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CC_HTCP(4)	       FreeBSD Kernel Interfaces Manual		    CC_HTCP(4)

     cc_htcp --	H-TCP Congestion Control Algorithm

     The H-TCP 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.  The window increase algorithm operates
     like NewReno for the first	second after a congestion event, and then
     switches to a high-speed mode based on a quadratic	increase function.

     The implementation	was done in a clean-room fashion, and is based on the
     Internet Draft and	other documents	referenced in the SEE ALSO section be-

MIB Variables
     The algorithm exposes the following tunable variables in the branch of the	sysctl(3) MIB:

     adaptive_backoff  Controls	use of the adaptive backoff algorithm, which
		       is designed to keep network queues non-empty during
		       congestion recovery episodes.  Default is 0 (disabled).

     rtt_scaling       Controls	use of the RTT scaling algorithm, which	is de-
		       signed to make congestion window	increase during	con-
		       gestion avoidance mode invariant	with respect to	RTT.
		       Default is 0 (disabled).

     cc_cdg(4),	cc_chd(4), cc_cubic(4),	cc_dctcp(4), cc_hd(4), cc_newreno(4),
     cc_vegas(4), mod_cc(4), tcp(4), mod_cc(9)

     D.	Leith and R. Shorten, H-TCP: TCP Congestion Control for	High
     Bandwidth-Delay Product Paths,

     D.	Leith, R. Shorten, and T. Yee, "H-TCP: A framework for congestion
     control in	high-speed and long-distance networks",	Proc. PFLDnet, 2005.

     G.	Armitage, L. Stewart, M. Welzl,	and J. Healy, "An independent H-TCP
     implementation under FreeBSD 7.0: description and observed	behaviour",
     SIGCOMM Comput. Commun. Rev., 3, 38, 27-38, 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_htcp congestion control module first appeared in FreeBSD 9.0.

     The module	was first released in 2007 by James Healy and Lawrence Stewart
     whilst working on the NewTCP research project at Swinburne	University of
     Technology's Centre for Advanced Internet Architectures, Melbourne, Aus-
     tralia, which was made possible in	part by	a grant	from the Cisco Univer-
     sity Research Program Fund	at Community Foundation	Silicon	Valley.	 More
     details are available at:

     The cc_htcp congestion control module was written by James	Healy
     <> and Lawrence Stewart <>.

     This manual page was written by Lawrence Stewart <>
     and David Hayes <>.

FreeBSD	13.0			 May 13, 2021			  FreeBSD 13.0


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