**Session Date/Time:** 25 Feb 2025 15:00

# [SCHC](../wg/schc.html)

## Summary

The SCHC Working Group held an interim meeting to review the status of several drafts, including a detailed discussion on the SCHC with IPsec/DTLS draft, which is currently in Working Group Last Call in the IPSEC WG. Key discussions centered on the application of SCHC compression within the IPsec framework, covering aspects like terminology, the omission of rule IDs, and the handling of padding. The working group also decided on the date for its next interim meeting and reviewed the progress of other SCHC documents.

## Key Discussion Points

*   **IETF Policies and Agenda**: The meeting opened with a review of IETF policies. The agenda focused on an update for the SCHC with IPsec/DTLS draft, emphasizing the need for timely feedback due to its advancement in another working group, and the progress on SID allocation for the SCHC YANG data model.
*   **Next Interim Meeting Date**: It was announced that there would be no SCHC meeting at the upcoming IETF in Bangkok. After discussion, the working group decided to hold its next interim meeting on **April 1st**. A proposed date before the IETF was rejected due to travel considerations.
*   **SCHC Architecture Draft Status**: An updated version of the SCHC Architecture draft has been published. The authors expressed satisfaction with its current state and encouraged immediate feedback to expedite its progression.
*   **SCHC over Networks Prone to Disruptions Draft**: Co-author Anna indicated that a new version of this expiring draft is under active development. Authors were encouraged to submit updates to maintain its active status.
*   **ICMP Compression Draft Status**: The chair noted he would check the Data Tracker for the current status of the ICMP Compression draft.
*   **New Drafts from Chair**: The chair briefly presented several new personal drafts intended as input for the SCHC architectural draft. These include work on a FEC rule format, message aggregation for Delay Tolerant Networks (DTN), and using fragmentation as a reliability mode. Collaboration on these efforts was welcomed.
*   **SCHC with IPsec/DTLS Draft Presentation**: Daniel and co-authors presented their work, currently in Working Group Last Call in the IPSEC WG.
    *   **Focus**: The draft uses SCHC as a means to illustrate the capability to compress and decompress structured payloads within IPsec, rather than integrating the full SCHC framework into ESP implementations.
    *   **Three "Compressors"**: The draft defines three points for compression within the IPsec process: the inner IP packet, the ESP payload wrapper, and the ESP header. There was discussion regarding whether these should be termed "stratums" as per the new SCHC architecture, but authors clarified that they are implemented as stages within a single IPsec process, simplifying the approach and not requiring multiple SCHC headers.
    *   **Rule ID Management**: The IPsec Security Association (SA) provides all necessary parameters for deriving SCHC rules, allowing the rule ID to be omitted (zero bits) in the compressed packet. Alexander suggested considering a mechanism to allow for configurable rule ID sizes (e.g., zero bits by default) for future flexibility or specialized profiles. Authors agreed to consider this as a potential clarification or for future work.
    *   **SCHC Padding**: The draft explicitly states that SCHC padding is not used.
        *   Discussion revealed that IPsec handles its own padding requirements for encryption block alignment, and the authors found it more practical to manage padding outside the SCHC mechanism due to how payload length is determined in IPsec.
        *   Laurent suggested that rules could be designed to ensure byte-aligned residues, potentially simplifying padding. Alexander noted that SCHC allows not using its padding, but the reasoning and potential implications should be clear.
    *   **Compression/Decompression Actions (CDAs)**: The draft introduces custom CDAs, such as `compute-minus-star` and `generate`, in addition to those defined in SCHC. Laurent suggested that new Field IDs and CDAs should formally be defined within the YANG data model. The authors noted that YANG integration might be a subsequent step.

## Decisions and Action Items

### Decisions

*   The next SCHC interim meeting will be held on **April 1st**.

### Action Items

*   **Alexander**: Check the Data Tracker for the current status of the ICMP Compression draft.
*   **Authors of SCHC over Networks Prone to Disruptions (Anna et al.)**: Submit an updated version of the draft to prevent expiration.
*   **Authors of SCHC with IPsec/DTLS (Daniel et al.)**:
    *   Consider clarifying the restriction on rule ID usage or allowing for a configurable rule ID size (e.g., zero bits by default) for future flexibility or specialized profiles.
    *   Continue the detailed discussion on padding, specifically differentiating between SCHC padding and ESP padding, on the mailing list.
    *   Ensure the GitHub version of the draft reflects clarifications made during the padding discussion.
    *   Consider the formalization of new Compression/Decompression Actions (CDAs) and Field IDs, potentially as part of a future YANG data model for the draft.

## Next Steps

*   Working group members are encouraged to provide feedback on the SCHC with IPsec/DTLS draft via the mailing list to support its progression from Working Group Last Call.
*   The next interim meeting is scheduled for April 1st.
*   Authors of all drafts are encouraged to continue their work and seek collaboration from the working group.