CoRE Resource DirectoryARM150 Rose OrchardSan Jose95134USA+1-408-203-9434zach.shelby@arm.comSmartThings665 Clyde AvenueMountain View94043USA+1-707-502-5136Michael.Koster@smartthings.comUniversitaet Bremen TZIPostfach 330440BremenD-28359Germany+49-421-218-63921cabo@tzi.orgconsultant+31-492474673 (Netherlands), +33-966015248 (France)consultancy@vanderstok.orgwww.vanderstok.orgEnergy Harvesting SolutionsHollandstr. 12/41020Austria+43-664-9790639c.amsuess@energyharvesting.at
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CoRECoRE, Web Linking, Resource Discovery, Resource DirectoryIn many M2M applications, direct discovery of resources is not practical
due to sleeping nodes, disperse networks, or networks where multicast traffic
is inefficient. These problems can be solved by employing an entity called
a Resource Directory (RD), which hosts descriptions of resources held on
other servers, allowing lookups to be performed for those resources. This
document specifies the web interfaces that a Resource Directory supports
in order for web servers to discover the RD and to register, maintain, lookup
and remove resource descriptions. Furthermore, new link attributes useful
in conjunction with an RD are defined.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 . The use of
Web Linking for the description and discovery of resources hosted by
constrained web servers is specified by the CoRE Link Format
. 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 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 , they
can be applied in an equivalent manner to HTTP .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 . 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 and . Readers should
also be familiar with the terms and concepts discussed in . To
describe the REST interfaces defined in this specification, the URI Template
format is used .This specification makes use of the following additional terminology:
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.
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.
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 (EP) is a term used to describe a web server or client in .
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.
When registering links to a Resource Directory, the Context refers to the
scheme, address, port, and base path for all the links registered on behalf of
an endpoint, of the general form scheme://host:port/path/ where the client may
explicitly set the scheme and host, and may supply the port and path as optional
parameters. When the context of a registration is explicitly set, the
URI resolution rules in MUST be applied.
Commissioning Tool (CT) is a device that assists during the installation of the
network by assigning values to parameters, naming endpoints and groups, or adapting
the installation to the needs of the applications.
Resource Directory Address Option.The Resource Directory is primarily a tool to make discovery operations more
efficient than querying /.well-known/core on all connected device, or across
boundaries that would be limiting those operations.It provides a cache (in the high-level sense, not as defined in
/) of data that could otherwise only be obtained by
directly querying the /.well-known/core resource on the target device, or by
accessing those resources with a multicast request.From that, it follows that no information should be stored in the resource
directory that cannot be discovered from querying the described device’s
/.well-known/core resource directly.It also follows that data in the resource directory can only be provided by the
device whose descriptions are cached or a dedicated Commissioning Tool (CT).
These CTs are thought to act on behalf agents too constrained, or generally
unable, to present that information themselves. No other client can modify data
in the resource directory or even expect those changes to propagate back to its
source.The resource directory architecture is illustrated in . A
Resource Directory (RD) is used as a repository for Web Links
about resources hosted on other web servers, which are called endpoints
(EP).
An endpoint is a web server associated with a scheme, IP address and port
(called Context), thus a physical node may host one or more endpoints. The
RD implements a set of REST interfaces for endpoints to register and maintain
sets of Web Links (called resource directory registration entries), and for clients to
lookup resources from the RD or maintain groups. Endpoints themselves can
also act as clients. An RD can be logically segmented by the use of Domains.
The domain an endpoint is associated with can be defined by the RD or configured
by an outside entity. This information hierarchy is shown in .A mechanism to discover an RD using CoRE Link Format is defined.Endpoints proactively register and maintain resource directory registration entries
on the RD, which are soft state and need to be periodically refreshed.An endpoint is provided with interfaces to register, update and remove a resource
directory registration entry. It is also possible for an RD to fetch Web Links
from endpoints and add them as resource directory entries.At the first registration of a set of entries, a “registration resource” is created,
the location of which is returned to the registering endpoint. The registering
endpoint uses this registration resource to manage the contents of the registration entry.A lookup interface for discovering any of the Web Links held in the RD is
provided using the CoRE Link Format.Over the last few years, mobile operators around the world
have focused on development of M2M solutions in order to
expand the business to the new type of users: machines. The
machines are connected directly to a mobile network using an appropriate
embedded air interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing
short and wide range wireless interfaces. From the system design point of
view, the ambition is to design horizontal solutions that can enable utilization
of machines in different applications depending on their current availability
and capabilities as well as application requirements, thus avoiding silo
like solutions. One of the crucial enablers of such design is the ability
to discover resources (machines — endpoints) capable of providing required
information at a given time or acting on instructions from the end users.In a typical scenario, during a boot-up procedure (and periodically afterwards),
the machines (endpoints) register with a Resource Directory (for example
EPs installed on vehicles enabling tracking of their position for fleet management
purposes and monitoring environment parameters) hosted by the mobile operator
or somewhere else in the network, periodically a description of its own capabilities.
Due to the usual network configuration of mobile networks, the EPs attached
to the mobile network may not always be efficiently reachable. Therefore, a remote
server is usually used to provide proxy access to the EPs. The address of
each (proxy) endpoint on this server is included in the resource description
stored in the RD. The users, for example mobile applications for environment
monitoring, contact the RD, look up the endpoints capable of providing information
about the environment using appropriate set of link parameters, obtain information
on how to contact them (URLs of the proxy server) and then initiate interaction
to obtain information that is finally processed, displayed on the screen
and usually stored in a database. Similarly, fleet management systems provide
the appropriate link parameters to the RD to look up for EPs deployed on
the vehicles the application is responsible for.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.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
RD Lookup to discover and resolve links
to the desired resources and endpoints. The Resource Directory service need
not be coupled with the data intermediary service. Mapping of Resource Directories
to data intermediaries may be many-to-many.Metadata in web link formats like are supplied by Resource Directories,
which may be internally stored as triples, or relation/attribute
pairs providing metadata about resource links. External catalogs that are
represented in other formats may be converted to common web linking formats for
storage and access by Resource Directories. Since it is common practice for these
to be URN encoded, simple and lossless structural transforms should
generally be sufficient to store external metadata in Resource Directories.The additional features of Resource Directory allow domains to be defined
to enable access to a particular set of resources from particular applications.
This provides isolation and protection of sensitive data when needed. Resource
groups may defined to allow batched reads from multiple resources.Several mechanisms can be employed for discovering the RD, including assuming a
default location (e.g. on an Edge Router in a LoWPAN), assigning an anycast address to the
RD, using DHCP, or discovering the RD using .well-known/core and hyperlinks as
specified in CoRE Link Format .
Endpoints that want to contact a Resource Directory can obtain candidate IP
addresses for such servers in a number of ways.In a 6LoWPAN, good candidates can be taken from:specific static configuration (e.g., anycast addresses), if any,the ABRO option of 6LoWPAN-ND ,other ND options that happen to point to servers (such as RDNSS),DHCPv6 options that might be defined later.The IPv6 Neighbor Discovery Resource Directory Address Option described in 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 ).Constrained nodes configured in large batches may be configured for an
anycast address for the RD. Each target network environment in which
some of these preconfigured nodes are to be brought up is then
configured with a route for this anycast address that leads to an RD
that is appropriate for the environment.As some of these sources are just (more or less educated) guesses, endpoints
MUST make use of any error messages to very strictly rate-limit requests to
candidate IP addresses that don’t work out. For example, an ICMP Destination
Unreachable message (and, in particular, the port unreachable code for this
message) may indicate the lack of a CoAP server on the candidate host, or a
CoAP error response code such as 4.05 “Method Not Allowed” may indicate
unwillingness of a CoAP server to act as a directory server.The Resource Directory Option (RDAO) using IPv6 neighbor Discovery (ND) carries
information about the address of the Resource Directory (RD). This information is
needed when endpoints cannot discover the Resource Directory with link-local
multicast address because the endpoint and the RD are separated by a border Router
(6LBR). In many circumstances the availability of DHCP cannot be guaranteed either
during commissioning of the network. The presence and the use of the RD is
essential during commissioning.It is possible to send multiple RDAO options in one message,
indicating as many resource directory addresses.The lifetime 0x0 means that the RD address is invalid and to be removed.The RDAO format is:This section defines the required set of REST interfaces between a Resource Directory
(RD) and endpoints. Although the examples throughout this section assume the use of
CoAP , these REST interfaces can also be realized using HTTP .
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 implementations using this specification MUST support the
application/link-format content format (ct=40).Resource Directories implementing this specification MAY support additional content formats.Any additional content format supported by a Resource Directory implementing this
specification MUST have an equivalent serialization in the application/link-format
content format.Before an endpoint can make use of an RD, it must first know the RD’s address
and port, and the URI path information for its REST APIs. This section defines
discovery of the RD and its URIs using the well-known interface of the
CoRE Link Format . It is however expected that RDs will also be
discoverable via other methods depending on the deployment.Discovery of the RD registration URI path is performed by sending either a multicast or
unicast GET request to /.well-known/core and including a Resource Type (rt)
parameter with the value “core.rd” in the query string. Likewise, a
Resource Type parameter value of “core.rd-lookup*” is used to discover the
URIs for RD Lookup operations, and “core.gp” is used to discover the URI path for RD
Group operations. Upon success, the response will contain a payload with
a link format entry for each RD function discovered, indicating the URI path
of the RD function returned and the corresponding Resource Type. When performing
multicast discovery, the multicast IP address used will depend on the scope required
and the multicast capabilities of the network.A Resource Directory MAY provide hints about the content-formats it supports in the links it exposes or registers, using the “ct” link attribute, as shown in the example below. Clients MAY use these hints to select alternate content-formats for interaction with the Resource Directory.HTTP does not support multicast and consequently only unicast discovery can be supported
using HTTP. Links to Resource Directories MAY be registered in other Resource Directories,
and well-known entry points SHOULD be provided to enable the bootstrapping of unicast discovery.An RD implementation of this specification MUST support query filtering for
the rt parameter as defined in .The discovery request interface is specified as follows:
EP -> RD
GET
/.well-known/core{?rt}
Resource Type (optional). MAY contain one of the values “core.rd”, “core.rd-lookup*”,
“core.rd-lookup-d”, “core.rd-lookup-res”, “core.rd-lookup-ep”, “core.rd-lookup-gp”,
“core.rd-group” or “core.rd*”
application/link-format (if any)
application/link-format+json (if any)
application/link-format+cbor (if any)The following response codes are defined for this interface:
2.05 “Content” or 200 “OK” 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.
4.04 “Not Found” or 404 “Not Found” is returned in case no matching entry is found for a unicast
request.
4.00 “Bad Request” or 400 “Bad Request” is returned in case of a malformed request for a unicast
request.
No error response to a multicast request.
YES (Unicast only)The following example shows an endpoint discovering an RD using this interface,
thus learning that the RD registration resource is, in this example, at /rd, and that the
content-format delivered by the server hosting the resource is application/link-format
(ct=40). Note that it is up to the RD to choose its RD resource paths.The following example shows the way of indicating that a client may request
alternate content-formats. The Content-Format code attribute “ct” MAY include a
space-separated sequence of Content-Format codes as specified in
Section 7.2.1 of , indicating that multiple content-formats are available.
The example below shows the required Content-Format 40 (application/link-format)
indicated as well as a more application-specific content format
(picked as 65225 in this example; this is in the experimental space, not an assigned value).
The RD resource paths /rd, /rd-lookup, and /rd-group are example values.
This server only implements some of the interfaces described in this document.After discovering the location of an RD, 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 , JSON CoRE Link Format (application/link-format+json), or CBOR CoRE Link Format (application/link-format+cbor) , along with query
parameters indicating the name of the endpoint, and optionally its domain
and the lifetime of the registration.
It is expected that other specifications will define further parameters (see
). The RD then creates a new registration 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 parameters ep and d does not create multiple RD entries.
A new registration may be created at any time to supersede an existing registration,
replacing the registration parameters and links.The registration request interface is specified as follows:
EP -> RD
POST
{+rd}{?ep,d,et,lt,con}
RD registration URI
(mandatory). This is the location of
the RD, as obtained from discovery.
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.
Domain (optional). The domain to which this endpoint belongs. The maximum
length of this parameter is 63 bytes. When this parameter is elided, the
RD MAY associate the endpoint with a configured default domain.
Endpoint Type (optional). The semantic type of the endpoint. This parameter
SHOULD be less than 63 bytes.
Lifetime (optional). Lifetime of the registration in seconds. Range of 60-4294967295.
If no lifetime is included in the initial registration, a default value of
86400 (24 hours) SHOULD be assumed. If the lt parameter is not included in a
registration refresh or update operation, the most recently supplied value SHALL be
re-used.
Context (optional). This parameter sets the scheme, address, port and path at
which this server is available in the form scheme://host:port/path. In
the absence of this parameter the scheme of the protocol, source address
and source port of the register request are assumed. This parameter is
mandatory when the directory is filled by a third party such as an
commissioning tool. When con is used, scheme and host are mandatory and
port and path parameters are optional.
If the endpoint uses an ephemeral port to register with, it MUST include the con:
parameter in the registration to provide a valid network path.
If the endpoint which is located behind a NAT gateway is registering with a Resource
Directory which is on the network service side of the NAT gateway, the endpoint MUST
use a persistent port for the outgoing registration in order to provide the NAT
gateway with a valid network address for replies and incoming requests.
application/link-format
application/link-format+json
application/link-format+cborThe following response codes are defined for this interface:
2.01 “Created” or 201 “Created”. The Location header option
MUST be included in the response when a new registration resource is created. This Location MUST be a stable identifier
generated by the RD as it is used for all subsequent
operations on this registration resource. The registration resource location thus returned is for the purpose of updating the lifetime
of the registration and for maintaining the content of the
registered links, including updating and deleting links.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.09 “Conflict” or 409 “Conflict”. Attempt to update the registration content with links resulting in plurality of references; see .
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.
YESThe following example shows an endpoint with the name “node1” registering
two resources to an RD using this interface. The location “/rd”
is an example RD location discovered in a request similar to .A Resource Directory may optionally support HTTP. Here is an example of the same registration operation above, when done using HTTP.Not all endpoints hosting resources are expected to know how to upload links to a RD as described in . Instead, simple endpoints can implement the Simple Registration approach described in this section. An RD implementing this specification MUST implement Simple Registration. However, there may
be security reasons why this form of directory discovery would be disabled.This approach requires that the endpoint makes available the hosted resources
that it wants to be discovered, as links on its /.well-known/core interface as
specified in .The endpoint then finds one or more addresses of the directory server as described in .An endpoint can send (a selection of) hosted resources to a directory server for publication as described in .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.An endpoint that wants to make itself discoverable occasionally sends a POST
request to the /.well-known/core URI of any candidate directory server that
it finds. The body of the POST request is empty, which triggers the resource
directory server to perform GET requests at the requesting server’s default
discovery URI to obtain the link-format payload to register.The endpoint MUST include the endpoint name and MAY include the registration parameters d, lt, and et, in the POST request as per .The following example shows an endpoint using simple publishing,
by simply sending an empty POST to a resource directory.For some applications, even Simple Registration 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 a commissioning tool. The commissioning
tool can fill the Resource Directory from a database or other means. For
that purpose the scheme, IP address and port of the registered device is
indicated in the Context parameter of the registration described in .Plurality of link references within a Registration (registration resource) is an indication of some error condition and should not be allowed.Plurality of link references exists if, and only if, two or more links in a Registration
contain identical context, target, and relation values. This condition would be likely to arise if there were multiple co-ordinators or configuration tools, each with a different
set of configuration values for the same resource.A Resource Directory SHOULD reject a registration, or an operation on a registration, which would result in a plurality of link references within the the context of the registration. There is no requirement in this document for a resource directory to check for plurality of reference between different registrations. Resource Directory operations which are rejected due to reference plurality SHOULD be returned the “Conflict” code, indicating that there is someting wrong with the request.After the initial registration, an endpoint should retain the returned location of the Registration Resource for further operations, including refreshing the registration in order to extend the lifetime and “keep-alive” the registration. If the lifetime of the registration expires, the RD SHOULD NOT respond to discovery queries with information from the endpoint. The RD SHOULD continue to provide access to the Registration Resource after a registration time-out occurs in order to enable the registering endpoint to eventually refresh the registration. The RD MAY eventually remove the registration resource for the purpose of resource recovery and garbage collection. If the Registration Resource is removed, the endpoint will need to re-register.The Registration Resource may also be used to inspect the registration resource using GET, update the registration link contents using PATCH (as introduced in ), or cancel the registration using DELETE.These operations are described in this section.In accordance with , operations which would result in plural link references within the context of a registration resource SHOULD be rejected using the “Conflict” result code.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 registration resource returned in the Location header option in the response returned from the intial registration operation.An update MAY update the lifetime or context registration parameters
“lt”, “con” as in ) if the previous settings are to be retained. Parameters that are not being changed changed SHOULD NOT
be included in an update. Adding parameters that have not changed increases
the size of the message but does not have any other implications.
Parameters MUST be included as query parameters in an update operation as
in .Upon receiving an update request, an RD MUST reset the timeout for that
endpoint and update the scheme, IP address and port of the endpoint, using
the source address of the update, or the context (“con”) parameter if present.
If the lifetime parameter “lt” is included in the received update request,
the RD MUST update the lifetime of the registration and set the timeout equal
to the new lifetime. If the lifetime parameter is not included in the registration
update, the most recent setting is re-used for the next registration time-out period.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. A link is replaced only if all of the target URI and relation type (if present) and anchor value (if present) match.If the link payload is included, it SHOULD be checked for reference plurality as described in and rejected with a “Conflict” result if there are plural link references detected.In addition to the use of POST, as described in this section, there is an
alternate way to add, replace, and delete links using PATCH as described
in .The update registration request interface is specified as follows:
EP -> RD
POST
{+location}{?lt,con}
This is the Location returned by the RD as a result of a successful
earlier registration.
Lifetime (optional). Lifetime of the registration in seconds. Range of 60-4294967295.
If no lifetime is included, the previous last
lifetime set on a previous update or the original registration
(falling back to 86400) SHOULD be used.
Context (optional). This parameter sets the scheme, address and port at
which this server is available in the form scheme://host:port/path. In
the absence of this parameter the scheme of the protocol, source address
and source port of the register request are assumed. This parameter is
mandatory when the directory is filled by a third party such as an
commissioning tool. When con is used, scheme and host are mandatory and
port and path parameters are optional.
application/link-format (mandatory)
application/link-format+json (optional)
application/link-format+cbor (optional)The following response codes are defined for this interface:
2.04 “Changed” or 204 “No Content” if the update was successfully processed.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. Registration does not exist (e.g. may have expired).
4.09 “Conflict” or 409 “Conflict”. Attempt to update the registration content with links resulting in plurality of references; see .
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.
YESThe following example shows an endpoint updating its registration at
an RD using this interface with the example location value: /rd/4521.The following example shows an endpoint updating its registration with a new lifetime and context, changing an existing link, and adding a new link using this interface with the example location value /rd/4521.
With the initial registration the client set the following values:lifetime (lt)=500context (con)=coap://local-proxy-old.example.com:5683resource= </sensors/temp>;ct=41;rt=”foobar”;if=”sensor”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:
EP -> RD
DELETE
{+location}
This is the Location returned by the RD as a result of a successful
earlier registration.The following responses codes are defined for this interface:
2.02 “Deleted” or 204 “No Content” upon successful deletion
4.00 “Bad Request” or 400 “Bad request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. Registration does not exist (e.g. may have expired).
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.HTTP support: YESThe following examples shows successful removal of the endpoint from the RD with example location value /rd/4521.Some endpoints may wish to manage their links as a collection, and may need to read the current set of links stored in the registration resource, in order to determine link maintenance operations.One or more links MAY be selected by using query filtering as specified in Section 4.1If no links are selected, the Resource Directory SHOULD return an empty payload.The read request interface is specified as follows:
EP -> RD
GET
{+location}{?href,rel,rt,if,ct}
This is the Location returned by the RD as a result of a successful
earlier registration.href,rel,rt,if,ct := link relations and attributes specified in the query in order to select particular links based on their relations and attributes. “href” denotes the URI target of the link. See Sec. 4.1The following responses codes are defined for this interface:
2.05 “Content” or 200 “OK” upon success with an application/link-format, application/link-format+cbor, or application/link-format+json payload.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. Registration does not exist (e.g. may have expired).
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.HTTP support: YESThe following examples show successful read of the endpoint links from the RD, with example location value /rd/4521.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
document.Other PATCH document formats may be used as appropriate for patching the array of objects format of a Registration Resource. In particular, a select-merge patch document format could combine the function of link selection query and link attribute replacement values.One or more links are selected for update by using query filtering as specified in Section 4.1The 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 no links are selected by the query parameters, the PATCH operation SHOULD NOT update the state of any resource, and SHOULD return a reply of “Changed”.If an attribute name specified in the PATCH document exists in any the set of selected links, all occurrences of the attribute value in the target document MUST be updated using the value from the PATCH payload. If the attribute name is not present in any selected links, the attribute MUST be added to the links.If the PATCH payload contains plural link references, or processing the PATCH payload would result in plural link references, the request SHOULD be rejected with a “Conflict” result.If the PATCH payload results in the modification of link target, context, or relation values, that is “href”, “rel”, or “anchor”, the request SHOULD be rejected with a “Conflict” result code.The update request interface is specified as follows:
EP -> RD
PATCH
{+location}{?href,rel,rt,if,ct}
This is the Location returned by the RD as a result of a successful
earlier registration.href,rel,rt,if,ct := link relations and attributes specified in the query in order to select particular links based on their relations and attributes. “href” denotes the URI target of the link. See Sec. 4.1
application/merge-patch+json (mandatory)The following response codes are defined for this interface:
2.04 “Changed” 0r 204 “No Content” in the update was successfully processed.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. Registration resource does not exist (e.g. may have expired).
4.09 “Conflict” or 409 “Conflict”. Attempt to update the registration content with links resulting in plurality of references; see .
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.HTTP support: YESThe following examples show an endpoint adding </sensors/humid>, modifying </sensors/temp>, and removing </sensors/light> links in RD using the Update Endpoint Links function with the example location value /rd/4521.The Registration Resource initial state is:The following example shows an EP adding the link </sensors/humid>;ct=41;rt=”humid-s”;if=”sensor” to the collection of links at the location /rd/4521.The following example shows an EP modifying all links at the example 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.This example shows an EP removing all links at the example location /rd/4521 which are identified by href=”/sensors/light”.This section defines the REST API for the creation, management, and lookup of endpoints for group operations.
Similar to endpoint registration entries in the RD, groups may be created or removed. However unlike an endpoint entry, a group entry consists of a list of endpoints and does
not have a lifetime associated with it. In order to make use of multicast requests with
CoAP, a group MAY have a multicast address associated with it.In order to create a group, a commissioning tool (CT) used to configure groups,
makes a request to the RD indicating the name of the group to create (or
update), optionally the domain the group belongs to, and optionally the multicast
address of the group. The registration message includes the list of endpoints
that belong to that group.All the endpoints in the group MUST be registered with the RD before registering a group. If an endpoint is not yet registered to the RD before registering the group, the registration message returns an error. The RD sends a blank target URI for every 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 .The registration request interface is specified as follows:
CT -> RD
POST
{+rd-group}{?gp,d,con}
RD Group URI (mandatory). This is the location of the RD Group
REST API.
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.
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.
Context (optional). This parameter sets the scheme, address and port at
which this server is available in the form scheme://host:port/path. In
the absence of this parameter the scheme of the protocol, source address
and source port of the register request are assumed. This parameter is
mandatory when the directory is filled by a third party such as an
commissioning tool. When con is used, scheme and host are mandatory and
port and path parameters are optional.
application/link-format
application/link-format+json
application/link-format+cborThe following response codes are defined for this interface:
2.01 “Created” or 201 “Created”. The Location header option MUST be returned in response to a successful group CREATE operation. This Location MUST be a stable identifier generated by the RD as it is used for delete operations of the group registration resource.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. An Endpoint is not registered in the RD (e.g. may have expired).
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.
YESThe following example shows an EP registering a group with the name “lights” which has two endpoints to an RD using this interface. The RD group path /rd-group
is an example RD location discovered in a request similar to .A group can be removed simply by sending a removal message to the location of the group registration resource which was
returned when intially 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:
CT -> RD
DELETE
{+location}
This is the Location returned by the RD as a result of a successful
group registration.The following responses codes are defined for this interface:
2.02 “Deleted” or 204 “No Content” upon successful deletion
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
4.04 “Not Found” or 404 “Not Found”. Group does not exist.
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.
YESThe following examples shows successful removal of the group from the RD with the example location value /rd-group/12.In order for an RD to be used for discovering resources registered with it,
an optional lookup interface may be provided. This lookup interface
is defined as a default, and it is assumed that RDs may also support lookups
to return resource descriptions in alternative formats (e.g. Atom or HTML
Link) or using more advanced interfaces (e.g. supporting context or semantic
based lookup).RD Lookup allows lookups for domains, groups, endpoints and resources
using attributes defined in this document and for use with the CoRE
Link Format. The result of a lookup request is the list of links (if any)
corresponding to the type of lookup. Thus, a domain lookup MUST return a list of domains, a group lookup MUST return a list of groups, an endpoint lookup MUST return a list of endpoints and a resource lookup MUST return a list of links to resources.RD Lookup does not expose registration resources directly, but returns link content from registration resource entries which satisfy RD Lookup queries.The lookup type is selected by a URI endpoint, which is indicated by a Resource Type as per below:Lookup TypeResource TypeMandatoryResourcecore.rd-lookup-resMandatoryEndpointcore.rd-lookup-epMandatoryDomaincore.rd-lookup-dOptionalGroupcore.rd-lookup-gpOptionalEach endpoint and resource lookup result returns respectively the scheme (IP address and port) followed by the path part of the URI of every endpoint and resource inside angle brackets (“<>”) and followed by the other parameters.The target of these links SHOULD be the actual location of the domain, endpoint or resource, but MAY be an intermediate proxy e.g. in the case of an HTTP lookup interface for CoAP endpoints.The domain lookup returns every lookup domain with a base RD resource value (e.g. “/rd”) encapsulated within angle brackets.In case that a group does not implement any multicast address, the group lookup returns every group lookup with a group base resource value encapsulated within angle brackets (e.g. “/rd/look-up”). Otherwise, the group lookup returns the multicast address of the group inside angle brackets.Using the Accept Option, the requester can control whether this list is returned in CoRE Link Format (application/link-format, default) or its alternate content-formats (application/link-format+json or application/link-format+cbor).The page and count parameters are used to obtain lookup results in specified increments using pagination, where count specifies how many links to return and page specifies which subset of links organized in sequential pages, each containing ‘count’ links, starting with link zero and page zero. Thus, specifying count of 10 and page of 0 will return the first 10 links in the result set (links 0-9). Count = 10 and page = 1 will return the next ‘page’ containing links 10-19, and so on.Multiple query parameters MAY be included in a lookup, all included parameters MUST match for a resource to be returned. The character’*’ MAY be included at the end of a parameter value as a wildcard operator.RD Lookup requests MAY use any set of query parameters to match the registered attributes and relations. In addition, this interface MAY be used with queries that specify domains, endpoints, and groups. For example, a domain lookup filtering on groups would return a list of domains that contain the specified groups. An endpoint lookup filtering on groups would return a list of endpoints that are in the specified groups.Clients that are interested in a lookup result repeatedly or continuously can use
mechanisms like ETag caching, resource observation (),
or any future mechanism that might allow more efficient observations of collections.
These are advertised, detected and used according to their own specifications
and can be used with the lookup interface as with any other resource.The lookup interface is specified as follows:
Client -> RD
GET
{+type-lookup-location}{?d,res,ep,gp,et,rt,page,count,resource-param}
RD Lookup URI for a given lookup type (mandatory). The address is
discovered as described in .
Endpoint name (optional). Used for endpoint, group and resource lookups.
Domain (optional). Used for domain, group, endpoint and resource lookups.
resource (optional). Used for domain, group, endpoint and resource lookups.
gp := Group name (optional). Used for endpoint, group and resource lookups.
Page (optional). Parameter can not be used without the count
parameter. Results are returned from result set in pages that contain
‘count’ links starting from index (page * count). Page numbering starts
with zero.
Count (optional). Number of results is limited to this parameter value. If
the page parameter is also present, the response MUST only include ‘count’
links starting with the (page * count) link in the result set from the query. If
the count parameter is not present, then the response MUST return all matching
links in the result set. Link numbering starts with zero.
Resource type (optional). Used for group, endpoint and resource lookups.
Endpoint type (optional). Used for group, endpoint and resource lookups.
Link attribute parameters (optional). Any link target attribute as defined in
Section 4.1 of , used for resource lookups.
application/link-format (optional)
application/link-format+json (optional)
application/link-format+cbor (optional)The following responses codes are defined for this interface:
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.
4.04 “Not Found” or 404 “Not Found” in case no matching entry is found for a unicast request.
No error response to a multicast request.
4.00 “Bad Request” or 400 “Bad Request”. Malformed request.
5.03 “Service Unavailable” or 503 “Service Unavailable”. Service could not perform the operation.
YESThe examples in this section assume CoAP hosts with a default CoAP port 61616. HTTP hosts are possible and do not change the nature of the examples.The following example shows a client performing a resource lookup with the example resource look-up locations discovered in :The following example shows a client performing an endpoint type lookup:The following example shows a client performing a domain lookup:The following example shows a client performing a group lookup for all groups:The following example shows a client performing a lookup for all endpoints
in a particular group:The following example shows a client performing a lookup for all groups an
endpoint belongs to:The following example shows a client performing a paginated lookupThe security considerations as described in Section 7 of and
Section 6 of apply. The /.well-known/core resource may be
protected e.g. using DTLS when hosted on a CoAP server as described in
. DTLS or TLS based security SHOULD be used on all resource
directory interfaces defined in this document.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.Access control SHOULD be performed separately for the RD registration, Lookup, and
group API paths, as different endpoints may be authorized to register
with an RD from those authorized to lookup endpoints from the RD. Such access
control SHOULD be performed in as fine-grained a level as possible. For example
access control for lookups could be performed either at the domain, endpoint
or resource level.Services that run over UDP unprotected are vulnerable to unknowingly
become part of a DDoS attack as UDP does not require return
routability check. Therefore, an attacker can easily spoof the source
IP of the target entity and send requests to such a service which
would then respond to the target entity. This can be used for
large-scale DDoS attacks on the target. Especially, if the service
returns a response that is order of magnitudes larger than the
request, the situation becomes even worse as now the attack can be
amplified. DNS servers have been widely used for DDoS amplification
attacks. There is also a danger that NTP Servers could become implicated in denial-of-service (DoS) attacks since they run on unprotected UDP, there
is no return routability check, and they can have a large amplification factor.
The responses from the NTP server were found to be
19 times larger than the request. A Resource Directory (RD) which responds
to wild-card lookups is potentially vulnerable if run with CoAP over UDP.
Since there is no return routability check and the responses can be significantly
larger than requests, RDs can unknowingly become part of a DDoS amplification
attack.“core.rd”, “core.rd-group”, “core.rd-lookup-ep”, “core.rd-lookup-res”,
“core.rd-lookup-d”, and “core.rd-lookup-gp” resource types need to be
registered with the resource type registry defined by .This document registers one new ND option type under the subregistry “IPv6 Neighbor Discovery Option Formats”:Resource Directory address Option (38)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 .Initial entries in this sub-registry are as follows:NameQueryValidityDescriptionEndpoint NameepName of the endpoint, max 63 bytesLifetimelt60-4294967295Lifetime of the registration in secondsDomaindDomain to which this endpoint belongsEndpoint TypeetSemantic name of the endpointContextconURIThe scheme, address and port and path at which this server is availableResource NameresName of the resourceGroup NamegpName of a group in the RDPagepageIntegerUsed for paginationCountcountIntegerUsed for paginationThe IANA policy for future additions to the sub-registry is “Expert Review”
as described in .Two examples are presented: a Lighting Installation example in and a LWM2M example in .This example shows a simplified lighting installation which makes use of
the Resource Directory (RD) with a CoAP interface to facilitate the installation and start up of
the application code in the lights and sensors. In particular, the example
leads to the definition of a group and the enabling of the corresponding
multicast address. No conclusions must be drawn on the realization of actual
installation or naming procedures, because the example only “emphasizes” some of the issues
that may influence the use of the RD and does not pretend to be normative.The example assumes that the installation is managed. That means that a Commissioning
Tool (CT) is used to authorize the addition of nodes, name them, and name
their services. The CT can be connected to the installation in many ways:
the CT can be part of the installation network, connected by WiFi to the
installation network, or connected via GPRS link, or other method.It is assumed that there are two naming authorities for the installation:
(1) the network manager that is responsible for the correct operation of
the network and the connected interfaces, and (2) the lighting manager that
is responsible for the correct functioning of networked lights and sensors.
The result is the existence of two naming schemes coming from the two managing
entities.The example installation consists of one presence sensor, and two luminaries,
luminary1 and luminary2, each with their own wireless interface. Each luminary
contains three lamps: left, right and middle. Each luminary is accessible
through one endpoint. For each lamp a resource exists to modify the settings
of a lamp in a luminary. The purpose of the installation is that the presence
sensor notifies the presence of persons to a group of lamps. The group of
lamps consists of: middle and left lamps of luminary1 and right lamp of luminary2.Before commissioning by the lighting manager, the network is installed and
access to the interfaces is proven to work by the network manager.At the moment of installation, the network under installation is not necessarily
connected to the DNS infra structure. Therefore, SLAAC IPv6 addresses are
assigned to CT, RD, luminaries and sensor shown in below:NameIPv6 addressluminary1FDFD::ABCD:1luminary2FDFD::ABCD:2Presence sensorFDFD::ABCD:3Resource directoryFDFD::ABCD:0In the use of resource directory during installation is
presented.It is assumed that access to the DNS infrastructure is not always possible
during installation. Therefore, the SLAAC addresses are used in this section.For discovery, the resource types (rt) of the devices are important. The
lamps in the luminaries have rt: light, and the presence sensor has rt: p-sensor.
The endpoints have names which are relevant to the light installation manager.
In this case luminary1, luminary2, and the presence sensor are located in
room 2-4-015, where luminary1 is located at the window and luminary2 and
the presence sensor are located at the door. The endpoint names reflect
this physical location. The middle, left and right lamps are accessed via
path /light/middle, /light/left, and /light/right respectively. The identifiers
relevant to the Resource Directory are shown in below:Nameendpointresource pathresource typeluminary1lm_R2-4-015_wndw/light/leftlightluminary1lm_R2-4-015_wndw/light/middlelightluminary1lm_R2-4-015_wndw/light/rightlightluminary2lm_R2-4-015_door/light/leftlightluminary2lm_R2-4-015_door/light/middlelightluminary2lm_R2-4-015_door/light/rightlightPresence sensorps_R2-4-015_door/psp-sensorIt is assumed that the CT knows of the RD’s address, and has performed URI
discovery on it that gave a response like the one in the example.The CT inserts the endpoints of the luminaries and the sensor in the RD
using the Context parameter (con) to specify the interface address:The domain name d=R2-4-015 has been added for an efficient lookup because
filtering on “ep” name is more awkward. The same domain name is communicated to
the two luminaries and the presence sensor by the CT.The group is specified in the RD. The Context parameter is set to the site-local
multicast address allocated to the group.
In the POST in the example below, these two endpoints and the endpoint
of the presence sensor are registered as members of the group.After the filling of the RD by the CT, the application in the luminaries
can learn to which groups they belong, and enable their interface for the
multicast address.The luminary, knowing its domain, queries the RD for the endpoint with rt=light
and d=R2-4-015. The RD returns all endpoints in the domain.Knowing its own IPv6 address, the luminary discovers its endpoint name. With
the endpoint name the luminary queries the RD for all groups to which the
endpoint belongs.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 .Dependent on the situation, only the address, “a”, or the name, “n”, is specified
in the coap-group resource.This example shows how the OMA LWM2M specification makes use of Resource Directory (RD).OMA LWM2M is a profile for device services based on CoAP(OMA Name Authority). LWM2M defines a simple object model and a number of abstract interfaces and operations for device management and device service enablement.An LWM2M server is an instance of an LWM2M middleware service layer, containing a Resource Directory along with other LWM2M interfaces defined by the LWM2M specification.CoRE Resource Directory (RD) is used to provide the LWM2M Registration interface.LWM2M does not provide for registration domains and does not currently
use the rd-group or rd-lookup interfaces.The LWM2M specification describes a set of interfaces and a resource model used between a LWM2M device and an LWM2M server. Other interfaces, proxies, and applications are currently out of scope for LWM2M.The location of the LWM2M Server and RD URI path is provided by the LWM2M Bootstrap process, so no dynamic discovery of the RD is used. LWM2M Servers and endpoints are not required to implement the /.well-known/core resource.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”.base-uri := Base URI for LWM2M resources or “undefined” for default (empty) base URIobject-id := OMNA (OMA Name Authority) registered object ID (0-65535)object-instance := Object instance identifier (0-65535) or
“undefined”/”empty” (see above)) to refer to all instances of an object IDresource-id := OMNA (OMA Name Authority) registered resource ID (0-65535) or “undefined” to refer to all resources within an instanceresource-instance := Resource instance identifier or “undefined” to refer to single instance of a resourceLWM2M 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: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).LWM2M defines a registration interface based on the REST API, described in . The
RD registration URI path of the LWM2M Resource Directory is specified to be “/rd”.LWM2M endpoints register object IDs, for example </1>, to indicate that a particular object type is supported, and register object instances, for example </1/0>, to indicate that a particular instance of that object type exists.Resources within the LWM2M object instance are not registered with the RD, but may be discovered by reading the resource links from the object instance using GET with a CoAP Content-Format of application/link-format. Resources may also be read as a structured object by performing a GET to the object instance with a Content-Format of senml+json.When an LWM2M object or instance is registered, this indicates to the LWM2M server that the object and its resources are available for management and service enablement (REST API) operations.LWM2M endpoints may use the following RD registration parameters as defined in :Endpoint Name is mandatory, all other registration parameters are optional.Additional optional LWM2M registration parameters are defined:NameQueryValidityDescriptionProtocol Bindingb{“U”,UQ”,”S”,”SQ”,”US”,”UQS”}Available ProtocolsLWM2M Versionver1.0Spec VersionSMS NumbersmsMSISDNThe following RD registration parameters are not currently specified for use in LWM2M: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: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.An LWM2M Registration update proceeds as described in , and adds some optional parameter updates: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.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 .Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders
Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola, Linyi
Tian, Chistian Amsuss, and Jan Newmarch have provided helpful comments, discussions and ideas to improve and
shape this document. Zach would also like to thank his colleagues from the
EU FP7 SENSEI project, where many of the resource directory concepts were
originally developed.changes from -09 to -10removed “ins” and “exp” link-format extensions.removed all text concerning DNS-SD.removed inconsistency in RDAO text.suggestions taken over from various sourcesreplaced “Function Set” with “REST API”, “base URI”, “base path”moved simple registration to registration sectionchanges from -08 to -09clarified the “example use” of the base RD resource values /rd, /rd-lookup, and /rd-group.changed “ins” ABNF notation.various editorial improvements, including in examplesclarifications for RDAOchanges from -07 to -08removed link target value returned from domain and group lookup typesMaximum length of domain parameter 63 bytes for consistency with groupremoved option for simple POST of link data, don’t require a .well-known/core resource to accept POST data and handle it in a special way; we already have /rd for thatadd IPv6 ND Option for discovery of an RDclarify group configuration section 6.1 that endpoints must be registered before including them in a groupremoved all superfluous client-server diagramssimplified lighting exampleintroduced Commissioning ToolRD-Look-up text is extended.changes from -06 to -07added text in the discovery section to allow content format hints to be exposed in the discovery link attributeseditorial updates to section 9update author informationminor text correctionsChanges from -05 to -06added note that the PATCH section is contingent on the progress of
the PATCH methodchanges from -04 to -05added Update Endpoint Links using PATCHhttp access made explicit in interface specificationAdded http examplesChanges from -03 to -04:Added http response codesClarified endpoint name usageAdd application/link-format+cbor content-formatChanges from -02 to -03:Added an example for lighting and DNS integrationAdded an example for RD use in OMA LWM2MAdded Read Links operation for link inspection by endpointsExpanded DNS-SD sectionAdded draft authors Peter van der Stok and Michael KosterChanges from -01 to -02:Added a catalogue use case.Changed the registration update to a POST with optional link format payload. Removed the endpoint type update from the update.Additional examples section added for more complex use cases.New DNS-SD mapping section.Added text on endpoint identification and authentication.Error code 4.04 added to Registration Update and Delete requests.Made 63 bytes a SHOULD rather than a MUST for endpoint name and resource type parameters.Changes from -00 to -01:Removed the ETag validation feature.Place holder for the DNS-SD mapping section.Explicitly disabled GET or POST on returned Location.New registry for RD parameters.Added support for the JSON Link Format.Added reference to the Groupcomm WG draft.Changes from -05 to WG Document -00:Updated the version and date.Changes from -04 to -05:Restricted Update to parameter updates.Added pagination support for the Lookup interface.Minor editing, bug fixes and reference updates.Added group support.Changed rt to et for the registration and update interface.Changes from -03 to -04:Added the ins= parameter back for the DNS-SD mapping.Integrated the Simple Directory Discovery from Carsten.Editorial improvements.Fixed the use of ETags.Fixed tickets 383 and 372Changes from -02 to -03:Changed the endpoint name back to a single registration parameter ep= and removed the h= and ins= parameters.Updated REST interface descriptions to use RFC6570 URI Template format.Introduced an improved RD Lookup design as its own function set.Improved the security considerations section.Made the POST registration interface idempotent by requiring the ep= parameter to be present.Changes from -01 to -02:Added a terminology section.Changed the inclusion of an ETag in registration or update to a MAY.Added the concept of an RD Domain and a registration parameter for it.Recommended the Location returned from a registration to be stable, allowing for endpoint and Domain information to be changed during updates.Changed the lookup interface to accept endpoint and Domain as query string parameters to control the scope of a lookup.Constrained RESTful Environments (CoRE) Link FormatThis specification defines Web Linking using a link format for use by constrained web servers to describe hosted resources, their attributes, and other relationships between links. Based on the HTTP Link Header field defined in RFC 5988, the Constrained RESTful Environments (CoRE) Link Format is carried as a payload and is assigned an Internet media type. "RESTful" refers to the Representational State Transfer (REST) architecture. A well-known URI is defined as a default entry point for requesting the links hosted by a server. [STANDARDS-TRACK]Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Uniform Resource Identifier (URI): Generic SyntaxA Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]Guidelines for Writing an IANA Considerations Section in RFCsMany protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Web LinkingThis document specifies relation types for Web links, and defines a registry for them. It also defines the use of such links in HTTP headers with the Link header field. [STANDARDS-TRACK]URI TemplateA URI Template is a compact sequence of characters for describing a range of Uniform Resource Identifiers through variable expansion. This specification defines the URI Template syntax and the process for expanding a URI Template into a URI reference, along with guidelines for the use of URI Templates on the Internet. [STANDARDS-TRACK]JSON Merge PatchThis specification defines the JSON merge patch format and processing rules. The merge patch format is primarily intended for use with the HTTP PATCH method as a means of describing a set of modifications to a target resource's content.PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)The methods defined in RFC 7252 for the Constrained Application Protocol (CoAP) only allow access to a complete resource, not to parts of a resource. In case of resources with larger or complex data, or in situations where resource continuity is required, replacing or requesting the whole resource is undesirable. Several applications using CoAP need to access parts of the resources.This specification defines the new CoAP methods, FETCH, PATCH, and iPATCH, which are used to access and update parts of a resource.Representing Constrained RESTful Environments (CoRE) Link Format in JSON and CBORJavaScript Object Notation, JSON (RFC7159) is a text-based data format which is popular for Web based data exchange. Concise Binary Object Representation, CBOR (RFC7049) is a binary data format which has been optimized for data exchange for the Internet of Things (IoT). For many IoT scenarios, CBOR formats will be preferred since it can help decrease transmission payload sizes as well as implementation code sizes compared to other data formats. Web Linking (RFC5988) provides a way to represent links between Web resources as well as the relations expressed by them and attributes of such a link. In constrained networks, a collection of Web links can be exchanged in the CoRE link format (RFC6690). Outside of constrained environments, it may be useful to represent these collections of Web links in JSON, and similarly, inside constrained environments, in CBOR. This specification defines a common format for this.The Constrained Application Protocol (CoAP)The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.Group Communication for the Constrained Application Protocol (CoAP)The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for constrained devices and constrained networks. It is anticipated that constrained devices will often naturally operate in groups (e.g., in a building automation scenario, all lights in a given room may need to be switched on/off as a group). This specification defines how CoAP should be used in a group communication context. An approach for using CoAP on top of IP multicast is detailed based on existing CoAP functionality as well as new features introduced in this specification. Also, various use cases and corresponding protocol flows are provided to illustrate important concepts. Finally, guidance is provided for deployment in various network topologies.Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)The IETF work in IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) defines 6LoWPANs such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow the traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non- transitive wireless links, as its reliance on the traditional IPv6 link concept and its heavy use of multicast make it inefficient and sometimes impractical in a low-power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, its addressing mechanisms, and duplicate address detection for Low- power Wireless Personal Area Networks and similar networks. The document thus updates RFC 4944 to specify the use of the optimizations defined here. [STANDARDS-TRACK]Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and RoutingThe Hypertext Transfer Protocol (HTTP) is a stateless application-level protocol for distributed, collaborative, hypertext information systems. This document provides an overview of HTTP architecture and its associated terminology, defines the "http" and "https" Uniform Resource Identifier (URI) schemes, defines the HTTP/1.1 message syntax and parsing requirements, and describes related security concerns for implementations.Observing Resources in the Constrained Application Protocol (CoAP)The Constrained Application Protocol (CoAP) is a RESTful application protocol for constrained nodes and networks. The state of a resource on a CoAP server can change over time. This document specifies a simple protocol extension for CoAP that enables CoAP clients to "observe" resources, i.e., to retrieve a representation of a resource and keep this representation updated by the server over a period of time. The protocol follows a best-effort approach for sending new representations to clients and provides eventual consistency between the state observed by each client and the actual resource state at the server.Hypertext Transfer Protocol -- HTTP/1.1HTTP has been in use by the World-Wide Web global information initiative since 1990. This specification defines the protocol referred to as "HTTP/1.1", and is an update to RFC 2068. [STANDARDS-TRACK]