diff options
Diffstat (limited to 'static/freebsd/man4/cc_chd.4')
| -rw-r--r-- | static/freebsd/man4/cc_chd.4 | 127 |
1 files changed, 127 insertions, 0 deletions
diff --git a/static/freebsd/man4/cc_chd.4 b/static/freebsd/man4/cc_chd.4 new file mode 100644 index 00000000..82a44dd2 --- /dev/null +++ b/static/freebsd/man4/cc_chd.4 @@ -0,0 +1,127 @@ +.\" +.\" Copyright (c) 2010-2011 The FreeBSD Foundation +.\" +.\" This documentation was written at the Centre for Advanced Internet +.\" Architectures, Swinburne University of Technology, Melbourne, Australia by +.\" David Hayes under sponsorship from the FreeBSD Foundation. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR +.\" ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.Dd May 13, 2021 +.Dt CC_CHD 4 +.Os +.Sh NAME +.Nm cc_chd +.Nd CHD Congestion Control Algorithm +.Sh DESCRIPTION +CHD enhances the HD algorithm implemented in +.Xr cc_hd 4 . +It provides tolerance to non-congestion related packet loss and improvements to +coexistence with traditional loss-based TCP flows, especially when the +bottleneck link is lightly multiplexed. +.Pp +Like HD, the algorithm aims to keep network queuing delays below a particular +threshold (queue_threshold) and decides to reduce the congestion window (cwnd) +probabilistically based on its estimate of the network queuing delay. +.Pp +It differs from HD in three key aspects: +.Bl -bullet +.It +The probability of cwnd reduction due to congestion is calculated once per round +trip time instead of each time an acknowledgement is received as done by +.Xr cc_hd 4 . +.It +Packet losses that occur while the queuing delay is less than queue_threshold +do not cause cwnd to be reduced. +.It +CHD uses a shadow window to help regain lost transmission opportunities when +competing with loss-based TCP flows. +.El +.Sh MIB Variables +The algorithm exposes the following tunable variables in the +.Va net.inet.tcp.cc.chd +branch of the +.Xr sysctl 3 +MIB: +.Bl -tag -width ".Va queue_threshold" +.It Va queue_threshold +Queueing congestion threshold (qth) in ticks. +Default is 20. +.It Va pmax +Per RTT maximum backoff probability as a percentage. +Default is 50. +.It Va qmin +Minimum queuing delay threshold (qmin) in ticks. +Default is 5. +.It Va loss_fair +If 1, cwnd is adjusted using the shadow window when a congestion +related loss is detected. +Default is 1. +.It Va use_max +If 1, the maximum RTT seen within the measurement period is used as the basic +delay measurement for the algorithm, otherwise a sampled RTT measurement +is used. +Default is 1. +.El +.Sh SEE ALSO +.Xr cc_cdg 4 , +.Xr cc_cubic 4 , +.Xr cc_dctcp 4 , +.Xr cc_hd 4 , +.Xr cc_htcp 4 , +.Xr cc_newreno 4 , +.Xr cc_vegas 4 , +.Xr h_ertt 4 , +.Xr mod_cc 4 , +.Xr tcp 4 , +.Xr khelp 9 , +.Xr mod_cc 9 +.Rs +.%A "D. A. Hayes" +.%A "G. Armitage" +.%T "Improved coexistence and loss tolerance for delay based TCP congestion control" +.%J "in 35th Annual IEEE Conference on Local Computer Networks" +.%D "October 2010" +.%P "24-31" +.Re +.Sh ACKNOWLEDGEMENTS +Development and testing of this software were made possible in part by grants +from the FreeBSD Foundation and Cisco University Research Program Fund at +Community Foundation Silicon Valley. +.Sh HISTORY +The +.Nm +congestion control module first appeared in +.Fx 9.0 . +.Pp +The module was first released in 2010 by David Hayes whilst working on the +NewTCP research project at Swinburne University of Technology's Centre for +Advanced Internet Architectures, Melbourne, Australia. +More details are available at: +.Pp +http://caia.swin.edu.au/urp/newtcp/ +.Sh AUTHORS +.An -nosplit +The +.Nm +congestion control module and this manual page were written by +.An David Hayes Aq Mt david.hayes@ieee.org . |