1.\" 2.\" Copyright (c) 2009 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 September 13, 2022 34.Dt CC_CUBIC 4 35.Os 36.Sh NAME 37.Nm cc_cubic 38.Nd CUBIC Congestion Control Algorithm 39.Sh DESCRIPTION 40The CUBIC congestion control algorithm was designed to provide increased 41throughput in fast and long-distance networks. 42The CUBIC congestion control algorithm is the default for TCP. 43It attempts to maintain fairness when competing with legacy NewReno TCP in lower 44speed scenarios where NewReno is able to operate adequately. 45.Pp 46The congestion window is increased as a function of the time elapsed since the 47last congestion event. 48During regular operation, the window increase function follows a cubic function, 49with the inflection point set to be the congestion window value reached at the 50last congestion event. 51CUBIC also calculates an estimate of the congestion window that NewReno would 52have achieved at a given time after a congestion event. 53When updating the congestion window, the algorithm will choose the larger of the 54calculated CUBIC and estimated NewReno windows. 55.Pp 56CUBIC also backs off less on congestion by changing the multiplicative decrease 57factor from 1/2 (used by standard NewReno TCP) to 4/5. 58.Pp 59The implementation was done in a clean-room fashion, and is based on the 60Internet Draft and paper referenced in the 61.Sx SEE ALSO 62section below. 63.Sh MIB Variables 64There are currently no tunable MIB variables. 65.Sh SEE ALSO 66.Xr cc_cdg 4 , 67.Xr cc_chd 4 , 68.Xr cc_dctcp 4 , 69.Xr cc_hd 4 , 70.Xr cc_htcp 4 , 71.Xr cc_newreno 4 , 72.Xr cc_vegas 4 , 73.Xr mod_cc 4 , 74.Xr tcp 4 , 75.Xr mod_cc 9 76.Rs 77.%A "Sangtae Ha" 78.%A "Injong Rhee" 79.%A "Lisong Xu" 80.%T "CUBIC for Fast Long-Distance Networks" 81.%U "https://tools.ietf.org/id/draft-rhee-tcpm-cubic-02.txt" 82.Re 83.Rs 84.%A "Sangtae Ha" 85.%A "Injong Rhee" 86.%A "Lisong Xu" 87.%T "CUBIC: a new TCP-friendly high-speed TCP variant" 88.%J "SIGOPS Oper. Syst. Rev." 89.%V "42" 90.%N "5" 91.%D "July 2008" 92.%P "64-74" 93.Re 94.Sh ACKNOWLEDGEMENTS 95Development and testing of this software were made possible in part by grants 96from the FreeBSD Foundation and Cisco University Research Program Fund at 97Community Foundation Silicon Valley. 98.Sh HISTORY 99The 100.Nm 101congestion control module first appeared in 102.Fx 9.0 . 103.Pp 104The module was first released in 2009 by Lawrence Stewart whilst studying at 105Swinburne University of Technology's Centre for Advanced Internet Architectures, 106Melbourne, Australia. 107More details are available at: 108.Pp 109http://caia.swin.edu.au/urp/newtcp/ 110.Sh AUTHORS 111.An -nosplit 112The 113.Nm 114congestion control module and this manual page were written by 115.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 116and 117.An David Hayes Aq Mt david.hayes@ieee.org . 118