139 lines
4.7 KiB
Groff
139 lines
4.7 KiB
Groff
.\"
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.\" Copyright (c) 2010-2011 The FreeBSD Foundation
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.\" All rights reserved.
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.\"
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.\" This documentation was written at the Centre for Advanced Internet
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.\" Architectures, Swinburne University of Technology, Melbourne, Australia by
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.\" David Hayes and Lawrence Stewart under sponsorship from the FreeBSD
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.\" Foundation.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
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.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 6, 2019
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.Dt MOD_CC 4
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.Os
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.Sh NAME
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.Nm mod_cc
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.Nd Modular congestion control
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.Sh DESCRIPTION
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The modular congestion control framework allows the TCP implementation to
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dynamically change the congestion control algorithm used by new and existing
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connections.
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Algorithms are identified by a unique
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.Xr ascii 7
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name.
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Algorithm modules can be compiled into the kernel or loaded as kernel modules
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using the
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.Xr kld 4
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facility.
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.Pp
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The default algorithm is NewReno, and all connections use the default unless
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explicitly overridden using the
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.Dv TCP_CONGESTION
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socket option (see
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.Xr tcp 4
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for details).
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The default can be changed using a
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.Xr sysctl 3
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MIB variable detailed in the
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.Sx MIB Variables
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section below.
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.Pp
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Algorithm specific parameters can be set or queried using the
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.Dv TCP_CCALGOOPT
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socket option (see
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.Xr tcp 4
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for details).
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Callers must pass a pointer to an algorithm specific data, and specify
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its size.
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.Sh MIB Variables
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The framework exposes the following variables in the
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.Va net.inet.tcp.cc
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branch of the
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.Xr sysctl 3
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MIB:
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.Bl -tag -width ".Va abe_frlossreduce"
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.It Va available
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Read-only list of currently available congestion control algorithms by name.
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.It Va algorithm
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Returns the current default congestion control algorithm when read, and changes
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the default when set.
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When attempting to change the default algorithm, this variable should be set to
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one of the names listed by the
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.Va net.inet.tcp.cc.available
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MIB variable.
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.It Va abe
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Enable support for RFC 8511,
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which alters the window decrease factor applied to the congestion window in
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response to an ECN congestion signal.
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Refer to individual congestion control man pages to determine if they implement
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support for ABE and for configuration details.
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.It Va abe_frlossreduce
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If non-zero, apply standard beta instead of ABE-beta during ECN-signalled
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congestion recovery episodes if loss also needs to be repaired.
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.El
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.Sh SEE ALSO
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.Xr cc_cdg 4 ,
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.Xr cc_chd 4 ,
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.Xr cc_cubic 4 ,
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.Xr cc_dctcp 4 ,
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.Xr cc_hd 4 ,
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.Xr cc_htcp 4 ,
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.Xr cc_newreno 4 ,
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.Xr cc_vegas 4 ,
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.Xr tcp 4 ,
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.Xr mod_cc 9
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.Sh ACKNOWLEDGEMENTS
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Development and testing of this software were made possible in part by grants
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from the FreeBSD Foundation and Cisco University Research Program Fund at
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Community Foundation Silicon Valley.
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.Sh HISTORY
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The
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.Nm
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modular congestion control framework first appeared in
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.Fx 9.0 .
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.Pp
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The framework was first released in 2007 by James Healy and Lawrence Stewart
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whilst working on the NewTCP research project at Swinburne University of
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Technology's Centre for Advanced Internet Architectures, Melbourne, Australia,
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which was made possible in part by a grant from the Cisco University Research
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Program Fund at Community Foundation Silicon Valley.
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More details are available at:
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.Pp
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http://caia.swin.edu.au/urp/newtcp/
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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facility was written by
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.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org ,
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.An James Healy Aq Mt jimmy@deefa.com
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and
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.An David Hayes Aq Mt david.hayes@ieee.org .
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.Pp
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This manual page was written by
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.An David Hayes Aq Mt david.hayes@ieee.org
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and
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.An Lawrence Stewart Aq Mt lstewart@FreeBSD.org .
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