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diff --git a/share/man/man4/cc_vegas.4 b/share/man/man4/cc_vegas.4 new file mode 100644 index 0000000..fa14a119 --- /dev/null +++ b/share/man/man4/cc_vegas.4 @@ -0,0 +1,138 @@ +.\" +.\" 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_VEGAS 4 +.Os +.Sh NAME +.Nm cc_vegas +.Nd Vegas Congestion Control Algorithm +.Sh DESCRIPTION +The Vegas congestion control algorithm uses what the authors term the actual and +expected transmission rates to determine whether there is congestion along the +network path i.e. +.Pp +.Bl -item -offset indent +.It +actual rate = (total data sent in a RTT) / RTT +.It +expected rate = cwnd / RTTmin +.It +diff = expected - actual +.El +.Pp +where RTT is the measured instantaneous round trip time and RTTmin is the +smallest round trip time observed during the connection. +.Pp +The algorithm aims to keep diff between two parameters alpha and beta, such +that: +.Pp +.Bl -item -offset indent +.It +alpha < diff < beta +.El +.Pp +If diff > beta, congestion is inferred and cwnd is decremented by one packet (or +the maximum TCP segment size). +If diff < alpha, then cwnd is incremented by one packet. +Alpha and beta govern the amount of buffering along the path. +.Pp +The implementation was done in a clean-room fashion, and is based on the +paper referenced in the +.Sx SEE ALSO +section below. +.Sh IMPLEMENTATION NOTES +The time from the transmission of a marked packet until the receipt of an +acknowledgement for that packet is measured once per RTT. +This implementation does not implement Brakmo's and Peterson's original +duplicate ACK policy since clock ticks in today's machines are not as coarse as +they were (i.e. 500ms) when Vegas was originally designed. +Note that modern TCP recovery processes such as fast retransmit and SACK are +enabled by default in the TCP stack. +.Sh MIB Variables +The algorithm exposes the following tunable variables in the +.Va net.inet.tcp.cc.vegas +branch of the +.Xr sysctl 3 +MIB: +.Bl -tag -width ".Va alpha" +.It Va alpha +Query or set the Vegas alpha parameter as a number of buffers on the path. +When setting alpha, the value must satisfy: 0 < alpha < beta. +Default is 1. +.It Va beta +Query or set the Vegas beta parameter as a number of buffers on the path. +When setting beta, the value must satisfy: 0 < alpha < beta. +Default is 3. +.El +.Sh SEE ALSO +.Xr cc 4 , +.Xr cc_chd 4 , +.Xr cc_cubic 4 , +.Xr cc_hd 4 , +.Xr cc_htcp 4 , +.Xr cc_newreno 4 , +.Xr h_ertt 4 , +.Xr tcp 4 , +.Xr cc 9 , +.Xr khelp 9 +.Rs +.%A "L. S. Brakmo" +.%A "L. L. Peterson" +.%T "TCP Vegas: end to end congestion avoidance on a global internet" +.%J "IEEE J. Sel. Areas Commun." +.%D "October 1995" +.%V "13" +.%N "8" +.%P "1465-1480" +.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 . |