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.Dd February 4, 2023 32.Dt CC_CUBIC 4 33.Os 34.Sh NAME 35.Nm cc_cubic 36.Nd CUBIC Congestion Control Algorithm 37.Sh DESCRIPTION 38The CUBIC congestion control algorithm was designed to provide increased 39throughput in fast and long-distance networks. 40The CUBIC congestion control algorithm is the default for TCP. 41It attempts to maintain fairness when competing with legacy NewReno TCP in lower 42speed scenarios where NewReno is able to operate adequately. 43.Pp 44The congestion window is increased as a function of the time elapsed since the 45last congestion event. 46During regular operation, the window increase function follows a cubic function, 47with the inflection point set to be the congestion window value reached at the 48last congestion event. 49CUBIC also calculates an estimate of the congestion window that NewReno would 50have achieved at a given time after a congestion event. 51When updating the congestion window, the algorithm will choose the larger of the 52calculated CUBIC and estimated NewReno windows. 53.Pp 54CUBIC also backs off less on congestion by changing the multiplicative decrease 55factor from 1/2 (used by standard NewReno TCP) to 4/5. 56.Pp 57The implementation was done in a clean-room fashion, and is based on the 58Internet Draft and paper referenced in the 59.Sx SEE ALSO 60section below. 61.Sh MIB Variables 62There are currently no tunable MIB variables. 63.Sh SEE ALSO 64.Xr cc_cdg 4 , 65.Xr cc_chd 4 , 66.Xr cc_dctcp 4 , 67.Xr cc_hd 4 , 68.Xr cc_htcp 4 , 69.Xr cc_newreno 4 , 70.Xr cc_vegas 4 , 71.Xr mod_cc 4 , 72.Xr tcp 4 , 73.Xr mod_cc 9 74.Rs 75.%A "Sangtae Ha" 76.%A "Injong Rhee" 77.%A "Lisong Xu" 78.%T "CUBIC for Fast Long-Distance Networks" 79.%U "https://tools.ietf.org/id/draft-rhee-tcpm-cubic-02.txt" 80.Re 81.Rs 82.%A "Sangtae Ha" 83.%A "Injong Rhee" 84.%A "Lisong Xu" 85.%T "CUBIC: a new TCP-friendly high-speed TCP variant" 86.%J "SIGOPS Oper. Syst. Rev." 87.%V "42" 88.%N "5" 89.%D "July 2008" 90.%P "64-74" 91.Re 92.Sh ACKNOWLEDGEMENTS 93Development and testing of this software were made possible in part by grants 94from the FreeBSD Foundation and Cisco University Research Program Fund at 95Community Foundation Silicon Valley. 96.Sh HISTORY 97The 98.Nm 99congestion control module first appeared in 100.Fx 9.0 . 101.Pp 102This became the default congestion algorithm for FreeBSD in version 103.Fx 14.0 , 104replacing 105.Xr cc_newreno 4 . 106.Pp 107The module was first released in 2009 by Lawrence Stewart whilst studying at 108Swinburne University of Technology's Centre for Advanced Internet Architectures, 109Melbourne, Australia. 110More details are available at: 111.Pp 112http://caia.swin.edu.au/urp/newtcp/ 113.Sh AUTHORS 114.An -nosplit 115The 116.Nm 117congestion control module and this manual page were written by 118.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 119and 120.An David Hayes Aq Mt david.hayes@ieee.org . 121