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Versions: (draft-bormann-core-simple-server-discovery) 00 01 02 03 04 05 draft-ietf-core-resource-directory

CoRE                                                           Z. Shelby
Internet-Draft                                                 Sensinode
Intended status: Standards Track                                 S. Krco
Expires: November 18, 2012                                      Ericsson
                                                            May 17, 2012


                        CoRE Resource Directory
                draft-shelby-core-resource-directory-03

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 November 18, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Architecture and Use Cases . . . . . . . . . . . . . . . . . .  4
     3.1.  Use Case: Cellular M2M . . . . . . . . . . . . . . . . . .  5
     3.2.  Use Case: Home and Building Automation . . . . . . . . . .  6
   4.  Resource Directory Function Set  . . . . . . . . . . . . . . .  6
     4.1.  Discovery  . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Registration . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3.  Update . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     4.4.  Validation . . . . . . . . . . . . . . . . . . . . . . . . 12
     4.5.  Removal  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   5.  RD Lookup Function Set . . . . . . . . . . . . . . . . . . . . 14
   6.  New Link-Format Attributes . . . . . . . . . . . . . . . . . . 16
     6.1.  Export 'exp' attribute . . . . . . . . . . . . . . . . . . 16
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 17
   10. Changelog  . . . . . . . . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     11.2. Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19



















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1.  Introduction

   The Constrained RESTful Environments (CoRE) working group 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
   [I-D.ietf-core-link-format].  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
   registrer, maintain, lookup and remove resources descriptions.
   Furthermore, new link attributes useful in conjunction with a
   Resource Directory are defined.  Although the examples in this
   document show the use of these interfaces with CoAP
   [I-D.ietf-core-coap], they may be applied in an equivalent manner to
   HTTP [RFC2616].


2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification requires readers to be familiar with all the terms
   and concepts that are discussed in [RFC5988] and
   [I-D.ietf-core-link-format].  Readers should also be familiar with
   the terms and concepts discussed in [I-D.ietf-core-coap].  The URI
   Template format is used to describe the REST interfaces defined in
   this specification [RFC6570].  This specification makes use of the



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   following additional terminology:

   Resource Directory
      An 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 end-points.  All end-point within a domain MUST be
      unique.  This specification assumes that the list of domains
      supported by an RD is pre-configured by that RD.

   End-point
      An end-point (EP) is a term used to describe a web server or
      client in [I-D.ietf-core-coap].  In the context of this
      specificaiton an end-point is used to describe a web server that
      registers resources to the Resource Directory.  An end-point is
      identified by its end-point name, which is included during
      registration, and MUST be unique within the associated domain of
      the registration.


3.  Architecture and Use Cases

   The resource directory architecture is shown 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 end-points
   (EP).  An end-point is a web server associated with a port, thus a
   physical node may host one or more end-points.  The RD implements a
   set of REST interfaces for end-points to register and maintain sets
   of Web Links (called resource directory entries), for the RD to
   validate entries, and for clients to lookup resources from the RD.
   End-points themselves can also act as clients.  An RD can be
   logically segmented by the use of Domains.  The domain an end-point
   is associated with can be defined by the RD or configured by an
   outside entity.

   End-points are assumed to proactively register and maintain resource
   directory entries on the RD, which are soft state and need to be
   periodially refreshed.  An EP is provided with interfaces to
   register, update and remove a resource directory entry.  Furthermore,
   a mechanism to discover a RD using the CoRE Link Format is defined.
   It is also possible for an RD to proactively discover Web Links from
   EPs and add them as resource directory entries, or to validate
   existing resource directory entries.  A lookup interface for
   discovering any of the Web Links held in the RD is provided using the
   CoRE Link Format.



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                Registration         Lookup
     +----+          |                 |
     | EP |----      |                 |
     +----+    ----  |                 |
                   --|-    +------+    |
     +----+          | ----|      |    |     +--------+
     | EP | ---------|-----|  RD  |----|-----| Client |
     +----+          | ----|      |    |     +--------+
                   --|-    +------+    |
     +----+    ----  |                 |
     | EP |----      |                 |
     +----+


              Figure 1: The resource directory architecture.

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, i.e. machines.  The machines are
   connected directly to a mobile network using 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 - End Points) 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 (EPs) register with a Resource Directory
   (for example EPs installed on vehicles enabling tracking of their
   position for the fleet management purposes and monitoring environment
   parameters) hosted by the mobile operator or somewhere else in the
   network, submiting a description of own capabilities.  Due to the
   usual network configuration of mobile networks, the EPs attached to
   the mobile network do not have routable addresses.  Therefore, a
   remote server is usually used to provide proxy access to the EPs.
   The address of each (proxy) EP on this server is included in the
   resource description stored in the RD.  The users, for example mobile
   applications for environment monitoring, contact the RD, look-up the
   EPs capable of providing information about the environment using
   appropriate set of tags, obtain information on how to contact them
   (URLs of the proxy server) and then initate interaction to obtain
   information that is finally processed, displayed on the screen and



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   usually stored in a database.  Similarly, fleet management systems
   provide a set of credentials along with the appropriate tags 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 use of CoRE in home automation across
   multiple subnets is described in [I-D.brandt-coap-subnet-discovery]
   and in commercial building automation in [I-D.vanderstok-core-bc].
   The discovery requirements of these applications are demanding.  Home
   automation usually relies on run-time discovery to commision 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 end-points, 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.


4.  Resource Directory Function Set

   This section defines the REST interfaces between an RD and end-point
   servers, which is called the Resource Directory Function Set.
   Although the examples throughout this section assume use of CoAP
   [I-D.ietf-core-coap], these REST interfaces can also be realized
   using HTTP [RFC2616].  An RD implementing this specification MUST
   support the discovery, registration, update, and removal interfaces
   defined in this section and MAY support the validation interface.
   For the purpose of validation, an end-point implementing this
   specification SHOULD support Etag validation on /.well-known/core.

4.1.  Discovery

   Before an end-point can make use of an RD, it must first know its 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.  This section defines discovery of the RD
   using the well-known interface of the CoRE Link Format
   [I-D.ietf-core-link-format] as the required mechanism.  It is however
   expected that RDs will also be discoverable via other methods



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   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 [I-D.ietf-core-link-format] 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 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.

   An implementation of this specification MUST support query filtering
   for the rt parameter as defined in [I-D.ietf-core-link-format].

   The discovery 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" or "core.rd*"

   Content-Type:  application/link-format (if any)

   Success:  2.05 "Content" with an application/link-format payload
      containing a matching entry for the RD resource.

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

   Failure:  No error response to a multicast request.

   Failure:  4.00 "Bad Request"

   The following example shows an end-point discovering an RD using this
   interface, thus learning that the base RD resource is at /rd.  Note
   that it is up to the RD to choose its base RD resource, although it
   is recommended to use default locations where possible.






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    End-point                                             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"

4.2.  Registration

   After discovering the location of an RD Function Set, an end-point
   MAY register its resources using the registration interface.  This
   interface accepts a POST from an end-point containing the list of
   resources to be added to the directory as the message payload in the
   CoRE Link Format along with query string parameters indicating the
   name of the end-point, its domain and the lifetime of the
   registration.  All parameters except the end-point name are optional.
   The RD then creates a new resource or updates an existing resource in
   the RD and returns its location.  An end-point MUST use that location
   when refreshing registrations using this interface.  End-point
   resources in the RD are kept active for the period indicated by the
   lifetime parameter.  The end-point 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 end-point
   parameter does not create multiple RD entries.

   The registration interface is specified as follows:

   Interaction:  EP -> RD

   Method:  POST

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

   URI Template Variables:






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      rd :=   RD Function Set path (mandatory).  This is the path of the
         RD Function Set. An RD SHOULD use the value "rd" for this
         variable whenever possible.

      ep :=   End-point (mandatory).  The end-point identifier or name
         of the registering node, unique within that domain.  The
         maximum length of this parameter is 63 octets.

      d :=   Domain (optional).  The domain to which this end-point
         belongs.  The maximum length of this parameter is 63 octets.
         Optional.  When this parameter is elided, the RD MAY associate
         the end-point with a configured default domain.

      rt :=   End-point Type (optional).  The semantic type of the end-
         point.  The maximum length of this parameter is 63 octets.
         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 used to register are assumed.

   Content-Type:  application/link-format

   Etag:  The Etag option MAY be included to allow an RD to perform
      validation in the future.

   Success:  2.01 "Created".  The Location header MUST be included with
      the new resource entry for the end-point.  This Location MUST be a
      stable identifier generated by the RD as it is used for all
      subsequent operations on this registration (update, delete).

   Failure:  4.00 "Bad Request".  Malformed request.

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

   The following example shows an end-point 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.





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    End-point                                             RD
        |                                                 |
        | --- POST /rd?ep=node1 "</sensors..." ------->   |
        |                                                 |
        |                                                 |
        | <-- 2.01 Created Location: /rd/4521 ----------  |
        |                                                 |


   Req: POST coap://rd.example.com/rd?ep=node1
   Etag: 0x3f
   Payload:
   </sensors/temp>;ct=41;rt="TemperatureC";if="sensor",
   </sensors/light>;ct=41;rt="LightLux";if="sensor"

   Res: 2.01 Created
   Location: /rd/4521

4.3.  Update

   The update interface is used by an end-point to refresh or update its
   registration with an RD.  To use the interface, the end-point sends a
   PUT request to the resource returned in the Location option in the
   response to the first registration.  An update MAY contain
   registration parameters or a payload in CoRE Link Format if there
   have been changes since the last registration or update.  Paremeters
   that have not changed SHOULD NOT be included in an update.

   The update interface is specified as follows:

   Interaction:  EP -> RD

   Method:  PUT

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

   URI Template Variables:

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

      rt :=   End-point Type (optional).  The semantic type of the end-
         point.  The maximum length of this parameter is 63 octets.
         Optional.







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      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.

   Content-Type:  application/link-format (if any)

   Etag:  The Etag option MAY be included to allow an RD to compare the
      existing entry and perform validation in the future.

   Success:  2.04 "Changed" in case the resource and/or lifetime was
      successfully updated

   Failure:  4.00 "Bad Request".  Malformed request.

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

   The following example shows an end-point updating a new set of
   resources to an RD using this interface.



    End-point                                             RD
        |                                                 |
        | --- PUT /rd/4521 "</sensors..." ------------>   |
        |                                                 |
        |                                                 |
        | <-- 2.04 Changed  ----------------------------  |
        |                                                 |


   Req: PUT /rd/4521
   Etag: 0x40
   Payload:
   </sensors/temp/1>;ct=41;ins="Indoor";rt="TemperatureC";if="sensor",
   </sensors/temp/2>;ct=41;ins="Outdoor";rt="TemperatureC";if="sensor",
   </sensors/light>;ct=41;rt="LightLux";if="sensor"

   Res: 2.04 Changed






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4.4.  Validation

   In some cases, an RD may want to validate that it has the latest
   version of an end-point's resources.  This can be performed with a
   GET on the well-known interface of the CoRE Link Format including the
   latest Etag stored for that end-point.  For the purpose of
   validation, an end-point implementing this specification SHOULD
   support Etag validation on /.well-known/core.

   The validation interface is specified as follows:

   Interaction:  RD -> EP

   Method:  GET

   Path:  /.well-known/core

   Parameters:  None

   Content-Type:  application/link-format (if any)

   Etag:  The Etag option MUST be included

   Success:  2.03 "Valid" in case the Etag matches

   Success:  2.05 "Content" in case the Etag does not match, the
      response MUST include the most recent resource representation and
      its corresponding Etag.

   Failure:  4.00 "Bad Request".  Malformed request.

   The following examples shows a successful validation.



    End-point                                             RD
        |                                                 |
        | <--- GET /.well-known/core Etag: 0x40 --------  |
        |                                                 |
        |                                                 |
        | --- 2.03 Valid  ----------------------------->  |
        |                                                 |


   Req: GET /.well-known/core
   Etag: 0x40

   Res: 2.03 Valid



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4.5.  Removal

   Although RD entries have soft state and will eventually timeout after
   their lifetime, an end-point 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 end-point resource.

   The removal interface is specified as follows:

   Interaction:  EP -> 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 registration.

   Content-Type:  None

   Success:  2.02 "Deleted" upon successful deletion

   Failure:  4.00 "Bad Request".  Malformed request.

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

   The following examples shows successful removal of the end-point from
   the RD.



    End-point                                             RD
        |                                                 |
        | --- DELETE /rd/4521  ------------------------>  |
        |                                                 |
        |                                                 |
        | <-- 2.02 Deleted  ----------------------------  |
        |                                                 |


   Req: DELETE /rd/4521

   Res: 2.02 Deleted




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5.  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, end-points 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) in CoRE Link Format corresponding to the type
   of lookup.  The target of these links SHOULD be the actual location
   of the domain, end-point or resource, but MAY be an intermediate
   proxy e.g. in the case of an HTTP lookup interface for CoAP end-
   points.

   The lookup interface is specified as follows:

   Interaction:  Client -> RD

   Method:  GET

   URI Template:  /{+rd-lookup-base}/{lookup-type}{?d,ep,resource-param}

   Parameters:

      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") (mandatory) This variable is
         used to select the kind of lookup to perform (domain, end-point
         or resource).

      ep :=   End-point (optional).  Used for end-point and resource
         lookups.

      d :=   Domain (optional).  Used for domain, end-point and resource
         lookups.

      rt :=   End-point type (optional).  Used for end-point lookups.

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




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   Content-Type:  application/link-format (if any)

   Success:  2.05 "Content" with an application/link-format payload
      containing a matching entries for the lookup.

   Failure:  4.04 "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".  Malformed request.

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

   The following example shows a client performing a resource lookup:



      Client                                                          RD
        |                                                             |
        | ----- GET /rd-lookup/res?rt=Temperature ----------------->  |
        |                                                             |
        |                                                             |
        | <-- 2.05 Content "<coap://node1/temp>;rt="Temperature" ---- |
        |                                                             |




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

   Res: 2.05 Content
   <coap://{ip:port}/temp>;rt="Temperature"

   The following example shows a client performing an end-point lookup:



      Client                                                          RD
        |                                                             |
        | ----- GET /rd-lookup/ep?rt=PowerNode -------------------->  |
        |                                                             |
        |                                                             |
        | <-- 2.05 Content "<coap://{ip:port}>;ep="node5" ----------- |
        |                                                             |





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   Req: GET /rd-lookup/ep?rt=PowerNode

   Res: 2.05 Content
   <coap://{ip:port}>;ep="node5"
   <coap://{ip:port}>;ep="node7"

   The following example shows a client performing a domain lookup:



      Client                                                          RD
        |                                                             |
        | ----- GET /rd-lookup/domain ----------------------------->  |
        |                                                             |
        |                                                             |
        | <-- 2.05 Content "</rd>;d=domain1,</rd>;d=domain2 --------- |
        |                                                             |




   Req: GET /rd-lookup/domain

   Res: 2.05 Content
   </rd>;d=domain1,
   </rd>;d=domain2


6.  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
   [I-D.ietf-core-link-format]:


      link-extension    = ( "exp" )


6.1.  Export 'exp' attribute

   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 end-
   points.  Some are useful mainly locally, for example checking the



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   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.


7.  Security Considerations

   This document needs the same security considerations as described in
   Section 7 of [RFC5988] and Section 6 of [I-D.ietf-core-link-format].
   The /.well-known/core resource may be protected e.g. using DTLS when
   hosted on a CoAP server as described in [I-D.ietf-core-coap].

   Access control SHOULD be performed separately for the RD Function Set
   and the RD Lookup Function Set independently, as different end-points
   may be authorized to register with an RD from those authorized to
   lookup end-points 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, end-
   point or resource level.


8.  IANA Considerations

   "core.rd" and "core.rd-lookup" resource type needs to be registered
   when the appropriate registry is created by
   [I-D.ietf-core-link-format].

   The "exp" attribute needs to be registered when a future Web Linking
   attribute is created.


9.  Acknowledgments

   Szymon Sasin, Carsten Bormann, Kerry Lynn, Peter van der Stok, Anders
   Brandt, Matthieu Vial, Sampo Ukkola and Linyi Tian have provided
   helpful comments, discussions and ideas to improve and shape this
   document.  The authors would also like to thank their collagues from
   the EU FP7 SENSEI project, where many of the resource directory
   concepts were originally developed.


10.  Changelog

   Changes from -02 to -03:

      o Changed the end-point name back to a single registration
      parameter ep= and removed the h= and ins= parameters.



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      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= paramter to be present.

   Changes from -01 to -02:

      o Added a terminology section.

      o Changed the inclusing of an Etag in registration or update to a
      MAY.

      o Added the concept of an RD domain and a registration parameter
      for it.

      o Recommended the Location returned from a registration to be
      stable, allowing for end-point and domain information to be
      changed during updates.

      o Changed the lookup interface to accept end-point and domain as
      query string parameters to control the scope of a lookup.


11.  References

11.1.  Normative References

   [I-D.ietf-core-link-format]
              Shelby, Z., "CoRE Link Format",
              draft-ietf-core-link-format-06 (work in progress),
              June 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5988]  Nottingham, M., "Web Linking", RFC 5988, October 2010.

   [RFC6570]  Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
              and D. Orchard, "URI Template", RFC 6570, March 2012.







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11.2.  Informative References

   [I-D.brandt-coap-subnet-discovery]
              Brandt, A., "Discovery of CoAP servers across subnets",
              draft-brandt-coap-subnet-discovery-00 (work in progress),
              March 2011.

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-06 (work in progress), May 2011.

   [I-D.vanderstok-core-bc]
              Stok, P. and K. Lynn, "CoAP Utilization for Building
              Control", draft-vanderstok-core-bc-03 (work in progress),
              March 2011.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.


Authors' Addresses

   Zach Shelby
   Sensinode
   Kidekuja 2
   Vuokatti  88600
   FINLAND

   Phone: +358407796297
   Email: zach@sensinode.com


   Srdjan Krco
   Ericsson


   Phone:
   Email: srdjan.krco@ericsson.com











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