CC_CUBIC(4)	       FreeBSD Kernel Interfaces Manual 	   CC_CUBIC(4)

NAME

     cc_cubic -- CUBIC Congestion Control Algorithm

DESCRIPTION

     The CUBIC congestion control algorithm was designed to provide increased
     throughput in fast and long-distance networks.  It attempts to maintain
     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.  During regular operation, the window
     increase function follows a cubic function, with the inflection point set
     to be the congestion window value reached at the last congestion event.
     CUBIC also calculates an estimate of the congestion window that NewReno
     would have achieved at a given time after a congestion event.  When
     updating the congestion window, the algorithm will choose the larger of
     the calculated CUBIC and estimated NewReno windows.

     CUBIC also backs off less on congestion by changing the multiplicative
     decrease factor from 1/2 (used by standard NewReno TCP) to 4/5.

     The implementation was done in a clean-room fashion, and is based on the
     Internet Draft and paper referenced in the SEE ALSO section below.

MIB Variables

     There are currently no tunable MIB variables.

SEE ALSO

     cc(4), cc_chd(4), cc_hd(4), cc_htcp(4), cc_newreno(4), cc_vegas(4),
     tcp(4), cc(9)

     Sangtae Ha, Injong Rhee, and Lisong Xu, CUBIC for Fast Long-Distance
     Networks, http://tools.ietf.org/id/draft-rhee-tcpm-cubic-02.txt.

     Sangtae Ha, Injong Rhee, and Lisong Xu, "CUBIC: a new TCP-friendly high-
     speed TCP variant", SIGOPS Oper. Syst. Rev., 5, 42, 64-74, July 2008.

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 cc_cubic congestion control module first appeared in FreeBSD 9.0.

     The module was first released in 2009 by Lawrence Stewart whilst studying
     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_cubic congestion control module and this manual page were written
     by Lawrence Stewart <lstewart@FreeBSD.org> and David Hayes
     <david.hayes@ieee.org>.

FreeBSD 9.0		       February 15, 2011		   FreeBSD 9.0