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cc_dctcp(4) [freebsd man page]

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

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 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,, 63-74, July 2010. Stephen Bensley, Lars Eggert, and Dave Thaler, Microsoft's Datacenter TCP (DCTCP): TCP Congestion Control for Datacenters, 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 and Lars Eggert with help and modifications from Hiren Panchasara BSD
January 12, 2015 BSD

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MOD_CC(4)						   BSD Kernel Interfaces Manual 						 MOD_CC(4)

mod_cc -- Modular congestion control DESCRIPTION
The modular congestion control framework allows the TCP implementation to dynamically change the congestion control algorithm used by new and existing connections. Algorithms are identified by a unique ascii(7) name. Algorithm modules can be compiled into the kernel or loaded as kernel modules using the kld(4) facility. The default algorithm is NewReno, and all connections use the default unless explicitly overridden using the TCP_CONGESTION socket option (see tcp(4) for details). The default can be changed using a sysctl(3) MIB variable detailed in the MIB Variables section below. MIB Variables The framework exposes the following variables in the branch of the sysctl(3) MIB: available Read-only list of currently available congestion control algorithms by name. algorithm Returns the current default congestion control algorithm when read, and changes the default when set. When attempting to change the default algorithm, this variable should be set to one of the names listed by the MIB variable. SEE ALSO
cc_cdg(4), cc_chd(4), cc_cubic(4), cc_dctcp(4), cc_hd(4), cc_htcp(4), cc_newreno(4), cc_vegas(4), tcp(4), mod_cc(9) 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 mod_cc modular congestion control framework first appeared in FreeBSD 9.0. The framework was first released in 2007 by James Healy and Lawrence Stewart whilst working on the NewTCP research project at Swinburne Uni- versity 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: AUTHORS
The mod_cc facility was written by Lawrence Stewart <>, James Healy <> and David Hayes <>. This manual page was written by David Hayes <> and Lawrence Stewart <>. BSD
January 12, 2015 BSD
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