Markdown Version | Session Recording

Session Date/Time: 18 Oct 2023 14:00

CBOR

Summary

The CBOR Working Group held a bi-weekly call to review the status of several drafts and plan the agenda for the upcoming IETF 118 meeting in Prague. Key discussions included the progress of the CBOR Time Tag and Extended Diagnostic Notation (EDN) documents, with decisions made to initiate Working Group Last Calls for EDN and the RFC 8610 grammar update. Martin presented an evaluation of name compression techniques for CBOR in DNS, comparing component referencing and packed CBOR Light, with a preference for the former due to conciseness and implementation simplicity. Further work was tasked to compare generic vs. specialized compression approaches. The agenda for IETF 118 was largely set, and future interim call dates were discussed.

Key Discussion Points

• CBOR Time Tag Document (draft-ietf-cbor-time-tag)

  • The document, -09, left the Working Group on August 23rd and is currently in ISG processing.
  • Following an AD review, -10 was submitted.
  • An IETF Last Call was initiated and is set to conclude on the upcoming weekend. A telechat is scheduled for October 26th.
  • Directorate reviews are ongoing, with substantive editorial clarifications leading to pull requests already merged or under review.
  • The document's dependency, the CATE document, is scheduled for a telechat on October 18th.
  • A -11 revision may be prepared before or after the telechat to incorporate outstanding pull requests.

• Extended Diagnostic Notation (EDN) Document (draft-ietf-cbor-edn)

  • The document (currently -05) aims to define and extend the CBOR diagnostic notation, distinct from CDDL.
  • The draft evolved from discussing application-oriented literals to encompassing broader EDN maintenance and extensions.
  • Significant feedback led to a more comprehensive -05 draft, submitted on October 17th, incorporating several enhancements:
    • A mechanism (tag 999) to preserve unknown application-oriented literals, represented as an array of the literal text.
    • Documentation of the "ellipses" feature (tag 888) for partial CBOR data item representations, useful in examples or specifications.
    • Formal documentation of chunked strings, previously described in Appendix G.4 of RFC 8610.
    • Inclusion of an application-oriented literal for IP addresses and prefixes, inspired by RFC 9164. This includes using uppercase (e.g., IPv6'/::1/24') to explicitly disambiguate address types when zero bytes are elided, a convention also extended to DayTime Strings (DTS).

• RFC 8610 Grammar Update

  • The accompanying draft to update the RFC 8610 grammar was noted as ready for Working Group Last Call.

• CBOR and DNS Name Compression

  • Martin presented an evaluation of name compression techniques for CBOR-encoded DNS messages, highlighting the potential for significant byte savings in DNS responses.
  • Two main approaches were evaluated:
    1. Component Referencing: Similar to DNS wire format, referencing name components within the CBOR object using a dedicated tag (e.g., placeholder Tag 7 or 48 for an unsigned integer offset). This approach builds an implicit table as names are encountered. It was noted that this differs from existing tag 25 (string referencing) due to forward counting and broader semantic scope (taking the rest of the array as part of the name).
    2. Packed CBOR Light: Utilizing a predefined explicit table of names/components, akin to the generic CBOR Pack format (e.g., implicit Tag 113 for the packed structure).
  • Evaluation Results: Both methods achieve significant compression, with marginal differences between them. Component referencing showed a slight edge in some scenarios, particularly for smaller compression ratios. Martin expressed a personal preference for component referencing due to its conciseness, simpler implementation, and familiarity for DNS implementers (as it mirrors classic DNS name compression).
  • The idea of rotating flags and options for further byte savings was dismissed due to negligible advantage and potential for implementation confusion.
  • A discussion arose regarding the trade-off between a specialized DNS compression mechanism (like component referencing) and a generic one (like CBOR Pack), which could benefit other applications within the CBOR ecosystem.

• IETF 118 (Prague) Agenda Planning

  • The agenda for the upcoming IETF 118 meeting will include:
    • Discussions on CBOR Pack and DNS representation, including the comparison of compression approaches.
    • Updates on documents currently in progress.
    • Review of results from recently concluded Working Group Last Calls.
    • A brief 5-minute update on "deterministic encoding profiles" (DCORE) to level-set participants and signal continued work in this area.

• Proposed Interim Call Dates

  • The Working Group plans to continue its bi-weekly interim call cadence, coordinating with the CoRE WG.
  • Discussion focused on whether to schedule an interim for March 6th, approximately a week and a half before IETF 119.

Decisions and Action Items

• Decision: Initiate a Working Group Last Call (WGLC) for draft-ietf-cbor-edn-05 and the RFC 8610 Grammar Update document. The WGLC will start on October 17th and conclude on Monday of the IETF 118 week, allowing for discussion of results at the meeting.
• Action Item (Martin): Conduct further evaluation comparing the specialized DNS name compression (component referencing) with the generic CBOR Pack format, possibly exploring implicit table setup with CBOR Pack, for presentation at IETF 118.
• Decision: Add "deterministic encoding profiles" (DCORE) to the IETF 118 agenda for a brief update (approximately 5 minutes).
• Decision: Schedule a Working Group interim call for March 6th. This call can be canceled if there is insufficient agenda, but provides a slot following the Internet-Draft submission deadline.

Next Steps

• The Working Group Last Calls for draft-ietf-cbor-edn-05 and the RFC 8610 Grammar Update will commence.
• Martin will prepare a version 5 of his CBOR DNS draft incorporating other previously discussed items and implementation notes, but not yet the detailed comparison of packing approaches, by Monday.
• Further analysis and comparisons of generic vs. specialized CBOR compression will be undertaken in preparation for IETF 118.
• The IETF 118 agenda will be finalized based on these discussions, and the proposed interim dates will be communicated to the mailing list.