wdiff draft-ietf-core-resource-directory-09.txt draft-ietf-core-resource-directory-10.txt

CoRE Z. Shelby
Internet-Draft ARM
Intended status: Standards Track M. Koster
Expires: May 4, September 14, 2017 SmartThings
C. Bormann
Universitaet Bremen TZI
P. van der Stok
consultant
October 31, 2016
March 13, 2017

CoRE Resource Directory
draft-ietf-core-resource-directory-09
draft-ietf-core-resource-directory-10

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 http://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 May 4, September 14, 2017.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 5
3.1. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 6
3.2. Use Case: Home and Building Automation . . . . . . . . . 7
3.3. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 7
4. Finding a Resource Directory Server . . . . . . . . . . . . . . . . . 8
4.1. Resource Directory Address Option (RDAO) . . . . . . . . 9
5. Simple Registration Resource Directory . . . . . . . . . . . . . . . . . . . . . 10
5.1. Simple publishing to Resource Directory Server Content Formats . . . . . 11
5.2. Third-party registration . . . . . . . . . . . . . . . . 12
6. Resource Directory Function Set 11
5.2. Base URI Discovery . . . . . . . . . . . . . . . . 12
6.1. Content Formats . . . 11
5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 13
6.2. Discovery
5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 16
5.3.2. Simple publishing to Resource Directory Server . . . 17
5.3.3. Third-party registration . . . . 13
6.3. Registration . . . . . . . . . . 17
5.3.4. Plurality of link references in a Registration . . . 18
5.4. Operations on the Registration Resource . . . . . . . . . 15
6.4. 18
5.4.1. Registration Update . . . . . . . . . . . . . . . . . . . 18
6.5. 19
5.4.2. Registration Removal . . . . . . . . . . . . . . . . . . 20
6.6. 21
5.4.3. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 21
6.7. 22
5.4.4. Update Endpoint Links . . . . . . . . . . . . . . . . 23
6. RD Groups . . 22
7. Group Function Set . . . . . . . . . . . . . . . . . . . . . 24
7.1. . . . 27
6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 24
7.2. 27
6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 26
8. 29
7. RD Lookup Function Set . . . . . . . . . . . . . . . . . . . 27
9. New Link-Format Attributes . . . . . . . . . 30
8. Security Considerations . . . . . . . . 32
9.1. Resource Instance attribute 'ins' . . . . . . . . . . . 35
8.1. Endpoint Identification and Authentication . 32
9.2. Export attribute 'exp' . . . . . . 35
8.2. Access Control . . . . . . . . . . . 33
10. DNS-SD Mapping . . . . . . . . . . 35
8.3. Denial of Service Attacks . . . . . . . . . . . . . 33
10.1. DNS-based Service discovery . . . 36
9. IANA Considerations . . . . . . . . . . . 33
10.2. mapping ins to <Instance> . . . . . . . . . . 36
9.1. Resource Types . . . . . 34
10.3. Mapping rt to <ServiceType> . . . . . . . . . . . . . . 35
10.4. Domain mapping . . 36
9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 36
9.3. RD Parameter Registry . . . . . . . . . . . 35
10.5. TXT Record key=value strings . . . . . . . 36
10. Examples . . . . . . . 35
10.6. Importing resource links into DNS-SD . . . . . . . . . . 36
11. Security Considerations . . . . . . . . . 37
10.1. Lighting Installation . . . . . . . . . . 37
11.1. Endpoint Identification and Authentication . . . . . . . 37
11.2. Access Control . .
10.1.1. Installation Characteristics . . . . . . . . . . . . 38
10.1.2. RD entries . . . . . . . 37
11.3. Denial of Service Attacks . . . . . . . . . . . . . . 39
10.2. OMA Lightweight M2M (LWM2M) Example . 37
12. IANA Considerations . . . . . . . . . 42
10.2.1. The LWM2M Object Model . . . . . . . . . . . . 38
12.1. Resource Types . . . 42
10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 44
10.2.3. LWM2M Update Endpoint Registration . . . . 38
12.2. Link Extension . . . . . 45
10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 46
11. Acknowledgments . . . 38
12.3. IPv6 ND Resource Directory Address Option . . . . . . . 38
12.4. RD Parameter Registry . . . . . . . . . . . . . 46
12. Changelog . . . . 38
13. Examples . . . . . . . . . . . . . . . . . . . . . . 46
13. References . . . . 39
13.1. Lighting Installation . . . . . . . . . . . . . . . . . 39
13.1.1. Installation Characteristics . . . . . . . . . . . . 40
13.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 41
13.1.3. DNS entries . . . . . . . . . . . . . . . . . . . . 44
13.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 44
13.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 45
13.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 46
13.2.3. Alternate Base URI . . . . . . . . . . . . . . . . . 48
13.2.4. LWM2M Update Endpoint Registration . . . . . . . . . 48
13.2.5. LWM2M De-Register Endpoint . . . . . . . . . . . . . 48
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48
15. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 49
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
16.1. 50
13.1. Normative References . . . . . . . . . . . . . . . . . . 52
16.2. 50
13.2. Informative References . . . . . . . . . . . . . . . . . 53 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54 51

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 requesting "/.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 [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:

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.

Domain
In the context of a Resource Directory, a domain is a logical
grouping of endpoints. This specification assumes that the list
of Domains supported by an RD is pre-configured by that RD. When
a domain is exported to DNS, the domain value equates to the DNS
domain name.

Group
In the context of a Resource Directory, a group is a logical
grouping of endpoints for the purpose of group communications.
All groups within a domain are unique.

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 is unique within
the associated domain of the registration.

Commissioning Tool
Commissioning Tool (CT) is

Context
When registering links to a device that assists during Resource Directory, the
installation of Context refers
to the scheme, address, port, and base path for all the links
registered on behalf of an endpoint, of the general form
scheme://host:port/path/ where the client may explicitly set the
scheme and host, and may supply the port and path as optional
parameters. When the context of a registration is explicitly set,
the URI resolution rules in [RFC3986] MUST be applied.

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.

RDAO
Resource Directory Address Option.

3. Architecture and Use Cases

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 (called Context), thus 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 Domains. The domain an endpoint is associated with can
be defined by the RD or configured by an outside entity. This
information hierarchy is shown in Figure 2.

Endpoints are assumed

A mechanism to discover an RD using CoRE Link Format [RFC6690] is
defined.

Endpoints proactively register and maintain resource directory
registration entries on the RD, which are soft state and need to be
periodically refreshed.

An endpoint is provided with interfaces to register, update and
remove a resource directory registration entry. Furthermore,
a mechanism to discover an RD using the CoRE Link Format [RFC6690] is
defined. It is also possible
for an RD to proactively discover fetch Web Links from endpoints and add them as resource
directory 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 the registration
entry.

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.

Figure 2: The resource directory information hierarchy.

3.1. 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
air interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing short
and wide range wireless interfaces. From the system design 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.

In a typical scenario, during a boot-up procedure (and periodically
afterwards), the machines (endpoints) register with a Resource
Directory (for example EPs installed on vehicles enabling tracking of
their position for fleet management purposes and monitoring
environment parameters) hosted by the mobile operator or somewhere
else in the network, periodically a description of its own
capabilities. Due to the usual network configuration of mobile
networks, the EPs attached to the mobile network may not always be
efficiently reachable. Therefore, a remote server is usually used to
provide proxy access to the EPs. The address of each (proxy)
endpoint on this server is included in the resource description
stored in the RD. The users, for example mobile applications for
environment monitoring, contact the RD, look up the endpoints capable
of providing information about the environment using 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.

3.2. 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.

The exporting of resource information to other discovery systems is
also important in these automation applications. In home automation
there is a need to interact with other consumer electronics, which
may already support DNS-SD, and in building automation DNS-SD in
combination with resource directories can cover multiple buildings.

3.3. 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.

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 the Resource
Directory lookup function set 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 compatible representations web link formats like [RFC6690] are supplied by Resource
Directories, which may be internally stored as triples, or
relation/attribute relation/
attribute pairs providing metadata about resource links. External
catalogs 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 domains 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. Resource groups may defined to allow
batched reads from multiple resources.

4. Finding a Resource Directory Server

Several mechanisms can be employed for discovering the RD, including
assuming a default location (e.g. on an Edge Router in a LoWPAN),
assigning an anycast address to the RD, using DHCP, or discovering
the RD using .well-known/core and hyperlinks as specified in CoRE
Link Format [RFC6690]. Endpoints that want to contact a directory server Resource
Directory can obtain candidate IP addresses for such servers in a
number of ways.

In a 6LoWPAN, good candidates can be taken from:

o specific static configuration (e.g., anycast addresses), if any,

o the ABRO option of 6LoWPAN-ND [RFC6775],

o other ND options that happen to point to servers (such as RDNSS),

o DHCPv6 options that might be defined later.

o The IPv6 Neighbor Discovery Resource Directory Address Option
described in Section 4.1

In networks with more inexpensive use of multicast, the candidate IP
address may be a well-known multicast address, i.e. directory servers
are found by simply sending GET requests to that well-known multicast
address (see Section 6.2).

As some of these sources are just (more or less 5.2).

Constrained nodes configured in large batches may be configured for
an anycast address for the RD. 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 RD
that is appropriate for the environment.

As some of these sources 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.

4.1. Resource Directory Address Option (RDAO)

The Resource Directory 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 link-local 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 lifetime 0x0 means that the RD address is invalid and to be
removed.

The RDAO format is:

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 set of border router information Resource Directory address is valid.
A value of all zero bits (0x0)
assumes a default value of 10,000
(~one week). 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 3: Resource Directory Address Option

5. Simple Registration

Not all endpoints hosting resources are expected to know how to
implement the Resource Directory Function Set (see Section 6) hence
cannot register with

This section defines the required set of REST interfaces between a
Resource Directory. Instead, simple endpoints
can implement the generic Simple Directory Discovery approach
described (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. section, both CoAP response codes (with dot
notation) and HTTP response codes (without dot notation) are shown.

An RD implementing this specification MUST implement Simple support the discovery,
registration, update, lookup, and removal interfaces defined in this
section.

5.1. Content Formats

Resource Directory Discovery. However, there may be
security reasons why implementations using this form of directory discovery would be
disabled.

This approach requires that specification MUST
support the endpoint makes available 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 hosted
resources that it wants to be discovered, as links on its "/.well-
known/core" interface as specified in [RFC6690].

The application/link-format content format.

5.2. Base URI Discovery

Before an endpoint then finds one or more addresses can make use of an RD, it must first know the directory server
as described in Section 4.

An endpoint can send (a selection of) hosted resources to a directory
server for publication as described in Section 5.1.

The directory server integrates RD's
address and port, and the base URI information it received this way
into for its resource directory. It MAY make REST API.
This section defines discovery of the information 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 RD and its base URI using the scope
well-known interface of this document.

5.1. Simple publishing to Resource Directory Server

An endpoint the CoRE Link Format [RFC6690]. It is
however expected that wants to make itself RDs will also be discoverable occasionally sends via other methods
depending on the deployment.

Discovery of the RD base URI is performed by sending either a POST
multicast or unicast GET request to the "/.well-known/core" URI of any candidate
directory server that it finds. The body of and including
a Resource Type (rt) parameter [RFC6690] with the POST request is
empty, which triggers value "core.rd" in
the resource directory server query string. Likewise, a Resource Type parameter value of
"core.rd-lookup*" is used to perform GET
requests at discover the requesting server's default discovery base URI for RD Lookup
operations, and "core.gp" is used to obtain discover the link-format payload to register.

The endpoint MAY include registration parameters in base URI for RD
Group operations. Upon success, the POST request
as per Section 6.3.

The following example shows an endpoint using simple publishing, by
simply sending an empty POST to response will contain a resource directory.

Req:(to RD server from [ff02::1])
POST coap://rd.example.com/.well-known/core?lt=6000

Content-Format: 40

payload:

(empty payload)

Res: 2.04 Changed

(later)

Req: (from RD server to [ff02::1])
GET coap://[ff02::1]/.well-known/core

Accept: 40

Res: 2.05 Content

payload:

</sen/temp>

5.2. Third-party registration

For some applications, even Simple Directory Discovery may be too
taxing payload
with a link format entry for certain very constrained devices, in particular if each RD function discovered, indicating
the
security requirements become too onerous.

In a controlled environment (e.g. building control), base URI of the Resource
Directory can be filled by a third device, called a commissioning
tool. The commissioning tool can fill RD function returned and the corresponding
Resource Directory from a
database or other means. For that purpose Type. When performing multicast discovery, the scheme, multicast IP
address and
port of used will depend on the registered device is indicated in scope required and the Context parameter multicast
capabilities of the registration described in Section 6.3.

6. network.

A Resource Directory Function Set

This section defines MAY provide hints about the REST interfaces between an RD and endpoints,
which is called content-formats it
supports in the Resource Directory Function Set. Although links it exposes or registers, using the
examples throughout this section assume "ct" link
attribute, as shown in the example below. Clients MAY use of CoAP [RFC7252], these REST interfaces
hints to select alternate content-formats for interaction with the
Resource Directory.

HTTP does not support multicast and consequently only unicast
discovery can also be realized supported using HTTP [RFC7230]. In
all definitions HTTP. Links to Resource Directories
MAY be registered in this section, both CoAP response codes (with dot
notation) other Resource Directories, and HTTP response codes (without dot notation) are shown. well-known entry
points SHOULD be provided to enable the bootstrapping of unicast
discovery.

An RD implementing implementation of this specification MUST support query
filtering for the discovery,
registration, update, lookup, and removal interfaces rt parameter as defined in this
section.

Resource directory entries are designed to be easily exported to
other [RFC6690].

The discovery mechanisms such request interface is specified as DNS-SD. For that reason,
parameters that would meaningfully be mapped to DNS SHOULD be limited
to a maximum length of 63 bytes.

6.1. Content Formats

Resource Directory implementations using this specification MUST
support the application/link-format content format (ct=40). follows:

Interaction: EP -> RD

Method: GET

URI Template: /.well-known/core{?rt}

URI Template Variables:

rt := Resource Directories implementing this specification Type (optional). MAY support
additional content formats.

Any additional content format supported by a Resource Directory
implementing this specification MUST have an equivalent serialization
in contain one of the values
"core.rd", "core.rd-lookup*", "core.rd-lookup-d", "core.rd-
lookup-res", "core.rd-lookup-ep", "core.rd-lookup-gp",
"core.rd-group" or "core.rd*"

Content-Format: application/link-format content format.

6.2. Discovery

Before an endpoint can make use of (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" with an RD, it must first know the RD's
address and port, and the path of its RD Function Set. There can be
several mechanisms application/link-format,
application/link-format+json, or application/link-format+cbor
payload containing one or more matching entries for discovering the RD including assuming
resource.

Failure: 4.04 "Not Found" is returned in case no matching entry is
found for a
default location (e.g. on an Edge Router unicast request.

Failure: 4.00 "Bad Request" is returned in case of a LoWPAN), by assigning
an anycast address malformed
request for a unicast request.

Failure: No error response to the RD, using DHCP, or by a multicast request.

HTTP support : YES (Unicast only)

The following example shows an endpoint discovering the an RD using this
interface, thus learning that the CoRE Link Format (see also Section 4). This section
defines discovery of the base RD using resource is, in this
example, at /rd and that the well-known interface of content-format delivered by the
CoRE Link Format [RFC6690] as server
hosting the required mechanism. It resource is however
expected application/link-format (ct=40). Note that RDs will also be discoverable via other methods
depending on the deployment.

Discovery of
it is up to the RD function set to choose its base RD resource, although
diagnostics and debugging is performed facilitated by sending either a
multicast or unicast using the base paths
specified here where possible.

Req: GET coap://[ff02::1]/.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-group>;rt="core.rd-group";ct=40

The following example shows the way of indicating that a client may
request to "/.well-known/core" and including alternate content-formats. The Content-Format code attribute
"ct" MAY include a Resource Type (rt) parameter [RFC6690] with the value "core.rd" space-separated sequence of Content-Format codes
as specified in
the query string. Likewise, a Resource Type parameter value Section 7.2.1 of
"core.rd-lookup" is used to discover the RD Lookup Function Set.
Upon success, [RFC7252], indicating that multiple
content-formats are available. The example below shows the response will contain a payload with required
Content-Format 40 (application/link-format) indicated as well as a link
more application-specific content format
entry for each RD discovered, with the URL indicating (picked as 65225 in this
example; this is in the root experimental space, not an assigned value).
The base RD resource of the RD. When performing multicast discovery, the
multicast IP address used will depend on the scope required values /rd, /rd-lookup, and /rd-group are
example values.

Req: GET coap://[ff02::1]/.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 65225",
</rd-lookup/ep>;rt="core.rd-lookup-ep";ct="40 65225",
</rd-group>;rt="core.rd-group";ct="40 65225"

5.3. Registration

After discovering the
multicast capabilities location of the network.

A Resource Directory an RD, an endpoint MAY provide hints about register its
resources using the content-formats it
supports in registration interface. This interface accepts a
POST from an endpoint containing the links it exposes or registers, using list of resources to be added to
the "ct" link
attribute, directory as shown the message payload in the example below. Clients MAY use these
hints to select alternate content-formats for interaction 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
Resource Directory.

HTTP does not support multicast name of the endpoint, and consequently only unicast
discovery can be supported using HTTP. Links to Resource Directories
MAY be registered in other Resource Directories, optionally its domain and well-known entry
points SHOULD be provided to enable the bootstrapping lifetime
of unicast
discovery.

An the registration. It is expected that other specifications will
define further parameters (see Section 9.3). The RD implementation of this specification then creates a
new registration resource in the RD and returns its location. An
endpoint MUST support query
filtering use that location when refreshing registrations using
this interface. Endpoint resources in the RD are kept active for the rt parameter as defined in [RFC6690].
period indicated by the lifetime parameter. The discovery request interface endpoint is specified as follows:

Interaction: EP -> RD

Method: GET

URI Template: /.well-known/core{?rt}

URI Template Variables:

rt := Resource Type (optional). MAY contain one or more of
responsible for refreshing the
values "core.rd", "core.rd-lookup", "core.rd-group" entry within this period using either
the registration 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) update interface. The following response codes are defined for this interface:

Success: 2.05 "Content" registration interface
MUST be implemented to be idempotent, so that registering twice with
the same endpoint parameters ep and d does not create multiple RD
entries. A new registration may be created at any time to supersede
an application/link-format,
application/link-format+json, or application/link-format+cbor
payload containing one or more matching entries for existing registration, replacing the registration parameters and
links.

The registration request interface is specified as follows:

Interaction: EP -> RD
resource.

Failure: 4.04 "Not Found"

Method: POST

URI Template: /{+rd}{?ep,d,et,lt,con}

URI Template Variables:

rd := RD Base URI path (mandatory). This is returned in case no matching entry the path of the RD,
as obtained from discovery. The value "rd" is
found recommended for a unicast request.

Failure: 4.00 "Bad Request"
this variable.

ep := Endpoint name (mandatory). The endpoint name is returned in case of a malformed
request for a unicast request.

Failure: No error response to an
identifier that MUST be unique within a multicast request.

HTTP support : YES (Unicast only) domain. The following example shows an maximum
length of this parameter is 63 bytes.

d := Domain (optional). The domain to which this endpoint discovering an RD using
belongs. The maximum length of this
interface, thus learning that parameter is 63 bytes.
When this parameter is elided, the base RD resource is, in this
example, at /rd and that MAY associate the content_format delivered by
endpoint with a configured default domain.

et := Endpoint Type (optional). The semantic type of the server
hosting
endpoint. This parameter SHOULD be less than 63 bytes.

lt := Lifetime (optional). Lifetime of the resource registration in
seconds. Range of 60-4294967295. If no lifetime is application.xml (ct=40). Note that it included
in the initial registration, a default value of 86400 (24
hours) SHOULD be assumed. If the lt parameter is up
to not included
in a registration refresh or update operation, the RD to choose its base RD resource, although diagnostics most
recently supplied value SHALL be re-used.

con := Context (optional). This parameter sets the scheme,
address and
debugging port at which this server is facilitated by using available in the base paths specified here where
possible.

Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*

Res: 2.05 Content
</rd>;rt="core.rd";ct=40,
</rd-lookup>;rt="core.rd-lookup";ct=40,
</rd-group>;rt="core.rd-group";ct=40

The following example shows form
scheme://host:port/path. In the way absence of indicating that a client may
request alternate content-formats. The Content-Format code attribute
"ct" MAY include a space-separated sequence this parameter the
scheme of Content-Format codes
as specified in Section 7.2.1 the protocol, source address and source port of [RFC7252], indicating that multiple
content-formats the
register request are available. The example below shows assumed. This parameter is mandatory when
the required
Content-Format 40 (application/link-format) indicated as well as directory is filled by a
more application-specific content format (picked third party such as 65225 in this
example; this is in the experimental space, not an assigned value).
The base RD resource values /rd, /rd-lookup,
commissioning tool. When con is used, scheme and /rd-group host are
example values.

Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*

Res: 2.05 Content
</rd>;rt="core.rd";ct="40 65225",
</rd-lookup>;rt="core.rd-lookup";ct="40 65225",
</rd-group>;rt="core.rd-group";ct="40 65225"

6.3. Registration

After discovering
mandatory and port and path parameters are optional. If the location of an RD Function Set, an
endpoint MAY uses an ephemeral port to register its resources using with, it MUST
include the con: parameter in the registration interface. This
interface accepts to provide a POST from an
valid network path. If the endpoint containing which is located behind a
NAT gateway is registering with a Resource Directory which is
on the list network service side of
resources to be added to the directory as NAT gateway, the message payload endpoint
MUST use a persistent port for the outgoing registration in
order to provide 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 NAT gateway with query string parameters
indicating the name of the endpoint, its domain a valid network address
for replies and the lifetime of
the registration. All parameters except the endpoint name incoming requests.

Content-Format: application/link-format

Content-Format: application/link-format+json

Content-Format: application/link-format+cbor

The following response codes are
optional. It is expected that other specifications will define
further parameters (see Section 12.4). defined for this interface:

Success: 2.01 "Created" or 201 "Created". The RD then creates Location header
option MUST be included in the response when a new registration
resource or updates an existing resource in the RD and returns its
location. An endpoint is created. This Location MUST use that location when refreshing
registrations using this interface. Endpoint resources in be a stable identifier
generated by the RD are
kept active as it is used for the period indicated by the lifetime parameter. all subsequent operations on
this registration resource. The
endpoint registration resource location
thus returned is responsible for refreshing the entry within this period
using either purpose of updating the lifetime of the
registration or update interface. The registration
interface MUST be implemented to be idempotent, so that registering
twice with and for maintaining the same endpoint parameter does not create multiple RD
entries. A new registration may be created at any time to supersede
an existing registration, replacing content of the registration parameters registered
links, including updating and deleting links.

The registration request interface is specified as follows:

Interaction: EP -> RD

Method: POST

URI Template: /{+rd}{?ep,d,et,lt,con}

URI Template Variables:

rd := RD Function Set path (mandatory). This is

Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.

Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the path
registration content with links resulting in plurality of
references; see Section 5.3.4.

Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the
RD Function Set, as obtained from discovery. The value "rd" is
recommended for this variable.

ep := Endpoint name (mandatory). operation.

HTTP support: YES

The following example shows an endpoint with the name is an
identifier that MUST be unique within a domain. The maximum
length of this parameter is 63 bytes.

d := Domain (optional). The domain "node1"
registering two resources to which an RD using this endpoint
belongs. interface. The maximum length of this parameter is 63 bytes.
When this parameter
location "/rd" is elided, the RD MAY associate the
endpoint with a configured default domain. The domain an example value of an RD base location.

Req: POST coap://rd.example.com/rd?ep=node1
Content-Format: 40
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

Res: 2.01 Created
Location: /rd/4521

A Resource Directory may optionally support HTTP. Here is
needed to export the endpoint to DNS-SD (see Section 10).

et := Endpoint Type (optional). The semantic type of the
endpoint. This parameter SHOULD be less than 63 bytes.

lt := Lifetime (optional). Lifetime an example
of the same registration in
seconds. Range of 60-4294967295. If no lifetime is included,
a default value of 86400 (24 hours) SHOULD be assumed.

con := Context (optional). This parameter sets the scheme,
address and port at which this server is available in the form
scheme://host:port. In the absence of this parameter the
scheme of the protocol, source IP address and source port of
the register request are assumed. This parameter is mandatory operation above, when the directory is filled by a third party such as an
commissioning tool.

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 MUST
be included with the new resource entry for the endpoint. This
Location MUST be a stable identifier generated by the RD as it is
used for all subsequent operations on this registration. The
resource returned in the Location 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.

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 endpoint with the name "node1"
registering two resources to an RD done using this interface. The
location "/rd" is an example value of an RD base location.

Req: POST coap://rd.example.com/rd?ep=node1
Content-Format: 40
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

Res: 2.01 Created
Location: /rd/4521 HTTP.

Req: POST /rd?ep=node1 HTTP/1.1
Host : example.com
Content-Type: application/link-format
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

Res: 201 Created
Location: /rd/4521

6.4.

5.3.1. Simple Registration Update

The update interface is used by an

Not all endpoints hosting resources are expected to know how to
upload links to a 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 endpoint makes available the hosted
resources that it wants to refresh be discovered, as links on its "/.well-
known/core" interface as specified in [RFC6690].

The endpoint then finds one or update more addresses of the directory server
as described in Section 4.

An endpoint can send (a selection of) hosted resources to a directory
server for publication as described in Section 5.3.2.

The directory server integrates the information it received this way
into its
registration with an RD. To use resource directory. It MAY make the interface, information 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.

5.3.2. Simple publishing to Resource Directory Server

An endpoint that wants to make itself discoverable occasionally sends
a POST request to the "/.well-known/core" URI of any candidate
directory server that it finds. The body of the POST request is
empty, which triggers the resource returned in directory server to perform GET
requests at the Location option in requesting server's default discovery URI to obtain
the
response link-format payload to register.

The endpoint MUST include the first registration.

An update endpoint name and MAY update include the lifetime or context
registration parameters
"lt", "con" as d, lt, and et, in Section 6.3 ) if they have changed since the last POST request as per
Section 5.3.

The following example shows an endpoint using simple publishing, by
simply sending an empty POST to a resource directory.

Req:(to RD server from [ff02::1])
POST coap://rd.example.com/.well-known/core?lt=6000;ep=node1

Content-Format: 40

payload:

(empty payload)

Res: 2.04 Changed

(later)

Req: (from RD server to [ff02::1])
GET coap://[ff02::1]/.well-known/core

Accept: 40

Res: 2.05 Content

payload:

</sen/temp>

5.3.3. Third-party registration or update. Parameters that have not changed SHOULD NOT

For some applications, even Simple Directory Discovery may be included too
taxing for certain very constrained devices, in an update. Adding parameters that have not changed
increases particular if the size of
security requirements become too onerous.

In a controlled environment (e.g. building control), the message but does not have any other
implications. Parameters MUST Resource
Directory can be included as query parameters in an
update operation as in Section 6.3.

Upon receiving an update request, an RD MUST reset filled by a third device, called a commissioning
tool. The commissioning tool can fill the timeout for Resource Directory from a
database or other means. For that endpoint and update purpose the scheme, IP address and
port of the
endpoint, using the source address of the update, or the context
("con") parameter if present. If the lifetime parameter "lt" registered device is
included indicated in the received update request, the RD MUST update the
lifetime Context parameter
of the registration and set the timeout equal to the new
lifetime.

An update MAY optionally add or replace links for the endpoint by
including those links described in the payload Section 5.3.

5.3.4. Plurality of the update as link references in a CoRE Link
Format document. A Registration

Plurality of link references within a Registration (registration
resource) is replaced only if both the target URI an indication of some error condition and
relation type match.

In addition to the use should not be
allowed.

Plurality of POST, as described in this section, there
is an alternate way to add, replace, link references exists if, and delete only if, two or more
links using PATCH as
described in Section 6.7.

The update registration request interface is specified as follows:

Interaction: EP -> RD

Method: POST

URI Template: /{+location}{?lt,con}

URI Template Variables:

location := a Registration contain identical context, target, and
relation values. This is the Location path returned by condition would be likely to arise if there
were multiple co-ordinators or configuration tools, each with a
different set of configuration values for the RD as same resource.

A Resource Directory SHOULD reject a registration, or an operation on
a registration, which would result of in a successful earlier registration.

lt := Lifetime (optional). Lifetime plurality of link references
within the registration in
seconds. Range the context of 60-4294967295. If no lifetime the registration. There is included, no requirement
in this document for a default value resource directory to check for plurality of 86400 (24 hours)
reference between different registrations. Resource Directory
operations which are rejected due to reference plurality SHOULD be assumed.

con := Context (optional). This parameter sets
returned the scheme,
address and port at which this server "Conflict" code, indicating that there is available in someting wrong
with the form
scheme://host:port. Optional. In request.

5.4. Operations on the absence of this
parameter Registration Resource

After the scheme initial registration, an endpoint should retain the
returned location of the protocol, source IP address Registration Resource for further
operations, including refreshing the registration in order to extend
the lifetie and
source port used "keep-alive" the registration. If the lifetime of
the registration expires, the RD SHOULD NOT respond to register are assumed. This parameter is
compulsory when discovery
queries with information from the directory is filled by a third party such
as endpoint. The RD SHOULD continue
to provide access to the Registration Resource after a commissioning tool.

Content-Format: application/link-format (mandatory)

Content-Format: application/link-format+json (optional)

Content-Format: application/link-format+cbor (optional) registration
time-out occurs in order to enable the registering endpoint to
eventually refresh the registration. The following response codes are defined RD MAY eventually remove
the registration resource 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". purpose of resource recovery and
garbage collection. If the Registration does not
exist (e.g. Resource is removed, the
endpoint will need to re-register.

The Registration Resource may have expired).

Failure: 5.03 "Service Unavailable" also be used to inspect the
registration resource using GET, update the registration link
contents using PATCH, or 503 "Service Unavailable".
Service could not perform cancel the operation.

HTTP support: YES

The following example shows an endpoint updating its registration at
an RD using DELETE.

These operations are described in this interface section.

In accordance with Section 5.3.4, operations which would result in
plural link references within the example location value: /rd/4521.

Req: POST /rd/4521

Res: 2.04 Changed context of a registration resource
SHOULD be rejected using the "Conflict" result code.

5.4.1. Registration Update

The following example shows update interface is used by an endpoint updating to refresh or update its
registration with a new lifetime and context, changing an existing link, and
adding a new link using this interface with RD. To use the example location
value /rd/4521. With interface, the endpoint sends a
POST request to the initial registration resource returned in the client set Location
header option in the response returned from the intial registration
operation.

An update MAY update the
following values:

o lifetime (lt)=500

o or context (con)=coap://local-proxy-old.example.com:5683

o resource= </sensors/temp>;ct=41;rt="foobar";if="sensor"
Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683"
Content-Format: 40
Payload:
</sensors/temp>;ct=41;rt="temperature-f";if="sensor",
</sensors/door>;ct=41;rt="door";if="sensor"

Res: 2.04 Changed

6.5. Registration Removal

Although RD entries registration parameters
"lt", "con" as in Section 5.3 ) if the previous settings are to be
retained. Parameters that are not being changed changed SHOULD NOT
be included in an update. Adding parameters that have soft state and will eventually timeout after
their lifetime, 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.

Upon receiving an update request, an RD MUST reset the timeout for
that endpoint SHOULD explicitly remove its entry from and update the RD scheme, IP address and port of the
endpoint, using the source address of the update, or the context
("con") parameter if it knows it will no longer be available (for example on
shut-down). This present. If the lifetime parameter "lt" is accomplished using a removal interface on
included in the received update request, the RD
by performing a DELETE on MUST update the endpoint resource.

The removal request interface
lifetime of the registration and set the timeout equal to the new
lifetime. If the lifetime parameter is specified as follows:

Interaction: EP -> RD

Method: DELETE

URI Template: /{+location}

URI Template Variables:

location := This not included in the
registration update, the most recent setting is re-used for the Location path returned next
registration time-out period.

An update MAY optionally add or replace links for the endpoint by
including those links in the RD as a
result payload of the update as a successful earlier 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". Registration does not
exist (e.g. may have expired).

Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.

HTTP support: YES

The following examples shows successful removal CoRE Link
Format document. A link is replaced only if all of the endpoint from
the RD with example location target URI
and relation type (if present) and anchor value /rd/4521.

Req: DELETE /rd/4521

Res: 2.02 Deleted

6.6. Read Endpoint Links

Some endpoints may wish to manage their links (if present) match.

If the link payload is included, it SHOULD be checked for reference
plurality as a collection, described in Section 5.3.4 and
may need rejected with a
"Conflict" result if there are plural link references detected.

In addition to read the current set use of links POST, as described in order this section, there
is an alternate way to determine link
maintenance operations.

One or more add, replace, and delete links MAY be selected by using query filtering PATCH as
specified
described in [RFC6690] Section 4.1 5.4.4.

The read update registration request interface is specified as follows:

Interaction: EP -> RD

Method: GET POST
URI Template: /{+location}{?href,rel,rt,if,ct} /{+location}{?lt,con}

URI Template Variables:

location := This is the Location path returned by the RD as a
result of a successful earlier registration.

href,rel,rt,if,ct

lt := link relations and attributes specified in Lifetime (optional). Lifetime of the query registration in order to select particular links based on their
relations and attributes. "href" denotes the URI target
seconds. Range of 60-4294967295. If no lifetime is included,
the
link. See [RFC6690] Sec. 4.1

The following responses codes are defined for this interface:

Success: 2.05 "Content" or 200 "OK" upon success with an
"application/link-format", "application/link-format+cbor", previous last lifetime set on a previous update or
"application/link-format+json" payload. the
original registration (falling back to 86400) SHOULD be used.

con := Context (optional). This parameter sets the scheme,
address and port at which this server is available in the form
scheme://host:port/path. In the absence of this parameter the
scheme of the protocol, source address and source port of the
register request are assumed. This parameter is mandatory when
the directory is filled by a third party such as an
commissioning tool. When con is used, scheme and host are
mandatory and port and path parameters are optional.

Content-Format: application/link-format (mandatory)

Content-Format: application/link-format+json (optional)

Content-Format: application/link-format+cbor (optional)

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: 4.09 "Conflict" or 409 "Conflict". Attempt to update the
registration content with links resulting in plurality of
references; see Section 5.3.4.

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 example shows an endpoint links
from the RD, updating its registration at
an RD using this interface with the example location value value: /rd/4521.

Req: GET POST /rd/4521

Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

6.7. Update Endpoint Links

[This section will be removed before or as 2.04 Changed

The following example shows an endpoint updating its registration
with a result of new lifetime and context, changing an existing link, and
adding a working-
group last-call if the PATCH methods do not achieve the same level of
consensus as new link using this interface with the present document.]

A PATCH update adds, removes or changes links for example location
value /rd/4521. With the endpoint by
including link update information in initial registration the payload of client set the update as a
merge-patch+json format [RFC7396] document.

One or more links are selected for update by using query filtering as
specified in [RFC6690] Section 4.1

The query filter selects the links to be modified or deleted, by
matching the query parameter values to the values of the link
attributes.

When the query parameters are not present in the request, the payload
specifies links to be added to the target document. When the query
parameters are present, the attribute names
following values:

o lifetime (lt)=500

o context (con)=coap://local-proxy-old.example.com:5683

o resource= </sensors/temp>;ct=41;rt="foobar";if="sensor"

Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683"
Content-Format: 40
Payload:
</sensors/temp>;ct=41;rt="temperature-f";if="sensor",
</sensors/door>;ct=41;rt="door";if="sensor"

Res: 2.04 Changed

5.4.2. Registration Removal

Although RD entries have soft state and values in the query
parameters select one or more links on which to apply the PATCH
operation.

If will eventually timeout after
their lifetime, an attribute name specified in the PATCH document exists in any
the set of selected links, all occurrences of the attribute value in
the target document MUST be updated using the value endpoint SHOULD explicitly remove its entry from
the PATCH
payload. If the attribute name RD if it knows it will no longer be available (for example on
shut-down). This is not present in any selected links, accomplished using a removal interface on the attribute MUST be added to RD
by performing a DELETE on the links. endpoint resource.

The update removal request interface is specified as follows:

Interaction: EP -> RD

Method: PATCH DELETE

URI Template: /{+location}{?href,rel,rt,if,ct} /{+location}

URI Template Variables:

location := This is the Location path 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

Content-Format: application/merge-patch+json (mandatory)

The following response responses codes are defined for this interface:

Success: 2.04 "Changed" 0r 2.02 "Deleted" or 204 "No Content" in the update was
successfully processed. upon successful deletion

Failure: 4.00 "Bad Request" or 400 "Bad Request". request". Malformed
request.

Failure: 4.04 "Not Found" or 404 "Not Found". Registration resource 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 an shows successful removal of the endpoint adding </sensors/humid>,
modifying </sensors/temp>, and removing </sensors/light> links in RD
using from
the Update Endpoint Links function RD with the example location value /rd/4521.

The following example shows an EP adding the link </sensors/
humid>;ct=41;rt="humid-s";if="sensor" to the collection of links at
the location /rd/4521.

Req: PATCH DELETE /rd/4521

Payload:
[{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}]

Content-Format:
application/merge-patch+json

Res: 2.04 Changed

The following example shows an EP modifying all 2.02 Deleted

5.4.3. Read Endpoint Links

Some endpoints may wish to manage their links at the example
location /rd/4521 which are identified by href="/sensors/temp", from
the initial link-value of </sensors/temp>;rt="temperature" as a collection, and
may need to read the new
link-value </sensors/temp>;rt="temperature-c";if="sensor" by changing
the value current set of links stored in the registration
resource, in order to determine link attribute "rt" and adding the link attribute
if="sensor" 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 PATCH operation with the supplied merge-
patch+json document payload.

Req: PATCH /rd/4521?href="/sensors/temp"

Payload:
{"rt": "temperature-c", "if": "sensor"},

Content-Format:
application/merge-patch+json

Res: 2.04 Changed

This example shows Resource Directory SHOULD return an
empty payload.

The read request interface is specified as follows:

Interaction: EP removing all links at the example -> RD

Method: GET

URI Template: /{+location}{?href,rel,rt,if,ct}

URI Template Variables:

location
/rd/4521 which are identified by href="/sensors/light".

Req: PATCH /rd/4521?href="/sensors/light"

Payload:
{null}

Content-Format:
application/merge-patch+json

Res: 2.04 Changed

7. Group Function Set := This section defines a function set for is the creation of groups of
endpoints for Location path returned by the purpose of managing and looking up endpoints for
group operations. The group function set is similar to the resource
directory function set, in that a group may be created or removed.
However unlike an endpoint entry, a group entry consists RD as a
result of a list of
endpoints successful earlier registration.

href,rel,rt,if,ct := link relations 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.

7.1. 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 attributes specified in
the group query in order to create (or update), optionally the domain the group
belongs to, select particular links based on their
relations and optionally attributes. "href" denotes the multicast address URI target of the group.
link. See [RFC6690] Sec. 4.1

The
registration message includes the list of endpoints that belong to
that group.

All the endpoints in the group MUST be registered following responses codes are defined for this interface:

Success: 2.05 "Content" or 200 "OK" upon success with the RD before
registering a group. If an endpoint is
"application/link-format", "application/link-format+cbor", or
"application/link-format+json" payload.

Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.

Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not yet registered to
exist (e.g. may have expired).

Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the RD
before registering operation.

HTTP support: YES

The following examples show successful read of the group, endpoint links
from the registration message returns an
error. The RD sends a blank target URI RD, with example location value /rd/4521.

Req: GET /rd/4521

Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

5.4.4. Update Endpoint Links

A PATCH update adds, removes or changes links for every the endpoint by
including link when
registering update information in the group.

Configuration payload of the endpoints themselves is out of scope of this
specification. Such an interface update as a
merge-patch+json format [RFC7396] document.

Other PATCH document formats may be used as appropriate for managing patching
the group membership array 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,con}

URI Template Variables:

rd-group := RD Group Function Set path (mandatory). This is the
path objects format of a Registration Resource. In
particular, a select-merge patch document format could combine the RD Group Function Set. The value "rd-group" is
recommended
function of link selection query and link attribute replacement
values.

One or more links are selected for this variable.

gp := Group Name (mandatory). update by using query filtering as
specified in [RFC6690] Section 4.1
The name of query filter selects the group links to be
created modified or replaced, unique within that domain. The maximum
length of this deleted, by
matching the query parameter is 63 bytes.

d := Domain (optional). The domain values to which this group belongs.
The maximum length the values of this parameter is 63 bytes. Optional. the link
attributes.

When this parameter is elided, the RD MAY associate query parameters are not present in the
endpoint with a configured default domain. The domain value is
needed to export request, the endpoint payload
specifies links to DNS-SD (see Section 10)

con := Context (optional). This parameter is used be added to set the IP
multicast address at target document. When the query
parameters are present, the attribute names and values in the query
parameters select one or more links on which this server to apply the PATCH
operation.

If no links are selected by the query parameters, the PATCH operation
SHOULD NOT update the state of any resource, and SHOULD return a
reply of "Changed".

If an attribute name specified in the PATCH document exists in any
the set of selected links, all occurrences of the attribute value in
the target document MUST be updated using the value from the PATCH
payload. If the attribute name is available not present in any selected links,
the form
scheme://multicast-address:port. Optional. In attribute MUST be added to the absence links.

If the PATCH payload contains plural link references, or processing
the PATCH payload would result in plural link references, the request
SHOULD be rejected with a "Conflict" result.

If the PATCH payload results in the modification of
this parameter no multicast address link target,
context, or relation values, that is "href", "rel", or "anchor", the
request SHOULD be rejected with a "Conflict" result code.

The update request interface is configured. specified as follows:

Interaction: EP -> RD

Method: PATCH

URI Template: /{+location}{?href,rel,rt,if,ct}

URI Template Variables:

location := This
parameter is compulsory when the directory is filled Location path returned by the RD as a
commissioning tool.

Content-Format: application/link-format

Content-Format: application/link-format+json
result of a successful earlier registration.

Content-Format: application/link-format+cbor application/merge-patch+json (mandatory)
The following response codes are defined for this interface:

Success: 2.01 "Created" or 201 "Created". The Location header MUST
be included with the new group entry. This Location MUST be a
stable identifier generated by 2.04 "Changed" 0r 204 "No Content" in the RD as it is used for delete
operations on this registration. update was
successfully processed.

Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.

Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is Registration resource
does not
registered in the RD exist (e.g. may have expired).

Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the
registration content with links resulting in plurality of
references; see Section 5.3.4.

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 to examples show an endpoint adding </sensors/humid>,
modifying </sensors/temp>, and removing </sensors/light> links in RD
using this interface. The
base the Update Endpoint Links function with the example location
value /rd-group is an /rd/4521.

The Registration Resource initial state is:

Req: GET /rd/4521

Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature",
</sensors/light>;ct=41;rt="light-lux";if="sensor"

The following example of shows an RD base location. EP adding the link </sensors/
humid>;ct=41;rt="humid-s";if="sensor" to the collection of links at
the location /rd/4521.

Req: POST coap://rd.example.com/rd-group?gp=lights
Content-Format: 40 PATCH /rd/4521

Payload:
<>;ep="node1",
<>;ep="node2"
[{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}]

Content-Format:
application/merge-patch+json

Res: 2.01 Created
Location: /rd-group/12 2.04 Changed
Req: POST /rd-group?gp=lights HTTP/1.1
Host: example.com
Content-Type: application/link-format
Payload:
<>;ep="node1",
<>;ep="node2" GET /rd/4521

Res: 201 Created
Location: /rd-group/12

7.2. Group Removal

A group can be removed simply by sending a removal message to 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature",
</sensors/light>;ct=41;rt="light-lux";if="sensor",
</sensors/humid>;ct=41;rt="humid-s";if="sensor"

The following example shows an EP modifying all links at the example
location returned when registering /rd/4521 which are identified by href="/sensors/temp", from
the group. Removing a group MUST
NOT remove initial link-value of </sensors/temp>;rt="temperature" to the endpoints new
link-value </sensors/temp>;rt="temperature-c";if="sensor" by changing
the value of the group from link attribute "rt" and adding 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 Location path 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

The following examples shows successful removal of the group from link attribute
if="sensor" using the
RD PATCH operation with the example location value /rd-group/12. supplied merge-
patch+json document payload.

Req: DELETE /rd-group/12 PATCH /rd/4521?href=/sensors/temp

Payload:
{"rt": "temperature-c", "if": "sensor"},

Content-Format:
application/merge-patch+json

Res: 2.02 Deleted

8. RD Lookup Function Set

In order for an RD to be used for discovering resources registered
with it, a lookup interface can be provided using this function set.
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). 2.04 Changed

Req: GET /rd/4521

Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/light>;ct=41;rt="light-lux";if="sensor",
</sensors/humid>;ct=41;rt="humid-s";if="sensor"

This function set allows lookups for domains, groups, endpoints and
resources using attributes defined in the RD Function Set and for use
with the CoRE Link Format. The result of a lookup request is the
list of example shows an EP removing all links (if any) corresponding to at the type of lookup. Thus, a
domain lookup MUST return a list of domains, 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.

Each endpoint and resource lookup result returns respectively the
scheme (IP address and port) followed by the path part of the URI of
every endpoint and resource inside angle brackets ("<>") and followed
by the other parameters.

The target of these links SHOULD be the actual example location of the
domain, endpoint or resource, but MAY be an intermediate proxy e.g.
in the case of an HTTP lookup interface for CoAP endpoints.

The domain lookup returns every lookup domain with a base RD resource
value (e.g. "/rd") encapsulated within angle brackets.

In case that a group does not implement any multicast address, the
group lookup returns every group lookup with a group base resource
value encapsulated within angle brackets (e.g. "/rd/look-up").
Otherwise, the group lookup returns the multicast address of the
group inside angle brackets.

Using the Accept Option, the requester can control whether this 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
/rd/4521 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 query parameters MAY be included in a lookup, all included
parameters MUST match are identified by href="/sensors/light".

Req: PATCH /rd/4521?href=/sensors/light

Payload:
{}

Content-Format:
application/merge-patch+json

Res: 2.04 Changed
Req: GET /rd/4521

Res: 2.01 Content
Payload:
</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
</sensors/humid>;ct=41;rt="humid-s";if="sensor"

6. RD Groups

This section defines the REST API for a resource to be returned. The
character'*' MAY be included at the end 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 parameter value as group entry consists of a
wildcard operator.

The rd-lookup interface MAY use any set list of query parameters to match
the registered attributes
endpoints and relations. does not have a lifetime associated with it. In addition, this interface order
to make use of multicast requests with CoAP, a group MAY be used have a
multicast address associated with queries that specify domains, endpoints, and groups.
For example, it.

6.1. Register a domain lookup filtering on groups would return 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 domain the group
belongs to, and optionally the multicast address of the group. The
registration message includes the list of domains endpoints that contain belong to
that group.

All the specified groups. An endpoints in the group MUST be registered with the RD before
registering a group. If an endpoint lookup
filtering on groups would return is not yet registered to the RD
before registering the group, the registration message returns an
error. The RD sends a list blank target URI for every endpoint link when
registering the group.

Configuration of the endpoints that are themselves is out of scope of this
specification. Such an interface for managing the group membership
of an endpoint has been defined in the
specified groups. [RFC7390].

The lookup registration request interface is specified as follows:

Interaction: Client CT -> RD

Method: GET POST

URI Template: /{+rd-lookup-base}/{lookup-
type}{?d,ep,gp,et,rt,page,count,resource-param} /{+rd-group}{?gp,d,con}

URI Template Variables:

rd-lookup-base

rd-group := RD Lookup Function Set Group Base URI path (mandatory). This is the path of the RD Lookup Function Set. The recommended
value for this variable is: "rd-lookup".

lookup-type := ("d", "ep", "res", "gp") (mandatory) This variable
is used to select the kind of lookup to perform (domain,
endpoint, resource, or group).

ep := Endpoint name (optional). Used for endpoint, group and
resource lookups.

d := Domain (optional). Used for domain, group, endpoint and
resource lookups.

res := resource (optional). Used for domain, group, endpoint and
resource lookups.

gp := Group name (optional). Used for endpoint, group and
resource lookups.

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.

rt := Resource type (optional). Used for group, endpoint and
resource lookups.

et := Endpoint type (optional). Used for group, endpoint and
resource lookups.

resource-param := Link attribute parameters (optional). Any link
attribute as defined in Section 4.1 of [RFC6690], used for
resource lookups.

Content-Format: application/link-format (optional)

Content-Format: application/link-format+json (optional)

Content-Format: application/link-format+cbor (optional) the path
of the RD Group REST API. The following responses codes are defined value "rd-group" is recommended
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 variable.

gp := Group Name (mandatory). The name of the lookup.

Failure: 4.04 "Not Found" group to be
created or 404 "Not Found" in case no matching
entry replaced, unique within that domain. The maximum
length of this parameter is found for a unicast request.

Failure: No error response 63 bytes.

d := Domain (optional). The domain 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 which this group belongs.
The examples in maximum length of this section assume a CoAP host parameter is 63 bytes. Optional.
When this parameter is elided, the RD MAY associate the
endpoint with IP address
FDFD::123 and a configured default CoAP port 61616. HTTP hosts are possible domain.

con := Context (optional). This parameter sets the scheme,
address and
do not change port at which this server is available in the nature form
scheme://host:port/path. In the absence of this parameter the examples.\

The following example shows a client performing a resource lookup
with
scheme of the example look-up location /rd-lookup/:

Req: GET /rd-lookup/res?rt=temperature

Res: 2.05 Content
<coap://[FDFD::123]:61616/temp>;rt="temperature"

The following example shows a client performing an endpoint type
lookup:

Req: GET /rd-lookup/ep?et=power-node

Res: 2.05 Content
<coap://[FDFD::123]:61616>;ep="node5",
<coap://[FDFD::123]:61616>;ep="node7"

The following example shows a client performing protocol, source address and source port of the
register request are assumed. This parameter is mandatory when
the directory is filled by a domain lookup:

Req: GET /rd-lookup/d

Res: 2.05 Content
<>;d="domain1",
<>;d="domain2" third party such as an
commissioning tool. When con is used, scheme and host are
mandatory and port and path parameters are optional.

Content-Format: application/link-format

Content-Format: application/link-format+json

Content-Format: application/link-format+cbor

The following example shows a client performing a group lookup response codes are defined for
all groups:

Req: GET /rd-lookup/gp

Res: 2.05 Content
<>;gp="lights1";d="example.com"
<>;gp="lights2";d="ecample.com" this interface:

Success: 2.01 "Created" or 201 "Created". The following example shows a client performing a lookup for all
endpoints Location header
option MUST be returned in response to a particular group:

Req: GET /rd-lookup/ep?gp=lights1

Res: 2.05 Content
<coap://[FDFD::123]:61616>;ep="node1",
<coap://[FDFD::123]:61616>;ep="node2"

The following example shows a client performing successful group CREATE
operation. This Location MUST be a lookup stable identifier generated by
the RD as it is used for all
groups an endpoint belongs to:

Req: GET /rd-lookup/gp?ep=node1

Res: 2.05 Content
<>;gp="lights1"

The following example shows a client performing a paginated lookup
Req: GET /rd-lookup/res?page=0&count=5

Res: 2.05 Content
<coap://[FDFD::123]:61616/res/0>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/1>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/2>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/3>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/4>;rt=sensor;ct=60

Req: GET /rd-lookup/res?page=1&count=5

Res: 2.05 Content
<coap://[FDFD::123]:61616/res/5>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/6>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/7>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/8>;rt=sensor;ct=60
<coap://[FDFD::123]:61616/res/9>;rt=sensor;ct=60

9. New Link-Format Attributes

When using delete operations of the CoRE Link Format to describe resources being
discovered by group
registration resource.

Failure: 4.00 "Bad Request" or posted to a resource directory service, additional
information about those resources 400 "Bad Request". Malformed
request.

Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is useful. This specification
defines the following new attributes for use not
registered in the CoRE Link Format
[RFC6690]:

link-extension = ( "ins" "=" (ptoken | quoted-string) )
; The token RD (e.g. may have expired).

Failure: 5.03 "Service Unavailable" or string is max 63 bytes
link-extension = ( "exp" )

9.1. Resource Instance attribute 'ins' 503 "Service Unavailable".
Service could not perform the operation.

HTTP support: YES
The Resource Instance "ins" attribute is following example shows an identifier for this
resource, EP registering a group with the name
"lights" which makes it possible has two endpoints to distinguish it from other
similar resources. This attribute an RD using this interface. The
base location value /rd-group is similar in use an example of an RD base location.

Req: POST coap://rd.example.com/rd-group?gp=lights
Content-Format: 40
Payload:
<>;ep="node1",
<>;ep="node2"

Res: 2.01 Created
Location: /rd-group/12

6.2. Group Removal

A group can be removed simply by sending a removal message to the
<Instance> portion
location of the group registration resource which was returned when
intially registering the group. Removing a DNS-SD record (see Section 10.1, and SHOULD
be unique across resources with group MUST NOT remove the same Resource Type attribute in
endpoints of the domain it group from the RD.

The removal request interface is used. A Resource Instance might be a descriptive
string like "Ceiling Light, Room 3", a short ID like "AF39" or a
unique UUID or iNumber. specified as follows:

Interaction: CT -> RD

Method: DELETE

URI Template: /{+location}

URI Template Variables:

location := This attribute is used the Location path returned by the RD as a Resource
Directory to distinguish between multiple instances
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 same
resource type within the directory.

This attribute MUST be no more than 63 bytes in length. operation.

HTTP support: YES
The resource
identifier attribute MUST NOT appear more than once in a link
description. This attribute MAY be used as a query parameter in following examples shows successful removal of the group from the
RD Lookup Function Set defined in Section with the example location value /rd-group/12.

Req: DELETE /rd-group/12

Res: 2.02 Deleted

9.2. Export attribute 'exp'

The Export "exp" attribute is used as a flag RD Lookup

In order for an RD to indicate that a link
description MAY be exported by a resource directory to external
directories.

The CoRE Link Format is used for many purposes between CoAP
endpoints. Some are useful mainly locally, for example checking the
observability of a resource before accessing discovering resources registered
with it, determining the size
of a resource, or traversing dynamic resource structures. However,
other links are very useful to an optional lookup interface may be exported to other directories, for
example the entry point resource to a functional service. provided. This
attribute MAY be used lookup
interface is defined as a query parameter default, and it is assumed that RDs may
also support lookups to return resource descriptions in the alternative
formats (e.g. Atom or HTML Link) or using more advanced interfaces
(e.g. supporting context or semantic based lookup).

RD Lookup Function
Set allows lookups for domains, groups, endpoints and resources
using attributes defined in Section 7.

10. DNS-SD Mapping

CoRE Resource Discovery is intended to support fine-grained discovery
of hosted resources, their attributes, and possibly other resource
relations [RFC6690]. In contrast, service discovery generally refers
to a coarse-grained resolution of an endpoint's IP address, port
number, and protocol.

Resource this document and service discovery are complementary in the case of large
networks, where for use with the latter can facilitate scaling. This document
defines a mapping between CoRE
Link Format attributes and DNS-Based
Service Discovery [RFC6763] fields that permits discovery Format. The result of CoAP
services by either method.

10.1. DNS-based Service discovery

DNS-Based Service Discovery (DNS-SD) defines a conventional method lookup request is the list of
configuring DNS PTR, SRV, and TXT resource records links (if
any) corresponding to facilitate
discovery the type of services (such as CoAP servers in lookup. Thus, a subdomain) using the
existing DNS infrastructure. This section gives domain lookup MUST
return a brief overview list of
DNS-SD; see [RFC6763] for domains, a detailed specification.

DNS-SD service names are limited to 255 octets group lookup MUST return a list of
groups, an endpoint lookup MUST return a list of endpoints and are a
resource lookup MUST return a list of the form:

Service Name = <Instance>.<ServiceType>.<Domain>. links to resources.

RD Lookup does not expose registration resources directly, but
returns link content from registration resource entries which satisfy
RD Lookup queries.

The service name lookup type is the label of SRV/TXT selected by a URI endpoint, which is indicated by
a Resource Type as per Table 1 below:

Table 1: Lookup Types

Each endpoint and resource records. The SRV
RR specifies lookup result returns respectively the host
scheme (IP address and port) followed by the port of the endpoint. The TXT RR
provides additional information in the form of key/value pairs.

The <Domain> part of the service name is identical to the global (DNS
subdomain) path part of the authority in URIs that identify servers or
groups of servers.

The <ServiceType> part is composed of at least two labels. The first
label URI of the pair is the application protocol name [RFC6335] preceded
by an underscore character. The second label indicates the transport
every endpoint and is always "_udp" for UDP-based CoAP services. In cases where
narrowing resource inside angle brackets ("<>") and followed
by the scope other parameters.

The target of the search may be useful, these labels may links SHOULD be
optionally preceded by a subtype name followed by the "_sub" label.
An example of this more specific <ServiceType> is
"light._sub._dali._udp".

A default <Instance> part actual location of the service name may be set at the
factory
domain, endpoint or during the commissioning process. It SHOULD uniquely
identify resource, but MAY be an instance intermediate proxy e.g.
in the case of <ServiceType> within a <Domain>. Taken
together, these three elements comprise a unique name for an SRV/ TXT
record pair within the DNS subdomain. HTTP lookup interface for CoAP endpoints.

The granularity of domain lookup returns every lookup domain with a service name MAY be base RD resource
value (e.g. "/rd") encapsulated within angle brackets.

In case that of a host or group, or
it could represent group does not implement any multicast address, the
group lookup returns every group lookup with a particular group base resource
value encapsulated within a CoAP server. The
SRV record contains angle brackets (e.g. "/rd/look-up").
Otherwise, the host name (AAAA record name) and port of group lookup returns the
service while protocol is part multicast address of the service name. In the case
where a service name identifies a particular resource,
group inside angle brackets.

Using the path part
of Accept Option, the URI must be carried in a corresponding TXT record.

A DNS TXT record is in practice limited to a few hundred octets in
length, which requester can control whether this list
is indicated in the resource record header returned in the DNS
response message. The data consists of one CoRE Link Format ("application/link-format", default)
or more strings
comprising a key=value pair. By convention, the first pair is
txtver=<number> (to support different versions of a service
description).

10.2. mapping ins to <Instance> its alternate content-formats ("application/link-format+json" or
"application/link-format+cbor").

The Resource Instance "ins" attribute maps to the <Instance> part of
a DNS-SD service name. It is stored directly in the DNS as a single
DNS label of canonical precomposed UTF-8 [RFC3629] "Net-Unicode"
(Unicode Normalization Form C) [RFC5198] text. However, to the
extent that the "ins" attribute may be chosen page and count parameters are used to match the DNS host
name of a service, it SHOULD use the syntax defined obtain lookup results in Section 3.5 of
[RFC1034]
specified increments using pagination, where count specifies how many
links to return and Section 2.1 page specifies which subset of [RFC1123].

The <Instance> part links organized in
sequential pages, each containing 'count' links, starting with link
zero and page zero. Thus, specifying count of the name 10 and page of a service being offered on 0 will
return the
network SHOULD be configurable by first 10 links in the user setting up result set (links 0-9). Count = 10
and page = 1 will return the service, next 'page' containing links 10-19, and
so
that he or she may give it an informative name. However, the device
or service SHOULD NOT require the user to configure a name before it
can on.

Multiple query parameters MAY be used. A sensible choice of default name can allow the device
or service included in a lookup, all included
parameters MUST match for a resource to be accessed in many cases without any manual
configuration at all. returned. The default name should be short and
descriptive, and
character'*' MAY include be included at the end of a collision-resistant substring such parameter value as
the lower bits a
wildcard operator.

RD Lookup requests MAY use any set of the device's MAC address, serial number,
fingerprint, or other identifier in an attempt query parameters to make match the name
relatively unique.

DNS labels are currently limited to 63 octets in length
registered attributes and the
entire service name may not exceed 255 octets.

10.3. Mapping rt to <ServiceType>

The resource type "rt" attribute is mapped into the <ServiceType>
part of relations. In addition, this interface MAY
be used with queries that specify domains, endpoints, and groups.
For example, a domain lookup filtering on groups would return a DNS-SD service name and SHOULD conform to the reg-rel-type
production list
of domains that contain the Link Format defined in Section 2 of [RFC6690]. The
"rt" attribute MUST be composed of at least specified groups. An endpoint lookup
filtering on groups would return a single Net-Unicode text
string, without underscore '_' or period '.' and limited to 15 octets list of endpoints that are in length, which represents the application protocol name.
specified groups.

The lookup interface is specified as follows:

Interaction: Client -> RD

Method: GET

URI Template: /{+rd-lookup-base}/{lookup-
type}{?d,res,ep,gp,et,rt,page,count,resource-param}

URI Template Variables:

rd-lookup-base := RD Lookup Base URI path (mandatory). This
string is mapped to the DNS-SD <ServiceType> by prepending an
underscore and appending a period followed by
the "_udp" label. For
example, rt="dali" is mapped into "_dali._udp". base path for RD Lookup requests. The application protocol name may be optionally followed by a period
and a service subtype name consisting of a Net-Unicode text string,
without underscore or period and limited to 63 octets. recommended value
for this variable is: "rd-lookup".

lookup-type := ("ep", "res") (mandatory), ("d","gp") (optional)
This string variable is mapped used to select the DNS-SD <ServiceType> by appending a period followed
by the "_sub" label and then appending a period followed by the
service type label pair derived of lookup to perform
(endpoint, resource, domain, or group). The values are
recommended defaults and MAY use other values as needed. The
supported lookup-types SHOULD be listed in .well-known/core
using the previous paragraph. For
example, rt="dali.light" is mapped into "light._sub._dali._udp".

The resulting string is used to form labels specified resource types.

ep := Endpoint name (optional). Used for DNS-SD records which endpoint, group and
resource lookups.

d := Domain (optional). Used for domain, group, endpoint and
resource lookups.

res := resource (optional). Used for domain, group, endpoint and
resource lookups.

gp := Group name (optional). Used for endpoint, group and
resource lookups.

page := Page (optional). Parameter can not be used without the
count parameter. Results are stored directly returned from result set in the DNS.

10.4. Domain mapping

DNS domains may be derived pages
that contain 'count' links starting from the "d" attribute. The domain
attribute may be suffixed index (page * count).
Page numbering starts with the zone name zero.

count := Count (optional). Number of the authoritative DNS
server to generate the domain name. The "ep" attribute results is prefixed limited to this
parameter value. If the domain name to generate page parameter is also present, the FQDN to be stored into DNS
response MUST only include 'count' links starting with an
AAAA RR.

10.5. TXT Record key=value strings

A number of [RFC6763] key/value pairs are derived from link-format
information, to be exported the
(page * count) link in the DNS-SD as key=value strings result set from the query. If the
count parameter is not present, then the response MUST return
all matching links in a
TXT record ([RFC6763], Section 6.3).

The the result set. Link numbering starts
with zero.

rt := Resource type (optional). Used for group, endpoint and
resource <URI> is exported as key/value pair "path=<URI>".

The Interface Description "if" attribute is exported as key/value
pair "if=<Interface Description>".

The DNS TXT record can be further populated by importing any other lookups.

et := Endpoint type (optional). Used for group, endpoint and
resource description attributes lookups.

resource-param := Link attribute parameters (optional). Any link
target attribute as they share the same key=value
format specified defined in Section 6 4.1 of [RFC6763].

10.6. Importing [RFC6690], used
for resource links into DNS-SD

Assuming lookups.

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 ability lookup.

Failure: 4.04 "Not Found" or 404 "Not Found" in case no matching
entry is found for a unicast request.

Failure: No error response to query a Resource Directory or multicast a GET
(?exp) over the local link, CoAP resource discovery may be used to
populate 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 DNS-SD database operation.

HTTP support: YES

The examples in an automated fashion. this section assume CoAP resource
descriptions (links) can be exported to DNS-SD for exposure to
service discovery by using the Resource Instance attribute as the
basis for a unique service name, composed hosts with the Resource Type as
the <ServiceType>, a default CoAP
port 61616. HTTP hosts are possible and registered in the correct <Domain>. The agent
responsible for exporting records to do not change the DNS zone file SHOULD be
authenticated to nature of
the DNS server. examples.

The following example, using the example shows a client performing a resource lookup
with the example look-up location /rd-lookup, /rd-lookup/:

Req: GET /rd-lookup/res?rt=temperature

Res: 2.05 Content
<coap://[FDFD::123]:61616/temp>;rt="temperature"

The following example shows a client performing an agent discovering endpoint type
lookup:

Req: GET /rd-lookup/ep?et=power-node

Res: 2.05 Content
<coap://[FDFD::127]:61616>;ep="node5",
<coap://[FDFD::129]:61616>;ep="node7"

The following example shows a
resource to be exported: client performing a domain lookup:

Req: GET /rd-lookup/res?exp /rd-lookup/d

Res: 2.05 Content
<coap://[FDFD::1234]:5683/light/1>;
exp;rt="dali.light";ins="Spot";
d="office";ep="node1"
<>;d="domain1",
<>;d="domain2"

The agent subsequently registers the following DNS-SD RRs, assuming example shows a
zone name "example.com" prefixed with "office":

node1.office.example.com. IN AAAA FDFD::1234
_dali._udp.office.example.com IN PTR
Spot._dali._udp.office.example.com
light._sub._dali._udp.example.com IN PTR
Spot._dali._udp.office.example.com
Spot._dali._udp.office.example.com IN SRV 0 0 5683
node1.office.example.com.
Spot._dali._udp.office.example.com IN TXT
txtver=1;path=/light/1

In the above figure the Service Name is chosen as
Spot._dali._udp.office.example.com without the light._sub service
prefix. An alternative Service Name would be:
Spot.light._sub._dali._udp.office.example.com.

11. client performing a group lookup for
all groups:

Req: GET /rd-lookup/gp

Res: 2.05 Content
<>;gp="lights1";d="example.com"
<>;gp="lights2";d="ecample.com"

The following example shows a client performing a lookup for all
endpoints in a particular group:

Req: GET /rd-lookup/ep?gp=lights1

Res: 2.05 Content
<coap://[FDFD::123]:61616>;ep="node1",
<coap://[FDFD::124]:61616>;ep="node2"

The following example shows a client performing a lookup for all
groups an endpoint belongs to:

Req: GET /rd-lookup/gp?ep=node1

Res: 2.05 Content
<>;gp="lights1"

The following example shows a client performing a paginated lookup
Req: GET /rd-lookup/res?page=0&count=5

Req: GET /rd-lookup/res?page=1&count=5

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.

11.1.

8.1. Endpoint Identification and Authentication

An Endpoint is determined to be unique by 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. Endpoints using a
Certificate MUST include the Endpoint identifier as the Subject of
the Certificate, and this identifier MUST be checked by a resource
directory to match the Endpoint identifier included in the
Registration message.

11.2.

8.2. Access Control

Access control SHOULD be performed separately for the RD Function Set
registration, Lookup, and the RD Lookup Function Set, group API base 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
domain, endpoint or resource level.

11.3.

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. Therefore, it is RECOMMENDED that implementations ensure
return routability. This can be done, for example by responding to
wild card lookups only over DTLS or TLS or TCP.

12.

9. IANA Considerations

12.1.

9.1. Resource Types

"core.rd", "core.rd-group" "core.rd-group", "core.rd-lookup-ep", "core.rd-lookup-
res", "core.rd-lookup-d", and "core.rd-lookup" "core.rd-lookup-gp" resource types need
to be registered with the resource type registry defined by
[RFC6690].

12.2. Link Extension

The "exp" and "ins" attributes need to be registered when a future
Web Linking link-extension registry is created (e.g. in RFC5988bis).

12.3.

9.2. 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)

12.4.

9.3. 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 the human readable name of
the parameter, the query parameter, validity requirements if any and
a description. The query parameter MUST be a valid URI query key
[RFC3986].

Initial entries in this sub-registry are as follows:

+-----------+-------+---------------+-------------------------------+

Table 1: 2: RD Parameters

The IANA policy for future additions to the sub-registry is "Expert
Review" as described in [RFC5226].

13.

10. Examples

13.1.

Two examples are presented: a Lighting Installation example in
Section 10.1 and a LWM2M example in Section 10.2.

10.1. 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
the issues that may influence the use of the RD and does not pretend
to be normative. The example uses the recommended values for the
base resources: "/rd", "/rd-lookup", and "/rd-group".

13.1.1.

10.1.1. 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 2 3 below:

Table 2: 3: interface SLAAC addresses

In Section 13.1.2 10.1.2 the use of resource directory during installation
is presented. In Section 13.1.3 the connection to DNS is discussed.

13.1.2.

10.1.2. 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 3 4
below:

Table 3: 4: Resource Directory identifiers

The CT inserts the endpoints of the luminaries and the sensor in the
RD using the Context parameter (con) to specify the interface
address:

Req: POST coap://[FDFD::ABCD:0]/rd
?ep=lm_R2-4-015_wndw&con=coap://[FDFD::ABCD:1]
Payload:
</light/left>;rt="light"; d="R2-4-015",
</light/middle>;rt="light"; d="R2-4-015",
</light/right>;rt="light";d="R2-4-015"

Res: 2.01 Created
Location: /rd/4521

Req: POST coap://[FDFD::ABCD:0]/rd
?ep=lm_R2-4-015_door&con=coap://[FDFD::ABCD:2]
Payload:
</light/left>;rt="light"; d="R2-4-015",
</light/middle>;rt="light"; d="R2-4-015",
</light/right>;rt="light"; d="R2-4-015"

Res: 2.01 Created
Location: /rd/4522

Req: POST coap://[FDFD::ABCD:0]/rd
?ep=ps_R2-4-015_door&con=coap://[FDFD::ABCD:3]
Payload:
</ps>;rt="p-sensor"; d="R2-4-015"

Res: 2.01 Created
Location: /rd/4523

The domain name d="R2-4-015" has been added for an efficient lookup
because filtering on "ep" name is more awkward. The same domain name
is communicated to the two luminaries and the presence sensor by the
CT.

The group is specified in the RD. The Context 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.

Req: POST coap://[FDFD::ABCD:0]/rd-group
?gp=grp_R2-4-015;con="coap//[FF05::1]";exp;ins="grp1234"
?gp=grp_R2-4-015;con="coap//[FF05::1]"
Payload:
<>ep=lm_R2-4-015_wndw,
<>ep=lm_R2-4-015_door,
<>ep=ps_R2-4-015_door

Res: 2.01 Created
Location: /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 domain, queries the RD for the endpoint
with rt=light and d=R2-4-015. The RD returns all endpoints in the
domain.

Req: GET coap://[FDFD::ABCD:0]/rd-lookup/ep
?d=R2-4-015;rt=light

Res: 2.05 Content
<coap://[FDFD::ABCD:1]>;
ep="lm_R2-4-015_wndw",
<coap://[FDFD::ABCD:2]>;
ep="lm_R2-4-015_door"

Knowing its own IPv6 address, the luminary discovers its endpoint
name. With the endpoint name the luminary queries the RD for all
groups to which the endpoint belongs.

Req: GET coap://[FDFD::ABCD:0]/rd-lookup/gp
?ep=lm_R2-4-015_wndw

Res: 2.05 Content
<coap://[FF05::1]>;gp="grp_R2-4-015"

From the context 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 //[FDFD::ABCD:1]/coap-group
Content-Format: application/coap-group+json
{ "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.

13.1.3. DNS entries

It may be profitable to discover the light groups for applications,
which are unaware ot the existence of the RD. An agent needs to
query the RD to return all groups which are exported to be inserted
into DNS.

Req: GET /rd-lookup/gp?exp

Res: 2.05 Content
<coap://[FF05::1]/>;exp;gp="grp_R2-4-015;ins="grp1234";
ep="lm_R2-4-015_wndw";
ep="lm_R2-4-015_door

The group with FQDN grp_R2-4-015.bc.example.com can be entered into
the DNS by the agent. The accompanying instance name is grp1234.
The <ServiceType> is chosen to be _group._udp. The agent enters the
following RRs into the DNS.

grp_R2-4-015.bc.example.com. IN AAAA FF05::1
_group._udp.bc.example.com IN PTR
grp1234._group._udp.bc.example.com
grp1234._group._udp.bc.example.com IN SRV 0 0 5683
grp_R2-4-015_door.bc.example.com.
grp1234._group._udp.bc.example.com IN TXT
txtver=1;path=/light/grp1

From then using the "coap-group" resource specified in
[RFC7390].

Req: POST //[FDFD::ABCD:1]/coap-group
Content-Format: application/coap-group+json
{ "a": "[FF05::1]",
"n": "grp_R2-4-015"}

Res: 2.01 Created
Location-Path: /coap-group/1

Dependent on applications, not familiar with the existence of situation, only the RD,
can use DNS to access address, "a", or the lighting group.

13.2. name, "n",
is specified in the coap-group resource.

10.2. 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
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 domains 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, applications, and function sets applications are currently out of scope for
LWM2M.

The location of the LWM2M Server and RD Function Set base URI path is provided by
the LWM2M Bootstrap process, so no dynamic discovery of the RD
function set is
used. LWM2M Servers and endpoints are not required to implement the
./well-known/core resource.

13.2.1.

10.2.1. 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}

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". [_TEMPLATE_TODO]

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).

13.2.2.

10.2.2. LWM2M Register Endpoint

LWM2M defines a registration interface based on the Resource
Directory Function Set, REST API,
described in Section 6. 5. The base URI path of the LWM2M Resource
Directory function set is specified to be "/rd" as recommended in Section 6.3. 5.3.

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
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 1 2 :

ep - Endpoint Name
lt - registration lifetime

Endpoint Name is mandatory, all other registration parameters are
optional.

Additional optional LWM2M registration parameters are defined:

+------------+-------+-------------------------------+--------------+
| Name | Query | Validity | Description |
+------------+-------+-------------------------------+--------------+
| Protocol | b | {"U",UQ","S","SQ","US","UQS"} | Available |
| Binding | | | Protocols |
| | | | |
| LWM2M | ver | 1.0 | Spec Version |
| Version | | | |
| | | | |
| SMS Number | sms | | MSISDN |
+------------+-------+-------------------------------+--------------+

Table 4: 5: LWM2M Additional Registration Parameters

The following RD registration parameters are not currently specified
for use in LWM2M:

et - Endpoint Type
con - Context

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:

</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.

13.2.3. Alternate Base URI

If the LWM2M endpoint exposes objects at a base URI other than the
default empty base path, the endpoint must register the base URI
using rt="oma.lwm2m". An example link payload using alternate base
URI would be:

</my_lwm2m>;rt="oma.lwm2m",</my_lwm2m/1>,<my_lwm2m/1/0>,<my_lwm2m/5>

This link payload indicates that the lwm2m objects will be placed
under the base URI "/my_lwm2m" and that object ID 1 (server) is
supported, with a single instance 0 existing, and object 5 (firmware
update) is supported.

13.2.4.

10.2.3. LWM2M Update Endpoint Registration

An LWM2M Registration update proceeds as described in Section 6.4, 5.4.1,
and adds some optional parameter updates:

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.

13.2.5.

10.2.4. 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 Section 6.5.

14. 5.4.2.

11. Acknowledgments

Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders
Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola and Ukkola, Linyi Tian Tian,
Chistian Amsuss, and Jan Newmarch have provided helpful comments,
discussions and ideas to improve and shape this document. Section 9 is based on an earlier draft by Kerry Lynn. Zach would
also like to thank his colleagues from the EU FP7 SENSEI project,
where many of the resource directory concepts were originally
developed.

15.

12. Changelog

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

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:

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:

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.

16.

13. References

16.1.

13.1. Normative References

[I-D.ietf-core-links-json]
Li, K., Rahman, A., and C. Bormann, "Representing CoRE
Formats in JSON and CBOR", draft-ietf-core-links-json-06
(work in progress), July 2016.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://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,
<http://www.rfc-editor.org/info/rfc3986>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.

[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<http://www.rfc-editor.org/info/rfc5988>.

[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>.

[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<http://www.rfc-editor.org/info/rfc6570>.

[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>.

[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.

[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
<http://www.rfc-editor.org/info/rfc7396>.

16.2.

13.2. Informative References

[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://www.rfc-editor.org/info/rfc1034>.

[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<http://www.rfc-editor.org/info/rfc1123>.

[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.

[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
<http://www.rfc-editor.org/info/rfc5198>.

[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,
<http://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,
<http://www.rfc-editor.org/info/rfc7230>.

[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://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,
<http://www.rfc-editor.org/info/rfc7390>.

Editorial Comments

[_TEMPLATE_TODO] This text needs some help from an RFC 6570 expert.

Authors' Addresses

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