Session Date/Time: 07 Dec 2021 15:00

LPWAN

Summary

This interim meeting of the LPWAN Working Group focused on updates to the LPWAN Architecture document, a new proposal for delay-tolerant firmware update over-the-air (FOTA) and large object transfer, and the status of the CHIC YANG data model integration and its extensions. Key discussions involved refining the scope of the architecture document, defining the path forward for the delay-tolerant FOTA work, and setting a publication target for the CHIC YANG models.

Key Discussion Points

Administrative Items:
- Notewell and IPR policy reminders were given. Participants were reminded of the Ombudsteam for misconduct reporting.
- Anna was thanked for volunteering as scribe, with Pascal assisting.
- The automatic presence logging by Meetecho was noted as a useful service.
LPWAN Architecture Document (draft-ietf-lpwan-architecture-01):
- The 01 version of the draft was published, with significant reshuffling and the addition of a new "Lifecycle" section (section 7).
- The "Lifecycle" section aims to describe the process of generating, publishing, and securing CHIC rules, emphasizing that rule creation should ideally occur during device development. It's an informational guide, not a set of requirements.
- A missing "Security Considerations" section was identified and will be added back.
- Discussion arose regarding section 6, "Data Model," and whether the document should be a pure architecture or include framework-like elements. It was noted that a list of CHIC-related data models (main, comp-ack, OAM) would be beneficial.
- The group opted to evolve the current document to incorporate framework aspects, such as listing data models, into section 6, rather than splitting it into separate architecture and framework documents at this stage. This would delay its publication but make it more comprehensive.
- Missing content includes more examples (e.g., GOOSE protocol for smart grids), further discussion on the proposed delay-tolerant FOTA, and detailed key management aspects within the lifecycle.
Delay Tolerant FOTA and Large Object Transfer (New Work Item Proposal):
- Problem Statement: NB-IoT modems, to save cost and avoid IPR, often implement only Data-over-NAS (control plane) and not the full user plane. This limits large file transfers (like FOTA or log uploads) which saturate high-priority control channels, impacting network capacity and other users. Operators are often banning such large transfers.
- Proposed Solution: Utilize CHIC fragmentation mechanisms to transmit large objects (e.g., firmware updates, log files) very slowly over extended periods (e.g., a week for 100MB), enabling "delay-tolerant" transfers that avoid congestion.
- Discussion:
  - This problem is relevant beyond NB-IoT to other LPWAN technologies.
  - While CHIC's fragmentation could be reused, modifications would likely be needed for long-lasting sessions, resilience to connectivity loss, and restart capabilities.
  - Concerns were raised about the scope of this work potentially overlapping with the transport layer and requiring rechartering of the WG. It was clarified that this is primarily a single-hop link-layer rate limitation/flow control problem, distinct from end-to-end transport congestion control.
  - The solution would involve dynamic configuration of CHIC parameters, potentially preemptively by the network, which differs from CHIC's initial static nature.
- Conclusion: This is a valuable area of work, but it cannot be included in the existing NB-IoT data model draft. It requires a dedicated problem statement and a new draft, and its scope will necessitate discussion with the IESG and likely a rechartering of the LPWAN WG.
CHIC YANG Module Integration and Extensions:
- Lauren presented on the process for augmenting the base CHIC YANG model using the augment statement, specifically for the comp-ack (Compressed Acknowledgment) and OAM extensions.
- Tools like pyang and yangvalidator.com were highlighted for validating YANG models.
- It was agreed that including the YANG module text directly in the respective drafts (e.g., comp-ack draft) is the correct approach.
- For the comp-ack draft, incorporating the YANG module would not require another Working Group Last Call, but would need review by YANG doctors and the IESG.
- The base CHIC data model's completeness against Appendix D of the main CHIC specification needs a final cross-check.

Decisions and Action Items

LPWAN Architecture Document (draft-ietf-lpwan-architecture):
- Decision: Section 6 will be enhanced to include framework aspects, such as listing related CHIC data models and their extensions, rather than splitting into a separate framework document.
- Action: Alex and Pascale to add a "Security Considerations" section to the architecture document.
- Action: Alex and Pascale to elaborate on examples, the delay-tolerant FOTA discussion, and key management within the lifecycle section.
Delay Tolerant FOTA and Large Object Transfer:
- Decision: This work will be pursued as a new, separate draft and will not be merged into the NB-IoT data model draft.
- Action: Edgar and Anna to prepare a problem statement for this new work item.
- Action: The chairs will need to discuss with the IESG whether this work fits the current LPWAN WG charter or if a rechartering is required.
CHIC YANG Data Models (draft-ietf-lpwan-chic-data-model & draft-ietf-lpwan-chic-comp-ack):
- Decision: The comp-ack YANG module will be integrated into the draft-ietf-lpwan-chic-comp-ack document. No new WG Last Call is needed for this.
- Action: Juan Carlos and Lauren to integrate the comp-ack YANG module text into draft-ietf-lpwan-chic-comp-ack and publish an updated version. Target: End of this week / early next week.
- Action: Dominique to perform a final cross-check of the base CHIC YANG model (draft-ietf-lpwan-chic-data-model) for completeness against Appendix D of the main CHIC specification. Target: Before next week.
- Action: Once both draft-ietf-lpwan-chic-data-model (after Dominique's review) and draft-ietf-lpwan-chic-comp-ack (after integration and publication) are ready, the chairs will request their publication to the IESG concurrently, requesting review by YANG doctors. Target: Next week.

Next Steps

Continue work on the LPWAN Architecture document to incorporate feedback and missing sections.
Initiate a problem statement for the delay-tolerant FOTA work and discuss its charter implications.
Finalize and publish the CHIC base data model and comp-ack extension YANG models for IESG processing.
The group aims to push both CHIC YANG-related drafts for publication next week, before the end of the year.