draft-ietf-core-dynlink-09.txt   draft-ietf-core-dynlink-10.txt 
CoRE Working Group Z. Shelby CoRE Working Group Z. Shelby
Internet-Draft ARM Internet-Draft ARM
Intended status: Informational M. Koster Intended status: Informational M. Koster
Expires: January 9, 2020 SmartThings Expires: January 23, 2020 SmartThings
C. Groves C. Groves
J. Zhu J. Zhu
Huawei Huawei
B. Silverajan, Ed. B. Silverajan, Ed.
Tampere University Tampere University
July 08, 2019 July 22, 2019
Dynamic Resource Linking for Constrained RESTful Environments Dynamic Resource Linking for Constrained RESTful Environments
draft-ietf-core-dynlink-09 draft-ietf-core-dynlink-10
Abstract Abstract
This specification defines Link Bindings, which provide dynamic This specification defines Link Bindings, which provide dynamic
linking of state updates between resources, either on an endpoint or linking of state updates between resources, either on an endpoint or
between endpoints, for systems using CoAP (RFC7252). This between endpoints, for systems using CoAP (RFC7252). This
specification also defines Conditional Notification Attributes that specification also defines Conditional Notification Attributes that
work with Link Bindings or with CoAP Observe (RFC7641). work with Link Bindings or with CoAP Observe (RFC7641).
Editor note Editor note
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on January 23, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.1.3. Change Step (st) . . . . . . . . . . . . . . . . . . 6 3.1.3. Change Step (st) . . . . . . . . . . . . . . . . . . 6
3.1.4. Greater Than (gt) . . . . . . . . . . . . . . . . . . 6 3.1.4. Greater Than (gt) . . . . . . . . . . . . . . . . . . 6
3.1.5. Less Than (lt) . . . . . . . . . . . . . . . . . . . 7 3.1.5. Less Than (lt) . . . . . . . . . . . . . . . . . . . 7
3.1.6. Notification Band (band) . . . . . . . . . . . . . . 7 3.1.6. Notification Band (band) . . . . . . . . . . . . . . 7
3.2. Server processing of Conditional Notification Attributes 8 3.2. Server processing of Conditional Notification Attributes 8
4. Link Bindings . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Link Bindings . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. The "bind" attribute and Binding Methods . . . . . . . . 10 4.1. The "bind" attribute and Binding Methods . . . . . . . . 10
4.1.1. Polling . . . . . . . . . . . . . . . . . . . . . . . 11 4.1.1. Polling . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.2. Observe . . . . . . . . . . . . . . . . . . . . . . . 11 4.1.2. Observe . . . . . . . . . . . . . . . . . . . . . . . 11
4.1.3. Push . . . . . . . . . . . . . . . . . . . . . . . . 12 4.1.3. Push . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1.4. Execute . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Link Relation . . . . . . . . . . . . . . . . . . . . . . 12 4.2. Link Relation . . . . . . . . . . . . . . . . . . . . . . 12
5. Binding Table . . . . . . . . . . . . . . . . . . . . . . . . 12 5. Binding Table . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Implementation Considerations . . . . . . . . . . . . . . . . 13 6. Implementation Considerations . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
8.1. Resource Type value 'core.bnd' . . . . . . . . . . . . . 14 8.1. Resource Type value 'core.bnd' . . . . . . . . . . . . . 15
8.2. Link Relation Type . . . . . . . . . . . . . . . . . . . 14 8.2. Link Relation Type . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16
11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 16
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
12.1. Normative References . . . . . . . . . . . . . . . . . . 17 12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 18 12.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 18 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 19
A.1. Minimum Period (pmin) example . . . . . . . . . . . . . . 18 A.1. Minimum Period (pmin) example . . . . . . . . . . . . . . 19
A.2. Maximum Period (pmax) example . . . . . . . . . . . . . . 19 A.2. Maximum Period (pmax) example . . . . . . . . . . . . . . 20
A.3. Greater Than (gt) example . . . . . . . . . . . . . . . . 20 A.3. Greater Than (gt) example . . . . . . . . . . . . . . . . 21
A.4. Greater Than (gt) and Period Max (pmax) example . . . . . 21 A.4. Greater Than (gt) and Period Max (pmax) example . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
IETF Standards for machine to machine communication in constrained IETF Standards for machine to machine communication in constrained
environments describe a REST protocol [RFC7252] and a set of related environments describe a REST protocol [RFC7252] and a set of related
information standards that may be used to represent machine data and information standards that may be used to represent machine data and
machine metadata in REST interfaces. CoRE Link-format [RFC6690] is a machine metadata in REST interfaces. CoRE Link-format [RFC6690] is a
standard for doing Web Linking [RFC8288] in constrained environments. standard for doing Web Linking [RFC8288] in constrained environments.
This specification introduces the concept of a Link Binding, which This specification introduces the concept of a Link Binding, which
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are sent over the link to the other. CoRE Link Format are sent over the link to the other. CoRE Link Format
representations are used to configure, inspect, and maintain Link representations are used to configure, inspect, and maintain Link
Bindings. This specification additionally defines Conditional Bindings. This specification additionally defines Conditional
Notification Attributes for use with Link Bindings and with CoRE Notification Attributes for use with Link Bindings and with CoRE
Observe [RFC7641]. Observe [RFC7641].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This specification requires readers to be familiar with all the terms This specification requires readers to be familiar with all the terms
and concepts that are discussed in [RFC8288] and [RFC6690]. This and concepts that are discussed in [RFC8288] and [RFC6690]. This
specification makes use of the following additional terminology: specification makes use of the following additional terminology:
Link Binding: A unidirectional logical link between a source Link Binding: A unidirectional logical link between a source
resource and a destination resource, over which state information resource and a destination resource, over which state information
is synchronized. is synchronized.
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this specification. this specification.
+---------+------------+-------------+---------------+ +---------+------------+-------------+---------------+
| Name | Identifier | Location | Method | | Name | Identifier | Location | Method |
+---------+------------+-------------+---------------+ +---------+------------+-------------+---------------+
| Polling | poll | Destination | GET | | Polling | poll | Destination | GET |
| | | | | | | | | |
| Observe | obs | Destination | GET + Observe | | Observe | obs | Destination | GET + Observe |
| | | | | | | | | |
| Push | push | Source | PUT | | Push | push | Source | PUT |
| | | | |
| Execute | exec | Source | POST |
+---------+------------+-------------+---------------+ +---------+------------+-------------+---------------+
Table 3: Binding Method Summary Table 3: Binding Method Summary
The description of a binding method defines the following aspects: The description of a binding method defines the following aspects:
Identifier: This is the value of the "bind" attribute used to Identifier: This is the value of the "bind" attribute used to
identify the method. identify the method.
Location: This information indicates whether the binding entry is Location: This information indicates whether the binding entry is
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the content from the source resource is copied to the destination the content from the source resource is copied to the destination
resource. The creation of the observation relationship requires the resource. The creation of the observation relationship requires the
CoAP Observation mechanism [RFC7641] hence this method is only CoAP Observation mechanism [RFC7641] hence this method is only
permitted when the resources are made available over CoAP. The permitted when the resources are made available over CoAP. The
binding entry for this method MUST be stored on the destination binding entry for this method MUST be stored on the destination
endpoint. The binding conditions are mapped as query parameters in endpoint. The binding conditions are mapped as query parameters in
the Observe request (see Section 3). the Observe request (see Section 3).
4.1.3. Push 4.1.3. Push
When the Push method is assigned to a binding, the source endpoint The Push method can be used to allow a source endpoint to replace an
sends PUT requests to the destination resource when the Conditional outdated resource state at the destination with a newer
Notification Attributes are satisfied for the source resource. The representation. When the Push method is assigned to a binding, the
source endpoint SHOULD only send a notification request if any source endpoint sends PUT requests to the destination resource when
included Conditional Notification Attributes are met. The binding the Conditional Notification Attributes are satisfied for the source
entry for this method MUST be stored on the source endpoint. resource. The source endpoint SHOULD only send a notification
request if any included Conditional Notification Attributes are met.
The binding entry for this method MUST be stored on the source
endpoint.
4.1.4. Execute
An alternative means for a source endpoint to deliver change-of-state
notifications to a destination resource is to use the Execute Method.
While the Push method simply updates the state of the destination
resource with the representation of the source resource, Execute can
be used when the destination endpoint wishes to receive all state
changes from a source. This allows, for example, the existence of a
resource collection consisting of all the state changes at the
destination endpoint. When the Execute method is assigned to a
binding, the source endpoint sends POST requests to the destination
resource when the Conditional Notification Attributes are satisfied
for the source resource. The source endpoint SHOULD only send a
notification request if any included Conditional Notification
Attributes are met. The binding entry for this method MUST be stored
on the source endpoint.
Note: Both the Push and the Execute methods are examples of Server
Push mechanisms that are being researched in the Thing-to-Thing
Research Group (T2TRG) [I-D.irtf-t2trg-rest-iot].
4.2. Link Relation 4.2. Link Relation
Since Binding involves the creation of a link between two resources, Since Binding involves the creation of a link between two resources,
Web Linking and the CoRE Link-Format used to represent binding Web Linking and the CoRE Link-Format used to represent binding
information. This involves the creation of a new relation type, information. This involves the creation of a new relation type,
"boundto". In a Web link with this relation type, the target URI "boundto". In a Web link with this relation type, the target URI
contains the location of the source resource and the context URI contains the location of the source resource and the context URI
points to the destination resource. points to the destination resource.
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9. Acknowledgements 9. Acknowledgements
Acknowledgement is given to colleagues from the SENSEI project who Acknowledgement is given to colleagues from the SENSEI project who
were critical in the initial development of the well-known REST were critical in the initial development of the well-known REST
interface concept, to members of the IPSO Alliance where further interface concept, to members of the IPSO Alliance where further
requirements for interface types have been discussed, and to Szymon requirements for interface types have been discussed, and to Szymon
Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann who have Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann who have
provided useful discussion and input to the concepts in this provided useful discussion and input to the concepts in this
specification. Christian Amsuss supplied a comprehensive review of specification. Christian Amsuss supplied a comprehensive review of
draft -06. Hannes Tschofenig and Mert Ocak highlighted syntactical draft -06. Hannes Tschofenig and Mert Ocak highlighted syntactical
corrections in the usage of pmax and pmin in a query. corrections in the usage of pmax and pmin in a query. Discussions
with Ari Keraenen led to the addition of an extra binding method
supporting POST operations.
10. Contributors 10. Contributors
Matthieu Vial Matthieu Vial
Schneider-Electric Schneider-Electric
Grenoble Grenoble
France France
Phone: +33 (0)47657 6522 Phone: +33 (0)47657 6522
EMail: matthieu.vial@schneider-electric.com EMail: matthieu.vial@schneider-electric.com
11. Changelog 11. Changelog
draft-ietf-core-dynlink-10
o Binding methods now support both POST and PUT operations for
server push.
draft-ietf-core-dynlink-09 draft-ietf-core-dynlink-09
o Corrections in Table 1, Table 2, Figure 2. o Corrections in Table 1, Table 2, Figure 2.
o Clarifications for additional operations to binding table added in o Clarifications for additional operations to binding table added in
section 5 section 5
o Additional examples in Appendix A o Additional examples in Appendix A
draft-ietf-core-dynlink-08 draft-ietf-core-dynlink-08
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, [RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017, DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>. <https://www.rfc-editor.org/info/rfc8288>.
12.2. Informative References 12.2. Informative References
[I-D.irtf-t2trg-rest-iot]
Keranen, A., Kovatsch, M., and K. Hartke, "RESTful Design
for Internet of Things Systems", draft-irtf-t2trg-rest-
iot-04 (work in progress), July 2019.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained [RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641, Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015, DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>. <https://www.rfc-editor.org/info/rfc7641>.
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