Congestion Control Working Group (ccwg) Internet Drafts


      
 BBR Congestion Control
 
 draft-ietf-ccwg-bbr-02.txt
 Date: 28/02/2025
 Authors: Neal Cardwell, Ian Swett, Joseph Beshay
 Working Group: Congestion Control Working Group (ccwg)
This document specifies the BBR congestion control algorithm. BBR ("Bottleneck Bandwidth and Round-trip propagation time") uses recent measurements of a transport connection's delivery rate, round-trip time, and packet loss rate to build an explicit model of the network path. BBR then uses this model to control both how fast it sends data and the maximum volume of data it allows in flight in the network at any time. Relative to loss-based congestion control algorithms such as Reno [RFC5681] or CUBIC [RFC9438], BBR offers substantially higher throughput for bottlenecks with shallow buffers or random losses, and substantially lower queueing delays for bottlenecks with deep buffers (avoiding "bufferbloat"). BBR can be implemented in any transport protocol that supports packet-delivery acknowledgment. Thus far, open source implementations are available for TCP [RFC9293] and QUIC [RFC9000]. This document specifies version 3 of the BBR algorithm, BBRv3.
 Increase of the Congestion Window when the Sender Is Rate-Limited
 
 draft-ietf-ccwg-ratelimited-increase-00.txt
 Date: 05/03/2025
 Authors: Michael Welzl, Tom Henderson, Gorry Fairhurst, Mohit Tahiliani
 Working Group: Congestion Control Working Group (ccwg)
This document specifies how transport protocols increase their congestion window when the sender is rate-limited, and updates RFC 5681, RFC 9002, RFC 9260, and RFC 9438. Such a limitation can be caused by the sending application not supplying data or by receiver flow control.


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Congestion Control Working Group (ccwg)

WG Name Congestion Control Working Group
Acronym ccwg
Area Web and Internet Transport (wit)
State Active
Charter charter-ietf-ccwg-01 Approved
Document dependencies
Additional resources GitHub Organization
Personnel Chairs Eric Kinnear, Reese Enghardt
Area Director Gorry Fairhurst
Mailing list Address ccwg@ietf.org
To subscribe https://www.ietf.org/mailman/listinfo/ccwg
Archive https://mailarchive.ietf.org/arch/browse/ccwg/
Chat Room address https://zulip.ietf.org/#narrow/stream/ccwg

Charter for Working Group

RFC 5033 describes a Best Current Practice to evaluate new congestion control algorithms as Experimental or Proposed Standard RFCs. TCP was the dominant consumer of this work, and proposals were typically discussed in research groups, for example the Internet Congestion Control Research Group (ICCRG).

Since RFC 5033 was published, many conditions have changed. Congestion control algorithm proponents now often have the opportunity to test and deploy at scale without IETF review. The set of protocols using these algorithms has spread beyond TCP and SCTP to include DCCP, QUIC, and beyond. There is more interest in specialized use cases such as data centers and real-time protocols. Finally, the community has gained much more experience with indications of congestion beyond packet loss.

The Congestion Control Working Group will analyze some of the impediments to congestion control work occurring in the IETF and can generalize transports from TCP to all of the relevant transport protocols. This will inform a revision of RFC 5033 (5033bis) that encourages IETF review of congestion control proposals and standardization of mature congestion control algorithms.

The congestion control expertise in the working group also makes it a natural venue to take on other work related to indications of congestion such as delay, queuing algorithms, rate pacing, multipath, interaction with other layers, among others. In particular, it can address congestion control algorithms with empirical evidence of safety (for example - avoiding congestion collapse) and stated intent to deploy by major implementations. The working group is intended to be a home for such work, and it is chartered to adopt proposals in this space if such congestion control algorithms are presented before or after the completion of the primary deliverable i.e. 5033bis.

The group will coordinate closely with other relevant working and research groups, including ICCRG, TCPM, QUIC, and TSVWG. Documents in CCWG will remain as transport protocol agnostic as possible, but they may have short specific instructions, such as header options or parameter formats, for one or more protocols. Documents that are wholly specific to mechanisms in a single protocol will remain in the maintenance working group for that protocol. Algorithms proposed for Experimental status, in consultation with ICCRG, based on an assessment of their maturity and likelihood of near-term wide-scale deployment, are in scope.

Publication of Informational RFCs analyzing the published standard congestion control algorithms is within CCWG scope. However, it is not chartered to document the state of congestion control in the Internet, including assessments of whether any particular implementation complies with existing standards. Other venues, such as the IRTF, may be more appropriate for publishing such documents.

Milestones

Date Milestone Associated documents
Dec 2024 Submit an Informational RFC analyzing the published standard congestion controllers
Jun 2024 Submit 5033bis to IESG for publication.