Compound TCP

<h2 id="principles-of-operation">Principles of operation</h2>
<p>Like <a href="/facts/FAST_TCP/c5JIdo8N">FAST TCP</a> and <a href="/facts/TCP_Vegas/FRcKp7Cq">TCP Vegas</a>, Compound TCP uses estimates of queuing delay as a measure of congestion; if the queuing delay is small, it assumes that no links on its path are congested, and rapidly increases its rate. Unlike them, it does not seek to maintain a constant number of packets queued.
</p><p>Compound TCP maintains two congestion windows: a regular <a href="/facts/Additive_increase/multiplicative_decrease/GmlKkQtu">AIMD</a> window and a delay-based window.  The size of the actual sliding window used is the sum of these two windows.  The AIMD window is increased the same way that <a href="/facts/TCP_Reno/gC9Fer09">TCP Reno</a> increases it.  If the delay is small, the delay-based window increases rapidly to improve the utilisation of the network.  Once queuing is experienced, the delay window gradually decreases to compensate for the increase in the AIMD window.  The aim is to keep their sum approximately constant, at what the algorithm estimates is the path's <a href="/facts/Bandwidth-delay_product/72txR7o3">bandwidth-delay product</a>.  In particular, when queuing is detected, the delay-based window is reduced by the estimated queue size to avoid the problem of "persistent congestion" reported for FAST and Vegas.  Thus, unlike <a href="/facts/TCP-Illinois/sTS6958a">TCP-Illinois</a> and its precursor TCP Africa, Compound TCP can reduce its window in response to delay.  This increases its fairness to Reno.
</p><p>Descriptions of Compound TCP can be found in a conference paper,<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> an Internet-Draft,<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> and a US patent.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h2 id="windows-2003-and-xp-x64">Windows 2003 and XP x64</h2>
<p>A hotfix is available that adds CTCP support to 64 bit Windows XP and Windows Server 2003.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p><p>The following registry key can be set to 1 to enable, or 0 to disable:
</p>
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\TCPCongestionControl

<h2 id="windows-vista20087">Windows Vista/2008/7</h2>
<p>CTCP is enabled by default in computers running beta versions of Windows Server 2008 and disabled by default in computers running Windows Vista and 7.
</p><p>CTCP can be enabled with the command:
</p>
netsh interface tcp set global congestionprovider=ctcp

<p>or disabled with the command:
</p>
netsh interface tcp set global congestionprovider=none

<p>To display the current setting for CTCP use:
</p>
netsh interface tcp show global

<p>Parameter "Add-On Congestion Control Provider" will either have a value of "none" if CTCP is disabled or "ctcp" if it is enabled.
</p>
<h2 id="windows-8-and-up">Windows 8 and up</h2>
<p>Since Windows 8, Windows uses <a href="/facts/Windows_PowerShell/G1d10lwn">PowerShell</a> command <a href="https://technet.microsoft.com/en-us/library/hh826132(v=wps.630).aspx">Set-NetTCPSetting</a> to modify the congestion control algorithm. Around 2018, Microsoft moved from CTCP to using CUBIC in Windows 10 and the Xbox, because it was seen as very delay sensitive and also worked poorly in data centre, where delay variation was an issue.
</p>
<h2 id="linux">Linux</h2>
<p>CTCP was ported to <a href="/facts/Linux/9FvCKSTq">Linux</a> by Angelo P. Castellani. A patch derived from this was developed at Caltech, which included CTCP's TUning By Emulation (TUBE, and only released to researchers due to <a href="/facts/Software_patent/wI6RrYh3">software patents</a>.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a>[<i>better source needed</i>] Since kernel version 2.6.17 the module has been incompatible and fails to compile due to kernel API changes.
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/TCP_congestion_avoidance_algorithm/gC9Fer09">TCP congestion avoidance algorithm</a></li>
<li><a href="/facts/Explicit_Congestion_Notification/VKfVXcKp">Explicit Congestion Notification</a></li>
<li><a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol — Development</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="http://tools.ietf.org/html/draft-sridharan-tcpm-ctcp">Compound TCP Internet-Draft</a></li>
<li><a href="https://web.archive.org/web/20060424082735/http://research.microsoft.com/research/pubs/view.aspx?type=Technical%20Report&id=940">"A Compound TCP Approach for High-speed and Long Distance Networks"</a> July 2005</li>
<li><a href="http://www.microsoft.com/technet/community/columns/cableguy/cg1105.mspx">Performance Enhancements in the Next Generation TCP/IP Stack</a>, The Cable Guy</li>
<li><a href="http://research.microsoft.com/en-us/projects/ctcp/">The Compound TCP for High-speed and Long Distance Networks</a>, Microsoft Research publication</li>
<li><a href="https://web.archive.org/web/20070110215723/http://www.networkperformancedaily.com/2006/12/vistas_tcpip_promises_and_peri.html">Vista's TCP/IP Promises and Perils</a>, Article at Network Performance Daily</li>
<li><a href="https://web.archive.org/web/20080802222857/http://netlab.caltech.edu/lachlan/ctcp/">Caltech's Compound TCP patch for Linux</a></li>
<li>Enabling CTCP on 2003/XP x64: <a href="http://blog.tiensivu.com/aaron/archives/1537-KB-949316-Add-Compound-TCP-CTCP-support-to-XP-and-Server-2003.html">[1]</a> <a href="https://web.archive.org/web/20080506141517/http://blog.tiensivu.com/aaron/archives/1537-KB-949316-Add-Compound-TCP-CTCP-support-to-XP-and-Server-2003.html">Archived</a> May 6, 2008, at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a>,<a href="http://blog.tiensivu.com/aaron/archives/901-Compound-TCP-congestion-control-algorithm-in-Vista-can-make-lossyhigh-latency-connections-behave-better..html">[2]</a> <a href="https://web.archive.org/web/20080430113637/http://blog.tiensivu.com/aaron/archives/901-Compound-TCP-congestion-control-algorithm-in-Vista-can-make-lossyhigh-latency-connections-behave-better..html">Archived</a> April 30, 2008, at the <a href="/facts/Wayback_Machine/nmQ3a6JC">Wayback Machine</a></li>
<li><a href="http://www.hamilton.ie/net/delay_tests_final.pdf">Report on experimental evaluation of Compound TCP</a> <a href="http://www.hamilton.ie">Hamilton Institute</a> and <a href="http://netlab.caltech.edu">Caltech</a>, March 2008.</li>
<li><a href="http://www.comp.nus.edu.sg/~wuxiucha/research/reactive/publication/ctcp_study.pdf">A simulation-based study of Compound TCP</a> [<i>dead link</i>‍] July 14, 2008</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>A hotfix that adds Compound TCP (CTCP) support to computers that are running Windows Server 2003 or Windows XP is available <a href="http://support.microsoft.com/kb/949316" target="_blank">http://support.microsoft.com/kb/949316</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Tan, K.; Song, J.; Zhang, Q.; Sridharan, M. (2006). "A Compound TCP Approach for High-Speed and Long Distance Networks". Proceedings IEEE INFOCOM 2006. 25TH IEEE International Conference on Computer Communications. pp. 1–12. doi:10.1109/INFOCOM.2006.188. ISBN 1-4244-0221-2. S2CID 1741788. <a href="1-4244-0221-2" target="_blank">1-4244-0221-2</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Tan, Kun; Sridharan, Murari; Bansal, Deepak; Thaler, Dave. "Compound TCP: A New TCP Congestion Control for High-Speed and Long Distance Networks". Ietf Datatracker. <a href="https://tools.ietf.org/html/draft-sridharan-tcpm-ctcp-02" target="_blank">https://tools.ietf.org/html/draft-sridharan-tcpm-ctcp-02</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>"Compound transmission control protocol [US7577097B2]". Google Patents. March 22, 2005. <a href="https://patents.google.com/patent/US7577097" target="_blank">https://patents.google.com/patent/US7577097</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>A hotfix that adds Compound TCP (CTCP) support to computers that are running Windows Server 2003 or Windows XP is available <a href="http://support.microsoft.com/kb/949316" target="_blank">http://support.microsoft.com/kb/949316</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>"Compound TCP in Linux". Archived from the original on August 2, 2008. Retrieved January 4, 2011. <a href="https://web.archive.org/web/20080802222857/http://netlab.caltech.edu/lachlan/ctcp/" target="_blank">https://web.archive.org/web/20080802222857/http://netlab.caltech.edu/lachlan/ctcp/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
</ol>

Compound TCP open-in-new

Compound TCP