cc_dctcp(4) [freebsd man page]

CC_DCTCP(4)						   BSD Kernel Interfaces Manual 					       CC_DCTCP(4)

NAME

     cc_dctcp -- DCTCP Congestion Control Algorithm

DESCRIPTION

     The DCTCP (data center TCP) congestion control algorithm aims to maximise throughput and minimise latency in data center networks by utilis-
     ing the proportion of Explicit Congestion Notification (ECN) marks received from capable hardware as a congestion signal.

     DCTCP uses fraction of ECN marked packets to update congestion window.  The window reduction ratio is always <= 1/2.  Only when all of the
     packets are marked, congestion window is halved.

     In order to keep the accuracy of the ECN marked fraction, a DCTCP receiver mirrors back incoming (or missing) CE marks by setting (or clear-
     ing) ECE marks.  This feedback methodology is also adopted when the receiver uses delayed ACK.

     The FreeBSD DCTCP implementation includes two minor modifications for the one-sided deployment.  Considering the situation that DCTCP is used
     as sender and classic ECN is used as receiver, DCTCP sets the CWR flag as the reaction to the ECE flag.  In addition, when classic ECN is
     used as sender and DCTCP is used as receiver, DCTCP avoids to mirror back ACKs only when the CWR flag is set in the incoming packet.

     The other specifications are based on the paper and Internet Draft referenced in the SEE ALSO section below.

MIB Variables
     The algorithm exposes the following tunable variables in the net.inet.tcp.cc.dctcp branch of the sysctl(3) MIB:

     alpha  An initial estimator of the congestion on the link.  Default is 0.

     dctcp_shift_g
	    An estimation gain in the alpha calculation.  Default is 16.

     slowstart
	    A trigger to halve congestion window after slow start.  Default does nothing to halve window.

SEE ALSO

     cc_chd(4), cc_cubic(4), cc_hd(4), cc_htcp(4), cc_newreno(4), cc_vegas(4), mod_cc(4), tcp(4), mod_cc(9)

     Mohammad Alizadeh, Albert Greenberg, David A. Maltz, Jitendra Padhye, Parveen Patel, Balaji Prabhakar, Sudipta Sengupta, and Murari
     Sridharan, "Data Center TCP (DCTCP)", ACM SIGCOMM 2010, http://research.microsoft.com/pubs/121386/dctcp-public.pdf, 63-74, July 2010.

     Stephen Bensley, Lars Eggert, and Dave Thaler, Microsoft's Datacenter TCP (DCTCP): TCP Congestion Control for Datacenters,
     http://tools.ietf.org/html/draft-bensley-tcpm-dctcp-01.

HISTORY

     The cc_dctcp congestion control module first appeared in FreeBSD 11.0.

     The module was first released in 2014 by Midori Kato studying at Keio University, Japan.

AUTHORS

     The cc_dctcp congestion control module and this manual page were written by Midori Kato katoon@sfc.wide.ad.jp and Lars Eggert lars@netapp.com
     with help and modifications from Hiren Panchasara hiren@FreeBSD.org

BSD
								 January 12, 2015							       BSD

CC_HTCP(4)						   BSD Kernel Interfaces Manual 						CC_HTCP(4)

NAME

     cc_htcp -- H-TCP Congestion Control Algorithm

DESCRIPTION

     The H-TCP congestion control algorithm was designed to provide increased throughput in fast and long-distance networks.  It attempts to main-
     tain fairness when competing with legacy NewReno TCP in lower speed scenarios where NewReno is able to operate adequately.

     The congestion window is increased as a function of the time elapsed since the last congestion event.  The window increase algorithm operates
     like NewReno for the first second after a congestion event, and then switches to a high-speed mode based on a quadratic increase function.

     The implementation was done in a clean-room fashion, and is based on the Internet Draft and other documents referenced in the SEE ALSO sec-
     tion below.

MIB Variables
     The algorithm exposes the following tunable variables in the net.inet.tcp.cc.htcp branch of the sysctl(3) MIB:

     adaptive_backoff  Controls use of the adaptive backoff algorithm, which is designed to keep network queues non-empty during congestion recov-
		       ery episodes.  Default is 0 (disabled).

     rtt_scaling       Controls use of the RTT scaling algorithm, which is designed to make congestion window increase during congestion avoidance
		       mode invariant with respect to RTT.  Default is 0 (disabled).

SEE ALSO

     cc_chd(4), cc_cubic(4), cc_hd(4), cc_newreno(4), cc_vegas(4), mod_cc(4), tcp(4), mod_cc(9)

     D. Leith and R. Shorten, H-TCP: TCP Congestion Control for High Bandwidth-Delay Product Paths, http://tools.ietf.org/id/draft-leith-tcp-
     htcp-06.txt.

     D. Leith, R. Shorten, and T. Yee, "H-TCP: A framework for congestion control in high-speed and long-distance networks", Proc. PFLDnet, 2005.

     G. Armitage, L. Stewart, M. Welzl, and J. Healy, "An independent H-TCP implementation under FreeBSD 7.0: description and observed behaviour",
     SIGCOMM Comput. Commun. Rev., 3, 38, 27-38, July 2008.

ACKNOWLEDGEMENTS

     Development and testing of this software were made possible in part by grants from the FreeBSD Foundation and Cisco University Research Pro-
     gram Fund at Community Foundation Silicon Valley.

HISTORY

     The cc_htcp congestion control module first appeared in FreeBSD 9.0.

     The module was first released in 2007 by James Healy and Lawrence Stewart whilst working on the NewTCP research project at Swinburne Univer-
     sity of Technology's Centre for Advanced Internet Architectures, Melbourne, Australia, which was made possible in part by a grant from the
     Cisco University Research Program Fund at Community Foundation Silicon Valley.  More details are available at:

     http://caia.swin.edu.au/urp/newtcp/

AUTHORS

     The cc_htcp congestion control module was written by James Healy <jimmy@deefa.com> and Lawrence Stewart <lstewart@FreeBSD.org>.

     This manual page was written by Lawrence Stewart <lstewart@FreeBSD.org> and David Hayes <david.hayes@ieee.org>.

BSD
								September 15, 2011							       BSD