H-TCP

<h2 id="principles-of-operation">Principles of operation</h2>
<p>H-TCP is a <a href="/facts/Packet_loss/6fuIcFHk">loss-based</a> algorithm, using additive-increase/multiplicative-decrease (AIMD) to control TCP's congestion window.  It is one of many <a href="/facts/TCP_congestion_control/gC9Fer09">TCP congestion avoidance algorithms</a> which seeks to increase the aggressiveness of TCP on high bandwidth-delay product (BDP) paths, while maintaining "TCP friendliness" for small BDP paths.  H-TCP increases its aggressiveness (in particular, the rate of additive increase) as the time since the previous loss increases.  This avoids the problem encountered by <a href="/facts/HSTCP/AFkHo6Cx">HSTCP</a> and <a href="/facts/BIC_TCP/LepFBbHI">BIC TCP</a> of making flows more aggressive if their windows are already large. Thus, new flows can be expected to converge to fairness faster under HTCP than HSTCP and BIC TCP.
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<h2 id="strengths-and-weaknesses">Strengths and weaknesses</h2>
<p>A side effect of increasing the rate of increase as the time since the last packet loss increases, is that flows which happen not to lose a packet when other flows do, can then take an unfair portion of the <a href="/facts/Bandwidth_(computing)/lY6Tb4gX">bandwidth</a>.  Techniques to overcome this are currently in the research phase.
</p><p>The Linux implementation of H-TCP also has an option for avoiding "<a href="/facts/Round-trip_delay_time/jYgNMK98">RTT</a> unfairness", which occurs in <a href="/facts/TCP_Reno/gC9Fer09">TCP Reno</a>, but is a particular problem for most high-speed variants of TCP (although not <a href="/facts/FAST_TCP/c5JIdo8N">FAST TCP</a>).
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<h2 id="name">Name</h2>
<p>The algorithm was initially introduced as H-TCP, without mention of what the H stands for.  However, it is often called <i>Hamilton TCP</i>, for the <a href="/facts/Hamilton_Institute/dH3LzMpC">Hamilton Institute</a> where it was created.
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/TCP_congestion_control/gC9Fer09">TCP congestion control</a></li>
<li><a href="/facts/Transmission_Control_Protocol/WW4sPrt9">Transmission Control Protocol#Historical origin</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li><a href="http://www.hamilton.ie/net/htcp/">H-TCP</a> Home Page</li></ul>

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

<ol>
<li id="fn:1"><p>Armitage, Grenville; Stewart, Lawrence; Welzl, Michael; Healy, James (2008). "An independent H-TCP implementation under FreeBSD 7.0". ACM SIGCOMM Computer Communication Review. 38 (3): 27–38. doi:10.1145/1384609.1384613. hdl:1959.3/40394. S2CID 7175592. <a href="http://dl.acm.org/citation.cfm?doid=1384609.1384613" target="_blank">http://dl.acm.org/citation.cfm?doid=1384609.1384613</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
</ol>

H-TCP open-in-new

H-TCP