Session Date/Time: 18 Mar 2025 02:30

ccwg

Summary

This meeting of the Congestion Control Working Group (CCWG) included updates on various congestion control tools and proposals. A significant portion was dedicated to updates on the BBR congestion control algorithm, including open issues, potential improvements, and the path towards RFC publication. Presentations were also given on CC-Perf, NEST, and rate limited senders.

Key Discussion Points

Congestion Control Testing Tools (CC-Perf, NEST):
- Undergraduate students from NITK presented CC-Perf and NEST.
- CC-Perf is built on NS3.
- NEST is built on Linux namespaces.
- Hackathon results were shared, including testing of FQ Codal and FQ PI queue disciplines.
- Concerns raised about lack of native QUIC model support in NS3.
BBR Updates:
- Discussion about the bar for publishing the BBR RFC, with a preference for multiple deployments at scale in both QUIC and TCP.
- Debate about including ECN support in the initial RFC versus a follow-on document (BBR-BIS).
- Open PRs: a correction to drain rate calculations.
- Discussion on how BBR should treat ECN signals, particularly ECT(0).
- Concerns raised about BBR's suitability for real-time applications due to probe RTT intervals.
- Need for clear documentation on areas of BBR that still needs improving.
Rate Limited Senders:
- Update on the draft concerning congestion window increases when the sender is rate-limited.
- Discussion on simplifying the rules and clarifying the definition of "rate limited".
- Pacing limits should also be considered.
aSearcH:
- Presentation positioning aSearcH relative to other algorithms.
- Memory usage analysis.
- Test framework described.
- Some discussion about algorithmic differences relative to HighStart and variations in RTT measurements.

Decisions and Action Items

BBR:
- File issues for tests that need to be considered for BBR.
- Re-review the BBR document for TCP specific language, so that the document is more transport agnostic.
- Consider publishing BBR without ECN support, and address ECN in a follow-on document (BBR-BIS).
- Determine as a group which BBR improvements/changes are in scope for "now" versus "next" (BBR vs BBR-BIS).
Rate Limited Senders:
- Re-evaluate the rules proposed in the draft.
- Clarify the definition of the term "rate limited" within the document.
- Take pacing limits into account.

Next Steps

Authors of various congestion control proposals to address feedback received during the meeting.
CCWG chairs to create a list of topics to be considered "now" vs "later".
Further discussion and contributions on the CCWG mailing list.