**Session Date/Time:** 27 Jul 2023 20:00

# tcpm

## Summary

The TCPM working group meeting covered several topics, including updates on PRR, Accurate ECN, Generalized ECN, TCP Aggregate Request option, and aggregated TCP options.  The discussion focused on implementation status, addressing open issues from previous meetings, and potential next steps for each draft.

## Key Discussion Points

*   **PRR (Proportional Rate Reduction):**
    *   The latest draft has been implemented in Linux and matches the latest specification.
    *   Discussion about outstanding comment on how to set congestion window after loss recovery.
*   **Accurate ECN:**
    *   Discussion centered on ongoing concerns regarding Axovax, particularly concerning whether it drags standard track receivers into experimental setups.
    *   Concerns about interacting with middleboxes were raised, specifically regarding MSS clamping if the MSS option is not present.
    *   Discussion around how to handle DSEC on Axovax.
*   **Generalized ECN (ECN++):**
    *   The draft is waiting for Accurate ECN to progress.
    *   Distinguishing acts of acts is now in this draft.
    *   Discussion on client-based caching of failed ECT attempts.
*   **TCP Aggregate Request Option:**
    *   Discussion about sender burstiness and use of TCP sender pacing, including whether "may" is sufficient or should be "should."
    *   Consideration of autonomous receiver decisions to send ACKs when a packet loss is suspected.
    *   Discussion about ACT frequency and RTT, aiming for better alignment between TCP and QUIC.
    *   Discussion of the impact of the change in BDP.
    *   Discussion about MTU size.
*   **Aggregated TCP Options:**
    *   Presentation on aggregating multiple TCP options into a single option to save space.
    *   Discussion focused on the appropriateness of aggregating the MSS option due to potential middlebox issues.
    *   Alternative approaches, like rate negotiation, were presented.
    *   Deployment strategies and trade-offs were discussed, considering the performance impact if the option is not supported.

## Decisions and Action Items

*   **PRR:** Ready for working group last call restart.
*   **Accurate ECN:** Continue discussions with Markku. Run short working class call on latest version shortly after the IETF.
*   **TCP Aggregate Request Option:** Authors will look into autonomous decisions by the receiver, the format of MTU size, consider whether "may" is sufficient or should be "should", and improve wording around ACT frequency/RTT.
*   **Aggregated TCP Options:** Consider removing aggregation of MSS from the draft. Author to address scope of deployment, and middlebox issue.

## Next Steps

*   Address feedback received during the meeting and incorporate changes into the relevant drafts.
*   Restart working group last call for PRR and Accurate ECN soon.
*   Continue discussions and reviews to progress Generalized ECN and TCP Aggregate Request option.
*   Further investigate MSS aggregation for aggregated TCP options and middlebox behavior.