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. The CUBIC congestion
control algorithm is the default for TCP. 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_cdg(4), cc_chd(4), cc_dctcp(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, https://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.
This became the default congestion algorithm for FreeBSD in version
FreeBSD 14.0, replacing cc_newreno(4).
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 <
[email protected]> and David Hayes
<
[email protected]>.
FreeBSD 14.1-RELEASE-p8 February 4, 2023 FreeBSD 14.1-RELEASE-p8