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TCP_BBR(4)	       FreeBSD Kernel Interfaces Manual		    TCP_BBR(4)

NAME
     tcp_bbr --	TCP Bottleneck Bandwidth and Round-Trip	Time Algorithm

SYNOPSIS
     To	use this TCP stack you have to place the following line	in your	kernel
     configuration file:

	   options TCPHPTS

     To	load the driver	as a module at boot time, place	the following line in
     loader.conf(5):

	   tcp_bbr_load="YES"

     To	enable the TCP stack you must place the	following line in the
     sysctl.conf(5):

	   net.inet.tcp.functions_default=bbr

DESCRIPTION
     Bottleneck	bandwidth and round-trip time (BBR) is a congestion control
     algorithm which seeks high	throughput with	a small	queue by probing BW
     and RTT.  It is a round-up	redesign of congestion control,	which is not
     loss-based, delay-based, ECN-based	or AIMD-based.

     The core design of	BBR is about creating a	model graph of the network
     path by estimating	the maximum BW and minimum RTT on each ACK.

MIB Variables
     The algorithm exposes the following scopes	in the net.inet.tcp.bbr	branch
     of	the sysctl(3) MIB:

     cwnd		Cwnd controls, for example "target cwnd	rtt measur-
			ment" and "BBR initial window".

     measure		Measurement controls.

     pacing		Connection pacing controls.

     policer		Policer	controls, for example "false detection thresh-
			old" and "loss threshold".

     probertt		Probe RTT controls.

     startup		Startup	controls.

     states		State controls.

     timeout		Time out controls.

     Besides the variables within the above scopes the following variables are
     also exposed in the net.inet.tcp.bbr branch:

     clrlost		Clear lost counters.

     software_pacing	Total number of	software paced flows.

     hdwr_pacing	Total number of	hardware paced flows.

     enob_no_hdwr_pacing
			Total number of	enobufs	for non-hardware paced flows.

     enob_hdwr_pacing	Total number of	enobufs	for hardware paced flows.

     rtt_tlp_thresh	What divisor for TLP rtt/retran	will be	added (1=rtt,
			2=1/2 rtt etc).

     reorder_fade	Does reorder detection fade, if	so how many ms (0
			means never).

     reorder_thresh	What factor for	rack will be added when	seeing re-
			ordering (shift	right).

     bb_verbose		Should BBR black box logging be	verbose.

     sblklimit		When do	we start ignoring small	sack blocks.

     resend_use_tso	Can resends use	TSO?

     data_after_close	Do we hold off sending a RST until all pending data is
			ack'd.

     kill_paceout	When we	hit this many errors in	a row, kill the	ses-
			sion?

     error_paceout	When we	hit an error what is the min to	pace out in
			usec's?

     cheat_rxt		Do we burst 1ms	between	sends on retransmissions (like
			rack)?

     minrto		Minimum	RTO in ms.

SEE ALSO
     cc_chd(4),	cc_cubic(4), cc_hd(4), cc_htcp(4), cc_newreno(4), cc_vegas(4),
     h_ertt(4),	mod_cc(4), tcp(4), mod_cc(9)

     Neal Cardwell, Yuchung Cheng, Stephen Gunn, Soheil	Hassas Yeganeh,	and
     Van Jacobson, "BBR: Congestion-Based Congestion Control", ACM Queue, Vol.
     14, September / October 2016.

     Dominik Scholz, Benedikt Jaeger, Lukas Schwaighofer, Daniel Raumer,
     Fabien Geyer, and Georg Carle, "Towards a Deeper Understanding of TCP BBR
     Congestion	Control", IFIP Networking 2018,
     http://www.net.in.tum.de/fileadmin/bibtex/publications/papers/IFIP-
     Networking-2018-TCP-BBR.pdf, May 2018.

HISTORY
     The tcp_bbr congestion control module first appeared in FreeBSD 13.0.

AUTHORS
     The tcp_bbr congestion control module was written by Randall Stewart
     <rrs@FreeBSD.org> and sponsored by	Netflix, Inc.  This manual page	was
     written by	Gordon Bergling	<gbe@FreeBSD.org>.

FreeBSD	13.0		      September	24, 2020		  FreeBSD 13.0

NAME | SYNOPSIS | DESCRIPTION | MIB Variables | SEE ALSO | HISTORY | AUTHORS

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