{"id":325,"date":"2020-11-30T15:54:25","date_gmt":"2020-11-30T20:54:25","guid":{"rendered":"https:\/\/www.alpharithms.com\/?post_type=term&#038;p=325"},"modified":"2021-07-27T08:08:32","modified_gmt":"2021-07-27T12:08:32","slug":"fast-restransmit","status":"publish","type":"post","link":"https:\/\/www.alpharithms.com\/fast-restransmit-255415\/","title":{"rendered":"Fast Restransmit (TCP)"},"content":{"rendered":"<p>Fast Retransmit is part of <a href=\"https:\/\/www.alpharithms.com\/tcp-network-congestion-control-514314\/\">TCP&#8217;s congestion control algorithm<\/a> that is responsible for retransmission of data segments that have been deemed to be missing. Fast retransmit is triggered when 3 duplicate <a href=\"https:\/\/www.alpharithms.com\/term\/acknowledgment-ack\/\">acknowledgments (ACKs)<\/a> are received for the same data segment.<\/p>\n<p>The receipt of 3 duplicate ACKs informs the sender that the receiver has not received the data segment directly proceeding the last ACKd segment. This reception of 3 Duplicate ACKs is the functional equivalent of a\u00a0<em>negative-acknowledgment<\/em> and indicative of <a href=\"https:\/\/www.alpharithms.com\/reliable-data-transfer-protocols-rdt-173114\/\">data loss or corruption<\/a>.<\/p>\n<p>Duplicate ACKs are also a form of indicating that data segments were received out-of-order from their intended sequence. In any of the above cases, the solution is to initiate retransmission of data.<\/p>\n<p>The term fast retransmit was first standardized in the <a href=\"https:\/\/tools.ietf.org\/html\/rfc2001\">1997 RFC2001<\/a> within a broader context of defining TCP&#8217;s Congestion Control algorithm. In this context, <em>fast retransmit<\/em> In a later 2009<a href=\"https:\/\/tools.ietf.org\/html\/rfc5681#section-3.2\"> RFC5681<\/a> the term was expanded as the following:<\/p>\n<p style=\"padding-left: 40px;\"><em>The TCP sender SHOULD use the &#8220;fast retransmit&#8221; algorithm to detect and repair loss, based on incoming duplicate ACKs. The fast retransmit algorithm uses the arrival of 3 duplicate ACKs &#8230;\u00a0as an indication that a segment has been lost. After receiving 3 duplicate ACKs, TCP performs a retransmission of what appears to be the missing segment, without waiting for the retransmission timer to expire.<\/em><\/p>\n<p><strong>TL;DR<\/strong> &#8211; Fast Retransmit is enacted by retransmitting a data segment for which 3 ACKs have been received <em>without<\/em> waiting for the timer for that data segment to expire.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Fast Retransmit is part of TCP&#8217;s congestion control algorithm that is responsible for retransmission of data segments that have been deemed to be missing. Fast retransmit is triggered when 3 duplicate acknowledgments (ACKs) are received for the same data segment. The receipt of 3 duplicate ACKs informs the sender that the receiver has not received [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":2472,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":""},"categories":[3,260],"tags":[84,461,6],"acf":[],"_links":{"self":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/325"}],"collection":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/comments?post=325"}],"version-history":[{"count":1,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/325\/revisions"}],"predecessor-version":[{"id":326,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/posts\/325\/revisions\/326"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media\/2472"}],"wp:attachment":[{"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/media?parent=325"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/categories?post=325"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.alpharithms.com\/wp-json\/wp\/v2\/tags?post=325"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}