Semantic Definition Format (SDF): Protocol Mapping for the Constrained Application Protocol (CoAP)

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Table of Contents

1. Introduction

This memo defines vocabulary to integrate the Constrained Application Protocol (CoAP) [RFC7252] into Protocol Mappings [I-D.ietf-asdf-sdf-protocol-mapping] for the Semantic Definition Format (SDF) for Data and Interactions of Things [RFC9880].¶

The vocabulary and "feature-based" approach taken within this document is heavily inspired by the CoAP Protocol Binding [WoT-CoAP-Binding] for the W3C Web of Things (WoT), which is to be used with WoT Thing Descriptions (TDs). Considering SDF's role as a "hub format", we aspire to be able to also take into account CoAP vocabulary when converting from and to TDs.¶

An important additional aspect to the base protocol-mapping specification [I-D.ietf-asdf-sdf-protocol-mapping] is the fact that we rely on instance-related messages [I-D.ietf-asdf-instance-information] to complement protocol information present in SDF models. Compared to the WoT approach, we achieve a stricter separation of model and instance information this way, reducing the amount of information that needs to be supplied by a Thing itself to a minimum to enable interactions.¶

2. Conventions and Definitions

The definitions of [RFC9880], [I-D.ietf-asdf-sdf-protocol-mapping], and [I-D.ietf-asdf-instance-information] apply.¶

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

3. Security Considerations

TODO Security¶

4. IANA Considerations

This document has no IANA actions.¶

5. Formal Syntax of the SDF Protocol Mapping for CoAP

This normative appendix describes the syntax of this protocol mapping definition using CDDL [RFC8610].¶

Via the defined extension points, future specifications may add new definitions to the CDDL schema.¶

same-document-pointer = text .regexp "[^:#]*"

$$SDF-PROPERTY-PROTOCOL-MAP //= (
  coap: coap-property-map
)

$$SDF-EVENT-PROTOCOL-MAP //= (
  coap: coap-event-map
)

$$SDF-ACTION-PROTOCOL-MAP //= (
  coap: coap-action-map
)

coap-parameters = {
    ? host: same-document-pointer
    ? ipAddress: same-document-pointer
}

common-coap-definitions = (
  sdfParameters: coap-parameters
)

coap-vocabulary = {
  scheme: "coap" / "coaps" / "coap+tcp" / "coaps+tcp" / "coap+ws" / "coaps+ws"
  method: "GET" / "POST" / "PUT" / "DELETE" / "FETCH" / "PATCH" / "iPATCH" ; TODO: Can we make this list extendable?
  href: text ; TODO: Should we support URI Template variables here?

  ; An affordance can support multiple Content-Formats as input/output
  ? contentFormat: [ * uint ]
  ? accept: [ * uint ]

  ? minPollingInterval: uint
  ? blockwise: blockwise-parameters
  ? qblockwise: blockwise-parameters
}

blockwise-parameters = {
  ? block1Size: 16 / 32 / 64 / 128 / 256 / 512 / 1024
  ? block2Size: 16 / 32 / 64 / 128 / 256 / 512 / 1024
}

coap-property-map = {
  common-coap-definitions
  sdfOperations: coap-property-operations
}

coap-action-map = {
  common-coap-definitions
  sdfOperations: coap-action-operations
}

coap-event-map = {
  common-coap-definitions
  sdfOperations: coap-event-operations
}

; TODO: Add extension points

coap-property-operations = {
    read: coap-vocabulary ; Also covers observe via the Observe option
    write: coap-vocabulary
}

coap-action-operations = {
    invoke: coap-vocabulary
}

coap-event-operations = {
    subscribe: coap-vocabulary
}

6. References

Acknowledgments

TODO acknowledge.¶

Author's Address