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.
Algorithm specific parameters can be set or queried using the
TCP_CCALGOOPT socket option (see
tcp(4) for details). Callers must pass a pointer to an algorithm
specific data, and specify its size.
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.
- abe
- Enable support for draft-ietf-tcpm-alternativebackoff-ecn, which alters the window decrease factor applied to the congestion window in response to an ECN congestion signal. Refer to individual congestion control man pages to determine if they implement support for ABE and for configuration details.
- abe_frlossreduce
- If non-zero, apply standard beta instead of ABE-beta during ECN-signalled congestion recovery episodes if loss also needs to be repaired.
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 Program 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 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 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>.