1.\" 2.\" Copyright (c) 2008 Lawrence Stewart <lstewart@FreeBSD.org> 3.\" Copyright (c) 2010-2011 The FreeBSD Foundation 4.\" All rights reserved. 5.\" 6.\" Portions of this documentation were written at the Centre for Advanced 7.\" Internet Architectures, Swinburne University of Technology, Melbourne, 8.\" Australia by David Hayes under sponsorship from the FreeBSD Foundation. 9.\" 10.\" Redistribution and use in source and binary forms, with or without 11.\" modification, are permitted provided that the following conditions 12.\" are met: 13.\" 1. Redistributions of source code must retain the above copyright 14.\" notice, this list of conditions and the following disclaimer. 15.\" 2. Redistributions in binary form must reproduce the above copyright 16.\" notice, this list of conditions and the following disclaimer in the 17.\" documentation and/or other materials provided with the distribution. 18.\" 19.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 20.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 21.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 22.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR 23.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 24.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 25.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 26.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 27.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 28.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 29.\" SUCH DAMAGE. 30.\" 31.\" $FreeBSD$ 32.\" 33.Dd May 13, 2021 34.Dt CC_HTCP 4 35.Os 36.Sh NAME 37.Nm cc_htcp 38.Nd H-TCP Congestion Control Algorithm 39.Sh DESCRIPTION 40The H-TCP congestion control algorithm was designed to provide increased 41throughput in fast and long-distance networks. 42It attempts to maintain fairness when competing with legacy NewReno TCP in lower 43speed scenarios where NewReno is able to operate adequately. 44.Pp 45The congestion window is increased as a function of the time elapsed since the 46last congestion event. 47The window increase algorithm operates like NewReno for the first second after a 48congestion event, and then switches to a high-speed mode based on a quadratic 49increase function. 50.Pp 51The implementation was done in a clean-room fashion, and is based on the 52Internet Draft and other documents referenced in the 53.Sx SEE ALSO 54section below. 55.Sh MIB Variables 56The algorithm exposes the following tunable variables in the 57.Va net.inet.tcp.cc.htcp 58branch of the 59.Xr sysctl 3 60MIB: 61.Bl -tag -width ".Va adaptive_backoff" 62.It Va adaptive_backoff 63Controls use of the adaptive backoff algorithm, which is designed to keep 64network queues non-empty during congestion recovery episodes. 65Default is 0 (disabled). 66.It Va rtt_scaling 67Controls use of the RTT scaling algorithm, which is designed to make congestion 68window increase during congestion avoidance mode invariant with respect to RTT. 69Default is 0 (disabled). 70.El 71.Sh SEE ALSO 72.Xr cc_cdg 4 , 73.Xr cc_chd 4 , 74.Xr cc_cubic 4 , 75.Xr cc_dctcp 4 , 76.Xr cc_hd 4 , 77.Xr cc_newreno 4 , 78.Xr cc_vegas 4 , 79.Xr mod_cc 4 , 80.Xr tcp 4 , 81.Xr mod_cc 9 82.Rs 83.%A "D. Leith" 84.%A "R. Shorten" 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" 87.Re 88.Rs 89.%A "D. Leith" 90.%A "R. Shorten" 91.%A "T. Yee" 92.%T "H-TCP: A framework for congestion control in high-speed and long-distance networks" 93.%B "Proc. PFLDnet" 94.%D "2005" 95.Re 96.Rs 97.%A "G. Armitage" 98.%A "L. Stewart" 99.%A "M. Welzl" 100.%A "J. Healy" 101.%T "An independent H-TCP implementation under FreeBSD 7.0: description and observed behaviour" 102.%J "SIGCOMM Comput. Commun. Rev." 103.%V "38" 104.%N "3" 105.%D "July 2008" 106.%P "27-38" 107.Re 108.Sh ACKNOWLEDGEMENTS 109Development and testing of this software were made possible in part by grants 110from the FreeBSD Foundation and Cisco University Research Program Fund at 111Community Foundation Silicon Valley. 112.Sh HISTORY 113The 114.Nm 115congestion control module first appeared in 116.Fx 9.0 . 117.Pp 118The module was first released in 2007 by James Healy and Lawrence Stewart whilst 119working on the NewTCP research project at Swinburne University of Technology's 120Centre for Advanced Internet Architectures, Melbourne, Australia, which was made 121possible in part by a grant from the Cisco University Research Program Fund at 122Community Foundation Silicon Valley. 123More details are available at: 124.Pp 125http://caia.swin.edu.au/urp/newtcp/ 126.Sh AUTHORS 127.An -nosplit 128The 129.Nm 130congestion control module was written by 131.An James Healy Aq Mt jimmy@deefa.com 132and 133.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 134.Pp 135This manual page was written by 136.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 137and 138.An David Hayes Aq Mt david.hayes@ieee.org . 139