CC_NEWRENO(4) FreeBSD Kernel Interfaces Manual CC_NEWRENO(4)
NAME
cc_newreno - NewReno Congestion Control Algorithm
SYNOPSIS
#include <netinet/cc/cc_newreno.h>
DESCRIPTION
Details about the algorithm can be found in RFC5681.
Socket Options
The cc_newreno module supports a number of socket options under
TCP_CCALGOOPT (refer to tcp(4) and mod_cc(9) for details) which can be
set with setsockopt(2) and tested with getsockopt(2). The cc_newreno
socket options use this structure defined in
<sys/netinet/cc/cc_newreno.h>:
struct cc_newreno_opts {
int name;
uint32_t val;
}
CC_NEWRENO_BETA Multiplicative window decrease factor, specified as
a percentage, applied to the congestion window in
response to a congestion signal per: cwnd = (cwnd *
CC_NEWRENO_BETA) / 100. Default is 50.
CC_NEWRENO_BETA_ECN Multiplicative window decrease factor, specified as
a percentage, applied to the congestion window in
response to an ECN congestion signal when
net.inet.tcp.cc.abe=1 per: cwnd = (cwnd *
CC_NEWRENO_BETA_ECN) / 100. Default is 80.
Note that currently the only way to enable hystart++
is to enable it via socket option. When enabling it
a value of 1 will enable precise internet-draft
(version 4) behavior (subject to any MIB variable
settings), other setting (2 and 3) are experimental.
Note that hystart++ requires the TCP stack be able to call to the
congestion controller with both the newround function as well as the
rttsample function. Currently the only TCP stacks that provide this
feedback to the congestion controller is rack.
MIB Variables
The algorithm exposes these variables in the net.inet.tcp.cc.newreno
branch of the sysctl(3) MIB:
beta Multiplicative window decrease factor, specified as a
percentage, applied to the congestion window in response to a
congestion signal per: cwnd = (cwnd * beta) / 100. Default is
50.
beta_ecn Multiplicative window decrease factor, specified as a
percentage, applied to the congestion window in response to an
ECN congestion signal when net.inet.tcp.cc.abe=1 per: cwnd =
(cwnd * beta_ecn) / 100. Default is 80.
SEE ALSO
cc_cdg(4), cc_chd(4), cc_cubic(4), cc_dctcp(4), cc_hd(4), cc_htcp(4),
cc_vegas(4), mod_cc(4), tcp(4), mod_cc(9)
Mark Allman, Vern Paxson, and Ethan Blanton, TCP Congestion Control, RFC
5681.
Naeem Khademi, Michael Welzl, Grenville Armitage, and Gorry Fairhurst,
TCP Alternative Backoff with ECN (ABE), RFC 8511.
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_newreno congestion control algorithm first appeared in its modular
form in FreeBSD 9.0.
This was the default congestion control algorithm in FreeBSD before
version FreeBSD 14.0, after which cc_cubic(4) replaced it.
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_newreno congestion control module was written by James Healy
<jimmy@deefa.com>, Lawrence Stewart <lstewart@FreeBSD.org> and David
Hayes <david.hayes@ieee.org>.
Support for TCP ABE was added by Tom Jones <tj@enoti.me>.
This manual page was written by Lawrence Stewart <lstewart@FreeBSD.org>.
FreeBSD 15.1-STABLE-HBSD February 4, 2023 CC_NEWRENO(4)