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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 ex- isting 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 un- less 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. Algorithm specific parameters can be set or queried using the TCP_CCALGOOPT socket option (see tcp(4) for details). Callers must pass a pointer to an algorithm specific data, and specify its size. 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 con- trol algorithms by name. algorithm Returns the current default congestion control algo- rithm 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. abe Enable support for RFC 8511, which alters the window decrease factor applied to the congestion window in re- sponse to an ECN congestion signal. Refer to individ- ual congestion control man pages to determine if they implement support for ABE and for configuration de- tails. abe_frlossreduce If non-zero, apply standard beta instead of ABE-beta during ECN-signalled congestion recovery episodes if loss also needs to be repaired. 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 Program 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, Mel- bourne, 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 August 6, 2019 BSD
NAME | DESCRIPTION | MIB Variables | SEE ALSO | ACKNOWLEDGEMENTS | HISTORY | AUTHORS
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