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mod_cc(4) [freebsd man page]

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

NAME
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 net.inet.tcp.cc 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 net.inet.tcp.cc.available 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: http://caia.swin.edu.au/urp/newtcp/ AUTHORS
The mod_cc facility was written by Lawrence Stewart <lstewart@FreeBSD.org>, James Healy <jimmy@deefa.com> and David Hayes <david.hayes@ieee.org>. This manual page was written by David Hayes <david.hayes@ieee.org> and Lawrence Stewart <lstewart@FreeBSD.org>. BSD
January 12, 2015 BSD

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CC_HD(4)						   BSD Kernel Interfaces Manual 						  CC_HD(4)

NAME
cc_hd -- HD Congestion Control Algorithm DESCRIPTION
The HD congestion control algorithm is an implementation of the Hamilton Institute's delay-based congestion control which aims to keep net- work queuing delays below a particular threshold (queue_threshold). HD probabilistically reduces the congestion window (cwnd) based on its estimate of the network queuing delay. The probability of reducing cwnd is zero at hd_qmin or less, rising to a maximum at queue_threshold, and then back to zero at the maximum queuing delay. Loss-based congestion control algorithms such as NewReno probe for network capacity by filling queues until there is a packet loss. HD com- petes with loss-based congestion control algorithms by allowing its probability of reducing cwnd to drop from a maximum at queue_threshold to be zero at the maximum queuing delay. This has been shown to work well when the bottleneck link is highly multiplexed. MIB Variables The algorithm exposes the following tunable variables in the net.inet.tcp.cc.hd branch of the sysctl(3) MIB: queue_threshold Queueing congestion threshold (qth) in ticks. Default is 20. pmax Per packet maximum backoff probability as a percentage. Default is 5. qmin Minimum queuing delay threshold (qmin) in ticks. Default is 5. SEE ALSO
cc_chd(4), cc_cubic(4), cc_htcp(4), cc_newreno(4), cc_vegas(4), h_ertt(4), mod_cc(4), tcp(4), khelp(9), mod_cc(9) L. Budzisz, R. Stanojevic, R. Shorten, and F. Baker, "A strategy for fair coexistence of loss and delay-based congestion control algorithms", IEEE Commun. Lett., 7, 13, 555-557, Jul 2009. 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. FUTURE WORK
The Hamilton Institute have recently made some improvements to the algorithm implemented by this module and have called it Coexistent-TCP (C- TCP). The improvements should be evaluated and potentially incorporated into this module. HISTORY
The cc_hd congestion control module first appeared in FreeBSD 9.0. The module was first released in 2010 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: http://caia.swin.edu.au/urp/newtcp/ AUTHORS
The cc_hd congestion control module and this manual page were written by David Hayes <david.hayes@ieee.org>. BSD
September 15, 2011 BSD

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