CoRE Resource Directory
draft-ietf-core-resource-directory-14
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9176.
|
|
|---|---|---|---|
| Authors | Zach Shelby , Michael Koster , Carsten Bormann , Peter Van der Stok , Christian Amsüss | ||
| Last updated | 2018-07-02 | ||
| Replaces | draft-shelby-core-resource-directory | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Telechat review
(of
-25)
by Russ Housley
Almost ready
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Jaime Jimenez | ||
| IESG | IESG state | Became RFC 9176 (Proposed Standard) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Alexey Melnikov | ||
| Send notices to | "Jaime Jimenez" <jaime.jimenez@ericsson.com> |
draft-ietf-core-resource-directory-14
CoRE Z. Shelby
Internet-Draft ARM
Intended status: Standards Track M. Koster
Expires: January 3, 2019 SmartThings
C. Bormann
Universitaet Bremen TZI
P. van der Stok
consultant
C. Amsuess, Ed.
July 02, 2018
CoRE Resource Directory
draft-ietf-core-resource-directory-14
Abstract
In many M2M applications, direct discovery of resources is not
practical due to sleeping nodes, disperse networks, or networks where
multicast traffic is inefficient. These problems can be solved by
employing an entity called a Resource Directory (RD), which hosts
descriptions of resources held on other servers, allowing lookups to
be performed for those resources. This document specifies the web
interfaces that a Resource Directory supports in order for web
servers to discover the RD and to register, maintain, lookup and
remove resource descriptions. Furthermore, new link attributes
useful in conjunction with an RD are defined.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 3, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 7
3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7
3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 9
3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 13
3.5. Use Case: Home and Building Automation . . . . . . . . . 14
3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 14
4. Finding a Resource Directory . . . . . . . . . . . . . . . . 15
4.1. Resource Directory Address Option (RDAO) . . . . . . . . 17
5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 18
5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 19
5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 19
5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 22
5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 27
5.3.2. Third-party registration . . . . . . . . . . . . . . 29
6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 30
6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 32
7. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 33
7.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 33
7.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 34
7.3. Resource lookup examples . . . . . . . . . . . . . . . . 36
8. Security Considerations . . . . . . . . . . . . . . . . . . . 39
8.1. Endpoint Identification and Authentication . . . . . . . 39
8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 40
8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 40
9. Authorization Server example . . . . . . . . . . . . . . . . 40
9.1. Registree-ep registers with RD . . . . . . . . . . . . . 42
9.2. Third party Commissioning Tool (CT) registers registree-
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ep with RD. . . . . . . . . . . . . . . . . . . . . . . . 42
9.3. Updating multiple links . . . . . . . . . . . . . . . . . 43
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
10.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 43
10.2. IPv6 ND Resource Directory Address Option . . . . . . . 44
10.3. RD Parameter Registry . . . . . . . . . . . . . . . . . 44
10.3.1. Full description of the "Endpoint Type" Registration
Parameter . . . . . . . . . . . . . . . . . . . . . 46
10.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . 46
10.5. Multicast Address Registration . . . . . . . . . . . . . 47
10.6. CBOR Web Token claims . . . . . . . . . . . . . . . . . 47
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 48
11.1. Lighting Installation . . . . . . . . . . . . . . . . . 48
11.1.1. Installation Characteristics . . . . . . . . . . . . 49
11.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 50
11.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 52
11.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 53
11.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 54
11.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 56
11.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 56
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 56
13. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 56
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 62
14.1. Normative References . . . . . . . . . . . . . . . . . . 63
14.2. Informative References . . . . . . . . . . . . . . . . . 63
Appendix A. Registration Management . . . . . . . . . . . . . . 65
A.1. Registration Update . . . . . . . . . . . . . . . . . . . 66
A.2. Registration Removal . . . . . . . . . . . . . . . . . . 69
A.3. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 70
A.4. Update Endpoint Links . . . . . . . . . . . . . . . . . . 71
A.5. Endpoint and group lookup . . . . . . . . . . . . . . . . 71
Appendix B. Web links and the Resource Directory . . . . . . . . 73
B.1. A simple example . . . . . . . . . . . . . . . . . . . . 73
B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 73
B.1.2. Interpreting attributes and relations . . . . . . . . 74
B.2. A slightly more complex example . . . . . . . . . . . . . 74
B.3. Enter the Resource Directory . . . . . . . . . . . . . . 75
B.4. A note on differences between link-format and Link
headers . . . . . . . . . . . . . . . . . . . . . . . . . 76
Appendix C. Syntax examples for Protocol Negotiation . . . . . . 77
Appendix D. Modernized Link Format parsing . . . . . . . . . . . 78
D.1. For endpoint developers . . . . . . . . . . . . . . . . . 79
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
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1. Introduction
The work on Constrained RESTful Environments (CoRE) aims at realizing
the REST architecture in a suitable form for the most constrained
nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and
networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M)
applications such as smart energy and building automation.
The discovery of resources offered by a constrained server is very
important in machine-to-machine applications where there are no
humans in the loop and static interfaces result in fragility. The
discovery of resources provided by an HTTP Web Server is typically
called Web Linking [RFC5988]. The use of Web Linking for the
description and discovery of resources hosted by constrained web
servers is specified by the CoRE Link Format [RFC6690]. However,
[RFC6690] only describes how to discover resources from the web
server that hosts them by querying "/.well-known/core". In many M2M
scenarios, direct discovery of resources is not practical due to
sleeping nodes, disperse networks, or networks where multicast
traffic is inefficient. These problems can be solved by employing an
entity called a Resource Directory (RD), which hosts descriptions of
resources held on other servers, allowing lookups to be performed for
those resources.
This document specifies the web interfaces that a Resource Directory
supports in order for web servers to discover the RD and to register,
maintain, lookup and remove resource descriptions. Furthermore, new
link attributes useful in conjunction with a Resource Directory are
defined. Although the examples in this document show the use of
these interfaces with CoAP [RFC7252], they can be applied in an
equivalent manner to HTTP [RFC7230].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. The term "byte" is used in its now customary sense as a
synonym for "octet".
This specification requires readers to be familiar with all the terms
and concepts that are discussed in [RFC3986], [RFC5988] and
[RFC6690]. Readers should also be familiar with the terms and
concepts discussed in [RFC7252]. To describe the REST interfaces
defined in this specification, the URI Template format is used
[RFC6570].
This specification makes use of the following additional terminology:
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resolve against
The expression "a URI-reference is _resolved against_ a base URI"
is used to describe the process of [RFC3986] Section 5.2.
Noteworthy corner cases are that resolving an absolute URI against
any base URI gives the original URI, and that resolving an empty
URI reference gives the base URI.
Resource Directory
A web entity that stores information about web resources and
implements the REST interfaces defined in this specification for
registration and lookup of those resources.
Sector
In the context of a Resource Directory, a sector is a logical
grouping of endpoints.
The abbreviation "d" is used for the sector in query parameters
for compatibility with deployed implementations.
Group
A group in the Resource Directory specifies a set of endpoints
that are enabled with the same multicast address for the purpose
of efficient group communications. All groups within a sector
have unique names.
Endpoint
Endpoint (EP) is a term used to describe a web server or client in
[RFC7252]. In the context of this specification an endpoint is
used to describe a web server that registers resources to the
Resource Directory. An endpoint is identified by its endpoint
name, which is included during registration, and has a unique name
within the associated sector of the registration.
Registration Base URI
The Base URI of a Registration is a URI that typically gives
scheme and authority information about an Endpoint. The
Registration Base URI is provided by the Endpoint at registration
time, and is used by the Resource Directory to resolve relative
references inside the registration into absolute URIs.
Target
The target of a link is the destination address (URI) of the link.
It is sometimes identified with "href=", or displayed as
"<target>". Relative targets need resolving with respect to the
Base URI (section 5.2 of [RFC3986]).
This use of the term Target is consistent with [RFC8288]'s use of
the term.
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Context
The context of a link is the source address (URI) of the link, and
describes which resource is linked to the target. A link's
context is made explicit in serialized links as the "anchor="
attribute.
This use of the term Context is consistent with [RFC8288]'s use of
the term.
Directory Resource
A resource in the Resource Directory (RD) containing registration
resources.
Group Resource
A resource in the RD containing registration resources of the
Endpoints that form a group.
Registration Resource
A resource in the RD that contains information about an Endpoint
and its links.
Commissioning Tool
Commissioning Tool (CT) is a device that assists during the
installation of the network by assigning values to parameters,
naming endpoints and groups, or adapting the installation to the
needs of the applications.
Registree-ep
Registree-ep is the endpoint that is registered into the RD. The
registree-ep can register itself, or a CT registers the registree-
ep.
RDAO
Resource Directory Address Option.
For several operations, interface descriptions are given in list
form; those describe the operation participants, request codes, URIs,
content formats and outcomes. Those templates contain normative
content in their Interaction, Method, URI Template and URI Template
Variables sections as well as the details of the Success condition.
The additional sections on options like Content-Format and on Failure
codes give typical cases that the implementing parties should be
prepared to deal with. Those serve to illustrate the typical
responses to readers who are not yet familiar with all the details of
CoAP based interfaces; they do not limit what a server may respond
under atypical circumstances.
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3. Architecture and Use Cases
3.1. Principles
The Resource Directory is primarily a tool to make discovery
operations more efficient than querying /.well-known/core on all
connected device, or across boundaries that would be limiting those
operations.
It provides a cache (in the high-level sense, not as defined in
[RFC7252]/[RFC2616]) of data that could otherwise only be obtained by
directly querying the /.well-known/core resource on the target
device, or by accessing those resources with a multicast request.
From that, it follows that only information should be stored in the
resource directory that is discovered from querying the described
device's /.well-known/core resource directly.
It also follows that data in the resource directory can only be
provided by the device whose descriptions are cached or a dedicated
Commissioning Tool (CT). These CTs are thought to act on behalf of
agents too constrained, or generally unable, to present that
information themselves. No other client can modify data in the
resource directory. Changes in the Resource Directory do not
propagate automatically back to the web server from where the links
originated.
3.2. Architecture
The resource directory architecture is illustrated in Figure 1. A
Resource Directory (RD) is used as a repository for Web Links
[RFC5988] about resources hosted on other web servers, which are
called endpoints (EP). An endpoint is a web server associated with a
scheme, IP address and port. A physical node may host one or more
endpoints. The RD implements a set of REST interfaces for endpoints
to register and maintain sets of Web Links (called resource directory
registration entries), and for clients to lookup resources from the
RD or maintain groups. Endpoints themselves can also act as clients.
An RD can be logically segmented by the use of Sectors. The set of
endpoints grouped for group communication can be defined by the RD or
configured by a Commissioning Tool. This information hierarchy is
shown in Figure 2.
A mechanism to discover an RD using CoRE Link Format [RFC6690] is
defined.
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Endpoints proactively register and maintain resource directory
registration entries on the RD, which are soft state and need to be
periodically refreshed.
An endpoint uses specific interfaces to register, update and remove a
resource directory registration entry. It is also possible for an RD
to fetch Web Links from endpoints and add them as resource directory
registration entries.
At the first registration of a set of entries, a "registration
resource" is created, the location of which is returned to the
registering endpoint. The registering endpoint uses this
registration resource to manage the contents of registration entries.
A lookup interface for discovering any of the Web Links held in the
RD is provided using the CoRE Link Format.
Registration Lookup, Group
Interface Interfaces
+----+ | |
| EP |---- | |
+----+ ---- | |
--|- +------+ |
+----+ | ----| | | +--------+
| EP | ---------|-----| RD |----|-----| Client |
+----+ | ----| | | +--------+
--|- +------+ |
+----+ ---- | |
| EP |---- | |
+----+
Figure 1: The resource directory architecture.
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+------------+
| Group | <-- Name, Scheme, IP, Port
+------------+
|
|
+------------+
| Endpoint | <-- Name, Scheme, IP, Port
+------------+
|
|
+------------+
| Resource | <-- Target, Parameters
+------------+
Figure 2: The resource directory information hierarchy.
3.3. RD Content Model
The Entity-Relationship (ER) models shown in Figure 3 and Figure 4
model the contents of /.well-known/core and the resource directory
respectively, with entity-relationship diagrams [ER]. Entities
(rectangles) are used for concepts that exist independently.
Attributes (ovals) are used for concepts that exist only in
connection with a related entity. Relations (diamonds) give a
semantic meaning to the relation between entities. Numbers specify
the cardinality of the relations.
Some of the attribute values are URIs. Those values are always full
URIs and never relative references in the information model. They
can, however, be expressed as relative references in serializations,
and often are.
These models provide an abstract view of the information expressed in
link-format documents and a Resource Directory. They cover the
concepts, but not necessarily all details of an RD's operation; they
are meant to give an overview, and not be a template for
implementations.
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+----------------------+
| /.well-known/core |
+----------------------+
|
| 1
////////\\\\\\\
< contains >
\\\\\\\\///////
|
| 0+
+--------------------+
| link |
+--------------------+
|
| 1 oooooooo
+-----o target o
| oooooooo
oooooooooooo 0+ |
o target o--------+
o attribute o | 0+ oooooo
oooooooooooo +-----o rel o
| oooooo
|
| 1 ooooooooo
+-----o context o
ooooooooo
Figure 3: E-R Model of the content of /.well-known/core
The model shown in Figure 3 models the contents of /.well-known/core
which contains:
o a set of links belonging to the hosting web server
The web server is free to choose links it deems appropriate to be
exposed in its ".well-known/core". Typically, the links describe
resources that are served by the host, but the set can also contain
links to resources on other servers (see examples in [RFC6690] page
14). The set does not necessarily contain links to all resources
served by the host.
A link has the following attributes (see [RFC5988]):
o Zero or more link relations: They describe relations between the
link context and the link target.
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In link-format serialization, they are expressed as space-
separated values in the "rel" attribute, and default to "hosts".
o A link context URI: It defines the source of the relation, eg.
_who_ "hosts" something.
In link-format serialization, it is expressed in the "anchor"
attribute. It defaults to that document's URI.
o A link target URI: It defines the destination of the relation (eg.
_what_ is hosted), and is the topic of all target attributes.
In link-format serialization, it is expressed between angular
brackets, and sometimes called the "href".
o Other target attributes (eg. resource type (rt), interface (if),
or content-type (ct)). These provide additional information about
the target URI.
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+----------------------+ 1 ooooooo
| resource-directory | +--o href o
+----------------------+ | ooooooo
| 1 |
| oooooooooo 0-1 | 1 oooooo
| o base o---+ | +------o gp o
| ooooooooooo | | | oooooo
| | | |
//////\\\\ 0+ +--------+ 0-1 ooooo
< contains >----------------| group |------o d o
\\\\\///// +--------+ ooooo
| | 0+
0+ | |
ooooooo 1 +---------------+ 1+ ///////\\\\\\
o base o-------| registration |---------< composed of >
ooooooo +---------------+ \\\\\\\//////
| | 1
| +--------------+
oooooooo 1 | |
o href o----+ /////\\\\
oooooooo | < contains >
| \\\\\/////
oooooooo 1 | |
o ep o----+ | 0+
oooooooo | +------------------+
| | link |
oooooooo 0-1 | +------------------+
o d o----+ |
oooooooo | | 1 oooooooo
| +-----o target o
oooooooo 1 | | oooooooo
o lt o----+ ooooooooooo 0+ |
oooooooo | o target o-----+
| o attribute o | 0+ oooooo
ooooooooooo 0+ | ooooooooooo +-----o rel o
o endpoint o----+ | oooooo
o attribute o |
ooooooooooo | 1 ooooooooo
+----o context o
ooooooooo
Figure 4: E-R Model of the content of the Resource Directory
The model shown in Figure 4 models the contents of the resource
directory which contains in addition to /.well-known/core:
o 0 to n Registration (entries) of endpoints,
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o 0 or more Groups
A Group has:
o a group name ("gp"),
o optionally a sector (abbreviated "d" for historical reasons),
o a group resource location inside the RD ("href"),
o zero or one multicast addresses expressed as a base URI ("base"),
o and is composed of zero or more registrations (endpoints).
A registration is associated with one endpoint. A registration can
be part of 0 or more Groups . A registration defines a set of links
as defined for /.well-known/core. A Registration has six types of
attributes:
o a unique endpoint name ("ep")
o a Registration Base URI ("base", a URI typically describing the
scheme://authority part)
o a lifetime ("lt"),
o a registration resource location inside the RD ("href"),
o optionally a sector ("d")
o optional additional endpoint attributes (from Section 10.3)
The cardinality of "base" is currently 1; future documents are
invited to extend the RD specification to support multiple values
(eg. [I-D.silverajan-core-coap-protocol-negotiation]). Its value is
used as a Base URI when resolving URIs in the links contained in the
endpoint.
Links are modelled as they are in Figure 3.
3.4. Use Case: Cellular M2M
Over the last few years, mobile operators around the world have
focused on development of M2M solutions in order to expand the
business to the new type of users: machines. The machines are
connected directly to a mobile network using an appropriate embedded
wireless interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing
short and wide range wireless interfaces. From the system design
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point of view, the ambition is to design horizontal solutions that
can enable utilization of machines in different applications
depending on their current availability and capabilities as well as
application requirements, thus avoiding silo like solutions. One of
the crucial enablers of such design is the ability to discover
resources (machines -- endpoints) capable of providing required
information at a given time or acting on instructions from the end
users.
Imagine a scenario where endpoints installed on vehicles enable
tracking of the position of these vehicles for fleet management
purposes and allow monitoring of environment parameters. During the
boot-up process endpoints register with a Resource Directory, which
is hosted by the mobile operator or somewhere in the cloud.
Periodically, these endpoints update their registration and may
modify resources they offer.
When endpoints are not always connected, for example because they
enter a sleep mode, a remote server is usually used to provide proxy
access to the endpoints. Mobile apps or web applications for
environment monitoring contact the RD, look up the endpoints capable
of providing information about the environment using an appropriate
set of link parameters, obtain information on how to contact them
(URLs of the proxy server), and then initiate interaction to obtain
information that is finally processed, displayed on the screen and
usually stored in a database. Similarly, fleet management systems
provide the appropriate link parameters to the RD to look up for EPs
deployed on the vehicles the application is responsible for.
3.5. Use Case: Home and Building Automation
Home and commercial building automation systems can benefit from the
use of M2M web services. The discovery requirements of these
applications are demanding. Home automation usually relies on run-
time discovery to commission the system, whereas in building
automation a combination of professional commissioning and run-time
discovery is used. Both home and building automation involve peer-
to-peer interactions between endpoints, and involve battery-powered
sleeping devices.
3.6. Use Case: Link Catalogues
Resources may be shared through data brokers that have no knowledge
beforehand of who is going to consume the data. Resource Directory
can be used to hold links about resources and services hosted
anywhere to make them discoverable by a general class of
applications.
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For example, environmental and weather sensors that generate data for
public consumption may provide the data to an intermediary server, or
broker. Sensor data are published to the intermediary upon changes
or at regular intervals. Descriptions of the sensors that resolve to
links to sensor data may be published to a Resource Directory.
Applications wishing to consume the data can use RD Lookup to
discover and resolve links to the desired resources and endpoints.
The Resource Directory service need not be coupled with the data
intermediary service. Mapping of Resource Directories to data
intermediaries may be many-to-many.
Metadata in web link formats like [RFC6690] are supplied by Resource
Directories, which may be internally stored as triples, or relation/
attribute pairs providing metadata about resource links. External
catalogues that are represented in other formats may be converted to
common web linking formats for storage and access by Resource
Directories. Since it is common practice for these to be URN
encoded, simple and lossless structural transforms should generally
be sufficient to store external metadata in Resource Directories.
The additional features of Resource Directory allow sectors to be
defined to enable access to a particular set of resources from
particular applications. This provides isolation and protection of
sensitive data when needed. Groups may be defined to support
efficient data transport.
4. Finding a Resource Directory
A (re-)starting device may want to find one or more resource
directories to make itself known with.
The device may be pre-configured to exercise specific mechanisms for
finding the resource directory:
1. It may be configured with a specific IP address for the RD. That
IP address may also be an anycast address, allowing the network
to forward RD requests to an RD that is topologically close; each
target network environment in which some of these preconfigured
nodes are to be brought up is then configured with a route for
this anycast address that leads to an appropriate RD. (Instead
of using an anycast address, a multicast address can also be
preconfigured. The RD servers then need to configure one of
their interfaces with this multicast address.)
2. It may be configured with a DNS name for the RD and a resource-
record type to look up under this name; it can find a DNS server
to perform the lookup using the usual mechanisms for finding DNS
servers.
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3. It may be configured to use a service discovery mechanism such as
DNS-SD [RFC6763]. The present specification suggests configuring
the service with name rd._sub._coap._udp, preferably within the
domain of the querying nodes.
For cases where the device is not specifically configured with a way
to find a resource directory, the network may want to provide a
suitable default.
1. If the address configuration of the network is performed via
SLAAC, this is provided by the RDAO option Section 4.1.
2. If the address configuration of the network is performed via
DHCP, this could be provided via a DHCP option (no such option is
defined at the time of writing).
Finally, if neither the device nor the network offers any specific
configuration, the device may want to employ heuristics to find a
suitable resource directory.
The present specification does not fully define these heuristics, but
suggests a number of candidates:
1. In a 6LoWPAN, just assume the Border Router (6LBR) can act as a
resource directory (using the ABRO option to find that
[RFC6775]). Confirmation can be obtained by sending a Unicast to
"coap://[6LBR]/.well-known/core?rt=core.rd*".
2. In a network that supports multicast well, discovering the RD
using a multicast query for /.well-known/core as specified in
CoRE Link Format [RFC6690]: Sending a Multicast GET to
"coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the
multicast scope will answer the query.
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
error messages to very strictly rate-limit requests to candidate IP
addresses that don't work out. For example, an ICMP Destination
Unreachable message (and, in particular, the port unreachable code
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
Not Allowed" may indicate unwillingness of a CoAP server to act as a
directory server.
If multiple candidate addresses are discovered, the device may pick
any of them initially, unless the discovery method indicates a more
precise selection scheme.
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4.1. Resource Directory Address Option (RDAO)
The Resource Directory Address Option (RDAO) using IPv6 neighbor
Discovery (ND) carries information about the address of the Resource
Directory (RD). This information is needed when endpoints cannot
discover the Resource Directory with a link-local or realm-local
scope multicast address because the endpoint and the RD are separated
by a Border Router (6LBR). In many circumstances the availability of
DHCP cannot be guaranteed either during commissioning of the network.
The presence and the use of the RD is essential during commissioning.
It is possible to send multiple RDAO options in one message,
indicating as many resource directory addresses.
The RDAO format is:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length = 3 | Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ RD Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: 38
Length: 8-bit unsigned integer. The length of
the option in units of 8 bytes.
Always 3.
Valid Lifetime: 16-bit unsigned integer. The length of
time in units of 60 seconds (relative to
the time the packet is received) that
this Resource Directory address is valid.
A value of all zero bits (0x0) indicates
that this Resource Directory address
is not valid anymore.
Reserved: This field is unused. It MUST be
initialized to zero by the sender and
MUST be ignored by the receiver.
RD Address: IPv6 address of the RD.
Figure 5: Resource Directory Address Option
5. Resource Directory
This section defines the required set of REST interfaces between a
Resource Directory (RD) and endpoints. Although the examples
throughout this section assume the use of CoAP [RFC7252], these REST
interfaces can also be realized using HTTP [RFC7230]. In all
definitions in this section, both CoAP response codes (with dot
notation) and HTTP response codes (without dot notation) are shown.
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An RD implementing this specification MUST support the discovery,
registration, update, lookup, and removal interfaces defined in this
section.
All operations on the contents of the Resource Directory MUST be
atomic and idempotent.
A resource directory MAY make the information submitted to it
available to further directories, if it can ensure that a loop does
not form. The protocol used between directories to ensure loop-free
operation is outside the scope of this document.
5.1. Payload Content Formats
Resource Directory implementations using this specification MUST
support the application/link-format content format (ct=40).
Resource Directories implementing this specification MAY support
additional content formats.
Any additional content format supported by a Resource Directory
implementing this specification MUST have an equivalent serialization
in the application/link-format content format.
5.2. URI Discovery
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.
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
RD discovery methods is described in Section 4.
Discovery of the RD registration URI path is performed by sending
either a multicast or unicast GET request to "/.well-known/core" and
including a Resource Type (rt) parameter [RFC6690] with the value
"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
operations, and "core.rd-group" is used to discover the URI path for
RD Group operations. Upon success, the response will contain a
payload with a link format entry for each RD function discovered,
indicating the URI of the RD function returned and the corresponding
Resource Type. When performing multicast discovery, the multicast IP
address used will depend on the scope required and the multicast
capabilities of the network.
A Resource Directory MAY provide hints about the content-formats it
supports in the links it exposes or registers, using the "ct" link
attribute, as shown in the example below. Clients MAY use these
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hints to select alternate content-formats for interaction with the
Resource Directory.
HTTP does not support multicast and consequently only unicast
discovery can be supported using HTTP. Links to Resource Directories
MAY be registered in other Resource Directories. The well-known
entry points SHOULD be provided to enable the bootstrapping of
unicast discovery.
An implementation of this resource directory specification MUST
support query filtering for the rt parameter as defined in [RFC6690].
While the link targets in this discovery step are often expressed in
path-absolute form, this is not a requirement. Clients SHOULD
therefore accept URIs of all schemes they support, both in absolute
and relative forms, and not limit the set of discovered URIs to those
hosted at the address used for URI discovery.
The URI Discovery operation can yield multiple URIs of a given
resource type. The client can use any of the discovered addresses
initially.
The discovery request interface is specified as follows (this is
exactly the Well-Known Interface of [RFC6690] Section 4, with the
additional requirement that the server MUST support query filtering):
Interaction: EP and Client -> RD
Method: GET
URI Template: /.well-known/core{?rt}
URI Template Variables:
rt := Resource Type (optional). MAY contain one of the values
"core.rd", "core.rd-lookup*", "core.rd-lookup-res", "core.rd-
lookup-ep", "core.rd-lookup-gp", "core.rd-group" or "core.rd*"
Content-Format: application/link-format (if any)
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:
Success: 2.05 "Content" or 200 "OK" with an application/link-format,
application/link-format+json, or application/link-format+cbor
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payload containing one or more matching entries for the RD
resource.
Failure: 4.00 "Bad Request" or 400 "Bad Request" is returned in case
of a malformed request for a unicast request.
Failure: No error response to a multicast request.
HTTP support : YES (Unicast only)
The following example shows an endpoint discovering an RD using this
interface, thus learning that the directory resource is, in this
example, at /rd, and that the content-format delivered by the server
hosting the resource is application/link-format (ct=40). Note that
it is up to the RD to choose its RD resource paths.
Req: GET coap://[MCD1]/.well-known/core?rt=core.rd*
Res: 2.05 Content
</rd>;rt="core.rd";ct=40,
</rd-lookup/ep>;rt="core.rd-lookup-ep";ct=40,
</rd-lookup/res>;rt="core.rd-lookup-res";ct=40,
</rd-lookup/gp>;rt="core.rd-lookup-gp";ct=40,
</rd-group>;rt="core.rd-group";ct=40
Figure 6: Example discovery exchange
The following example shows the way of indicating that a client may
request alternate content-formats. The Content-Format code attribute
"ct" MAY include a space-separated sequence of Content-Format codes
as specified in Section 7.2.1 of [RFC7252], indicating that multiple
content-formats are available. The example below shows the required
Content-Format 40 (application/link-format) indicated as well as the
CBOR and JSON representation of link format. The RD resource paths
/rd, /rd-lookup, and /rd-group 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 these and later occurrences of
TBD64 and TBD504 with 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. ]
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Req: GET coap://[MCD1]/.well-known/core?rt=core.rd*
Res: 2.05 Content
</rd>;rt="core.rd";ct="40 65225",
</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/gp>;rt="core.rd-lookup-gp";ct=40 TBD64 TBD504",
</rd-group>;rt="core.rd-group";ct="40 TBD64 TBD504"
From a management and maintenance perspective, it is necessary to
identify the components that constitute the server. The
identification refers to information about for example client-server
incompatibilities, supported features, required updates and other
aspects. The URI discovery address, a described in section 4 of
[RFC6690] can be used to find the identification.
It would typically be stored in an implementation information link
(as described in [I-D.bormann-t2trg-rel-impl]):
Req: GET /.well-known/core?rel=impl-info
Res: 2.05 Content
<http://software.example.com/shiny-resource-directory/1.0beta1>;
rel="impl-info"
Note that depending on the particular server's architecture, such a
link could be anchored at the server's root, at the discovery site
(as in this example) or at individual RD components. The latter is
to be expected when different applications are run on the same
server.
5.3. Registration
After discovering the location of an RD, a registree-ep or CT MAY
register the resources of the registree-ep using the registration
interface. This interface accepts a POST from an endpoint containing
the list of resources to be added to the directory as the message
payload in the CoRE Link Format [RFC6690], JSON CoRE Link Format
(application/link-format+json), or CBOR CoRE Link Format
(application/link-format+cbor) [I-D.ietf-core-links-json], along with
query parameters indicating the name of the endpoint, and optionally
the sector, lifetime and base URI of the registration. It is
expected that other specifications will define further parameters
(see Section 10.3). The RD then creates a new registration resource
in the RD and returns its location. The receiving endpoint MUST use
that location when refreshing registrations using this interface.
Registration resources in the RD are kept active for the period
indicated by the lifetime parameter. The endpoint is responsible for
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refreshing the registration resource within this period using either
the registration or update interface. The registration interface
MUST be implemented to be idempotent, so that registering twice with
the same endpoint parameters ep and d (sector) 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
attribute values as already present, the location of the already
existing registration is returned.
o when for a given (ep, d) value pair the update generates attribute
values which are different from the existing one, the existing
registration is removed and a new registration with a new location
is created.
o when the (ep, d) value pair of the update is different from any
existing registration, a new registration is generated.
The posted link-format document can (and typically does) contain
relative references both in its link targets and in its anchors, or
contain empty anchors. The RD server needs to resolve these
references in order to faithfully represent them in lookups. They
are resolved against the base URI of the registration, which is
provided either explicitly in the "base" parameter or constructed
implicitly from the requester's network address.
Link format documents submitted to the resource directory are
interpreted as Modernized Link Format (see Appendix D) by the RD. A
registree-ep SHOULD NOT submit documents whose interpretations
according to [RFC6690] and Appendix D differ and RFC6690
interpretation is intended to avoid the ambiguities 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:
Interaction: EP -> RD
Method: POST
URI Template: {+rd}{?ep,d,lt,base,extra-attrs*}
URI Template Variables:
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rd := RD registration URI (mandatory). This is the location of
the RD, as obtained from discovery.
ep := Endpoint name (mostly mandatory). The endpoint name is an
identifier that MUST be unique within a sector. The maximum
length of this parameter is 63 bytes. If the RD is configured
to recognize the endpoint (eg. based on its security context),
the endpoint sets no endpoint name, and the RD assigns one
based on a set of configuration parameter values.
d := Sector (optional). The sector to which this endpoint
belongs. The maximum length of this parameter is 63 bytes.
When this parameter is not present, the RD MAY associate the
endpoint with a configured default sector or leave it empty.
The endpoint name and sector name are not set when one or both
are set in an accompanying authorization token.
lt := Lifetime (optional). Lifetime of the registration in
seconds. Range of 60-4294967295. If no lifetime is included
in the initial registration, a default value of 90000 (25
hours) SHOULD be assumed.
base := Base URI (optional). This parameter sets the base URI of
the registration, under which the request's links are to be
interpreted. The specified URI typically does not have a path
component of its own, and MUST be suitable as a base URI to
resolve any relative references given in the registration. The
parameter is therefore usually of the shape
"scheme://authority" for HTTP and CoAP URIs. The URI SHOULD
NOT have a query or fragment component as any non-empty
relative part in a reference would remove those parts from the
resulting URI.
In the absence of this parameter the scheme of the protocol,
source address and source port of the registration request are
assumed. This parameter is mandatory when the directory is
filled by a third party such as an commissioning tool.
If the endpoint uses an ephemeral port to register with, it
MUST include the base parameter in the registration to provide
a valid network path.
If the endpoint which is located behind a NAT gateway is
registering with a Resource Directory which is on the network
service side of the NAT gateway, the endpoint MUST use a
persistent port for the outgoing registration in order to
provide the NAT gateway with a valid network address for
replies and incoming requests.
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Endpoints that register with a base that contains a path
component can not meaningfully use [RFC6690] Link Format due to
its prevalence of the Origin concept in relative reference
resolution; they can submit payloads for interpretation as
Modernized Link Format. Typically, links submitted by such an
endpoint are of the "path-noscheme" (starts with a path not
preceded by a slash, precisely defined in [RFC3986]
Section 3.3) form.
extra-attrs := Additional registration attributes (optional).
The endpoint can pass any parameter registered at Section 10.3
to the directory. If the RD is aware of the parameter's
specified semantics, it processes it accordingly. Otherwise,
it MUST store the unknown key and its value(s) as an endpoint
attribute for further lookup.
Content-Format: application/link-format
Content-Format: application/link-format+json
Content-Format: application/link-format+cbor
The following response codes are defined for this interface:
Success: 2.01 "Created" or 201 "Created". The Location-Path option
or Location header MUST be included in the response. This
location MUST be a stable identifier generated by the RD as it is
used for all subsequent operations on this registration resource.
The registration resource location thus returned is for the
purpose of updating the lifetime of the registration and for
maintaining the content of the registered links, including
updating and deleting links.
A registration with an already registered ep and d value pair
responds with the same success code and location as the original
registration; the set of links registered with the endpoint is
replaced with the links from the payload.
The location MUST NOT have a query or fragment component, as that
could conflict with query parameters during the Registration
Update operation. Therefore, the Location-Query option MUST NOT
be present in a successful response.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
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HTTP support: YES
If the registration 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 Service
Unavailable error persists after several retries, or indicates a
longer time than the endpoint is willing to wait, it SHOULD pick
another registration URI from the "URI Discovery" step and if there
is only one or the list is exhausted, pick other choices from the
"Finding a Resource Directory" step. Care has to be taken to
consider the freshness of results obtained earlier, eg. of the result
of a "/.well-known/core" response, the lifetime of an RDAO option and
of DNS responses. Any rate limits and persistent errors from the
"Finding a Resource Directory" step must be considered for the whole
registration time, not only for a single operation.
The following example shows a registree-ep with the name "node1"
registering two resources to an RD using this interface. The
location "/rd" is an example RD location discovered in a request
similar to Figure 6.
Req: POST coap://rd.example.com/rd?ep=node1
Content-Format: 40
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"
Res: 2.01 Created
Location-Path: /rd/4521
Figure 7: Example registration payload
A Resource Directory may optionally support HTTP. Here is an example
of almost the same registration operation above, when done using HTTP
and the JSON Link Format.
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Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1
Host: example.com
Content-Type: application/link-format+json
Payload:
[
{"href": "/sensors/temp", "ct": "41", "rt": "temperature-c",
"if": "sensor", "anchor": "coap://spurious.example.com:5683"},
{"href": "/sensors/light", "ct": "41", "rt": "light-lux",
"if": "sensor"}
]
Res: 201 Created
Location: /rd/4521
5.3.1. Simple Registration
Not all endpoints hosting resources are expected to know how to
upload links to an RD as described in Section 5.3. Instead, simple
endpoints can implement the Simple Registration approach described in
this section. An RD implementing this specification MUST implement
Simple Registration. However, there may be security reasons why this
form of directory discovery would be disabled.
This approach requires that the registree-ep makes available the
hosted resources that it wants to be discovered, as links on its
"/.well-known/core" interface as specified in [RFC6690]. The links
in that document are subject to the same limitations as the payload
of a registration (with respect to Appendix D).
The registree-ep then finds one or more addresses of the directory
server as described in Section 4.
The registree-ep finally asks the selected directory server to probe
it for resources and publish them as follows:
The registree-ep sends (and regularly refreshes with) a POST request
to the "/.well-known/core" URI of the directory server of choice.
The body of the POST request is empty, and triggers the resource
directory server to perform GET requests at the requesting registree-
ep's default discovery URI to obtain the link-format payload to
register.
The registree-ep includes the same registration parameters in the
POST request as it would per Section 5.3. The registration base URI
of the registration is taken from the requesting server's URI.
The Resource Directory MUST NOT query the registree-ep's data before
sending the response; this is to accommodate very limited endpoints.
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The success condition only indicates that the request was valid (ie.
the passed parameters are valid per se), not that the link data could
be obtained or parsed or was successfully registered into the RD.
The simple registration request interface is specified as follows:
Interaction: EP -> RD
Method: POST
URI Template: /.well-known/core{?ep,d,lt,extra-attrs*}
URI Template Variables are as they are for registration in
Section 5.3. The base attribute is not accepted to keep the
registration interface simple; that rules out registration over CoAP-
over-TCP or HTTP that would need to specify one.
The following response codes are defined for this interface:
Success: 2.04 "Changed".
Failure: 4.00 "Bad Request". Malformed request.
Failure: 5.03 "Service Unavailable". Service could not perform the
operation.
HTTP support: NO
For the second interaction triggered by the above, the registree-ep
takes the role of server and the RD the role of client. (Note that
this is exactly the Well-Known Interface of [RFC6690] Section 4):
Interaction: RD -> EP
Method: GET
URI Template: /.well-known/core
The following response codes are defined for this interface:
Success: 2.05 "Content".
Failure: 4.00 "Bad Request". Malformed request.
Failure: 4.04 "Not Found". /.well-known/core does not exist or is
empty.
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Failure: 5.03 "Service Unavailable". Service could not perform the
operation.
HTTP support: NO
The registration resources MUST be deleted after the expiration of
their lifetime. Additional operations on the registration resource
cannot be executed because no registration location is returned.
The following example shows a registree-ep using Simple Registration,
by simply sending an empty POST to a resource directory.
Req:(to RD server from [2001:db8:2::1])
POST /.well-known/core?lt=6000&ep=node1
No payload
Res: 2.04 Changed
(later)
Req: (from RD server to [2001:db8:2::1])
GET /.well-known/core
Accept: 40
Res: 2.05 Content
Content-Format: 40
Payload:
</sen/temp>
5.3.2. Third-party registration
For some applications, even Simple Registration may be too taxing for
some very constrained devices, in particular if the security
requirements become too onerous.
In a controlled environment (e.g. building control), the Resource
Directory can be filled by a third party device, called a
commissioning tool. The commissioning tool can fill the Resource
Directory from a database or other means. For that purpose the
scheme, IP address and port of the registered device is indicated in
the "base" parameter of the registration described in Section 5.3.
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
value of the individual links as exemplified in Appendix B. An
eventual (currently non-existing) "base" attribute of the link is not
affected by the value of "base" parameter in the registration.
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6. RD Groups
This section defines the REST API for the creation, management, and
lookup of endpoints for group operations. Similar to endpoint
registration entries in the RD, groups may be created or removed.
However unlike an endpoint entry, a group entry consists of a list of
endpoints and does not have a lifetime associated with it. In order
to make use of multicast requests with CoAP, a group MAY have a
multicast address associated with it.
6.1. Register a Group
In order to create a group, a commissioning tool (CT) used to
configure groups, makes a request to the RD indicating the name of
the group to create (or update), optionally the sector the group
belongs to, and optionally the multicast address of the group. This
specification does not require that the endpoints belong to the same
sector as the group, but a Resource Directory implementation can
impose requirements on the sectors of groups and endpoints depending
on its configuration.
The registration message is a list of links to registration resources
of the endpoints that belong to that group. The CT can use any URI
reference discovered using endpoint lookup from the same server or
obtained by registering an endpoint using third party registration
and enter it into a group. The use of other URIs is not specified in
this document and can be defined in others.
The commissioning tool SHOULD not send any target attributes with the
links to the registration resources, and the resource directory
SHOULD reject registrations that contain links with unprocessable
attributes.
Configuration of the endpoints themselves is out of scope of this
specification. Such an interface for managing the group membership
of an endpoint has been defined in [RFC7390].
The registration request interface is specified as follows:
Interaction: CT -> RD
Method: POST
URI Template: {+rd-group}{?gp,d,base}
URI Template Variables:
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rd-group := RD Group URI (mandatory). This is the location of
the RD Group REST API.
gp := Group Name (mandatory). The name of the group to be
created or replaced, unique within that sector. The maximum
length of this parameter is 63 bytes.
d := Sector (optional). The sector to which this group belongs.
The maximum length of this parameter is 63 bytes. When this
parameter is not present, the RD MAY associate the group with a
configured default sector or leave it empty.
base := Group Base URI (optional). This parameter sets the
scheme, address and port of the multicast address associated
with the group. When base is used, scheme and host are
mandatory and port parameter is optional.
Content-Format: application/link-format
Content-Format: application/link-format+json
Content-Format: application/link-format+cbor
The following response codes are defined for this interface:
Success: 2.01 "Created" or 201 "Created". The Location header or
Location-Path option MUST be returned in response to a successful
group CREATE operation. This location MUST be a stable identifier
generated by the RD as it is used for delete operations of the
group resource.
As with the Registration operation, the location MUST NOT have a
query or fragment component.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following example shows an EP registering a group with the name
"lights" which has two endpoints. The RD group path /rd-group is an
example RD location discovered in a request similar to Figure 6.
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Req: POST coap://rd.example.com/rd-group?gp=lights
&base=coap://[ff35:30:2001:db8::1]
Content-Format: 40
Payload:
</rd/4521>,
</rd/4522>
Res: 2.01 Created
Location-Path: /rd-group/12
A relative href value denotes the path to the registration resource
of the Endpoint. When pointing to a registration resource on a
different RD, the href value is an absolute URI.
6.2. Group Removal
A group can be removed simply by sending a removal message to the
location of the group registration resource which was returned when
initially registering the group. Removing a group MUST NOT remove
the endpoints of the group from the RD.
The removal request interface is specified as follows:
Interaction: CT -> RD
Method: DELETE
URI Template: {+location}
URI Template Variables:
location := This is the path of the group resource returned by
the RD as a result of a successful group registration.
The following responses 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". Group does not exist.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
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The following examples shows successful removal of the group from the
RD with the example location value /rd-group/12.
Req: DELETE /rd-group/12
Res: 2.02 Deleted
7. RD Lookup
To discover the resources registered with the RD, a lookup interface
must be provided. This lookup interface is defined as a default, and
it is assumed that RDs may also support lookups to return resource
descriptions in alternative formats (e.g. Atom or HTML Link) or
using more advanced interfaces (e.g. supporting context or semantic
based lookup).
RD Lookup allows lookups for groups, endpoints and resources using
attributes 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)
corresponding to the type of lookup. Thus, a group lookup MUST
return a list of groups, an endpoint lookup MUST return a list of
endpoints and a resource lookup MUST return a list of links to
resources.
The lookup type is selected by a URI endpoint, which is indicated by
a Resource Type as per Table 1 below:
+-------------+--------------------+-----------+
| Lookup Type | Resource Type | Mandatory |
+-------------+--------------------+-----------+
| Resource | core.rd-lookup-res | Mandatory |
| Endpoint | core.rd-lookup-ep | Mandatory |
| Group | core.rd-lookup-gp | Optional |
+-------------+--------------------+-----------+
Table 1: Lookup Types
7.1. Resource lookup
Resource lookup results in links that are semantically equivalent to
the links submitted to the RD if they were accessed on the endpoint
itself. The links and link parameters returned are equal to the
submitted, except that the target and anchor references are fully
resolved.
Links that did not have an anchor attribute are therefore returned
with the (explicitly or implicitly set) base URI of the registration
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as the anchor. Links whose href or anchor was submitted as an
absolute URI are returned with respective attributes unmodified.
Above rules allow the client to interpret the response as links
without any further knowledge of what the RD does. The Resource
Directory MAY replace the registration base URIs with a configured
intermediate proxy, e.g. in the case of an HTTP lookup interface for
CoAP endpoints.
7.2. Lookup filtering
Using the Accept Option, the requester can control whether the
returned list is returned in CoRE Link Format ("application/link-
format", default) or its alternate content-formats ("application/
link-format+json" or "application/link-format+cbor").
The page and count parameters are used to obtain lookup results in
specified increments using pagination, where count specifies how many
links to return and page specifies which subset of links organized in
sequential pages, each containing 'count' links, starting with link
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
and page = 1 will return the next 'page' containing links 10-19, and
so on.
Multiple search criteria MAY be included in a lookup. All included
criteria MUST match for a link to be returned. The Resource
Directory MUST support matching with multiple search criteria.
A link matches a search criterion if it has an attribute of the same
name and the same value, allowing for a trailing "*" wildcard
operator as in Section 4.1 of [RFC6690]. Attributes that are defined
as "link-type" match if the search value matches any of their values
(see Section 4.1 of [RFC6690]; eg. "?if=core.s" matches ";if="abc
core.s";"). A link also matches a search criterion if the link that
would be produced for any of its containing entities would match the
criterion, or an entity contained in it would: A search criterion
matches an endpoint if it matches the endpoint itself, any of the
groups it is contained in or any resource it contains. A search
criterion matches a resource if it matches the resource itself, the
resource's endpoint, or any of the endpoint's groups.
Note that "href" is also a valid search criterion and matches target
references. Like all search criteria, on a resource lookup it can
match the target reference of the resource link itself, but also the
registration resource of the endpoint that registered it, or any
group resource that endpoint is contained in. Queries for resource
link targets MUST be in absolute form and are matched against a
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resolved link target. Queries for groups and endpoints SHOULD be
expressed in path-absolute form if possible and MUST be expressed in
absolute form otherwise; the RD SHOULD recognize either.
Clients that are interested in a lookup result repeatedly or
continuously can use mechanisms like ETag caching, resource
observation ([RFC7641]), or any future mechanism that might allow
more efficient observations of collections. These are advertised,
detected and used according to their own specifications and can be
used with the lookup interface as with any other resource.
When resource observation is used, every time the set of matching
links changes, or the content of a matching link changes, the RD
sends a notification with the matching link set. The notification
contains the successful current response to the given request,
especially with respect to representing zero matching links (see
"Success" item below).
The lookup interface is specified as follows:
Interaction: Client -> RD
Method: GET
URI Template: {+type-lookup-location}{?page,count,search*}
URI Template Variables:
type-lookup-location := RD Lookup URI for a given lookup type
(mandatory). The address is discovered as described in
Section 5.2.
search := Search criteria for limiting the number of results
(optional).
page := Page (optional). Parameter can not be used without the
count parameter. Results are returned from result set in pages
that contain 'count' links starting from index (page * count).
Page numbering starts with zero.
count := Count (optional). Number of results is limited to this
parameter value. If the page parameter is also present, the
response MUST only include 'count' links starting with the
(page * count) link in the result set from the query. If the
count parameter is not present, then the response MUST return
all matching links in the result set. Link numbering starts
with zero.
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Content-Format: application/link-format (optional)
Content-Format: application/link-format+json (optional)
Content-Format: application/link-format+cbor (optional)
The following responses codes are defined for this interface:
Success: 2.05 "Content" or 200 "OK" with an "application/link-
format", "application/link-format+cbor", or "application/link-
format+json" payload containing matching entries for the lookup.
The payload can contain zero links (which is an empty payload,
"80" (hex) or "[]" in the respective content format), indicating
that no entities matched the request.
Failure: No error response to a multicast request.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The group and endpoint lookup return registration resources which can
only be manipulated by the registering endpoint. Examples of group
and 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.
7.3. Resource lookup examples
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
the nature of the examples.
The following example shows a client performing a resource lookup
with the example resource look-up locations discovered in Figure 6:
Req: GET /rd-lookup/res?rt=temperature
Res: 2.05 Content
<coap://[2001:db8:3::123]:61616/temp>;rt="temperature";
anchor="coap://[2001:db8:3::123]:61616"
The same lookup using the CBOR Link Format media type:
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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
can use observation:
Req: GET /rd-lookup/res?rt=light
Observe: 0
Res: 2.05 Content
Observe: 23
Payload: empty
(at a later point in time)
Res: 2.05 Content
Observe: 24
Payload:
<coap://[2001:db8:3::124]/west>;rt="light";
anchor="coap://[2001:db8:3::124]",
<coap://[2001:db8:3::124]/south>;rt="light";
anchor="coap://[2001:db8:3::124]",
<coap://[2001:db8:3::124]/east>;rt="light";
anchor="coap://[2001:db8:3::124]"
The following example shows a client performing a paginated resource
lookup
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Req: GET /rd-lookup/res?page=0&count=5
Res: 2.05 Content
<coap://[2001:db8:3::123]:61616/res/0>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/1>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/2>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/3>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/4>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616"
Req: GET /rd-lookup/res?page=1&count=5
Res: 2.05 Content
<coap://[2001:db8:3::123]:61616/res/5>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/6>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/7>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/8>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616",
<coap://[2001:db8:3::123]:61616/res/9>;rt=sensor;ct=60;
anchor="coap://[2001:db8:3::123]:61616"
The following example shows a client performing a lookup of all
resources from endpoints of all endpoints of a given endpoint type.
It assumes that two endpoints (with endpoint names "sensor1" and
"sensor2") have previously registered with their respective addresses
"coap://sensor1.example.com" and "coap://sensor2.example.com", and
posted the very payload of the 6th request of section 5 of [RFC6690].
It demonstrates how absolute link targets stay unmodified, while
relative ones are resolved:
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Req: GET /rd-lookup/res?et=oic.d.sensor
<coap://sensor1.example.com/sensors>;ct=40;title="Sensor Index";
anchor="coap://sensor1.example.com",
<coap://sensor1.example.com/sensors/temp>;rt="temperature-c";
if="sensor"; anchor="coap://sensor1.example.com",
<coap://sensor1.example.com/sensors/light>;rt="light-lux";
if="sensor"; anchor="coap://sensor1.example.com",
<http://www.example.com/sensors/t123>;rel="describedby";
anchor="coap://sensor1.example.com/sensors/temp",
<coap://sensor1.example.com/t>;rel="alternate";
anchor="coap://sensor1.example.com/sensors/temp",
<coap://sensor2.example.com/sensors>;ct=40;title="Sensor Index";
anchor="coap://sensor2.example.com",
<coap://sensor2.example.com/sensors/temp>;rt="temperature-c";
if="sensor"; anchor="coap://sensor2.example.com",
<coap://sensor2.example.com/sensors/light>;rt="light-lux";
if="sensor"; anchor="coap://sensor2.example.com",
<http://www.example.com/sensors/t123>;rel="describedby";
anchor="coap://sensor2.example.com/sensors/temp",
<coap://sensor2.example.com/t>;rel="alternate";
anchor="coap://sensor2.example.com/sensors/temp"
8. Security Considerations
The security considerations as described in Section 7 of [RFC5988]
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
described in [RFC7252]. DTLS or TLS based security SHOULD be used on
all resource directory interfaces defined in this document.
8.1. Endpoint Identification and Authentication
An Endpoint is determined to be unique within (the sector of) an RD
by the Endpoint identifier parameter included during Registration,
and any associated TLS or DTLS security bindings. An Endpoint MUST
NOT be identified by its protocol, port or IP address as these may
change over the lifetime of an Endpoint.
Every operation performed by an Endpoint or Client on a resource
directory SHOULD be mutually authenticated using Pre-Shared Key, Raw
Public Key or Certificate based security.
Consider the following threat: two devices A and B are managed by a
single server. Both devices have unique, per-device credentials for
use with DTLS to make sure that only parties with authorization to
access A or B can do so.
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Now, imagine that a malicious device A wants to sabotage the device
B. It uses its credentials during the DTLS exchange. Then, it puts
the endpoint name of device B. If the server does not check whether
the identifier provided in the DTLS handshake matches the identifier
used at the CoAP layer then it may be inclined to use the endpoint
name for looking up what information to provision to the malicious
device.
Section 9 specifies an example that removes this threat by using an
Authorization Server for endpoints that have a certificate installed.
8.2. Access Control
Access control SHOULD be performed separately for the RD
registration, Lookup, and group API paths, as different endpoints may
be authorized to register with an RD from those authorized to lookup
endpoints from the RD. Such access control SHOULD be performed in as
fine-grained a level as possible. For example access control for
lookups could be performed either at the sector, endpoint or resource
level.
8.3. Denial of Service Attacks
Services that run over UDP unprotected are vulnerable to unknowingly
become part of a DDoS attack as UDP does not require return
routability check. Therefore, an attacker can easily spoof the
source IP of the target entity and send requests to such a service
which would then respond to the target entity. This can be used for
large-scale DDoS attacks on the target. Especially, if the service
returns a response that is order of magnitudes larger than the
request, the situation becomes even worse as now the attack can be
amplified. DNS servers have been widely used for DDoS amplification
attacks. There is also a danger that NTP Servers could become
implicated in denial-of-service (DoS) attacks since they run on
unprotected UDP, there is no return routability check, and they can
have a large amplification factor. The responses from the NTP server
were found to be 19 times larger than the request. A Resource
Directory (RD) which responds to wild-card lookups is potentially
vulnerable if run with CoAP over UDP. Since there is no return
routability check and the responses can be significantly larger than
requests, RDs can unknowingly become part of a DDoS amplification
attack.
9. Authorization Server example
When threats may occur as described in Section 8.1, an Authorization
Server (AS) as specified in [I-D.ietf-ace-oauth-authz] can be used to
remove the threat. An authorized registry request to the Resource
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Directory (RD) is accompanied by an Access Token that validates the
access of the client to the RD. In this example, the contents of the
Access Token is specified by a CBOR Web Token (CWT) [RFC8392].
Selecting one of the scenarios of
[I-D.ietf-anima-bootstrapping-keyinfra], the registree-ep has a
certificate that has been inserted at manufacturing time. The
contents of the certificate will be used to generate the unique
endpoint name. The certificate is uniquely identified by the
leftmost CNcomponent of the subject name appended with the serial
number. The unique certificate identifier is used as the unique
endpoint name. The same unique identification is used for the
registree-ep and the Commissioning Tool.
The case of using RPK or PSK is outside the scope of this example.
Figure 8 shows the example certificate used to specify the claim
values in the CWT. Serial number 01:02:03:04:05:06:07:08, and CN
field, Fairhair, in the subject field are concatenated to create a
unique certificate identifier: Fairhair-01:02:03:04:05:06:07:08,
which is used in Figure 9 and Figure 10 as "sub" claim and "epn"
claim values respectively.
Certificate: Data:
Version: 3 (0x2)
Serial Number: 01:02:03:04:05:06:07:08
Signature Algorithm: md5WithRSA
Encryption Issuer: C=US, ST=Florida, O=Acme, Inc., OU=Security,
CN=CA
Authority/emailAddress=ca@acme.com
Validity Not Before: Aug 20 12:59:55 2013 GMT
Not After : Aug 20 12:59:55 2013 GMT
Subject: C=US, ST=Florida, O=Acme, Inc., OU=Sales, CN=Fairhair
Subject Public Key
Info: Public Key Algorithm: rsaEncryption
RSA Public Key: (1024 bit) Modulus (1024 bit):
00:be:5e:6e:f8:2c:c7:8c:07:7e:f0:ab:a5:12:db:
fc:5a:1e:27:ba:49:b0:2c:e1:cb:4b:05:f2:23:09:
77:13:75:57:08:29:45:29:d0:db:8c:06:4b:c3:10:
88:e1:ba:5e:6f:1e:c0:2e:42:82:2b:e4:fa:ba:bc:
45:e9:98:f8:e9:00:84:60:53:a6:11:2e:18:39:6e:
ad:76:3e:75:8d:1e:b1:b2:1e:07:97:7f:49:31:35:
25:55:0a:28:11:20:a6:7d:85:76:f7:9f:c4:66:90:
e6:2d:ce:73:45:66:be:56:aa:ee:93:ae:10:f9:ba:
24:fe:38:d0:f0:23:d7:a1:3b
Exponent: 65537 (0x10001)
Figure 8: Sample X.509 version 3 certificate for Fairhair device
issued by the Acme corporation.
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Three sections for as many authorized RD registration scenarios
describe: (1) the registree-ep registers itself with the RD, (2) a
3rd party Commissioning Tool (CT) registers the registree-ep with the
RD, and (3) A client updates multiple links in an RD.
9.1. Registree-ep registers with RD
The registree-ep sends a Request to the RD accompanied by a CBOR Web
Token (CWT). To prevent ambiguities, the URI of the authorized
request cannot contain the ep= or the d= parameters which are
specified in the CWT. When these parameters are present in the URI,
the request is rejected with CoAP response code 4.00 (bad request).
The CWT of Figure 9 authorizes the registree-ep to register itself in
the RD by specifying the certificate identifier of the registree-ep
in the sub claim. The same value is assigned to the endpoint name of
the registree-ep in the RD.
The claim set of the CWT is represented in CBOR diagnostic notation
{
/iss/ 1: "coaps://as.example.com", / identifies the AS/
/sub/ 2: "Fairhair_01:02:03:04:05:06:07:08",
/ certificate identifier uniquely identifies registree-ep/
/aud/ 3: "coaps://rd.example.com" / audience is the RD/
}
Figure 9: Claim set of CWT for registering registree-ep
9.2. Third party Commissioning Tool (CT) registers registree-ep with
RD.
The CT sends a Request to the RD accompanied by a CBOR Web Token
(CWT). To prevent ambiguities, the URI of an authorized request
cannot contain the ep= or the d= parameters which are specified in
the CWT. When these parameters are present in the URI, the request
is rejected with CoAP response code 4.00 (bad request). The CWT of
Figure 10 authorizes the CT to register the registree-ep by
specifying the certificate identifier,
Fairhair_08:07:06:05:04:03:02:01, of the CT in the "sub" claim. Next
to the certificate identifier of the CT, the CWT needs to specify the
security identifier of the registree-ep. The new "rd_epn" claim is
used to specify the value of the certificate identifier
Fairhair_01:02:03:04:05:06:07:08, of the registree-ep. The CWT may
contain the optional new "rd_sct" claim to assign a sector name to
the registree-ep.
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The claim set is represented in CBOR diagnostic notation
{
/iss/ 1: "coaps://as.example.com", / identifies the AS/
/sub/ 2: "Fairhair_08:07:06:05:04:03:02:01",
/ certificate identifier uniquely identifies CT/
/aud/ 3: "coaps://rd.example.com", / audience is the RD/
/rd_epn/ y: "Fairhair_01:02:03:04:05:06:07:08",
/certificate identifier uniquely identifies registree-ep/
/rd_sct/ z: "my-devices" /optional sector name/
}
Figure 10: Claim set of CWT for registering registree-ep by CT
9.3. Updating multiple links
Appendix A.4 of RD specifies that multiple links can be updated with
a media format to be specified. The updating endpoint sends a
Request to the RD accompanied by a CWT. The "sub" claim of the CWT
contains the certificate identifier of the updating endpoint.
Updating registrations and links cannot not change or delete the
endpoint names. Consequently, the updating endpoint is authorized by
the CWT to change all links of its registrations but cannot delete or
add registrations. The CWT of Figure 9 and Figure 10 authorize an
updating registree-ep or an updating CT respectively.
10. IANA Considerations
10.1. Resource Types
IANA is asked to enter the following values into the Resource Type
(rt=) Link Target Attribute Values subregistry of the Constrained
Restful Environments (CoRE) Parameters registry defined in [RFC6690]:
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+--------------------+----------------------------+-----------------+
| Value | Description | Reference |
+--------------------+----------------------------+-----------------+
| core.rd | Directory resource of an | RFCTHIS Section |
| | RD | 5.2 |
| core.rd-group | Group directory resource | RFCTHIS Section |
| | of an RD | 5.2 |
| core.rd-lookup-res | Resource lookup of an RD | RFCTHIS Section |
| | | 5.2 |
| core.rd-lookup-ep | Endpoint lookup of an RD | RFCTHIS Section |
| | | 5.2 |
| core.rd-lookup-gp | Group lookup of an RD | RFCTHIS Section |
| | | 5.2 |
| core.rd-ep | Endpoint resource of an RD | RFCTHIS Section |
| | | 7 |
| core.rd-gp | Group resource of an RD | RFCTHIS Section |
| | | 7 |
+--------------------+----------------------------+-----------------+
10.2. IPv6 ND Resource Directory Address Option
This document registers one new ND option type under the subregistry
"IPv6 Neighbor Discovery Option Formats":
o Resource Directory address Option (38)
10.3. RD Parameter Registry
This specification defines a new sub-registry for registration and
lookup parameters called "RD Parameters" under "CoRE Parameters".
Although this specification defines a basic set of parameters, it is
expected that other standards that make use of this interface will
define new ones.
Each entry in the registry must include
o the human readable name of the parameter,
o the short name as used in query parameters or link attributes,
o indication of whether it can be passed as a query parameter at
registration of endpoints or groups, as a query parameter in
lookups, or be expressed as a link attribute,
o validity requirements if any, and
o a description.
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The query parameter MUST be both a valid URI query key [RFC3986] and
a parmname as used in [RFC5988].
The description must give details on which registrations they apply
to (Endpoint, group registrations or both? Can they be updated?),
and how they are to be processed in lookups.
The mechanisms around new RD parameters should be designed in such a
way that they tolerate RD implementations that are unaware of the
parameter and expose any parameter passed at registration or updates
on in endpoint lookups. (For example, if a parameter used at
registration were to be confidential, the registering endpoint should
be instructed to only set that parameter if the RD advertises support
for keeping it confidential at the discovery step.)
Initial entries in this sub-registry are as follows:
+--------------+-------+---------------+-----+----------------------+
| Full name | Short | Validity | Use | Description |
+--------------+-------+---------------+-----+----------------------+
| Endpoint | ep | | RLA | Name of the |
| Name | | | | endpoint, max 63 |
| | | | | bytes |
| Lifetime | lt | 60-4294967295 | R | Lifetime of the |
| | | | | registration in |
| | | | | seconds |
| Sector | d | | RLA | Sector to which this |
| | | | | endpoint belongs |
| Registration | base | URI | RLA | The scheme, address |
| Base URI | | | | and port and path at |
| | | | | which this server is |
| | | | | available |
| Group Name | gp | | RLA | Name of a group in |
| | | | | the RD |
| Page | page | Integer | L | Used for pagination |
| Count | count | Integer | L | Used for pagination |
| Endpoint | et | | RLA | Semantic name of the |
| Type | | | | endpoint (see |
| | | | | Section 10.4) |
+--------------+-------+---------------+-----+----------------------+
Table 2: RD Parameters
(Short: Short name used in query parameters or link attributes. Use:
R = used at registration, L = used at lookup, A = expressed in link
attribute
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The descriptions for the options defined in this document are only
summarized here. To which registrations they apply and when they are
to be shown is described in the respective sections of this document.
The IANA policy for future additions to the sub-registry is "Expert
Review" as described in [RFC8126]. The evaluation should consider
formal criteria, duplication of functionality (Is the new entry
redundant with an existing one?), topical suitability (Eg. is the
described property actually a property of the endpoint and not a
property of a particular resource, in which case it should go into
the payload of the registration and need not be registered?), and the
potential for conflict with commonly used link attributes (For
example, "if" could be used as a parameter for conditional
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
an "if" query parameter could ambiguously filter by the registered
endpoint property or the [RFC6690] link attribute). It is expected
that the registry will receive between 5 and 50 registrations in
total over the next years.
10.3.1. Full description of the "Endpoint Type" Registration Parameter
An endpoint registering at an RD can describe itself with endpoint
types, similar to how resources are described with Resource Types in
[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
subregistry. Endpoint types can be passed in the "et" query
parameter as part of extra-attrs at the Registration step, are shown
on endpoint lookups using the "et" target attribute, and can be
filtered for using "et" as a search criterion in resource and
endpoint lookup. Multiple endpoint types are given as separate query
parameters or link attributes.
Note that Endpoint Type differs from Resource Type in that it uses
multiple attributes rather than space separated values. As a result,
Resource Directory implementations automatically support correct
filtering in the lookup interfaces from the rules for unknown
endpoint attributes.
10.4. "Endpoint Type" (et=) RD Parameter values
This specification establishes a new sub-registry under "CoRE
Parameters" called '"Endpoint Type" (et=) RD Parameter values'. The
registry properties (required policy, requirements, template) are
identical to those of the Resource Type parameters in [RFC6690], in
short:
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The review policy is IETF Review for values starting with "core", and
Specification Required for others.
The requirements to be enforced are:
o The values MUST be related to the purpose described in
Section 10.3.1.
o The registered values MUST conform to the ABNF reg-rel-type
definition of [RFC6690] and MUST NOT be a URI.
o It is recommended to use the period "." character for
segmentation.
The registry is initially empty.
10.5. Multicast Address Registration
IANA has assigned the following multicast addresses for use by CoAP
nodes:
IPv4 - "all CoRE resource directories" address, from the "IPv4
Multicast Address Space Registry" equal to "All CoAP Nodes",
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
Block (224.0.1.x, RFC 5771).
IPv6 - "all CoRE resource directories" address MCD1 (suggestions
FF0X::FE), from the "IPv6 Multicast Address Space Registry", in the
"Variable Scope Multicast Addresses" space (RFC 3307). Note that
there is a distinct multicast address for each scope that interested
CoAP nodes should listen to; CoAP needs the Link-Local and Site-Local
scopes only.
10.6. CBOR Web Token claims
This specification registers the following new claims in the CBOR Web
Token (CWT) registry of CBOR Web Token Claims:
Claim "rd_epn"
o Claim Name: "rd_epn"
o Claim Description: The endpoint name of the RD entry as described
in Section 9 of RFCTHIS.
o JWT Claim Name: N/A
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o Claim Key: y
o Claim Value Type(s): 0 (uint), 2 (byte string), 3 (text string)
o Change Controller: IESG
o Specification Document(s): Section 9 of RFCTHIS
Claim "rd_sct"
o Claim Name: "rd_sct"
o Claim Description: The sector name of the RD entry as described in
Section 9 of RFCTHIS.
o JWT Claim Name: N/A
o Claim Key: z
o Claim Value Type(s): 0 (uint), 2 (byte string), 3 (text string)
o Change Controller: IESG
o Specification Document(s): Section 9 of RFCTHIS
Mapping of claim name to CWT key
+----------------+----------+-------------+
| Parameter name | CBOR key | Value type |
+----------------+----------+-------------+
| rd_epn | y | Text string |
| rd_sct | z | Text string |
+----------------+----------+-------------+
11. Examples
Two examples are presented: a Lighting Installation example in
Section 11.1 and a LWM2M example in Section 11.2.
11.1. Lighting Installation
This example shows a simplified lighting installation which makes use
of the Resource Directory (RD) with a CoAP interface to facilitate
the installation and start up of the application code in the lights
and sensors. In particular, the example leads to the definition of a
group and the enabling of the corresponding multicast address. No
conclusions must be drawn on the realization of actual installation
or naming procedures, because the example only "emphasizes" some of
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the issues that may influence the use of the RD and does not pretend
to be normative.
11.1.1. Installation Characteristics
The example assumes that the installation is managed. That means
that a Commissioning Tool (CT) is used to authorize the addition of
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
installation network, connected by WiFi to the installation network,
or connected via GPRS link, or other method.
It is assumed that there are two naming authorities for the
installation: (1) the network manager that is responsible for the
correct operation of the network and the connected interfaces, and
(2) the lighting manager that is responsible for the correct
functioning of networked lights and sensors. The result is the
existence of two naming schemes coming from the two managing
entities.
The example installation consists of one presence sensor, and two
luminaries, luminary1 and luminary2, each with their own wireless
interface. Each luminary contains three lamps: left, right and
middle. Each luminary is accessible through one endpoint. For each
lamp a resource exists to modify the settings of a lamp in a
luminary. The purpose of the installation is that the presence
sensor notifies the presence of persons to a group of lamps. The
group of lamps consists of: middle and left lamps of luminary1 and
right lamp of luminary2.
Before commissioning by the lighting manager, the network is
installed and access to the interfaces is proven to work by the
network manager.
At the moment of installation, the network under installation is not
necessarily connected to the DNS infra structure. Therefore, SLAAC
IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in
Table 3 below:
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+--------------------+----------------+
| Name | IPv6 address |
+--------------------+----------------+
| luminary1 | 2001:db8:4::1 |
| luminary2 | 2001:db8:4::2 |
| Presence sensor | 2001:db8:4::3 |
| Resource directory | 2001:db8:4::ff |
+--------------------+----------------+
Table 3: interface SLAAC addresses
In Section 11.1.2 the use of resource directory during installation
is presented.
11.1.2. RD entries
It is assumed that access to the DNS infrastructure is not always
possible during installation. Therefore, the SLAAC addresses are
used in this section.
For discovery, the resource types (rt) of the devices are important.
The lamps in the luminaries have rt: light, and the presence sensor
has rt: p-sensor. The endpoints have names which are relevant to the
light installation manager. In this case luminary1, luminary2, and
the presence sensor are located in room 2-4-015, where luminary1 is
located at the window and luminary2 and the presence sensor are
located at the door. The endpoint names reflect this physical
location. The middle, left and right lamps are accessed via path
/light/middle, /light/left, and /light/right respectively. The
identifiers relevant to the Resource Directory are shown in Table 4
below:
+----------------+------------------+---------------+---------------+
| Name | endpoint | resource path | resource type |
+----------------+------------------+---------------+---------------+
| luminary1 | lm_R2-4-015_wndw | /light/left | light |
| luminary1 | lm_R2-4-015_wndw | /light/middle | light |
| luminary1 | lm_R2-4-015_wndw | /light/right | light |
| luminary2 | lm_R2-4-015_door | /light/left | light |
| luminary2 | lm_R2-4-015_door | /light/middle | light |
| luminary2 | lm_R2-4-015_door | /light/right | light |
| Presence | ps_R2-4-015_door | /ps | p-sensor |
| sensor | | | |
+----------------+------------------+---------------+---------------+
Table 4: Resource Directory identifiers
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It is assumed that the CT knows the RD's address, and has performed
URI discovery on it that returned a response like the one in the
Section 5.2 example.
The CT inserts the endpoints of the luminaries and the sensor in the
RD using the registration base URI parameter (base) to specify the
interface address:
Req: POST coap://[2001:db8:4::ff]/rd
?ep=lm_R2-4-015_wndw&base=coap://[2001:db8:4::1]&d=R2-4-015
Payload:
</light/left>;rt="light",
</light/middle>;rt="light",
</light/right>;rt="light"
Res: 2.01 Created
Location-Path: /rd/4521
Req: POST coap://[2001:db8:4::ff]/rd
?ep=lm_R2-4-015_door&base=coap://[2001:db8:4::2]&d=R2-4-015
Payload:
</light/left>;rt="light",
</light/middle>;rt="light",
</light/right>;rt="light"
Res: 2.01 Created
Location-Path: /rd/4522
Req: POST coap://[2001:db8:4::ff]/rd
?ep=ps_R2-4-015_door&base=coap://[2001:db8:4::3]d&d=R2-4-015
Payload:
</ps>;rt="p-sensor"
Res: 2.01 Created
Location-Path: /rd/4523
The sector name d=R2-4-015 has been added for an efficient lookup
because filtering on "ep" name is more awkward. The same sector name
is communicated to the two luminaries and the presence sensor by the
CT.
The group is specified in the RD. The base parameter is set to the
site-local multicast address allocated to the group. In the POST in
the example below, these two endpoints and the endpoint of the
presence sensor are registered as members of the group.
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Req: POST coap://[2001:db8:4::ff]/rd-group
?gp=grp_R2-4-015&base=coap://[ff05::1]
Payload:
</rd/4521>,
</rd/4522>,
</rd/4523>
Res: 2.01 Created
Location-Path: /rd-group/501
After the filling of the RD by the CT, the application in the
luminaries can learn to which groups they belong, and enable their
interface for the multicast address.
The luminary, knowing its sector and own IPv6 address, looks up the
groups containing light resources it is assigned to:
Req: GET coap://[2001:db8:4::ff]/rd-lookup/gp
?d=R2-4-015&base=coap://[2001:db8:4::1]&rt=light
Res: 2.05 Content
</rd-group/501>;gp="grp_R2-4-015";base="coap://[ff05::1]"
From the returned base parameter value, the luminary learns the
multicast address of the multicast group.
Alternatively, the CT can communicate the multicast address directly
to the luminaries by using the "coap-group" resource specified in
[RFC7390].
Req: POST coap://[2001:db8:4::1]/coap-group
Content-Format: application/coap-group+json
Payload:
{ "a": "[ff05::1]", "n": "grp_R2-4-015"}
Res: 2.01 Created
Location-Path: /coap-group/1
Dependent on the situation, only the address, "a", or the name, "n",
is specified in the coap-group resource.
11.2. OMA Lightweight M2M (LWM2M) Example
This example shows how the OMA LWM2M specification makes use of
Resource Directory (RD).
OMA LWM2M is a profile for device services based on CoAP(OMA Name
Authority). LWM2M defines a simple object model and a number of
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abstract interfaces and operations for device management and device
service enablement.
An LWM2M server is an instance of an LWM2M middleware service layer,
containing a Resource Directory along with other LWM2M interfaces
defined by the LWM2M specification.
CoRE Resource Directory (RD) is used to provide the LWM2M
Registration interface.
LWM2M does not provide for registration sectors and does not
currently use the rd-group or rd-lookup interfaces.
The LWM2M specification describes a set of interfaces and a resource
model used between a LWM2M device and an LWM2M server. Other
interfaces, proxies, and applications are currently out of scope for
LWM2M.
The location of the LWM2M Server and RD URI path is provided by the
LWM2M Bootstrap process, so no dynamic discovery of the RD is used.
LWM2M Servers and endpoints are not required to implement the /.well-
known/core resource.
11.2.1. The LWM2M Object Model
The OMA LWM2M object model is based on a simple 2 level class
hierarchy consisting of Objects and Resources.
An LWM2M Resource is a REST endpoint, allowed to be a single value or
an array of values of the same data type.
An LWM2M Object is a resource template and container type that
encapsulates a set of related resources. An LWM2M Object represents
a specific type of information source; for example, there is a LWM2M
Device Management object that represents a network connection,
containing resources that represent individual properties like radio
signal strength.
Since there may potentially be more than one of a given type object,
for example more than one network connection, LWM2M defines instances
of objects that contain the resources that represent a specific
physical thing.
The URI template for LWM2M consists of a base URI followed by Object,
Instance, and Resource IDs:
{/base-uri}{/object-id}{/object-instance}{/resource-id}{/resource-
instance}
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The five variables given here are strings. base-uri can also have
the special value "undefined" (sometimes called "null" in RFC 6570).
Each of the variables object-instance, resource-id, and resource-
instance can be the special value "undefined" only if the values
behind it in this sequence also are "undefined". As a special case,
object-instance can be "empty" (which is different from "undefined")
if resource-id is not "undefined".
base-uri := Base URI for LWM2M resources or "undefined" for default
(empty) base URI
object-id := OMNA (OMA Name Authority) registered object ID (0-65535)
object-instance := Object instance identifier (0-65535) or
"undefined"/"empty" (see above)) to refer to all instances of an
object ID
resource-id := OMNA (OMA Name Authority) registered resource ID
(0-65535) or "undefined" to refer to all resources within an instance
resource-instance := Resource instance identifier or "undefined" to
refer to single instance of a resource
LWM2M IDs are 16 bit unsigned integers represented in decimal (no
leading zeroes except for the value 0) by URI format strings. For
example, a LWM2M URI might be:
/1/0/1
The base uri is empty, the Object ID is 1, the instance ID is 0, the
resource ID is 1, and the resource instance is "undefined". This
example URI points to internal resource 1, which represents the
registration lifetime configured, in instance 0 of a type 1 object
(LWM2M Server Object).
11.2.2. LWM2M Register Endpoint
LWM2M defines a registration interface based on the REST API,
described in Section 5. The RD registration URI path of the LWM2M
Resource Directory is specified to be "/rd".
LWM2M endpoints register object IDs, for example </1>, to indicate
that a particular object type is supported, and register object
instances, for example </1/0>, to indicate that a particular instance
of that object type exists.
Resources within the LWM2M object instance are not registered with
the RD, but may be discovered by reading the resource links from the
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object instance using GET with a CoAP Content-Format of application/
link-format. Resources may also be read as a structured object by
performing a GET to the object instance with a Content-Format of
senml+json.
When an LWM2M object or instance is registered, this indicates to the
LWM2M server that the object and its resources are available for
management and service enablement (REST API) operations.
LWM2M endpoints may use the following RD registration parameters as
defined in Table 2 :
ep - Endpoint Name
lt - registration lifetime
Endpoint Name, Lifetime, and LWM2M Version are mandatory parameters
for the register operation, all other registration parameters are
optional.
Additional optional LWM2M registration parameters are defined:
+-----------+-------+-------------------------------+---------------+
| Name | Query | Validity | Description |
+-----------+-------+-------------------------------+---------------+
| Binding | b | {"U",UQ","S","SQ","US","UQS"} | Available |
| Mode | | | Protocols |
| | | | |
| LWM2M | ver | 1.0 | Spec Version |
| Version | | | |
| | | | |
| SMS | sms | | MSISDN |
| Number | | | |
+-----------+-------+-------------------------------+---------------+
Table 5: LWM2M Additional Registration Parameters
The following RD registration parameters are not currently specified
for use in LWM2M:
et - Endpoint Type
base - Registration Base URI
The endpoint registration must include a payload containing links to
all supported objects and existing object instances, optionally
including the appropriate link-format relations.
Here is an example LWM2M registration payload:
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</1>,</1/0>,</3/0>,</5>
This link format payload indicates that object ID 1 (LWM2M Server
Object) is supported, with a single instance 0 existing, object ID 3
(LWM2M Device object) is supported, with a single instance 0
existing, and object 5 (LWM2M Firmware Object) is supported, with no
existing instances.
11.2.3. LWM2M Update Endpoint Registration
The LwM2M update is really very similar to the registration update as
described in Appendix A.1, with the only difference that there are
more parameters defined and available. All the parameters listed in
that section are also available with the initial registration but are
all optional:
lt - Registration Lifetime
b - Protocol Binding
sms - MSISDN
link payload - new or modified links
A Registration update is also specified to be used to update the
LWM2M server whenever the endpoint's UDP port or IP address are
changed.
11.2.4. LWM2M De-Register Endpoint
LWM2M allows for de-registration using the delete method on the
returned location from the initial registration operation. LWM2M de-
registration proceeds as described in Appendix A.2.
12. Acknowledgments
Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders
Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen,
Hannes Tschofenig, Sampo Ukkola, Linyi Tian, and Jan Newmarch have
provided helpful comments, discussions and ideas to improve and shape
this document. Zach would also like to thank his colleagues from the
EU FP7 SENSEI project, where many of the resource directory concepts
were originally developed.
13. Changelog
changes from -13 to -14
o Rename "registration context" to "registration base URI" (and
"con" to "base") and "domain" to "sector" (where the abbreviation
"d" stays for compatibility reasons)
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o Introduced resource types core.rd-ep and core.rd-gp
o Registration management moved to appendix A, including endpoint
and group lookup
o Minor editorial changes
* PATCH/iPATCH is clearly deferred to another document
* Recommend against query / fragment identifier in con=
* Interface description lists are described as illustrative
* Rewording of Simple Registration
o Simple registration carries no error information and succeeds
immediately (previously, sequence was unspecified)
o Lookup: href are matched against resolved values (previously, this
was unspecified)
o Lookup: lt are not exposed any more
o con/base: Paths are allowed
o Registration resource locations can not have query or fragment
parts
o Default life time extended to 25 hours
o clarified registration update rules
o lt-value semantics for lookup clarified.
o added template for simple registration
changes from -12 to -13
o Added "all resource directory" nodes MC address
o Clarified observation behavior
o version identification
o example rt= and et= values
o domain from figure 2
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o more explanatory text
o endpoints of a groups hosted by different RD
o resolve RFC6690-vs-8288 resolution ambiguities:
* require registered links not to be relative when using anchor
* return absolute URIs in resource lookup
changes from -11 to -12
o added Content Model section, including ER diagram
o removed domain lookup interface; domains are now plain attributes
of groups and endpoints
o updated chapter "Finding a Resource Directory"; now distinguishes
configuration-provided, network-provided and heuristic sources
o improved text on: atomicity, idempotency, lookup with multiple
parameters, endpoint removal, simple registration
o updated LWM2M description
o clarified where relative references are resolved, and how context
and anchor interact
o new appendix on the interaction with RFCs 6690, 5988 and 3986
o lookup interface: group and endpoint lookup return group and
registration resources as link targets
o lookup interface: search parameters work the same across all
entities
o removed all methods that modify links in an existing registration
(POST with payload, PATCH and iPATCH)
o removed plurality definition (was only needed for link
modification)
o enhanced IANA registry text
o state that lookup resources can be observable
o More examples and improved text
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changes from -09 to -10
o removed "ins" and "exp" link-format extensions.
o removed all text concerning DNS-SD.
o removed inconsistency in RDAO text.
o suggestions taken over from various sources
o replaced "Function Set" with "REST API", "base URI", "base path"
o moved simple registration to registration section
changes from -08 to -09
o clarified the "example use" of the base RD resource values /rd,
/rd-lookup, and /rd-group.
o changed "ins" ABNF notation.
o various editorial improvements, including in examples
o clarifications for RDAO
changes from -07 to -08
o removed link target value returned from domain and group lookup
types
o Maximum length of domain parameter 63 bytes for consistency with
group
o removed option for simple POST of link data, don't require a
.well-known/core resource to accept POST data and handle it in a
special way; we already have /rd for that
o add IPv6 ND Option for discovery of an RD
o clarify group configuration section 6.1 that endpoints must be
registered before including them in a group
o removed all superfluous client-server diagrams
o simplified lighting example
o introduced Commissioning Tool
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o RD-Look-up text is extended.
changes from -06 to -07
o added text in the discovery section to allow content format hints
to be exposed in the discovery link attributes
o editorial updates to section 9
o update author information
o minor text corrections
Changes from -05 to -06
o added note that the PATCH section is contingent on the progress of
the PATCH method
changes from -04 to -05
o added Update Endpoint Links using PATCH
o http access made explicit in interface specification
o Added http examples
Changes from -03 to -04:
o Added http response codes
o Clarified endpoint name usage
o Add application/link-format+cbor content-format
Changes from -02 to -03:
o Added an example for lighting and DNS integration
o Added an example for RD use in OMA LWM2M
o Added Read Links operation for link inspection by endpoints
o Expanded DNS-SD section
o Added draft authors Peter van der Stok and Michael Koster
Changes from -01 to -02:
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o Added a catalogue use case.
o Changed the registration update to a POST with optional link
format payload. Removed the endpoint type update from the update.
o Additional examples section added for more complex use cases.
o New DNS-SD mapping section.
o Added text on endpoint identification and authentication.
o Error code 4.04 added to Registration Update and Delete requests.
o Made 63 bytes a SHOULD rather than a MUST for endpoint name and
resource type parameters.
Changes from -00 to -01:
o Removed the ETag validation feature.
o Place holder for the DNS-SD mapping section.
o Explicitly disabled GET or POST on returned Location.
o New registry for RD parameters.
o Added support for the JSON Link Format.
o Added reference to the Groupcomm WG draft.
Changes from -05 to WG Document -00:
o Updated the version and date.
Changes from -04 to -05:
o Restricted Update to parameter updates.
o Added pagination support for the Lookup interface.
o Minor editing, bug fixes and reference updates.
o Added group support.
o Changed rt to et for the registration and update interface.
Changes from -03 to -04:
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o Added the ins= parameter back for the DNS-SD mapping.
o Integrated the Simple Directory Discovery from Carsten.
o Editorial improvements.
o Fixed the use of ETags.
o Fixed tickets 383 and 372
Changes from -02 to -03:
o Changed the endpoint name back to a single registration parameter
ep= and removed the h= and ins= parameters.
o Updated REST interface descriptions to use RFC6570 URI Template
format.
o Introduced an improved RD Lookup design as its own function set.
o Improved the security considerations section.
o Made the POST registration interface idempotent by requiring the
ep= parameter to be present.
Changes from -01 to -02:
o Added a terminology section.
o Changed the inclusion of an ETag in registration or update to a
MAY.
o Added the concept of an RD Domain and a registration parameter for
it.
o Recommended the Location returned from a registration to be
stable, allowing for endpoint and Domain information to be changed
during updates.
o Changed the lookup interface to accept endpoint and Domain as
query string parameters to control the scope of a lookup.
14. References
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14.1. 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
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<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.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<https://www.rfc-editor.org/info/rfc6763>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
14.2. Informative References
[ER] Chen, P., "The entity-relationship model---toward a
unified view of data", ACM Transactions on Database
Systems Vol. 1, pp. 9-36, DOI 10.1145/320434.320440, March
1976.
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[I-D.arkko-core-dev-urn]
Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource
Names for Device Identifiers", draft-arkko-core-dev-urn-05
(work in progress), October 2017.
[I-D.bormann-t2trg-rel-impl]
Bormann, C., "impl-info: A link relation type for
disclosing implementation information", draft-bormann-
t2trg-rel-impl-00 (work in progress), January 2018.
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-12
(work in progress), May 2018.
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., Bjarnason,
S., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-16 (work in progress), June 2018.
[I-D.silverajan-core-coap-protocol-negotiation]
Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation",
draft-silverajan-core-coap-protocol-negotiation-08 (work
in progress), March 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.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
the Constrained Application Protocol (CoAP)", RFC 7390,
DOI 10.17487/RFC7390, October 2014,
<https://www.rfc-editor.org/info/rfc7390>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
Appendix A. Registration Management
This section describes how the registering endpoint can maintain the
registries that it created. The registering endpoint can be the
registree-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 and
remove it from any group it belongs to. If the Registration Resource
is removed, the corresponding endpoint will need to be re-registered.
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The Registration Resource may also be used to inspect the
registration resource using GET, update the registration, cancel the
registration using DELETE, do an endpoint lookup, or a group 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 explicitly
or implicitly, relative references submitted in the original
registration or later updates are resolved anew against the new
context (like in the original registration).
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.
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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 context
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 links of the
registration, following the same restrictions as in the
registration. If the parameter is not set and was set
explicitly before, the previous Base URI value is kept
unmodified. If the parameter is not set and was not set
explicitly 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 excedes the remaining lifetime, the registering
endpoint SHOULD attempt registration again.
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The following example shows 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 context (con)=coap://local-proxy-old.example.com:5683
o payload of Figure 7
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:
<coap://local-proxy-old.example.com:5683/sensors/temp>;ct=41;
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"
The following example shows the registering endpoint changing the
context to "coaps://new.example.com:5684":
Req: POST /rd/4521?con=coaps://new.example.com:5684
Res: 2.04 Changed
The consecutive query returns:
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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",
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.
Removed registrations are implicitly removed from the groups to which
they belong.
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
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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.
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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 and group lookup
Endpoint and group lookups result in links to registration resources
and group resources, respectively. 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.
Group resources are annotated with their group names (gp), sector (d,
if present) and multicast address (base, if present) as well as a
constant resource type (rt="core.rd-gp").
Serializations derived from Link Format, SHOULD present links to
groups and endpoints in path-absolute form or, if required, as
absolute references. (This approach avoids the RFC6690 ambiguities.)
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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 or groups in lookup that
are not hosted at the same address. Lookup clients MUST be prepared
to see arbitrary URIs as registration or group resources in the
results and treat them as opaque identifiers; the precise semantics
of such links are left to future specifications.
For groups, a Resource Directory as specified here does not provide a
lookup mechanism for the resources that can be accessed on a group's
multicast address (ie. no lookup will return links like
"<coap://[ff35:30:2001:db8::1]/light>;..." for a group registered
with "base=coap://[ff35...]"). Such an additional lookup interface
could be specified in an extension document.
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",
</rd/4521>;base="coap://[2001:db8:3::129]:61616";ep="node7";
et="oic.d.sensor";ct="40";d="floor-3"
The following example shows a client performing a group lookup for
all groups:
Req: GET /rd-lookup/gp
Res: 2.05 Content
</rd-group/1>;gp="lights1";d="example.com";
base="coap://[ff35:30:2001:db8::1]",
</rd-group/2>;gp="lights2";d="example.com";
base="coap://[ff35:30:2001:db8::2]"
The following example shows a client performing a lookup for all
groups the endpoint "node1" belongs to:
Req: GET /rd-lookup/gp?ep=node1
Res: 2.05 Content
</rd-group/1>;gp="lights1"
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Appendix B. Web links and the Resource Directory
Understanding the semantics of a link-format document and its URI
references is a journey through different documents ([RFC3986]
defining URIs, [RFC6690] defining link-format documents based on
[RFC8288] which defines link headers, and [RFC7252] providing the
transport). This appendix summarizes the mechanisms and semantics at
play from an entry in ".well-known/core" to a resource lookup.
This text is primarily aimed at people entering the field of
Constrained Restful Environments from applications that previously
did not use web mechanisms.
B.1. A simple example
Let's start this example with a very simple host, "2001:db8:f0::1".
A client that follows classical CoAP Discovery ([RFC7252] Section 7),
sends the following multicast request to learn about neighbours
supporting resources with resource-type "temperature".
The client sends a link-local multicast:
GET coap://[ff02::fd]:5683/.well-known/core?rt=temperature
RES 2.05 Content
</temp>;rt=temperature;ct=0
where the response is sent by the server, "[2001:db8:f0::1]:5683".
While the client - on the practical or implementation side - can just
go ahead and create a new request to "[2001:db8:f0::1]:5683" with
Uri-Path: "temp", the full resolution steps without any shortcuts
are:
B.1.1. Resolving the URIs
The client parses the single returned record. The link's target
(sometimes called "href") is ""/temp"", which is a relative URI that
needs resolving. As long as all involved links follow the
restrictions set forth for this document (see Appendix B.4), the base
URI to resolve this against the requested URI.
The URI of the requested resource can be composed by following the
steps of [RFC7252] section 6.5 (with an addition at the end of 8.2)
into ""coap://[2001:db8:f0::1]/.well-known/core"".
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The record's target is resolved by replacing the path ""/.well-known/
core"" from the Base URI (section 5.2 [RFC3986]) with the relative
target URI ""/temp"" into ""coap://[2001:db8:f0::1]/temp"".
B.1.2. Interpreting attributes and relations
Some more information but the record's target can be obtained from
the payload: the resource type of the target is "temperature", and
its content type is text/plain (ct=0).
A relation in a web link is a three-part statement that the context
resource has a named relation to the target resource, like "_This
page_ has _its table of contents_ at _/toc.html_". In [RFC6690]
link-format documents, there is an implicit "host relation" specified
with default parameter: rel="hosts".
In our example, the context of the link is the URI of the requested
document itself. A 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]/temp", which is of the resource type
"temperature" and can be accessed using the text/plain content
format.'
B.2. A slightly more complex example
Omitting the "rt=temperature" filter, the discovery query would have
given some more records in the payload:
</temp>;rt=temperature;ct=0,
</light>;rt=light-lux;ct=0,
</t>;anchor="/sensors/temp";rel=alternate,
<http://www.example.com/sensors/t123>;anchor="/sensors/temp";
rel="describedby"
Parsing the third record, the client encounters the "anchor"
parameter. It is a URI relative to the document's Base URI and is
thus resolved to ""coap://[2001:db8:f0::1]/sensors/temp"". That is
the context resource of the link, so the "rel" statement is not about
the target and the document Base URI any more, but about the target
and that address.
Thus, the third record could be read as
""coap://[2001:db8:f0::1]/sensors/temp" has an alternate
representation at "coap://[2001:db8:f0::1]/t"".
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The fourth record can be read as ""coap://[2001:db8:f0::1]/sensors/
temp" is described by "http://www.example.com/sensors/t123"".
B.3. Enter the Resource Directory
The resource directory tries to carry the semantics obtainable by
classical CoAP discovery over to the resource lookup interface as
faithfully as possible.
For the following queries, we will assume that the simple host has
used Simple Registration to register at the resource directory that
was announced to it, sending this request from its UDP port
"[2001:db8:f0::1]:6553":
POST coap://[2001:db8:f01::ff]/.well-known/core?ep=simple-host1
The resource directory would have accepted the registration, and
queried the simple host's ".well-known/core" by itself. As a result,
the host is registered as an endpoint in the RD with the name
"simple-host1". The registration is active for 90000 seconds, and
the endpoint registration Base URI is ""coap://[2001:db8:f0::1]/""
because that is the address the registration was sent from (and no
explicit "con=" was given).
If the client now queries the RD as it would previously have issued a
multicast request, it would go through the RD discovery steps by
fetching "coap://[2001:db8:f0::ff]/.well-known/core?rt=core.rd-
lookup-res", obtain "coap://[2001:db8:f0::ff]/rd-lookup/res" as the
resource lookup endpoint, and issue a request to
"coap://[2001:db8:f0::ff]/rd-lookup/res?rt=temperature" to receive
the following data:
<coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0;
anchor="coap://[2001:db8:f0::1]"
This is not _literally_ the same response that it would have received
from a multicast request, but it would contain the (almost) same
statement:
'"coap://[2001:db8:f0::1]" is hosting the resource
"coap://[2001:db8:f0::1]/temp", which is of the resource type
"temperature" and can be accessed using the text/plain content
format.'
(The difference is whether "/" or "/.well-known/core" hosts the
resources, which is subject of ongoing discussion about RFC6690).
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To complete the examples, the client could also query all resources
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"
would return
<coap://[2001:db8:f0::1]/temp>;rt=temperature;ct=0;
anchor="coap://[2001:db8:f0::1]",
<coap://[2001:db8:f0::1]/light>;rt=light-lux;ct=0;
anchor="coap://[2001:db8:f0::1]",
<coap://[2001:db8:f0::1]/t>;
anchor="coap://[2001:db8:f0::1]/sensors/temp";rel=alternate,
<http://www.example.com/sensors/t123>;
anchor="coap://[2001:db8:f0::1]/sensors/temp";rel="describedby"
All the target and anchor references are already in absolute form
there, which don't need to be resolved any further.
Had the simple host registered with an explicit context (eg.
"?ep=simple-host1&con=coap+tcp://simple-host1.example.com"), that
context would have been used to resolve the relative anchor values
instead, giving
<coap+tcp://simple-host1.example.com/temp>;rt=temperature;ct=0;
anchor="coap+tcp://simple-host1.example.com"
and analogous records.
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
the same model of typed links, there are some differences between
[RFC6690] and [RFC5988], which are dealt with differently:
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
which the term inside the angle brackets (the target) is resolved,
falling back to the resource's URI with paths stripped off (its
"Origin"). [RFC8288] Section B.2 describes that the anchor is
immaterial to the resolution of the target reference.
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
off, while according to [RFC8288] Section 3.2, the context is the
resource's base URI.
In the context of a Resource Directory, the authors decided not to
not let this become an issue by requiring that RFC6690 links be
serialized in a way that either rule set can be applied and give
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the same results. Note that all examples of [RFC6690], [RFC8288]
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.
A link-format document is a UTF-8 encoded string of Unicode
characters and does not have percent encoding, while Link headers
are practically ASCII strings that use percent encoding for non-
ASCII characters, stating the encoding explicitly when required.
For example, while a Link header in a page about a Swedish city
might read
"Link: </temperature/Malm%C3%B6>;rel="live-environment-data""
a link-format document from the same source might describe the
link as
"</temperature/Malmoe>;rel="live-environment-data""
Parsers and producers of link-format and header data need to be
aware of this difference.
Appendix C. Syntax examples for Protocol Negotiation
[ 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":
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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";con="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. If it is a relative reference, it is
resolved against the base URI of the document.
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o The context of the link is expressed by the "anchor" parameter; if
it is a relative reference, it is resolved against the document's
base URI. In absence of the "anchor" attribute, the base URI is
the link's context.
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 (eg. 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, ie. 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 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""
Authors' Addresses
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Zach Shelby
ARM
150 Rose Orchard
San Jose 95134
USA
Phone: +1-408-203-9434
Email: zach.shelby@arm.com
Michael Koster
SmartThings
665 Clyde Avenue
Mountain View 94043
USA
Phone: +1-707-502-5136
Email: Michael.Koster@smartthings.com
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
Peter van der Stok
consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
Christian Amsuess (editor)
Hollandstr. 12/4
1020
Austria
Phone: +43-664-9790639
Email: christian@amsuess.com
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