link interwiki-az mw-list-item"><a href="https://az.wikipedia.org/wiki/X.25" title="X.25 – Azerbaijani" lang="az" hreflang="az" data-title="X.25" data-language-autonym="Azərbaycanca" data-language-local-name="Azerbaijani" class="interlanguage-link-target"><span>Azərbaycanca</span></a></li><li class="interlanguage-link interwiki-bs mw-list-item"><a href="https://bs.wikipedia.org/wiki/X.25" title="X.25 – Bosnian" lang="bs" hreflang="bs" data-title="X.25" data-language-autonym="Bosanski" data-language-local-name="Bosnian" class="interlanguage-link-target"><span>Bosanski</span></a></li><li class="interlanguage-link interwiki-ca mw-list-item"><a href="https://ca.wikipedia.org/wiki/X.25" title="X.25 – Catalan" lang="ca" hreflang="ca" data-title="X.25" 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/X.25" title="X.25 – Czech" lang="cs" hreflang="cs" data-title="X.25" data-language-autonym="Čeština" data-language-local-name="Czech" class="interlanguage-link-target"><span>Čeština</span></a></li><li class="interlanguage-link interwiki-da mw-list-item"><a href="https://da.wikipedia.org/wiki/X.25" title="X.25 – Danish" lang="da" hreflang="da" data-title="X.25" data-language-autonym="Dansk" data-language-local-name="Danish" class="interlanguage-link-target"><span>Dansk</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/X.25" title="X.25 – German" lang="de" hreflang="de" data-title="X.25" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-et mw-list-item"><a href="https://et.wikipedia.org/wiki/X.25" title="X.25 – Estonian" lang="et" hreflang="et" data-title="X.25" data-language-autonym="Eesti" data-language-local-name="Estonian" class="interlanguage-link-target"><span>Eesti</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Norma_X.25" title="Norma X.25 – Spanish" lang="es" hreflang="es" data-title="Norma X.25" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-eu mw-list-item"><a href="https://eu.wikipedia.org/wiki/X.25" title="X.25 – Basque" lang="eu" hreflang="eu" data-title="X.25" data-language-autonym="Euskara" data-language-local-name="Basque" class="interlanguage-link-target"><span>Euskara</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D8%A7%DA%A9%D8%B3_%DB%B2%DB%B5" title="اکس ۲۵ – Persian" lang="fa" hreflang="fa" data-title="اکس ۲۵" 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/X.25" title="X.25 – French" lang="fr" hreflang="fr" data-title="X.25" 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/X.25" title="X.25 – Korean" lang="ko" hreflang="ko" data-title="X.25" data-language-autonym="한국어" data-language-local-name="Korean" class="interlanguage-link-target"><span>한국어</span></a></li><li class="interlanguage-link interwiki-id mw-list-item"><a href="https://id.wikipedia.org/wiki/X.25" title="X.25 – Indonesian" lang="id" hreflang="id" data-title="X.25" data-language-autonym="Bahasa Indonesia" data-language-local-name="Indonesian" class="interlanguage-link-target"><span>Bahasa Indonesia</span></a></li><li class="interlanguage-link interwiki-it mw-list-item"><a href="https://it.wikipedia.org/wiki/X.25" title="X.25 – Italian" lang="it" hreflang="it" data-title="X.25" data-language-autonym="Italiano" data-language-local-name="Italian" class="interlanguage-link-target"><span>Italiano</span></a></li><li class="interlanguage-link interwiki-he mw-list-item"><a href="https://he.wikipedia.org/wiki/X.25" title="X.25 – Hebrew" lang="he" hreflang="he" data-title="X.25" data-language-autonym="עברית" data-language-local-name="Hebrew" class="interlanguage-link-target"><span>עברית</span></a></li><li class="interlanguage-link interwiki-lv mw-list-item"><a href="https://lv.wikipedia.org/wiki/X.25" title="X.25 – Latvian" lang="lv" hreflang="lv" data-title="X.25" data-language-autonym="Latviešu" data-language-local-name="Latvian" class="interlanguage-link-target"><span>Latviešu</span></a></li><li class="interlanguage-link interwiki-hu mw-list-item"><a href="https://hu.wikipedia.org/wiki/X.25" title="X.25 – Hungarian" lang="hu" hreflang="hu" data-title="X.25" data-language-autonym="Magyar" data-language-local-name="Hungarian" class="interlanguage-link-target"><span>Magyar</span></a></li><li class="interlanguage-link interwiki-ms mw-list-item"><a href="https://ms.wikipedia.org/wiki/X.25" title="X.25 – Malay" lang="ms" hreflang="ms" data-title="X.25" data-language-autonym="Bahasa Melayu" data-language-local-name="Malay" class="interlanguage-link-target"><span>Bahasa Melayu</span></a></li><li class="interlanguage-link interwiki-nl mw-list-item"><a href="https://nl.wikipedia.org/wiki/X.25" title="X.25 – Dutch" lang="nl" hreflang="nl" data-title="X.25" 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/X.25" title="X.25 – Japanese" lang="ja" hreflang="ja" data-title="X.25" 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-nn mw-list-item"><a href="https://nn.wikipedia.org/wiki/X.25" title="X.25 – Norwegian Nynorsk" lang="nn" hreflang="nn" data-title="X.25" data-language-autonym="Norsk nynorsk" data-language-local-name="Norwegian Nynorsk" class="interlanguage-link-target"><span>Norsk nynorsk</span></a></li><li class="interlanguage-link interwiki-pl mw-list-item"><a href="https://pl.wikipedia.org/wiki/X.25" title="X.25 – Polish" lang="pl" hreflang="pl" data-title="X.25" 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/X.25" title="X.25 – Portuguese" lang="pt" hreflang="pt" data-title="X.25" data-language-autonym="Português" data-language-local-name="Portuguese" class="interlanguage-link-target"><span>Português</span></a></li><li class="interlanguage-link interwiki-ru mw-list-item"><a href="https://ru.wikipedia.org/wiki/X.25" title="X.25 – Russian" lang="ru" hreflang="ru" data-title="X.25" data-language-autonym="Русский" data-language-local-name="Russian" class="interlanguage-link-target"><span>Русский</span></a></li><li class="interlanguage-link interwiki-sr mw-list-item"><a href="https://sr.wikipedia.org/wiki/X.25" title="X.25 – Serbian" lang="sr" hreflang="sr" data-title="X.25" data-language-autonym="Српски / srpski" data-language-local-name="Serbian" class="interlanguage-link-target"><span>Српски / srpski</span></a></li><li class="interlanguage-link interwiki-fi mw-list-item"><a href="https://fi.wikipedia.org/wiki/X.25" title="X.25 – Finnish" lang="fi" hreflang="fi" data-title="X.25" 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/X.25" title="X.25 – Swedish" lang="sv" hreflang="sv" data-title="X.25" data-language-autonym="Svenska" data-language-local-name="Swedish" class="interlanguage-link-target"><span>Svenska</span></a></li><li class="interlanguage-link interwiki-th mw-list-item"><a href="https://th.wikipedia.org/wiki/X.25" title="X.25 – Thai" lang="th" hreflang="th" data-title="X.25" data-language-autonym="ไทย" data-language-local-name="Thai" class="interlanguage-link-target"><span>ไทย</span></a></li><li class="interlanguage-link interwiki-tr mw-list-item"><a href="https://tr.wikipedia.org/wiki/X.25" title="X.25 – Turkish" lang="tr" hreflang="tr" data-title="X.25" data-language-autonym="Türkçe" data-language-local-name="Turkish" class="interlanguage-link-target"><span>Türkçe</span></a></li><li class="interlanguage-link interwiki-uk mw-list-item"><a href="https://uk.wikipedia.org/wiki/X.25" title="X.25 – Ukrainian" lang="uk" hreflang="uk" data-title="X.25" 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/X.25" title="X.25 – Chinese" lang="zh" hreflang="zh" data-title="X.25" 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/Q622993#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" 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class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Standard protocol suite for packet switched wide area network (WAN) communication</div> <p class="mw-empty-elt"> </p> <style data-mw-deduplicate="TemplateStyles:r1257001546">.mw-parser-output .infobox-subbox{padding:0;border:none;margin:-3px;width:auto;min-width:100%;font-size:100%;clear:none;float:none;background-color:transparent}.mw-parser-output .infobox-3cols-child{margin:auto}.mw-parser-output .infobox .navbar{font-size:100%}@media screen{html.skin-theme-clientpref-night .mw-parser-output .infobox-full-data:not(.notheme)>div:not(.notheme)[style]{background:#1f1f23!important;color:#f8f9fa}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .infobox-full-data:not(.notheme) div:not(.notheme){background:#1f1f23!important;color:#f8f9fa}}@media(min-width:640px){body.skin--responsive .mw-parser-output .infobox-table{display:table!important}body.skin--responsive .mw-parser-output .infobox-table>caption{display:table-caption!important}body.skin--responsive .mw-parser-output .infobox-table>tbody{display:table-row-group}body.skin--responsive .mw-parser-output .infobox-table tr{display:table-row!important}body.skin--responsive .mw-parser-output .infobox-table th,body.skin--responsive .mw-parser-output .infobox-table td{padding-left:inherit;padding-right:inherit}}</style><table class="infobox hproduct"><caption class="infobox-title fn">X.25</caption><tbody><tr><td colspan="2" class="infobox-subheader">Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit</td></tr><tr><td colspan="2" class="infobox-image"><span class="mw-default-size" typeof="mw:File/Frameless"><a href="/wiki/File:X25-network-diagram-0a.svg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/X25-network-diagram-0a.svg/220px-X25-network-diagram-0a.svg.png" decoding="async" width="220" height="156" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/5/5c/X25-network-diagram-0a.svg/330px-X25-network-diagram-0a.svg.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/5/5c/X25-network-diagram-0a.svg/440px-X25-network-diagram-0a.svg.png 2x" data-file-width="1052" data-file-height="744" /></a></span></td></tr><tr><th scope="row" class="infobox-label">Status</th><td class="infobox-data">In force</td></tr><tr><th scope="row" class="infobox-label">Year started</th><td class="infobox-data">1976</td></tr><tr><th scope="row" class="infobox-label">Latest version</th><td class="infobox-data">(10/96)<br />October 1996</td></tr><tr><th scope="row" class="infobox-label">Organization</th><td class="infobox-data"><a href="/wiki/ITU-T" title="ITU-T">ITU-T</a></td></tr><tr><th scope="row" class="infobox-label">Committee</th><td class="infobox-data">Study Group VII</td></tr><tr><th scope="row" class="infobox-label">Domain</th><td class="infobox-data"><a href="/wiki/Telecommunications_network" title="Telecommunications network">networking</a></td></tr><tr><th scope="row" class="infobox-label">Website</th><td class="infobox-data"><a rel="nofollow" class="external free" href="https://www.itu.int/rec/T-REC-X.25/">https://www.itu.int/rec/T-REC-X.25/</a></td></tr></tbody></table> <p><b>X.25</b> is an <a href="/wiki/ITU-T" title="ITU-T">ITU-T</a> standard protocol suite for <a href="/wiki/Packet_switched_network" class="mw-redirect" title="Packet switched network">packet-switched</a> <a href="/wiki/Data_communication" title="Data communication">data communication</a> in <a href="/wiki/Wide_area_network" title="Wide area network">wide area networks</a> (WAN). It was originally defined by the <a href="/wiki/CCITT" class="mw-redirect" title="CCITT">International Telegraph and Telephone Consultative Committee</a> (CCITT, now ITU-T) in a series of drafts and finalized in a publication known as <i>The Orange Book</i> in 1976.<sup id="cite_ref-draft1976_1-0" class="reference"><a href="#cite_note-draft1976-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup><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>The protocol suite is designed as three conceptual layers, which correspond closely to the lower three layers of the seven-layer <a href="/wiki/OSI_model" title="OSI model">OSI Reference Model</a>, although it was developed several years before the OSI model (1984).<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><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> It also supports functionality not found in the OSI <a href="/wiki/Network_layer" title="Network layer">network layer</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup><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> An X.25 WAN consists of <a href="/wiki/Packet_switching" title="Packet switching">packet-switching exchange</a> (PSE) nodes as the networking hardware, and <a href="/wiki/Leased_line" title="Leased line">leased lines</a>, <a href="/wiki/Plain_old_telephone_service" title="Plain old telephone service">plain old telephone service</a> connections, or <a href="/wiki/ISDN" title="ISDN">ISDN</a> connections as physical links. </p><p>X.25 was popular with <a href="/wiki/Telecommunications_company" title="Telecommunications company">telecommunications companies</a> for their <a href="/wiki/Public_data_network" title="Public data network">public data networks</a> from the late 1970s to 1990s, which provided worldwide coverage. It was also used in <a href="/wiki/Financial_transaction" title="Financial transaction">financial transaction</a> systems, such as <a href="/wiki/Automated_teller_machine" class="mw-redirect" title="Automated teller machine">automated teller machines</a>, and by the credit card payment industry.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> However, most users have since moved to the <a href="/wiki/Internet_protocol_suite" title="Internet protocol suite">Internet Protocol Suite</a> (TCP/IP). X.25 is still used, for example by the aviation industry.<sup class="noprint Inline-Template Template-Fact" style="white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed"><span title="This claim needs references to reliable sources. (May 2024)">citation needed</span></a></i>]</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=X.25&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:CCITT_SGVII_X25_Advocates.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e5/CCITT_SGVII_X25_Advocates.jpg/220px-CCITT_SGVII_X25_Advocates.jpg" decoding="async" width="220" height="121" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e5/CCITT_SGVII_X25_Advocates.jpg/330px-CCITT_SGVII_X25_Advocates.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e5/CCITT_SGVII_X25_Advocates.jpg/440px-CCITT_SGVII_X25_Advocates.jpg 2x" data-file-width="1193" data-file-height="658" /></a><figcaption> Representatives of PTTs and private companies who championed the development of X.25-based networks and services in Europe, North America and Japan. Photographed at the CCITT Rapporteur-group meeting of March 1975 in Ottawa, where they drafted the first X.25 proposal.</figcaption></figure> <figure class="mw-halign-right" typeof="mw:File/Thumb"><a href="/wiki/File:CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/24/CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png/199px-CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png" decoding="async" width="199" height="124" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/24/CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png/298px-CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png 1.5x, //upload.wikimedia.org/wikipedia/commons/2/24/CCITT_SGVIi_chairman_and_X25_Rapporteur_and_supporters.png 2x" data-file-width="320" data-file-height="200" /></a><figcaption> Major contributors to CCITT X.25, photographed just after its approval in March 1976.</figcaption></figure> <p>The <a href="/wiki/CCITT" class="mw-redirect" title="CCITT">CCITT</a> (later <a href="/wiki/ITU-T" title="ITU-T">ITU-T</a>), the organization responsible for international standardization of telecom services, began developing a standard for packet-switched data communication in the mid-1970s based upon a number of emerging data network projects.<sup id="cite_ref-Sirbu1985_8-0" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> Participants in the design of X.25 included engineers from Canada, France, Japan, the UK, and the USA representing a mix of national <a href="/wiki/Postal,_telegraph_and_telephone_service" title="Postal, telegraph and telephone service">PTTs</a> (France, Japan, UK) and private operators (Canada, USA). In particular, the work of <a href="/wiki/R%C3%A9mi_Despr%C3%A9s" title="Rémi Després">Rémi Després</a>, contributed significantly to the standard, which was based on a <a href="/wiki/Virtual_circuit" title="Virtual circuit">virtual circuit</a> service. A few minor changes, which complemented the proposed specification, were accommodated to enable <a href="/wiki/Lawrence_Roberts_(scientist)" class="mw-redirect" title="Lawrence Roberts (scientist)">Larry Roberts</a> to join the agreement.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-10" class="reference"><a href="#cite_note-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-11" class="reference"><a href="#cite_note-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> Various updates and additions were worked into the standard, eventually recorded in the ITU series of technical books describing the telecommunication systems. These books were published every fourth year with different-colored covers. The X.25 specification is part of the larger set of X-Series.<sup id="cite_ref-12" class="reference"><a href="#cite_note-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Friend_1988_230_13-0" class="reference"><a href="#cite_note-Friend_1988_230-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="How_the_CCITT_standardized_virtual_circuits">How the CCITT standardized virtual circuits</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=2" title="Edit section: How the CCITT standardized virtual circuits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p><span class="anchor" id="How_the_CCITT_standardized_virtual_circuits"></span> </p> <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/Protocol_Wars" title="Protocol Wars">Protocol Wars</a></div> <p>The CCITT appointed a special Rapporteur on packet switching, <a href="/wiki/Halvor_Bothner-By" title="Halvor Bothner-By">Halvor Bothner-By</a>, who held an initial meeting in January 1974. This resulted in a question, to be answered by study group (SG) VII for the next CCITT plenary in 1976, which was “Should the packet-node of operation be provided on public data networks and, if so, how should it be implemented?”. A list of packet switching networks “to be considered” was provided: <a href="/wiki/ARPANET" title="ARPANET">ARPANET</a> (of the <a href="/wiki/Advanced_Research_Projects_Agency" class="mw-redirect" title="Advanced Research Projects Agency">ARPA</a> in the USA), <a href="/wiki/Packet_switching#EIN" title="Packet switching">EIN</a> (of the European COST), <a href="/wiki/Packet_Switch_Stream#EPSS" title="Packet Switch Stream">EPSS</a> (of the British <a href="/wiki/Post_Office_Telecommunications" class="mw-redirect" title="Post Office Telecommunications">Post Office Telecommunications</a>),<a href="/wiki/Packet_switching#RCP" title="Packet switching"> RCP</a> (of the <a href="/wiki/Postes,_T%C3%A9l%C3%A9graphes_et_T%C3%A9l%C3%A9phones" title="Postes, Télégraphes et Téléphones">French PTT</a>), <a href="/wiki/CYCLADES" title="CYCLADES">CYCLADES</a> (of <a href="/wiki/French_Institute_for_Research_in_Computer_Science_and_Automation" title="French Institute for Research in Computer Science and Automation">IRIA</a> in France), the <a href="/wiki/NPL_network" title="NPL network">NPL network</a> (of the <a href="/wiki/National_Physical_Laboratory_(United_Kingdom)" title="National Physical Laboratory (United Kingdom)">NPL</a> in the UK), the SWIFT network (of the international <a href="/wiki/SWIFT" title="SWIFT">SWIFT society</a>), and the <a href="/wiki/Packet_switching#SITA_Data_Transport_Network" title="Packet switching">SITA network</a> (of the international <a href="/wiki/SITA_(business_services_company)" title="SITA (business services company)">SITA company</a>).<sup id="cite_ref-14" class="reference"><a href="#cite_note-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> </p><p>The second Rapporteur meeting, hosted in Oslo by the Norwegian Telecommunications Administration in November 1974, gathered 24 participants, including representatives of other international organizations (<a href="/wiki/International_Organization_for_Standardization" title="International Organization for Standardization">ISO</a>, <a href="/wiki/International_Federation_for_Information_Processing" title="International Federation for Information Processing">IFIP</a>, <a href="/wiki/Ecma_International" title="Ecma International">ECMA</a>).<sup id="cite_ref-ccitt1974-08_15-0" class="reference"><a href="#cite_note-ccitt1974-08-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> A document submitted by France “with the active support of a number of European administrations” served as “main basis for discussion in this meeting”. It was then “agreed that two types of services should be considered, a ‘datagram’ service and a ‘virtual call’ service”.<sup id="cite_ref-ccitt1974-08_15-1" class="reference"><a href="#cite_note-ccitt1974-08-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p3">: p3 </span></sup> </p><p>At the third meeting, focus had moved from whether there should be packet-mode networks to whether there could be “a standard for the interface between the network and the computers”.<sup id="cite_ref-Sirbu1985_8-1" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p39">: p39 </span></sup> </p><p>Starting in January 1975, several bilateral and multilateral meetings took place between network operators having commitments for a packet switching service, in view to draft a common interface specification. Meetings started between the Canadian <a href="/wiki/DATAPAC" title="DATAPAC">DATAPAC</a> and the French <a href="/wiki/Transpac_(data_network)" title="Transpac (data network)">TRANSPAC</a>, continued with the startup <a href="/wiki/Telenet" title="Telenet">Telenet</a> of the USA, and continued with the BPO of the UK.<sup id="cite_ref-Sirbu1985_8-2" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p39">: p39 </span></sup><sup id="cite_ref-:20_16-0" class="reference"><a href="#cite_note-:20-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p44">: p44 </span></sup> </p><p>In March 1975, Halvor Bothner-By produced a list of recommendations to be created, or simply updated, for a packet switching standard to become possible. It was used as a framework at a drafting meeting in Ottawa between engineers of the four operators wishing to have a standard as soon as possible in the USA, Canada, France, UK and Japan. They prepared contributions to be submitted to SG VII in their name by administrations having voting right in CCITT. One contribution was a X.2x interface specification, the first version of what will become X.25).<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-:4_18-0" class="reference"><a href="#cite_note-:4-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> </p><p>The fourth Rapporteur meeting, in May 1975 in Geneva, had 45 participants and 27 new documents. The Rapporteur asked whether packet switching recommendations should be issued "with a view to making international interworking possible”, "the French administration answered in the affirmative and Canada strongly supported the French proposal". No firm conclusion was however obtained yet.<sup id="cite_ref-CcittMay1975_19-0" class="reference"><a href="#cite_note-CcittMay1975-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p><p>The fifth Rapporteur meeting, in September 1975 in Geneva, had about 60 participants. After discussions on the proposed virtual circuit interface, numerous issues were left unresolved.<sup id="cite_ref-Sirbu1985_8-3" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p40">: p40 </span></sup> Concerning datagrams, ‘It was proposed by Larry Roberts of the US delegation and supported by representatives from France and Canada respectively that the datagram classification be changed from “E” to “A”’, i.e., from essential "to be available internationally” to additional that "may be available in certain countries and internationally”.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup> The Rapporteur's last report expressed doubts “that a standard would be ready for adoption by SG VII”.<sup id="cite_ref-Sirbu1985_8-4" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p40">: p40 </span></sup> </p><p>At the last meeting of the full SG VII before the CCITT plenary of September 1976, the available draft X.25 raised numerous clarification questions and/or and technical objections. SG VII's chairman Vern MacDonald appointed an editor and provided a meeting facility for the weekend. After intense work during it, all issues had been dealt with. For an approval by the full study group, a challenge remained: copies of the updated X.25 draft had to be available in two languages. To get them in due time, Tony Rybczynski of DATAPAC and Paul Guinaudeau of TRANSPAC spent a full night to handwrite all negotiated amendments, and to assemble them with paste and scissors into clean documents. COM VII then reviewed distributed copies, and unanimously approved them for submission to the forthcoming CCITT plenary. <sup id="cite_ref-:20_16-1" class="reference"><a href="#cite_note-:20-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> At this plenary of September 1976, the X.25 recommendation and the other 10 of SG VII were unanimously approved.<sup id="cite_ref-Sirbu1985_8-5" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p40">: p40 </span></sup> </p><p>As requested by the USA, an optional datagram service was added to the revised X.25 of 1980, together with an alignment of its link layer, now called LAPB, with a recent evolution of HDLC in <a href="/wiki/ISO" class="mw-redirect" title="ISO">ISO</a>. In absence of any public network operator implementing this option, datagrams were finally deleted from X.25 in its update of 1984.<sup id="cite_ref-Sirbu1985_8-6" class="reference"><a href="#cite_note-Sirbu1985-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page: p41">: p41 </span></sup> </p> <div class="mw-heading mw-heading3"><h3 id="Worldwide_public_data_networks">Worldwide public data networks</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=3" title="Edit section: Worldwide public data networks"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951" /><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Public_data_network" title="Public data network">Public data network</a></div> <p>Publicly accessible X.25 networks, commonly called <a href="/wiki/Public_data_network" title="Public data network">public data networks</a>, were set up in many countries during the late 1970s and 1980s to lower the cost of accessing various <a href="/wiki/Online_service" class="mw-redirect" title="Online service">online services</a>. Examples include <a href="/wiki/Iberpac" title="Iberpac">Iberpac</a>, <a href="/wiki/Transpac_(network)" class="mw-redirect" title="Transpac (network)">TRANSPAC</a>, <a href="/wiki/Compuserve" class="mw-redirect" title="Compuserve">Compuserve</a>, <a href="/wiki/Tymnet" title="Tymnet">Tymnet</a>, <a href="/wiki/Telenet" title="Telenet">Telenet</a>, <a href="/wiki/Packet_switching#Euronet" title="Packet switching">Euronet</a>, <a href="/wiki/Packet_Switch_Stream" title="Packet Switch Stream">PSS</a>, <a href="/wiki/Datapac" class="mw-redirect" title="Datapac">Datapac</a>, <a href="/wiki/Packet-switched_network#Datanet_1" class="mw-redirect" title="Packet-switched network">Datanet 1</a> and <a href="/wiki/AUSTPAC" title="AUSTPAC">AUSTPAC</a> as well as the <a href="/wiki/International_Packet_Switched_Service" title="International Packet Switched Service">International Packet Switched Service</a>. Their combined network had large global coverage during the 1980s and into the 1990s.<sup id="cite_ref-Schatt_1991_200_21-0" class="reference"><a href="#cite_note-Schatt_1991_200-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> </p><p>Beginning in the early 1990s, in North America, use of X.25 networks (predominated by Telenet and Tymnet)<sup id="cite_ref-Schatt_1991_200_21-1" class="reference"><a href="#cite_note-Schatt_1991_200-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> started to be replaced by <a href="/wiki/Frame_Relay" title="Frame Relay">Frame Relay</a> services offered by national telephone companies.<sup id="cite_ref-22" class="reference"><a href="#cite_note-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> Most systems that required X.25 now use <a href="/wiki/TCP/IP" class="mw-redirect" title="TCP/IP">TCP/IP</a>, however it is possible to transport X.25 over TCP/IP when necessary.<sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup> </p><p>X.25 networks are still in use throughout the world. A variant called <a href="/wiki/AX.25" title="AX.25">AX.25</a> is used widely by <a href="/wiki/Amateur_radio" title="Amateur radio">amateur</a> <a href="/wiki/Packet_radio" title="Packet radio">packet radio</a>. <a href="/wiki/Racal" title="Racal">Racal</a> Paknet, now known as Widanet, remains in operation in many regions of the world, running on an X.25 protocol base. In some countries, like the Netherlands or Germany, it is possible to use a stripped version of X.25 via the <a href="/wiki/Integrated_Services_Digital_Network#Bearer_channel" class="mw-redirect" title="Integrated Services Digital Network">D-channel</a> of an <a href="/wiki/ISDN" title="ISDN">ISDN</a>-2 (or <a href="/wiki/Basic_rate_interface" class="mw-redirect" title="Basic rate interface">ISDN BRI</a>) connection for low-volume applications such as <a href="/wiki/Point-of-sale" class="mw-redirect" title="Point-of-sale">point-of-sale</a> terminals; but, the future of this service in the Netherlands is uncertain. </p><p>X.25 is still used in the aeronautical business (especially in Asia) even though a transition to modern protocols is increasingly important as X.25 hardware becomes increasingly rare and costly.<sup class="noprint Inline-Template" style="margin-left:0.1em; white-space:nowrap;">[<i><a href="/wiki/Wikipedia:Please_clarify" title="Wikipedia:Please clarify"><span title="The text near this tag may need clarification or removal of jargon. (April 2013)">clarification needed</span></a></i>]</sup> As recently as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with <a href="/wiki/Air_route_traffic_control_center" class="mw-redirect" title="Air route traffic control center">air route traffic control centers</a>. </p><p>France was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as <a href="/wiki/Minitel" title="Minitel">Minitel</a> it was based on <a href="/wiki/Videotex" title="Videotex">Videotex</a>, itself running on X.25. In 2002, <a href="/wiki/Minitel" title="Minitel">Minitel</a> had about 9 million users, and in 2011 it accounted for about 2 million users in France when France Télécom announced it would shut down the service by 30 June 2012.<sup id="cite_ref-24" class="reference"><a href="#cite_note-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup> As planned, service was terminated 30 June 2012. There were 800,000 terminals in operation at the time.<sup id="cite_ref-25" class="reference"><a href="#cite_note-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup> An X.25 service was still purchasable from BT in the United Kingdom in 2019.<sup id="cite_ref-26" class="reference"><a href="#cite_note-26"><span class="cite-bracket">[</span>26<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=X.25&action=edit&section=4" title="Edit section: Architecture"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The general concept of the X.25 was to create a universal and global <a href="/wiki/Packet_switched_network" class="mw-redirect" title="Packet switched network">packet-switched network</a>. Much of the X.25 system is a description of the rigorous <a href="/wiki/Error_correction" class="mw-redirect" title="Error correction">error correction</a> needed to achieve this, as well as more efficient sharing of capital-intensive physical resources. </p><p>The X.25 specification defines only the interface between a subscriber (DTE) and an X.25 network (DCE). <a href="/wiki/X.75" title="X.75">X.75</a>, a protocol very similar to X.25, defines the interface between two X.25 networks to allow connections to traverse two or more networks. X.25 does not specify how the network operates internally –  many X.25 network implementations used something very similar to X.25 or <a href="/wiki/X.75" title="X.75">X.75</a> internally, but others used quite different protocols internally. The ISO protocol equivalent to X.25, ISO 8208, is compatible with X.25, but additionally includes provision for two X.25 DTEs to be directly connected to each other with no network in between. By separating the <a href="/wiki/Packet-Layer_Protocol" class="mw-redirect" title="Packet-Layer Protocol">Packet-Layer Protocol</a>, ISO 8208 permits operation over additional networks such as ISO 8802 LLC2 (ISO LAN) and the OSI data link layer.<sup id="cite_ref-27" class="reference"><a href="#cite_note-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup> </p><p>X.25 originally defined three basic protocol levels or architectural layers. In the original specifications these were referred to as <i>levels</i> and also had a level number, whereas all ITU-T X.25 recommendations and ISO 8208 standards released after 1984 refer to them as <i>layers</i>.<sup id="cite_ref-28" class="reference"><a href="#cite_note-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup> The layer numbers were dropped to avoid confusion with the OSI Model layers.<sup id="cite_ref-draft1976_1-1" class="reference"><a href="#cite_note-draft1976-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p> <ul><li>Physical layer: This layer specifies the physical, electrical, functional and procedural characteristics to control the physical link between a DTE and a DCE. Common implementations use <a href="/wiki/X.21" title="X.21">X.21</a>, EIA-232, EIA-449 or other serial protocols.</li> <li>Data link layer: The data link layer consists of the link access procedure for data interchange on the link between a DTE and a DCE. In its implementation, the <a href="/wiki/LAPB" title="LAPB">Link Access Procedure, Balanced</a> (LAPB) is a data link protocol that manages a communication session and controls the packet framing. It is a bit-oriented protocol that provides error correction and orderly delivery.</li> <li>Packet layer: This layer defined a packet-layer protocol for exchanging control and user data packets to form a packet-switching network based on virtual calls, according to the <a href="/wiki/Packet_Layer_Protocol" title="Packet Layer Protocol">Packet Layer Protocol</a>.</li></ul> <p>The X.25 model was based on the traditional telephony concept of establishing reliable circuits through a shared network, but using software to create "<a href="/wiki/Virtual_call_capability" class="mw-redirect" title="Virtual call capability">virtual calls</a>" through the network. These calls interconnect <a href="/wiki/Data_terminal_equipment" title="Data terminal equipment">"data terminal equipment" (DTE)</a> providing endpoints to users, which looked like <a href="/wiki/Point-to-point_(telecommunications)" title="Point-to-point (telecommunications)">point-to-point connections</a>. Each endpoint can establish many separate virtual calls to different endpoints. </p><p>For a brief period, the specification also included a connectionless datagram service, but this was dropped in the next revision. The "fast select with restricted response facility" is intermediate between full call establishment and connectionless communication. It is widely used in query-response transaction applications involving a single request and response limited to 128 bytes of data carried each way. The data is carried in an extended call request packet and the response is carried in an extended field of the call reject packet, with a connection never being fully established. </p><p>Closely related to the X.25 protocol are the protocols to connect asynchronous devices (such as dumb terminals and printers) to an X.25 network: <a href="/wiki/X.3" title="X.3">X.3</a>, <a href="/wiki/X.28" title="X.28">X.28</a> and <a href="/wiki/X.29" class="mw-redirect" title="X.29">X.29</a>. This functionality was performed using a <a href="/wiki/Packet_assembler/disassembler" title="Packet assembler/disassembler">packet assembler/disassembler</a> or PAD (also known as a <i>triple-X device</i>, referring to the three protocols used). </p> <div class="mw-heading mw-heading3"><h3 id="Relation_to_the_OSI_Reference_Model">Relation to the OSI Reference Model</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=5" title="Edit section: Relation to the OSI Reference Model"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Although X.25 predates the <a href="/wiki/OSI_model" title="OSI model">OSI Reference Model</a> (OSIRM), the <a href="/wiki/Physical_layer" title="Physical layer">physical layer</a> of the OSI model corresponds to the X.25 <i>physical layer</i>, the <a href="/wiki/Data_link_layer" title="Data link layer">data link layer</a> to the X.25 <i>data link layer</i>, and the <a href="/wiki/Network_layer" title="Network layer">network layer</a> to the X.25 <i>packet layer</i>.<sup id="cite_ref-Friend_1988_230_13-1" class="reference"><a href="#cite_note-Friend_1988_230-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> The X.25 <i>data link layer</i>, <a href="/wiki/LAPB" title="LAPB">LAPB</a>, provides a reliable data path across a data link (or multiple parallel data links, multilink) which may not be reliable itself. The X.25 <i>packet layer</i> provides the virtual call mechanisms, running over X.25 <a href="/wiki/LAPB" title="LAPB">LAPB</a>. The <i>packet layer</i> includes mechanisms to maintain virtual calls and to signal data errors in the event that the <i>data link layer</i> cannot recover from data transmission errors. All but the earliest versions of X.25 include facilities<sup id="cite_ref-29" class="reference"><a href="#cite_note-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> which provide for OSI <a href="/wiki/Network_layer" title="Network layer">network layer</a> Addressing (NSAP addressing, see below).<sup id="cite_ref-30" class="reference"><a href="#cite_note-30"><span class="cite-bracket">[</span>30<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading3"><h3 id="User_device_support">User device support</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=6" title="Edit section: User device support"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Televideo925Terminal.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/8/87/Televideo925Terminal.jpg/250px-Televideo925Terminal.jpg" decoding="async" width="220" height="182" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/8/87/Televideo925Terminal.jpg/330px-Televideo925Terminal.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/8/87/Televideo925Terminal.jpg/500px-Televideo925Terminal.jpg 2x" data-file-width="1145" data-file-height="949" /></a><figcaption>A <a href="/wiki/Televideo" class="mw-redirect" title="Televideo">Televideo</a> terminal model 925 made around 1982</figcaption></figure> <p>X.25 was developed in the era of <a href="/wiki/Computer_terminal" title="Computer terminal">computer terminals</a> connecting to host computers, although it also can be used for communications between computers. Instead of dialing directly “into” the host computer –  which would require the host to have its own pool of modems and phone lines, and require non-local callers to make long-distance calls –  the host could have an X.25 connection to a network service provider. Now dumb-terminal users could dial into the network's local “PAD” (<a href="/wiki/Packet_assembler/disassembler" title="Packet assembler/disassembler">packet assembly/disassembly</a> facility), a gateway device connecting modems and serial lines to the X.25 link as defined by the <a href="/wiki/X.29" class="mw-redirect" title="X.29">X.29</a> and <a href="/wiki/X.3" title="X.3">X.3</a> standards. </p><p>Having connected to the PAD, the dumb-terminal user tells the PAD which host to connect to, by giving a phone-number-like address in the <a href="/wiki/X.121" title="X.121">X.121</a> address format (or by giving a host name, if the service provider allows for names that map to <a href="/wiki/X.121" title="X.121">X.121</a> addresses). The PAD then places an X.25 call to the host, establishing a <a href="/wiki/Virtual_call_capability" class="mw-redirect" title="Virtual call capability">virtual call</a>. Note that X.25 provides for virtual calls, so <i>appears</i> to be a <a href="/wiki/Circuit_switched" class="mw-redirect" title="Circuit switched">circuit switched</a> network, even though in fact the data itself is <a href="/wiki/Packet_switching" title="Packet switching">packet switched</a> internally, similar to the way TCP provides connections even though the underlying data is packet switched. Two X.25 hosts could, of course, call one another directly; no PAD is involved in this case. In theory, it doesn't matter whether the X.25 caller and X.25 destination are both connected to the same carrier, but in practice it was not always possible to make calls from one carrier to another. </p><p>For the purpose of flow-control, a <a href="/wiki/Sliding_window" class="mw-redirect" title="Sliding window">sliding window</a> protocol is used with the default window size of 2. The acknowledgements may have either local or end to end significance. A D bit (Data Delivery bit) in each data packet indicates if the sender requires end to end acknowledgement. When D=1, it means that the acknowledgement has end to end significance and must take place only after the remote DTE has acknowledged receipt of the data. When D=0, the network is permitted (but not required) to acknowledge before the remote DTE has acknowledged or even received the data. </p><p>While the PAD function defined by <a href="/wiki/X.28" title="X.28">X.28</a> and <a href="/wiki/X.29" class="mw-redirect" title="X.29">X.29</a> specifically supported asynchronous character terminals, PAD equivalents were developed to support a wide range of proprietary intelligent communications devices, such as those for IBM <a href="/wiki/System_Network_Architecture" class="mw-redirect" title="System Network Architecture">System Network Architecture</a> (SNA). </p> <div class="mw-heading mw-heading3"><h3 id="Error_control">Error control</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=7" title="Edit section: Error control"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Error recovery procedures at the packet layer assume that the data link layer is responsible for retransmitting data received in error. Packet layer error handling focuses on resynchronizing the information flow in calls, as well as clearing calls that have gone into unrecoverable states: </p> <ul><li>Level 3 Reset packets, which re-initializes the flow on a virtual call (but does not break the virtual call).</li> <li>Restart packet, which clears down all virtual calls on the data link and resets all permanent virtual circuits on the data link.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Addressing_and_virtual_circuits">Addressing and virtual circuits</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=8" title="Edit section: Addressing and virtual circuits"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Siemens-DAG-64_front.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/6/64/Siemens-DAG-64_front.jpg/250px-Siemens-DAG-64_front.jpg" decoding="async" width="220" height="109" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/6/64/Siemens-DAG-64_front.jpg/330px-Siemens-DAG-64_front.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/6/64/Siemens-DAG-64_front.jpg/500px-Siemens-DAG-64_front.jpg 2x" data-file-width="1424" data-file-height="706" /></a><figcaption>An X.25 modem once used to connect to the German Datex-P network</figcaption></figure> <p>X.25 supports two types of <a href="/wiki/Virtual_circuit" title="Virtual circuit">virtual circuits</a>; <a href="/wiki/Virtual_call_capability" class="mw-redirect" title="Virtual call capability">virtual calls</a> (VC) and <a href="/wiki/Permanent_virtual_circuit" class="mw-redirect" title="Permanent virtual circuit">permanent virtual circuits</a> (PVC). Virtual calls are established on an as-needed basis. For example, a VC is established when a call is placed and torn down after the call is complete. VCs are established through a call establishment and clearing procedure. On the other hand, <a href="/wiki/Permanent_virtual_circuit" class="mw-redirect" title="Permanent virtual circuit">permanent virtual circuits</a> are preconfigured into the network.<sup id="cite_ref-31" class="reference"><a href="#cite_note-31"><span class="cite-bracket">[</span>31<span class="cite-bracket">]</span></a></sup> PVCs are seldom torn down and thus provide a dedicated connection between end points. </p><p>VC may be established using X.121 addresses. The X.121 address consists of a three-digit data country code (DCC) plus a network digit, together forming the four-digit data network identification code (DNIC), followed by the national terminal number (NTN) of at most ten digits. Note the use of a single network digit, seemingly allowing for only 10 network carriers per country, but some countries are assigned more than one DCC to avoid this limitation. Networks often used fewer than the full NTN digits for routing, and made the spare digits available to the subscriber (sometimes called the sub-address) where they could be used to identify applications or for further routing on the subscribers networks. </p><p><a href="/wiki/NSAP_address" class="mw-redirect" title="NSAP address">NSAP addressing</a> facility was added in the X.25(1984) revision of the specification, and this enabled X.25 to better meet the requirements of <a href="/wiki/Open_Systems_Interconnection" class="mw-redirect" title="Open Systems Interconnection">OSI</a> <a href="/wiki/CONS" class="mw-redirect" title="CONS">Connection Oriented Network Service (CONS)</a>.<sup id="cite_ref-x223_32-0" class="reference"><a href="#cite_note-x223-32"><span class="cite-bracket">[</span>32<span class="cite-bracket">]</span></a></sup> Public X.25 networks were not required to make use of NSAP addressing, but, to support OSI CONS, were required to carry the NSAP addresses and other ITU-T specified DTE facilities transparently from DTE to DTE.<sup id="cite_ref-33" class="reference"><a href="#cite_note-33"><span class="cite-bracket">[</span>33<span class="cite-bracket">]</span></a></sup> Later revisions allowed multiple addresses in addition to X.121 addresses to be carried on the same DTE-DCE interface: Telex addressing (<a href="/wiki/Telex" title="Telex">F.69</a>), <a href="/wiki/Public_switched_telephone_network" title="Public switched telephone network">PSTN</a> addressing (<a href="/wiki/E.163" class="mw-redirect" title="E.163">E.163</a>), <a href="/wiki/Integrated_Services_Digital_Network" class="mw-redirect" title="Integrated Services Digital Network">ISDN</a> addressing (<a href="/wiki/E.164" title="E.164">E.164</a>), <a href="/wiki/Internet_Protocol" title="Internet Protocol">Internet Protocol</a> addresses (IANA ICP), and local <a href="/wiki/IEEE_802.2" title="IEEE 802.2">IEEE 802.2</a> <a href="/wiki/MAC_address" title="MAC address">MAC addresses</a>.<sup id="cite_ref-34" class="reference"><a href="#cite_note-34"><span class="cite-bracket">[</span>34<span class="cite-bracket">]</span></a></sup> </p><p>PVCs are permanently established in the network and therefore do not require the use of addresses for call setup. PVCs are identified at the subscriber interface by their logical channel identifier (see below). However, in practice not many of the national X.25 networks supported PVCs. </p><p>One DTE-DCE interface to an X.25 network has a maximum of 4095 logical channels on which it is allowed to establish virtual calls and permanent virtual circuits,<sup id="cite_ref-channels_35-0" class="reference"><a href="#cite_note-channels-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> although networks are not expected to support a full 4095 virtual circuits.<sup id="cite_ref-36" class="reference"><a href="#cite_note-36"><span class="cite-bracket">[</span>36<span class="cite-bracket">]</span></a></sup> For identifying the channel to which a packet is associated, each packet contains a 12 bit logical channel identifier made up of an 8-bit logical channel number and a 4-bit logical channel group number.<sup id="cite_ref-channels_35-1" class="reference"><a href="#cite_note-channels-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> Logical channel identifiers remain assigned to a virtual circuit for the duration of the connection.<sup id="cite_ref-channels_35-2" class="reference"><a href="#cite_note-channels-35"><span class="cite-bracket">[</span>35<span class="cite-bracket">]</span></a></sup> Logical channel identifiers identify a specific logical channel between the <a href="/wiki/Data_terminal_equipment" title="Data terminal equipment">DTE</a> (subscriber appliance) and the <a href="/wiki/Data_circuit-terminating_equipment" title="Data circuit-terminating equipment">DCE</a> (network), and only has local significance on the link between the subscriber and the network. The other end of the connection at the remote DTE is likely to have assigned a different logical channel identifier. The range of possible logical channels is split into 4 groups: channels assigned to permanent virtual circuits, assigned to incoming virtual calls, two-way (incoming or outgoing) virtual calls, and outgoing virtual calls.<sup id="cite_ref-x25annexa_37-0" class="reference"><a href="#cite_note-x25annexa-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> (Directions refer to the direction of virtual call initiation as viewed by the DTE –  they all carry data in both directions.)<sup id="cite_ref-38" class="reference"><a href="#cite_note-38"><span class="cite-bracket">[</span>38<span class="cite-bracket">]</span></a></sup> The ranges allowed a subscriber to be configured to handle significantly differing numbers of calls in each direction while reserving some channels for calls in one direction. All international networks are required to implement support for permanent virtual circuits, two-way logical channels and one-way logical channels outgoing; one-way logical channels incoming is an additional optional facility.<sup id="cite_ref-39" class="reference"><a href="#cite_note-39"><span class="cite-bracket">[</span>39<span class="cite-bracket">]</span></a></sup> DTE-DCE interfaces are not required to support more than one logical channel.<sup id="cite_ref-x25annexa_37-1" class="reference"><a href="#cite_note-x25annexa-37"><span class="cite-bracket">[</span>37<span class="cite-bracket">]</span></a></sup> Logical channel identifier zero will not be assigned to a permanent virtual circuit or virtual call.<sup id="cite_ref-40" class="reference"><a href="#cite_note-40"><span class="cite-bracket">[</span>40<span class="cite-bracket">]</span></a></sup> The logical channel identifier of zero is used for packets which don't relate to a specific virtual circuit (e.g. packet layer restart, registration, and diagnostic packets). </p> <div class="mw-heading mw-heading2"><h2 id="Billing">Billing</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=9" title="Edit section: Billing"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In public networks, X.25 was typically billed as a flat monthly service fee depending on link speed, and then a price-per-segment on top of this.<sup id="cite_ref-41" class="reference"><a href="#cite_note-41"><span class="cite-bracket">[</span>41<span class="cite-bracket">]</span></a></sup> Link speeds varied, typically from 2400 bit/s up to 2 Mbit/s, although speeds above 64 kbit/s were uncommon in the public networks. A segment was 64 bytes of data (rounded up, with no carry-over between packets),<sup id="cite_ref-42" class="reference"><a href="#cite_note-42"><span class="cite-bracket">[</span>42<span class="cite-bracket">]</span></a></sup> charged to the caller<sup id="cite_ref-43" class="reference"><a href="#cite_note-43"><span class="cite-bracket">[</span>43<span class="cite-bracket">]</span></a></sup> (or callee in the case of reverse charged calls, where supported).<sup id="cite_ref-44" class="reference"><a href="#cite_note-44"><span class="cite-bracket">[</span>44<span class="cite-bracket">]</span></a></sup> Calls invoking the <i>Fast Select</i> facility (allowing 128 bytes of data in call request, call confirmation and call clearing phases)<sup id="cite_ref-45" class="reference"><a href="#cite_note-45"><span class="cite-bracket">[</span>45<span class="cite-bracket">]</span></a></sup> would generally attract an extra charge, as might use of some of the other X.25 facilities. PVCs would have a monthly rental charge and a lower price-per-segment than VCs, making them cheaper only where large volumes of data are passed. </p> <div class="mw-heading mw-heading2"><h2 id="X.25_packet_types">X.25 packet types</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=10" title="Edit section: X.25 packet types"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <table class="wikitable"> <tbody><tr> <th>Packet Type </th> <th>DCE → DTE </th> <th>DTE → DCE </th> <th>Service </th> <th>VC </th> <th>PVC </th></tr> <tr> <td>Calling the Super Setup </td> <td>Incoming Call </td> <td>Call Request </td> <td> </td> <td>X </td> <td> </td></tr> <tr> <td> </td> <td>Call Connected Gaming </td> <td>Call Accepted Regaining </td> <td> </td> <td>X </td> <td> </td></tr> <tr> <td> </td> <td>Clear Indication Request </td> <td>Clear Request Indication </td> <td> </td> <td>X </td> <td> </td></tr> <tr> <td> </td> <td>Clear Confirmation City </td> <td>Clear Confirmation City </td> <td> </td> <td>X </td> <td> </td></tr> <tr> <td>Data and Interrupt or Currput </td> <td>Data </td> <td>Data </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>Interrupt </td> <td>Interrupt </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>Interrupt Confirmation </td> <td>Interrupt Confirmation </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td>Flow Control and Reset </td> <td>RR </td> <td>RR </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>RNR </td> <td>RNR </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>REJ </td> <td>REJ </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>Reset Indication </td> <td>Reset Request </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td> </td> <td>Reset Confirmation </td> <td>Reset Confirmation </td> <td> </td> <td>X </td> <td>X </td></tr> <tr> <td>Restart </td> <td>Restart Indication </td> <td>Restart Request </td> <td>X </td> <td> </td> <td> </td></tr> <tr> <td> </td> <td>Restart Confirmation </td> <td>Restart Confirmation </td> <td>X </td> <td> </td> <td> </td></tr> <tr> <td>Diagnostic </td> <td>Diagnostic </td> <td> </td> <td>X </td> <td> </td> <td> </td></tr> <tr> <td>Registration </td> <td>Registration Confirmation </td> <td>Registration Request </td> <td>X </td> <td> </td> <td> </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="X.25_details">X.25 details</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=11" title="Edit section: X.25 details"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The network may allow the selection of the maximal length in range 16 to 4096 octets (2<sup>n</sup> values only) per virtual circuit by negotiation as part of the call setup procedure. The maximal length may be different at the two ends of the virtual circuit. </p> <ul><li><a href="/wiki/Data_terminal_equipment" title="Data terminal equipment">Data terminal equipment</a> constructs control packets which are encapsulated into data packets. The packets are sent to the data circuit-terminating equipment, using <a href="/wiki/LAPB" title="LAPB">LAPB</a> Protocol.</li> <li>Data circuit-terminating equipment strips the layer-2 headers in order to encapsulate packets to the internal network protocol.</li></ul> <div class="mw-heading mw-heading3"><h3 id="X.25_facilities">X.25 facilities</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=12" title="Edit section: X.25 facilities"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>X.25 provides a set of user facilities defined and described in ITU-T Recommendation X.2.<sup id="cite_ref-46" class="reference"><a href="#cite_note-46"><span class="cite-bracket">[</span>46<span class="cite-bracket">]</span></a></sup> The X.2 user facilities fall into five categories: </p> <ul><li>Essential facilities;</li> <li>Additional facilities;</li> <li>Conditional facilities;</li> <li>Mandatory facilities; and,</li> <li>Optional facilities.</li></ul> <p>X.25 also provides X.25 and ITU-T specified DTE optional user facilities defined and described in ITU-T Recommendation X.7.<sup id="cite_ref-47" class="reference"><a href="#cite_note-47"><span class="cite-bracket">[</span>47<span class="cite-bracket">]</span></a></sup> The X.7 optional user facilities fall into four categories of user facilities that require: </p> <ul><li>Subscription only;</li> <li>Subscription followed by dynamic invocation;</li> <li>Subscription or dynamic invocation; and,</li> <li>Dynamic invocation only.</li></ul> <div class="mw-heading mw-heading3"><h3 id="X.25_protocol_versions">X.25 protocol versions</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=13" title="Edit section: X.25 protocol versions"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The CCITT/ITU-T versions of the protocol specifications are for <a href="/wiki/Public_data_network" title="Public data network">public data networks</a> (PDN).<sup id="cite_ref-48" class="reference"><a href="#cite_note-48"><span class="cite-bracket">[</span>48<span class="cite-bracket">]</span></a></sup> The ISO/IEC versions address additional features for private networks (e.g. <a href="/wiki/Local_area_network" title="Local area network">local area networks</a> (LAN) use) while maintaining compatibility with the CCITT/ITU-T specifications.<sup id="cite_ref-49" class="reference"><a href="#cite_note-49"><span class="cite-bracket">[</span>49<span class="cite-bracket">]</span></a></sup> </p><p>The user facilities and other features supported by each version of X.25 and ISO/IEC 8208 have varied from edition to edition.<sup id="cite_ref-annexc_50-0" class="reference"><a href="#cite_note-annexc-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> Several major protocol versions of X.25 exist:<sup id="cite_ref-51" class="reference"><a href="#cite_note-51"><span class="cite-bracket">[</span>51<span class="cite-bracket">]</span></a></sup> </p> <ul><li>CCITT Recommendation X.25 (1976) Orange Book</li> <li>CCITT Recommendation X.25 (1980) Yellow Book</li> <li>CCITT Recommendation X.25 (1984) Red Book</li> <li>CCITT Recommendation X.25 (1988) Blue Book</li> <li>ITU-T Recommendation X.25 (1993) White Book<sup id="cite_ref-52" class="reference"><a href="#cite_note-52"><span class="cite-bracket">[</span>52<span class="cite-bracket">]</span></a></sup></li> <li>ITU-T Recommendation X.25 (1996) Grey Book<sup id="cite_ref-53" class="reference"><a href="#cite_note-53"><span class="cite-bracket">[</span>53<span class="cite-bracket">]</span></a></sup></li></ul> <p>The X.25 Recommendation allows many options for each network to choose when deciding which features to support and how certain operations are performed. This means each network needs to publish its own document giving the specification of its X.25 implementation, and most networks required DTE appliance manufacturers to undertake protocol conformance testing, which included testing for strict adherence and enforcement of their network specific options. (Network operators were particularly concerned about the possibility of a badly behaving or misconfigured DTE appliance taking out parts of the network and affecting other subscribers.) Therefore, subscriber's DTE appliances have to be configured to match the specification of the particular network to which they are connecting. Most of these were sufficiently different to prevent interworking if the subscriber didn't configure their appliance correctly or the appliance manufacturer didn't include specific support for that network. In spite of protocol conformance testing, this often lead to interworking problems when initially attaching an appliance to a network. </p><p>In addition to the CCITT/ITU-T versions of the protocol, four editions of ISO/IEC 8208 exist:<sup id="cite_ref-annexc_50-1" class="reference"><a href="#cite_note-annexc-50"><span class="cite-bracket">[</span>50<span class="cite-bracket">]</span></a></sup> </p> <ul><li>ISO/IEC 8208:1987, First Edition, compatible with X.25 (1980) and (1984)</li> <li>ISO/IEC 8208:1990, Second Edition, compatible with 1st Ed. and X.25 (1988)</li> <li>ISO/IEC 8208:1995, Third Edition, compatible with 2nd Ed. and X.25 (1993)</li> <li>ISO/IEC 8208:2000, Fourth Edition, compatible with 3rd Ed. and X.25 (1996)</li></ul> <div class="mw-heading mw-heading2"><h2 id="Legacy">Legacy</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=X.25&action=edit&section=14" title="Edit section: Legacy"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The X.25 protocol had a lot of overhead to deal with data loss, since circuits back then ran over poor-grade cabling and had a lot of single-bit errors to deal with. As circuits became more and more reliable, the overhead was no longer needed, and less expensive <a href="/wiki/Frame_Relay" title="Frame Relay">Frame Relay</a> took over. Frame Relay has its technical base in X.25, but does not attempt to correct errors. </p><p>The world-wide <a href="/wiki/Public_data_network" title="Public data network">public data networks</a> based on X.25 helped grow IP as a protocol riding on top. </p><p>X.25 was also available in niche applications such as Retronet that allow <a href="/wiki/Retrocomputing" title="Retrocomputing">vintage computers</a> to use the <a href="/wiki/Internet" title="Internet">Internet</a>. </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=X.25&action=edit&section=15" title="Edit section: See also"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <ul><li><a href="/wiki/History_of_the_Internet" title="History of the Internet">History of the Internet</a></li> <li><a href="/wiki/OSI_protocol_suite" class="mw-redirect" title="OSI protocol suite">OSI protocol suite</a></li> <li><a href="/wiki/Packet_switching" title="Packet switching">Packet switched networks</a> – are networks, including X.25, that have protocols using "packets"</li> <li><a href="/wiki/Protocol_Wars" title="Protocol Wars">Protocol Wars</a></li> <li><a href="/wiki/XOT" title="XOT">XOT</a> – is an "X.25 Over TCP" protocol, i.e. with X.25 encapsulation on TCP/IP networks</li> <li><a href="/wiki/X.PC" title="X.PC">X.PC</a></li> <li><a href="/wiki/AX.25" title="AX.25">AX.25</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=X.25&action=edit&section=16" 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 .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 30em;"> <ol class="references"> <li id="cite_note-draft1976-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-draft1976_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-draft1976_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">CCITT, Study Group VII, <i>Draft Recommendation X-25</i>, March 1976</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"><a rel="nofollow" class="external text" href="http://www.itu.int/ITU-T/studygroups/com17/history.html">History of X.25, CCITT Plenary Assemblies and Book Colors</a></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">(<a href="#CITEREFFriendFikeBakerBellamy1988">Friend et al. 1988</a>, p. 242)</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">(<a href="#CITEREFFriendFikeBakerBellamy1988">Friend et al. 1988</a>, p. 243)</span> </li> <li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.28/en/">ITU-T Recommendation X.28</a>.</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"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.3/en/">ITU-T Recommendation X.3</a>.</span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><style 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 no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .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="CITEREFForegenix2012" class="citation web cs1">Foregenix (February 2012). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160304054052/http://www.mastercard.com/us/company/en/docs/X25_within_the_Payment_Card_Industry.pdf">"X.25 within the Payment Card Industry"</a> <span class="cs1-format">(PDF)</span>. Archived from <a rel="nofollow" class="external text" href="http://www.mastercard.com/us/company/en/docs/X25_within_the_Payment_Card_Industry.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 4 March 2016<span class="reference-accessdate">. Retrieved <span class="nowrap">25 May</span> 2016</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=X.25+within+the+Payment+Card+Industry&rft.date=2012-02&rft.au=Foregenix&rft_id=http%3A%2F%2Fwww.mastercard.com%2Fus%2Fcompany%2Fen%2Fdocs%2FX25_within_the_Payment_Card_Industry.pdf&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-Sirbu1985-8"><span class="mw-cite-backlink">^ <a href="#cite_ref-Sirbu1985_8-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-4"><sup><i><b>e</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-5"><sup><i><b>f</b></i></sup></a> <a href="#cite_ref-Sirbu1985_8-6"><sup><i><b>g</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFSirbuZwimpfer1985" class="citation web cs1">Sirbu, Marvin A; Zwimpfer, Laurence E (March 1985). <a rel="nofollow" class="external text" href="https://www.academia.edu/2850947/Standards_setting_for_computer_communication_the_case_of_X_25?email_work_card=title%7C">"Standards Setting for Computer Communication: The Case of X.25"</a>. IEEE.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Standards+Setting+for+Computer+Communication%3A+The+Case+of+X.25&rft.pub=IEEE&rft.date=1985-03&rft.aulast=Sirbu&rft.aufirst=Marvin+A&rft.au=Zwimpfer%2C+Laurence+E&rft_id=https%3A%2F%2Fwww.academia.edu%2F2850947%2FStandards_setting_for_computer_communication_the_case_of_X_25%3Femail_work_card%3Dtitle%257C&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFDespres2010" class="citation journal cs1">Despres, Remi (2010). "X.25 Virtual Circuits - TRANSPAC in France - Pre-Internet Data Networking". <i>IEEE Communications Magazine</i>. <b>48</b> (11): <span class="nowrap">40–</span>46. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FMCOM.2010.5621965">10.1109/MCOM.2010.5621965</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1558-1896">1558-1896</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=IEEE+Communications+Magazine&rft.atitle=X.25+Virtual+Circuits+-+TRANSPAC+in+France+-+Pre-Internet+Data+Networking&rft.volume=48&rft.issue=11&rft.pages=%3Cspan+class%3D%22nowrap%22%3E40-%3C%2Fspan%3E46&rft.date=2010&rft_id=info%3Adoi%2F10.1109%2FMCOM.2010.5621965&rft.issn=1558-1896&rft.aulast=Despres&rft.aufirst=Remi&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-10"><span class="mw-cite-backlink"><b><a href="#cite_ref-10">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFRybczynski2009" class="citation journal cs1">Rybczynski, Tony (2009). "Commercialization of packet switching (1975-1985): A Canadian perspective [History of Communications]". <i>IEEE Communications Magazine</i>. <b>47</b> (12): <span class="nowrap">26–</span>31. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FMCOM.2009.5350364">10.1109/MCOM.2009.5350364</a>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/1558-1896">1558-1896</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:23243636">23243636</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=IEEE+Communications+Magazine&rft.atitle=Commercialization+of+packet+switching+%281975-1985%29%3A+A+Canadian+perspective+%5BHistory+of+Communications%5D&rft.volume=47&rft.issue=12&rft.pages=%3Cspan+class%3D%22nowrap%22%3E26-%3C%2Fspan%3E31&rft.date=2009&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A23243636%23id-name%3DS2CID&rft.issn=1558-1896&rft_id=info%3Adoi%2F10.1109%2FMCOM.2009.5350364&rft.aulast=Rybczynski&rft.aufirst=Tony&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-11">^</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="https://www.itu.int/en/ITU-T/studygroups/com17/Pages/history.aspx">"Short History of Study Group ... 7"</a>. <i>www.itu.int</i><span class="reference-accessdate">. Retrieved <span class="nowrap">4 February</span> 2020</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.itu.int&rft.atitle=Short+History+of+Study+Group+...+7&rft_id=https%3A%2F%2Fwww.itu.int%2Fen%2FITU-T%2Fstudygroups%2Fcom17%2FPages%2Fhistory.aspx&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-12"><span class="mw-cite-backlink"><b><a href="#cite_ref-12">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X/en/">X-Series recommendations</a></span> </li> <li id="cite_note-Friend_1988_230-13"><span class="mw-cite-backlink">^ <a href="#cite_ref-Friend_1988_230_13-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Friend_1988_230_13-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">(<a href="#CITEREFFriendFikeBakerBellamy1988">Friend et al. 1988</a>, p. 230)</span> </li> <li id="cite_note-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-14">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFBothner-By1974" class="citation web cs1">Bothner-By, Halvor (July 1974). <a rel="nofollow" class="external text" href="https://umedia.lib.umn.edu/item/p16022coll270:13778">"REPORT OF THE RAPPORTEUR'S GROUP ON POINT C -"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=REPORT+OF+THE+RAPPORTEUR%27S+GROUP+ON+POINT+C+-&rft.date=1974-07&rft.aulast=Bothner-By&rft.aufirst=Halvor&rft_id=https%3A%2F%2Fumedia.lib.umn.edu%2Fitem%2Fp16022coll270%3A13778&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-ccitt1974-08-15"><span class="mw-cite-backlink">^ <a href="#cite_ref-ccitt1974-08_15-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-ccitt1974-08_15-1"><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 id="CITEREFRapporteur_group_on_packet_switching" class="citation web cs1">Rapporteur group on packet switching. <a rel="nofollow" class="external text" href="https://umedia.lib.umn.edu/item/p16022coll270:13778/p16022coll270:13739?child_index=116&query=&sidebar_page=39">"Report of Meeting in Oslo (15 - 16 AUGUST 1974)"</a>. CCITT.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Report+of+Meeting+in+Oslo+%2815+-+16+AUGUST+1974%29&rft.pub=CCITT&rft.au=Rapporteur+group+on+packet+switching&rft_id=https%3A%2F%2Fumedia.lib.umn.edu%2Fitem%2Fp16022coll270%3A13778%2Fp16022coll270%3A13739%3Fchild_index%3D116%26query%3D%26sidebar_page%3D39&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-:20-16"><span class="mw-cite-backlink">^ <a href="#cite_ref-:20_16-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:20_16-1"><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 id="CITEREFDesprés2010" class="citation journal cs1">Després, Rémi (2010). Schwartz, Mischa (ed.). "X.25 Virtual Circuits – TRANSPAC In France – Pre-Internet Data Networking". <i>IEEE Communications Magazine</i>. <b>48</b> (11): <span class="nowrap">40–</span>46. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FMCOM.2010.5621965">10.1109/MCOM.2010.5621965</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:23639680">23639680</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=IEEE+Communications+Magazine&rft.atitle=X.25+Virtual+Circuits+%E2%80%93+TRANSPAC+In+France+%E2%80%93+Pre-Internet+Data+Networking&rft.volume=48&rft.issue=11&rft.pages=%3Cspan+class%3D%22nowrap%22%3E40-%3C%2Fspan%3E46&rft.date=2010&rft_id=info%3Adoi%2F10.1109%2FMCOM.2010.5621965&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A23639680%23id-name%3DS2CID&rft.aulast=Despr%C3%A9s&rft.aufirst=R%C3%A9mi&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFCCITT_Rapporteur_on_packet_switching1975" class="citation web cs1">CCITT Rapporteur on packet switching (26 March 1975). <a rel="nofollow" class="external text" href="https://www.dropbox.com/scl/fi/zc7pc47nfku3wytj3mqcs/1975-03-26-CCITT-Bothner-BY-Proposals-for-Recommendations.pdf?rlkey=g3e8o8a4y8wulel9lf3mh7qh2&dl=0">"Proposals for Recommendations"</a> <span class="cs1-format">(PDF)</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Proposals+for+Recommendations&rft.date=1975-03-26&rft.au=CCITT+Rapporteur+on+packet+switching&rft_id=https%3A%2F%2Fwww.dropbox.com%2Fscl%2Ffi%2Fzc7pc47nfku3wytj3mqcs%2F1975-03-26-CCITT-Bothner-BY-Proposals-for-Recommendations.pdf%3Frlkey%3Dg3e8o8a4y8wulel9lf3mh7qh2%26dl%3D0&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-:4-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-:4_18-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFRybczynski2009" class="citation journal cs1">Rybczynski, Tony (December 2009). "Commercialization of packet switching (1975-1985): A Canadian perspective [History of Communications]". <i>IEEE Communications Magazine</i>. <b>47</b> (12): <span class="nowrap">26–</span>31. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1109%2FMCOM.2009.5350364">10.1109/MCOM.2009.5350364</a>. <a href="/wiki/S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:23243636">23243636</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=IEEE+Communications+Magazine&rft.atitle=Commercialization+of+packet+switching+%281975-1985%29%3A+A+Canadian+perspective+%5BHistory+of+Communications%5D&rft.volume=47&rft.issue=12&rft.pages=%3Cspan+class%3D%22nowrap%22%3E26-%3C%2Fspan%3E31&rft.date=2009-12&rft_id=info%3Adoi%2F10.1109%2FMCOM.2009.5350364&rft_id=https%3A%2F%2Fapi.semanticscholar.org%2FCorpusID%3A23243636%23id-name%3DS2CID&rft.aulast=Rybczynski&rft.aufirst=Tony&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-CcittMay1975-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-CcittMay1975_19-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFINWG#99" class="citation web cs1">INWG#99. <a rel="nofollow" class="external text" href="https://umedia.lib.umn.edu/item/p16022coll270:13610/p16022coll270:13465?child_index=90&query=&sidebar_page=31">"Report of the Meeting in Geneva (28 May - 6 June 1975) (Extracts)"</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Report+of+the+Meeting+in+Geneva+%2828+May+-+6+June+1975%29+%28Extracts%29&rft.au=INWG%2399&rft_id=https%3A%2F%2Fumedia.lib.umn.edu%2Fitem%2Fp16022coll270%3A13610%2Fp16022coll270%3A13465%3Fchild_index%3D90%26query%3D%26sidebar_page%3D31&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_web" title="Template:Cite web">cite web</a>}}</code>: CS1 maint: numeric names: authors list (<a href="/wiki/Category:CS1_maint:_numeric_names:_authors_list" title="Category:CS1 maint: numeric names: authors list">link</a>)</span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFPouzin1975" class="citation web cs1">Pouzin, Louis (October 1975). <a rel="nofollow" class="external text" href="https://umedia.lib.umn.edu/item/p16022coll270:13610/p16022coll270:13486?child_index=111&query=&sidebar_page=38">"Meeting of the CCITT Rapporteur group on packet switching – (Geneva, 16 – 19 September 1975)"</a>. p. 6 in Annex 4.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Meeting+of+the+CCITT+Rapporteur+group+on+packet+switching+%E2%80%93+%28Geneva%2C+16+%E2%80%93+19+September+1975%29&rft.pages=6+in+Annex+4&rft.date=1975-10&rft.aulast=Pouzin&rft.aufirst=Louis&rft_id=https%3A%2F%2Fumedia.lib.umn.edu%2Fitem%2Fp16022coll270%3A13610%2Fp16022coll270%3A13486%3Fchild_index%3D111%26query%3D%26sidebar_page%3D38&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-Schatt_1991_200-21"><span class="mw-cite-backlink">^ <a href="#cite_ref-Schatt_1991_200_21-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Schatt_1991_200_21-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">(<a href="#CITEREFSchatt1991">Schatt 1991</a>, p. 200).</span> </li> <li id="cite_note-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-22">^</a></b></span> <span class="reference-text">(<a href="#CITEREFSchatt1991">Schatt 1991</a>, p. 207).</span> </li> <li id="cite_note-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-23">^</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="https://web.archive.org/web/20120121002501/http://www.techrepublic.com/article/running-x25-over-tcpip-on-cisco-routers/1056023">"Running X.25 over TCP/IP on Cisco routers"</a>. 1 February 2001. Archived from <a rel="nofollow" class="external text" href="https://www.techrepublic.com/article/running-x25-over-tcpip-on-cisco-routers/1056023">the original</a> on 21 January 2012.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Running+X.25+over+TCP%2FIP+on+Cisco+routers&rft.date=2001-02-01&rft_id=http%3A%2F%2Fwww.techrepublic.com%2Farticle%2Frunning-x25-over-tcpip-on-cisco-routers%2F1056023&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-24">^</a></b></span> <span class="reference-text"><span class="languageicon">(in French)</span> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFPresse2011" class="citation news cs1 cs1-prop-foreign-lang-source">Presse, Agence France (21 July 2011). <a rel="nofollow" class="external text" href="http://www.lefigaro.fr/flash-actu/2011/07/21/97001-20110721FILWWW00446-le-minitel-disparaitra-en-juin-2012.php">"Le Minitel disparaîtra en juin 2012"</a> [Minitel will disappear in June 2012]. <i>Le Figaro</i> (in French).</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=Le+Figaro&rft.atitle=Le+Minitel+dispara%C3%AEtra+en+juin+2012&rft.date=2011-07-21&rft.aulast=Presse&rft.aufirst=Agence+France&rft_id=http%3A%2F%2Fwww.lefigaro.fr%2Fflash-actu%2F2011%2F07%2F21%2F97001-20110721FILWWW00446-le-minitel-disparaitra-en-juin-2012.php&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-25">^</a></b></span> <span class="reference-text"><span class="languageicon">(in French)</span><a rel="nofollow" class="external autonumber" href="http://www.zdnet.fr/actualites/minitel-dernier-rappel-arret-definitif-le-30-juin-2012-39769465.htm">[1]</a></span> </li> <li id="cite_note-26"><span class="mw-cite-backlink"><b><a href="#cite_ref-26">^</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="https://www.bt.com/pricing/current/BT_IP_Networking_boo/2-0177_d0e27.htm">"BT price list: Section 13:BT IP Networking"</a>. <i>BT</i><span class="reference-accessdate">. Retrieved <span class="nowrap">30 May</span> 2019</span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=BT&rft.atitle=BT+price+list%3A+Section+13%3ABT+IP+Networking&rft_id=https%3A%2F%2Fwww.bt.com%2Fpricing%2Fcurrent%2FBT_IP_Networking_boo%2F2-0177_d0e27.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></span> </li> <li id="cite_note-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-27">^</a></b></span> <span class="reference-text">ISO 8208:2000</span> </li> <li id="cite_note-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-28">^</a></b></span> <span class="reference-text">ISO 8208, Annex B.</span> </li> <li id="cite_note-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-29">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25</a>, G.3.2 Called address extension facility, pp. 141–142.</span> </li> <li id="cite_note-30"><span class="mw-cite-backlink"><b><a href="#cite_ref-30">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.223/en/">ITU-T Recommendation X.223</a>, Appendix II.</span> </li> <li id="cite_note-31"><span class="mw-cite-backlink"><b><a href="#cite_ref-31">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.7-200404-I/en/">ITU-T Recommendation X.7 (04/2004)</a>, pp. 17–18.</span> </li> <li id="cite_note-x223-32"><span class="mw-cite-backlink"><b><a href="#cite_ref-x223_32-0">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.223/en/">ITU-T Recommendation X.223</a>.</span> </li> <li id="cite_note-33"><span class="mw-cite-backlink"><b><a href="#cite_ref-33">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25 (10/96)</a>, Annex G, p. 140.</span> </li> <li id="cite_note-34"><span class="mw-cite-backlink"><b><a href="#cite_ref-34">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.213-200110-I/en/">ITU-T Recommendation X.213</a>, Annex A.</span> </li> <li id="cite_note-channels-35"><span class="mw-cite-backlink">^ <a href="#cite_ref-channels_35-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-channels_35-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-channels_35-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25 (10/96)</a>, p. 45.</span> </li> <li id="cite_note-36"><span class="mw-cite-backlink"><b><a href="#cite_ref-36">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.283-199712-I/en/">ITU-T Recommendation X.283 (12/97)</a>, p. 42.</span> </li> <li id="cite_note-x25annexa-37"><span class="mw-cite-backlink">^ <a href="#cite_ref-x25annexa_37-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-x25annexa_37-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25 (10/96)</a>, Annex A, pp. 119–120.</span> </li> <li id="cite_note-38"><span class="mw-cite-backlink"><b><a href="#cite_ref-38">^</a></b></span> <span class="reference-text">ISO/IEC 8208:2000, Fourth Edition, p. 61.</span> </li> <li id="cite_note-39"><span class="mw-cite-backlink"><b><a href="#cite_ref-39">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.2-200003-I/en/">ITU-T Recommendation X.2 (03/2000)</a>, p. 4.</span> </li> <li id="cite_note-40"><span class="mw-cite-backlink"><b><a href="#cite_ref-40">^</a></b></span> <span class="reference-text">ISO/IEC 8208:2000, Fourth Edition, 3.7.1, p. 7.</span> </li> <li id="cite_note-41"><span class="mw-cite-backlink"><b><a href="#cite_ref-41">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-D.11-199103-I/en/">ITU-T Recommendation D.11 (03/91)</a>, p. 2.</span> </li> <li id="cite_note-42"><span class="mw-cite-backlink"><b><a href="#cite_ref-42">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-D.12-198811-I/en/">ITU-T Recommendation D.12 (11/88)</a>, p. 1.</span> </li> <li id="cite_note-43"><span class="mw-cite-backlink"><b><a href="#cite_ref-43">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.7-200404-I/en/">ITU-T Recommendation X.7 (04/2004)</a>, p. 42.</span> </li> <li id="cite_note-44"><span class="mw-cite-backlink"><b><a href="#cite_ref-44">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-D.11-199103-I/en/">ITU-T Recommendation D.11 (03/91)</a>, p. 3.</span> </li> <li id="cite_note-45"><span class="mw-cite-backlink"><b><a href="#cite_ref-45">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.7-200404-I/en/">ITU-T Recommendation X.7 (04/2004)</a>, p. 38.</span> </li> <li id="cite_note-46"><span class="mw-cite-backlink"><b><a href="#cite_ref-46">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.2/en/">ITU-T Recommendation X.2</a></span> </li> <li id="cite_note-47"><span class="mw-cite-backlink"><b><a href="#cite_ref-47">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.7/en/">ITU-T Recommendation X.7</a></span> </li> <li id="cite_note-48"><span class="mw-cite-backlink"><b><a href="#cite_ref-48">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25 (10/96)</a>, Summary, p. v.</span> </li> <li id="cite_note-49"><span class="mw-cite-backlink"><b><a href="#cite_ref-49">^</a></b></span> <span class="reference-text">ISO/IEC 8208:2000, Fourth Edition, Section 1: Scope, p. 1.</span> </li> <li id="cite_note-annexc-50"><span class="mw-cite-backlink">^ <a href="#cite_ref-annexc_50-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-annexc_50-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">ISO/IEC 8208:2000, Fourth Edition, Annex C.</span> </li> <li id="cite_note-51"><span class="mw-cite-backlink"><b><a href="#cite_ref-51">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25/en/">ITU-T Recommendation X.25</a>.</span> </li> <li id="cite_note-52"><span class="mw-cite-backlink"><b><a href="#cite_ref-52">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199303-S/en/">ITU-T Recommendation X.25 (1993) White Book</a></span> </li> <li id="cite_note-53"><span class="mw-cite-backlink"><b><a href="#cite_ref-53">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itu.int/rec/T-REC-X.25-199610-I/en/">ITU-T Recommendation X.25 (1996) Grey Book</a></span> </li> </ol></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=X.25&action=edit&section=17" title="Edit section: Further reading"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1239549316">.mw-parser-output .refbegin{margin-bottom:0.5em}.mw-parser-output .refbegin-hanging-indents>ul{margin-left:0}.mw-parser-output .refbegin-hanging-indents>ul>li{margin-left:0;padding-left:3.2em;text-indent:-3.2em}.mw-parser-output .refbegin-hanging-indents ul,.mw-parser-output .refbegin-hanging-indents ul li{list-style:none}@media(max-width:720px){.mw-parser-output .refbegin-hanging-indents>ul>li{padding-left:1.6em;text-indent:-1.6em}}.mw-parser-output .refbegin-columns{margin-top:0.3em}.mw-parser-output .refbegin-columns ul{margin-top:0}.mw-parser-output .refbegin-columns li{page-break-inside:avoid;break-inside:avoid-column}@media screen{.mw-parser-output .refbegin{font-size:90%}}</style><div class="refbegin" style=""> <ul><li>Computer Communications, lecture notes by Prof. Chaim Ziegler PhD, <a href="/wiki/Brooklyn_College" title="Brooklyn College">Brooklyn College</a></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFMotorola_Codex1992" class="citation book cs1">Motorola Codex (1992). <i>The Basics Book of X.25 Packet Switching</i>. The Basics Book Series (2nd ed.). Reading, MA: Addison-Wesley. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-201-56369-X" title="Special:BookSources/0-201-56369-X"><bdi>0-201-56369-X</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+Basics+Book+of+X.25+Packet+Switching&rft.place=Reading%2C+MA&rft.series=The+Basics+Book+Series&rft.edition=2nd&rft.pub=Addison-Wesley&rft.date=1992&rft.isbn=0-201-56369-X&rft.au=Motorola+Codex&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFDeasington1985" class="citation book cs1">Deasington, Richard (1985). <i>X.25 Explained</i>. Computer Communications and Networking (2nd ed.). Chichester UK: Ellis Horwood. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-85312-626-3" title="Special:BookSources/978-0-85312-626-3"><bdi>978-0-85312-626-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=X.25+Explained&rft.place=Chichester+UK&rft.series=Computer+Communications+and+Networking&rft.edition=2nd&rft.pub=Ellis+Horwood&rft.date=1985&rft.isbn=978-0-85312-626-3&rft.aulast=Deasington&rft.aufirst=Richard&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFFriendFikeBakerBellamy1988" class="citation book cs1">Friend, George E.; Fike, John L.; Baker, H. Charles; Bellamy, John C. (1988). <i>Understanding Data Communications</i> (2nd ed.). Indianapolis: Howard W. Sams & Company. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-672-27270-9" title="Special:BookSources/0-672-27270-9"><bdi>0-672-27270-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Understanding+Data+Communications&rft.place=Indianapolis&rft.edition=2nd&rft.pub=Howard+W.+Sams+%26+Company&rft.date=1988&rft.isbn=0-672-27270-9&rft.aulast=Friend&rft.aufirst=George+E.&rft.au=Fike%2C+John+L.&rft.au=Baker%2C+H.+Charles&rft.au=Bellamy%2C+John+C.&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFPoochWilliam_H._GreeneGary_G._Moss1983" class="citation book cs1">Pooch, Udo W.; William H. Greene; Gary G. Moss (1983). <i>Telecommunications and Networking</i>. Boston: Little, Brown and Company. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-316-71498-4" title="Special:BookSources/0-316-71498-4"><bdi>0-316-71498-4</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Telecommunications+and+Networking&rft.place=Boston&rft.pub=Little%2C+Brown+and+Company&rft.date=1983&rft.isbn=0-316-71498-4&rft.aulast=Pooch&rft.aufirst=Udo+W.&rft.au=William+H.+Greene&rft.au=Gary+G.+Moss&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFSchatt1991" class="citation book cs1">Schatt, Stan (1991). <i>Linking LANs: A Micro Manager's Guide</i>. McGraw-Hill. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8306-3755-9" title="Special:BookSources/0-8306-3755-9"><bdi>0-8306-3755-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Linking+LANs%3A+A+Micro+Manager%27s+Guide&rft.pub=McGraw-Hill&rft.date=1991&rft.isbn=0-8306-3755-9&rft.aulast=Schatt&rft.aufirst=Stan&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li> <li><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222" /><cite id="CITEREFThorpeRoss1992" class="citation book cs1">Thorpe, Nicolas M.; Ross, Derek (1992). <i>X.25 Made Easy</i>. Prentice Hall. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-13-972183-5" title="Special:BookSources/0-13-972183-5"><bdi>0-13-972183-5</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=X.25+Made+Easy&rft.pub=Prentice+Hall&rft.date=1992&rft.isbn=0-13-972183-5&rft.aulast=Thorpe&rft.aufirst=Nicolas+M.&rft.au=Ross%2C+Derek&rfr_id=info%3Asid%2Fen.wikipedia.org%3AX.25" class="Z3988"></span></li></ul> </div> <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=X.25&action=edit&section=18" 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.itu.int/rec/T-REC-X.25/en">Recommendation X.25</a> at ITU-T</li> <li><a rel="nofollow" class="external text" href="http://docwiki.cisco.com/wiki/X.25">Cisco X.25 Reference</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20180619040925/http://docwiki.cisco.com/wiki/X.25">Archived</a> 19 June 2018 at the <a href="/wiki/Wayback_Machine" title="Wayback Machine">Wayback Machine</a></li> <li><a rel="nofollow" class="external text" href="http://www.farsite.com/X.25/X.25_info/X.25.htm">An X.25 Networking Guide with comparisons to TCP/IP</a></li> <li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20110723064137/http://softtechinfo.com/network/x25.html">X.25 – Directory & Informational Resource</a></li> <li><a rel="nofollow" class="external text" href="https://archive.today/20121220213108/http://search.dmoz.org/cgi-bin/search?search=X.25">RFCs and other resources by Open Directory</a></li></ul> <div class="navbox-styles"><style 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<script>(RLQ=window.RLQ||[]).push(function(){mw.config.set({"wgHostname":"mw-web.codfw.main-65585cc8dc-62g4w","wgBackendResponseTime":134,"wgPageParseReport":{"limitreport":{"cputime":"0.575","walltime":"0.693","ppvisitednodes":{"value":5726,"limit":1000000},"postexpandincludesize":{"value":53627,"limit":2097152},"templateargumentsize":{"value":2905,"limit":2097152},"expansiondepth":{"value":15,"limit":100},"expensivefunctioncount":{"value":6,"limit":500},"unstrip-depth":{"value":1,"limit":20},"unstrip-size":{"value":93362,"limit":5000000},"entityaccesscount":{"value":1,"limit":400},"timingprofile":["100.00% 610.822 1 -total"," 41.34% 252.485 1 Template:Reflist"," 14.58% 89.034 10 Template:Cite_web"," 12.72% 77.694 2 Template:In_lang"," 10.46% 63.864 1 Template:Authority_control"," 9.33% 56.960 8 Template:R"," 8.66% 52.917 1 Template:Short_description"," 8.33% 50.885 8 Template:R/ref"," 6.09% 37.177 5 Template:Harv"," 5.91% 36.081 8 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1,\n [\"Citation needed\"] = 1,\n [\"Cite book\"] = 6,\n [\"Cite journal\"] = 4,\n [\"Cite news\"] = 1,\n [\"Cite web\"] = 10,\n [\"Clarify\"] = 1,\n [\"Harv\"] = 5,\n [\"In lang\"] = 2,\n [\"Infobox technology standard\"] = 1,\n [\"Main\"] = 1,\n [\"R\"] = 8,\n [\"Refbegin\"] = 1,\n [\"Refend\"] = 1,\n [\"Reflist\"] = 1,\n [\"See also\"] = 1,\n [\"Short description\"] = 1,\n [\"Snd\"] = 4,\n [\"Use dmy dates\"] = 1,\n [\"Webarchive\"] = 1,\n}\narticle_whitelist = table#1 {\n}\nciteref_patterns = table#1 {\n}\n"},"cachereport":{"origin":"mw-web.codfw.main-684955989f-n87qp","timestamp":"20250331180246","ttl":2592000,"transientcontent":false}}});});</script> <script type="application/ld+json">{"@context":"https:\/\/schema.org","@type":"Article","name":"X.25","url":"https:\/\/en.wikipedia.org\/wiki\/X.25","sameAs":"http:\/\/www.wikidata.org\/entity\/Q622993","mainEntity":"http:\/\/www.wikidata.org\/entity\/Q622993","author":{"@type":"Organization","name":"Contributors to Wikimedia projects"},"publisher":{"@type":"Organization","name":"Wikimedia Foundation, Inc.","logo":{"@type":"ImageObject","url":"https:\/\/www.wikimedia.org\/static\/images\/wmf-hor-googpub.png"}},"datePublished":"2002-03-08T07:54:45Z","dateModified":"2025-03-10T08:38:16Z","image":"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/5\/5c\/X25-network-diagram-0a.svg","headline":"standard protocol suite for packet switched wide area network (WAN) communication"}</script> </body> </html>