1.\" 2.\" Copyright (c) 2009 Lawrence Stewart <lstewart@FreeBSD.org> 3.\" Copyright (c) 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 Lawrence Stewart 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_NEWRENO 4 33.Os 34.Sh NAME 35.Nm cc_newreno 36.Nd NewReno Congestion Control Algorithm 37.Sh SYNOPSIS 38.In netinet/cc/cc_newreno.h 39.Sh DESCRIPTION 40Details about the algorithm can be found in RFC5681. 41.Sh Socket Options 42The 43.Nm 44module supports a number of socket options under TCP_CCALGOOPT (refer to 45.Xr tcp 4 46and 47.Xr mod_cc 9 for details) 48which can 49be set with 50.Xr setsockopt 2 51and tested with 52.Xr getsockopt 2 . 53The 54.Nm 55socket options use this structure defined in 56<sys/netinet/cc/cc_newreno.h>: 57.Bd -literal 58struct cc_newreno_opts { 59 int name; 60 uint32_t val; 61} 62.Ed 63.Bl -tag -width ".Va CC_NEWRENO_BETA_ECN" 64.It Va CC_NEWRENO_BETA 65Multiplicative window decrease factor, specified as a percentage, applied to 66the congestion window in response to a congestion signal per: cwnd = (cwnd * 67CC_NEWRENO_BETA) / 100. 68Default is 50. 69.It Va CC_NEWRENO_BETA_ECN 70Multiplicative window decrease factor, specified as a percentage, applied to 71the congestion window in response to an ECN congestion signal when 72.Va net.inet.tcp.cc.abe=1 73per: cwnd = (cwnd * CC_NEWRENO_BETA_ECN) / 100. 74Default is 80. 75.Pp 76Note that currently the only way to enable 77hystart++ is to enable it via socket option. 78When enabling it a value of 1 will enable precise internet-draft (version 4) behavior 79(subject to any MIB variable settings), other setting (2 and 3) are experimental. 80.El 81.Pp 82Note that hystart++ requires the TCP stack be able to call to the congestion 83controller with both the 84.Va newround 85function as well as the 86.Va rttsample 87function. 88Currently the only TCP stacks that provide this feedback to the 89congestion controller is rack. 90.Sh MIB Variables 91The algorithm exposes these variables in the 92.Va net.inet.tcp.cc.newreno 93branch of the 94.Xr sysctl 3 95MIB: 96.Bl -tag -width ".Va beta_ecn" 97.It Va beta 98Multiplicative window decrease factor, specified as a percentage, applied to 99the congestion window in response to a congestion signal per: cwnd = (cwnd * 100beta) / 100. 101Default is 50. 102.It Va beta_ecn 103Multiplicative window decrease factor, specified as a percentage, applied to 104the congestion window in response to an ECN congestion signal when 105.Va net.inet.tcp.cc.abe=1 106per: cwnd = (cwnd * beta_ecn) / 100. 107Default is 80. 108.El 109.Sh SEE ALSO 110.Xr cc_cdg 4 , 111.Xr cc_chd 4 , 112.Xr cc_cubic 4 , 113.Xr cc_dctcp 4 , 114.Xr cc_hd 4 , 115.Xr cc_htcp 4 , 116.Xr cc_vegas 4 , 117.Xr mod_cc 4 , 118.Xr tcp 4 , 119.Xr mod_cc 9 120.Rs 121.%A "Mark Allman" 122.%A "Vern Paxson" 123.%A "Ethan Blanton" 124.%T "TCP Congestion Control" 125.%O "RFC 5681" 126.Re 127.Rs 128.%A "Naeem Khademi" 129.%A "Michael Welzl" 130.%A "Grenville Armitage" 131.%A "Gorry Fairhurst" 132.%T "TCP Alternative Backoff with ECN (ABE)" 133.%O "RFC 8511" 134.Re 135.Sh ACKNOWLEDGEMENTS 136Development and testing of this software were made possible in part by grants 137from the FreeBSD Foundation and Cisco University Research Program Fund at 138Community Foundation Silicon Valley. 139.Sh HISTORY 140The 141.Nm 142congestion control algorithm first appeared in its modular form in 143.Fx 9.0 . 144.Pp 145This was the default congestion control algorithm in FreeBSD before 146version 147.Fx 14.0 , 148after which 149.Xr cc_cubic 4 150replaced it. 151.Pp 152The module was first released in 2007 by James Healy and Lawrence Stewart whilst 153working on the NewTCP research project at Swinburne University of Technology's 154Centre for Advanced Internet Architectures, Melbourne, Australia, which was made 155possible in part by a grant from the Cisco University Research Program Fund at 156Community Foundation Silicon Valley. 157More details are available at: 158.Pp 159http://caia.swin.edu.au/urp/newtcp/ 160.Sh AUTHORS 161.An -nosplit 162The 163.Nm 164congestion control module was written by 165.An James Healy Aq Mt jimmy@deefa.com , 166.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 167and 168.An David Hayes Aq Mt david.hayes@ieee.org . 169.Pp 170Support for TCP ABE was added by 171.An Tom Jones Aq Mt tj@enoti.me . 172.Pp 173This manual page was written by 174.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 175