CC_HTCP(4)						   BSD Kernel Interfaces Manual 						CC_HTCP(4)

NAME

     cc_htcp -- H-TCP Congestion Control Algorithm

DESCRIPTION

     The H-TCP congestion control algorithm was designed to provide increased throughput in fast and long-distance networks.  It attempts to main-
     tain 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 sec-
     tion below.

MIB Variables
     The algorithm exposes the following tunable variables in the net.inet.tcp.cc.htcp 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 recov-
		       ery episodes.  Default is 0 (disabled).

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

SEE ALSO

     cc_chd(4), cc_cubic(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, http://tools.ietf.org/id/draft-leith-tcp-
     htcp-06.txt.

     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.

ACKNOWLEDGEMENTS

     Development and testing of this software were made possible in part by grants from the FreeBSD Foundation and Cisco University Research Pro-
     gram Fund at Community Foundation Silicon Valley.

HISTORY

     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 Univer-
     sity of Technology's Centre for Advanced Internet Architectures, Melbourne, 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 cc_htcp congestion control module was written by James Healy <jimmy@deefa.com> and Lawrence Stewart <lstewart@FreeBSD.org>.

     This manual page was written by Lawrence Stewart <lstewart@FreeBSD.org> and David Hayes <david.hayes@ieee.org>.

BSD
								September 15, 2011							       BSD