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The BBR team developed an improved version, BBRv2, to address some shortcomings with the original version of BBR. BBRv2 should no longer starve instances of other TCP implementations (e.g. Reno or CUBIC) sharing the same bottleneck, or induce high loss rates when the queue at the bottleneck is limited. BBRv2 also supports some forms of ECN signals; not the "classical" version where each "congestion experienced" bit is supposed to be interpreted like a lost packet for congestion control, but the newer "DCTCP-style" ECN variants, including Prague TCP/L4S. Unlike BBR"v1", BBRv2 interprets loss as a signal, and tries to respect a (configurable) target loss rate ceiling.
The use of BBR is not limited to TCP anymore. It is used on a large scale in QUIC (see under "implementations" below), and it has been proposed as CCID (Congestion Control ID) 5 in DCCP, the Datagram Congestion Control Protocol.
Operation
A description of the BBR (v1) algorithm was published in the September/October 2016 issue of ACM Queue. An implementation in the Linux kernel has been proposed as a patch. Dave Taht posted a preliminary evaluation ("a quick look...") on his blog. An good description of the BBR's motivation and approach is included in the proposed kernel patch (see below).
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Netflix has contributed an implementation of BBR to FreeBSD. See the main/sys/netinet/tcp_stacks/bbr.c source file and the commented commit by Randall Stewart from September 2019.
Microsoft Windows
Recent Insider Builds for Windows 11 contain an experimental knob to enable BBR in TCP, according to a presentation at the ICCRG meeting at IETF 112.
BBR in QUIC
BBR has also been implemented for QUIC (including BBRv2, see above), and is in active use on Google's servers. Source code can be found in the congestion_control part of Google's QUICHE project. This is also used by Chromium, the open-source upstream project for Google Chrome. The main logic can be found in the tcp_sender.{cc,h} files.
Cloudflare has an independent implementation of QUIC and HTTP/3, written in Rust. Somewhat confusingly, this is also called QUICHE and can be found on GitHub under cloudflare/quiche. Support BBR support has been announced as possible future work in a blog post about CUBIC and HyStart++ Support in quiche, but, as of November 2021, hasn't appeared in the official source tree yet.
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- BBR Congestion Control Development, Google Groups, last accessed February 2019, mailing list with overview page full of pointers
- BBR: Congestion-Based Congestion Control, ACM Queue, Vol. 14 No. 5, September-October 2016 (HTML/PDF)
- tcp_bbr: add BBR congestion control, N. Cardwell, V. Jacobson, Y. Cheng, N. Dukkipati, E. Dumazet, S. Yeganeh, commit 0f8782ea14974ce992618b55f0c041ef43ed0b78, Linus Torvalds's Linux Git tree, September 2016
- draft-cardwell-iccrg-bbr-congestion-control-01, BBR Congestion Control, Neal Cardwell, Yuchung Cheng, Soheil Hassas Yeganeh, Ian Swett, Van Jacobson, November 2021 (work in progress)
- draft-cheng-iccrg-delivery-rate-estimation-01, Delivery Rate Estimation, Yuchung Cheng, Neal Cardwell, Soheil Hassas Yeganeh, Van Jacobson, November 2021 (work in progress)
- A Quick Look at TCP BBR, D. Taht, blog post, 19 September 2016
- Making Linux TCP Fast, Y. Cheng, N. Cardwell, netdevconf 1.2, October 2016, (abstract, video)
- TCP BBR Quick-Start: Building and Running TCP BBR on Google Compute Engine, N. Cardwell, October 2016 (last accessed)
- BBR Congestion Control, N. Cardwell, Y. Cheng, Presentation to ICCRG at IETF 97, Seoul, November 2016 (video, starting ~57'00", slides)
- BBR congestion control, J. Corbet, LWN.net, September 2016
- BBR Congestion Control: An Update, N. Cardwell, Y. Cheng, Presentation to ICCRG at IETF 98, Chicago, March 2017 (video, starting ~1h35'28", slides)
Driving Linux TCP Congestion Control algorithms around the LTE network Highway, Jae Chung, Feng Li, and Xiaoxiao Jiang, NetDev 2.1, April 2017 (abstract, slides)
- BBR TCP Opportunities, Matt Mathis, Presentation at the Quilt, 19 October 2016 (PDF slides)
- BBR TCP, Geoff Huston, May 2017, Potaroo blog/RIPELabs
- CS 244 '17: ReBBR: Reproducing BBR Performance In Lossy Networks, Luke Hsiao and Jervis Muindi, June 2017 CS244 blog
- CS 244 '17: Congestion-Based Congestion Control With BBR, Brad Girardeau and Samantha Steele, June 2017 CS244 blog
- BBR Congestion Control: IETF 99 Update, N. Cardwell, Y. Cheng, C. S. Dunn, S. H. Yeganeh, I. Swett, J. Iyengar, V. Vasiliev, V. Jacobson, Presentation to ICCRG at IETF 99, Prague, July 2017 (video, slides)
- How Google is speeding up the Internet, B. Butler, Network World, August 2017
- BBR Congestion Control: IETF 100 Update: BBR in shallow buffers, N.l Cardwell, Y. Cheng, C. S. Gunn, S. Hassas Yeganeh, I. Swett, J. Iyengar, V. Vasiliev, V. Jacobson, Presentation to ICCRG, Singapore, Nov 2017 (video, slides)
- BBR Congestion Control Work at Google: IETF 101 Update, N. Cardwell, Y. Cheng, C. S. Gunn, S. Hassas Yeganeh, I. Swett, J. Iyengar, V. Vasiliev, P. Jha, Y. Seung, V. Jacobson, Presentation to ICCRG, London, March 2018 (video, slides)
- BBR Congestion Control Work at Google: IETF 102 Update, N. Cardwell, Y. Cheng, C. S. Gunn, S. Hassas Yeganeh, I. Swett, J. Iyengar, V. Vasiliev, P. Jha, Y. Seung, K. Yang, M. Mathis, V. Jacobson, Presentation to ICCRG, Montréal, July 2018 (video, slides)
- BBR Congestion Control: IETF 102 Update: BBR Startup, Ian Swett, Montréal, July 2018 (video, slides)
- BBRx: Extending BBR for Customized TCP Performance, Jae Won Chung, Feng Li, Beomjun Kim, NetDev 0x12, Montréal, July 2018 (abstract, video, slides, paper)
- BBR v2: A Model-based Congestion Control, N. Cardwell, Y. Cheng, S. Hassas Yeganeh, I. Swett, V. Vasiliev, P. Jha, Y. Seung, M. Mathis, V. Jacobson, Presentation to ICCRG at IETF 104, Prague, March 2019 (slides, video)
- BBR v2: A Model-based Congestion Control—IETF 105 Update, N. Cardwell, Y. Cheng, S. Hassas Yeganeh, P. Jha, Y. Seung, I. Swett, V. Vasiliev, Bin Wu, M. Mathis, V. Jacobson, Presentation to ICCRG, Montréal, July 2019 (slides)
- Understanding of BBRv2: Evaluation and Comparison With BBRv1 Congestion Control Algorithm, Y. Song, G. Kim, I. Mahmud, W. Seo, Y. Cho, IEEE Access (Vol. 9), February 2021
- draft-romo-iccrg-ccid5-00.html, Profile for Datagram Congestion Control Protocol (DCCP) Congestion Control ID 5, N. Romo, J. Kim, M. Amend, October 2021 (work in progress)