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.\" $FreeBSD$ 32.\" 33.Dd September 13, 2022 34.Dt CC_NEWRENO 4 35.Os 36.Sh NAME 37.Nm cc_newreno 38.Nd NewReno Congestion Control Algorithm 39.Sh SYNOPSIS 40.In netinet/cc/cc_newreno.h 41.Sh DESCRIPTION 42Details about the algorithm can be found in RFC5681. 43.Sh Socket Options 44The 45.Nm 46module supports a number of socket options under TCP_CCALGOOPT (refer to 47.Xr tcp 4 48and 49.Xr mod_cc 9 for details) 50which can 51be set with 52.Xr setsockopt 2 53and tested with 54.Xr getsockopt 2 . 55The 56.Nm 57socket options use this structure defined in 58<sys/netinet/cc/cc_newreno.h>: 59.Bd -literal 60struct cc_newreno_opts { 61 int name; 62 uint32_t val; 63} 64.Ed 65.Bl -tag -width ".Va CC_NEWRENO_BETA_ECN" 66.It Va CC_NEWRENO_BETA 67Multiplicative window decrease factor, specified as a percentage, applied to 68the congestion window in response to a congestion signal per: cwnd = (cwnd * 69CC_NEWRENO_BETA) / 100. 70Default is 50. 71.It Va CC_NEWRENO_BETA_ECN 72Multiplicative window decrease factor, specified as a percentage, applied to 73the congestion window in response to an ECN congestion signal when 74.Va net.inet.tcp.cc.abe=1 75per: cwnd = (cwnd * CC_NEWRENO_BETA_ECN) / 100. 76Default is 80. 77.Pp 78Note that currently the only way to enable 79hystart++ is to enable it via socket option. 80When enabling it a value of 1 will enable precise internet-draft (version 4) behavior 81(subject to any MIB variable settings), other setting (2 and 3) are experimental. 82.El 83.Pp 84Note that hystart++ requires the TCP stack be able to call to the congestion 85controller with both the 86.Va newround 87function as well as the 88.Va rttsample 89function. 90Currently the only TCP stacks that provide this feedback to the 91congestion controller is rack. 92.Sh MIB Variables 93The algorithm exposes these variables in the 94.Va net.inet.tcp.cc.newreno 95branch of the 96.Xr sysctl 3 97MIB: 98.Bl -tag -width ".Va beta_ecn" 99.It Va beta 100Multiplicative window decrease factor, specified as a percentage, applied to 101the congestion window in response to a congestion signal per: cwnd = (cwnd * 102beta) / 100. 103Default is 50. 104.It Va beta_ecn 105Multiplicative window decrease factor, specified as a percentage, applied to 106the congestion window in response to an ECN congestion signal when 107.Va net.inet.tcp.cc.abe=1 108per: cwnd = (cwnd * beta_ecn) / 100. 109Default is 80. 110.El 111.Sh SEE ALSO 112.Xr cc_cdg 4 , 113.Xr cc_chd 4 , 114.Xr cc_cubic 4 , 115.Xr cc_dctcp 4 , 116.Xr cc_hd 4 , 117.Xr cc_htcp 4 , 118.Xr cc_vegas 4 , 119.Xr mod_cc 4 , 120.Xr tcp 4 , 121.Xr mod_cc 9 122.Rs 123.%A "Mark Allman" 124.%A "Vern Paxson" 125.%A "Ethan Blanton" 126.%T "TCP Congestion Control" 127.%O "RFC 5681" 128.Re 129.Rs 130.%A "Naeem Khademi" 131.%A "Michael Welzl" 132.%A "Grenville Armitage" 133.%A "Gorry Fairhurst" 134.%T "TCP Alternative Backoff with ECN (ABE)" 135.%O "RFC 8511" 136.Re 137.Sh ACKNOWLEDGEMENTS 138Development and testing of this software were made possible in part by grants 139from the FreeBSD Foundation and Cisco University Research Program Fund at 140Community Foundation Silicon Valley. 141.Sh HISTORY 142The 143.Nm 144congestion control algorithm first appeared in its modular form in 145.Fx 9.0 . 146.Pp 147The module was first released in 2007 by James Healy and Lawrence Stewart whilst 148working on the NewTCP research project at Swinburne University of Technology's 149Centre for Advanced Internet Architectures, Melbourne, Australia, which was made 150possible in part by a grant from the Cisco University Research Program Fund at 151Community Foundation Silicon Valley. 152More details are available at: 153.Pp 154http://caia.swin.edu.au/urp/newtcp/ 155.Sh AUTHORS 156.An -nosplit 157The 158.Nm 159congestion control module was written by 160.An James Healy Aq Mt jimmy@deefa.com , 161.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 162and 163.An David Hayes Aq Mt david.hayes@ieee.org . 164.Pp 165Support for TCP ABE was added by 166.An Tom Jones Aq Mt tj@enoti.me . 167.Pp 168This manual page was written by 169.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 170