**Session Date/Time:** 20 Mar 2026 01:00

# [TSVWG](../wg/tsvwg.html)

## Summary
The Transport Area Working Group (TSVWG) met at IETF 125 in Shenzhen to discuss a variety of transport-related specifications and operational updates. Key topics included the security of SCTP via DTLS, refinements to the FQ-PIE algorithm, new IPFIX elements for ECN monitoring, and large-scale operational reports on L4S deployment. Significant progress was reported on the DTLS chunk for SCTP, which is nearing Working Group Last Call (WGLC).

## Key Discussion Points

### 1. Chairs' Introduction and Agenda Bashing
**Speakers:** Zaheduzzaman Sarker, Martin Duke
- **Slides:** [Chairs slides](https://datatracker.ietf.org/meeting/125/materials/slides-125-tsvwg-chairs-slides-00)
- One RFC was recently published, and several others are in the RFC Editor queue.
- **Milestones:** Chairs adjusted milestone dates to provide better predictability for other Standards Development Organizations (SDOs).
- **Document Review:** A call was made for more cross-sector reviews. [draft-ietf-tsvwg-l4sops](https://datatracker.ietf.org/meeting/125/materials/slides-125-tsvwg-chairs-slides-00) is currently in Last Call.
- **TSV Review Team:** Participants were encouraged to join the Transport Area Review Team to assist with IESG reviews.

### 2. DTLS Chunk for SCTP
**Speaker:** Magnus Westerlund
- **Slides:** [DTLS Chunk for SCTP](https://datatracker.ietf.org/meeting/125/materials/slides-125-tsvwg-dtls-chunk-for-sctp-00)
- **Drafts:** [draft-ietf-tsvwg-sctp-dtls-chunk](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-sctp-dtls-chunk), [draft-ietf-tsvwg-dtls-chunk-key-management](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-dtls-chunk-key-management)
- **Design Update:** The design team decided to remove the **DTLS Connection ID (CID)**. SCTP already provides robust demultiplexing via V-tags and port/address pairs, making the CID redundant and adding unnecessary complexity to the API.
- **ASCONF Updates:** The draft now updates RFC 5061 to specify that the DTLS chunk (rather than SCTP-AUTH) should be used for authenticating address reconfiguration messages.
- **Interoperability:** Implementation work is ongoing in FreeBSD and Linux. No major technical hurdles remain.
- **Key Management:** Work on [draft-ietf-tsvwg-dtls-chunk-key-management](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-dtls-chunk-key-management) is trailing the main chunk draft to ensure API alignment.

### 3. FQ-PIE Refinements
**Speaker:** Mohit P. Tahiliani
- **Slides:** [FQ-PIE](https://datatracker.ietf.org/meeting/125/materials/slides-125-fq-pie-00)
- **Draft:** [draft-ietf-tsvwg-fq-pie](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-fq-pie)
- **Technical Detail:** The draft recommends using the **timestamps approach** for calculating queue delay rather than Little’s Law.
- **L4S Support:** Discussion continues on adding L4S support (CE threshold). Mohit P. Tahiliani suggested that a separate draft might be appropriate to define L4S support across all FQ-based mechanisms (FQ-CoDel, FQ-PIE, FQ-Cobalt).
- **Implementations:** FQ-PIE is now supported in the Linux kernel (OpenWrt), FreeBSD, and the ns-3 simulator. Recent work integrated FQ-PIE into `go-tc` and `QOSMate`.

### 4. Export of ECN Information in IPFIX
**Speaker:** Shueyan
- **Slides:** [Export of ECN information in IPFIX](https://datatracker.ietf.org/meeting/125/materials/slides-125-export-of-ecn-information-in-ipfix-00)
- This individual draft proposes new IPFIX Information Elements (IEs) to monitor L4S traffic (ECT(1), ECT(0), CE, and non-ECT) across IPv4, IPv6, and MPLS.
- **Discussion:** Gorry Fairhurst questioned why only the 2 ECN bits were being exported instead of the full 8-bit Traffic Class/DSCP field. Shueyan noted that while DSCP IEs exist, specific ECN statistical IEs are needed for L4S visibility.
- **Operator Feedback:** Jason Livingood expressed strong support, noting that the lack of standardized IPFIX ECN reporting is currently an operational gap for ISPs deploying L4S.

### 5. HP-WAN Hackathon Report
**Speaker:** Daniel Huang
- **Slides:** [HP-WAN Hackathon report](https://datatracker.ietf.org/meeting/125/materials/slides-125-hp-wan-hackathon-report-00)
- Results from a prototype of High-Performance Wide Area Networking (HP-WAN) were presented. The project used RSVP-based signaling for host-to-network coordination to achieve high throughput and low latency.
- **Collaboration:** Daniel King noted that the hackathon highlighted a need for a consistent "workload model" and a feedback loop from the network to the orchestrator regarding congestion state.

### 6. L4S Operational Update
**Speaker:** Jason Livingood
- **Slides:** [L4S Update - Livingood](https://datatracker.ietf.org/meeting/125/materials/slides-125-l4s-update-livingood-00)
- **Deployment:** Comcast has enabled L4S and NQB for over 10 million homes (approx. 350 million devices). Key use cases include cloud gaming (NVIDIA GeForce NOW, Valve Steam) and real-time communications (FaceTime).
- **Technical Challenges:**
    - **FEC Interactions:** Jason Livingood noted that existing Forward Error Correction (FEC) algorithms often have baked-in delay assumptions that conflict with the ultra-low latency provided by L4S.
    - **ECN Bleaching:** Stuart Cheshire (Apple) reported instances of ECN bleaching or incorrect CE marking (e.g., in certain mobile networks) which causes throughput degradation.
- **Client Status:** Stuart Cheshire confirmed that Apple products support Prague (as a modification to Cubic/QUIC) and are currently performing A/B testing in the field.

## Decisions and Action Items
- **Decision:** The design team for [draft-ietf-tsvwg-sctp-dtls-chunk](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-sctp-dtls-chunk) confirmed the removal of the DTLS Connection ID from the specification.
- **Action:** Participants are requested to review [draft-ietf-tsvwg-l4sops](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-l4sops) before the end of the Last Call period.
- **Action:** Magnus Westerlund to perform an editorial pass on the SCTP DTLS Chunk draft to prepare for WGLC.
- **Action:** Jonathan Lennox noted that AVTCORE drafts regarding DTLS in STUN and SCTP in SDP should be cross-posted/presented in TSVWG due to shared interest.

## Next Steps
- **WGLC Target:** The chairs and authors aim to issue a Working Group Last Call for [draft-ietf-tsvwg-sctp-dtls-chunk](https://datatracker.ietf.org/meeting/125/materials/draft-ietf-tsvwg-sctp-dtls-chunk) prior to the IETF 126 meeting in Vienna.
- **L4S Operations:** The working group will continue to monitor field results from the Comcast and Apple deployments to refine operational guidance.