2 .\" Copyright (c) 2008 Lawrence Stewart <lstewart@FreeBSD.org>
3 .\" Copyright (c) 2010-2011 The FreeBSD Foundation
4 .\" All rights reserved.
6 .\" Portions of this documentation were written at the Centre for Advanced
7 .\" Internet Architectures, Swinburne University of Technology, Melbourne,
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38 .Nd H-TCP Congestion Control Algorithm
40 The H-TCP congestion control algorithm was designed to provide increased
41 throughput in fast and long-distance networks.
42 It attempts to maintain fairness when competing with legacy NewReno TCP in lower
43 speed scenarios where NewReno is able to operate adequately.
45 The congestion window is increased as a function of the time elapsed since the
46 last congestion event.
47 The window increase algorithm operates like NewReno for the first second after a
48 congestion event, and then switches to a high-speed mode based on a quadratic
51 The implementation was done in a clean-room fashion, and is based on the
52 Internet Draft and other documents referenced in the
56 The algorithm exposes the following tunable variables in the
57 .Va net.inet.tcp.cc.htcp
61 .Bl -tag -width ".Va adaptive_backoff"
62 .It Va adaptive_backoff
63 Controls use of the adaptive backoff algorithm, which is designed to keep
64 network queues non-empty during congestion recovery episodes.
65 Default is 0 (disabled).
67 Controls use of the RTT scaling algorithm, which is designed to make congestion
68 window increase during congestion avoidance mode invariant with respect to RTT.
69 Default is 0 (disabled).
85 .%T "H-TCP: TCP Congestion Control for High Bandwidth-Delay Product Paths"
86 .%U "https://tools.ietf.org/id/draft-leith-tcp-htcp-06.txt"
92 .%T "H-TCP: A framework for congestion control in high-speed and long-distance networks"
101 .%T "An independent H-TCP implementation under FreeBSD 7.0: description and observed behaviour"
102 .%J "SIGCOMM Comput. Commun. Rev."
109 Development and testing of this software were made possible in part by grants
110 from the FreeBSD Foundation and Cisco University Research Program Fund at
111 Community Foundation Silicon Valley.
115 congestion control module first appeared in
118 The module was first released in 2007 by James Healy and Lawrence Stewart whilst
119 working on the NewTCP research project at Swinburne University of Technology's
120 Centre for Advanced Internet Architectures, Melbourne, Australia, which was made
121 possible in part by a grant from the Cisco University Research Program Fund at
122 Community Foundation Silicon Valley.
123 More details are available at:
125 http://caia.swin.edu.au/urp/newtcp/
130 congestion control module was written by
131 .An James Healy Aq Mt jimmy@deefa.com
133 .An Lawrence Stewart Aq Mt lstewart@FreeBSD.org .
135 This manual page was written by
136 .An Lawrence Stewart Aq Mt lstewart@FreeBSD.org
138 .An David Hayes Aq Mt david.hayes@ieee.org .