Session Date/Time: 11 May 2022 14:00

CORE

Summary

The CORE Working Group held an intermeeting to discuss the progress of three drafts: "Conditional Attributes," "Problem Details," and "DNS over CoAP." The working group decided to initiate Working Group Last Calls for both the "Conditional Attributes" and "Problem Details" drafts. Key technical discussions for "Problem Details" included the management of human-readable text with language and direction tags in CBOR. For "DNS over CoAP," discussions covered caching evaluations and the necessary level of abstraction to avoid protocol restatement, with further reviews and mailing list discussions planned before considering adoption.

Key Discussion Points

Conditional Attributes (draft-ietf-core-conditional-attributes):
- The draft was updated to version 04, incorporating a straightforward reference code update and changing the band parameter type to a presence parameter.
- To prevent parameter name clashes, the draft proposes prepending c. (e.g., c.pmin). While acknowledged as a simple solution, there were comments on its somewhat "official" appearance and potential future implications for other drafts that might adopt similar naming conventions. All identified issues in the draft were considered resolved.
Problem Details (draft-ietf-core-problem-details-coap):
- The document aims to extend HTTP RFC 7807 Problem Details for CoAP/CBOR environments, driven by urgent 3GPP requirements.
- The design emphasizes the use of a registry for "Custom Problem Details Entries" to define problem types and their context-specific parameters, allowing for composition. This approach was favored over implicitly invoked URI resolution as seen in some HTTP API group discussions for RFC 7807bis.
- A mechanism to tunnel RFC 7807 problem details within CoAP problem details was presented. However, the inverse (CoAP problem details within RFC 7807) is currently difficult due to RFC 7807 lacking a registry, which is expected to be addressed in RFC 7807bis.
- A significant discussion point arose regarding the proper handling of human-consumable text with language tags (e.g., for end-users). It was noted that CBOR Tag 38 ([language tag, text]) is insufficient as text direction (LTR/RTL) cannot be reliably inferred from a language tag alone.
- The proposed solution is to update the definition of CBOR Tag 38 to include an optional third element for base direction (e.g., false for LTR, true for RTL), effectively fixing what was described as a "severe bug" in its original definition. This change would also import language text syntax from RFC 5 into CDDL.
DNS over CoAP (DoC) (draft-ietf-core-dns-over-coap):
- The draft proposes using CoAP with DTLS or OSCORE for encrypted DNS queries, offering advantages for constrained IoT such as shared system resources and CoAP API features like block-wise transfer.
- An evaluation of caching strategies (DoH-like vs. EOL) showed benefits for GET and FETCH methods, particularly when responses are cacheable.
- Discussion focused on the level of abstraction in the draft. Participants emphasized avoiding the "restatement anti-pattern," where normative statements might inadvertently duplicate or contradict normative references (e.g., CoAP), potentially leading to a non-standard "special version" of CoAP. The advice was to define interactions on resources and rely on resource discovery for server-defined URIs, while providing clear examples without making them normative protocol definitions.
- Other important topics, such as the utility of CoAP Observe for DNS (e.g., tracking IP address changes for DNS names) and the factoring out of a CBOR-based message content format into a separate document, were noted for further discussion on the mailing list.

Decisions and Action Items

Conditional Attributes:
- Decision: The draft draft-ietf-core-conditional-attributes is ready for a Working Group Last Call.
- Action Item: Marco Tiloca (Co-chair) will open the Working Group Last Call on the mailing list, starting today (May 10th) and ending on May 25th.
Problem Details:
- Decision: The draft draft-ietf-core-problem-details-coap is ready for a Working Group Last Call.
- Action Item: Marco Tiloca (Co-chair) will open the Working Group Last Call on the mailing list, terminating on May 24th to allow for discussion at the next interim meeting.
- Action Item: Carsten Bormann will ensure the HTTP API working group is included in the WGLC notification.
- Action Item: Marco Tiloca and Christian Amsüss will review the draft.
DNS over CoAP:
- Action Item: Martin will continue discussions on specific subtopics (e.g., Observe, CBOR content format) on the mailing list.
- Action Item: Martin will reactivate previously interested reviewers and solicit reviews from the DNS-OP working group, clarifying that feedback is sought for adoption readiness rather than final minor details.
- Action Item: Marco Tiloca will perform a review of the draft.

Next Steps

Conditional Attributes: Address any feedback received during the Working Group Last Call.
Problem Details: Address any feedback received during the Working Group Last Call, particularly regarding the proposed update to CBOR Tag 38 for language text direction.
DNS over CoAP: Incorporate feedback from ongoing mailing list discussions and reviews. The aim is to prepare a next version for the IETF 114 cutoff, anticipated around mid-July. The working group chairs will consider adoption once sufficient reviews indicate readiness and alignment with the charter.
The next CORE intermeeting is scheduled in two weeks.