{"id":242,"date":"2022-11-28T19:18:36","date_gmt":"2022-11-28T19:18:36","guid":{"rendered":"http:\/\/learnlearn.uk\/ibcs\/?page_id=242"},"modified":"2022-11-28T19:18:36","modified_gmt":"2022-11-28T19:18:36","slug":"automatic-repeat-requests-arqs","status":"publish","type":"page","link":"https:\/\/learnlearn.uk\/ibcs\/automatic-repeat-requests-arqs\/","title":{"rendered":"Automatic Repeat Requests (ARQs)"},"content":{"rendered":"<div class=\"responsive-tabs\">\n<h2 class=\"tabtitle\">ARQ Protocol<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Automatic Repeat Request Protocol<\/h3>\n<p>This is a protocol for error control over unreliable or noisy network connections. For each frame sent an acknowledgement is sent from the receiver to indicate that the frame has been successfully used. Checksums \/ check-digits are used to check the data integrity and timeouts are used if not reply is received.<br \/>\nThere are 3 versions of ARQ:<\/p>\n<ul>\n<li>Stop &amp; Wait<\/li>\n<li>Stop n go back<\/li>\n<li>Selective repeat<\/li>\n<\/ul>\n\n<\/div><h2 class=\"tabtitle\">Stop &amp; Wait<\/h2>\n<div class=\"tabcontent\">\n\n<h3>The Stop and Wait ARQ<\/h3>\n<div id=\"attachment_223\" style=\"width: 959px\" class=\"wp-caption alignnone\"><a href=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/Stop-and-wait-ARQ-1.jpg\"><img aria-describedby=\"caption-attachment-223\" decoding=\"async\" loading=\"lazy\" class=\"size-full wp-image-223\" src=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/Stop-and-wait-ARQ-1.jpg\" alt=\"\" width=\"949\" height=\"230\" \/><\/a><p id=\"caption-attachment-223\" class=\"wp-caption-text\">Stop and wait ARQ<\/p><\/div>\n<ol>\n<li>Data is sent from the sender to the receiver. Once sent the sender waits a certain amount of time for a response from the receiver.<\/li>\n<li>The receiver uses the checksum\/check digit from the frame to check the frame and ensure that data has been received correctly.<\/li>\n<li>The user sends a <strong>positive acknowledgement<\/strong>(ACK) to the sender to indicate the data been received correctly or a <strong>negative acknowledgement<\/strong> to indicate that the data has been corrupted.<\/li>\n<li>If the data has been incorrectly received or a <strong>time-out<\/strong> occurs(the time wait limit is exceeded) the sender resends the data.<\/li>\n<li>This process is repeated until all data has been received.<\/li>\n<\/ol>\n\n<\/div><h2 class=\"tabtitle\">Go back N ARQ<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Go back &amp; ARQ<\/h3>\n<div id=\"attachment_225\" style=\"width: 959px\" class=\"wp-caption alignnone\"><a href=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/Stop-go-back-ARQ-1.jpg\"><img aria-describedby=\"caption-attachment-225\" decoding=\"async\" loading=\"lazy\" class=\"size-full wp-image-225\" src=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/Stop-go-back-ARQ-1.jpg\" alt=\"\" width=\"949\" height=\"230\" \/><\/a><p id=\"caption-attachment-225\" class=\"wp-caption-text\">Stop &amp; Go Back ARQ<\/p><\/div>\n<p>In stop and go back ARQ the sender keeps sending data through in a constant stream, without waiting for an acknowledgment from the receiver &#8211; it just assumes that the data has been received successfully. If a negative acknowledgement is received or a timeout occurs the sender goes back to the last known good acknowledgement and starts again from there.<\/p>\n<p>This is an improvement over stop and wait because the senders full bandwidth can be used.<\/p>\n<p>&nbsp;<\/p>\n\n<\/div><h2 class=\"tabtitle\">Selective Repeat ARQ<\/h2>\n<div class=\"tabcontent\">\n\n<h3>Selective Repeat ARQ<\/h3>\n<p>&nbsp;<\/p>\n<div id=\"attachment_226\" style=\"width: 958px\" class=\"wp-caption alignnone\"><a href=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/selective-repeat-ARQ-1.jpg\"><img aria-describedby=\"caption-attachment-226\" decoding=\"async\" loading=\"lazy\" class=\"size-full wp-image-226\" src=\"https:\/\/learnlearn.uk\/igcsecs\/wp-content\/uploads\/sites\/23\/2021\/03\/selective-repeat-ARQ-1.jpg\" alt=\"\" width=\"948\" height=\"180\" \/><\/a><p id=\"caption-attachment-226\" class=\"wp-caption-text\">Selective Repeat ARQ<\/p><\/div>\n<p>Selective Repeat is an improvement over Go Back &amp; ARQ because only the frames that have been unsuccessfully received are retransmitted, rather than having to start all over again.<\/p>\n<p>&nbsp;<\/p>\n\n<\/div><h2 class=\"tabtitle\">Resources<\/h2>\n<div class=\"tabcontent\">\n\n<p><a href=\"https:\/\/docs.google.com\/presentation\/d\/1Fct7mRZSFp6H-i0CgFdHil8u7_3k2C1kKKI6dWgLYvg\/edit?usp=sharing\">Teacher Presentation<\/a><\/p>\n<p><a href=\"https:\/\/pastpapers.papacambridge.com\/viewer\/caie\/cambridge-upper-secondary-igcse-computer-science-0478-2016-nov-0478-w16-qp-11-pdf\">0478\/11 Paper 1 Theory October\/November 2016 Qn3<\/a><\/p>\n<p><a href=\"https:\/\/pastpapers.papacambridge.com\/viewer\/caie\/cambridge-upper-secondary-igcse-computer-science-0478-2017-jun-0478-s17-qp-11-pdf\">0478\/11 &#8211; Paper 1 Theory May\/June 2017 Qn 5<\/a>b<\/p>\n<p><a href=\"https:\/\/pastpapers.papacambridge.com\/viewer\/caie\/cambridge-upper-secondary-igcse-computer-science-0478-2017-jun-0478-s17-qp-12-pdf\">0478\/12 &#8211; Paper 1 Theory May\/June 2017<\/a>\u00a0 \u00a0Qn4<\/p>\n<p>&nbsp;<\/p>\n<\/div><\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Automatic Repeat Request Protocol This is a protocol for error control over unreliable or noisy network connections. For each frame sent an acknowledgement is sent from the receiver to indicate that the frame has been successfully used. Checksums \/ check-digits are used to check the data integrity and timeouts are used if not reply is&hellip;&nbsp;<a href=\"https:\/\/learnlearn.uk\/ibcs\/automatic-repeat-requests-arqs\/\" class=\"\" rel=\"bookmark\">Read More &raquo;<span class=\"screen-reader-text\">Automatic Repeat Requests (ARQs)<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"","neve_meta_content_width":70,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v20.6 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Automatic Repeat Requests (ARQs) - IB Computer Science<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/learnlearn.uk\/ibcs\/automatic-repeat-requests-arqs\/\" \/>\n<meta property=\"og:locale\" content=\"en_GB\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Automatic Repeat Requests (ARQs) - IB Computer Science\" \/>\n<meta property=\"og:description\" content=\"Automatic Repeat Request Protocol This is a protocol for error control over unreliable or noisy network connections. 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