Import an implementation of the CAIA Delay-Gradient (CDG) congestion control

algorithm, which is based on the 2011 v0.1 patch release and described in the
paper "Revisiting TCP Congestion Control using Delay Gradients" by David Hayes
and Grenville Armitage. It is implemented as a kernel module compatible with the
modular congestion control framework.

CDG is a hybrid congestion control algorithm which reacts to both packet loss
and inferred queuing delay. It attempts to operate as a delay-based algorithm
where possible, but utilises heuristics to detect loss-based TCP cross traffic
and will compete effectively as required. CDG is therefore incrementally
deployable and suitable for use on shared networks.

In collaboration with:	David Hayes <david.hayes at ieee.org> and
		Grenville Armitage <garmitage at swin edu au>
MFC after:	4 days
Sponsored by:	Cisco University Research Program and FreeBSD Foundation

1 files changed, 155 insertions, 0 deletions

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+.\"
+.\" Copyright (c) 2013 Swinburne University of Technology, Melbourne, Australia
+.\" All rights reserved.
+.\"
+.\" 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 July 2, 2013
+.Dt CC_CDG 4
+.Os
+.Sh NAME
+.Nm cc_cdg
+.Nd CDG Congestion Control Algorithm
+.Sh DESCRIPTION
+CAIA-Delay Gradient (CDG) is a hybrid congestion control algorithm which reacts
+to both packet loss and inferred queuing delay.
+It attempts to operate as a delay-based algorithm where possible, but utilises
+heuristics to detect loss-based TCP cross traffic and will compete effectively
+as required.
+CDG is therefore incrementally deployable and suitable for use on shared
+networks.
+.Pp
+During delay-based operation, CDG uses a delay-gradient based probabilistic
+backoff mechanism, and will also try to infer non congestion related
+packet losses and avoid backing off when they occur.
+During loss-based operation, CDG essentially reverts to
+.Xr cc_newreno 4 Ns - Ns like
+behaviour.
+.Pp
+CDG switches to loss-based operation when it detects that a configurable number
+of consecutive delay-based backoffs have had no measurable effect.
+It periodically attempts to return to delay-based operation, but will keep
+switching back to loss-based operation as required.
+.Sh MIB Variables
+The algorithm exposes the following variables in the
+.Va net.inet.tcp.cc.cdg
+branch of the
+.Xr sysctl 3
+MIB:
+.Bl -tag -width ".Va exp_backoff_scale"
+.It Va version
+Current algorithm/implementation version number.
+.It Va beta_delay
+Delay-based window decrease factor as a percentage (on delay-based backoff, w =
+w * beta_delay / 100).
+Default is 70.
+.It Va beta_loss
+Loss-based window decrease factor as a percentage (on loss-based backoff, w =
+w * beta_loss / 100).
+Default is 50.
+.It Va exp_backoff_scale
+Scaling parameter for the probabilistic exponential backoff.
+Default is 2.
+.It Va smoothing_factor
+Number of samples used for moving average smoothing (0 means no smoothing).
+Default is 8.
+.It Va loss_compete_consec_cong
+Number of consecutive delay-gradient based congestion episodes which will
+trigger loss-based CC compatibility.
+Default is 5.
+.It Va loss_compete_hold_backoff
+Number of consecutive delay-gradient based congestion episodes to hold the
+window backoff for loss-based CC compatibility.
+Default is 5.
+.It Va alpha_inc
+If non-zero, this enables an experimental mode where CDG's window increase
+factor (alpha) is increased by 1 MSS every
+.Va alpha_inc
+RTTs during congestion avoidance mode.
+(Setting
+.Va alpha_inc
+to 1 results in the most aggressive growth of the window increase factor over
+time.
+Use higher
+.Va alpha_inc
+values for slower growth.)
+Default is 0.
+.El
+.Sh SEE ALSO
+.Xr cc_chd 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 mod_cc 4 ,
+.Xr tcp 4 ,
+.Xr khelp 9 ,
+.Xr mod_cc 9
+.Rs
+.%A "D. A. Hayes"
+.%A "G. Armitage"
+.%T "Revisiting TCP Congestion Control using Delay Gradients"
+.%J "Networking 2011 Proceedings, Part II"
+.%D "May 2011"
+.%P "328-341"
+.Re
+.Rs
+.%A "N. Khademi"
+.%A "G. Armitage"
+.%T "Minimising RTT across homogeneous 802.11 WLANs with CAIA Delay-Gradient TCP (v0.1)"
+.%R "CAIA Technical Report 121113A"
+.%D "November 2012"
+.%U "http://caia.swin.edu.au/reports/121113A/CAIA-TR-121113A.pdf"
+.Re
+.Sh ACKNOWLEDGEMENTS
+Development and testing of this software were made possible in part by grants
+from the FreeBSD Foundation and The Cisco University Research Program Fund, a
+corporate advised fund of Silicon Valley Community Foundation.
+.Sh HISTORY
+The
+.Nm
+congestion control module first appeared in
+.Fx 9.2 .
+.Pp
+The module was first released in 2011 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 was written by
+.An David Hayes Aq david.hayes@ieee.org .
+This manual page was written by
+.An Lawrence Stewart Aq lstewart@FreeBSD.org
+and
+.An Grenville Armitage Aq garmitage@swin.edu.au .
+.Sh BUGS
+The underlying algorithm and parameter values are still a work in progress and
+may not be optimal for some network scenarios.