[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-shelby-core-resource-directory) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17

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.




Shelby, et al.           Expires April 18, 2016                 [Page 1]


Internet-Draft           CoRE Resource Directory            October 2015


   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Architecture and Use Cases  . . . . . . . . . . . . . . . . .   5
     3.1.  Use Case: Cellular M2M  . . . . . . . . . . . . . . . . .   6
     3.2.  Use Case: Home and Building Automation  . . . . . . . . .   7
     3.3.  Use Case: Link Catalogues . . . . . . . . . . . . . . . .   7
   4.  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



Shelby, et al.           Expires April 18, 2016                 [Page 2]


Internet-Draft           CoRE Resource Directory            October 2015


     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



Shelby, et al.           Expires April 18, 2016                 [Page 3]


Internet-Draft           CoRE Resource Directory            October 2015


   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.






Shelby, et al.           Expires April 18, 2016                 [Page 4]


Internet-Draft           CoRE Resource Directory            October 2015


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.









Shelby, et al.           Expires April 18, 2016                 [Page 5]


Internet-Draft           CoRE Resource Directory            October 2015


                  +------------+
                  |   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



Shelby, et al.           Expires April 18, 2016                 [Page 6]


Internet-Draft           CoRE Resource Directory            October 2015


   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



Shelby, et al.           Expires April 18, 2016                 [Page 7]


Internet-Draft           CoRE Resource Directory            October 2015


   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.





Shelby, et al.           Expires April 18, 2016                 [Page 8]


Internet-Draft           CoRE Resource Directory            October 2015


   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.





Shelby, et al.           Expires April 18, 2016                 [Page 9]


Internet-Draft           CoRE Resource Directory            October 2015


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



Shelby, et al.           Expires April 18, 2016                [Page 10]


Internet-Draft           CoRE Resource Directory            October 2015


   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




Shelby, et al.           Expires April 18, 2016                [Page 11]


Internet-Draft           CoRE Resource Directory            October 2015


   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:




Shelby, et al.           Expires April 18, 2016                [Page 12]


Internet-Draft           CoRE Resource Directory            October 2015


   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:





Shelby, et al.           Expires April 18, 2016                [Page 13]


Internet-Draft           CoRE Resource Directory            October 2015


   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




Shelby, et al.           Expires April 18, 2016                [Page 14]


Internet-Draft           CoRE Resource Directory            October 2015


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)



Shelby, et al.           Expires April 18, 2016                [Page 15]


Internet-Draft           CoRE Resource Directory            October 2015


   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}



Shelby, et al.           Expires April 18, 2016                [Page 16]


Internet-Draft           CoRE Resource Directory            October 2015


   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




Shelby, et al.           Expires April 18, 2016                [Page 17]


Internet-Draft           CoRE Resource Directory            October 2015


   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"



Shelby, et al.           Expires April 18, 2016                [Page 18]


Internet-Draft           CoRE Resource Directory            October 2015


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:





Shelby, et al.           Expires April 18, 2016                [Page 19]


Internet-Draft           CoRE Resource Directory            October 2015


   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.




Shelby, et al.           Expires April 18, 2016                [Page 20]


Internet-Draft           CoRE Resource Directory            October 2015


        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




Shelby, et al.           Expires April 18, 2016                [Page 21]


Internet-Draft           CoRE Resource Directory            October 2015


   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




Shelby, et al.           Expires April 18, 2016                [Page 22]


Internet-Draft           CoRE Resource Directory            October 2015


         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







Shelby, et al.           Expires April 18, 2016                [Page 23]


Internet-Draft           CoRE Resource Directory            October 2015


   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.






Shelby, et al.           Expires April 18, 2016                [Page 24]


Internet-Draft           CoRE Resource Directory            October 2015


       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:





Shelby, et al.           Expires April 18, 2016                [Page 25]


Internet-Draft           CoRE Resource Directory            October 2015


      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.





Shelby, et al.           Expires April 18, 2016                [Page 26]


Internet-Draft           CoRE Resource Directory            October 2015


   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:









Shelby, et al.           Expires April 18, 2016                [Page 27]


Internet-Draft           CoRE Resource Directory            October 2015


      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",




Shelby, et al.           Expires April 18, 2016                [Page 28]


Internet-Draft           CoRE Resource Directory            October 2015


   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.







Shelby, et al.           Expires April 18, 2016                [Page 29]


Internet-Draft           CoRE Resource Directory            October 2015


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.





Shelby, et al.           Expires April 18, 2016                [Page 30]


Internet-Draft           CoRE Resource Directory            October 2015


   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,



Shelby, et al.           Expires April 18, 2016                [Page 31]


Internet-Draft           CoRE Resource Directory            October 2015


   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>".




Shelby, et al.           Expires April 18, 2016                [Page 32]


Internet-Draft           CoRE Resource Directory            October 2015


   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




Shelby, et al.           Expires April 18, 2016                [Page 33]


Internet-Draft           CoRE Resource Directory            October 2015


   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



Shelby, et al.           Expires April 18, 2016                [Page 34]


Internet-Draft           CoRE Resource Directory            October 2015


   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:








Shelby, et al.           Expires April 18, 2016                [Page 35]


Internet-Draft           CoRE Resource Directory            October 2015


   +----------+-------+---------------+--------------------------------+
   | 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



Shelby, et al.           Expires April 18, 2016                [Page 36]


Internet-Draft           CoRE Resource Directory            October 2015


   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:




Shelby, et al.           Expires April 18, 2016                [Page 37]


Internet-Draft           CoRE Resource Directory            October 2015


                   +--------------------+--------------+
                   | 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





Shelby, et al.           Expires April 18, 2016                [Page 38]


Internet-Draft           CoRE Resource Directory            October 2015


   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



Shelby, et al.           Expires April 18, 2016                [Page 39]


Internet-Draft           CoRE Resource Directory            October 2015


   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.






Shelby, et al.           Expires April 18, 2016                [Page 40]


Internet-Draft           CoRE Resource Directory            October 2015


   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:



Shelby, et al.           Expires April 18, 2016                [Page 41]


Internet-Draft           CoRE Resource Directory            October 2015


   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



Shelby, et al.           Expires April 18, 2016                [Page 42]


Internet-Draft           CoRE Resource Directory            October 2015


   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







Shelby, et al.           Expires April 18, 2016                [Page 43]


Internet-Draft           CoRE Resource Directory            October 2015


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



Shelby, et al.           Expires April 18, 2016                [Page 44]


Internet-Draft           CoRE Resource Directory            October 2015


   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



Shelby, et al.           Expires April 18, 2016                [Page 45]


Internet-Draft           CoRE Resource Directory            October 2015


   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:



Shelby, et al.           Expires April 18, 2016                [Page 46]


Internet-Draft           CoRE Resource Directory            October 2015


   +------------+-------+-------------------------------+--------------+
   | 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.




Shelby, et al.           Expires April 18, 2016                [Page 47]


Internet-Draft           CoRE Resource Directory            October 2015


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:



Shelby, et al.           Expires April 18, 2016                [Page 48]


Internet-Draft           CoRE Resource Directory            October 2015


   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:




Shelby, et al.           Expires April 18, 2016                [Page 49]


Internet-Draft           CoRE Resource Directory            October 2015


   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.





Shelby, et al.           Expires April 18, 2016                [Page 50]


Internet-Draft           CoRE Resource Directory            October 2015


   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>.





Shelby, et al.           Expires April 18, 2016                [Page 51]


Internet-Draft           CoRE Resource Directory            October 2015


   [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>.





Shelby, et al.           Expires April 18, 2016                [Page 52]


Internet-Draft           CoRE Resource Directory            October 2015


   [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







Shelby, et al.           Expires April 18, 2016                [Page 53]


Internet-Draft           CoRE Resource Directory            October 2015


   Peter van der Stok
   consultant

   Phone: +31-492474673 (Netherlands), +33-966015248 (France)
   Email: consultancy@vanderstok.org
   URI:   www.vanderstok.org













































Shelby, et al.           Expires April 18, 2016                [Page 54]


Html markup produced by rfcmarkup 1.128b, available from https://tools.ietf.org/tools/rfcmarkup/