1.\" 2.\" Copyright (c) 2010-2011 The FreeBSD Foundation 3.\" All rights reserved. 4.\" 5.\" This documentation was written at the Centre for Advanced Internet 6.\" Architectures, Swinburne University of Technology, Melbourne, Australia by 7.\" David Hayes and Lawrence Stewart under sponsorship from the FreeBSD 8.\" 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 August 6, 2019 34.Dt MOD_CC 4 35.Os 36.Sh NAME 37.Nm mod_cc 38.Nd Modular congestion control 39.Sh DESCRIPTION 40The modular congestion control framework allows the TCP implementation to 41dynamically change the congestion control algorithm used by new and existing 42connections. 43Algorithms are identified by a unique 44.Xr ascii 7 45name. 46Algorithm modules can be compiled into the kernel or loaded as kernel modules 47using the 48.Xr kld 4 49facility. 50.Pp 51The default algorithm is NewReno, and all connections use the default unless 52explicitly overridden using the 53.Dv TCP_CONGESTION 54socket option (see 55.Xr tcp 4 56for details). 57The default can be changed using a 58.Xr sysctl 3 59MIB variable detailed in the 60.Sx MIB Variables 61section below. 62.Pp 63Algorithm specific parameters can be set or queried using the 64.Dv TCP_CCALGOOPT 65socket option (see 66.Xr tcp 4 67for details). 68Callers must pass a pointer to an algorithm specific data, and specify 69its size. 70.Sh MIB Variables 71The framework exposes the following variables in the 72.Va net.inet.tcp.cc 73branch of the 74.Xr sysctl 3 75MIB: 76.Bl -tag -width ".Va abe_frlossreduce" 77.It Va available 78Read-only list of currently available congestion control algorithms by name. 79.It Va algorithm 80Returns the current default congestion control algorithm when read, and changes 81the default when set. 82When attempting to change the default algorithm, this variable should be set to 83one of the names listed by the 84.Va net.inet.tcp.cc.available 85MIB variable. 86.It Va abe 87Enable support for RFC 8511, 88which alters the window decrease factor applied to the congestion window in 89response to an ECN congestion signal. 90Refer to individual congestion control man pages to determine if they implement 91support for ABE and for configuration details. 92.It Va abe_frlossreduce 93If non-zero, apply standard beta instead of ABE-beta during ECN-signalled 94congestion recovery episodes if loss also needs to be repaired. 95.El 96.Sh SEE ALSO 97.Xr cc_cdg 4 , 98.Xr cc_chd 4 , 99.Xr cc_cubic 4 , 100.Xr cc_dctcp 4 , 101.Xr cc_hd 4 , 102.Xr cc_htcp 4 , 103.Xr cc_newreno 4 , 104.Xr cc_vegas 4 , 105.Xr tcp 4 , 106.Xr mod_cc 9 107.Sh ACKNOWLEDGEMENTS 108Development and testing of this software were made possible in part by grants 109from the FreeBSD Foundation and Cisco University Research Program Fund at 110Community Foundation Silicon Valley. 111.Sh HISTORY 112The 113.Nm 114modular congestion control framework first appeared in 115.Fx 9.0 . 116.Pp 117The framework was first released in 2007 by James Healy and Lawrence Stewart 118whilst working on the NewTCP research project at Swinburne University of 119Technology's Centre for Advanced Internet Architectures, Melbourne, Australia, 120which was made possible in part by a grant from the Cisco University Research 121Program Fund at Community Foundation Silicon Valley. 122More details are available at: 123.Pp 124http://caia.swin.edu.au/urp/newtcp/ 125.Sh AUTHORS 126.An -nosplit 127The 128.Nm 129facility was written by 130.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org , 131.An James Healy Aq Mt jimmy@deefa.com 132and 133.An David Hayes Aq Mt david.hayes@ieee.org . 134.Pp 135This manual page was written by 136.An David Hayes Aq Mt david.hayes@ieee.org 137and 138.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 139