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Go-Back-N ARQ
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<h2 id="pseudocode">Pseudocode</h2> <p>These examples assume an infinite number of sequence and request numbers.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <i>N</i> := window size <i>Rn</i> := request number <i>Sn</i> := sequence number <i>Sb</i> := sequence base <i>Sm</i> := sequence max function receiver is <i>Rn</i> := 0 Do the following forever: if the packet received = Rn and the packet is error free then Accept the packet and send it to a higher layer <i>Rn</i> := <i>Rn</i> + 1 else Refuse packet Send a Request for <i>Rn</i> function sender is <i>Sb</i> := 0 <i>Sm</i> := <i>N</i> + 1 Repeat the following steps forever: if you receive a request number where <i>Rn</i> > <i>Sb</i> then <i>Sm</i> := (<i>Sm</i> − <i>Sb</i>) + <i>Rn</i> <i>Sb</i> := <i>Rn</i> if no packet is in transmission then Transmit a packet where <i>Sb</i> ≤ <i>Sn</i> ≤ <i>Sm</i>. Packets are transmitted in order. <h2 id="choosing-a-window-size-n">Choosing a window size (<i>N</i>)</h2> <p>There are a few things to keep in mind when choosing a value for N: </p> <ol><li>The sender must not transmit too fast. N should be bounded by the receiver’s ability to process packets.</li> <li>N must be smaller than the number of sequence numbers (if they are numbered from zero to N) to verify transmission in cases of any packet (any data or ACK packet) being dropped.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li> <li>Given the bounds presented in (1) and (2), choose N to be the largest number possible.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li></ol> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Reliable_Data_Transfer/HQ8SD4NP">Reliable Data Transfer</a></li> <li><a href="/facts/Pipeline_(software)/vNahQdsH">Pipeline (software)</a></li> <li><a href="/facts/Automatic_repeat_request/1bR2urmF">Automatic repeat request</a></li> <li><a href="/facts/Computer_networking/3w5RM99p">Computer networking</a></li> <li><a href="/facts/Selective_Repeat_ARQ/cuMB31b5">Selective Repeat ARQ</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="http://media.pearsoncmg.com/aw/aw_kurose_network_4/applets/go-back-n/index.html">Go-Back-N ARQ demonstration in a Java applet</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Kurose, James F.; Keith W. Ross. Computer Networking: A Top-Down Approach. ISBN 0-321-49770-8. <a href="0-321-49770-8" target="_blank">0-321-49770-8</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Tanenbaum, Andrew S. (2003). Computer Networks (4th ed.). Prentice Hall. ISBN 0-13-066102-3. <a href="0-13-066102-3" target="_blank">0-13-066102-3</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Kurose, James F.; Keith W. Ross. Computer Networking: A Top-Down Approach. ISBN 0-321-49770-8. <a href="0-321-49770-8" target="_blank">0-321-49770-8</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Tanenbaum, Andrew S. (2003). Computer Networks (4th ed.). Prentice Hall. ISBN 0-13-066102-3. <a href="0-13-066102-3" target="_blank">0-13-066102-3</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Marbach, Peter. "ARQ Protocols" (PDF). Retrieved August 24, 2013. <a href="http://www.cs.toronto.edu/~marbach/COURSES/CSC358_S14/l4.pdf" target="_blank">http://www.cs.toronto.edu/~marbach/COURSES/CSC358_S14/l4.pdf</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> </ol>