Draft: draft-ietf-core-resource-directory

Commentary: This is a series of commits removing cruft in the examples as discussed in Diverging from the discussion outcome , more than a single line was kept of 10.2 , as the historical note left in , by analogy , means that we should mention that application 's choice of a fixed path as well . Some commits may be still as I 'm going through the list . 
 I 'm merging this in to ensure it interacts well with the example updates ( where the resource types were replaced with actual example values ) ; any follow - ups will go to a separate PR .
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Alternatively, the CT can communicate the multicast address directly
to the luminaries by using the "coap-group" resource specified in
RFC7390.
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Dependent on the situation, only the address, "a", or the name, "n",
is specified in the coap-group resource.
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This example shows how the OMA LWM2M specification makes use of RDs.
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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.
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An LWM2M server is an instance of an LWM2M middleware service layer,
containing an RD along with other LWM2M interfaces defined by the
LWM2M specification.
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The registration interface of this specification is used to provide
the LWM2M Registration interface.
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LWM2M does not provide for registration sectors and does not
currently use the rd-lookup interface.
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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.
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The OMA LWM2M object model is based on a simple 2 level class
hierarchy consisting of Objects and Resources.
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An LWM2M Resource is a REST endpoint, allowed to be a single value or
an array of values of the same data type.
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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.
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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.
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The five variables given here are strings.  base-uri can also have
the special value "undefined" (sometimes called "null" in RFC 6570).
Each of the variables object-instance, resource-id, and resource-
instance can be the special value "undefined" only if the values
behind it in this sequence also are "undefined".  As a special case,
object-instance can be "empty" (which is different from "undefined")
if resource-id is not "undefined".
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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).
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LWM2M defines a registration interface based on the REST API,
described in registration.  The RD registration URI path of the LWM2M
RD is specified to be "/rd".
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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.
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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.
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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.
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Endpoint Name, Lifetime, and LWM2M Version are mandatory parameters
for the register operation, all other registration parameters are
optional.
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The endpoint registration must include a payload containing links to
all supported objects and existing object instances, optionally
including the appropriate link-format relations.
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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.
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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.
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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 removal.
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OMA LwM2M is a profile for device services based on CoAP, providing
interfaces and operations for device management and device service
enablement.
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An LwM2M server is an instance of an LwM2M middleware service layer,
containing an RD (LwM2M page 36f).
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That RD only implements the registration interface, and no lookup is
implemented.  Instead, the LwM2M server provides access to the
registered resources, in a similar way to a reverse proxy.
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The LwM2M example was reduced from an outdated explanation of
the complete LwM2M model to a summary of how RD is used in
there, with a reference to the current specification.