draft-ietf-core-resource-directory-17.txt   draft-ietf-core-resource-directory-18.txt 
CoRE Z. Shelby CoRE Z. Shelby
Internet-Draft ARM Internet-Draft ARM
Intended status: Standards Track M. Koster Intended status: Standards Track M. Koster
Expires: April 26, 2019 SmartThings Expires: June 23, 2019 SmartThings
C. Bormann C. Bormann
Universitaet Bremen TZI Universitaet Bremen TZI
P. van der Stok P. van der Stok
consultant consultant
C. Amsuess, Ed. C. Amsuess, Ed.
October 23, 2018 December 20, 2018
CoRE Resource Directory CoRE Resource Directory
draft-ietf-core-resource-directory-17 draft-ietf-core-resource-directory-18
Abstract Abstract
In many M2M applications, direct discovery of resources is not In many M2M applications, direct discovery of resources is not
practical due to sleeping nodes, disperse networks, or networks where practical due to sleeping nodes, disperse networks, or networks where
multicast traffic is inefficient. These problems can be solved by multicast traffic is inefficient. These problems can be solved by
employing an entity called a Resource Directory (RD), which hosts employing an entity called a Resource Directory (RD), which contains
registrations of resources held on other servers, allowing lookups to information about resources held on other servers, allowing lookups
be performed for those resources. This document specifies the web to be performed for those resources. The input to an RD is composed
of links and the output is composed of links constructed from the
information stored in the RD. This document specifies the web
interfaces that a Resource Directory supports for web servers to interfaces that a Resource Directory supports for web servers to
discover the RD and to register, maintain, lookup and remove resource discover the RD and to register, maintain, lookup and remove
descriptions. Furthermore, new link attributes useful in conjunction information on resources. Furthermore, new target attributes useful
with an RD are defined. in conjunction with an RD are defined.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 April 26, 2019. This Internet-Draft will expire on June 23, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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
skipping to change at page 2, line 28 skipping to change at page 2, line 28
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 6 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 6
3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7
3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 8 3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 8
3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12 3.4. Link-local addresses . . . . . . . . . . . . . . . . . . 12
3.5. Use Case: Home and Building Automation . . . . . . . . . 13 3.5. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12
3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 13 3.6. Use Case: Home and Building Automation . . . . . . . . . 13
3.7. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 13
4. Finding a Resource Directory . . . . . . . . . . . . . . . . 14 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 14
4.1. Resource Directory Address Option (RDAO) . . . . . . . . 15 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 16
5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 17 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 17
5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 17 5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 18
5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 17 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 18
5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 20 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 21
5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 25 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 25
5.3.2. Third-party registration . . . . . . . . . . . . . . 27 5.3.2. Third-party registration . . . . . . . . . . . . . . 28
5.3.3. RD-Groups . . . . . . . . . . . . . . . . . . . . . . 28 5.4. Operations on the Registration Resource . . . . . . . . . 28
6. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 29 5.4.1. Registration Update . . . . . . . . . . . . . . . . . 29
6.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 29 5.4.2. Registration Removal . . . . . . . . . . . . . . . . 32
6.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 30 5.4.3. Further operations . . . . . . . . . . . . . . . . . 33
6.3. Resource lookup examples . . . . . . . . . . . . . . . . 32 6. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7. Security policies . . . . . . . . . . . . . . . . . . . . . . 35 6.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 34
7.1. Secure RD discovery . . . . . . . . . . . . . . . . . . . 36 6.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 34
7.2. Secure RD filtering . . . . . . . . . . . . . . . . . . . 37 6.3. Resource lookup examples . . . . . . . . . . . . . . . . 36
7.3. Secure endpoint Name assignment . . . . . . . . . . . . . 37 6.4. Endpoint lookup . . . . . . . . . . . . . . . . . . . . . 39
8. Security Considerations . . . . . . . . . . . . . . . . . . . 37 7. Security policies . . . . . . . . . . . . . . . . . . . . . . 40
8.1. Endpoint Identification and Authentication . . . . . . . 38 7.1. Secure RD discovery . . . . . . . . . . . . . . . . . . . 41
8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 38 7.2. Secure RD filtering . . . . . . . . . . . . . . . . . . . 41
8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 38 7.3. Secure endpoint Name assignment . . . . . . . . . . . . . 42
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 39 8. Security Considerations . . . . . . . . . . . . . . . . . . . 42
9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 39 8.1. Endpoint Identification and Authentication . . . . . . . 42
9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 39 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 43
8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 43
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 43
9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 44
9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 44
9.3.1. Full description of the "Endpoint Type" Registration 9.3.1. Full description of the "Endpoint Type" Registration
Parameter . . . . . . . . . . . . . . . . . . . . . . 42 Parameter . . . . . . . . . . . . . . . . . . . . . . 46
9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 42 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 46
9.5. Multicast Address Registration . . . . . . . . . . . . . 43 9.5. Multicast Address Registration . . . . . . . . . . . . . 47
10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 43 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.1. Lighting Installation . . . . . . . . . . . . . . . . . 43 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 47
10.1.1. Installation Characteristics . . . . . . . . . . . . 43 10.1.1. Installation Characteristics . . . . . . . . . . . . 47
10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 44 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 49
10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 47 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 51
10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 48 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 52
10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 49 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 53
10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 51 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 55
10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 51 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 55
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 51 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 55
12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 51 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 55
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 58 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 63
13.1. Normative References . . . . . . . . . . . . . . . . . . 58 13.1. Normative References . . . . . . . . . . . . . . . . . . 63
13.2. Informative References . . . . . . . . . . . . . . . . . 59 13.2. Informative References . . . . . . . . . . . . . . . . . 64
Appendix A. Registration Management . . . . . . . . . . . . . . 61 Appendix A. Groups Registration and Lookup . . . . . . . . . . . 66
A.1. Registration Update . . . . . . . . . . . . . . . . . . . 62
A.2. Registration Removal . . . . . . . . . . . . . . . . . . 65
A.3. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 66
A.4. Update Endpoint Links . . . . . . . . . . . . . . . . . . 67
A.5. Endpoint lookup . . . . . . . . . . . . . . . . . . . . . 67
Appendix B. Web links and the Resource Directory . . . . . . . . 68 Appendix B. Web links and the Resource Directory . . . . . . . . 68
B.1. A simple example . . . . . . . . . . . . . . . . . . . . 68 B.1. A simple example . . . . . . . . . . . . . . . . . . . . 68
B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 69 B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 68
B.1.2. Interpreting attributes and relations . . . . . . . . 69 B.1.2. Interpreting attributes and relations . . . . . . . . 69
B.2. A slightly more complex example . . . . . . . . . . . . . 69 B.2. A slightly more complex example . . . . . . . . . . . . . 69
B.3. Enter the Resource Directory . . . . . . . . . . . . . . 70 B.3. Enter the Resource Directory . . . . . . . . . . . . . . 70
B.4. A note on differences between link-format and Link B.4. A note on differences between link-format and Link
headers . . . . . . . . . . . . . . . . . . . . . . . . . 72 headers . . . . . . . . . . . . . . . . . . . . . . . . . 71
Appendix C. Syntax examples for Protocol Negotiation . . . . . . 73 Appendix C. Limited Link Format . . . . . . . . . . . . . . . . 72
Appendix D. Modernized Link Format parsing . . . . . . . . . . . 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73
D.1. For endpoint developers . . . . . . . . . . . . . . . . . 74
D.2. Examples of links with differing interpretations . . . . 75
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 75
1. Introduction 1. Introduction
The work on Constrained RESTful Environments (CoRE) aims at realizing The work on Constrained RESTful Environments (CoRE) aims at realizing
the REST architecture in a suitable form for the most constrained the REST architecture in a suitable form for the most constrained
nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and
networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M) networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M)
applications such as smart energy and building automation. applications such as smart energy and building automation.
The discovery of resources offered by a constrained server is very The discovery of resources offered by a constrained server is very
important in machine-to-machine applications where there are no important in machine-to-machine applications where there are no
humans in the loop and static interfaces result in fragility. The humans in the loop and static interfaces result in fragility. The
discovery of resources provided by an HTTP Web Server is typically discovery of resources provided by an HTTP Web Server is typically
called Web Linking [RFC5988]. The use of Web Linking for the called Web Linking [RFC8288]. The use of Web Linking for the
description and discovery of resources hosted by constrained web description and discovery of resources hosted by constrained web
servers is specified by the CoRE Link Format [RFC6690]. However, servers is specified by the CoRE Link Format [RFC6690]. However,
[RFC6690] only describes how to discover resources from the web [RFC6690] only describes how to discover resources from the web
server that hosts them by querying "/.well-known/core". In many M2M server that hosts them by querying "/.well-known/core". In many M2M
scenarios, direct discovery of resources is not practical due to scenarios, direct discovery of resources is not practical due to
sleeping nodes, disperse networks, or networks where multicast sleeping nodes, disperse networks, or networks where multicast
traffic is inefficient. These problems can be solved by employing an traffic is inefficient. These problems can be solved by employing an
entity called a Resource Directory (RD), which hosts registrations of entity called a Resource Directory (RD), which contains information
resources held on other servers, allowing lookups to be performed for about resources held on other servers, allowing lookups to be
those resources. performed for those resources.
This document specifies the web interfaces that a Resource Directory This document specifies the web interfaces that a Resource Directory
supports for web servers to discover the RD and to register, supports for web servers to discover the RD and to register,
maintain, lookup and remove resource descriptions. Furthermore, new maintain, lookup and remove information on resources. Furthermore,
link attributes useful in conjunction with a Resource Directory are new target attributes useful in conjunction with a Resource Directory
defined. Although the examples in this document show the use of are defined. Although the examples in this document show the use of
these interfaces with CoAP [RFC7252], they can be applied in an these interfaces with CoAP [RFC7252], they can be applied in an
equivalent manner to HTTP [RFC7230]. equivalent manner to HTTP [RFC7230].
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 "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. The term "byte" is used in its now customary sense as a [RFC2119]. The term "byte" is used in its now customary sense as a
synonym for "octet". synonym for "octet".
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 [RFC3986], [RFC5988] and and concepts that are discussed in [RFC3986], [RFC8288] and
[RFC6690]. Readers should also be familiar with the terms and [RFC6690]. Readers should also be familiar with the terms and
concepts discussed in [RFC7252]. To describe the REST interfaces concepts discussed in [RFC7252]. To describe the REST interfaces
defined in this specification, the URI Template format is used defined in this specification, the URI Template format is used
[RFC6570]. [RFC6570].
This specification makes use of the following additional terminology: This specification makes use of the following additional terminology:
resolve against resolve against
The expression "a URI-reference is _resolved against_ a base URI" The expression "a URI-reference is _resolved against_ a base URI"
is used to describe the process of [RFC3986] Section 5.2. is used to describe the process of [RFC3986] Section 5.2.
skipping to change at page 6, line 23 skipping to change at page 6, line 23
needs of the applications. needs of the applications.
Registrant-ep Registrant-ep
Registrant-ep is the endpoint that is registered into the RD. The Registrant-ep is the endpoint that is registered into the RD. The
registrant-ep can register itself, or a CT registers the registrant-ep can register itself, or a CT registers the
registrant-ep. registrant-ep.
RDAO RDAO
Resource Directory Address Option. Resource Directory Address Option.
For several operations, interface descriptions are given in list For several operations, interface templates are given in list form;
form; those describe the operation participants, request codes, URIs, those describe the operation participants, request codes, URIs,
content formats and outcomes. Those templates contain normative content formats and outcomes. Sections of those templates contain
content in their Interaction, Method, URI Template and URI Template normative content about Interaction, Method, URI Template and URI
Variables sections as well as the details of the Success condition. Template Variables as well as the details of the Success condition.
The additional sections on options like Content-Format and on Failure The additional sections on options like Content-Format and on Failure
codes give typical cases that an implementation of the RD should deal codes give typical cases that an implementation of the RD should deal
with. Those serve to illustrate the typical responses to readers who with. Those serve to illustrate the typical responses to readers who
are not yet familiar with all the details of CoAP based interfaces; are not yet familiar with all the details of CoAP based interfaces;
they do not limit what a server may respond under atypical they do not limit what a server may respond under atypical
circumstances. circumstances.
3. Architecture and Use Cases 3. Architecture and Use Cases
3.1. Principles 3.1. Principles
The Resource Directory is primarily a tool to make discovery The Resource Directory is primarily a tool to make discovery
operations more efficient than querying /.well-known/core on all operations more efficient than querying /.well-known/core on all
connected devices, or across boundaries that would be limiting those connected devices, or across boundaries that would be limiting those
operations. operations.
It provides a cache (in the high-level sense, not as defined in It provides information about resources hosted by other devices that
[RFC7252]/[RFC2616]) of data that could otherwise only be obtained by could otherwise only be obtained by directly querying the /.well-
directly querying the /.well-known/core resource on the target known/core resource on these other devices, either by a unicast
device, or by accessing those resources with a multicast request. request or a multicast request.
Only information SHOULD be stored in the resource directory that is Only information SHOULD be stored in the resource directory that can
discoverable from querying the described device's /.well-known/core be obtained by querying the described device's /.well-known/core
resource directly. resource directly.
Data in the resource directory can only be provided by the device Data in the resource directory can only be provided by the device
which hosts those data or a dedicated Commissioning Tool (CT). These which hosts those data or a dedicated Commissioning Tool (CT). These
CTs are thought to act on behalf of endpoints too constrained, or CTs are thought to act on behalf of endpoints too constrained, or
generally unable, to present that information themselves. No other generally unable, to present that information themselves. No other
client can modify data in the resource directory. Changes in the client can modify data in the resource directory. Changes to the
Resource Directory do not propagate automatically back to the web information in the Resource Directory do not propagate automatically
server from where the links originated. back to the web servers from where the information originated.
3.2. Architecture 3.2. Architecture
The resource directory architecture is illustrated in Figure 1. A The resource directory architecture is illustrated in Figure 1. A
Resource Directory (RD) is used as a repository for Web Links Resource Directory (RD) is used as a repository of registrations
[RFC5988] describing resources hosted on other web servers, also describing resources hosted on other web servers, also called
called endpoints (EP). An endpoint is a web server associated with a endpoints (EP). An endpoint is a web server associated with a
scheme, IP address and port. A physical node may host one or more scheme, IP address and port. A physical node may host one or more
endpoints. The RD implements a set of REST interfaces for endpoints endpoints. The RD implements a set of REST interfaces for endpoints
to register and maintain sets of Web Links (called resource directory to register and maintain resource directory registrations, and for
registration entries), and for endpoints to lookup resources from the endpoints to lookup resources from the RD. An RD can be logically
RD. An RD can be logically segmented by the use of Sectors. This segmented by the use of Sectors.
information hierarchy is shown in Figure 2.
A mechanism to discover an RD using CoRE Link Format [RFC6690] is A mechanism to discover an RD using CoRE Link Format [RFC6690] is
defined. defined.
Registration entries in the RD are soft state and need to be Registrations in the RD are soft state and need to be periodically
periodically refreshed. refreshed.
An endpoint uses specific interfaces to register, update and remove a An endpoint uses specific interfaces to register, update and remove a
resource directory registration entry. It is also possible for an RD registration. It is also possible for an RD to fetch Web Links from
to fetch Web Links from endpoints and add them as resource directory endpoints and add their contents to resource directory registrations.
registration entries.
At the first registration of a set of entries, a "registration At the first registration of an endpoint, a "registration resource"
resource" is created, the location of which is returned to the is created, the location of which is returned to the registering
registering endpoint. The registering endpoint uses this endpoint. The registering endpoint uses this registration resource
registration resource to manage the contents of registration entries. to manage the contents of registrations.
A lookup interface for discovering any of the Web Links held in the A lookup interface for discovering any of the Web Links stored in the
RD is provided using the CoRE Link Format. RD is provided using the CoRE Link Format.
Registration Lookup Registration Lookup
Interface Interface Interface Interface
+----+ | | +----+ | |
| EP |---- | | | EP |---- | |
+----+ ---- | | +----+ ---- | |
--|- +------+ | --|- +------+ |
+----+ | ----| | | +--------+ +----+ | ----| | | +--------+
| EP | ---------|-----| RD |----|-----| Client | | EP | ---------|-----| RD |----|-----| Client |
+----+ | ----| | | +--------+ +----+ | ----| | | +--------+
--|- +------+ | --|- +------+ |
+----+ ---- | | +----+ ---- | |
| EP |---- | | | EP |---- | |
+----+ +----+
Figure 1: The resource directory architecture. Figure 1: The resource directory architecture.
+------------+
| Endpoint | <-- Name, Scheme, IP, Port
+------------+
|
|
+------------+
| Resource | <-- Target, Parameters
+------------+
Figure 2: The resource directory information hierarchy.
A Registrant-EP MAY keep concurrent registrations to more than one RD A Registrant-EP MAY keep concurrent registrations to more than one RD
at the same time if explicitly configured to do so, but that is not at the same time if explicitly configured to do so, but that is not
expected to be supported by typical EP implementations. Any such expected to be supported by typical EP implementations. Any such
registrations are independent of each other. The usual expectation registrations are independent of each other. The usual expectation
when multiple discovery mechanisms or addresses are configured is when multiple discovery mechanisms or addresses are configured is
that they constitute a fallback path for a single registration. that they constitute a fall-back path for a single registration.
3.3. RD Content Model 3.3. RD Content Model
The Entity-Relationship (ER) models shown in Figure 3 and Figure 4 The Entity-Relationship (ER) models shown in Figure 2 and Figure 3
model the contents of /.well-known/core and the resource directory model the contents of /.well-known/core and the resource directory
respectively, with entity-relationship diagrams [ER]. Entities respectively, with entity-relationship diagrams [ER]. Entities
(rectangles) are used for concepts that exist independently. (rectangles) are used for concepts that exist independently.
Attributes (ovals) are used for concepts that exist only in Attributes (ovals) are used for concepts that exist only in
connection with a related entity. Relations (diamonds) give a connection with a related entity. Relations (diamonds) give a
semantic meaning to the relation between entities. Numbers specify semantic meaning to the relation between entities. Numbers specify
the cardinality of the relations. the cardinality of the relations.
Some of the attribute values are URIs. Those values are always full Some of the attribute values are URIs. Those values are always full
URIs and never relative references in the information model. They URIs and never relative references in the information model. They
skipping to change at page 9, line 43 skipping to change at page 9, line 32
oooooooooooo 0+ | oooooooooooo 0+ |
o target o--------+ o target o--------+
o attribute o | 0+ oooooo o attribute o | 0+ oooooo
oooooooooooo +-----o rel o oooooooooooo +-----o rel o
| oooooo | oooooo
| |
| 1 ooooooooo | 1 ooooooooo
+-----o context o +-----o context o
ooooooooo ooooooooo
Figure 3: E-R Model of the content of /.well-known/core Figure 2: E-R Model of the content of /.well-known/core
The model shown in Figure 3 models the contents of /.well-known/core The model shown in Figure 2 models the contents of /.well-known/core
which contains: which contains:
o a set of links belonging to the hosting web server o a set of links belonging to the hosting web server
The web server is free to choose links it deems appropriate to be The web server is free to choose links it deems appropriate to be
exposed in its ".well-known/core". Typically, the links describe exposed in its ".well-known/core". Typically, the links describe
resources that are served by the host, but the set can also contain resources that are served by the host, but the set can also contain
links to resources on other servers (see examples in [RFC6690] page links to resources on other servers (see examples in [RFC6690] page
14). The set does not necessarily contain links to all resources 14). The set does not necessarily contain links to all resources
served by the host. served by the host.
A link has the following attributes (see [RFC5988]): A link has the following attributes (see [RFC8288]):
o Zero or more link relations: They describe relations between the o Zero or more link relations: They describe relations between the
link context and the link target. link context and the link target.
In link-format serialization, they are expressed as space- In link-format serialization, they are expressed as space-
separated values in the "rel" attribute, and default to "hosts". separated values in the "rel" attribute, and default to "hosts".
o A link context URI: It defines the source of the relation, e.g. o A link context URI: It defines the source of the relation, e.g.
_who_ "hosts" something. _who_ "hosts" something.
skipping to change at page 11, line 46 skipping to change at page 11, line 46
o lt o----+ ooooooooooo 0+ | o lt o----+ ooooooooooo 0+ |
oooooooo | o target o-----+ oooooooo | o target o-----+
| o attribute o | 0+ oooooo | o attribute o | 0+ oooooo
ooooooooooo 0+ | ooooooooooo +-----o rel o ooooooooooo 0+ | ooooooooooo +-----o rel o
o endpoint o----+ | oooooo o endpoint o----+ | oooooo
o attribute o | o attribute o |
ooooooooooo | 1 ooooooooo ooooooooooo | 1 ooooooooo
+----o context o +----o context o
ooooooooo ooooooooo
Figure 4: E-R Model of the content of the Resource Directory Figure 3: E-R Model of the content of the Resource Directory
The model shown in Figure 4 models the contents of the resource The model shown in Figure 3 models the contents of the resource
directory which contains in addition to /.well-known/core: directory which contains in addition to /.well-known/core:
o 0 to n Registration (entries) of endpoints, o 0 to n Registrations of endpoints,
A registration is associated with one endpoint. A registration A registration is associated with one endpoint. A registration
defines a set of links as defined for /.well-known/core. A defines a set of links as defined for /.well-known/core. A
Registration has six types of attributes: Registration has six types of attributes:
o a unique endpoint name ("ep") within a sector o a unique endpoint name ("ep") within a sector
o a Registration Base URI ("base", a URI typically describing the o a Registration Base URI ("base", a URI typically describing the
scheme://authority part) scheme://authority part)
o a lifetime ("lt"), o a lifetime ("lt"),
skipping to change at page 12, line 27 skipping to change at page 12, line 27
o optionally a sector ("d") o optionally a sector ("d")
o optional additional endpoint attributes (from Section 9.3) o optional additional endpoint attributes (from Section 9.3)
The cardinality of "base" is currently 1; future documents are The cardinality of "base" is currently 1; future documents are
invited to extend the RD specification to support multiple values invited to extend the RD specification to support multiple values
(e.g. [I-D.silverajan-core-coap-protocol-negotiation]). Its value (e.g. [I-D.silverajan-core-coap-protocol-negotiation]). Its value
is used as a Base URI when resolving URIs in the links contained in is used as a Base URI when resolving URIs in the links contained in
the endpoint. the endpoint.
Links are modelled as they are in Figure 3. Links are modelled as they are in Figure 2.
3.4. Use Case: Cellular M2M 3.4. Link-local addresses
Registration requests to the RD may arrive from link-local IP
addresses. When building a Registration Base URI from that source IP
address (which would become part of the resolved URIs in resource
lookup), its link-local IP literal typically contains a zone
identifier of the RD, and is not usable across hosts (see [RFC6874]
Section 1).
Therefore, RD servers SHOULD reject registrations which use of URIs
containing link-local IP addresses.
3.5. Use Case: Cellular M2M
Over the last few years, mobile operators around the world have Over the last few years, mobile operators around the world have
focused on development of M2M solutions in order to expand the focused on development of M2M solutions in order to expand the
business to the new type of users: machines. The machines are business to the new type of users: machines. The machines are
connected directly to a mobile network using an appropriate embedded connected directly to a mobile network using an appropriate embedded
wireless interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing wireless interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing
short and wide range wireless interfaces. From the system design short and wide range wireless interfaces. From the system design
point of view, the ambition is to design horizontal solutions that point of view, the ambition is to design horizontal solutions that
can enable utilization of machines in different applications can enable utilization of machines in different applications
depending on their current availability and capabilities as well as depending on their current availability and capabilities as well as
skipping to change at page 13, line 20 skipping to change at page 13, line 30
access to the endpoints. Mobile apps or web applications for access to the endpoints. Mobile apps or web applications for
environment monitoring contact the RD, look up the endpoints capable environment monitoring contact the RD, look up the endpoints capable
of providing information about the environment using an appropriate of providing information about the environment using an appropriate
set of link parameters, obtain information on how to contact them set of link parameters, obtain information on how to contact them
(URLs of the proxy server), and then initiate interaction to obtain (URLs of the proxy server), and then initiate interaction to obtain
information that is finally processed, displayed on the screen and information that is finally processed, displayed on the screen and
usually stored in a database. Similarly, fleet management systems usually stored in a database. Similarly, fleet management systems
provide the appropriate link parameters to the RD to look up for EPs provide the appropriate link parameters to the RD to look up for EPs
deployed on the vehicles the application is responsible for. deployed on the vehicles the application is responsible for.
3.5. Use Case: Home and Building Automation 3.6. Use Case: Home and Building Automation
Home and commercial building automation systems can benefit from the Home and commercial building automation systems can benefit from the
use of M2M web services. The discovery requirements of these use of M2M web services. The discovery requirements of these
applications are demanding. Home automation usually relies on run- applications are demanding. Home automation usually relies on run-
time discovery to commission the system, whereas in building time discovery to commission the system, whereas in building
automation a combination of professional commissioning and run-time automation a combination of professional commissioning and run-time
discovery is used. Both home and building automation involve peer- discovery is used. Both home and building automation involve peer-
to-peer interactions between endpoints, and involve battery-powered to-peer interactions between endpoints, and involve battery-powered
sleeping devices. sleeping devices.
3.6. Use Case: Link Catalogues 3.7. Use Case: Link Catalogues
Resources may be shared through data brokers that have no knowledge Resources may be shared through data brokers that have no knowledge
beforehand of who is going to consume the data. Resource Directory beforehand of who is going to consume the data. Resource Directory
can be used to hold links about resources and services hosted can be used to hold links about resources and services hosted
anywhere to make them discoverable by a general class of anywhere to make them discoverable by a general class of
applications. applications.
For example, environmental and weather sensors that generate data for For example, environmental and weather sensors that generate data for
public consumption may provide data to an intermediary server, or public consumption may provide data to an intermediary server, or
broker. Sensor data are published to the intermediary upon changes broker. Sensor data are published to the intermediary upon changes
skipping to change at page 15, line 27 skipping to change at page 15, line 39
resource directory (using the ABRO option to find that resource directory (using the ABRO option to find that
[RFC6775]). Confirmation can be obtained by sending a Unicast to [RFC6775]). Confirmation can be obtained by sending a Unicast to
"coap://[6LBR]/.well-known/core?rt=core.rd*". "coap://[6LBR]/.well-known/core?rt=core.rd*".
2. In a network that supports multicast well, discovering the RD 2. In a network that supports multicast well, discovering the RD
using a multicast query for /.well-known/core as specified in using a multicast query for /.well-known/core as specified in
CoRE Link Format [RFC6690]: Sending a Multicast GET to CoRE Link Format [RFC6690]: Sending a Multicast GET to
"coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the "coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the
multicast scope will answer the query. multicast scope will answer the query.
When answering a link-local multicast request, the RD SHOULD NOT
respond with their link-local addresses but use a routable one;
otherwise the registrant-ep would later need to pick an explicit base
address to avoid the issue of Section 3.4.
As some of the RD addresses obtained by the methods listed here are As some of the RD addresses obtained by the methods listed here are
just (more or less educated) guesses, endpoints MUST make use of any just (more or less educated) guesses, endpoints MUST make use of any
error messages to very strictly rate-limit requests to candidate IP error messages to very strictly rate-limit requests to candidate IP
addresses that don't work out. For example, an ICMP Destination addresses that don't work out. For example, an ICMP Destination
Unreachable message (and, in particular, the port unreachable code Unreachable message (and, in particular, the port unreachable code
for this message) may indicate the lack of a CoAP server on the for this message) may indicate the lack of a CoAP server on the
candidate host, or a CoAP error response code such as 4.05 "Method candidate host, or a CoAP error response code such as 4.05 "Method
Not Allowed" may indicate unwillingness of a CoAP server to act as a Not Allowed" may indicate unwillingness of a CoAP server to act as a
directory server. directory server.
skipping to change at page 16, line 48 skipping to change at page 17, line 43
A value of all zero bits (0x0) indicates A value of all zero bits (0x0) indicates
that this Resource Directory address that this Resource Directory address
is not valid anymore. is not valid anymore.
Reserved: This field is unused. It MUST be Reserved: This field is unused. It MUST be
initialized to zero by the sender and initialized to zero by the sender and
MUST be ignored by the receiver. MUST be ignored by the receiver.
RD Address: IPv6 address of the RD. RD Address: IPv6 address of the RD.
Figure 5: Resource Directory Address Option Figure 4: Resource Directory Address Option
5. Resource Directory 5. Resource Directory
This section defines the required set of REST interfaces between a This section defines the required set of REST interfaces between a
Resource Directory (RD) and endpoints. Although the examples Resource Directory (RD) and endpoints. Although the examples
throughout this section assume the use of CoAP [RFC7252], these REST throughout this section assume the use of CoAP [RFC7252], these REST
interfaces can also be realized using HTTP [RFC7230]. In all interfaces can also be realized using HTTP [RFC7230]. In all
definitions in this section, both CoAP response codes (with dot definitions in this section, both CoAP response codes (with dot
notation) and HTTP response codes (without dot notation) are shown. notation) and HTTP response codes (without dot notation) are shown.
An RD implementing this specification MUST support the discovery, An RD implementing this specification MUST support the discovery,
registration, update, lookup, and removal interfaces defined in this registration, update, lookup, and removal interfaces defined in this
section. section.
All operations on the contents of the Resource Directory MUST be All operations on the contents of the Resource Directory MUST be
atomic and idempotent. atomic and idempotent.
A resource directory MAY make the information submitted to it A resource directory MAY make the information submitted to it
available to further directories, if it can ensure that a loop does available to further directories, if it can ensure that a loop does
not form. The protocol used between directories to ensure loop-free not form. The protocol used between directories to ensure loop-free
skipping to change at page 17, line 34 skipping to change at page 18, line 26
5.1. Payload Content Formats 5.1. Payload Content Formats
Resource Directory implementations using this specification MUST Resource Directory implementations using this specification MUST
support the application/link-format content format (ct=40). support the application/link-format content format (ct=40).
Resource Directories implementing this specification MAY support Resource Directories implementing this specification MAY support
additional content formats. additional content formats.
Any additional content format supported by a Resource Directory Any additional content format supported by a Resource Directory
implementing this specification MUST have an equivalent serialization implementing this specification SHOULD be able to express all the
in the application/link-format content format. information expressible in link-format. It MAY be able to express
information that is inexpressible in link-format, but those
expressions SHOULD be avoided where possible.
5.2. URI Discovery 5.2. URI Discovery
Before an endpoint can make use of an RD, it must first know the RD's Before an endpoint can make use of an RD, it must first know the RD's
address and port, and the URI path information for its REST APIs. address and port, and the URI path information for its REST APIs.
This section defines discovery of the RD and its URIs using the well- This section defines discovery of the RD and its URIs using the well-
known interface of the CoRE Link Format [RFC6690]. A complete set of known interface of the CoRE Link Format [RFC6690]. A complete set of
RD discovery methods is described in Section 4. RD discovery methods is described in Section 4.
Discovery of the RD registration URI path is performed by sending Discovery of the RD registration URI path is performed by sending
either a multicast or unicast GET request to "/.well-known/core" and either a multicast or unicast GET request to "/.well-known/core" and
including a Resource Type (rt) parameter [RFC6690] with the value including a Resource Type (rt) parameter [RFC6690] with the value
"core.rd" in the query string. Likewise, a Resource Type parameter "core.rd" in the query string. Likewise, a Resource Type parameter
value of "core.rd-lookup*" is used to discover the URIs for RD Lookup value of "core.rd-lookup*" is used to discover the URIs for RD Lookup
operations, core.rd* is used to discover all URI paths for RD operations, core.rd* is used to discover all URI paths for RD
operations. Upon success, the response will contain a payload with a operations. Upon success, the response will contain a payload with a
link format entry for each RD function discovered, indicating the URI link format entry for each RD function discovered, indicating the URI
of the RD function returned and the corresponding Resource Type. of the RD function returned and the corresponding Resource Type.
When performing multicast discovery, the multicast IP address used When performing multicast discovery, the multicast IP address used
will depend on the scope required and the multicast capabilities of will depend on the scope required and the multicast capabilities of
the network (see Section 9.5. the network (see Section 9.5).
A Resource Directory MAY provide hints about the content-formats it A Resource Directory MAY provide hints about the content-formats it
supports in the links it exposes or registers, using the "ct" link supports in the links it exposes or registers, using the "ct" target
attribute, as shown in the example below. Clients MAY use these attribute, as shown in the example below. Clients MAY use these
hints to select alternate content-formats for interaction with the hints to select alternate content-formats for interaction with the
Resource Directory. Resource Directory.
HTTP does not support multicast and consequently only unicast HTTP does not support multicast and consequently only unicast
discovery can be supported using HTTP. The well-known entry points discovery can be supported using HTTP. The well-known entry points
SHOULD be provided to enable unicast discovery. SHOULD be provided to enable unicast discovery.
An implementation of this resource directory specification MUST An implementation of this resource directory specification MUST
support query filtering for the rt parameter as defined in [RFC6690]. support query filtering for the rt parameter as defined in [RFC6690].
skipping to change at page 18, line 48 skipping to change at page 19, line 44
Method: GET Method: GET
URI Template: /.well-known/core{?rt} URI Template: /.well-known/core{?rt}
URI Template Variables: URI Template Variables:
rt := Resource Type. SHOULD contain one of the values "core.rd", rt := Resource Type. SHOULD contain one of the values "core.rd",
"core.rd-lookup*", "core.rd-lookup-res", "core.rd-lookup-ep", "core.rd-lookup*", "core.rd-lookup-res", "core.rd-lookup-ep",
or "core.rd*" or "core.rd*"
Content-Format: application/link-format (if any) Accept: absent, application/link-format or any other media type
representing web links
Content-Format: application/link-format+json (if any)
Content-Format: application/link-format+cbor (if any)
The following response codes are defined for this interface: The following response codes are defined for this interface:
Success: 2.05 "Content" or 200 "OK" with an application/link-format, Success: 2.05 "Content" or 200 "OK" with an application/link-format
application/link-format+json, or application/link-format+cbor or other web link payload containing one or more matching entries
payload containing one or more matching entries for the RD for the RD resource.
resource.
Failure: 4.00 "Bad Request" or 400 "Bad Request" is returned in case Failure: 4.00 "Bad Request" or 400 "Bad Request" is returned in case
of a malformed request for a unicast request. of a malformed request for a unicast request.
Failure: No error response to a multicast request. Failure: No error response to a multicast request.
HTTP support : YES (Unicast only) HTTP support : YES (Unicast only)
The following example shows an endpoint discovering an RD using this The following example shows an endpoint discovering an RD using this
interface, thus learning that the directory resource location, in interface, thus learning that the directory resource location, in
skipping to change at page 19, line 33 skipping to change at page 20, line 25
server hosting the resource is application/link-format (ct=40). Note server hosting the resource is application/link-format (ct=40). Note
that it is up to the RD to choose its RD locations. that it is up to the RD to choose its RD locations.
Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* Req: GET coap://[MCD1]/.well-known/core?rt=core.rd*
Res: 2.05 Content Res: 2.05 Content
</rd>;rt="core.rd";ct=40, </rd>;rt="core.rd";ct=40,
</rd-lookup/ep>;rt="core.rd-lookup-ep";ct=40, </rd-lookup/ep>;rt="core.rd-lookup-ep";ct=40,
</rd-lookup/res>;rt="core.rd-lookup-res";ct=40, </rd-lookup/res>;rt="core.rd-lookup-res";ct=40,
Figure 6: Example discovery exchange Figure 5: Example discovery exchange
The following example shows the way of indicating that a client may The following example shows the way of indicating that a client may
request alternate content-formats. The Content-Format code attribute request alternate content-formats. The Content-Format code attribute
"ct" MAY include a space-separated sequence of Content-Format codes "ct" MAY include a space-separated sequence of Content-Format codes
as specified in Section 7.2.1 of [RFC7252], indicating that multiple as specified in Section 7.2.1 of [RFC7252], indicating that multiple
content-formats are available. The example below shows the required content-formats are available. The example below shows the required
Content-Format 40 (application/link-format) indicated as well as the Content-Format 40 (application/link-format) indicated as well as a
CBOR and JSON representation of link format. The RD resource CBOR and JSON representation from [I-D.ietf-core-links-json] (which
locations /rd, and /rd-lookup are example values. The server in this have no numeric values assigned yet, so they are shown as TBD64 and
example also indicates that it is capable of providing observation on TBD504 as in that draft). The RD resource locations /rd, and /rd-
resource lookups. lookup are example values. The server in this example also indicates
that it is capable of providing observation on resource lookups.
[ The RFC editor is asked to replace this and later occurrences of
MCD1 with the assigned IPv6 site-local address for "all CoRE Resource
Directories". ]
[ The RFC editor is asked to replace these and later occurrences of
MCD1, TBD64 and TBD504 with the assigned IPv6 site-local address for
"all CoRE Resource Directories" and the numeric ID values assigned by
IANA to application/link-format+cbor and application/link-
format+json, respectively, as they are defined in I-D.ietf-core-
links-json. ]
Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* Req: GET coap://[MCD1]/.well-known/core?rt=core.rd*
Res: 2.05 Content Res: 2.05 Content
</rd>;rt="core.rd";ct="40 65225", </rd>;rt="core.rd";ct="40 65225",
</rd-lookup/res>;rt="core.rd-lookup-res";ct="40 TBD64 TBD504";obs, </rd-lookup/res>;rt="core.rd-lookup-res";ct="40 TBD64 TBD504";obs,
</rd-lookup/ep>;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504", </rd-lookup/ep>;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504",
From a management and maintenance perspective, it is necessary to From a management and maintenance perspective, it is necessary to
identify the components that constitute the RD server. The identify the components that constitute the RD server. The
identification refers to information about for example client-server identification refers to information about for example client-server
skipping to change at page 20, line 39 skipping to change at page 21, line 29
(as in this example) or at individual RD components. The latter is (as in this example) or at individual RD components. The latter is
to be expected when different applications are run on the same to be expected when different applications are run on the same
server. server.
5.3. Registration 5.3. Registration
After discovering the location of an RD, a registrant-ep or CT MAY After discovering the location of an RD, a registrant-ep or CT MAY
register the resources of the registrant-ep using the registration register the resources of the registrant-ep using the registration
interface. This interface accepts a POST from an endpoint containing interface. This interface accepts a POST from an endpoint containing
the list of resources to be added to the directory as the message the list of resources to be added to the directory as the message
payload in the CoRE Link Format [RFC6690], JSON CoRE Link Format payload in the CoRE Link Format [RFC6690] or other representations of
(application/link-format+json), or CBOR CoRE Link Format web links, along with query parameters indicating the name of the
(application/link-format+cbor) [I-D.ietf-core-links-json], along with endpoint, and optionally the sector, lifetime and base URI of the
query parameters indicating the name of the endpoint, and optionally registration. It is expected that other specifications will define
the sector, lifetime and base URI of the registration. It is further parameters (see Section 9.3). The RD then creates a new
expected that other specifications will define further parameters registration resource in the RD and returns its location. The
(see Section 9.3). The RD then creates a new registration resource receiving endpoint MUST use that location when refreshing
in the RD and returns its location. The receiving endpoint MUST use registrations using this interface. Registration resources in the RD
that location when refreshing registrations using this interface. are kept active for the period indicated by the lifetime parameter.
Registration resources in the RD are kept active for the period The creating endpoint is responsible for refreshing the registration
indicated by the lifetime parameter. The creating endpoint is resource within this period using either the registration or update
responsible for refreshing the registration resource within this interface. The registration interface MUST be implemented to be
period using either the registration or update interface. The idempotent, so that registering twice with the same endpoint
registration interface MUST be implemented to be idempotent, so that parameters ep and d (sector) does not create multiple registration
registering twice with the same endpoint parameters ep and d (sector) resources.
does not create multiple registration resources.
The following rules apply for an update identified by a given (ep, d)
value pair:
o when the parameter values of the Update generate the same The following rules apply for a registration request targeting a
attribute values as already present, the location of the already given (ep, d) value pair:
existing registration is returned.
o when for a given (ep, d) value pair the update generates attribute o When the (ep, d) value pair of the registration-request is
values which are different from the existing one, the existing different from any existing registration, a new registration is
registration is removed and a new registration with a new location generated.
is created.
o when the (ep, d) value pair of the update is different from any o When the (ep, d) value pair of the registration-request is equal
existing registration, a new registration is generated. to an existing registration, the content and parameters of the
existing registration are replaced with the content of the
registration request.
The posted link-format document can (and typically does) contain The posted link-format document can (and typically does) contain
relative references both in its link targets and in its anchors, or relative references both in its link targets and in its anchors, or
contain empty anchors. The RD server needs to resolve these contain empty anchors. The RD server needs to resolve these
references in order to faithfully represent them in lookups. They references in order to faithfully represent them in lookups. They
are resolved against the base URI of the registration, which is are resolved against the base URI of the registration, which is
provided either explicitly in the "base" parameter or constructed provided either explicitly in the "base" parameter or constructed
implicitly from the requester's URI as constructed from its network implicitly from the requester's URI as constructed from its network
address and scheme. address and scheme.
Link format documents submitted to the resource directory are For media types to which Appendix C applies (i.e. documents in
interpreted as Modernized Link Format (see Appendix D) by the RD. A application/link-format), the RD only needs to accept representations
registrant-ep SHOULD NOT submit documents whose interpretations in Limited Link Format as described there. Its behavior with
according to [RFC6690] and Appendix D differ to avoid the ambiguities representations outside that subset is implementation defined.
described in Appendix B.4.
In practice, most links (precisely listed in Appendix D.1) can be
submitted without consideration for those details.
The registration request interface is specified as follows: The registration request interface is specified as follows:
Interaction: EP -> RD Interaction: EP -> RD
Method: POST Method: POST
URI Template: {+rd}{?ep,d,lt,base,extra-attrs*} URI Template: {+rd}{?ep,d,lt,base,extra-attrs*}
URI Template Variables: URI Template Variables:
rd := RD registration URI (mandatory). This is the location of rd := RD registration URI (mandatory). This is the location of
the RD, as obtained from discovery. the RD, as obtained from discovery.
ep := Endpoint name (mostly mandatory). The endpoint name is an ep := Endpoint name (mostly mandatory). The endpoint name is an
identifier that MUST be unique within a sector. The maximum identifier that MUST be unique within a sector. The maximum
length of this parameter is 63 bytes. If the RD is configured length of this parameter is 63 bytes. If the RD is configured
to recognize the endpoint (e.g. based on its security context), to recognize the endpoint (e.g. based on its security context),
the endpoint sets no endpoint name, and the RD assigns one the RD assigns an endpoint name based on a set of configuration
based on a set of configuration parameter values. parameter values.
d := Sector (optional). The sector to which this endpoint d := Sector (optional). The sector to which this endpoint
belongs. The maximum length of this parameter is 63 bytes. belongs. The maximum length of this parameter is 63 bytes.
When this parameter is not present, the RD MAY associate the When this parameter is not present, the RD MAY associate the
endpoint with a configured default sector or leave it empty. endpoint with a configured default sector or leave it empty.
The endpoint name and sector name are not set when one or both The endpoint name and sector name are not set when one or both
are set in an accompanying authorization token. are set in an accompanying authorization token.
lt := Lifetime (optional). Lifetime of the registration in lt := Lifetime (optional). Lifetime of the registration in
seconds. Range of 60-4294967295. If no lifetime is included seconds. Range of 60-4294967295. If no lifetime is included
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have a path component of its own, and MUST be suitable as a have a path component of its own, and MUST be suitable as a
base URI to resolve any relative references given in the base URI to resolve any relative references given in the
registration. The parameter is therefore usually of the shape registration. The parameter is therefore usually of the shape
"scheme://authority" for HTTP and CoAP URIs. The URI SHOULD "scheme://authority" for HTTP and CoAP URIs. The URI SHOULD
NOT have a query or fragment component as any non-empty NOT have a query or fragment component as any non-empty
relative part in a reference would remove those parts from the relative part in a reference would remove those parts from the
resulting URI. resulting URI.
In the absence of this parameter the scheme of the protocol, In the absence of this parameter the scheme of the protocol,
source address and source port of the registration request are source address and source port of the registration request are
assumed. That Base URI is constructed by concatenating the assumed. The Base URI is consecutively constructed by
used protcol's scheme with the characters "://", the concatenating the used protocol's scheme with the characters
requester's source address as an address literal and ":" "://", the requester's source address as an address literal and
followed by its port (if it was not the protocol's default one) ":" followed by its port (if it was not the protocol's default
in analogy to [RFC7252] Section 6.5. one) in analogy to [RFC7252] Section 6.5.
This parameter is mandatory when the directory is filled by a This parameter is mandatory when the directory is filled by a
third party such as an commissioning tool. third party such as an commissioning tool.
If the registrant-ep uses an ephemeral port to register with, If the registrant-ep uses an ephemeral port to register with,
it MUST include the base parameter in the registration to it MUST include the base parameter in the registration to
provide a valid network path. provide a valid network path.
If the registrant-ep, located behind a NAT gateway, is If the registrant-ep, located behind a NAT gateway, is
registering with a Resource Directory which is on the network registering with a Resource Directory which is on the network
service side of the NAT gateway, the endpoint MUST use a service side of the NAT gateway, the endpoint MUST use a
persistent port for the outgoing registration in order to persistent port for the outgoing registration in order to
provide the NAT gateway with a valid network address for provide the NAT gateway with a valid network address for
replies and incoming requests. replies and incoming requests.
If the registrant-ep uses a link-local address to register, it
MUST give an explicit routable base address unless configured
otherwise as per Section 3.4 (or just register from that
address in the first place).
Endpoints that register with a base that contains a path Endpoints that register with a base that contains a path
component can not meaningfully use [RFC6690] Link Format due to component can not meaningfully use [RFC6690] Link Format due to
its prevalence of the Origin concept in relative reference its prevalence of the Origin concept in relative reference
resolution; they can submit payloads for interpretation as resolution. Those applications should use different
Modernized Link Format. Typically, links submitted by such an representations of links to which Appendix C is not applicable
endpoint are of the "path-noscheme" (starts with a path not (e.g. [I-D.hartke-t2trg-coral]).
preceded by a slash, precisely defined in [RFC3986]
Section 3.3) form.
extra-attrs := Additional registration attributes (optional). extra-attrs := Additional registration attributes (optional).
The endpoint can pass any parameter registered at Section 9.3 The endpoint can pass any parameter registered at Section 9.3
to the directory. If the RD is aware of the parameter's to the directory. If the RD is aware of the parameter's
specified semantics, it processes it accordingly. Otherwise, specified semantics, it processes it accordingly. Otherwise,
it MUST store the unknown key and its value(s) as an endpoint it MUST store the unknown key and its value(s) as an endpoint
attribute for further lookup. attribute for further lookup.
Content-Format: application/link-format Content-Format: application/link-format or any other indicated media
type representing web links
Content-Format: application/link-format+json
Content-Format: application/link-format+cbor
The following response codes are defined for this interface: The following response codes are defined for this interface:
Success: 2.01 "Created" or 201 "Created". The Location-Path option Success: 2.01 "Created" or 201 "Created". The Location-Path option
or Location header MUST be included in the response. This or Location header MUST be included in the response. This
location MUST be a stable identifier generated by the RD as it is location MUST be a stable identifier generated by the RD as it is
used for all subsequent operations on this registration resource. used for all subsequent operations on this registration resource.
The registration resource location thus returned is for the The registration resource location thus returned is for the
purpose of updating the lifetime of the registration and for purpose of updating the lifetime of the registration and for
maintaining the content of the registered links, including maintaining the content of the registered links, including
skipping to change at page 24, line 33 skipping to change at page 25, line 13
"Finding a Resource Directory" step. Care has to be taken to "Finding a Resource Directory" step. Care has to be taken to
consider the freshness of results obtained earlier, e.g. of the consider the freshness of results obtained earlier, e.g. of the
result of a "/.well-known/core" response, the lifetime of an RDAO result of a "/.well-known/core" response, the lifetime of an RDAO
option and of DNS responses. Any rate limits and persistent errors option and of DNS responses. Any rate limits and persistent errors
from the "Finding a Resource Directory" step must be considered for from the "Finding a Resource Directory" step must be considered for
the whole registration time, not only for a single operation. the whole registration time, not only for a single operation.
The following example shows a registrant-ep with the name "node1" The following example shows a registrant-ep with the name "node1"
registering two resources to an RD using this interface. The registering two resources to an RD using this interface. The
location "/rd" is an example RD location discovered in a request location "/rd" is an example RD location discovered in a request
similar to Figure 6. similar to Figure 5.
Req: POST coap://rd.example.com/rd?ep=node1 Req: POST coap://rd.example.com/rd?ep=node1
Content-Format: 40 Content-Format: 40
Payload: Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor"; </sensors/temp>;ct=41;rt="temperature-c";if="sensor";
anchor="coap://spurious.example.com:5683", anchor="coap://spurious.example.com:5683",
</sensors/light>;ct=41;rt="light-lux";if="sensor" </sensors/light>;ct=41;rt="light-lux";if="sensor"
Res: 2.01 Created Res: 2.01 Created
Location-Path: /rd/4521 Location-Path: /rd/4521
Figure 7: Example registration payload Figure 6: Example registration payload
A Resource Directory may optionally support HTTP. Here is an example A Resource Directory may optionally support HTTP. Here is an example
of almost the same registration operation above, when done using HTTP of almost the same registration operation above, when done using
and the JSON Link Format. HTTP.
Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1 Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/link-format+json Content-Type: application/link-format
Payload: Payload:
[ </sensors/temp>;ct=41;rt="temperature-c";if="sensor";
{"href": "/sensors/temp", "ct": "41", "rt": "temperature-c", anchor="coap://spurious.example.com:5683",
"if": "sensor", "anchor": "coap://spurious.example.com:5683"}, </sensors/light>;ct=41;rt="light-lux";if="sensor"
{"href": "/sensors/light", "ct": "41", "rt": "light-lux",
"if": "sensor"}
]
Res: 201 Created Res: 201 Created
Location: /rd/4521 Location: /rd/4521
5.3.1. Simple Registration 5.3.1. Simple Registration
Not all endpoints hosting resources are expected to know how to Not all endpoints hosting resources are expected to know how to
upload links to an RD as described in Section 5.3. Instead, simple upload links to an RD as described in Section 5.3. Instead, simple
endpoints can implement the Simple Registration approach described in endpoints can implement the Simple Registration approach described in
this section. An RD implementing this specification MUST implement this section. An RD implementing this specification MUST implement
Simple Registration. However, there may be security reasons why this Simple Registration. However, there may be security reasons why this
form of directory discovery would be disabled. form of directory discovery would be disabled.
This approach requires that the registrant-ep makes available the This approach requires that the registrant-ep makes available the
hosted resources that it wants to be discovered, as links on its hosted resources that it wants to be discovered, as links on its
"/.well-known/core" interface as specified in [RFC6690]. The links "/.well-known/core" interface as specified in [RFC6690]. The links
in that document are subject to the same limitations as the payload in that document are subject to the same limitations as the payload
of a registration (with respect to Appendix D). of a registration (with respect to Appendix C).
The registrant-ep finds one or more addresses of the directory server The registrant-ep finds one or more addresses of the directory server
as described in Section 4. as described in Section 4.
The registrant-ep asks the selected directory server to probe its The registrant-ep asks the selected directory server to probe its
/.well-known/core and publish the links as follows: /.well-known/core and publish the links as follows:
The registrant-ep sends (and regularly refreshes with) a POST request The registrant-ep sends (and regularly refreshes with) a POST request
to the "/.well-known/core" URI of the directory server of choice. to the "/.well-known/core" URI of the directory server of choice.
The body of the POST request is empty, and triggers the resource The body of the POST request is empty, and triggers the resource
directory server to perform GET requests at the requesting directory server to perform GET requests at the requesting
registrant-ep's /.well-known/core to obtain the link-format payload registrant-ep's /.well-known/core to obtain the link-format payload
to register. to register.
The registrant-ep includes the same registration parameters in the The registrant-ep includes the same registration parameters in the
POST request as it would per Section 5.3. The registration base URI POST request as it would per Section 5.3. The registration base URI
of the registration is taken from the requesting server's URI. of the registration is taken from the registrant-ep's network address
(as is default with regular registrations).
The Resource Directory MUST NOT query the registrant-ep's data before The Resource Directory needs to query the registrant-ep's discovery
sending the response; this is to accommodate very limited endpoints. resource to determine the success of the operation. It SHOULD keep a
cache of the discovery resource and not query it again as long as it
is fresh.
The success condition only indicates that the request was valid (i.e. (This is to accomodate constrained registrant devices that can not
the passed parameters are valid per se), not that the link data could process an incoming and outgoing request at the same time.
be obtained or parsed or was successfully registered into the RD. Registrants MUST be able to serve a GET request to "/.well-known/
core" after having requested registration. Constrained devices MAY
regard the initial request as temporarily failed when they need RAM
occupied by their own request to serve the RD's GET, and retry later
when the RD already has a cached representation of their discovery
resources. Then, the RD can reply immediately and the registrant can
receive the response.)
The simple registration request interface is specified as follows: The simple registration request interface is specified as follows:
Interaction: EP -> RD Interaction: EP -> RD
Method: POST Method: POST
URI Template: /.well-known/core{?ep,d,lt,extra-attrs*} URI Template: /.well-known/core{?ep,d,lt,extra-attrs*}
URI Template Variables are as they are for registration in URI Template Variables are as they are for registration in
Section 5.3. The base attribute is not accepted to keep the Section 5.3. The base attribute is not accepted to keep the
registration interface simple; that rules out registration over CoAP- registration interface simple; that rules out registration over CoAP-
over-TCP or HTTP that would need to specify one. over-TCP or HTTP that would need to specify one.
The following response codes are defined for this interface: The following response codes are defined for this interface:
Success: 2.04 "Changed". Success: 2.04 "Changed".
Failure: 4.00 "Bad Request". Malformed request. Failure: 4.00 "Bad Request". Malformed request.
skipping to change at page 26, line 49 skipping to change at page 27, line 36
Method: GET Method: GET
URI Template: /.well-known/core URI Template: /.well-known/core
The following response codes are defined for this interface: The following response codes are defined for this interface:
Success: 2.05 "Content". Success: 2.05 "Content".
Failure: 4.00 "Bad Request". Malformed request. Failure: 4.00 "Bad Request". Malformed request.
Failure: 4.04 "Not Found". /.well-known/core does not exist or is Failure: 4.04 "Not Found". /.well-known/core does not exist.
empty.
Failure: 5.03 "Service Unavailable". Service could not perform the Failure: 5.03 "Service Unavailable". Service could not perform the
operation. operation.
HTTP support: NO HTTP support: NO
The registration resources MUST be deleted after the expiration of The registration resources MUST be deleted after the expiration of
their lifetime. Additional operations on the registration resource their lifetime. Additional operations on the registration resource
cannot be executed because no registration location is returned. cannot be executed because no registration location is returned.
The following example shows a registrant-ep using Simple The following example shows a registrant-ep using Simple
Registration, by simply sending an empty POST to a resource Registration, by simply sending an empty POST to a resource
directory. directory.
Req:(to RD server from [2001:db8:2::1]) Req: (to RD server from [2001:db8:2::1])
POST /.well-known/core?lt=6000&ep=node1 POST /.well-known/core?lt=6000&ep=node1
No payload No payload
Res: 2.04 Changed
(later)
Req: (from RD server to [2001:db8:2::1]) Req: (from RD server to [2001:db8:2::1])
GET /.well-known/core GET /.well-known/core
Accept: 40 Accept: 40
Res: 2.05 Content Res: (to the RD from [2001:db8:2::1] ) 2.05 Content
Content-Format: 40 Content-Format: 40
Payload: Payload:
</sen/temp> </sen/temp>
Res: (from the RD to [2001:db8:2::1]) 2.04 Changed
5.3.2. Third-party registration 5.3.2. Third-party registration
For some applications, even Simple Registration may be too taxing for For some applications, even Simple Registration may be too taxing for
some very constrained devices, in particular if the security some very constrained devices, in particular if the security
requirements become too onerous. requirements become too onerous.
In a controlled environment (e.g. building control), the Resource In a controlled environment (e.g. building control), the Resource
Directory can be filled by a third party device, called a Directory can be filled by a third party device, called a
Commissioning Tool (CT). The commissioning tool can fill the Commissioning Tool (CT). The commissioning tool can fill the
Resource Directory from a database or other means. For that purpose Resource Directory from a database or other means. For that purpose
scheme, IP address and port of the URI of the registered device is scheme, IP address and port of the URI of the registered device is
the value of the "base" parameter of the registration described in the value of the "base" parameter of the registration described in
Section 5.3. Section 5.3.
It should be noted that the value of the "base" parameter applies to It should be noted that the value of the "base" parameter applies to
all the links of the registration and has consequences for the anchor all the links of the registration and has consequences for the anchor
value of the individual links as exemplified in Appendix B. An value of the individual links as exemplified in Appendix B. An
eventual (currently non-existing) "base" attribute of the link is not eventual (currently non-existing) "base" attribute of the link is not
affected by the value of "base" parameter in the registration. affected by the value of "base" parameter in the registration.
5.3.3. RD-Groups 5.4. Operations on the Registration Resource
The RD-Groups usage pattern allows announcing application groups This section describes how the registering endpoint can maintain the
inside a Resource Directory. registrations that it created. The registering endpoint can be the
registrant-ep or the CT. An endpoint SHOULD NOT use this interface
for registrations that it did not create. The registrations are
resources of the RD.
Groups are represented by endpoint registrations. Their base address After the initial registration, the registering endpoint retains the
is a multicast address, and they SHOULD be entered with the endpoint returned location of the Registration Resource for further
type "core.rd-group". The endpoint name can also be referred to as a operations, including refreshing the registration in order to extend
group name in this context. the lifetime and "keep-alive" the registration. When the lifetime of
the registration has expired, the RD SHOULD NOT respond to discovery
queries concerning this endpoint. The RD SHOULD continue to provide
access to the Registration Resource after a registration time-out
occurs in order to enable the registering endpoint to eventually
refresh the registration. The RD MAY eventually remove the
registration resource for the purpose of garbage collection. If the
Registration Resource is removed, the corresponding endpoint will
need to be re-registered.
The registration is inserted into the RD by a Commissioning Tool, The Registration Resource may also be used cancel the registration
which might also be known as a group manager here. It performs third using DELETE, and to perform further operations beyond the scope of
party registration and registration updates. this specification.
The links it registers SHOULD be available on all members that join These operations are described below.
the group. Depending on the application, members that lack some
resource MAY be permissible if requests to them fail gracefully.
The following example shows a CT registering a group with the name 5.4.1. Registration Update
"lights" which provides two resources. The directory resource path
/rd is an example RD location discovered in a request similar to
Figure 6.
Req: POST coap://rd.example.com/rd?ep=lights&et=core.rd-group The update interface is used by the registering endpoint to refresh
&base=coap://[ff35:30:2001:db8::1] or update its registration with an RD. To use the interface, the
Content-Format: 40 registering endpoint sends a POST request to the registration
resource returned by the initial registration operation.
An update MAY update the lifetime- or the context- registration
parameters "lt", "base" as in Section 5.3. Parameters that are not
being changed SHOULD NOT be included in an update. Adding parameters
that have not changed increases the size of the message but does not
have any other implications. Parameters MUST be included as query
parameters in an update operation as in Section 5.3.
A registration update resets the timeout of the registration to the
(possibly updated) lifetime of the registration, independent of
whether a "lt" parameter was given.
If the context of the registration is changed in an update, relative
references submitted in the original registration or later updates
are resolved anew against the new context.
The registration update operation only describes the use of POST with
an empty payload. Future standards might describe the semantics of
using content formats and payloads with the POST method to update the
links of a registration (see Section 5.4.3).
The update registration request interface is specified as follows:
Interaction: EP -> RD
Method: POST
URI Template: {+location}{?lt,base,extra-attrs*}
URI Template Variables:
location := This is the Location returned by the RD as a result
of a successful earlier registration.
lt := Lifetime (optional). Lifetime of the registration in
seconds. Range of 60-4294967295. If no lifetime is included,
the previous last lifetime set on a previous update or the
original registration (falling back to 90000) SHOULD be used.
base := Base URI (optional). This parameter updates the Base URI
established in the original registration to a new value. If
the parameter is set in an update, it is stored by the RD as
the new Base URI under which to interpret the relative links
present in the payload of the original registration, following
the same restrictions as in the registration. If the parameter
is not set in the request but was set before, the previous Base
URI value is kept unmodified. If the parameter is not set in
the request and was not set before either, the source address
and source port of the update request are stored as the Base
URI.
extra-attrs := Additional registration attributes (optional). As
with the registration, the RD processes them if it knows their
semantics. Otherwise, unknown attributes are stored as
endpoint attributes, overriding any previously stored endpoint
attributes of the same key.
Content-Format: none (no payload)
The following response codes are defined for this interface:
Success: 2.04 "Changed" or 204 "No Content" if the update was
successfully processed.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have been removed).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
If the registration update fails with a "Service Unavailable"
response and a Max-Age option or Retry-After header, the registering
endpoint SHOULD retry the operation after the time indicated. If the
registration fails in another way, including request timeouts, or if
the time indicated exceeds the remaining lifetime, the registering
endpoint SHOULD attempt registration again.
The following example shows how the registering endpoint updates its
registration resource at an RD using this interface with the example
location value: /rd/4521.
Req: POST /rd/4521
Res: 2.04 Changed
The following example shows the registering endpoint updating its
registration resource at an RD using this interface with the example
location value: /rd/4521. The initial registration by the
registering endpoint set the following values:
o endpoint name (ep)=endpoint1
o lifetime (lt)=500
o Base URI (base)=coap://local-proxy-old.example.com:5683
o payload of Figure 6
The initial state of the Resource Directory is reflected in the
following request:
Req: GET /rd-lookup/res?ep=endpoint1
Res: 2.01 Content
Payload: Payload:
</light>;rt="light";if="core.a", <coap://local-proxy-old.example.com:5683/sensors/temp>;ct=41;
</color-temperature>;if="core.p";u="K" rt="temperature"; anchor="coap://spurious.example.com:5683",
<coap://local-proxy-old.example.com:5683/sensors/light>;ct=41;
rt="light-lux"; if="sensor";
anchor="coap://local-proxy-old.example.com:5683"
Res: 2.01 Created The following example shows the registering endpoint changing the
Location-Path: /rd/12 Base URI to "coaps://new.example.com:5684":
In this example, the group manager can easily permit devices that Req: POST /rd/4521?base=coaps://new.example.com:5684
have no writable color-temperature to join, as they would still
respond to brightness changing commands. Had the group instead
contained a single resource that sets brightness and color
temperature atomically, endpoints would need to support both
properties.
The resources of a group can be looked up like any other resource, Res: 2.04 Changed
and the group registrations (along with any additional registration
parameters) can be looked up using the endpoint lookup interface. The consecutive query returns:
Req: GET /rd-lookup/res?ep=endpoint1
Res: 2.01 Content
Payload:
<coaps://new.example.com:5684/sensors/temp>;ct=41;rt="temperature";
anchor="coap://spurious.example.com:5683",
<coaps://new.example.com:5684/sensors/light>;ct=41;rt="light-lux";
if="sensor"; anchor="coaps://new.example.com:5684",
5.4.2. Registration Removal
Although RD registrations have soft state and will eventually timeout
after their lifetime, the registering endpoint SHOULD explicitly
remove an entry from the RD if it knows it will no longer be
available (for example on shut-down). This is accomplished using a
removal interface on the RD by performing a DELETE on the endpoint
resource.
The removal request interface is specified as follows:
Interaction: EP -> RD
Method: DELETE
URI Template: {+location}
URI Template Variables:
location := This is the Location returned by the RD as a result
of a successful earlier registration.
The following response codes are defined for this interface:
Success: 2.02 "Deleted" or 204 "No Content" upon successful deletion
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may already have been removed).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following examples shows successful removal of the endpoint from
the RD with example location value /rd/4521.
Req: DELETE /rd/4521
Res: 2.02 Deleted
5.4.3. Further operations
Additional operations on the registration can be specified in future
documents, for example:
o Send iPATCH (or PATCH) updates ([RFC8132]) to add, remove or
change the links of a registration.
o Use GET to read the currently stored set of links in a
registration resource.
Those operations are out of scope of this document, and will require
media types suitable for modifying sets of links.
6. RD Lookup 6. RD Lookup
To discover the resources registered with the RD, a lookup interface To discover the resources registered with the RD, a lookup interface
must be provided. This lookup interface is defined as a default, and must be provided. This lookup interface is defined as a default, and
it is assumed that RDs may also support lookups to return resource it is assumed that RDs may also support lookups to return resource
descriptions in alternative formats (e.g. Atom or HTML Link) or descriptions in alternative formats (e.g. JSON or CBOR link format
using more advanced interfaces (e.g. supporting context or semantic [I-D.ietf-core-links-json]) or using more advanced interfaces (e.g.
based lookup). supporting context or semantic based lookup) on different resources
that are discovered independently.
RD Lookup allows lookups for endpoints and resources using attributes RD Lookup allows lookups for endpoints and resources using attributes
defined in this document and for use with the CoRE Link Format. The defined in this document and for use with the CoRE Link Format. The
result of a lookup request is the list of links (if any) result of a lookup request is the list of links (if any)
corresponding to the type of lookup. Thus, an endpoint lookup MUST corresponding to the type of lookup. Thus, an endpoint lookup MUST
return a list of endpoints and a resource lookup MUST return a list return a list of endpoints and a resource lookup MUST return a list
of links to resources. of links to resources.
The lookup type is selected by a URI endpoint, which is indicated by The lookup type is selected by a URI endpoint, which is indicated by
a Resource Type as per Table 1 below: a Resource Type as per Table 1 below:
skipping to change at page 30, line 9 skipping to change at page 34, line 27
Above rules allow the client to interpret the response as links Above rules allow the client to interpret the response as links
without any further knowledge of the storage conventions of the RD. without any further knowledge of the storage conventions of the RD.
The Resource Directory MAY replace the registration base URIs with a The Resource Directory MAY replace the registration base URIs with a
configured intermediate proxy, e.g. in the case of an HTTP lookup configured intermediate proxy, e.g. in the case of an HTTP lookup
interface for CoAP endpoints. interface for CoAP endpoints.
6.2. Lookup filtering 6.2. Lookup filtering
Using the Accept Option, the requester can control whether the Using the Accept Option, the requester can control whether the
returned list is returned in CoRE Link Format ("application/link- returned list is returned in CoRE Link Format ("application/link-
format", default) or its alternate content-formats ("application/ format", default) or in alternate content-formats (e.g. from
link-format+json" or "application/link-format+cbor"). [I-D.ietf-core-links-json]).
The page and count parameters are used to obtain lookup results in The page and count parameters are used to obtain lookup results in
specified increments using pagination, where count specifies how many specified increments using pagination, where count specifies how many
links to return and page specifies which subset of links organized in links to return and page specifies which subset of links organized in
sequential pages, each containing 'count' links, starting with link sequential pages, each containing 'count' links, starting with link
zero and page zero. Thus, specifying count of 10 and page of 0 will zero and page zero. Thus, specifying count of 10 and page of 0 will
return the first 10 links in the result set (links 0-9). Count = 10 return the first 10 links in the result set (links 0-9). Count = 10
and page = 1 will return the next 'page' containing links 10-19, and and page = 1 will return the next 'page' containing links 10-19, and
so on. so on.
skipping to change at page 31, line 39 skipping to change at page 36, line 10
Page numbering starts with zero. Page numbering starts with zero.
count := Count (optional). Number of results is limited to this count := Count (optional). Number of results is limited to this
parameter value. If the page parameter is also present, the parameter value. If the page parameter is also present, the
response MUST only include 'count' links starting with the response MUST only include 'count' links starting with the
(page * count) link in the result set from the query. If the (page * count) link in the result set from the query. If the
count parameter is not present, then the response MUST return count parameter is not present, then the response MUST return
all matching links in the result set. Link numbering starts all matching links in the result set. Link numbering starts
with zero. with zero.
Content-Format: application/link-format (optional) Accept: absent, application/link-format or any other indicated
media type representing web links
Content-Format: application/link-format+json (optional)
Content-Format: application/link-format+cbor (optional)
The following responses codes are defined for this interface: The following responses codes are defined for this interface:
Success: 2.05 "Content" or 200 "OK" with an "application/link- Success: 2.05 "Content" or 200 "OK" with an "application/link-
format", "application/link-format+cbor", or "application/link- format" or other web link payload containing matching entries for
format+json" payload containing matching entries for the lookup. the lookup. The payload can contain zero links (which is an empty
The payload can contain zero links (which is an empty payload, payload in [RFC6690] link format, but could also be "[]" in JSON
"80" (hex) or "[]" in the respective content format), indicating based formats), indicating that no entities matched the request.
that no entities matched the request.
Failure: No error response to a multicast request. Failure: No error response to a multicast request.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request. request.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation. Service could not perform the operation.
HTTP support: YES HTTP support: YES
The endpoint lookup returns registration resources which can only be
manipulated by the registering endpoint. Examples of endpoint lookup
belong to the management aspects of the RD and are shown in
Appendix A.5. The resource lookup examples are shown in this
section.
6.3. Resource lookup examples 6.3. Resource lookup examples
The examples in this section assume the existence of CoAP hosts with The examples in this section assume the existence of CoAP hosts with
a default CoAP port 61616. HTTP hosts are possible and do not change a default CoAP port 61616. HTTP hosts are possible and do not change
the nature of the examples. the nature of the examples.
The following example shows a client performing a resource lookup The following example shows a client performing a resource lookup
with the example resource look-up locations discovered in Figure 6: with the example resource look-up locations discovered in Figure 5:
Req: GET /rd-lookup/res?rt=temperature Req: GET /rd-lookup/res?rt=temperature
Res: 2.05 Content Res: 2.05 Content
<coap://[2001:db8:3::123]:61616/temp>;rt="temperature"; <coap://[2001:db8:3::123]:61616/temp>;rt="temperature";
anchor="coap://[2001:db8:3::123]:61616" anchor="coap://[2001:db8:3::123]:61616"
The same lookup using the CBOR Link Format media type:
Req: GET /rd-lookup/res?rt=temperature
Accept: TBD64
Res: 2.05 Content
Content-Format: TBD64
Payload in Hex notation:
81A3017823636F61703A2F2F5B323030313A6462383A333A3A3132335D3A363136313
62F74656D7003781E636F61703A2F2F5B323030313A6462383A333A3A3132335D3A36
31363136096B74656D7065726174757265
Decoded payload:
[{1: "coap://[2001:db8:3::123]:61616/temp", 9: "temperature",
3: "coap://[2001:db8:3::123]:61616"}]
A client that wants to be notified of new resources as they show up A client that wants to be notified of new resources as they show up
can use observation: can use observation:
Req: GET /rd-lookup/res?rt=light Req: GET /rd-lookup/res?rt=light
Observe: 0 Observe: 0
Res: 2.05 Content Res: 2.05 Content
Observe: 23 Observe: 23
Payload: empty Payload: empty
skipping to change at page 35, line 28 skipping to change at page 39, line 28
anchor="coap://sensor2.example.com", anchor="coap://sensor2.example.com",
<coap://sensor2.example.com/sensors/temp>;rt="temperature-c"; <coap://sensor2.example.com/sensors/temp>;rt="temperature-c";
if="sensor"; anchor="coap://sensor2.example.com", if="sensor"; anchor="coap://sensor2.example.com",
<coap://sensor2.example.com/sensors/light>;rt="light-lux"; <coap://sensor2.example.com/sensors/light>;rt="light-lux";
if="sensor"; anchor="coap://sensor2.example.com", if="sensor"; anchor="coap://sensor2.example.com",
<http://www.example.com/sensors/t123>;rel="describedby"; <http://www.example.com/sensors/t123>;rel="describedby";
anchor="coap://sensor2.example.com/sensors/temp", anchor="coap://sensor2.example.com/sensors/temp",
<coap://sensor2.example.com/t>;rel="alternate"; <coap://sensor2.example.com/t>;rel="alternate";
anchor="coap://sensor2.example.com/sensors/temp" anchor="coap://sensor2.example.com/sensors/temp"
The following example shows a client performing a lookup of all 6.4. Endpoint lookup
resources of all endpoints (groups) with et=core.rd-group.
Req: GET /rd-lookup/res?et=core.rd-group The endpoint lookup returns registration resources which can only be
manipulated by the registering endpoint.
<coap://[ff35:30:2001:db8::1]/light>;rt="light";if="core.a"; Endpoint registration resources are annotated with their endpoint
et="core.rd-group";anchor="coap://[ff35:30:2001:db8::1]", names (ep), sectors (d, if present) and registration base URI (base;
<coap://[ff35:30:2001:db8::1]/color-temperature>;if="core.p";u="K"; reports the registrant-ep's address if no explicit base was given) as
et="core.rd-group"; well as a constant resource type (rt="core.rd-ep"); the lifetime (lt)
anchor="coap://[ff35:30:2001:db8::1]" is not reported. Additional endpoint attributes are added as target
attributes to their endpoint link unless their specification says
otherwise.
Links to endpoints SHOULD be presented in path-absolute form or, if
required, as absolute references. (This avoids the RFC6690
ambiguities.)
While Endpoint Lookup does expose the registration resources, the RD
does not need to make them accessible to clients. Clients SHOULD NOT
attempt to dereference or manipulate them.
A Resource Directory can report endpoints in lookup that are not
hosted at the same address. Lookup clients MUST be prepared to see
arbitrary URIs as registration resources in the results and treat
them as opaque identifiers; the precise semantics of such links are
left to future specifications.
The following example shows a client performing an endpoint type (et)
lookup with the value oic.d.sensor (which is currently a registered
rt value):
Req: GET /rd-lookup/ep?et=oic.d.sensor
Res: 2.05 Content
</rd/1234>;base="coap://[2001:db8:3::127]:61616";ep="node5";
et="oic.d.sensor";ct="40";rt="core.rd-ep",
</rd/4521>;base="coap://[2001:db8:3::129]:61616";ep="node7";
et="oic.d.sensor";ct="40";d="floor-3";rt="core.rd-ep"
7. Security policies 7. Security policies
The Resource Directory (RD) provides assistance to applications The Resource Directory (RD) provides assistance to applications
situated on a selection of nodes to discover endpoints on connected situated on a selection of nodes to discover endpoints on connected
nodes. This section discusses different security aspects of nodes. This section discusses different security aspects of
accessing the RD. accessing the RD.
The contents of the RD are inserted in two ways: The contents of the RD are inserted in two ways:
skipping to change at page 36, line 31 skipping to change at page 41, line 12
authorized to learn the contents of a given RD. Within a region, for authorized to learn the contents of a given RD. Within a region, for
a given RD, a more fine-grained security division is possible based a given RD, a more fine-grained security division is possible based
on the values of the endpoint registration parameters. Authorization on the values of the endpoint registration parameters. Authorization
to discover endpoints with a given set of filter values is to discover endpoints with a given set of filter values is
recommended for those cases. recommended for those cases.
When a node registers its endpoints, criteria are needed to authorize When a node registers its endpoints, criteria are needed to authorize
the node to enter them. An important aspect is the uniqueness of the the node to enter them. An important aspect is the uniqueness of the
(endpoint name, and optional sector) pair within the RD. Consider (endpoint name, and optional sector) pair within the RD. Consider
the two cases separately: (1) CT registers endpoints, and (2) the the two cases separately: (1) CT registers endpoints, and (2) the
registering node registers its own endpoint(s). * A CT needs registering node registers its own endpoint(s).
authorization to register a set of endpoints. This authorization can
be based on the region, i.e. a given CT is authorized to register any o A CT needs authorization to register a set of endpoints. This
endpoint (endpoint name, sector) into a given RD, or to register an authorization can be based on the region, i.e. a given CT is
endpoint with (endpoint name, sector) value pairs assigned by the AS, authorized to register any endpoint (endpoint name, sector) into a
or can be more fine-grained, including a subset of registration given RD, or to register an endpoint with (endpoint name, sector)
parameter values. * A given endpoint that registers itself, needs to value pairs assigned by the AS, or can be more fine-grained,
proof its possession of its unique (endpoint name, sector) value including a subset of registration parameter values.
pair. Alternatively, the AS can authorize the endpoint to register
with an (endpoint name, sector) value pair assigned by the AS. * A o A given endpoint that registers itself, needs to proof its
separate document needs to specify these aspects to ensure possession of its unique (endpoint name, sector) value pair.
Alternatively, the AS can authorize the endpoint to register with
an (endpoint name, sector) value pair assigned by the AS.
A separate document needs to specify these aspects to ensure
interoperability between registering nodes and RD. The subsections interoperability between registering nodes and RD. The subsections
below give some hints how to handle a subset of the different below give some hints how to handle a subset of the different
aspects. aspects.
7.1. Secure RD discovery 7.1. Secure RD discovery
The Resource Server (RS) discussed in [I-D.ietf-ace-oauth-authz] is The Resource Server (RS) discussed in [I-D.ietf-ace-oauth-authz] is
equated to the RD. The client (C) needs to discover the RD as equated to the RD. The client (C) needs to discover the RD as
discussed in Section 4. C can discover the related AS by sending a discussed in Section 4. C can discover the related AS by sending a
request to the RD. The RD denies the request by sending the address request to the RD. The RD denies the request by sending the address
skipping to change at page 37, line 43 skipping to change at page 42, line 29
checked by encrypting the certificate identifier with the private key checked by encrypting the certificate identifier with the private key
of the registering endpoint, which the RD can decrypt with the public of the registering endpoint, which the RD can decrypt with the public
key stored in the certificate. Even simpler, the authorized key stored in the certificate. Even simpler, the authorized
registering endpoint can generate a random number (or string) that registering endpoint can generate a random number (or string) that
identifies the endpoint. The RD can check for the improbable identifies the endpoint. The RD can check for the improbable
replication of the random value. The RD MUST check that registering replication of the random value. The RD MUST check that registering
endpoint uses only one random value for each authorized endpoint. endpoint uses only one random value for each authorized endpoint.
8. Security Considerations 8. Security Considerations
The security considerations as described in Section 7 of [RFC5988] The security considerations as described in Section 5 of [RFC8288]
and Section 6 of [RFC6690] apply. The "/.well-known/core" resource and Section 6 of [RFC6690] apply. The "/.well-known/core" resource
may be protected e.g. using DTLS when hosted on a CoAP server as may be protected e.g. using DTLS when hosted on a CoAP server as
described in [RFC7252]. DTLS or TLS based security SHOULD be used on described in [RFC7252]. DTLS or TLS based security SHOULD be used on
all resource directory interfaces defined in this document. all resource directory interfaces defined in this document.
8.1. Endpoint Identification and Authentication 8.1. Endpoint Identification and Authentication
An Endpoint (name, sector) pair is unique within the et of endpoints An Endpoint (name, sector) pair is unique within the et of endpoints
regsitered by the RD. An Endpoint MUST NOT be identified by its registered by the RD. An Endpoint MUST NOT be identified by its
protocol, port or IP address as these may change over the lifetime of protocol, port or IP address as these may change over the lifetime of
an Endpoint. an Endpoint.
Every operation performed by an Endpoint on a resource directory Every operation performed by an Endpoint on a resource directory
SHOULD be mutually authenticated using Pre-Shared Key, Raw Public Key SHOULD be mutually authenticated using Pre-Shared Key, Raw Public Key
or Certificate based security. or Certificate based security.
Consider the following threat: two devices A and B are registered at Consider the following threat: two devices A and B are registered at
a single server. Both devices have unique, per-device credentials a single server. Both devices have unique, per-device credentials
for use with DTLS to make sure that only parties with authorization for use with DTLS to make sure that only parties with authorization
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9.3. RD Parameter Registry 9.3. RD Parameter Registry
This specification defines a new sub-registry for registration and This specification defines a new sub-registry for registration and
lookup parameters called "RD Parameters" under "CoRE Parameters". lookup parameters called "RD Parameters" under "CoRE Parameters".
Although this specification defines a basic set of parameters, it is Although this specification defines a basic set of parameters, it is
expected that other standards that make use of this interface will expected that other standards that make use of this interface will
define new ones. define new ones.
Each entry in the registry must include Each entry in the registry must include
o the human readable name of the parameter, o the human readable name of the parameter,
o the short name as used in query parameters or link attributes, o the short name as used in query parameters or target attributes,
o indication of whether it can be passed as a query parameter at o indication of whether it can be passed as a query parameter at
registration of endpoints, as a query parameter in lookups, or be registration of endpoints, as a query parameter in lookups, or be
expressed as a link attribute, expressed as a target attribute,
o validity requirements if any, and o validity requirements if any, and
o a description. o a description.
The query parameter MUST be both a valid URI query key [RFC3986] and The query parameter MUST be both a valid URI query key [RFC3986] and
a parmname as used in [RFC5988]. a token as used in [RFC8288].
The description must give details on whether the parameter can be The description must give details on whether the parameter can be
updated, and how it is to be processed in lookups. updated, and how it is to be processed in lookups.
The mechanisms around new RD parameters should be designed in such a The mechanisms around new RD parameters should be designed in such a
way that they tolerate RD implementations that are unaware of the way that they tolerate RD implementations that are unaware of the
parameter and expose any parameter passed at registration or updates parameter and expose any parameter passed at registration or updates
on in endpoint lookups. (For example, if a parameter used at on in endpoint lookups. (For example, if a parameter used at
registration were to be confidential, the registering endpoint should registration were to be confidential, the registering endpoint should
be instructed to only set that parameter if the RD advertises support be instructed to only set that parameter if the RD advertises support
skipping to change at page 41, line 29 skipping to change at page 45, line 39
| | | | | available | | | | | | available |
| Page | page | Integer | L | Used for pagination | | Page | page | Integer | L | Used for pagination |
| Count | count | Integer | L | Used for pagination | | Count | count | Integer | L | Used for pagination |
| Endpoint | et | | RLA | Semantic name of the | | Endpoint | et | | RLA | Semantic name of the |
| Type | | | | endpoint (see | | Type | | | | endpoint (see |
| | | | | Section 9.4) | | | | | | Section 9.4) |
+--------------+-------+---------------+-----+----------------------+ +--------------+-------+---------------+-----+----------------------+
Table 2: RD Parameters Table 2: RD Parameters
(Short: Short name used in query parameters or link attributes. Use: (Short: Short name used in query parameters or target attributes.
R = used at registration, L = used at lookup, A = expressed in link Use: R = used at registration, L = used at lookup, A = expressed in
attribute target attribute
The descriptions for the options defined in this document are only The descriptions for the options defined in this document are only
summarized here. To which registrations they apply and when they are summarized here. To which registrations they apply and when they are
to be shown is described in the respective sections of this document. to be shown is described in the respective sections of this document.
The IANA policy for future additions to the sub-registry is "Expert The IANA policy for future additions to the sub-registry is "Expert
Review" as described in [RFC8126]. The evaluation should consider Review" as described in [RFC8126]. The evaluation should consider
formal criteria, duplication of functionality (Is the new entry formal criteria, duplication of functionality (Is the new entry
redundant with an existing one?), topical suitability (E.g. is the redundant with an existing one?), topical suitability (E.g. is the
described property actually a property of the endpoint and not a described property actually a property of the endpoint and not a
property of a particular resource, in which case it should go into property of a particular resource, in which case it should go into
the payload of the registration and need not be registered?), and the the payload of the registration and need not be registered?), and the
potential for conflict with commonly used link attributes (For potential for conflict with commonly used target attributes (For
example, "if" could be used as a parameter for conditional example, "if" could be used as a parameter for conditional
registration if it were not to be used in lookup or attributes, but registration if it were not to be used in lookup or attributes, but
would make a bad parameter for lookup, because a resource lookup with would make a bad parameter for lookup, because a resource lookup with
an "if" query parameter could ambiguously filter by the registered an "if" query parameter could ambiguously filter by the registered
endpoint property or the [RFC6690] link attribute). It is expected endpoint property or the [RFC6690] target attribute). It is expected
that the registry will receive between 5 and 50 registrations in that the registry will receive between 5 and 50 registrations in
total over the next years. total over the next years.
9.3.1. Full description of the "Endpoint Type" Registration Parameter 9.3.1. Full description of the "Endpoint Type" Registration Parameter
An endpoint registering at an RD can describe itself with endpoint An endpoint registering at an RD can describe itself with endpoint
types, similar to how resources are described with Resource Types in types, similar to how resources are described with Resource Types in
[RFC6690]. An endpoint type is expressed as a string, which can be [RFC6690]. An endpoint type is expressed as a string, which can be
either a URI or one of the values defined in the Endpoint Type sub- either a URI or one of the values defined in the Endpoint Type sub-
registry. Endpoint types can be passed in the "et" query parameter registry. Endpoint types can be passed in the "et" query parameter
skipping to change at page 42, line 48 skipping to change at page 47, line 10
Section 9.3.1. Section 9.3.1.
o The registered values MUST conform to the ABNF reg-rel-type o The registered values MUST conform to the ABNF reg-rel-type
definition of [RFC6690] and MUST NOT be a URI. definition of [RFC6690] and MUST NOT be a URI.
o It is recommended to use the period "." character for o It is recommended to use the period "." character for
segmentation. segmentation.
The registry initially contains one value: The registry initially contains one value:
o "core.rd-group": An application group as described in o "core.rd-group": An application group as described in Appendix A.
Section 5.3.3.
9.5. Multicast Address Registration 9.5. Multicast Address Registration
IANA has assigned the following multicast addresses for use by CoAP IANA has assigned the following multicast addresses for use by CoAP
nodes: nodes:
IPv4 - "all CoRE resource directories" address, from the "IPv4 IPv4 - "all CoRE resource directories" address, from the "IPv4
Multicast Address Space Registry" equal to "All CoAP Nodes", Multicast Address Space Registry" equal to "All CoAP Nodes",
224.0.1.187. As the address is used for discovery that may span 224.0.1.187. As the address is used for discovery that may span
beyond a single network, it has come from the Internetwork Control beyond a single network, it has come from the Internetwork Control
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10. Examples 10. Examples
Two examples are presented: a Lighting Installation example in Two examples are presented: a Lighting Installation example in
Section 10.1 and a LWM2M example in Section 10.2. Section 10.1 and a LWM2M example in Section 10.2.
10.1. Lighting Installation 10.1. Lighting Installation
This example shows a simplified lighting installation which makes use This example shows a simplified lighting installation which makes use
of the Resource Directory (RD) with a CoAP interface to facilitate of the Resource Directory (RD) with a CoAP interface to facilitate
the installation and start up of the application code in the lights the installation and start-up of the application code in the lights
and sensors. In particular, the example leads to the definition of a and sensors. In particular, the example leads to the definition of a
group and the enabling of the corresponding multicast address as group and the enabling of the corresponding multicast address as
described in Section 5.3.3. No conclusions must be drawn on the described in Appendix A. No conclusions must be drawn on the
realization of actual installation or naming procedures, because the realization of actual installation or naming procedures, because the
example only "emphasizes" some of the issues that may influence the example only "emphasizes" some of the issues that may influence the
use of the RD and does not pretend to be normative. use of the RD and does not pretend to be normative.
10.1.1. Installation Characteristics 10.1.1. Installation Characteristics
The example assumes that the installation is managed. That means The example assumes that the installation is managed. That means
that a Commissioning Tool (CT) is used to authorize the addition of that a Commissioning Tool (CT) is used to authorize the addition of
nodes, name them, and name their services. The CT can be connected nodes, name them, and name their services. The CT can be connected
to the installation in many ways: the CT can be part of the to the installation in many ways: the CT can be part of the
skipping to change at page 47, line 10 skipping to change at page 51, line 17
The luminary, knowing its sector and being configured to join any The luminary, knowing its sector and being configured to join any
group containing lights, searches for candidate groups and joins group containing lights, searches for candidate groups and joins
them: them:
Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep
?d=R2-4-015&et=core.rd-group&rt=light ?d=R2-4-015&et=core.rd-group&rt=light
Res: 2.05 Content Res: 2.05 Content
</rd/501>;ep="grp_R2-4-015";et="core.rd-group"; </rd/501>;ep="grp_R2-4-015";et="core.rd-group";
base="coap://[ff05::1]" base="coap://[ff05::1]";rt="core.rd-ep"
From the returned base parameter value, the luminary learns the From the returned base parameter value, the luminary learns the
multicast address of the multicast group. multicast address of the multicast group.
Alternatively, the CT can communicate the multicast address directly Alternatively, the CT can communicate the multicast address directly
to the luminaries by using the "coap-group" resource specified in to the luminaries by using the "coap-group" resource specified in
[RFC7390]. [RFC7390].
Req: POST coap://[2001:db8:4::1]/coap-group Req: POST coap://[2001:db8:4::1]/coap-group
Content-Format: application/coap-group+json Content-Format: application/coap-group+json
skipping to change at page 50, line 45 skipping to change at page 55, line 4
et - Endpoint Type et - Endpoint Type
base - Registration Base URI base - Registration Base URI
The endpoint registration must include a payload containing links to The endpoint registration must include a payload containing links to
all supported objects and existing object instances, optionally all supported objects and existing object instances, optionally
including the appropriate link-format relations. including the appropriate link-format relations.
Here is an example LWM2M registration payload: Here is an example LWM2M registration payload:
</1>,</1/0>,</3/0>,</5> </1>,</1/0>,</3/0>,</5>
This link format payload indicates that object ID 1 (LWM2M Server This link format payload indicates that object ID 1 (LWM2M Server
Object) is supported, with a single instance 0 existing, object ID 3 Object) is supported, with a single instance 0 existing, object ID 3
(LWM2M Device object) is supported, with a single instance 0 (LWM2M Device object) is supported, with a single instance 0
existing, and object 5 (LWM2M Firmware Object) is supported, with no existing, and object 5 (LWM2M Firmware Object) is supported, with no
existing instances. existing instances.
10.2.3. LWM2M Update Endpoint Registration 10.2.3. LWM2M Update Endpoint Registration
The LwM2M update is really very similar to the registration update as The LwM2M update is really very similar to the registration update as
described in Appendix A.1, with the only difference that there are described in Section 5.4.1, with the only difference that there are
more parameters defined and available. All the parameters listed in more parameters defined and available. All the parameters listed in
that section are also available with the initial registration but are that section are also available with the initial registration but are
all optional: all optional:
lt - Registration Lifetime lt - Registration Lifetime
b - Protocol Binding b - Protocol Binding
sms - MSISDN sms - MSISDN
link payload - new or modified links link payload - new or modified links
A Registration update is also specified to be used to update the A Registration update is also specified to be used to update the
LWM2M server whenever the endpoint's UDP port or IP address are LWM2M server whenever the endpoint's UDP port or IP address are
changed. changed.
10.2.4. LWM2M De-Register Endpoint 10.2.4. LWM2M De-Register Endpoint
LWM2M allows for de-registration using the delete method on the LWM2M allows for de-registration using the delete method on the
returned location from the initial registration operation. LWM2M de- returned location from the initial registration operation. LWM2M de-
registration proceeds as described in Appendix A.2. registration proceeds as described in Section 5.4.2.
11. Acknowledgments 11. Acknowledgments
Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders
Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen, Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen,
Hannes Tschofenig, Sampo Ukkola, Linyi Tian, and Jan Newmarch have Hannes Tschofenig, Sampo Ukkola, Linyi Tian, and Jan Newmarch have
provided helpful comments, discussions and ideas to improve and shape provided helpful comments, discussions and ideas to improve and shape
this document. Zach would also like to thank his colleagues from the this document. Zach would also like to thank his colleagues from the
EU FP7 SENSEI project, where many of the resource directory concepts EU FP7 SENSEI project, where many of the resource directory concepts
were originally developed. were originally developed.
12. Changelog 12. Changelog
changes from -17 to -18
o Rather than re-specifying link format (Modernized Link Format),
describe a Limited Link Format that's the uncontested subset of
Link Format
o Acknowledging the -17 version as part of the draft
o Move "Read endpoint links" operation to future specification like
PATCH
o Demote links-json to an informative reference, and removed them
from exchange examples
o Add note on unusability of link-local IP addresses, and describe
mitigation.
o Reshuffling of sections: Move additional operations and endpoint
lookup back from appendix, and groups into one
o Lookup interface tightened to not imply applicability for non
link-format lookups (as those can have vastly different views on
link cardinality)
o Simple registration: Change sequence of GET and POST-response,
ensuring unsuccessful registrations are reported as such, and
suggest how devices that would have required the inverse behavior
can still cope with it.
o Abstract and introduction reworded to avoid the impression that
resources are stored in full in the RD
o Simplify the rules governing when a registration resource can or
must be changed.
o Drop a figure that has become useless due to the changes of and
-13 and -17
o Wording consistency fixes: Use "Registrations" and "target
attributes"
o Fix incorrect use of content negotiation in discovery interface
description (Content-Format -> Accept)
o State that the base attribute value is part of endpoint lookup
even when implicit in the registration
o Update references from RFC5988 to its update RFC8288
o Remove appendix on protocol-negotiation (which had a note to be
removed before publication)
changes from -16 to -17 changes from -16 to -17
(Note that -17 is published as a direct follow-up to -16, containing (Note that -17 is published as a direct follow-up to -16, containing
a single change to be discussed at IETF103) a single change to be discussed at IETF103)
o Removed groups that are enumerations of registrations and have o Removed groups that are enumerations of registrations and have
dedicated mechanism dedicated mechanism
o Add groups that are enumerations of shared resources and are a o Add groups that are enumerations of shared resources and are a
special case of endpoint registrations special case of endpoint registrations
changes from -15 to -16 changes from -15 to -16
o Recommend a common set of resources for members of a group o Recommend a common set of resources for members of a group
o Clarified use of multicast group in lighting example o Clarified use of multicast group in lighting example
o Add note on concurrent registrations from one EP being possible o Add note on concurrent registrations from one EP being possible
but not expected but not expected
o Refresh web examples appendix to reflect current use of Modernized o Refresh web examples appendix to reflect current use of Modernized
Link Format Link Format
skipping to change at page 58, line 39 skipping to change at page 63, line 49
stable, allowing for endpoint and Domain information to be changed stable, allowing for endpoint and Domain information to be changed
during updates. during updates.
o Changed the lookup interface to accept endpoint and Domain as o Changed the lookup interface to accept endpoint and Domain as
query string parameters to control the scope of a lookup. query string parameters to control the scope of a lookup.
13. References 13. References
13.1. Normative References 13.1. Normative References
[I-D.ietf-core-links-json]
Li, K., Rahman, A., and C. Bormann, "Representing
Constrained RESTful Environments (CoRE) Link Format in
JSON and CBOR", draft-ietf-core-links-json-10 (work in
progress), February 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<https://www.rfc-editor.org/info/rfc5988>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570, and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012, DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>. <https://www.rfc-editor.org/info/rfc6570>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>. <https://www.rfc-editor.org/info/rfc6690>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
skipping to change at page 60, line 5 skipping to change at page 64, line 45
[I-D.arkko-core-dev-urn] [I-D.arkko-core-dev-urn]
Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource
Names for Device Identifiers", draft-arkko-core-dev-urn-05 Names for Device Identifiers", draft-arkko-core-dev-urn-05
(work in progress), October 2017. (work in progress), October 2017.
[I-D.bormann-t2trg-rel-impl] [I-D.bormann-t2trg-rel-impl]
Bormann, C., "impl-info: A link relation type for Bormann, C., "impl-info: A link relation type for
disclosing implementation information", draft-bormann- disclosing implementation information", draft-bormann-
t2trg-rel-impl-00 (work in progress), January 2018. t2trg-rel-impl-00 (work in progress), January 2018.
[I-D.hartke-t2trg-coral]
Hartke, K., "The Constrained RESTful Application Language
(CoRAL)", draft-hartke-t2trg-coral-06 (work in progress),
October 2018.
[I-D.ietf-ace-oauth-authz] [I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0 Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16 Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-17
(work in progress), October 2018. (work in progress), November 2018.
[I-D.ietf-anima-bootstrapping-keyinfra] [I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason, Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-16 (work in progress), June 2018. keyinfra-17 (work in progress), November 2018.
[I-D.ietf-core-links-json]
Li, K., Rahman, A., and C. Bormann, "Representing
Constrained RESTful Environments (CoRE) Link Format in
JSON and CBOR", draft-ietf-core-links-json-10 (work in
progress), February 2018.
[I-D.silverajan-core-coap-protocol-negotiation] [I-D.silverajan-core-coap-protocol-negotiation]
Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation", Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation",
draft-silverajan-core-coap-protocol-negotiation-09 (work draft-silverajan-core-coap-protocol-negotiation-09 (work
in progress), July 2018. in progress), July 2018.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616,
DOI 10.17487/RFC2616, June 1999,
<https://www.rfc-editor.org/info/rfc2616>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)", Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012, RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>. <https://www.rfc-editor.org/info/rfc6775>.
[RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing
IPv6 Zone Identifiers in Address Literals and Uniform
Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874,
February 2013, <https://www.rfc-editor.org/info/rfc6874>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>. <https://www.rfc-editor.org/info/rfc7230>.
[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>.
skipping to change at page 61, line 23 skipping to change at page 66, line 28
<https://www.rfc-editor.org/info/rfc8132>. <https://www.rfc-editor.org/info/rfc8132>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>. May 2018, <https://www.rfc-editor.org/info/rfc8392>.
Appendix A. Registration Management Appendix A. Groups Registration and Lookup
This section describes how the registering endpoint can maintain the
registries that it created. The registering endpoint can be the
registrant-ep or the CT. An endpoint SHOULD NOT use this interface
for registries that it did not create. The registries are resources
of the RD.
After the initial registration, the registering endpoint retains the
returned location of the Registration Resource for further
operations, including refreshing the registration in order to extend
the lifetime and "keep-alive" the registration. When the lifetime of
the registration has expired, the RD SHOULD NOT respond to discovery
queries concerning this endpoint. The RD SHOULD continue to provide
access to the Registration Resource after a registration time-out
occurs in order to enable the registering endpoint to eventually
refresh the registration. The RD MAY eventually remove the
registration resource for the purpose of garbage collection. If the
Registration Resource is removed, the corresponding endpoint will
need to be re-registered.
The Registration Resource may also be used to inspect the
registration resource using GET, update the registration, cancel the
registration using DELETE, or do an endpoint lookup.
These operations are described below.
A.1. Registration Update
The update interface is used by the registering endpoint to refresh
or update its registration with an RD. To use the interface, the
registering endpoint sends a POST request to the registration
resource returned by the initial registration operation.
An update MAY update the lifetime- or the context- registration
parameters "lt", "base" as in Section 5.3. Parameters that are not
being changed SHOULD NOT be included in an update. Adding parameters
that have not changed increases the size of the message but does not
have any other implications. Parameters MUST be included as query
parameters in an update operation as in Section 5.3.
A registration update resets the timeout of the registration to the
(possibly updated) lifetime of the registration, independent of
whether a "lt" parameter was given.
If the context of the registration is changed in an update, relative
references submitted in the original registration or later updates
are resolved anew against the new context.
The registration update operation only describes the use of POST with
an empty payload. Future standards might describe the semantics of
using content formats and payloads with the POST method to update the
links of a registration (see Appendix A.4).
The update registration request interface is specified as follows:
Interaction: EP -> RD
Method: POST
URI Template: {+location}{?lt,con,extra-attrs*}
URI Template Variables:
location := This is the Location returned by the RD as a result
of a successful earlier registration.
lt := Lifetime (optional). Lifetime of the registration in
seconds. Range of 60-4294967295. If no lifetime is included,
the previous last lifetime set on a previous update or the
original registration (falling back to 90000) SHOULD be used.
base := Base URI (optional). This parameter updates the Base URI
established in the original registration to a new value. If
the parameter is set in an update, it is stored by the RD as
the new Base URI under which to interpret the relative links
present in the payload of the original registration, following
the same restrictions as in the registration. If the parameter
is not set in the request but was set before, the previous Base
URI value is kept unmodified. If the parameter is not set in
the request and was not set before either, the source address
and source port of the update request are stored as the Base
URI.
extra-attrs := Additional registration attributes (optional). As
with the registration, the RD processes them if it knows their
semantics. Otherwise, unknown attributes are stored as
endpoint attributes, overriding any previously stored endpoint
attributes of the same key.
Content-Format: none (no payload)
The following response codes are defined for this interface:
Success: 2.04 "Changed" or 204 "No Content" if the update was
successfully processed.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have expired).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
If the registration update fails with a "Service Unavailable"
response and a Max-Age option or Retry-After header, the registering
endpoint SHOULD retry the operation after the time indicated. If the
registration fails in another way, including request timeouts, or if
the time indicated exceeds the remaining lifetime, the registering
endpoint SHOULD attempt registration again.
The following example shows how the registering endpoint updates its
registration resource at an RD using this interface with the example
location value: /rd/4521.
Req: POST /rd/4521
Res: 2.04 Changed
The following example shows the registering endpoint updating its
registration resource at an RD using this interface with the example
location value: /rd/4521. The initial registration by the
registering endpoint set the following values:
o endpoint name (ep)=endpoint1
o lifetime (lt)=500 The RD-Groups usage pattern allows announcing application groups
inside a Resource Directory.
o Base URI (base)=coap://local-proxy-old.example.com:5683 Groups are represented by endpoint registrations. Their base address
is a multicast address, and they SHOULD be entered with the endpoint
type "core.rd-group". The endpoint name can also be referred to as a
group name in this context.
o payload of Figure 7 The registration is inserted into the RD by a Commissioning Tool,
which might also be known as a group manager here. It performs third
party registration and registration updates.
The initial state of the Resource Directory is reflected in the The links it registers SHOULD be available on all members that join
following request: the group. Depending on the application, members that lack some
resource MAY be permissible if requests to them fail gracefully.
Req: GET /rd-lookup/res?ep=endpoint1 The following example shows a CT registering a group with the name
"lights" which provides two resources. The directory resource path
/rd is an example RD location discovered in a request similar to
Figure 5.
Res: 2.01 Content Req: POST coap://rd.example.com/rd?ep=lights&et=core.rd-group
&base=coap://[ff35:30:2001:db8::1]
Content-Format: 40
Payload: Payload:
<coap://local-proxy-old.example.com:5683/sensors/temp>;ct=41; </light>;rt="light";if="core.a",
rt="temperature"; anchor="coap://spurious.example.com:5683", </color-temperature>;if="core.p";u="K"
<coap://local-proxy-old.example.com:5683/sensors/light>;ct=41;
rt="light-lux"; if="sensor";
anchor="coap://local-proxy-old.example.com:5683"
The following example shows the registering endpoint changing the
Base URI to "coaps://new.example.com:5684":
Req: POST /rd/4521?base=coaps://new.example.com:5684
Res: 2.04 Changed
The consecutive query returns: Res: 2.01 Created
Location-Path: /rd/12
Req: GET /rd-lookup/res?ep=endpoint1 In this example, the group manager can easily permit devices that
have no writable color-temperature to join, as they would still
respond to brightness changing commands. Had the group instead
contained a single resource that sets brightness and color
temperature atomically, endpoints would need to support both
properties.
Res: 2.01 Content The resources of a group can be looked up like any other resource,
Payload: and the group registrations (along with any additional registration
<coaps://new.example.com:5684/sensors/temp>;ct=41;rt="temperature"; parameters) can be looked up using the endpoint lookup interface.
anchor="coap://spurious.example.com:5683",
<coaps://new.example.com:5684/sensors/light>;ct=41;rt="light-lux";
if="sensor"; anchor="coaps://new.example.com:5684",
The following example shows a client performing and enpoint lookup The following example shows a client performing and endpoint lookup
for all groups. for all groups.
Req: GET /rd-lookup/ep?et=core.rd-group Req: GET /rd-lookup/ep?et=core.rd-group
Res: 2.01 Content Res: 2.01 Content
Payload: Payload:
</rd/501>;ep="GRP_R2-4-015";et="core.rd-group"; </rd/501>;ep="GRP_R2-4-015";et="core.rd-group";
base="coap://[ff05:;1]", base="coap://[ff05::1]",
<rd/12>;ep=lights&et=core.rd-group; </rd/12>;ep=lights&et=core.rd-group;
base="coap://[ff35:30:2001:db8::1]" base="coap://[ff35:30:2001:db8::1]";rt="core.rd-ep"
A.2. Registration Removal
Although RD entries have soft state and will eventually timeout after
their lifetime, the registering endpoint SHOULD explicitly remove an
entry from the RD if it knows it will no longer be available (for
example on shut-down). This is accomplished using a removal
interface on the RD by performing a DELETE on the endpoint resource.
The removal request interface is specified as follows:
Interaction: EP -> RD
Method: DELETE
URI Template: {+location}
URI Template Variables:
location := This is the Location returned by the RD as a result
of a successful earlier registration.
The following response codes are defined for this interface:
Success: 2.02 "Deleted" or 204 "No Content" upon successful deletion
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have expired).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following examples shows successful removal of the endpoint from
the RD with example location value /rd/4521.
Req: DELETE /rd/4521
Res: 2.02 Deleted
A.3. Read Endpoint Links
Some registering endpoints may wish to manage their links as a
collection, and may need to read the current set of links stored in
the registration resource, in order to determine link maintenance
operations.
One or more links MAY be selected by using query filtering as
specified in [RFC6690] Section 4.1
If no links are selected, the Resource Directory SHOULD return an
empty payload.
The read request interface is specified as follows:
Interaction: EP -> RD
Method: GET
URI Template: {+location}{?href,rel,rt,if,ct}
URI Template Variables:
location := This is the Location returned by the RD as a result
of a successful earlier registration.
href,rel,rt,if,ct := link relations and attributes specified in
the query in order to select particular links based on their
relations and attributes. "href" denotes the URI target of the
link. See [RFC6690] Sec. 4.1
The following response codes are defined for this interface:
Success: 2.05 "Content" or 200 "OK" upon success with an
"application/link-format", "application/link-format+cbor", or
"application/link-format+json" payload.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have expired).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following examples show successful read of the endpoint links
from the RD, with example location value /rd/4521 and example
registration payload of Figure 7.
Req: GET /rd/4521
Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor";
anchor="coap://spurious.example.com:5683",
</sensors/light>;ct=41;rt="light-lux";if="sensor"
A.4. Update Endpoint Links
An iPATCH (or PATCH) update ([RFC8132]) can add, remove or change the
links of a registration.
Those operations are out of scope of this document, and will require
media types suitable for modifying sets of links.
A.5. Endpoint lookup
Endpoint lookups result in links to registration resources. Endpoint
registration resources are annotated with their endpoint names (ep),
sectors (d, if present) and registration base URI (base) as well as a
constant resource type (rt="core.rd-ep"); the lifetime (lt) is not
reported. Additional endpoint attributes are added as link
attributes to their endpoint link unless their specification says
otherwise.
Serializations derived from Link Format, SHOULD present links to
endpoints in path-absolute form or, if required, as absolute
references. (This approach avoids the RFC6690 ambiguities.)
While Endpoint Lookup does expose the registration resources, the RD
does not need to make them accessible to clients. Clients SHOULD NOT
attempt to dereference or manipulate them.
A Resource Directory can report endpoints in lookup that are not
hosted at the same address. Lookup clients MUST be prepared to see
arbitrary URIs as registration resources in the results and treat
them as opaque identifiers; the precise semantics of such links are
left to future specifications.
The following example shows a client performing an endpoint type (et) The following example shows a client performing a lookup of all
lookup with the value oic.d.sensor (which is currently a registered resources of all endpoints (groups) with et=core.rd-group.
rt value):
Req: GET /rd-lookup/ep?et=oic.d.sensor Req: GET /rd-lookup/res?et=core.rd-group
Res: 2.05 Content <coap://[ff35:30:2001:db8::1]/light>;rt="light";if="core.a";
</rd/1234>;base="coap://[2001:db8:3::127]:61616";ep="node5"; et="core.rd-group";anchor="coap://[ff35:30:2001:db8::1]",
et="oic.d.sensor";ct="40", <coap://[ff35:30:2001:db8::1]/color-temperature>;if="core.p";u="K";
</rd/4521>;base="coap://[2001:db8:3::129]:61616";ep="node7"; et="core.rd-group";
et="oic.d.sensor";ct="40";d="floor-3" anchor="coap://[ff35:30:2001:db8::1]"
Appendix B. Web links and the Resource Directory Appendix B. Web links and the Resource Directory
Understanding the semantics of a link-format document and its URI Understanding the semantics of a link-format document and its URI
references is a journey through different documents ([RFC3986] references is a journey through different documents ([RFC3986]
defining URIs, [RFC6690] defining link-format documents based on defining URIs, [RFC6690] defining link-format documents based on
[RFC8288] which defines link headers, and [RFC7252] providing the [RFC8288] which defines link headers, and [RFC7252] providing the
transport). This appendix summarizes the mechanisms and semantics at transport). This appendix summarizes the mechanisms and semantics at
play from an entry in ".well-known/core" to a resource lookup. play from an entry in ".well-known/core" to a resource lookup.
This text is primarily aimed at people entering the field of This text is primarily aimed at people entering the field of
Constrained Restful Environments from applications that previously Constrained Restful Environments from applications that previously
did not use web mechanisms. did not use web mechanisms.
At all examples in this section give compatible results for both The explanation of the steps makes some shortcuts in the more
Modernized and RFC6690 Link Format; the explanation of the steps confusing details of [RFC6690], which are justified as all examples
follow Modernized Link Format. being in Limited Link Format.
B.1. A simple example B.1. A simple example
Let's start this example with a very simple host, "2001:db8:f0::1". Let's start this example with a very simple host, "2001:db8:f0::1".
A client that follows classical CoAP Discovery ([RFC7252] Section 7), A client that follows classical CoAP Discovery ([RFC7252] Section 7),
sends the following multicast request to learn about neighbours sends the following multicast request to learn about neighbours
supporting resources with resource-type "temperature". supporting resources with resource-type "temperature".
The client sends a link-local multicast: The client sends a link-local multicast:
skipping to change at page 69, line 33 skipping to change at page 69, line 22
B.1.2. Interpreting attributes and relations B.1.2. Interpreting attributes and relations
Some more information but the record's target can be obtained from Some more information but the record's target can be obtained from
the payload: the resource type of the target is "temperature", and the payload: the resource type of the target is "temperature", and
its content type is text/plain (ct=0). its content type is text/plain (ct=0).
A relation in a web link is a three-part statement that specifies a A relation in a web link is a three-part statement that specifies a
named relation between the so-called "context resource" and the named relation between the so-called "context resource" and the
target resource, like "_This page_ has _its table of contents_ at _/ target resource, like "_This page_ has _its table of contents_ at _/
toc.html_". In [RFC6690] and modernized link-format documents, there toc.html_". In link format documents, there is an implicit "host
is an implicit "host relation" specified with default parameter: relation" specified with default parameter: rel="hosts".
rel="hosts".
In our example, the context resource of the link is the URI specified In our example, the context resource of the link is the URI specified
in the GET request "coap:://[2001:db8:f0::1]/.well-known/core". A in the GET request "coap:://[2001:db8:f0::1]/.well-known/core". A
full English expression of the "host relation" is: full English expression of the "host relation" is:
'"coap://[2001:db8:f0::1]/.well-known/core" is hosting the resource '"coap://[2001:db8:f0::1]/.well-known/core" is hosting the resource
"coap://[2001:db8:f0::1]/temp", which is of the resource type "coap://[2001:db8:f0::1]/temp", which is of the resource type
"temperature" and can be accessed using the text/plain content "temperature" and can be accessed using the text/plain content
format.' format.'
skipping to change at page 71, line 18 skipping to change at page 71, line 4
<coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0; <coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0;
anchor="coap://[2001:db8:f0::1]" anchor="coap://[2001:db8:f0::1]"
This is not _literally_ the same response that it would have received This is not _literally_ the same response that it would have received
from a multicast request, but it contains the equivalent statement: from a multicast request, but it contains the equivalent statement:
'"coap://[2001:db8:f0::1]" is hosting the resource '"coap://[2001:db8:f0::1]" is hosting the resource
"coap://[2001:db8:f0::1]/temp", which is of the resource type "coap://[2001:db8:f0::1]/temp", which is of the resource type
"temperature" and can be accessed using the text/plain content "temperature" and can be accessed using the text/plain content
format.' format.'
(The difference is whether "/" or "/.well-known/core" hosts the (The difference is whether "/" or "/.well-known/core" hosts the
resources, which is one of the often misunderstood subtleties resources, which does not matter in this application; if it did, the
Modernized Link Format addresses. Actually, /.well-known/core does endpoint would have been more explicit. Actually, /.well-known/core
NOT host the resource but stores a URI reference to the resource.) does NOT host the resource but stores a URI reference to the
resource.)
To complete the examples, the client could also query all resources To complete the examples, the client could also query all resources
hosted at the endpoint with the known endpoint name "simple-host1". hosted at the endpoint with the known endpoint name "simple-host1".
A request to "coap://[2001:db8:f0::ff]/rd-lookup/res?ep=simple-host1" A request to "coap://[2001:db8:f0::ff]/rd-lookup/res?ep=simple-host1"
would return would return
<coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0; <coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0;
anchor="coap://[2001:db8:f0::1]", anchor="coap://[2001:db8:f0::1]",
<coap://[2001:db8:f0::1]/light>;rt=light-lux;ct=0; <coap://[2001:db8:f0::1]/light>;rt=light-lux;ct=0;
anchor="coap://[2001:db8:f0::1]", anchor="coap://[2001:db8:f0::1]",
skipping to change at page 72, line 9 skipping to change at page 71, line 41
<coap+tcp://simple-host1.example.com/temp>;rt=temperature;ct=0; <coap+tcp://simple-host1.example.com/temp>;rt=temperature;ct=0;
anchor="coap+tcp://simple-host1.example.com" anchor="coap+tcp://simple-host1.example.com"
and analogous records. and analogous records.
B.4. A note on differences between link-format and Link headers B.4. A note on differences between link-format and Link headers
While link-format and Link headers look very similar and are based on While link-format and Link headers look very similar and are based on
the same model of typed links, there are some differences between the same model of typed links, there are some differences between
[RFC6690] and [RFC5988], which are dealt with differently: [RFC6690] and [RFC8288], which are dealt with differently:
o "Resolving the target against the anchor": [RFC6690] Section 2.1 o "Resolving the target against the anchor": [RFC6690] Section 2.1
states that the anchor of a link is used as the Base URI against states that the anchor of a link is used as the Base URI against
which the term inside the angle brackets (the target) is resolved, which the term inside the angle brackets (the target) is resolved,
falling back to the resource's URI with paths stripped off (its falling back to the resource's URI with paths stripped off (its
"Origin"). In contrast to that, [RFC8288] Section B.2 describes "Origin"). In contrast to that, [RFC8288] Section B.2 describes
that the anchor is immaterial to the resolution of the target that the anchor is immaterial to the resolution of the target
reference. reference.
RFC6690, in the same section, also states that absent anchors set RFC6690, in the same section, also states that absent anchors set
the context of the link to the target's URI with its path stripped the context of the link to the target's URI with its path stripped
off, while according to [RFC8288] Section 3.2, the context is the off, while according to [RFC8288] Section 3.2, the context is the
resource's base URI. resource's base URI.
In the context of a Resource Directory, the authors decided to not The rules introduced in Appendix C ensure that an RD does not need
let this become an issue by recommending that links in the to deal with those differences when processing input data. Lookup
Resource Directory be _deserializable_ by either rule set to give results are required to be absolute references for the same
the same results. Note that all examples of [RFC6690], [RFC8288] reason.
and this document comply with that rule.
The Modernized Link Format is introduced in Appendix D to
formalize what it means to apply the ruleset of RFC8288 to Link
Format documents.
o There is no percent encoding in link-format documents. o There is no percent encoding in link-format documents.
A link-format document is a UTF-8 encoded string of Unicode A link-format document is a UTF-8 encoded string of Unicode
characters and does not have percent encoding, while Link headers characters and does not have percent encoding, while Link headers
are practically ASCII strings that use percent encoding for non- are practically ASCII strings that use percent encoding for non-
ASCII characters, stating the encoding explicitly when required. ASCII characters, stating the encoding explicitly when required.
For example, while a Link header in a page about a Swedish city For example, while a Link header in a page about a Swedish city
might read might read
skipping to change at page 73, line 5 skipping to change at page 72, line 35
"Link: </temperature/Malm%C3%B6>;rel="live-environment-data"" "Link: </temperature/Malm%C3%B6>;rel="live-environment-data""
a link-format document from the same source might describe the a link-format document from the same source might describe the
link as link as
"</temperature/Malmoe>;rel="live-environment-data"" "</temperature/Malmoe>;rel="live-environment-data""
Parsers and producers of link-format and header data need to be Parsers and producers of link-format and header data need to be
aware of this difference. aware of this difference.
Appendix C. Syntax examples for Protocol Negotiation Appendix C. Limited Link Format
[ This appendix should not show up in a published version of this
document. ]
The protocol negotiation that is being worked on in
[I-D.silverajan-core-coap-protocol-negotiation] makes use of the
Resource Directory.
Until that document is update to use the latest resource-directory
specification, here are some examples of protocol negotiation with
the current Resource Directory:
An endpoint could register as follows from its address
[2001:db8:f1::2]:5683:
Req: POST coap://rd.example.com/rd?ep=node1
&at=coap+tcp://[2001:db8:f1::2]
Content-Format: 40
Payload:
</temperature>;ct=0;rt="temperature";if="core.s"
Res: 2.01 Created
Location-Path: /rd/1234
An endpoint lookup would just reflect the registered attributes:
Req: GET /rd-lookup/ep
Res: 2.05 Content
</rd/1234>;ep="node1";base="coap://[2001:db8:f1::2]:5683";
at="coap+tcp://[2001:db8:f1::2]"
A UDP client would then see the following in a resource lookup:
Req: GET /rd-lookup/res?rt=temperature
Res: 2.05 Content
<coap://[2001:db8:f1::2]/temperature>;ct=0;rt="temperature";
if="core.s"; anchor="coap://[2001:db8:f1::2]"
while a TCP capable client could say:
Req: GET /rd-lookup/res?rt=temperature&tt=tcp
Res: 2.05 Content
<coap+tcp://[2001:db8:f1::2]/temperature>;ct=0;rt="temperature";
if="core.s";anchor="coap+tcp://[2001:db8:f1::2]"
Appendix D. Modernized Link Format parsing
The CoRE Link Format as described in [RFC6690] is unsuitable for some
use cases of the Resource Directory, and their resolution scheme is
often misunderstood by developers familiar with [RFC8288].
For the correct application of base URIs, we describe the
interpretation of a Link Format document as a Modernized Link Format.
In Modernized Link Format, the document is processed as in Link
Format, with the exception of Section 2.1 of [RFC6690]:
o The URI-reference inside angle brackets ("<>") describes the
target URI of the link.
o The context of the link is expressed by the "anchor" parameter.
If the anchor attribute is absent, it defaults to the empty
reference ("").
o Both these references are resolved according to Section 5 of
[RFC3986].
Content formats derived from [RFC6690] which inherit its resolution
rules, like JSON and CBOR link format of [I-D.ietf-core-links-json],
can be interpreted in analogy to that.
For where the Resource Directory is concerned, all common forms of
links (e.g. all the examples of RFC6690) yield identical results.
When interpreting data read from ".well-known/core", differences in
interpretation only affect links where the absent anchor attribute
means "coap://host/" according to RFC6690 and "coap://host/.well-
known/core" according to Modernized Link format; those typically only
occur in conjunction with the vaguely defined implicit "hosts"
relationship.
D.1. For endpoint developers
When developing endpoints, i.e. when generating documents that will
be submitted to a Resource Directory, the differences between
Modernized Link Format and RFC6690 can be ignored as long as
o all relative references start with a slash,
and any of the following applies:
o There is no anchor attribute, and the context of the link does not
matter to the application.
Example: "</sensors>;ct=40"
o The anchor is a relative reference.
Example: "</t>;anchor="/sensors/temp";rel="alternate""
o The target is an absolute reference.
Example: "<http://www.example.com/sensors/t123>;anchor="/sensors/
temp";rel="describedby""
D.2. Examples of links with differing interpretations
Examples of links with different interpretations from either applying The CoRE Link Format as described in [RFC6690] has been interpreted
RFC6690 or Modernized Link Format are shown here. The example is differently by implementers, and a strict implementation rules out
assumed to be obtained from a </device/index> document. some use cases of a Resource Directory (e.g. base values with path
components).
o "<sensors>": The target is "/sensors" in RFC6690 and "/device/ This appendix describes a subset of link format documents called
sensors" in Modernized Link Format (whereas "</sensors>" would be Limited Link Format. The rules herein are not very limiting in
unambiguous). practice - all examples in RFC6690, and all deployments the authors
are aware of already stick to them - but ease the implementation of
resource directory servers.
o "<?which=these>": The target is "/?which=these" in RFC6690 and It is applicable to representations in the application/link-format
"/device/index?which=these" in Modernized Link Format. media type, and any other media types that inherit [RFC6690]
Section 2.1.
o "<sensors>;anchor="http://example.com/calib- A link format representation is in Limited Link format if, for each
proto/1234";rel="topic"" is about "http://example.com/sensors" in link in it, the following applies:
RFC6690 and about "/device/sensors" in Modernized Link Format.
This link can not be expressed in RFC6690 link format without the o All URI references either follow the URI or the path-absolute ABNF
server explicitly expressing most of its own URI (which is rule of RFC3986 (i.e. target and anchor each either start with a
problematic in reverse proxy scenarios or when the Uri-Host option scheme or with a single slash),
is not sent).
o "</i>;rel="alternate";anchor=""": According to RFC6690, this o if the anchor reference starts with a scheme, the target reference
states that the "/" resource has an alternative representation at starts with a scheme as well (i.e. relative references in target
"/i", whereas Modernized Link Format says that "/devices/index" cannot be used when the anchor is a full URI), and
has an alternative representation at "/i".
The "anchor" attribute is usually left out; the link o the application does not care whether links without an explicitly
"</i>;rel="alternate"" is equivalent to the above and results in given anchor have the origin's "/" or "/.well-known/core" resource
the same interpretations. as their link context.
Authors' Addresses Authors' Addresses
Zach Shelby Zach Shelby
ARM ARM
150 Rose Orchard 150 Rose Orchard
San Jose 95134 San Jose 95134
USA USA
Phone: +1-408-203-9434 Phone: +1-408-203-9434
Email: zach.shelby@arm.com Email: zach.shelby@arm.com
Michael Koster Michael Koster
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