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 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 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 recovery 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 Program 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  University  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>.

Debian                                         September 15, 2011                                     CC_HTCP(4)