mod_cc(4) [freebsd man page]

MOD_CC(4)						   BSD Kernel Interfaces Manual 						 MOD_CC(4)

NAME

     mod_cc -- Modular congestion control

DESCRIPTION

     The modular congestion control framework allows the TCP implementation to dynamically change the congestion control algorithm used by new and
     existing connections.  Algorithms are identified by a unique ascii(7) name.  Algorithm modules can be compiled into the kernel or loaded as
     kernel modules using the kld(4) facility.

     The default algorithm is NewReno, and all connections use the default unless explicitly overridden using the TCP_CONGESTION socket option
     (see tcp(4) for details).	The default can be changed using a sysctl(3) MIB variable detailed in the MIB Variables section below.

MIB Variables
     The framework exposes the following variables in the net.inet.tcp.cc branch of the sysctl(3) MIB:

     available	Read-only list of currently available congestion control algorithms by name.

     algorithm	Returns the current default congestion control algorithm when read, and changes the default when set.  When attempting to change
		the default algorithm, this variable should be set to one of the names listed by the net.inet.tcp.cc.available MIB variable.

SEE ALSO

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

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 mod_cc modular congestion control framework first appeared in FreeBSD 9.0.

     The framework was first released in 2007 by James Healy and Lawrence Stewart whilst working on the NewTCP research project at Swinburne Uni-
     versity 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 mod_cc facility was written by Lawrence Stewart <lstewart@FreeBSD.org>, James Healy <jimmy@deefa.com> and David Hayes
     <david.hayes@ieee.org>.

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

BSD
								 January 12, 2015							       BSD

CC_VEGAS(4)						   BSD Kernel Interfaces Manual 					       CC_VEGAS(4)

NAME

     cc_vegas -- Vegas Congestion Control Algorithm

DESCRIPTION

     The Vegas congestion control algorithm uses what the authors term the actual and expected transmission rates to determine whether there is
     congestion along the network path i.e.

	   actual rate = (total data sent in a RTT) / RTT

	   expected rate = cwnd / RTTmin

	   diff = expected - actual

     where RTT is the measured instantaneous round trip time and RTTmin is the smallest round trip time observed during the connection.

     The algorithm aims to keep diff between two parameters alpha and beta, such that:

	   alpha < diff < beta

     If diff > beta, congestion is inferred and cwnd is decremented by one packet (or the maximum TCP segment size).  If diff < alpha, then cwnd
     is incremented by one packet.  Alpha and beta govern the amount of buffering along the path.

     The implementation was done in a clean-room fashion, and is based on the paper referenced in the SEE ALSO section below.

IMPLEMENTATION NOTES

     The time from the transmission of a marked packet until the receipt of an acknowledgement for that packet is measured once per RTT.  This
     implementation does not implement Brakmo's and Peterson's original duplicate ACK policy since clock ticks in today's machines are not as
     coarse as they were (i.e. 500ms) when Vegas was originally designed.  Note that modern TCP recovery processes such as fast retransmit and
     SACK are enabled by default in the TCP stack.

MIB Variables
     The algorithm exposes the following tunable variables in the net.inet.tcp.cc.vegas branch of the sysctl(3) MIB:

     alpha  Query or set the Vegas alpha parameter as a number of buffers on the path.	When setting alpha, the value must satisfy: 0 < alpha <
	    beta.  Default is 1.

     beta   Query or set the Vegas beta parameter as a number of buffers on the path.  When setting beta, the value must satisfy: 0 < alpha <
	    beta.  Default is 3.

SEE ALSO

     cc_chd(4), cc_cubic(4), cc_hd(4), cc_htcp(4), cc_newreno(4), h_ertt(4), mod_cc(4), tcp(4), khelp(9), mod_cc(9)

     L. S. Brakmo and L. L. Peterson, "TCP Vegas: end to end congestion avoidance on a global internet", IEEE J. Sel. Areas Commun., 8, 13,
     1465-1480, October 1995.

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_vegas congestion control module first appeared in FreeBSD 9.0.

     The module was first released in 2010 by David Hayes whilst working on the NewTCP research project 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_vegas congestion control module and this manual page were written by David Hayes <david.hayes@ieee.org>.

BSD
								September 15, 2011							       BSD