CoRE Z. Shelby
Internet-Draft M. Koster
Intended status: Standards Track ARM
Expires: April 18, 2016 C. Bormann
Universitaet Bremen TZI
P. van der Stok
consultant
October 16, 2015
CoRE Resource Directory
draft-ietf-core-resource-directory-05
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 resources 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 April 18, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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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. Simple Directory Discovery . . . . . . . . . . . . . . . . . 8
4.1. Finding a Directory Server . . . . . . . . . . . . . . . 9
4.2. Third-party registration . . . . . . . . . . . . . . . . 10
5. Resource Directory Function Set . . . . . . . . . . . . . . . 10
5.1. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Registration . . . . . . . . . . . . . . . . . . . . . . 12
5.3. Update . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.4. Removal . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.5. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 17
5.6. Update Endpoint Links . . . . . . . . . . . . . . . . . . 19
6. Group Function Set . . . . . . . . . . . . . . . . . . . . . 21
6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 22
6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 24
7. RD Lookup Function Set . . . . . . . . . . . . . . . . . . . 25
8. New Link-Format Attributes . . . . . . . . . . . . . . . . . 29
8.1. Resource Instance attribute 'ins' . . . . . . . . . . . . 29
8.2. Export attribute 'exp' . . . . . . . . . . . . . . . . . 30
9. DNS-SD Mapping . . . . . . . . . . . . . . . . . . . . . . . 30
9.1. DNS-based Service discovery . . . . . . . . . . . . . . . 30
9.2. mapping ins to <Instance> . . . . . . . . . . . . . . . . 31
9.3. Mapping rt to <ServiceType> . . . . . . . . . . . . . . . 32
9.4. Domain mapping . . . . . . . . . . . . . . . . . . . . . 32
9.5. TXT Record key=value strings . . . . . . . . . . . . . . 32
9.6. Importing resource links into DNS-SD . . . . . . . . . . 33
10. Security Considerations . . . . . . . . . . . . . . . . . . . 34
10.1. Endpoint Identification and Authentication . . . . . . . 34
10.2. Access Control . . . . . . . . . . . . . . . . . . . . . 34
10.3. Denial of Service Attacks . . . . . . . . . . . . . . . 34
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
11.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 35
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11.2. Link Extension . . . . . . . . . . . . . . . . . . . . . 35
11.3. RD Parameter Registry . . . . . . . . . . . . . . . . . 35
12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 36
12.1. Lighting Installation . . . . . . . . . . . . . . . . . 36
12.1.1. Installation Characteristics . . . . . . . . . . . . 36
12.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 38
12.1.3. DNS entries . . . . . . . . . . . . . . . . . . . . 41
12.1.4. RD Operation . . . . . . . . . . . . . . . . . . . . 44
12.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 44
12.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 45
12.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 46
12.2.3. Alternate Base URI . . . . . . . . . . . . . . . . . 47
12.2.4. LWM2M Update Endpoint Registration . . . . . . . . . 48
12.2.5. LWM2M De-Register Endpoint . . . . . . . . . . . . . 48
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48
14. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 48
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 51
15.1. Normative References . . . . . . . . . . . . . . . . . . 51
15.2. Informative References . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53
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]. This
specification however 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
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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.
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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 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 to proactively register and maintain resource
directory 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 entry. Furthermore,
a mechanism to discover an RD using the CoRE Link Format is defined.
It is also possible for an RD to proactively discover Web Links from
endpoints and add them as resource directory entries. A lookup
interface for discovering any of the Web Links held in the RD is
provided using the CoRE Link Format.
Registration Lookup, Group
Interface Interfaces
+----+ | |
| EP |---- | |
+----+ ---- | |
--|- +------+ |
+----+ | ----| | | +--------+
| EP | ---------|-----| RD |----|-----| Client |
+----+ | ----| | | +--------+
--|- +------+ |
+----+ ---- | |
| EP |---- | |
+----+
Figure 1: The resource directory architecture.
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+------------+
| Domain | <-- Name
+------------+
| |
| +------------+
| | Group | <-- Name, IP
| +------------+
| |
+------------+
| Endpoint | <-- Name, Scheme, IP, Port
+------------+
|
|
+------------+
| Resource | <-- Target, Parameters
+------------+
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
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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 larger
resource directories or DNS-SD covering 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 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 link-format, link-format+cbor, or link-format+json
representations are supplied by Resource Directories, which may be
internally stored as triples, or relation/attribute pairs providing
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metadata about resource links. External catalogs that are
represented in other formats may be converted to link-format, link-
format+json, or link-format+cbor for storage and access by Resource
Directories. Since it is common practice for these to be URN
encoded, simple and lossless structural transforms will 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. Simple Directory Discovery
Not all endpoints hosting resources are expected to know how to
implement the Resource Directory Function Set (see Section 5) and
thus explicitly register with a Resource Directory (or other such
directory server). Instead, simple endpoints can implement the
generic Simple Directory Discovery approach described in this
section. An RD implementing this specification MUST implement Simple
Directory Discovery. 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 be discovered, as links on its "/.well-
known/core" interface as specified in [RFC6690].
The endpoint then finds one or more IP addresses of the directory
server it wants to know about its resources as described in
Section 4.1.
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
either
o empty, in which case the directory server is encouraged by this
POST request to perform GET requests at the requesting server's
default discovery URI.
or
o a non-empty link-format document, which indicates the specific
services that the requesting server wants to make known to the
directory server.
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The directory server integrates the information it received this way
into its resource directory. It MAY make 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 the scope of this document.
The following example shows an endpoint using simple resource
discovery, by simply sending a POST with its links in the body to a
directory.
EP RD
| |
| -- POST /.well-known/core "</sen/temp>..." ---> |
| |
| |
| <---- 2.01 Created ------------------------- |
| |
4.1. Finding a Directory Server
Endpoints that want to contact a directory server 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.
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 5.1).
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.
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4.2. Third-party registration
For some applications, even Simple Directory Discovery may be too
taxing for certain very constrained devices, in particular if the
security requirements become too onerous.
In a controlled environment (e.g. building control), the Resource
Directory can be filled by a third device, called an installation
tool. The installation tool can fill the Resource Directory from a
database or other means. For that purpose the scheme, IP address and
port of the registered device is indicated in the Context parameter
of the registration as well.
5. Resource Directory Function Set
This section defines the REST interfaces between an RD and endpoints,
which is called the Resource Directory Function Set. Although the
examples throughout this section assume the use of CoAP [RFC7252],
these REST interfaces can also be realized using HTTP [RFC7230]. In
all definitions in this section, both CoAP response codes (with dot
notation) and HTTP response codes (without dot notation) are shown.
An RD implementing this specification MUST support the discovery,
registration, update, lookup, and removal interfaces defined in this
section.
Resource directory entries are designed to be easily exported to
other discovery mechanisms such as DNS-SD. For that reason,
parameters that would meaningfully be mapped to DNS SHOULD be limited
to a maximum length of 63 bytes.
5.1. Discovery
Before an endpoint can make use of an RD, it must first know the RD's
IP address, port and the path of its RD Function Set. There can be
several mechanisms for discovering the RD including assuming a
default location (e.g. on an Edge Router in a LoWPAN), by assigning
an anycast address to the RD, using DHCP, or by discovering the RD
using the CoRE Link Format (see also Section 4.1). This section
defines discovery of the RD using the well-known interface of the
CoRE Link Format [RFC6690] as the required mechanism. It is however
expected that RDs will also be discoverable via other methods
depending on the deployment.
Discovery is performed by sending either a multicast or unicast GET
request to "/.well-known/core" and including a Resource Type (rt)
parameter [RFC6690] with the value "core.rd" in the query string.
Likewise, a Resource Type parameter value of "core.rd-lookup" is used
to discover the RD Lookup Function Set. Upon success, the response
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will contain a payload with a link format entry for each RD
discovered, with the URL indicating the root resource of the RD.
When performing multicast discovery, the multicast IP address used
will depend on the scope required and the multicast capabilities of
the network.
HTTP does not support multicast and consequently discovery has no
HTTP interface.
An RD implementation of this specification MUST support query
filtering for the rt parameter as defined in [RFC6690].
The discovery request interface is specified as follows:
Interaction: EP -> RD
Method: GET
URI Template: /.well-known/core{?rt}
URI Template Variables:
rt := Resource Type (optional). MAY contain the value "core.rd",
"core.rd-lookup", "core.rd-group" or "core.rd*"
Content-Type: application/link-format (if any)
Content-Type: application/link-format+json (if any)
Content-Type: application/link-format+cbor (if any)
The following response codes are defined for this interface:
Success: 2.05 "Content" with an application/link-format,
application/link-format+json, or application/link-format+cbor
payload containing one or more matching entries for the RD
resource.
Failure: 4.04 "Not Found" is returned in case no matching entry is
found for a unicast request.
Failure: 4.00 "Bad Request" is returned in case of a malformed
request for a unicast request.
Failure: No error response to a multicast request.
HTTP support : NO
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The following example shows an endpoint discovering an RD using this
interface, thus learning that the base RD resource is, in this
example, at /rd. Note that it is up to the RD to choose its base RD
resource, although diagnostics and debugging is facilitated by using
the base paths specified here where possible.
EP RD
| |
| ----- GET /.well-known/core?rt=core.rd* ------> |
| |
| |
| <---- 2.05 Content "</rd>;rt="core.rd" ------- |
| |
Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*
Res: 2.05 Content
</rd>;rt="core.rd",
</rd-lookup>;rt="core.rd-lookup",
</rd-group>;rt="core.rd-group"
5.2. Registration
After discovering the location of an RD Function Set, an endpoint MAY
register its resources using the registration interface. This
interface accepts a POST from an endpoint containing the list of
resources to be added to the directory as the message payload in the
CoRE Link Format [RFC6690], JSON CoRE Link Format (application/link-
format+json), or CBOR CoRE Link Format (application/link-format+cbor)
[I-D.ietf-core-links-json], along with query string parameters
indicating the name of the endpoint, its domain and the lifetime of
the registration. All parameters except the endpoint name are
optional. It is expected that other specifications will define
further parameters (see Section 11.3). The RD then creates a new
resource or updates an existing resource in the RD and returns its
location. An endpoint MUST use that location when refreshing
registrations using this interface. Endpoint resources in the RD are
kept active for the period indicated by the lifetime parameter. The
endpoint is responsible for refreshing the entry within this period
using either the registration or update interface. The registration
interface MUST be implemented to be idempotent, so that registering
twice with the same endpoint parameter does not create multiple RD
entries.
The registration request interface is specified as follows:
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Interaction: EP -> RD
Method: POST
URI Template: /{+rd}{?ep,d,et,lt,con}
URI Template Variables:
rd := RD Function Set path (mandatory). This is the path of the
RD Function Set, as obtained from discovery. An RD SHOULD use
the value "rd" for this variable whenever possible.
ep := Endpoint name (mandatory). The endpoint 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 to which this endpoint
belongs. This parameter SHOULD be less than 63 bytes.
Optional. When this parameter is elided, the RD MAY associate
the endpoint with a configured default domain. The domain
value is needed to export the endpoint to DNS-SD (see
Section 9).
et := Endpoint Type (optional). The semantic type of the
endpoint. This parameter SHOULD be less than 63 bytes.
Optional.
lt := Lifetime (optional). Lifetime of the 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. Optional. 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 when the directory is filled by a third
party such as an installation tool.
Content-Type: application/link-format
Content-Type: application/link-format+json
Content-Type: application/link-format+cbor
The following response codes are defined for this interface:
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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 only for the purpose of the
Update (POST) and Removal (DELETE), and MUST NOT implement GET or
PUT methods.
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 using this interface. The
resulting location /rd/4521 is just an example of an RD generated
location.
EP RD
| |
| --- POST /rd?ep=node1 "</sensors..." -------> |
| |
| |
| <-- 2.01 Created Location: /rd/4521 ---------- |
| |
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
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
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5.3. Update
The update interface is used by an endpoint to refresh or update its
registration with an RD. To use the interface, the endpoint sends a
POST request to the resource returned in the Location option in the
response to the first registration. An update MAY update the
lifetime or context parameters if they have changed since the last
registration or update. Parameters that have not changed SHOULD NOT
be included in an update. Upon receiving an update request, the RD
resets the timeout for that endpoint and updates the scheme, IP
address and port of the endpoint (using the source address of the
update, or the context parameter if present).
An update MAY optionally add or replace links for the endpoint by
including those links in the payload of the update as a CoRE Link
Format document. Including links in an update message greatly
increases the load on an RD and SHOULD be done infrequently. A link
is replaced only if both the target URI and relation type match (see
Section 10.1)
The update request interface is specified as follows:
Interaction: EP -> RD
Method: POST
URI Template: /{+location}{?lt,con}
URI Template Variables:
location := This is the Location path returned by the RD as a
result of a successful earlier registration.
lt := Lifetime (optional). Lifetime of the registration in
seconds. Range of 60-4294967295. If no lifetime is included,
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. Optional. In the absence of this
parameter the scheme of the protocol, source IP address and
source port used to register are assumed. This parameter is
compulsory when the directory is filled by a third party such
as an installation tool.
Content-Type: application/link-format (optional)
Content-Type: application/link-format+json (optional)
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Content-Type: application/link-format+cbor (optional)
The following response codes are defined for this interface:
Success: 2.04 "Changed" or 204 "No Content" in the update was
successfully processed.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have expired).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following example shows an endpoint updating its registration at
an RD using this interface.
EP RD
| |
| --- POST /rd/4521 --------------------------> |
| |
| |
| <-- 2.04 Changed ---------------------------- |
| |
Req: POST /rd/4521
Res: 2.04 Changed
5.4. Removal
Although RD entries have soft state and will eventually timeout after
their lifetime, an endpoint SHOULD explicitly remove its entry from
the RD if it knows it will no longer be available (for example on
shut-down). This is accomplished using a removal interface on the RD
by performing a DELETE on the endpoint resource.
The removal request interface is specified as follows:
Interaction: EP -> RD
Method: DELETE
URI Template: /{+location}
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URI Template Variables:
location := This is the Location path returned by the RD as a
result of 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 of the endpoint from
the RD.
EP RD
| |
| --- DELETE /rd/4521 ------------------------> |
| |
| |
| <-- 2.02 Deleted ---------------------------- |
| |
Req: DELETE /rd/4521
Res: 2.02 Deleted
5.5. Read Endpoint Links
Some endpoints may wish to manage their links as a collection, and
may need to read the current set of links in order to determine link
maintenance operations.
One or more links MAY be selected by using query filtering as
specified in [RFC6690] Section 4.1
The read request interface is specified as follows:
Interaction: EP -> RD
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Method: GET
URI Template: /{+location}{?href,rel,rt,if,ct}
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
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", or
"application/link-format+json" payload.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
exist (e.g. may have expired).
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following examples show successful read of the endpoint links
from the RD.
EP RD
| |
| --- GET /rd/4521 ------------------------> |
| |
| |
| <-- 2.05 Content </sensors... ---------------- |
| |
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"
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5.6. Update Endpoint Links
A PATCH update adds, removes or changes links for the endpoint by
including link update information in the payload of 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 and values in the query
parameters select one or more links on which to apply the PATCH
operation.
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 not present in any selected links,
the attribute MUST be added to the links.
The update request interface is specified as follows:
Interaction: EP -> RD
Method: PATCH
URI Template: /{+location}{?href,rel,rt,if,ct}
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 codes are defined for this interface:
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Success: 2.04 "Changed" 0r 204 "No Content" in 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 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 endpoint adding </sensors/humid>,
modifying </sensors/temp>, and removing </sensors/light> links in RD
using the Update Endpoint Links function.
The following example shows an EP adding the link </sensors/
humid>;ct=41;rt="humidity-s";if="sensor" to the collection of links
at the location /rd/4521.
EP RD
| |
| --- PATCH /rd/4521---------------------------> |
| |
| |
| <-- 2.04 Changed ---------------------------- |
| |
Req: PATCH /rd/4521
Payload:
[{"href":"/sensors/humid","ct": 41, "rt": "humidity-s", "if": "sensor"}]
Content-Format:
application/merge-patch+json
Res: 2.04 Changed
The following example shows an EP modifying all links at the location
/rd/4521 which are identified by href="/sensors/temp", from the
initial link-value of </sensors/temp>;rt="temperature" to the new
link-value </sensors/temp>;rt="temperature-c";if="sensor" by changing
the value of the link attribute "rt" and adding the link attribute
if="sensor" using the PATCH operation with the supplied merge-
patch+json document payload.
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EP RD
| |
| --- PATCH /rd/4521?href="/sensors/temp" ----> |
| |
| |
| <-- 2.04 Changed ---------------------------- |
| |
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 an EP removing all links at the location /rd/4521
which are identified by href="/sensors/light".
EP RD
| |
| --- PATCH /rd/4521?href="/sensors/light" ----> |
| |
| |
| <-- 2.04 Changed ---------------------------- |
| |
Req: PATCH /rd/4521?href="/sensors/light"
Payload:
{null}
Content-Format:
application/merge-patch+json
Res: 2.04 Changed
6. Group Function Set
This section defines a function set for the creation of groups of
endpoints for 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 of a list of
endpoints and does not have a lifetime associated with it. In order
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to make use of multicast requests with CoAP, a group MAY have a
multicast address associated with it.
6.1. Register a Group
In order to create a group, a management entity 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 endpoints that belong to that group. If
an endpoint has already registered with the RD, the RD attempts to
use the context of the endpoint from its RD endpoint entry. If the
client registering the group knows the endpoint has already
registered, then it MAY send a blank target URI for that endpoint
link when registering the group. Configuration of the endpoints
themselves is out of scope of this specification. Such an interface
for managing the group membership of an endpoint has been defined in
[RFC7390].
The registration request interface is specified as follows:
Interaction: Manager -> 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 of the RD Group Function Set. An RD SHOULD use the value
"rd-group" for this variable whenever possible.
gp := Group Name (mandatory). The name of the group to be
created or replaced, unique within that domain. The maximum
length of this parameter is 63 bytes.
d := Domain (optional). The domain to which this group belongs.
The maximum length of this parameter is 63 bytes. Optional.
When this parameter is elided, the RD MAY associate the
endpoint with a configured default domain. The domain value is
needed to export the endpoint to DNS-SD (see Section 9)
con := Context (optional). This parameter is used to set the IP
multicast address at which this server is available in the form
scheme://multicast-address:port. Optional. In the absence of
this parameter no multicast address is configured. This
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parameter is compulsory when the directory is filled by an
installation tool.
Content-Type: application/link-format
Content-Type: application/link-format+json
Content-Type: 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 group entry. This Location MUST be a
stable identifier generated by the RD as it is used for delete
operations on this registration.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The following example shows an EP registering a group with the name
"lights" which has two endpoints to an RD using this interface. The
resulting location /rd-group/12 is just an example of an RD generated
group location.
EP RD
| |
| - POST /rd-group?gp=lights "<>;ep=node1..." --> |
| |
| |
| <---- 2.01 Created Location: /rd-group/12 ---- |
| |
Req: POST coap://rd.example.com/rd-group?gp=lights
Payload:
<>;ep="node1",
<>;ep="node2"
Res: 2.01 Created
Location: /rd-group/12
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Req: POST /rd-group?gp=lights HTTP/1.1
Host: example.com
Accept: application/link-format
Payload:
<>;ep="node1",
<>;ep="node2"
Res: 201 Created
Location: /rd-group/12
6.2. Group Removal
A group can be removed simply by sending a removal message to the
location returned when registering the group. Removing a group MUST
NOT remove the endpoints of the group from the RD.
The removal request interface is specified as follows:
Interaction: Manager -> 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 the
RD.
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EP RD
| |
| --- DELETE /rd-group/412 -------------------> |
| |
| |
| <-- 2.02 Deleted ---------------------------- |
| |
Req: DELETE /rd-group/12
Res: 2.02 Deleted
7. 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).
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 links (if any) corresponding to the type of lookup. 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 target of these links SHOULD be the actual 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. Multiple
query parameters MAY be included in a lookup, all included parameters
MUST match for a resource to be returned. The character '*' MAY be
included at the end of a parameter value as a wildcard operator.
The lookup interface is specified as follows:
Interaction: Client -> RD
Method: GET
URI Template: /{+rd-lookup-base}/{lookup-
type}{?d,ep,gp,et,rt,page,count,resource-param}
URI Template Variables:
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rd-lookup-base := RD Lookup Function Set path (mandatory). This
is the path of the RD Lookup Function Set. An RD SHOULD use the
value "rd-lookup" for this variable whenever possible.
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.
page := Page (optional). Parameter can not be used without the
count parameter. Results are returned from result set in pages
that contains 'count' results starting from index (page *
count).
count := Count (optional). Number of results is limited to this
parameter value. If the parameter is not present, then an RD
implementation specific default value SHOULD be used.
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.
The following responses codes are defined for this interface:
Success: 2.05 "Content" or 200 "OK" with an "application/link-
format", "application/link-format+cbor", or "application/link-
format+json" payload containing matching entries for the lookup.
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 a multicast request.
Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
request.
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Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
Service could not perform the operation.
HTTP support: YES
The examples in this section assume a CoAP host with IP address
FDFD::123 and a default CoAP port 61616. HTTP hosts are possible and
do not change the nature of the examples. The following example
shows a client performing a resource lookup:
Client RD
| |
| ----- GET /rd-lookup/res?rt=temperature -----------------> |
| |
| |
| <-- 2.05 Content <coap://[FDFD::123]:61616/temp>;--------- |
| rt="temperature" -------- |
| |
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:
Client RD
| |
| ----- GET /rd-lookup/ep?et=power-node --------------------> |
| |
| |
| <-- 2.05 Content <coap://[FDFD::123]:61616>;ep="node5" ---- |
| |
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 a domain lookup:
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Client RD
| |
| ----- GET /rd-lookup/d ----------------------------------> |
| |
| |
| <-- 2.05 Content </rd>;d=domain1,</rd>;d=domain2 ---------- |
| |
Req: GET /rd-lookup/d
Res: 2.05 Content
</rd>;d="domain1",
</rd>;d="domain2"
The following example shows a client performing a group lookup for
all groups:
Client RD
| |
| ----- GET /rd-lookup/gp ---------------------------------> |
| |
| |
| <-- 2.05 Content </rd-group/12>;gp="lights1"; ------------- |
| d="example.com" ------------- |
| |
Req: GET /rd-lookup/gp
Res: 2.05 Content
</rd-group/12>;gp="lights1";d="example.com"
The following example shows a client performing a lookup for all
endpoints in a particular group:
Client RD
| |
| ----- GET /rd-lookup/ep?gp=lights1-----------------------> |
| |
| |
| <-- 2.05 Content <coap://[FDFD::123]:61616>;ep="node1" ---- |
| |
Req: GET /rd-lookup/ep?gp=lights1
Res: 2.05 Content
<coap://[FDFD::123]:61616>;ep="node1",
<coap://[FDFD::123]:61616>;ep="node2",
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The following example shows a client performing a lookup for all
groups an endpoint belongs to:
Client RD
| |
| ----- GET /rd-lookup/gp?ep=node1 -----------------------> |
| |
| |
|< 2.05 Content <coap://[FDFD::123]:61616>;gp="lights1"; -- |
| ep="node1" ------ |
| |
Req: GET /rd-lookup/gp?ep=node1
Res: 2.05 Content
<coap://[FDFD::123]:61616>;gp="lights1";ep="node1",
8. New Link-Format Attributes
When using the CoRE Link Format to describe resources being
discovered by or posted to a resource directory service, additional
information about those resources is useful. This specification
defines the following new attributes for use in the CoRE Link Format
[RFC6690]:
link-extension = ( "ins" "=" quoted-string ) ; Max 63 bytes
link-extension = ( "exp" )
8.1. Resource Instance attribute 'ins'
The Resource Instance "ins" attribute is an identifier for this
resource, which makes it possible to distinguish it from other
similar resources. This attribute is similar in use to the
<Instance> portion of a DNS-SD record (see Section 9.1, and SHOULD be
unique across resources with the same Resource Type attribute in the
domain it 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. This attribute is used by a Resource Directory to
distinguish between multiple instances of the same resource type
within the directory.
This attribute MUST be no more than 63 bytes in length. The resource
identifier attribute MUST NOT appear more than once in a link
description.
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8.2. Export attribute 'exp'
The Export "exp" attribute is used as a flag 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 it, determining the size
of a resource, or traversing dynamic resource structures. However,
other links are very useful to be exported to other directories, for
example the entry point resource to a functional service.
9. 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 and service discovery are complementary in the case of large
networks, where 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 of CoAP
services by either means.
9.1. DNS-based Service discovery
DNS-Based Service Discovery (DNS-SD) defines a conventional method of
configuring DNS PTR, SRV, and TXT resource records to facilitate
discovery of services (such as CoAP servers in a subdomain) using the
existing DNS infrastructure. This section gives a brief overview of
DNS-SD; see [RFC6763] for a detailed specification.
DNS-SD service names are limited to 255 octets and are of the form:
Service Name = <Instance>.<ServiceType>.<Domain>.
The service name is the label of SRV/TXT resource records. The SRV
RR specifies the host and the port of the endpoint. The TXT RR
provides additional information.
The <Domain> part of the service name is identical to the global (DNS
subdomain) part of the authority in URIs that identify servers or
groups of servers.
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The <ServiceType> part is composed of at least two labels. The first
label of the pair is the application protocol name [RFC6335] preceded
by an underscore character. The second label indicates the transport
and is always "_udp" for UDP-based CoAP services. In cases where
narrowing the scope of the search may be useful, these labels may be
optionally preceded by a subtype name followed by the "_sub" label.
An example of this more specific <ServiceType> is
"lamp._sub._dali._udp".
The default <Instance> part of the service name may be set at the
factory or during the commissioning process. It SHOULD uniquely
identify an instance of <ServiceType> within a <Domain>. Taken
together, these three elements comprise a unique name for an SRV/ TXT
record pair within the DNS subdomain.
The granularity of a service name MAY be that of a host or group, or
it could represent a particular resource within a CoAP server. The
SRV record contains the host name (AAAA record name) and port of the
service while protocol is part of the service name. In the case
where a service name identifies a particular resource, the path part
of 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 is indicated in the resource record header in the DNS
response message. The data consists of one or more strings
comprising a key=value pair. By convention, the first pair is
txtver=<number> (to support different versions of a service
description).
9.2. mapping ins to <Instance>
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 to match the DNS host
name of a service, it SHOULD use the syntax defined in Section 3.5 of
[RFC1034] and Section 2.1 of [RFC1123].
The <Instance> part of the name of a service being offered on the
network SHOULD be configurable by the user setting up the service, 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 be used. A sensible choice of default name can allow the device
or service to be accessed in many cases without any manual
configuration at all. The default name should be short and
descriptive, and MAY include a collision-resistant substring such as
the lower bits of the device's MAC address, serial number,
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fingerprint, or other identifier in an attempt to make the name
relatively unique.
DNS labels are currently limited to 63 octets in length and the
entire service name may not exceed 255 octets.
9.3. Mapping rt to <ServiceType>
The resource type "rt" attribute is mapped into the <ServiceType>
part of a DNS-SD service name and SHOULD conform to the reg-rel-type
production of the Link Format defined in Section 2 of [RFC6690]. The
"rt" attribute MUST be composed of at least a single Net-Unicode text
string, without underscore '_' or period '.' and limited to 15 octets
in length, which represents the application protocol name. 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".
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. This string
is mapped to 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 as in the previous paragraph. For
example, rt="dali.light" is mapped into "light._sub._dali._udp".
The resulting string is used to form labels for DNS-SD records which
are stored directly in the DNS.
9.4. Domain mapping
DNS domains may be derived from the "d" attribute. The domain
attribute may be suffixed with the zone name of the authoritative DNS
server to generate the domain name. The "ep" attribute is prefixed
to the domain name to generate the FQDN to be stored into DNS with an
AAAA RR.
9.5. TXT Record key=value strings
A number of [RFC6763] key/value pairs are derived from link-format
information, to be exported in the DNS-SD as key=value strings in a
TXT record ([RFC6763], Section 6.3).
The resource <URI> is exported as key/value pair "path=<URI>".
The Interface Description "if" attribute is exported as key/value
pair "if=<Interface Description>".
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The DNS TXT record can be further populated by importing any other
resource description attributes as they share the same key=value
format specified in Section 6 of [RFC6763].
9.6. Importing resource links into DNS-SD
Assuming the ability to query a Resource Directory or multicast a GET
(?exp) over the local link, CoAP resource discovery may be used to
populate the DNS-SD database in an automated fashion. 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 with the Resource Type as
the <ServiceType>, and registered in the correct <Domain>. The agent
responsible for exporting records to the DNS zone file SHOULD be
authenticated to the DNS server. The following example shows an
agent discovering a resource to be exported:
Agent RD
| |
| --- GET /rd-lookup/res?exp ------------------------------> |
| |
| |
| <-- 2.05 Content "<coap://[FDFD::1234]:5683/light/1>;exp; |
| rt="dali.light";ins="Spot"; |
| d="office";ep="node1" |
| |
Req: GET /rd-lookup/res?exp
Res: 2.05 Content
<coap://[FDFD::1234]:5683/light/1>;
exp;rt="dali.light";ins="Spot";
d="office";ep="node1"
The agent subsequently registers the following DNS-SD RRs, assuming 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
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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.
10. 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.
10.1. 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.
10.2. Access Control
Access control SHOULD be performed separately for the RD Function Set
and the RD Lookup Function Set, 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.
10.3. 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
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request, the situation becomes even worse as now the attack can be
amplified. DNS servers have been widely used for DDoS amplification
attacks. Recently, it has been observed that NTP Servers, that also
run on unprotected UDP have been used for DDoS attacks
(http://tools.cisco.com/security/center/content/CiscoSecurityNotice/
CVE-2013-5211) since there is no return routability check and 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.
11. IANA Considerations
11.1. Resource Types
"core.rd", "core.rd-group" and "core.rd-lookup" resource types need
to be registered with the resource type registry defined by
[RFC6690].
11.2. Link Extension
The "exp" attribute needs to be registered when a future Web Linking
link-extension registry is created (e.g. in RFC5988bis).
11.3. 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:
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+----------+-------+---------------+--------------------------------+
| Name | Query | Validity | Description |
+----------+-------+---------------+--------------------------------+
| Endpoint | ep | | Name of the endpoint |
| Name | | | |
| Lifetime | lt | 60-4294967295 | Lifetime of the registration |
| | | | in seconds |
| Domain | d | | Domain to which this endpoint |
| | | | belongs |
| Endpoint | et | | Semantic name of the endpoint |
| Type | | | |
| Context | con | URI | The scheme, address and port |
| | | | at which this server is |
| | | | available |
| Endpoint | ep | | Name of the endpoint, max 63 |
| Name | | | bytes |
| Group | gp | | Name of a group in the RD |
| Name | | | |
| Page | page | Integer | Used for pagination |
| Count | count | Integer | Used for pagination |
+----------+-------+---------------+--------------------------------+
Table 1: RD Parameters
The IANA policy for future additions to the sub-registry is "Expert
Review" as described in [RFC5226].
12. Examples
Examples are added here.
12.1. 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
procedures, because the example "emphasizes" some of the issues that
may influence the use of the RD.
12.1.1. 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
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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 end-point. 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. Following the lay-out of cables and routers the
network manager has defined DNS domains. The presence sensor and
luminary1 are part of DNS domain: rtr_5612_rrt.example.com and
luminary2 is part of rtr_7899_pfa.example.com. The names of
luminary1- luminary2-, and sensor- interfaces are respectively:
lm_12-345-678, lm_12-456-378, and sn_12-345-781. These names are
stored in DNS together with their IP addresses. The FQDN of the
interfaces is shown in Table 2 below:
+--------------------+----------------------------------------+
| Name | FQDN |
+--------------------+----------------------------------------+
| luminary1 | lm_12-345-678.rtr_5612_rrt.example.com |
| luminary2 | lm_12-456-378.rtr_7899_pfa.example.com |
| Presence sensor | sn_12-345-781.rtr_5612_rrt.example.com |
| Resource directory | pc_123456.rtr_5612_rrt.example.com |
+--------------------+----------------------------------------+
Table 2: interface FQDNs
At the moment of installation, the network under installation is not
necessarily connected to the DNS infra structure. Therefore, SLAAC
IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in
Table 3 below:
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+--------------------+--------------+
| Name | IPv6 address |
+--------------------+--------------+
| luminary1 | FDFD::ABCD:1 |
| luminary2 | FDFD::ABCD:2 |
| Presence sensor | FDFD::ABCD:3 |
| Resource directory | FDFD::ABCD:0 |
+--------------------+--------------+
Table 3: interface SLAAC addresses
In Section 12.1.2 the use of resource directory during installation
is presented. In Section 12.1.3 the connection to DNS is discussed.
12.1.2. 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 end-points 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 end-point names reflect this physical
location. The middle, left and right lamps are accessed via path
/light/middle, /light/left, and /light/right respectively. The
identifiers relevant to the Resource Directory are shown in Table 4
below:
+----------------+------------------+---------------+---------------+
| Name | end-point | resource path | resource type |
+----------------+------------------+---------------+---------------+
| luminary1 | lm_R2-4-015_wndw | /light/left | light |
| luminary1 | lm_R2-4-015_wndw | /light/middle | light |
| luminary1 | lm_R2-4-015_wndw | /light/right | light |
| luminary2 | lm_R2-4-015_door | /light/left | light |
| luminary2 | lm_R2-4-015_door | /light/middle | light |
| luminary2 | lm_R2-4-015_door | /light/right | light |
| Presence | ps_R2-4-015_door | /ps | p-sensor |
| sensor | | | |
+----------------+------------------+---------------+---------------+
Table 4: Resource Directory identifiers
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The CT inserts the end-points 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";ins="lamp4444";exp,
</light/middle>;rt="light";
d="R2-4-015";ins="lamp5555";exp,
</light/right>;rt="light";
d="R2-4-015";ins="lamp6666";exp
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";ins="lamp1111";exp,
</light/middle>;rt="light";
d="R2-4-015";ins="lamp2222";exp,
</light/right>;rt="light";
d="R2-4-015";ins="lamp3333";exp
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";ins="pres1234";exp
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 awkward. The same domain name is
communicated to the two luminaries and the presence sensor by the CT.
The "exp" attribute is set for the later administration in DNS of the
instance name ins="lampxxxx".
Once the individual endpoints are registered, the group needs to be
registered. Because the presence sensor sends one multicast message
to the luminaries, all lamps in the group need to have an identical
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path. This path is created on the two luminaries using the batch
command defined in [I-D.ietf-core-interfaces]. The path to a batch
of lamps is defined as: /light/grp1. In the example below, two
endpoints are updated with an additional resource using the path
/light/grp1 on the two luminaries.
Req: POST
coap://[FDFD::ABCD:1]/light/grp1
(content-type:application/link-format)<light/middle>,<light/left>
Res: 2.04 Changed
Req: POST
coap://[FDFD::ABCD:2]/light/grp1
(content-type:application/link-format)<light/right>
Res: 2.04 Changed
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 end-points and the end-point of the
presence sensor are registered as members of the group.
It is expected that Standards Developing Organizations (SDOs) may
develop other special purpose protocols to specify additional group
links, group membership, group names and other parameters in the
individual nodes.
Req: POST coap://[FDFD::ABCD:0]/rd-group
?gp=grp_R2-4-015;con="coap//[FF05::1]";exp;ins="grp1234"
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 end-point
with rt=light and d=R2-4-015. The RD returns all end-points in the
domain.
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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 end-point name the luminary queries the RD for all
groups to which the end-point 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. Instead of the RD group
name also the DNS group name can be used.
12.1.3. DNS entries
The network manager assigns the domain bc.example.com to the entries
coming from the RD. The agent that looks up the resource directory
uses the domain name bc.example.com as prescribed, to enter the
services and hosts into the DNS.
The agent does a lookup as specified in Section 9.6. The RD returns
all entries annotated with "exp". The agent subsequently registers
the following DNS-SD RRs:
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lm_R2-4-015_wndw.bc.example.com. IN AAAA FDFD::ABCD:1
lm_R2-4-015_door.bc.example.com. IN AAAA FDFD::ABCD:2
ps_R2-4-015_door.bc.example.com. IN AAAA FDFD::ABCD:3
_light._udp.bc.example.com IN PTR
lamp1111._light._udp.bc.example.com
_light._udp.bc.example.com IN PTR
lamp2222._light._udp.bc.example.com
_light._udp.bc.example.com IN PTR
lamp3333._light._udp.bc.example.com
_light._udp.bc.example.com IN PTR
lamp4444._light._udp.bc.example.com
_light._udp.bc.example.com IN PTR
lamp5555._light._udp.bc.example.com
_light._udp.bc.example.com IN PTR
lamp6666._light._udp.bc.example.com
_p-sensor._udp.bc.example.com IN PTR
pres12324._p-sensor._udp.bc.example.com
lamp1111._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_door.bc.example.com.
lamp1111._light._udp.bc.example.com IN TXT
txtver=1;path=/light/left
lamp2222._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_door.bc.example.com.
lamp2222._light._udp.bc.example.com IN TXT
txtver=1;path=/light/middle
lamp3333._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_door.bc.example.com.
lamp3333._light._udp.bc.example.com IN TXT
txtver=1;path=/light/right
lamp4444._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_wndw.bc.example.com.
lamp4444._light._udp.bc.example.com IN TXT
txtver=1;path=/light/left
lamp5555._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_wndw.bc.example.com.
lamp5555._light._udp.bc.example.com IN TXT
txtver=1;path=/light/middle
lamp6666._light._udp.bc.example.com IN SRV 0 0 5683
lm_R2-4-015_wndw.bc.example.com.
lamp6666._light._udp.bc.example.com IN TXT
txtver=1;path=/light/right
pres1234._p-sensor._udp.bc.example.com IN SRV 0 0 5683
ps_R2-4-015_door.bc.example.com.
pres1234._p-sensor._udp.bc.example.com IN TXT
txtver=1;path=/ps
To ask for all lamps is equivalent to returning all PTR RR with label
_light.udp.bc.example.com. from the DNS. When it is required to
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filter on the rd=R2-4-015 value in the DNS, additional PTR RRs have
to be entered into the DNS.
R2-4-015._light._udp.bc.example.com IN PTR
lamp1111._light._udp.bc.example.com
R2-4-015._light._udp.bc.example.com IN PTR
lamp2222._light._udp.bc.example.com
R2-4-015._light._udp.bc.example.com IN PTR
lamp3333._light._udp.bc.example.com
R2-4-015._light._udp.bc.example.com IN PTR
lamp4444._light._udp.bc.example.com
R2-4-015._light._udp.bc.example.com IN PTR
lamp5555._light._udp.bc.example.com
R2-4-015._light._udp.bc.example.com IN PTR
lamp6666._light._udp.bc.example.com
Returning all PTR RRs with label R2-4-015._light._udp.bc.example.com
provides all service instances within the domain R2-4-015. This
filtering can be handy when there are many rooms. In the example
there is only one room, making the filtering superfluous.
The agent can also discover groups that need to be discovered. It
queries RD to return all groups which are exported.
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
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12.1.4. RD Operation
The specification of the group can be used by devices other than the
luminaries and the sensor to learn the multicast address of the group
in a given room. For example a smart phone may be used to adjust the
lamps in the room.
After entry into the room, on request of the user, the smart phone
queries the presence of RDs and may display all the domain names
found on the RDs. The user can, for example, scroll all domains
(room names in this case) and select the room that he entered. After
selection the phone shows all groups in the selected room with their
members. Selecting a group, the user can dim, switch on/off the
group of lights, or possibly even create temporary new groups.
In all examples the SLAAC IPv6 address can be exchanged with the
FQDN, when a connection to DNS exists. Using the FQDN, a node learns
the interface's IPv6 address, or the group's multicast address from
DNS. In the same way the presence sensor can learn the multicast
address to which it should send its presence messages.
12.2. 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, CoRE RD,
and other IETF RFCs and drafts. 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 are currently
out of scope for LWM2M.
The location of the LWM2M Server and RD Function Set is provided by
the LWM2M Bootstrap process, so no dynamic discovery of the RD
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function set is used. LWM2M Servers and endpoints are not required
to implement the ./well-known/core resource.
12.2.1. 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 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 registered resource ID (0-65535) or "undefined"
to refer to all resources within an instance
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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).
12.2.2. LWM2M Register Endpoint
LWM2M defines a registration interface based on the Resource
Directory Function Set, described in Section 5. The URI of the LWM2M
Resource Directory function set is specified to be "/rd" as
recommended in Section 5.2.
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 it's 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 :
ep - Endpoint Name
lt - registration lifetime
Endpoint Name is mandatory, all other registration parameters are
optional.
Additional optional LWM2M registration parameters are defined:
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+------------+-------+-------------------------------+--------------+
| 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 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.
12.2.3. 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.
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12.2.4. LWM2M Update Endpoint Registration
An LWM2M Registration update proceeds as described in Section 5.3,
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.
12.2.5. 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 5.4.
13. Acknowledgments
Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders Brandt,
Matthieu Vial, Mohit Sethi, Sampo Ukkola and Linyi Tian have provided
helpful comments, discussions and ideas to improve and shape this
document. Zach would also like to thank his colleagues from the EU
FP7 SENSEI project, where many of the resource directory concepts
were originally developed.
14. Changelog
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:
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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:
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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.
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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.
15. References
15.1. 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-03
(work in progress), July 2015.
[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>.
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[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>.
15.2. Informative References
[I-D.ietf-core-interfaces]
Shelby, Z., Vial, M., and M. Koster, "CoRE Interfaces",
draft-ietf-core-interfaces-03 (work in progress), July
2015.
[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>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<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
ARM
150 Rose Orchard
San Jose 95134
USA
Phone: +1-408-576-1500 x11516
Email: Michael.Koster@arm.com
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
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Peter van der Stok
consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
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