Session Date/Time: 23 Jul 2025 09:30

tcpm

Summary

The TCPM working group meeting covered working group status, presentations on working group documents (PRR Bis, TCP Accrate Request Option) and individual submissions (TCP Extended Option, Extended Timestamp Options, MPTCP Extensions, Opportunistic ACK in TCP). Discussions focused on clarifying implementation details, addressing potential middlebox issues, and exploring mitigation strategies for opportunistic ACK attacks.

Key Discussion Points

PRR Bis: Focused on editorial changes since Rev 13 to improve clarity and consistency. No changes to the algorithm itself. A final call for editorial comments was issued before submission to the RFC editor.
TCP Accrate Request Option: Updates to sender behavior were presented, specifically addressing scenarios where the congestion window decreases or stretch ACKs exacerbate middlebox issues. Discussion on whether to force R=2 after retransmissions.
TCP Extended Option: A proposal to extend the TCP option field beyond 40 bytes was presented. Discussion centered on middlebox compatibility, the potential for using happy eyeballs, and whether to limit deployment to known environments.
Extended Timestamp Options: Proposal to extend and subsume the current TCP timestamp option with microsecond granularity. The goal is to improve RTT measurement for delay-based congestion control in data centers. Discussion about the Nick TX timestamp usage and how to filter congestion vs power state induced delays.
MPTCP Extensions: Two independent extensions were proposed: DSX (extending data-level length beyond 64K) and External Keys (securing MPTCP with application-level keys). The discussion about jumbo frames and integrity checks and the review feedback by Yoshi.
Opportunistic ACK in TCP: A discussion of the potential for opportunistic ACK attacks in TCP and potential mitigation strategies. Discussion of the viability of the attack and the difficulty of detecting it, as well as countermeasure and cost/benefits.

Decisions and Action Items

PRR Bis: Neil Cardwell will send an email to the TCPM list with a deadline of two weeks for final editorial comments before submitting the draft to the RFC editor.
TCP Accrate Request Option: The authors will consider Yoshi's comments on the behavior around retransmission timeouts and propose an updated solution. Encourage working group people to read the document and provide some API text.
TCP Extended Option: Ron Bonica will consider the feedback on middlebox and happy eyeballs approach and refine the experiment.
Extended Timestamp Options: Yuchin to prepare an internet draft to be submitted soon.

Next Steps

Working group members are encouraged to review the PRR Bis and TCP Accrate Request Option drafts and provide feedback on the mailing list.
Authors of the individual submissions will continue refining their drafts based on the feedback received during the meeting.