Session Date/Time: 04 Jan 2022 15:00

LPWAN

Summary

This interim meeting focused primarily on the status and pending issues for the draft-ietf-lpwan-schc-compound-ack and draft-ietf-lpwan-schc-yang documents. Key discussions revolved around ensuring consistency between a draft's normative text and its YANG model, clarifying how updates to existing RFCs should be expressed, and identifying additional parameters for inclusion in the YANG model that impact implementation behavior. The working group also reviewed its milestones, adjusting the target for the OAM document.

Key Discussion Points

draft-ietf-lpwan-oam Document Status: Dominic indicated his intention to revive the document. The existing milestone was recognized as outdated.
- Decision: The milestone for draft-ietf-lpwan-oam was updated to targeting submission to IESG by the end of December (this year).
draft-ietf-lpwan-schc-compound-ack (Compound ACK) - Version 02 Review:
- Data Model Inclusion: Confirmed that the Compound ACK's data model elements are now part of draft-ietf-lpwan-schc-yang, with no data model content remaining in the Compound ACK draft.
- Bitmap Compression: Discussion clarified that bitmap compression is supported only for the last bitmap within a compound ACK, or if there is only a single bitmap. Intermediate bitmaps do not support compression. This was deemed unambiguous and not requiring additional YANG model modification.
- Consistency between Section 4 and YANG Model: A key concern was raised regarding parameters described in Section 4 of the Compound ACK draft (e.g., "usage or not of the compressed bitmap format in the last window," "usage of Compound ACK or not") not being reflected in the YANG model (Section 3).
  - Sense of those present: All parameters affecting configuration or behavior, even if systematic, should be reflected in the YANG model for completeness and implementer clarity.
  - Decision: The draft-ietf-lpwan-schc-compound-ack needs an 03 version to augment its YANG model (in draft-ietf-lpwan-schc-yang) with all parameters specified in its Section 4.
- Handling of Invalid 'W' values: Confirmed that text has been added to Section 3.1 of the Compound ACK draft stating that a SCHC sender must discard the entire SCHC compound ACK if it contains invalid 'W' values (e.g., duplicates or values not yet sent). Dominic expressed satisfaction with this change.
- Updating/Extending RFC 8724: A significant discussion focused on whether the Compound ACK draft "extends" or "updates" RFC 8724.
  - Discussion: While Compound ACK introduces new functionality, it also modifies the behavior of existing ACK interpretation and usage for implementations that adopt it. This implies an "update" rather than a mere "extension."
  - Decision: The xml2rfc metadata for the Compound ACK draft should be set to "updates RFC 8724."
  - Clarifying the Delta Text: Concerns were raised about the clarity for implementers regarding the exact changes to RFC 8724. It was suggested that the draft needs to provide a clear "delta" (e.g., a "diff-like" description) rather than just stating "besides the ACK-REQ behavior."
  - Decision: A new sub-section (e.g., 3.2.3) will be added to the Compound ACK draft to explicitly detail how RFC 8724's ACK-REQ behavior is updated or extended. This section should use clear "old text / new text" or similar explicit language to guide implementers.
- Document Shepherd: A call for volunteers for a document shepherd was made.
  - Action Item: Chairs will issue a call for a document shepherd for draft-ietf-lpwan-schc-compound-ack on the mailing list. If no volunteers, chairs will shepherd.
draft-ietf-lpwan-schc-yang (YANG Data Model) Discussion:
- Status: The repository has been updated with language corrections by Dominic.
- Maximum Interleaved Fragments: Discussion centered on whether to include a max-interleaved-packets parameter in the YANG model, as it directly impacts memory requirements and buffer allocation for implementations.
  - Sense of those present: Such a parameter would be beneficial for implementers.
- D-Tag Lifetime at Receiver: It was discussed that the lifetime of a D-tag at the receiver, especially in NOACK mode, is a critical parameter not currently in the model but affects receiver behavior.
  - Sense of those present: Parameters like D-tag lifetime, which impact behavior on both sides and could lead to out-of-sync states if not agreed upon, should be part of the YANG model. An existing "inactivity timer" in the model might be repurposed or extended for this.
- General Parameter Inclusion: The need to systematically identify and include all non-protocol parameters (e.g., timers, lifetimes, buffers) that are relevant to device behavior and interaction in the YANG model was highlighted.
  - Action Item: Dominic and Laurel (or the document authors) will compile a list of such non-protocol parameters that affect implementation behavior and should be included in draft-ietf-lpwan-schc-yang, and circulate it on the mailing list for review.

Decisions and Action Items

Decision: The milestone for draft-ietf-lpwan-oam is adjusted to December of the current year (submit to IESG).
Decision: draft-ietf-lpwan-schc-compound-ack requires an 03 version to:
- Augment its YANG model (defined in draft-ietf-lpwan-schc-yang) with all parameters specified in Section 4 of the compound-ack draft.
- Update its xml2rfc metadata to "updates RFC 8724."
- Add a new sub-section (e.g., 3.2.3) that explicitly details how RFC 8724's ACK-REQ behavior is updated or extended, using clear "old text / new text" or similar explicit language.
Action Item (Chairs): Issue a call for a document shepherd for draft-ietf-lpwan-schc-compound-ack on the mailing list.
Action Item (Dominic & Laurel/Authors): Compile a list of non-protocol parameters (e.g., max-interleaved-packets, d-tag lifetime) that affect implementation behavior and should be included in draft-ietf-lpwan-schc-yang, and circulate it on the mailing list.
Action Item (Dominic): Revive draft-ietf-lpwan-oam.
Action Item (Sergio/Authors of compound-ack): Address the clarity of delta text for RFC 8724 updates in draft-ietf-lpwan-schc-compound-ack in line with the discussion on new sub-section and explicit wording.

Next Steps

Continue detailed discussions on draft-ietf-lpwan-schc-yang issues (e.g., specific parameters for inclusion) on the mailing list.
The chairs will schedule the next interim meetings to occur every other week, tentatively starting January 25th, to maintain momentum on these documents.