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.Dd May 13, 2021 32.Dt CC_HTCP 4 33.Os 34.Sh NAME 35.Nm cc_htcp 36.Nd H-TCP Congestion Control Algorithm 37.Sh DESCRIPTION 38The H-TCP congestion control algorithm was designed to provide increased 39throughput in fast and long-distance networks. 40It attempts to maintain fairness when competing with legacy NewReno TCP in lower 41speed scenarios where NewReno is able to operate adequately. 42.Pp 43The congestion window is increased as a function of the time elapsed since the 44last congestion event. 45The window increase algorithm operates like NewReno for the first second after a 46congestion event, and then switches to a high-speed mode based on a quadratic 47increase function. 48.Pp 49The implementation was done in a clean-room fashion, and is based on the 50Internet Draft and other documents referenced in the 51.Sx SEE ALSO 52section below. 53.Sh MIB Variables 54The algorithm exposes the following tunable variables in the 55.Va net.inet.tcp.cc.htcp 56branch of the 57.Xr sysctl 3 58MIB: 59.Bl -tag -width ".Va adaptive_backoff" 60.It Va adaptive_backoff 61Controls use of the adaptive backoff algorithm, which is designed to keep 62network queues non-empty during congestion recovery episodes. 63Default is 0 (disabled). 64.It Va rtt_scaling 65Controls use of the RTT scaling algorithm, which is designed to make congestion 66window increase during congestion avoidance mode invariant with respect to RTT. 67Default is 0 (disabled). 68.El 69.Sh SEE ALSO 70.Xr cc_cdg 4 , 71.Xr cc_chd 4 , 72.Xr cc_cubic 4 , 73.Xr cc_dctcp 4 , 74.Xr cc_hd 4 , 75.Xr cc_newreno 4 , 76.Xr cc_vegas 4 , 77.Xr mod_cc 4 , 78.Xr tcp 4 , 79.Xr mod_cc 9 80.Rs 81.%A "D. Leith" 82.%A "R. Shorten" 83.%T "H-TCP: TCP Congestion Control for High Bandwidth-Delay Product Paths" 84.%U "https://tools.ietf.org/id/draft-leith-tcp-htcp-06.txt" 85.Re 86.Rs 87.%A "D. Leith" 88.%A "R. Shorten" 89.%A "T. Yee" 90.%T "H-TCP: A framework for congestion control in high-speed and long-distance networks" 91.%B "Proc. PFLDnet" 92.%D "2005" 93.Re 94.Rs 95.%A "G. Armitage" 96.%A "L. Stewart" 97.%A "M. Welzl" 98.%A "J. Healy" 99.%T "An independent H-TCP implementation under FreeBSD 7.0: description and observed behaviour" 100.%J "SIGCOMM Comput. Commun. Rev." 101.%V "38" 102.%N "3" 103.%D "July 2008" 104.%P "27-38" 105.Re 106.Sh ACKNOWLEDGEMENTS 107Development and testing of this software were made possible in part by grants 108from the FreeBSD Foundation and Cisco University Research Program Fund at 109Community Foundation Silicon Valley. 110.Sh HISTORY 111The 112.Nm 113congestion control module first appeared in 114.Fx 9.0 . 115.Pp 116The module was first released in 2007 by James Healy and Lawrence Stewart whilst 117working on the NewTCP research project at Swinburne University of Technology's 118Centre for Advanced Internet Architectures, Melbourne, Australia, which was made 119possible in part by a grant from the Cisco University Research Program Fund at 120Community Foundation Silicon Valley. 121More details are available at: 122.Pp 123http://caia.swin.edu.au/urp/newtcp/ 124.Sh AUTHORS 125.An -nosplit 126The 127.Nm 128congestion control module was written by 129.An James Healy Aq Mt jimmy@deefa.com 130and 131.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 132.Pp 133This manual page was written by 134.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 135and 136.An David Hayes Aq Mt david.hayes@ieee.org . 137