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     cc_cubic — CUBIC Congestion Control Algorithm


     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.


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

     Sangtae Ha, Injong Rhee, and Lisong Xu, CUBIC for Fast Long-Distance Networks,

     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.


     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.


     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:


     The cc_cubic congestion control module and this manual page were written by Lawrence Stewart
     <> and David Hayes <>.