mod_cc —
Modular
congestion control
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.
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 RFC 8511, 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.
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)
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
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/
The
mod_cc facility was written by
Lawrence Stewart
<
[email protected]>,
James Healy
<
[email protected]>
and
David Hayes
<
[email protected]>.
This manual page was written by
David Hayes
<
[email protected]>
and
Lawrence Stewart
<
[email protected]>.