NAME

cc_newreno —

NewReno Congestion Control Algorithm

SYNOPSIS

#include
  <netinet/cc/cc_newreno.h>

DESCRIPTION

The NewReno congestion control algorithm is the default for TCP. 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.

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.

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.

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>.