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 May 13, 2021 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 42The NewReno congestion control algorithm is the default for TCP. 43Details about the algorithm can be found in RFC5681. 44.Sh Socket Options 45The 46.Nm 47module supports a number of socket options under TCP_CCALGOOPT (refer to 48.Xr tcp 4 49and 50.Xr mod_cc 9 for details) 51which can 52be set with 53.Xr setsockopt 2 54and tested with 55.Xr getsockopt 2 . 56The 57.Nm 58socket options use this structure defined in 59<sys/netinet/cc/cc_newreno.h>: 60.Bd -literal 61struct cc_newreno_opts { 62 int name; 63 uint32_t val; 64} 65.Ed 66.Bl -tag -width ".Va CC_NEWRENO_BETA_ECN" 67.It Va CC_NEWRENO_BETA 68Multiplicative window decrease factor, specified as a percentage, applied to 69the congestion window in response to a congestion signal per: cwnd = (cwnd * 70CC_NEWRENO_BETA) / 100. 71Default is 50. 72.It Va CC_NEWRENO_BETA_ECN 73Multiplicative window decrease factor, specified as a percentage, applied to 74the congestion window in response to an ECN congestion signal when 75.Va net.inet.tcp.cc.abe=1 76per: cwnd = (cwnd * CC_NEWRENO_BETA_ECN) / 100. 77Default is 80. 78.Pp 79Note that currently the only way to enable 80hystart++ is to enable it via socket option. 81When enabling it a value of 1 will enable precise internet-draft (version 4) behavior 82(subject to any MIB variable settings), other setting (2 and 3) are experimental. 83.El 84.Pp 85Note that hystart++ requires the TCP stack be able to call to the congestion 86controller with both the 87.Va newround 88function as well as the 89.Va rttsample 90function. 91Currently the only TCP stacks that provide this feedback to the 92congestion controller is rack. 93.Sh MIB Variables 94The algorithm exposes these variables in the 95.Va net.inet.tcp.cc.newreno 96branch of the 97.Xr sysctl 3 98MIB: 99.Bl -tag -width ".Va beta_ecn" 100.It Va beta 101Multiplicative window decrease factor, specified as a percentage, applied to 102the congestion window in response to a congestion signal per: cwnd = (cwnd * 103beta) / 100. 104Default is 50. 105.It Va beta_ecn 106Multiplicative window decrease factor, specified as a percentage, applied to 107the congestion window in response to an ECN congestion signal when 108.Va net.inet.tcp.cc.abe=1 109per: cwnd = (cwnd * beta_ecn) / 100. 110Default is 80. 111.El 112.Sh SEE ALSO 113.Xr cc_cdg 4 , 114.Xr cc_chd 4 , 115.Xr cc_cubic 4 , 116.Xr cc_dctcp 4 , 117.Xr cc_hd 4 , 118.Xr cc_htcp 4 , 119.Xr cc_vegas 4 , 120.Xr mod_cc 4 , 121.Xr tcp 4 , 122.Xr mod_cc 9 123.Rs 124.%A "Mark Allman" 125.%A "Vern Paxson" 126.%A "Ethan Blanton" 127.%T "TCP Congestion Control" 128.%O "RFC 5681" 129.Re 130.Rs 131.%A "Naeem Khademi" 132.%A "Michael Welzl" 133.%A "Grenville Armitage" 134.%A "Gorry Fairhurst" 135.%T "TCP Alternative Backoff with ECN (ABE)" 136.%O "RFC 8511" 137.Re 138.Sh ACKNOWLEDGEMENTS 139Development and testing of this software were made possible in part by grants 140from the FreeBSD Foundation and Cisco University Research Program Fund at 141Community Foundation Silicon Valley. 142.Sh HISTORY 143The 144.Nm 145congestion control algorithm first appeared in its modular form in 146.Fx 9.0 . 147.Pp 148The module was first released in 2007 by James Healy and Lawrence Stewart whilst 149working on the NewTCP research project at Swinburne University of Technology's 150Centre for Advanced Internet Architectures, Melbourne, Australia, which was made 151possible in part by a grant from the Cisco University Research Program Fund at 152Community Foundation Silicon Valley. 153More details are available at: 154.Pp 155http://caia.swin.edu.au/urp/newtcp/ 156.Sh AUTHORS 157.An -nosplit 158The 159.Nm 160congestion control module was written by 161.An James Healy Aq Mt jimmy@deefa.com , 162.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org 163and 164.An David Hayes Aq Mt david.hayes@ieee.org . 165.Pp 166Support for TCP ABE was added by 167.An Tom Jones Aq Mt tj@enoti.me . 168.Pp 169This manual page was written by 170.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org . 171