**Session Date/Time:** 01 Apr 2025 14:00

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

## Summary

The SCHC working group convened for its fifth interim meeting to discuss several key technical topics. Discussions covered the review of an external draft utilizing SCHC, the introduction of a modular "Chicklet" concept for the SCHC framework, proposed evolutions to RFC 9363 concerning seed allocation, a new aggregation rule format, and a reliability mechanism for small messages. Decisions were made regarding the integration of Chicklets into the architecture draft and initiating a request for an IANA seed block. The meeting concluded with a humorous presentation on "Quantum Context Error Compression" (Quick Shake).

## Key Discussion Points

*   **Diet ISP ESP Draft Review**: The latest version of the Diet ISP ESP draft, which incorporates SCHC, was highlighted as needing review by the working group. Concerns were raised about a lack of responses to previously submitted comments and the insufficient documentation regarding the derivation of SCHC rules from IKE. Volunteers are sought to review the updated draft.
*   **SCHC Chicklets**:
    *   A new concept, "Chicklets," was presented to introduce modularity into the SCHC framework, allowing for selective implementation of specific functionalities (e.g., compression, fragmentation, aggregation, reliability) rather than requiring a monolithic "all or nothing" approach.
    *   Chicklets are envisioned as atomic, self-contained sub-functions that can be configured with fixed parameters for narrow use cases and can interoperate with full SCHC implementations through standardized configurations (e.g., Yang).
    *   A show of hands indicated support for integrating the Chicklet notion into the SCHC architecture draft.
*   **SCHC Seed Allocation (RFC 9363 Evolution)**:
    *   The working group discussed the need to evolve RFC 9363, which defines the current Yang data model for SCHC seed allocation.
    *   Proposed improvements include defining specific ordering for entries (user order instead of alphabetical) and allowing for manual ordering of seeds to achieve more optimal encoding (e.g., to reduce bit/byte usage for frequently used fields).
    *   The concept of "Universal Options" was introduced, suggesting the use of generic seeds to identify protocol spaces (e.g., CoAP) and then reusing the protocol's native values, thereby enhancing interoperability and reducing mapping complexity.
    *   A request for an IANA block of approximately 250 seeds for SCHC was supported by a show of hands.
*   **Aggregation Rule Format**:
    *   A proposal for a new rule format to aggregate multiple small SCHC-compressed messages into a single "Aggregation Data Unit (ADU)" was presented.
    *   The primary goal is to minimize transmissions and associated energy consumption in constrained networks by reducing the overhead of connection establishment and security handshakes for individual small packets.
    *   Triggers for sending ADUs would include reaching an MTU threshold, exceeding a maximum delay for queued packets, or maintaining a minimum packet rate.
    *   The proposed format allows for concatenated SCHC-compressed payloads, where each aggregated segment retains its own SCHC Rule ID and header.
    *   Discussion emphasized the need for precise definition of how segments within an ADU are described, with parallels drawn to existing methods in Quick compression for handling variable frames.
*   **Reliability Mechanism for Small Messages**:
    *   A mechanism to adapt existing RFC 8724 fragmentation features (specifically No-Ack and AON-Error) was proposed to provide reliability for individual small messages (those smaller than the MTU).
    *   This aims to address the inherent penalty small messages face compared to larger fragmented ones that benefit from explicit acknowledgment mechanisms.
    *   Target use cases include high-density smart gas meter deployments and networks with challenged bidirectionality (e.g., certain satellite IoT constellations).
    *   The solution would utilize a continuous, never-closed session with wrapping windows and could incorporate Forward Error Correction (FAC) fragments for recovery.
    *   Open questions include configuring whether receivers should deliver messages out-of-order or wait for recovery, and defining configurable delivery thresholds (e.g., 90% delivery acceptance).
*   **Quantum Context Error Compression (Quick Shake)**: A lighthearted, conceptual presentation on "Quantum Context Error Compression," or "Quick Shake," was given. This proposal humorously describes a protocol where all contexts are in superposition and collapse upon observation, with applications envisioned for "extreme constraint and quantum-aware environments."

## Decisions and Action Items

*   **Decision**: The working group indicated support for integrating the "Chicklet" notion into the SCHC architecture draft.
*   **Decision**: The working group indicated support for initiating a request for an IANA seed block for SCHC.
*   **Action Item**: Chairs (Alexander Pelov) to send a request to IANA for a SCHC seed block, inquiring about accommodating the requested size of approximately 250 seeds.
*   **Action Item**: Working group participants are encouraged to review the latest Diet ISP ESP draft and provide feedback, particularly regarding previous unanswered comments and the documentation of rule derivation from IKE.
*   **Action Item**: Alexander Pelov to send an email to the mailing list to gather further feedback and comments on the Chicklet draft.
*   **Action Item**: Alexander Pelov to make the Markdown sources for the Aggregation and Reliability rule format drafts available for community contribution.

## Next Steps

*   Continue discussions on the evolution of RFC 9363 to incorporate proposed improvements for SCHC seed allocation, including optimal ordering and universal options. A new draft is expected to be published soon.
*   Further review and refinement of the Aggregation rule format, potentially exploring alignment with approaches used in Quick compression for handling variable frames.
*   Further discussion and development of the Reliability mechanism for small messages, including defining configurable thresholds and strategies for out-of-order delivery.
*   (Humorous) Participants are encouraged to bring quantum computers to a planned hackathon in Madrid focused on "Quick Shake."