128 lines
4.4 KiB
Groff
128 lines
4.4 KiB
Groff
|
.\"
|
||
|
|
.\" Copyright (c) 2010-2011 The FreeBSD Foundation
|
||
|
|
.\" All rights reserved.
|
||
|
|
.\"
|
||
|
|
.\" This documentation was written at the Centre for Advanced Internet
|
||
|
|
.\" Architectures, Swinburne University, 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.
|
||
|
|
.\"
|
||
|
|
.\" $FreeBSD$
|
||
|
|
.\"
|
||
|
|
.Dd February 15, 2011
|
||
|
|
.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.
|
||
|
|
.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 4 ,
|
||
|
|
.Xr cc_cubic 4 ,
|
||
|
|
.Xr cc_hd 4 ,
|
||
|
|
.Xr cc_htcp 4 ,
|
||
|
|
.Xr cc_newreno 4 ,
|
||
|
|
.Xr cc_vegas 4 ,
|
||
|
|
.Xr h_ertt 4 ,
|
||
|
|
.Xr tcp 4 ,
|
||
|
|
.Xr cc 9 ,
|
||
|
|
.Xr khelp 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'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 david.hayes@ieee.org .
|