**Session Date/Time:** 06 May 2026 14:00

# [CORE](../wg/core.html)

**CoRE Working Group Interim Meeting**
**Date:** 2026-06-11 (Interim 06)
**Chairs:** Marco Tiloca, Carsten Bormann

## Summary

The CoRE working group held an interim meeting to discuss optimization of join proxy discovery (relevant to ANIMA), resource type flexibility in `draft-ietf-core-coap-pubsub`, and the technical mapping of SIDs to Normalized Instance Trees (NITs) in the context of CORECONF and YANG-CBOR.

## Key Discussion Points

### Join Proxy Discovery and Payload Shortening
**Esko Dijk** presented two approaches to shorten the payload of discovery responses for constrained join proxies (connecting to work in ANIMA). The goal is to reduce the size of link-format responses sent over link-local multicast.

*   **Approach 1: URI Reference with Empty Hostname**
    *   Proposed format: `<//:port/path>;rt="core.jp"`. This uses a relative-ref with a zero-length registered-name for the host.
    *   **Michael Richardson** noted that `//` is used in browsers to maintain schemes across different authorities.
    *   **Carsten Bormann** cautioned that while URI references are standard, an empty hostname with a port number should be checked against RFC 3986 resolution rules to ensure it does not cause implementation conflicts.
    *   **Marco Tiloca** and **Maria Matějka** discussed the semantic implications of the scheme (CoAP vs. CoAPS). The resource type `core.jp` could implicitly signal the requirement for security (DTLS).

*   **Approach 2: Custom Attribute**
    *   Proposed format: `<>;rt="core.jp";jp="port"`. This moves the port information to a new attribute to keep the URI target empty.
    *   **Carsten Bormann** noted that an empty target `<>` refers to the resource where the request was made (e.g., `.well-known/core`), which might be safer from a BCP 190 perspective than pointing to the root.

### CoAP Pubsub (`draft-ietf-core-coap-pubsub`)
**Esko Dijk** raised a question regarding the `core.ps.data` resource type. Currently, it is a default, but the specification was unclear on how extensions or future versions should be handled.

*   **Discussion:** The group discussed whether a resource should support multiple resource types (RTs).
*   **Carsten Bormann** emphasized that the protocol must allow for smooth transitions and evolution. A data resource should be able to offer both the standard `core.ps.data` and a potential future version simultaneously.
*   **Outcome:** The group favored allowing multiple space-separated resource types in the configuration, effectively treating the RT field as an array or a space-separated string to ensure future-proofing and extensibility.

### YANG NITs and SIDs
The group discussed a recent mailing list thread regarding how Actions and RPCs are represented in Normalized Instance Trees (NITs).

*   **Vojtěch Vilímek** argued that since Actions and RPCs are not "data nodes" in the YANG sense, they should not be included in instance identifier paths.
*   **Carsten Bormann** explained that in the context of YANG-CBOR and SIDs, the goal is maximum compression. Including the action point and its input/output details in the NIT allows for a single SID to cover the entire path.
*   **Discussion:** There is a technical distinction between the schema path (used for NITs) and the instance identifier path. **Carsten Bormann** argued that a SID must map to a single NIT (a functional mapping), even if the string representation is unique to the YANG-CBOR context.

## Decisions and Action Items

*   **Pubsub:** **Esko Dijk** and the authors of `draft-ietf-core-coap-pubsub` will add text to clarify that `core.ps.data` is an extension point and that multiple resource types can be associated with a topic.
*   **Join Proxy:** **Esko Dijk** will review RFC 3986 resolution rules regarding empty hostnames and provide a proposal for the join proxy discovery format to the CoRE and ANIMA mailing lists.

## Next Steps

*   Continued discussion on the mailing list regarding the terminology of NITs and SIDs to resolve the discrepancies between schema paths and instance identifiers.
*   The chairs will schedule the next interim in two weeks.

## Presentation Materials
*   [Chairs' slides](https://datatracker.ietf.org/meeting/interim-2026-core-06/materials/slides-interim-2026-core-06-sessa-chairs-slides-00)