--- 1/draft-ietf-core-resource-directory-13.txt 2018-07-02 07:16:41.107103388 -0700 +++ 2/draft-ietf-core-resource-directory-14.txt 2018-07-02 07:16:41.247106741 -0700 @@ -1,24 +1,24 @@ CoRE Z. Shelby Internet-Draft ARM Intended status: Standards Track M. Koster -Expires: September 2, 2018 SmartThings +Expires: January 3, 2019 SmartThings C. Bormann Universitaet Bremen TZI P. van der Stok consultant C. Amsuess, Ed. - March 01, 2018 + July 02, 2018 CoRE Resource Directory - draft-ietf-core-resource-directory-13 + draft-ietf-core-resource-directory-14 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 @@ -34,105 +34,113 @@ 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 https://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 September 2, 2018. + This Internet-Draft will expire on January 3, 2019. Copyright Notice Copyright (c) 2018 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 (https://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 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 6 - 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 6 - 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 6 - 3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 8 - 3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12 - 3.5. Use Case: Home and Building Automation . . . . . . . . . 13 - 3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 13 - 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 14 - 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 15 - 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 17 - 5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 18 - 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 18 - 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 21 - 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 25 - 5.3.2. Third-party registration . . . . . . . . . . . . . . 26 - 5.4. Operations on the Registration Resource . . . . . . . . . 26 - 5.4.1. Registration Update . . . . . . . . . . . . . . . . . 27 - 5.4.2. Registration Removal . . . . . . . . . . . . . . . . 30 - 5.4.3. Read Endpoint Links . . . . . . . . . . . . . . . . . 31 - 5.4.4. Update Endpoint Links . . . . . . . . . . . . . . . . 32 - 6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 32 - 6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 32 - 6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 34 - 7. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 35 - 7.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 36 - 7.2. Endpoint and group lookup . . . . . . . . . . . . . . . . 36 - 7.3. Lookup filtering . . . . . . . . . . . . . . . . . . . . 37 - 7.4. Lookup examples . . . . . . . . . . . . . . . . . . . . . 39 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 43 - 8.1. Endpoint Identification and Authentication . . . . . . . 43 - 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 44 - 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 44 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 - 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 45 - 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 45 - 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 45 - 9.3.1. Full description of the "Endpoint Type" Registration - Parameter . . . . . . . . . . . . . . . . . . . . . . 47 - 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 47 - 9.5. Multicast Address Registration . . . . . . . . . . . . . 48 - 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 48 - 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 48 - 10.1.1. Installation Characteristics . . . . . . . . . . . . 48 - 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 49 - 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 52 - 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 53 - 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 54 - 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 56 - 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 56 - 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 56 - 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 56 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 62 - 13.2. Informative References . . . . . . . . . . . . . . . . . 63 - Appendix A. Web links and the Resource Directory . . . . . . . . 64 - A.1. A simple example . . . . . . . . . . . . . . . . . . . . 64 - A.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 64 - A.1.2. Interpreting attributes and relations . . . . . . . . 65 - A.2. A slightly more complex example . . . . . . . . . . . . . 65 - A.3. Enter the Resource Directory . . . . . . . . . . . . . . 66 - A.4. A note on differences between link-format and Link - headers . . . . . . . . . . . . . . . . . . . . . . . . . 67 - Appendix B. Syntax examples for Protocol Negotiation . . . . . . 68 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 69 + 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 7 + 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 7 + 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7 + 3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 9 + 3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 13 + 3.5. Use Case: Home and Building Automation . . . . . . . . . 14 + 3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 14 + 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 15 + 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 17 + 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 18 + 5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 19 + 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 19 + 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 22 + 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 27 + 5.3.2. Third-party registration . . . . . . . . . . . . . . 29 + 6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 30 + 6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 30 + 6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 32 + 7. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 33 + 7.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 33 + 7.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 34 + 7.3. Resource lookup examples . . . . . . . . . . . . . . . . 36 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 39 + 8.1. Endpoint Identification and Authentication . . . . . . . 39 + 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 40 + 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 40 + 9. Authorization Server example . . . . . . . . . . . . . . . . 40 + 9.1. Registree-ep registers with RD . . . . . . . . . . . . . 42 + 9.2. Third party Commissioning Tool (CT) registers registree- + ep with RD. . . . . . . . . . . . . . . . . . . . . . . . 42 + 9.3. Updating multiple links . . . . . . . . . . . . . . . . . 43 + 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43 + 10.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 43 + 10.2. IPv6 ND Resource Directory Address Option . . . . . . . 44 + 10.3. RD Parameter Registry . . . . . . . . . . . . . . . . . 44 + 10.3.1. Full description of the "Endpoint Type" Registration + Parameter . . . . . . . . . . . . . . . . . . . . . 46 + 10.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . 46 + 10.5. Multicast Address Registration . . . . . . . . . . . . . 47 + 10.6. CBOR Web Token claims . . . . . . . . . . . . . . . . . 47 + 11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 48 + 11.1. Lighting Installation . . . . . . . . . . . . . . . . . 48 + 11.1.1. Installation Characteristics . . . . . . . . . . . . 49 + 11.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 50 + 11.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 52 + 11.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 53 + 11.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 54 + 11.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 56 + 11.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 56 + 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 56 + 13. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 56 + 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 + 14.1. Normative References . . . . . . . . . . . . . . . . . . 63 + 14.2. Informative References . . . . . . . . . . . . . . . . . 63 + Appendix A. Registration Management . . . . . . . . . . . . . . 65 + A.1. Registration Update . . . . . . . . . . . . . . . . . . . 66 + A.2. Registration Removal . . . . . . . . . . . . . . . . . . 69 + A.3. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 70 + A.4. Update Endpoint Links . . . . . . . . . . . . . . . . . . 71 + A.5. Endpoint and group lookup . . . . . . . . . . . . . . . . 71 + Appendix B. Web links and the Resource Directory . . . . . . . . 73 + B.1. A simple example . . . . . . . . . . . . . . . . . . . . 73 + B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 73 + B.1.2. Interpreting attributes and relations . . . . . . . . 74 + B.2. A slightly more complex example . . . . . . . . . . . . . 74 + B.3. Enter the Resource Directory . . . . . . . . . . . . . . 75 + B.4. A note on differences between link-format and Link + headers . . . . . . . . . . . . . . . . . . . . . . . . . 76 + Appendix C. Syntax examples for Protocol Negotiation . . . . . . 77 + Appendix D. Modernized Link Format parsing . . . . . . . . . . . 78 + D.1. For endpoint developers . . . . . . . . . . . . . . . . . 79 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79 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 @@ -181,105 +189,146 @@ is used to describe the process of [RFC3986] Section 5.2. Noteworthy corner cases are that resolving an absolute URI against any base URI gives the original URI, and that resolving an empty URI reference gives the base URI. 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 + Sector + In the context of a Resource Directory, a sector is a logical grouping of endpoints. + The abbreviation "d" is used for the sector in query parameters + for compatibility with deployed implementations. + 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 have unique names. + A group in the Resource Directory specifies a set of endpoints + that are enabled with the same multicast address for the purpose + of efficient group communications. All groups within a sector + have unique names. 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 has a unique name - within the associated domain of the registration. + within the associated sector of the registration. + + Registration Base URI + The Base URI of a Registration is a URI that typically gives + scheme and authority information about an Endpoint. The + Registration Base URI is provided by the Endpoint at registration + time, and is used by the Resource Directory to resolve relative + references inside the registration into absolute URIs. + + Target + The target of a link is the destination address (URI) of the link. + It is sometimes identified with "href=", or displayed as + "". Relative targets need resolving with respect to the + Base URI (section 5.2 of [RFC3986]). + + This use of the term Target is consistent with [RFC8288]'s use of + the term. Context - A Context is a base URL that gives scheme and (typically) - authority information about an Endpoint. The Context of an - Endpoint is provided at registration time, and is used by the - Resource Directory to resolve relative references inside the - registration into absolute URIs. + The context of a link is the source address (URI) of the link, and + describes which resource is linked to the target. A link's + context is made explicit in serialized links as the "anchor=" + attribute. + + This use of the term Context is consistent with [RFC8288]'s use of + the term. Directory Resource A resource in the Resource Directory (RD) containing registration resources. Group Resource A resource in the RD containing registration resources of the Endpoints that form a group. Registration Resource A resource in the RD that contains information about an Endpoint and its links. Commissioning Tool Commissioning Tool (CT) is a device that assists during the installation of the network by assigning values to parameters, naming endpoints and groups, or adapting the installation to the needs of the applications. + Registree-ep + Registree-ep is the endpoint that is registered into the RD. The + registree-ep can register itself, or a CT registers the registree- + ep. + RDAO Resource Directory Address Option. + For several operations, interface descriptions are given in list + form; those describe the operation participants, request codes, URIs, + content formats and outcomes. Those templates contain normative + content in their Interaction, Method, URI Template and URI Template + Variables sections as well as the details of the Success condition. + The additional sections on options like Content-Format and on Failure + codes give typical cases that the implementing parties should be + prepared to deal with. Those serve to illustrate the typical + responses to readers who are not yet familiar with all the details of + CoAP based interfaces; they do not limit what a server may respond + under atypical circumstances. + 3. Architecture and Use Cases 3.1. Principles The Resource Directory is primarily a tool to make discovery operations more efficient than querying /.well-known/core on all connected device, or across boundaries that would be limiting those operations. It provides a cache (in the high-level sense, not as defined in [RFC7252]/[RFC2616]) of data that could otherwise only be obtained by directly querying the /.well-known/core resource on the target device, or by accessing those resources with a multicast request. From that, it follows that only information should be stored in the resource directory that is discovered from querying the described device's /.well-known/core resource directly. It also follows that data in the resource directory can only be provided by the device whose descriptions are cached or a dedicated - Commissioning Tool (CT). These CTs are thought to act on behalf + Commissioning Tool (CT). These CTs are thought to act on behalf of agents too constrained, or generally unable, to present that information themselves. No other client can modify data in the resource directory. Changes in the Resource Directory do not - propagate automatically back to its source. + propagate automatically back to the web server from where the links + originated. 3.2. Architecture 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. A physical node may host one or more endpoints. The RD implements a set of REST interfaces for endpoints to register and maintain sets of Web Links (called resource directory registration entries), and for clients to lookup resources from the RD or maintain groups. Endpoints themselves can also act as clients. - An RD can be logically segmented by the use of Groups. The group an - endpoint is part of, can be defined by the RD or configured by a - Commissioning Tool. This information hierarchy is shown in Figure 2. + An RD can be logically segmented by the use of Sectors. The set of + endpoints grouped for group communication can be defined by the RD or + configured by a Commissioning Tool. This information hierarchy is + shown in Figure 2. A mechanism to discover an RD using CoRE Link Format [RFC6690] is defined. Endpoints proactively register and maintain resource directory registration entries on the RD, which are soft state and need to be periodically refreshed. An endpoint uses specific interfaces to register, update and remove a resource directory registration entry. It is also possible for an RD @@ -357,150 +406,152 @@ < contains > \\\\\\\\/////// | | 0+ +--------------------+ | link | +--------------------+ | | 1 oooooooo +-----o target o - 0+ | oooooooo - oooooooooooo | + | oooooooo + oooooooooooo 0+ | o target o--------+ o attribute o | 0+ oooooo oooooooooooo +-----o rel o | oooooo | | 1 ooooooooo +-----o context o ooooooooo Figure 3: E-R Model of the content of /.well-known/core The model shown in Figure 3 models the contents of /.well-known/core which contains: - o a set of links belonging to the host + o a set of links belonging to the hosting web server - The host is free to choose links it deems appropriate to be exposed - in its ".well-known/core". Typically, the links describe resources - that are served by the host, but the set can also contain links to - resources on other servers (see examples in [RFC6690] page 14). The - set does not necessarily contain links to all resources served by the - host. + The web server is free to choose links it deems appropriate to be + exposed in its ".well-known/core". Typically, the links describe + resources that are served by the host, but the set can also contain + links to resources on other servers (see examples in [RFC6690] page + 14). The set does not necessarily contain links to all resources + served by the host. A link has the following attributes (see [RFC5988]): o Zero or more link relations: They describe relations between the link context and the link target. In link-format serialization, they are expressed as space- separated values in the "rel" attribute, and default to "hosts". o A link context URI: It defines the source of the relation, eg. _who_ "hosts" something. In link-format serialization, it is expressed in the "anchor" - attribute. There, it can be a relative reference, in which case - it gets resolved against the URI of the ".well-known/core" - document it was obtained from. It defaults to that document's - URI. + attribute. It defaults to that document's URI. o A link target URI: It defines the destination of the relation (eg. _what_ is hosted), and is the topic of all target attributes. In link-format serialization, it is expressed between angular brackets, and sometimes called the "href". - If there is an anchor attribute present and the link is serialized in - [RFC6690] link format, this document will require that the link is an - absolute reference to avoid the ambiguities outlined in Appendix A.4. - - Otherwise, it can be serialized as a relative URI, and gets resolved - against the document's URI. - o Other target attributes (eg. resource type (rt), interface (if), - cor content-type (ct)). These provide additional information - about the target URI. + or content-type (ct)). These provide additional information about + the target URI. - +----------------------+ - | resource-directory | - +----------------------+ - | - | oooooooooooo 0-1 - | o MC address o---+ - | oooooooooooo | - | | - //////\\\\ 0+ +--------+ - < contains >----------------| group | - \\\\\///// +--------+ - | | - 0-n | | 1+ - ooooooo 1 +---------------+ ///////\\\\\\ - o con o-------| registration |---------< composed of > + +----------------------+ 1 ooooooo + | resource-directory | +--o href o + +----------------------+ | ooooooo + | 1 | + | oooooooooo 0-1 | 1 oooooo + | o base o---+ | +------o gp o + | ooooooooooo | | | oooooo + | | | | + //////\\\\ 0+ +--------+ 0-1 ooooo + < contains >----------------| group |------o d o + \\\\\///// +--------+ ooooo + | | 0+ + 0+ | | + ooooooo 1 +---------------+ 1+ ///////\\\\\\ + o base o-------| registration |---------< composed of > ooooooo +---------------+ \\\\\\\////// - | | + | | 1 | +--------------+ oooooooo 1 | | - o loc o----+ /////\\\\ + o href o----+ /////\\\\ oooooooo | < contains > | \\\\\///// oooooooo 1 | | o ep o----+ | 0+ oooooooo | +------------------+ | | link | oooooooo 0-1 | +------------------+ o d o----+ | oooooooo | | 1 oooooooo | +-----o target o - oooooooo 0-1 | | oooooooo + oooooooo 1 | | oooooooo o lt o----+ ooooooooooo 0+ | oooooooo | o target o-----+ | o attribute o | 0+ oooooo ooooooooooo 0+ | ooooooooooo +-----o rel o o endpoint o----+ | oooooo o attribute o | ooooooooooo | 1 ooooooooo +----o context o ooooooooo Figure 4: E-R Model of the content of the Resource Directory The model shown in Figure 4 models the contents of the resource directory which contains in addition to /.well-known/core: - o 0 to n Registration (entries), + o 0 to n Registration (entries) of endpoints, o 0 or more Groups - A Group has no or one Multicast address attribute and is composed of - 0 or more endpoints. A registration is associated with one endpoint - (ep). An endpoint can be part of 0 or more Groups . A registration - defines a set of links as defined for /.well-known/core. A - Registration has six attributes: + A Group has: - o one ep (endpoint with a unique name) + o a group name ("gp"), - o one con (a string describing the scheme://authority part) + o optionally a sector (abbreviated "d" for historical reasons), - o one lt (lifetime), + o a group resource location inside the RD ("href"), - o one loc (location in the RD) + o zero or one multicast addresses expressed as a base URI ("base"), - o optional one d (domain for query filtering), + o and is composed of zero or more registrations (endpoints). - o optional additional endpoint attributes (from Section 9.3) + A registration is associated with one endpoint. A registration can + be part of 0 or more Groups . A registration defines a set of links + as defined for /.well-known/core. A Registration has six types of + attributes: - The cardinality of con is currently 1; future documents are invited - to extend the RD specification to support multiple values (eg. - [I-D.silverajan-core-coap-protocol-negotiation]). Its value is used - as a Base URI when resolving URIs in the links contained in the + o a unique endpoint name ("ep") + + o a Registration Base URI ("base", a URI typically describing the + scheme://authority part) + + o a lifetime ("lt"), + + o a registration resource location inside the RD ("href"), + + o optionally a sector ("d") + + o optional additional endpoint attributes (from Section 10.3) + + The cardinality of "base" is currently 1; future documents are + invited to extend the RD specification to support multiple values + (eg. [I-D.silverajan-core-coap-protocol-negotiation]). Its value is + used as a Base URI when resolving URIs in the links contained in the endpoint. Links are modelled as they are in Figure 3. 3.4. 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 @@ -561,86 +612,86 @@ links to sensor data may be published to a Resource Directory. Applications wishing to consume the data can use RD Lookup to discover and resolve links to the desired resources and endpoints. The Resource Directory service need not be coupled with the data intermediary service. Mapping of Resource Directories to data intermediaries may be many-to-many. Metadata in web link formats like [RFC6690] are supplied by Resource Directories, which may be internally stored as triples, or relation/ attribute pairs providing metadata about resource links. External - catalogs that are represented in other formats may be converted to + catalogues that are represented in other formats may be converted to common web linking formats for storage and access by Resource Directories. Since it is common practice for these to be URN encoded, simple and lossless structural transforms should generally be sufficient to store external metadata in Resource Directories. - The additional features of Resource Directory allow domains to be + The additional features of Resource Directory allow sectors 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. + sensitive data when needed. Groups may be defined to support + efficient data transport. 4. Finding a Resource Directory - A (re-e)starting device may want to find one or more resource + A (re-)starting device may want to find one or more resource directories to make itself known with. The device may be pre-configured to exercise specific mechanisms for finding the resource directory: - o It may be configured with a specific IP address for the RD. That - IP address may also be an anycast address, allowing the network to - forward RD requests to an RD that is topologically close; each + 1. It may be configured with a specific IP address for the RD. That + IP address may also be an anycast address, allowing the network + to forward RD requests to an RD that is topologically close; each target network environment in which some of these preconfigured nodes are to be brought up is then configured with a route for - this anycast address that leads to an appropriate RD. (Instead of - using an anycast address, a multicast address can also be - preconfigured. The RD directory servers then need to configure - one of their interfaces with this multicast address.) + this anycast address that leads to an appropriate RD. (Instead + of using an anycast address, a multicast address can also be + preconfigured. The RD servers then need to configure one of + their interfaces with this multicast address.) - o It may be configured with a DNS name for the RD and a resource- + 2. It may be configured with a DNS name for the RD and a resource- record type to look up under this name; it can find a DNS server to perform the lookup using the usual mechanisms for finding DNS servers. - o It may be configured to use a service discovery mechanism such as + 3. It may be configured to use a service discovery mechanism such as DNS-SD [RFC6763]. The present specification suggests configuring the service with name rd._sub._coap._udp, preferably within the domain of the querying nodes. For cases where the device is not specifically configured with a way to find a resource directory, the network may want to provide a suitable default. - o If the address configuration of the network is performed via + 1. If the address configuration of the network is performed via SLAAC, this is provided by the RDAO option Section 4.1. - o If the address configuration of the network is performed via DHCP, - this could be provided via a DHCP option (no such option is + 2. If the address configuration of the network is performed via + DHCP, this could be provided via a DHCP option (no such option is defined at the time of writing). - Finally, if neither the device nor the network offer any specific + Finally, if neither the device nor the network offers any specific configuration, the device may want to employ heuristics to find a suitable resource directory. The present specification does not fully define these heuristics, but suggests a number of candidates: - o In a 6LoWPAN, just assume the Edge Router (6LBR) can act as a - resource directory (using the ABRO option to find that [RFC6775]). - Confirmation can be obtained by sending a Unicast to + 1. In a 6LoWPAN, just assume the Border Router (6LBR) can act as a + resource directory (using the ABRO option to find that + [RFC6775]). Confirmation can be obtained by sending a Unicast to "coap://[6LBR]/.well-known/core?rt=core.rd*". - o In a network that supports multicast well, discovering the RD - using a multicast query for /.well-known/core as specified in CoRE - Link Format [RFC6690]: Sending a Multicast GET to + 2. In a network that supports multicast well, discovering the RD + using a multicast query for /.well-known/core as specified in + CoRE Link Format [RFC6690]: Sending a Multicast GET to "coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the multicast scope will answer the query. As some of the RD addresses obtained by the methods listed here 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 @@ -649,32 +700,29 @@ If multiple candidate addresses are discovered, the device may pick any of them initially, unless the discovery method indicates a more precise selection scheme. 4.1. Resource Directory Address Option (RDAO) The Resource Directory Address Option (RDAO) using IPv6 neighbor Discovery (ND) carries information about the address of the Resource Directory (RD). This information is needed when endpoints cannot - discover the Resource Directory with a link-local multicast address - because the endpoint and the RD are separated by a border Router - (6LBR). In many circumstances the availability of DHCP cannot be - guaranteed either during commissioning of the network. The presence - and the use of the RD is essential during commissioning. + discover the Resource Directory with a link-local or realm-local + scope multicast address because the endpoint and the RD are separated + by a Border Router (6LBR). In many circumstances the availability of + DHCP cannot be guaranteed either during commissioning of the network. + The presence and the use of the RD is essential during commissioning. It is possible to send multiple RDAO options in one message, indicating as many resource directory addresses. - The lifetime 0x0 means that the RD address is invalid and to be - removed. - The RDAO format is: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length = 3 | Valid Lifetime | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | @@ -782,23 +830,25 @@ While the link targets in this discovery step are often expressed in path-absolute form, this is not a requirement. Clients SHOULD therefore accept URIs of all schemes they support, both in absolute and relative forms, and not limit the set of discovered URIs to those hosted at the address used for URI discovery. The URI Discovery operation can yield multiple URIs of a given resource type. The client can use any of the discovered addresses initially. - The discovery request interface is specified as follows: + The discovery request interface is specified as follows (this is + exactly the Well-Known Interface of [RFC6690] Section 4, with the + additional requirement that the server MUST support query filtering): - Interaction: EP -> RD + Interaction: EP and Client -> RD Method: GET URI Template: /.well-known/core{?rt} URI Template Variables: rt := Resource Type (optional). MAY contain one of the values "core.rd", "core.rd-lookup*", "core.rd-lookup-res", "core.rd- lookup-ep", "core.rd-lookup-gp", "core.rd-group" or "core.rd*" @@ -839,38 +889,38 @@ ;rt="core.rd-group";ct=40 Figure 6: Example discovery exchange The following example shows the way of indicating that a client may request alternate content-formats. The Content-Format code attribute "ct" MAY include a space-separated sequence of Content-Format codes as specified in Section 7.2.1 of [RFC7252], indicating that multiple content-formats are available. The example below shows the required Content-Format 40 (application/link-format) indicated as well as the - the CBOR and JSON representation of link format. The RD resource - paths /rd, /rd-lookup, and /rd-group are example values. The server - in this example also indicates that it is capable of providing + CBOR and JSON representation of link format. The RD resource paths + /rd, /rd-lookup, and /rd-group are example values. The server in + this example also indicates that it is capable of providing observation on resource lookups. [ The RFC editor is asked to replace these and later occurrences of TBD64 and TBD504 with the numeric ID values assigned by IANA to application/link-format+cbor and application/link-format+json, respectively, as they are defined in I-D.ietf-core-links-json. ] - Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* Res: 2.05 Content ;rt="core.rd";ct="40 65225", ;rt="core.rd-lookup-res";ct="40 TBD64 TBD504";obs, ;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504", ;rt="core.rd-lookup-gp";ct=40 TBD64 TBD504", ;rt="core.rd-group";ct="40 TBD64 TBD504" + From a management and maintenance perspective, it is necessary to identify the components that constitute the server. The identification refers to information about for example client-server incompatibilities, supported features, required updates and other aspects. The URI discovery address, a described in section 4 of [RFC6690] can be used to find the identification. It would typically be stored in an implementation information link (as described in [I-D.bormann-t2trg-rel-impl]): @@ -881,641 +931,466 @@ rel="impl-info" Note that depending on the particular server's architecture, such a link could be anchored at the server's root, at the discovery site (as in this example) or at individual RD components. The latter is to be expected when different applications are run on the same server. 5.3. Registration - After discovering the location of an RD, an endpoint MAY register its - resources using the registration interface. This interface accepts a - POST from an endpoint containing the list of resources to be added to - the directory as the message payload in the CoRE Link Format - [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 parameters indicating - the name of the endpoint, and optionally the domain and the lifetime - of the registration. It is expected that other specifications will - define further parameters (see Section 9.3). The RD then creates a - new registration resource in the RD and returns its location. An - endpoint MUST use that location when refreshing registrations using - this interface. Registration resources in the RD are kept active for - the period indicated by the lifetime parameter. The endpoint is - responsible for refreshing the registration resource within this - period using either the registration or update interface. The - registration interface MUST be implemented to be idempotent, so that - registering twice with the same endpoint parameters ep and d does not - create multiple registration resources. A new registration resource - may be created at any time to supersede an existing registration, - replacing the registration parameters and links. + After discovering the location of an RD, a registree-ep or CT MAY + register the resources of the registree-ep 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 parameters indicating the name of the endpoint, and optionally + the sector, lifetime and base URI of the registration. It is + expected that other specifications will define further parameters + (see Section 10.3). The RD then creates a new registration resource + in the RD and returns its location. The receiving endpoint MUST use + that location when refreshing registrations using this interface. + Registration resources in the RD are kept active for the period + indicated by the lifetime parameter. The endpoint is responsible for + refreshing the registration resource within this period using either + the registration or update interface. The registration interface + MUST be implemented to be idempotent, so that registering twice with + the same endpoint parameters ep and d (sector) does not create + multiple registration resources. + + The following rules apply for an update identified by a given (ep, d) + value pair: + + o when the parameter values of the Update generate the same + attribute values as already present, the location of the already + existing registration is returned. + + o when for a given (ep, d) value pair the update generates attribute + values which are different from the existing one, the existing + registration is removed and a new registration with a new location + is created. + + o when the (ep, d) value pair of the update is different from any + existing registration, a new registration is generated. The posted link-format document can (and typically does) contain relative references both in its link targets and in its anchors, or contain empty anchors. The RD server needs to resolve these - references in order to faithfully represent them in lookups. The - Base URI against which they are resolved is the context of the - registration, which is provided either explicitly in the "con" - parameter or constructed implicitly from the requester's network - address. + references in order to faithfully represent them in lookups. They + are resolved against the base URI of the registration, which is + provided either explicitly in the "base" parameter or constructed + implicitly from the requester's network address. - Documents in [RFC6690] Link Format SHOULD NOT contain links in which - resolving the target literal against the base URI gives a different - result than resolving it against the resolved anchor; this is to - avoid the ambiguities described in Appendix A.4. * Entries in which - there is no anchor attribute, * entries in which the target is an - absolute reference and * entries in which both the target and the - anchor start with a slash ("/") + Link format documents submitted to the resource directory are + interpreted as Modernized Link Format (see Appendix D) by the RD. A + registree-ep SHOULD NOT submit documents whose interpretations + according to [RFC6690] and Appendix D differ and RFC6690 + interpretation is intended to avoid the ambiguities described in + Appendix B.4. - never cause that kind of ambiguity. + In practice, most links (precisely listed in Appendix D.1) can be + submitted without consideration for those details. The registration request interface is specified as follows: Interaction: EP -> RD Method: POST - URI Template: {+rd}{?ep,d,lt,con,extra-attrs*} + URI Template: {+rd}{?ep,d,lt,base,extra-attrs*} URI Template Variables: rd := RD registration URI (mandatory). This is the location of the RD, as obtained from discovery. ep := Endpoint name (mostly mandatory). The endpoint name is an - identifier that MUST be unique within a domain. The maximum + identifier that MUST be unique within a sector. The maximum length of this parameter is 63 bytes. If the RD is configured to recognize the endpoint (eg. based on its security context), - the endpoint can ignore the endpoint name, and assign one based - on a se of configuration parameter values. + the endpoint sets no endpoint name, and the RD assigns one + based on a set of configuration parameter values. - d := Domain (optional). The domain to which this endpoint + d := Sector (optional). The sector to which this endpoint belongs. The maximum length of this parameter is 63 bytes. When this parameter is not present, the RD MAY associate the - endpoint with a configured default domain or leave it empty. + endpoint with a configured default sector or leave it empty. + The endpoint name and sector name are not set when one or both + are set in an accompanying authorization token. lt := Lifetime (optional). Lifetime of the registration in seconds. Range of 60-4294967295. If no lifetime is included - in the initial registration, a default value of 86400 (24 + in the initial registration, a default value of 90000 (25 hours) SHOULD be assumed. - con := Context (optional). This parameter sets the Default Base - URI under which the request's links are to be interpreted. The - specified URI MUST NOT have a path component of its own, but - MUST be suitable as a base URI to resolve any relative - references given in the registration. The parameter is - therefore of the shape "scheme://authority" for HTTP and CoAP - URIs. In the absence of this parameter the scheme of the - protocol, source address and source port of the registration - request are assumed. This parameter is mandatory when the - directory is filled by a third party such as an commissioning - tool. If the endpoint uses an ephemeral port to register with, - it MUST include the con parameter in the registration to - provide a valid network path. If the endpoint which is located - behind a NAT gateway is registering with a Resource Directory - which is on the network service side of the NAT gateway, the - endpoint MUST use a persistent port for the outgoing - registration in order to provide the NAT gateway with a valid - network address for replies and incoming requests. + base := Base URI (optional). This parameter sets the base URI of + the registration, under which the request's links are to be + interpreted. The specified URI typically does not have a path + component of its own, and MUST be suitable as a base URI to + resolve any relative references given in the registration. The + parameter is therefore usually of the shape + "scheme://authority" for HTTP and CoAP URIs. The URI SHOULD + NOT have a query or fragment component as any non-empty + relative part in a reference would remove those parts from the + resulting URI. + + In the absence of this parameter the scheme of the protocol, + source address and source port of the registration request are + assumed. This parameter is mandatory when the directory is + filled by a third party such as an commissioning tool. + + If the endpoint uses an ephemeral port to register with, it + MUST include the base parameter in the registration to provide + a valid network path. + + If the endpoint which is located behind a NAT gateway is + registering with a Resource Directory which is on the network + service side of the NAT gateway, the endpoint MUST use a + persistent port for the outgoing registration in order to + provide the NAT gateway with a valid network address for + replies and incoming requests. + + Endpoints that register with a base that contains a path + component can not meaningfully use [RFC6690] Link Format due to + its prevalence of the Origin concept in relative reference + resolution; they can submit payloads for interpretation as + Modernized Link Format. Typically, links submitted by such an + endpoint are of the "path-noscheme" (starts with a path not + preceded by a slash, precisely defined in [RFC3986] + Section 3.3) form. extra-attrs := Additional registration attributes (optional). - The endpoint can pass any parameter registered at Section 9.3 + The endpoint can pass any parameter registered at Section 10.3 to the directory. If the RD is aware of the parameter's specified semantics, it processes it accordingly. Otherwise, it MUST store the unknown key and its value(s) as an endpoint attribute for further lookup. Content-Format: application/link-format Content-Format: application/link-format+json Content-Format: application/link-format+cbor The following response codes are defined for this interface: - Success: 2.01 "Created" or 201 "Created". The Location header - option MUST be included in the response when a new registration - resource is created. This Location MUST be a stable identifier - generated by the RD as it is used for all subsequent operations on - this registration resource. The registration resource location - thus returned is for the purpose of updating the lifetime of the - registration and for maintaining the content of the registered - links, including updating and deleting links. A registration with - an already registered ep and d value pair responds with the same - success code and Location as the original registration; the set of - links registered with the endpoint is replaced with the links from - the payload. + Success: 2.01 "Created" or 201 "Created". The Location-Path option + or Location header MUST be included in the response. This + location MUST be a stable identifier generated by the RD as it is + used for all subsequent operations on this registration resource. + The registration resource location thus returned is for the + purpose of updating the lifetime of the registration and for + maintaining the content of the registered links, including + updating and deleting links. + + A registration with an already registered ep and d value pair + responds with the same success code and location as the original + registration; the set of links registered with the endpoint is + replaced with the links from the payload. + + The location MUST NOT have a query or fragment component, as that + could conflict with query parameters during the Registration + Update operation. Therefore, the Location-Query option MUST NOT + be present in a successful response. 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 If the registration fails with a Service Unavailable response and a - Max-Age option or Retry-After header, the client SHOULD retry the - operation after the time indicated. If the registration fails in - another way, including request timeouts, or if the Service + Max-Age option or Retry-After header, the registering endpoint SHOULD + retry the operation after the time indicated. If the registration + fails in another way, including request timeouts, or if the Service Unavailable error persists after several retries, or indicates a longer time than the endpoint is willing to wait, it SHOULD pick another registration URI from the "URI Discovery" step and if there is only one or the list is exhausted, pick other choices from the "Finding a Resource Directory" step. Care has to be taken to consider the freshness of results obtained earlier, eg. of the result of a "/.well-known/core" response, the lifetime of an RDAO option and of DNS responses. Any rate limits and persistent errors from the "Finding a Resource Directory" step must be considered for the whole registration time, not only for a single operation. - The following example shows an endpoint with the name "node1" + The following example shows a registree-ep with the name "node1" registering two resources to an RD using this interface. The location "/rd" is an example RD location discovered in a request similar to Figure 6. Req: POST coap://rd.example.com/rd?ep=node1 Content-Format: 40 Payload: ;ct=41;rt="temperature-c";if="sensor"; anchor="coap://spurious.example.com:5683", ;ct=41;rt="light-lux";if="sensor" Res: 2.01 Created - Location: /rd/4521 + Location-Path: /rd/4521 Figure 7: Example registration payload A Resource Directory may optionally support HTTP. Here is an example of almost the same registration operation above, when done using HTTP and the JSON Link Format. -Req: POST /rd?ep=node1&con=http://[2001:db8:1::1] HTTP/1.1 + Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1 Host : example.com Content-Type: application/link-format+json Payload: [ -{"href": "/sensors/temp", "ct": "41", "rt": "temperature-c", "if": "sensor", - "anchor": "coap://spurious.example.com:5683"}, -{"href": "/sensors/light", "ct": "41", "rt": "light-lux", "if": "sensor"} + {"href": "/sensors/temp", "ct": "41", "rt": "temperature-c", + "if": "sensor", "anchor": "coap://spurious.example.com:5683"}, + {"href": "/sensors/light", "ct": "41", "rt": "light-lux", + "if": "sensor"} ] Res: 201 Created Location: /rd/4521 5.3.1. Simple Registration Not all endpoints hosting resources are expected to know how to - upload links to a RD as described in Section 5.3. Instead, simple + upload links to an RD as described in Section 5.3. Instead, simple endpoints can implement the Simple Registration approach described in this section. An RD implementing this specification MUST implement Simple Registration. However, there may be security reasons why this form of directory discovery would be disabled. - This approach requires that the endpoint makes available the hosted - resources that it wants to be discovered, as links on its "/.well- - known/core" interface as specified in [RFC6690]. The links in that - document are subject to the same limitations as the payload of a - registration (no relative target references when anchor is present). - - The endpoint then finds one or more addresses of the directory server - as described in Section 4. - - An endpoint finally asks the selected directory server to probe it - for resources and publish them as follows: - - The endpoint sends (and regularly refreshes with) a POST request to - the "/.well-known/core" URI of the directory server of choice. The - body of the POST request is empty, which triggers the resource - directory server to perform GET requests at the requesting server's - default discovery URI to obtain the link-format payload to register. - - The endpoint includes the same registration parameters in the POST - request as it would per Section 5.3. The context of the registration - is taken from the requesting server's URI. - - The endpoints MUST be deleted after the expiration of their lifetime. - Additional operations on the registration resource cannot be executed - because no registration location is returned. - - The following example shows an endpoint using Simple Registration, by - simply sending an empty POST to a resource directory. - - Req:(to RD server from [2001:db8:2::1]) - POST /.well-known/core?lt=6000&ep=node1 - Content-Format: 40 - No payload - - Res: 2.04 Changed - - (later) - - Req: (from RD server to [2001:db8:2::1]) - GET /.well-known/core - Accept: 40 - - Res: 2.05 Content - Payload: - - -5.3.2. Third-party registration - - For some applications, even Simple Registration may be too taxing for - some very constrained devices, in particular if the security - requirements become too onerous. - - In a controlled environment (e.g. building control), the Resource - Directory can be filled by a third device, called a commissioning - tool. The commissioning tool can fill the Resource Directory from a - database or other means. For that purpose the scheme, IP address and - port of the registered device is indicated in the Context parameter - of the registration described in Section 5.3. - - It should be noted that the value of the con parameter applies to all - the links of the registration and has consequences for the anchor - value of the individual links as exemplified in Appendix A. An - eventual (currently non-existing) con attribute of the link is not - affected by the value of con parameter in the registration. - -5.4. Operations on the Registration Resource - - After the initial registration, an endpoint should retain the - returned location of the Registration Resource for further - operations, including refreshing the registration in order to extend - the lifetime and "keep-alive" the registration. When the lifetime of - the registration has expired, the RD SHOULD NOT respond to discovery - queries concerning this endpoint. The RD SHOULD continue to provide - access to the Registration Resource after a registration time-out - occurs in order to enable the registering endpoint to eventually - refresh the registration. The RD MAY eventually remove the - registration resource for the purpose of garbage collection and - remove it from any group it belongs to. If the Registration Resource - is removed, the endpoint will need to re-register. - - The Registration Resource may also be used to inspect the - registration resource using GET, update the registration, or cancel - the registration using DELETE. - - These operations are described in this section. + This approach requires that the registree-ep makes available the + hosted resources that it wants to be discovered, as links on its + "/.well-known/core" interface as specified in [RFC6690]. The links + in that document are subject to the same limitations as the payload + of a registration (with respect to Appendix D). -5.4.1. Registration Update + The registree-ep then finds one or more addresses of the directory + server as described in Section 4. - The update interface is used by an endpoint to refresh or update its - registration with an RD. To use the interface, the endpoint sends a - POST request to the registration resource returned by the initial - registration operation. + The registree-ep finally asks the selected directory server to probe + it for resources and publish them as follows: - An update MAY update the lifetime- or the context- registration - parameters "lt", "con" as in Section 5.3. Parameters that are not - being changed SHOULD NOT be included in an update. Adding parameters - that have not changed increases the size of the message but does not - have any other implications. Parameters MUST be included as query - parameters in an update operation as in Section 5.3. + The registree-ep sends (and regularly refreshes with) a POST request + to the "/.well-known/core" URI of the directory server of choice. + The body of the POST request is empty, and triggers the resource + directory server to perform GET requests at the requesting registree- + ep's default discovery URI to obtain the link-format payload to + register. - A registration update resets the timeout of the registration to the - (possibly updated) lifetime of the registration, independent of - whether a "lt" parameter was given. + The registree-ep includes the same registration parameters in the + POST request as it would per Section 5.3. The registration base URI + of the registration is taken from the requesting server's URI. - If the context of the registration is changed in an update explicitly - or implicitly, relative references submitted in the original - registration or later updates are resolved anew against the new - context (like in the original registration). + The Resource Directory MUST NOT query the registree-ep's data before + sending the response; this is to accommodate very limited endpoints. - The registration update operation only describes the use of POST with - an empty payload. Future standards might describe the semantics of - using content formats and payloads with the POST method to update the - links of a registration (see Section 5.4.4). + The success condition only indicates that the request was valid (ie. + the passed parameters are valid per se), not that the link data could + be obtained or parsed or was successfully registered into the RD. - The update registration request interface is specified as follows: + The simple registration request interface is specified as follows: Interaction: EP -> RD Method: POST - URI Template: {+location}{?lt,con,extra-attrs*} - URI Template Variables: - - location := This is the Location 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, - the previous last lifetime set on a previous update or the - original registration (falling back to 86400) SHOULD be used. - - con := Context (optional). This parameter updates the context - established in the original registration to a new value. If - the parameter is set in an update, it is stored by the RD as - the new Base URI under which to interpret the links of the - registration, following the same restrictions as in the - registration. If the parameter is not set and was set - explicitly before, the previous context value is kept - unmodified. If the parameter is not set and was not set - explicitly before either, the source address and source port of - the update request are stored as the context. - - extra-attrs := Additional registration attributes (optional). As - with the registration, the RD processes them if it knows their - semantics. Otherwise, unknown attributes are stored as - endpoint attributes, overriding any previously stored endpoint - attributes of the same key. + URI Template: /.well-known/core{?ep,d,lt,extra-attrs*} - Content-Format: none (no payload) + URI Template Variables are as they are for registration in + Section 5.3. The base attribute is not accepted to keep the + registration interface simple; that rules out registration over CoAP- + over-TCP or HTTP that would need to specify one. The following response codes are defined for this interface: - Success: 2.04 "Changed" or 204 "No Content" if 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). + Success: 2.04 "Changed". - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". - Service could not perform the operation. + Failure: 4.00 "Bad Request". Malformed request. - HTTP support: YES + Failure: 5.03 "Service Unavailable". Service could not perform the + operation. - If the registration update fails with a "Service Unavailable" - response and a Max-Age option or Retry-After header, the client - SHOULD retry the operation after the time indicated. If the - registration fails in another way, including request timeouts, or if - the time indicated excedes the remaining lifetime, the client SHOULD - attempt registration again. + HTTP support: NO - The following example shows an endpoint updating its registration - resource at an RD using this interface with the example location - value: /rd/4521. + For the second interaction triggered by the above, the registree-ep + takes the role of server and the RD the role of client. (Note that + this is exactly the Well-Known Interface of [RFC6690] Section 4): - Req: POST /rd/4521 + Interaction: RD -> EP - Res: 2.04 Changed + Method: GET - The following example shows an endpoint updating its registration - resource at an RD using this interface with the example location - value: /rd/4521. The initial registration by the client set the - following values: + URI Template: /.well-known/core - o endpoint name (ep)=endpoint1 + The following response codes are defined for this interface: - o lifetime (lt)=500 + Success: 2.05 "Content". - o context (con)=coap://local-proxy-old.example.com:5683 + Failure: 4.00 "Bad Request". Malformed request. - o payload of Figure 7 + Failure: 4.04 "Not Found". /.well-known/core does not exist or is + empty. - The initial state of the Resource Directory is reflected in the - following request: + Failure: 5.03 "Service Unavailable". Service could not perform the + operation. -Req: GET /rd-lookup/res?ep=endpoint1 + HTTP support: NO -Res: 2.01 Content -Payload: -;ct=41;rt="temperature"; - anchor="coap://spurious.example.com:5683", -;ct=41;rt="light-lux"; - if="sensor";anchor="coap://local-proxy-old.example.com:5683" + The registration resources MUST be deleted after the expiration of + their lifetime. Additional operations on the registration resource + cannot be executed because no registration location is returned. - The following example shows an EP changing the context to - "coaps://new.example.com:5684": + The following example shows a registree-ep using Simple Registration, + by simply sending an empty POST to a resource directory. - Req: POST /rd/4521?con=coaps://new.example.com:5684 + Req:(to RD server from [2001:db8:2::1]) + POST /.well-known/core?lt=6000&ep=node1 + No payload Res: 2.04 Changed - The consecutive query returns: + (later) -Req: GET /rd-lookup/res?ep=endpoint1 + Req: (from RD server to [2001:db8:2::1]) + GET /.well-known/core + Accept: 40 -Res: 2.01 Content + Res: 2.05 Content + Content-Format: 40 Payload: -;ct=41;rt="temperature"; - anchor="coap://spurious.example.com:5683", -;ct=41;rt="light-lux";if="sensor"; - anchor="coaps://new.example.com:5684", - -5.4.2. Registration 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. - - Removed endpoints are implicitly removed from the groups to which - they belong. - - The removal request interface is specified as follows: - - Interaction: EP -> RD - - Method: DELETE - - URI Template: {+location} - - URI Template Variables: - - location := This is the Location returned by the RD as a result - of a successful earlier registration. - - The following responses codes are defined for this interface: - - 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 with example location value /rd/4521. - - Req: DELETE /rd/4521 - - Res: 2.02 Deleted - -5.4.3. Read Endpoint Links - - Some endpoints may wish to manage their links as a collection, and - may need to read the current set of links stored in the registration - resource, in order to determine link maintenance operations. - - One or more links MAY be selected by using query filtering as - specified in [RFC6690] Section 4.1 - - If no links are selected, the Resource Directory SHOULD return an - empty payload. - - The read request interface is specified as follows: - - Interaction: EP -> RD - - Method: GET - - URI Template: {+location}{?href,rel,rt,if,ct} - - URI Template Variables: - - location := This is the Location returned by the RD as a result - of a successful earlier registration. - - href,rel,rt,if,ct := link relations and attributes specified in - the query in order to select particular links based on their - relations and attributes. "href" denotes the URI target of the - link. See [RFC6690] Sec. 4.1 - - The following response 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, with example location value /rd/4521 and example - registration payload of Figure 7. + - Req: GET /rd/4521 +5.3.2. Third-party registration - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature-c";if="sensor"; - anchor="coap://spurious.example.com:5683", - ;ct=41;rt="light-lux";if="sensor" + For some applications, even Simple Registration may be too taxing for + some very constrained devices, in particular if the security + requirements become too onerous. -5.4.4. Update Endpoint Links + In a controlled environment (e.g. building control), the Resource + Directory can be filled by a third party device, called a + commissioning tool. The commissioning tool can fill the Resource + Directory from a database or other means. For that purpose the + scheme, IP address and port of the registered device is indicated in + the "base" parameter of the registration described in Section 5.3. - An iPATCH (or PATCH) update [RFC8132] adds, removes or changes links - of a registration by including link update information in the payload - of the update with a media type that still needs to be defined. + It should be noted that the value of the "base" parameter applies to + all the links of the registration and has consequences for the anchor + value of the individual links as exemplified in Appendix B. An + eventual (currently non-existing) "base" attribute of the link is not + affected by the value of "base" parameter in the registration. 6. RD Groups This section defines the REST API for the creation, management, and lookup of endpoints for group operations. Similar to endpoint registration entries in the RD, groups may be created or removed. However unlike an endpoint entry, a group entry consists of a list of endpoints and does not have a lifetime associated with it. In order to make use of multicast requests with CoAP, a group MAY have a multicast address associated with it. 6.1. Register a Group In order to create a group, a commissioning tool (CT) used to configure groups, makes a request to the RD indicating the name of - the group to create (or update), optionally the domain the group + the group to create (or update), optionally the sector the group belongs to, and optionally the multicast address of the group. This specification does not require that the endpoints belong to the same - domain as the group, but a Resource Directory implementation can - impose requirements on the domains of groups and endpoints depending + sector as the group, but a Resource Directory implementation can + impose requirements on the sectors of groups and endpoints depending on its configuration. The registration message is a list of links to registration resources - of the endpoints that belong to that group. The registration - resources MAY be located on different hosts than the group hosting - RD. In that case the endpoint link points to the registration - resource on the other RD. The commissioning tool SHOULD NOT attempt - to enter a foreign registration in a group unless it found it in the - group RD's lookup results, or has other reasons to assume that the - foreign registration will be accepted. + of the endpoints that belong to that group. The CT can use any URI + reference discovered using endpoint lookup from the same server or + obtained by registering an endpoint using third party registration + and enter it into a group. The use of other URIs is not specified in + this document and can be defined in others. The commissioning tool SHOULD not send any target attributes with the links to the registration resources, and the resource directory SHOULD reject registrations that contain links with unprocessable attributes. 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: CT -> RD Method: POST - URI Template: {+rd-group}{?gp,d,con} + URI Template: {+rd-group}{?gp,d,base} URI Template Variables: rd-group := RD Group URI (mandatory). This is the location of the RD Group REST API. gp := Group Name (mandatory). The name of the group to be - created or replaced, unique within that domain. The maximum + created or replaced, unique within that sector. The maximum length of this parameter is 63 bytes. - d := Domain (optional). The domain to which this group belongs. + d := Sector (optional). The sector to which this group belongs. The maximum length of this parameter is 63 bytes. When this parameter is not present, the RD MAY associate the group with a - configured default domain or leave it empty. + configured default sector or leave it empty. - con := Context (optional). This parameter sets the scheme, - address and port of the multicast address associated with the - group. When con is used, scheme and host are mandatory and - port parameter is optional. + base := Group Base URI (optional). This parameter sets the + scheme, address and port of the multicast address associated + with the group. When base is used, scheme and host are + mandatory and port parameter is optional. Content-Format: application/link-format Content-Format: application/link-format+json Content-Format: application/link-format+cbor The following response codes are defined for this interface: - Success: 2.01 "Created" or 201 "Created". The Location header - option MUST be returned in response to a successful group CREATE - operation. This Location MUST be a stable identifier generated by - the RD as it is used for delete operations of the group resource. + Success: 2.01 "Created" or 201 "Created". The Location header or + Location-Path option MUST be returned in response to a successful + group CREATE operation. This location MUST be a stable identifier + generated by the RD as it is used for delete operations of the + group resource. + + As with the Registration operation, the location MUST NOT have a + query or fragment component. Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed request. - Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is not - registered in the RD (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 EP registering a group with the name "lights" which has two endpoints. The RD group path /rd-group is an example RD location discovered in a request similar to Figure 6. Req: POST coap://rd.example.com/rd-group?gp=lights - &con=coap://[ff35:30:2001:db8::1] + &base=coap://[ff35:30:2001:db8::1] Content-Format: 40 Payload: - , + , Res: 2.01 Created - Location: /rd-group/12 + Location-Path: /rd-group/12 A relative href value denotes the path to the registration resource of the Endpoint. When pointing to a registration resource on a different RD, the href value is an absolute URI. 6.2. Group Removal A group can be removed simply by sending a removal message to the location of the group registration resource which was returned when initially registering the group. Removing a group MUST NOT remove @@ -1586,60 +1461,31 @@ 7.1. Resource lookup Resource lookup results in links that are semantically equivalent to the links submitted to the RD if they were accessed on the endpoint itself. The links and link parameters returned are equal to the submitted, except that the target and anchor references are fully resolved. Links that did not have an anchor attribute are therefore returned - with the (explicitly or implicitly set) context URI of the - registration as the anchor. Links whose href or anchor was submitted - as an absolute URI are returned with respective attributes - unmodified. + with the (explicitly or implicitly set) base URI of the registration + as the anchor. Links whose href or anchor was submitted as an + absolute URI are returned with respective attributes unmodified. Above rules allow the client to interpret the response as links without any further knowledge of what the RD does. The Resource - Directory MAY replace the contexts with a configured intermediate - proxy, e.g. in the case of an HTTP lookup interface for CoAP - endpoints. - -7.2. Endpoint and group lookup - - Endpoint and group lookups result in links to registration resources - and group resources, respectively. Endpoint registration resources - are annotated with their endpoint names (ep), domains (d, if - present), context (con) and lifetime (lt, if present). Additional - endpoint attributes are added as link attributes to their endpoint - link unless their specification says otherwise. Group resources are - annotated with their group names (gp), domain (d, if present) and - multicast address (con, if present). - - While Endpoint Lookup does expose the registration resources, the RD - does not need to make them accessible to clients. Clients SHOULD NOT - attempt to dereference or manipulate them. - - A Resource Directory can report endpoints or groups in lookup that - are not hosted at the same address. While the setup and management - of such a distributed system is out of scope for this document, - lookup clients MUST be prepared to see arbitrary URIs as registration - or group resources in the results. - - For groups, a Resource Directory as specified here does not provide a - lookup mechanism for the resources that can be accessed on a group's - multicast address (ie. no lookup will return links like - ";..." for a group registered - with "con=coap://[ff35...]"). Such an additional lookup interface - could be specified in an extension document. + Directory MAY replace the registration base URIs with a configured + intermediate proxy, e.g. in the case of an HTTP lookup interface for + CoAP endpoints. -7.3. Lookup filtering +7.2. Lookup filtering Using the Accept Option, the requester can control whether the returned list is returned in CoRE Link Format ("application/link- format", default) or its alternate content-formats ("application/ link-format+json" or "application/link-format+cbor"). The page and count parameters are used to obtain lookup results in specified increments using pagination, where count specifies how many links to return and page specifies which subset of links organized in sequential pages, each containing 'count' links, starting with link @@ -1662,21 +1508,25 @@ criterion, or an entity contained in it would: A search criterion matches an endpoint if it matches the endpoint itself, any of the groups it is contained in or any resource it contains. A search criterion matches a resource if it matches the resource itself, the resource's endpoint, or any of the endpoint's groups. Note that "href" is also a valid search criterion and matches target references. Like all search criteria, on a resource lookup it can match the target reference of the resource link itself, but also the registration resource of the endpoint that registered it, or any - group resource that endpoint is contained in. + group resource that endpoint is contained in. Queries for resource + link targets MUST be in absolute form and are matched against a + resolved link target. Queries for groups and endpoints SHOULD be + expressed in path-absolute form if possible and MUST be expressed in + absolute form otherwise; the RD SHOULD recognize either. Clients that are interested in a lookup result repeatedly or continuously can use mechanisms like ETag caching, resource observation ([RFC7641]), or any future mechanism that might allow more efficient observations of collections. These are advertised, detected and used according to their own specifications and can be used with the lookup interface as with any other resource. When resource observation is used, every time the set of matching links changes, or the content of a matching link changes, the RD @@ -1732,45 +1583,52 @@ Failure: No error response to a multicast request. 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 -7.4. Lookup examples + The group and endpoint lookup return registration resources which can + only be manipulated by the registering endpoint. Examples of group + and endpoint lookup belong to the management aspects of the RD and + are shown in Appendix A.5. The resource lookup examples are shown in + this section. + +7.3. Resource lookup examples The examples in this section assume the existence of CoAP hosts with a default CoAP port 61616. HTTP hosts are possible and do not change the nature of the examples. The following example shows a client performing a resource lookup with the example resource look-up locations discovered in Figure 6: Req: GET /rd-lookup/res?rt=temperature Res: 2.05 Content -;rt="temperature";anchor="coap://[2001:db8:3::123]:61616" + ;rt="temperature"; + anchor="coap://[2001:db8:3::123]:61616" The same lookup using the CBOR Link Format media type: Req: GET /rd-lookup/res?rt=temperature Accept: TBD64 Res: 2.05 Content Content-Format: TBD64 Payload in Hex notation: -81A3017823636F61703A2F2F5B323030313A6462383A333A3A3132335D3A36313631362F -74656D7003781E636F61703A2F2F5B323030313A6462383A333A3A3132335D3A36313631 -36096B74656D7065726174757265 + 81A3017823636F61703A2F2F5B323030313A6462383A333A3A3132335D3A363136313 + 62F74656D7003781E636F61703A2F2F5B323030313A6462383A333A3A3132335D3A36 + 31363136096B74656D7065726174757265 Decoded payload: [{1: "coap://[2001:db8:3::123]:61616/temp", 9: "temperature", 3: "coap://[2001:db8:3::123]:61616"}] A client that wants to be notified of new resources as they show up can use observation: Req: GET /rd-lookup/res?rt=light Observe: 0 @@ -1783,60 +1641,20 @@ Res: 2.05 Content Observe: 24 Payload: ;rt="light"; anchor="coap://[2001:db8:3::124]", ;rt="light"; anchor="coap://[2001:db8:3::124]", ;rt="light"; anchor="coap://[2001:db8:3::124]" - The following example shows a client performing an endpoint type (et) - lookup with the value oic.d.sensor (which is currently a registered - rt value): - - Req: GET /rd-lookup/ep?et=oic.d.sensor - - Res: 2.05 Content - ;con="coap://[2001:db8:3::127]:61616";ep="node5"; - et="oic.d.sensor";ct="40";lt="600", - ;con="coap://[2001:db8:3::129]:61616";ep="node7"; - et="oic.d.sensor";ct="40";lt="600";d="floor-3" - The following example shows a client performing a group lookup for - all groups: - -Req: GET /rd-lookup/gp - -Res: 2.05 Content -;gp="lights1";d="example.com";con="coap://[ff35:30:2001:db8::1]", -;gp="lights2";d="example.com";con="coap://[ff35:30:2001:db8::2]" - - The following example shows a client performing a lookup for all - endpoints in a particular group, with one endpoint hosted by another - RD: - -Req: GET /rd-lookup/ep?gp=lights1 - -Res: 2.05 Content -;con="coap://[2001:db8:3::123]:61616"; -anchor="coap://[other-rd]";ep="node1";et="oic.d.sensor";ct="40";lt="600", -;con="coap://[2001:db8:3::124]:61616"; -ep="node2";et="oic.d.sensor";ct="40";lt="600" - - The following example shows a client performing a lookup for all - groups the endpoint "node1" belongs to: - - Req: GET /rd-lookup/gp?ep=node1 - - Res: 2.05 Content - ;gp="lights1" - The following example shows a client performing a paginated resource lookup Req: GET /rd-lookup/res?page=0&count=5 Res: 2.05 Content ;rt=sensor;ct=60; anchor="coap://[2001:db8:3::123]:61616", ;rt=sensor;ct=60; anchor="coap://[2001:db8:3::123]:61616", ;rt=sensor;ct=60; @@ -1867,85 +1685,83 @@ "coap://sensor1.example.com" and "coap://sensor2.example.com", and posted the very payload of the 6th request of section 5 of [RFC6690]. It demonstrates how absolute link targets stay unmodified, while relative ones are resolved: Req: GET /rd-lookup/res?et=oic.d.sensor ;ct=40;title="Sensor Index"; anchor="coap://sensor1.example.com", -;rt="temperature-c";if="sensor"; - anchor="coap://sensor1.example.com", -;rt="light-lux";if="sensor"; - anchor="coap://sensor1.example.com", + ;rt="temperature-c"; + if="sensor"; anchor="coap://sensor1.example.com", + ;rt="light-lux"; + if="sensor"; anchor="coap://sensor1.example.com", ;rel="describedby"; anchor="coap://sensor1.example.com/sensors/temp", ;rel="alternate"; anchor="coap://sensor1.example.com/sensors/temp", ;ct=40;title="Sensor Index"; anchor="coap://sensor2.example.com", -;rt="temperature-c";if="sensor"; - anchor="coap://sensor2.example.com", -;rt="light-lux";if="sensor"; - anchor="coap://sensor2.example.com", + ;rt="temperature-c"; + if="sensor"; anchor="coap://sensor2.example.com", + ;rt="light-lux"; + if="sensor"; anchor="coap://sensor2.example.com", ;rel="describedby"; anchor="coap://sensor2.example.com/sensors/temp", ;rel="alternate"; anchor="coap://sensor2.example.com/sensors/temp" 8. 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. 8.1. Endpoint Identification and Authentication - An Endpoint is determined to be unique within (the domain of) an RD + An Endpoint is determined to be unique within (the sector of) 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. - Consider te following threat: two devices A and B are managed by a + Consider the following threat: two devices A and B are managed by a single server. Both devices have unique, per-device credentials for use with DTLS to make sure that only parties with authorization to access A or B can do so. Now, imagine that a malicious device A wants to sabotage the device B. It uses its credentials during the DTLS exchange. Then, it puts the endpoint name of device B. If the server does not check whether the identifier provided in the DTLS handshake matches the identifier used at the CoAP layer then it may be inclined to use the endpoint name for looking up what information to provision to the malicious device. - Therfore, Endpoints MUST include the Endpoint identifier in the - message, and this identifier MUST be checked by a resource directory - to match the Endpoint identifier included in the Registration - message. + Section 9 specifies an example that removes this threat by using an + Authorization Server for endpoints that have a certificate installed. 8.2. Access Control Access control SHOULD be performed separately for the RD registration, Lookup, and group API paths, as different endpoints may be authorized to register with an RD from those authorized to lookup endpoints from the RD. Such access control SHOULD be performed in as fine-grained a level as possible. For example access control for - lookups could be performed either at the domain, endpoint or resource + lookups could be performed either at the sector, endpoint or resource level. 8.3. 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 @@ -1956,36 +1772,179 @@ implicated in denial-of-service (DoS) attacks since they run on unprotected UDP, there is no return routability check, and they can have a large amplification factor. The responses from the NTP server were found to be 19 times larger than the request. A Resource Directory (RD) which responds to wild-card lookups is potentially vulnerable if run with CoAP over UDP. Since there is no return routability check and the responses can be significantly larger than requests, RDs can unknowingly become part of a DDoS amplification attack. -9. IANA Considerations +9. Authorization Server example -9.1. Resource Types + When threats may occur as described in Section 8.1, an Authorization + Server (AS) as specified in [I-D.ietf-ace-oauth-authz] can be used to + remove the threat. An authorized registry request to the Resource + Directory (RD) is accompanied by an Access Token that validates the + access of the client to the RD. In this example, the contents of the + Access Token is specified by a CBOR Web Token (CWT) [RFC8392]. + Selecting one of the scenarios of + [I-D.ietf-anima-bootstrapping-keyinfra], the registree-ep has a + certificate that has been inserted at manufacturing time. The + contents of the certificate will be used to generate the unique + endpoint name. The certificate is uniquely identified by the + leftmost CNcomponent of the subject name appended with the serial + number. The unique certificate identifier is used as the unique + endpoint name. The same unique identification is used for the + registree-ep and the Commissioning Tool. - "core.rd", "core.rd-group", "core.rd-lookup-ep", "core.rd-lookup- - res", and "core.rd-lookup-gp" resource types need to be registered - with the resource type registry defined by [RFC6690]. + The case of using RPK or PSK is outside the scope of this example. -9.2. IPv6 ND Resource Directory Address Option + Figure 8 shows the example certificate used to specify the claim + values in the CWT. Serial number 01:02:03:04:05:06:07:08, and CN + field, Fairhair, in the subject field are concatenated to create a + unique certificate identifier: Fairhair-01:02:03:04:05:06:07:08, + which is used in Figure 9 and Figure 10 as "sub" claim and "epn" + claim values respectively. + + Certificate: Data: + Version: 3 (0x2) + Serial Number: 01:02:03:04:05:06:07:08 + Signature Algorithm: md5WithRSA + Encryption Issuer: C=US, ST=Florida, O=Acme, Inc., OU=Security, + CN=CA + Authority/emailAddress=ca@acme.com + Validity Not Before: Aug 20 12:59:55 2013 GMT + Not After : Aug 20 12:59:55 2013 GMT + Subject: C=US, ST=Florida, O=Acme, Inc., OU=Sales, CN=Fairhair + Subject Public Key + Info: Public Key Algorithm: rsaEncryption + RSA Public Key: (1024 bit) Modulus (1024 bit): + 00:be:5e:6e:f8:2c:c7:8c:07:7e:f0:ab:a5:12:db: + fc:5a:1e:27:ba:49:b0:2c:e1:cb:4b:05:f2:23:09: + 77:13:75:57:08:29:45:29:d0:db:8c:06:4b:c3:10: + 88:e1:ba:5e:6f:1e:c0:2e:42:82:2b:e4:fa:ba:bc: + 45:e9:98:f8:e9:00:84:60:53:a6:11:2e:18:39:6e: + ad:76:3e:75:8d:1e:b1:b2:1e:07:97:7f:49:31:35: + 25:55:0a:28:11:20:a6:7d:85:76:f7:9f:c4:66:90: + e6:2d:ce:73:45:66:be:56:aa:ee:93:ae:10:f9:ba: + 24:fe:38:d0:f0:23:d7:a1:3b + Exponent: 65537 (0x10001) + + Figure 8: Sample X.509 version 3 certificate for Fairhair device + issued by the Acme corporation. + + Three sections for as many authorized RD registration scenarios + describe: (1) the registree-ep registers itself with the RD, (2) a + 3rd party Commissioning Tool (CT) registers the registree-ep with the + RD, and (3) A client updates multiple links in an RD. + +9.1. Registree-ep registers with RD + + The registree-ep sends a Request to the RD accompanied by a CBOR Web + Token (CWT). To prevent ambiguities, the URI of the authorized + request cannot contain the ep= or the d= parameters which are + specified in the CWT. When these parameters are present in the URI, + the request is rejected with CoAP response code 4.00 (bad request). + The CWT of Figure 9 authorizes the registree-ep to register itself in + the RD by specifying the certificate identifier of the registree-ep + in the sub claim. The same value is assigned to the endpoint name of + the registree-ep in the RD. + + The claim set of the CWT is represented in CBOR diagnostic notation + { + /iss/ 1: "coaps://as.example.com", / identifies the AS/ + /sub/ 2: "Fairhair_01:02:03:04:05:06:07:08", + / certificate identifier uniquely identifies registree-ep/ + /aud/ 3: "coaps://rd.example.com" / audience is the RD/ + } + + Figure 9: Claim set of CWT for registering registree-ep + +9.2. Third party Commissioning Tool (CT) registers registree-ep with + RD. + + The CT sends a Request to the RD accompanied by a CBOR Web Token + (CWT). To prevent ambiguities, the URI of an authorized request + cannot contain the ep= or the d= parameters which are specified in + the CWT. When these parameters are present in the URI, the request + is rejected with CoAP response code 4.00 (bad request). The CWT of + Figure 10 authorizes the CT to register the registree-ep by + specifying the certificate identifier, + Fairhair_08:07:06:05:04:03:02:01, of the CT in the "sub" claim. Next + to the certificate identifier of the CT, the CWT needs to specify the + security identifier of the registree-ep. The new "rd_epn" claim is + used to specify the value of the certificate identifier + Fairhair_01:02:03:04:05:06:07:08, of the registree-ep. The CWT may + contain the optional new "rd_sct" claim to assign a sector name to + the registree-ep. + + The claim set is represented in CBOR diagnostic notation + { + /iss/ 1: "coaps://as.example.com", / identifies the AS/ + /sub/ 2: "Fairhair_08:07:06:05:04:03:02:01", + / certificate identifier uniquely identifies CT/ + /aud/ 3: "coaps://rd.example.com", / audience is the RD/ + /rd_epn/ y: "Fairhair_01:02:03:04:05:06:07:08", + /certificate identifier uniquely identifies registree-ep/ + /rd_sct/ z: "my-devices" /optional sector name/ + } + + Figure 10: Claim set of CWT for registering registree-ep by CT + +9.3. Updating multiple links + + Appendix A.4 of RD specifies that multiple links can be updated with + a media format to be specified. The updating endpoint sends a + Request to the RD accompanied by a CWT. The "sub" claim of the CWT + contains the certificate identifier of the updating endpoint. + Updating registrations and links cannot not change or delete the + endpoint names. Consequently, the updating endpoint is authorized by + the CWT to change all links of its registrations but cannot delete or + add registrations. The CWT of Figure 9 and Figure 10 authorize an + updating registree-ep or an updating CT respectively. + +10. IANA Considerations + +10.1. Resource Types + + IANA is asked to enter the following values into the Resource Type + (rt=) Link Target Attribute Values subregistry of the Constrained + Restful Environments (CoRE) Parameters registry defined in [RFC6690]: + + +--------------------+----------------------------+-----------------+ + | Value | Description | Reference | + +--------------------+----------------------------+-----------------+ + | core.rd | Directory resource of an | RFCTHIS Section | + | | RD | 5.2 | + | core.rd-group | Group directory resource | RFCTHIS Section | + | | of an RD | 5.2 | + | core.rd-lookup-res | Resource lookup of an RD | RFCTHIS Section | + | | | 5.2 | + | core.rd-lookup-ep | Endpoint lookup of an RD | RFCTHIS Section | + | | | 5.2 | + | core.rd-lookup-gp | Group lookup of an RD | RFCTHIS Section | + | | | 5.2 | + | core.rd-ep | Endpoint resource of an RD | RFCTHIS Section | + | | | 7 | + | core.rd-gp | Group resource of an RD | RFCTHIS Section | + | | | 7 | + +--------------------+----------------------------+-----------------+ + +10.2. IPv6 ND Resource Directory Address Option This document registers one new ND option type under the subregistry "IPv6 Neighbor Discovery Option Formats": o Resource Directory address Option (38) -9.3. RD Parameter Registry +10.3. 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 o the human readable name of the parameter, @@ -2010,48 +1969,49 @@ The mechanisms around new RD parameters should be designed in such a way that they tolerate RD implementations that are unaware of the parameter and expose any parameter passed at registration or updates on in endpoint lookups. (For example, if a parameter used at registration were to be confidential, the registering endpoint should be instructed to only set that parameter if the RD advertises support for keeping it confidential at the discovery step.) Initial entries in this sub-registry are as follows: - +----------+-------+---------------+-----+--------------------------+ - | Full | Short | Validity | Use | Description | - | name | | | | | - +----------+-------+---------------+-----+--------------------------+ - | Endpoint | ep | | RLA | Name of the endpoint, | - | Name | | | | max 63 bytes | - | Lifetime | lt | 60-4294967295 | RLA | Lifetime of the | - | | | | | registration in seconds | - | Domain | d | | RLA | Domain to which this | + +--------------+-------+---------------+-----+----------------------+ + | Full name | Short | Validity | Use | Description | + +--------------+-------+---------------+-----+----------------------+ + | Endpoint | ep | | RLA | Name of the | + | Name | | | | endpoint, max 63 | + | | | | | bytes | + | Lifetime | lt | 60-4294967295 | R | Lifetime of the | + | | | | | registration in | + | | | | | seconds | + | Sector | d | | RLA | Sector to which this | | | | | | endpoint belongs | - | Context | con | URI | RLA | The scheme, address and | - | | | | | port and path at which | - | | | | | this server is available | - | Group | gp | | RLA | Name of a group in the | - | Name | | | | RD | + | Registration | base | URI | RLA | The scheme, address | + | Base URI | | | | and port and path at | + | | | | | which this server is | + | | | | | available | + | Group Name | gp | | RLA | Name of a group in | + | | | | | the RD | | Page | page | Integer | L | Used for pagination | | Count | count | Integer | L | Used for pagination | | Endpoint | et | | RLA | Semantic name of the | - | Type | | | | endpoint (see Section | - | | | | | 9.4) | - +----------+-------+---------------+-----+--------------------------+ + | Type | | | | endpoint (see | + | | | | | Section 10.4) | + +--------------+-------+---------------+-----+----------------------+ Table 2: RD Parameters (Short: Short name used in query parameters or link attributes. Use: R = used at registration, L = used at lookup, A = expressed in link attribute - The descriptions for the options defined in this document are only summarized here. To which registrations they apply and when they are to be shown is described in the respective sections of this document. The IANA policy for future additions to the sub-registry is "Expert Review" as described in [RFC8126]. The evaluation should consider formal criteria, duplication of functionality (Is the new entry redundant with an existing one?), topical suitability (Eg. is the described property actually a property of the endpoint and not a property of a particular resource, in which case it should go into @@ -2058,99 +2018,146 @@ the payload of the registration and need not be registered?), and the potential for conflict with commonly used link attributes (For example, "if" could be used as a parameter for conditional registration if it were not to be used in lookup or attributes, but would make a bad parameter for lookup, because a resource lookup with an "if" query parameter could ambiguously filter by the registered endpoint property or the [RFC6690] link attribute). It is expected that the registry will receive between 5 and 50 registrations in total over the next years. -9.3.1. Full description of the "Endpoint Type" Registration Parameter +10.3.1. Full description of the "Endpoint Type" Registration Parameter An endpoint registering at an RD can describe itself with endpoint types, similar to how resources are described with Resource Types in [RFC6690]. An endpoint type is expressed as a string, which can be either a URI or one of the values defined in the Endpoint Type subregistry. Endpoint types can be passed in the "et" query parameter as part of extra-attrs at the Registration step, are shown on endpoint lookups using the "et" target attribute, and can be filtered for using "et" as a search criterion in resource and endpoint lookup. Multiple endpoint types are given as separate query parameters or link attributes. Note that Endpoint Type differs from Resource Type in that it uses multiple attributes rather than space separated values. As a result, Resource Directory implementations automatically support correct filtering in the lookup interfaces from the rules for unknown endpoint attributes. -9.4. "Endpoint Type" (et=) RD Parameter values +10.4. "Endpoint Type" (et=) RD Parameter values This specification establishes a new sub-registry under "CoRE Parameters" called '"Endpoint Type" (et=) RD Parameter values'. The registry properties (required policy, requirements, template) are identical to those of the Resource Type parameters in [RFC6690], in short: The review policy is IETF Review for values starting with "core", and Specification Required for others. The requirements to be enforced are: o The values MUST be related to the purpose described in - Section 9.3.1. + Section 10.3.1. o The registered values MUST conform to the ABNF reg-rel-type definition of [RFC6690] and MUST NOT be a URI. o It is recommended to use the period "." character for segmentation. The registry is initially empty. -9.5. Multicast Address Registration +10.5. Multicast Address Registration IANA has assigned the following multicast addresses for use by CoAP nodes: IPv4 - "all CoRE resource directories" address, from the "IPv4 Multicast Address Space Registry" equal to "All CoAP Nodes", 224.0.1.187. As the address is used for discovery that may span beyond a single network, it has come from the Internetwork Control Block (224.0.1.x, RFC 5771). - IPv6 - "all CoRE resource directories" address MCD1 (uggestions + IPv6 - "all CoRE resource directories" address MCD1 (suggestions FF0X::FE), from the "IPv6 Multicast Address Space Registry", in the "Variable Scope Multicast Addresses" space (RFC 3307). Note that there is a distinct multicast address for each scope that interested CoAP nodes should listen to; CoAP needs the Link-Local and Site-Local scopes only. -10. Examples +10.6. CBOR Web Token claims + + This specification registers the following new claims in the CBOR Web + Token (CWT) registry of CBOR Web Token Claims: + + Claim "rd_epn" + + o Claim Name: "rd_epn" + + o Claim Description: The endpoint name of the RD entry as described + in Section 9 of RFCTHIS. + + o JWT Claim Name: N/A + o Claim Key: y + + o Claim Value Type(s): 0 (uint), 2 (byte string), 3 (text string) + + o Change Controller: IESG + + o Specification Document(s): Section 9 of RFCTHIS + + Claim "rd_sct" + + o Claim Name: "rd_sct" + + o Claim Description: The sector name of the RD entry as described in + Section 9 of RFCTHIS. + + o JWT Claim Name: N/A + + o Claim Key: z + + o Claim Value Type(s): 0 (uint), 2 (byte string), 3 (text string) + + o Change Controller: IESG + + o Specification Document(s): Section 9 of RFCTHIS + + Mapping of claim name to CWT key + + +----------------+----------+-------------+ + | Parameter name | CBOR key | Value type | + +----------------+----------+-------------+ + | rd_epn | y | Text string | + | rd_sct | z | Text string | + +----------------+----------+-------------+ + +11. Examples Two examples are presented: a Lighting Installation example in - Section 10.1 and a LWM2M example in Section 10.2. + Section 11.1 and a LWM2M example in Section 11.2. -10.1. Lighting Installation +11.1. 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 or naming procedures, because the example only "emphasizes" some of the issues that may influence the use of the RD and does not pretend to be normative. -10.1.1. Installation Characteristics +11.1.1. 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 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 @@ -2183,24 +2190,24 @@ | Name | IPv6 address | +--------------------+----------------+ | luminary1 | 2001:db8:4::1 | | luminary2 | 2001:db8:4::2 | | Presence sensor | 2001:db8:4::3 | | Resource directory | 2001:db8:4::ff | +--------------------+----------------+ Table 3: interface SLAAC addresses - In Section 10.1.2 the use of resource directory during installation + In Section 11.1.2 the use of resource directory during installation is presented. -10.1.2. RD entries +11.1.2. 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 endpoints have names which are relevant to the light installation manager. In this case luminary1, luminary2, and the presence sensor are located in room 2-4-015, where luminary1 is @@ -2224,146 +2231,133 @@ | sensor | | | | +----------------+------------------+---------------+---------------+ Table 4: Resource Directory identifiers It is assumed that the CT knows the RD's address, and has performed URI discovery on it that returned a response like the one in the Section 5.2 example. The CT inserts the endpoints of the luminaries and the sensor in the - RD using the Context parameter (con) to specify the interface - address: + RD using the registration base URI parameter (base) to specify the + interface address: Req: POST coap://[2001:db8:4::ff]/rd - ?ep=lm_R2-4-015_wndw&con=coap://[2001:db8:4::1]&d=R2-4-015 + ?ep=lm_R2-4-015_wndw&base=coap://[2001:db8:4::1]&d=R2-4-015 Payload: ;rt="light", ;rt="light", ;rt="light" Res: 2.01 Created - Location: /rd/4521 + Location-Path: /rd/4521 + Req: POST coap://[2001:db8:4::ff]/rd - ?ep=lm_R2-4-015_door&con=coap://[2001:db8:4::2]&d=R2-4-015 + ?ep=lm_R2-4-015_door&base=coap://[2001:db8:4::2]&d=R2-4-015 Payload: ;rt="light", ;rt="light", ;rt="light" Res: 2.01 Created - Location: /rd/4522 + Location-Path: /rd/4522 Req: POST coap://[2001:db8:4::ff]/rd - ?ep=ps_R2-4-015_door&con=coap://[2001:db8:4::3]d&d=R2-4-015 + ?ep=ps_R2-4-015_door&base=coap://[2001:db8:4::3]d&d=R2-4-015 Payload: ;rt="p-sensor" Res: 2.01 Created - Location: /rd/4523 + Location-Path: /rd/4523 - The domain name d=R2-4-015 has been added for an efficient lookup - because filtering on "ep" name is more awkward. The same domain name + The sector name d=R2-4-015 has been added for an efficient lookup + because filtering on "ep" name is more awkward. The same sector name is communicated to the two luminaries and the presence sensor by the CT. - The group is specified in the RD. The Context parameter is set to - the site-local multicast address allocated to the group. In the POST - in the example below, these two endpoints and the endpoint of the + The group is specified in the RD. The base parameter is set to the + site-local multicast address allocated to the group. In the POST in + the example below, these two endpoints and the endpoint of the presence sensor are registered as members of the group. Req: POST coap://[2001:db8:4::ff]/rd-group - ?gp=grp_R2-4-015&con=coap://[ff05::1] + ?gp=grp_R2-4-015&base=coap://[ff05::1] Payload: , , Res: 2.01 Created - Location: /rd-group/501 + Location-Path: /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 endpoint - with rt=light and d=R2-4-015. The RD returns all endpoints in the - domain. - - Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep - ?d=R2-4-015&rt=light - - Res: 2.05 Content - ;con="coap://[2001:db8:4::1]"; - ep="lm_R2-4-015_wndw", - ;con="coap://[2001:db8:4::2]"; - ep="lm_R2-4-015_door" - - Knowing its own IPv6 address, the luminary discovers its endpoint - name. With the endpoint name the luminary queries the RD for all - groups to which the endpoint belongs. + The luminary, knowing its sector and own IPv6 address, looks up the + groups containing light resources it is assigned to: Req: GET coap://[2001:db8:4::ff]/rd-lookup/gp - ?ep=lm_R2-4-015_wndw + ?d=R2-4-015&base=coap://[2001:db8:4::1]&rt=light Res: 2.05 Content - ;gp="grp_R2-4-015";con="coap://[ff05::1]" + ;gp="grp_R2-4-015";base="coap://[ff05::1]" - From the context parameter value, the luminary learns the multicast - address of the multicast group. + From the returned base 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 coap://[2001:db8:4::1]/coap-group Content-Format: application/coap-group+json Payload: { "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. -10.2. OMA Lightweight M2M (LWM2M) Example +11.2. 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(OMA Name Authority). LWM2M defines a simple object model and a number of abstract interfaces and operations for device management and device service enablement. An LWM2M server is an instance of an LWM2M middleware service layer, containing a Resource Directory along with other LWM2M interfaces defined by the LWM2M specification. CoRE Resource Directory (RD) is used to provide the LWM2M Registration interface. - LWM2M does not provide for registration domains and does not + LWM2M does not provide for registration sectors and does not currently use the rd-group or rd-lookup interfaces. The LWM2M specification describes a set of interfaces and a resource model used between a LWM2M device and an LWM2M server. Other interfaces, proxies, and applications are currently out of scope for LWM2M. The location of the LWM2M Server and RD URI path is provided by the LWM2M Bootstrap process, so no dynamic discovery of the RD is used. LWM2M Servers and endpoints are not required to implement the /.well- known/core resource. -10.2.1. The LWM2M Object Model +11.2.1. 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 @@ -2411,21 +2403,21 @@ 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). -10.2.2. LWM2M Register Endpoint +11.2.2. LWM2M Register Endpoint LWM2M defines a registration interface based on the REST API, described in Section 5. The RD registration URI path of the LWM2M Resource Directory is specified to be "/rd". LWM2M endpoints register object IDs, for example , to indicate that a particular object type is supported, and register object instances, for example , to indicate that a particular instance of that object type exists. @@ -2464,81 +2456,124 @@ | SMS | sms | | MSISDN | | Number | | | | +-----------+-------+-------------------------------+---------------+ Table 5: LWM2M Additional Registration Parameters The following RD registration parameters are not currently specified for use in LWM2M: et - Endpoint Type - con - Context + base - Registration Base URI The endpoint registration must include a payload containing links to all supported objects and existing object instances, optionally including the appropriate link-format relations. Here is an example LWM2M registration payload: ,,, + This link format payload indicates that object ID 1 (LWM2M Server Object) is supported, with a single instance 0 existing, object ID 3 (LWM2M Device object) is supported, with a single instance 0 existing, and object 5 (LWM2M Firmware Object) is supported, with no existing instances. -10.2.3. LWM2M Update Endpoint Registration +11.2.3. LWM2M Update Endpoint Registration The LwM2M update is really very similar to the registration update as - described in Section 5.4.1, with the only difference that there are + described in Appendix A.1, with the only difference that there are more parameters defined and available. All the parameters listed in that section are also available with the initial registration but are all optional: 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. -10.2.4. LWM2M De-Register Endpoint +11.2.4. 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 5.4.2. + registration proceeds as described in Appendix A.2. -11. Acknowledgments +12. Acknowledgments Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen, Hannes Tschofenig, Sampo Ukkola, Linyi Tian, and Jan Newmarch have provided helpful comments, discussions and ideas to improve and shape this document. Zach would also like to thank his colleagues from the EU FP7 SENSEI project, where many of the resource directory concepts were originally developed. -12. Changelog +13. Changelog + + changes from -13 to -14 + + o Rename "registration context" to "registration base URI" (and + "con" to "base") and "domain" to "sector" (where the abbreviation + "d" stays for compatibility reasons) + + o Introduced resource types core.rd-ep and core.rd-gp + + o Registration management moved to appendix A, including endpoint + and group lookup + + o Minor editorial changes + + * PATCH/iPATCH is clearly deferred to another document + + * Recommend against query / fragment identifier in con= + + * Interface description lists are described as illustrative + + * Rewording of Simple Registration + + o Simple registration carries no error information and succeeds + immediately (previously, sequence was unspecified) + + o Lookup: href are matched against resolved values (previously, this + was unspecified) + + o Lookup: lt are not exposed any more + + o con/base: Paths are allowed + + o Registration resource locations can not have query or fragment + parts + + o Default life time extended to 25 hours + + o clarified registration update rules + + o lt-value semantics for lookup clarified. + + o added template for simple registration changes from -12 to -13 o Added "all resource directory" nodes MC address o Clarified observation behavior o version identification + o example rt= and et= values o domain from figure 2 - o more explanatory text o endpoints of a groups hosted by different RD o resolve RFC6690-vs-8288 resolution ambiguities: * require registered links not to be relative when using anchor * return absolute URIs in resource lookup @@ -2756,23 +2792,22 @@ 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 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. -13. References - -13.1. Normative References +14. References +14.1. Normative References [I-D.ietf-core-links-json] Li, K., Rahman, A., and C. Bormann, "Representing Constrained RESTful Environments (CoRE) Link Format in JSON and CBOR", draft-ietf-core-links-json-10 (work in progress), February 2018. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, @@ -2798,46 +2833,54 @@ [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, . [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . - [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and - FETCH Methods for the Constrained Application Protocol - (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, - . - -13.2. Informative References +14.2. Informative References [ER] Chen, P., "The entity-relationship model---toward a unified view of data", ACM Transactions on Database Systems Vol. 1, pp. 9-36, DOI 10.1145/320434.320440, March 1976. [I-D.arkko-core-dev-urn] Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource Names for Device Identifiers", draft-arkko-core-dev-urn-05 (work in progress), October 2017. [I-D.bormann-t2trg-rel-impl] Bormann, C., "impl-info: A link relation type for disclosing implementation information", draft-bormann- t2trg-rel-impl-00 (work in progress), January 2018. + [I-D.ietf-ace-oauth-authz] + Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and + H. Tschofenig, "Authentication and Authorization for + Constrained Environments (ACE) using the OAuth 2.0 + Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-12 + (work in progress), May 2018. + + [I-D.ietf-anima-bootstrapping-keyinfra] + Pritikin, M., Richardson, M., Behringer, M., Bjarnason, + S., and K. Watsen, "Bootstrapping Remote Secure Key + Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- + keyinfra-16 (work in progress), June 2018. + [I-D.silverajan-core-coap-protocol-negotiation] Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation", - draft-silverajan-core-coap-protocol-negotiation-07 (work - in progress), October 2017. + draft-silverajan-core-coap-protocol-negotiation-08 (work + in progress), March 2018. [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, DOI 10.17487/RFC2616, June 1999, . [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", @@ -2857,96 +2900,450 @@ [RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for the Constrained Application Protocol (CoAP)", RFC 7390, DOI 10.17487/RFC7390, October 2014, . [RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015, . + [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and + FETCH Methods for the Constrained Application Protocol + (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, + . + [RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017, . -Appendix A. Web links and the Resource Directory + [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, + "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, + May 2018, . + +Appendix A. Registration Management + + This section describes how the registering endpoint can maintain the + registries that it created. The registering endpoint can be the + registree-ep or the CT. An endpoint SHOULD NOT use this interface + for registries that it did not create. The registries are resources + of the RD. + + After the initial registration, the registering endpoint retains the + returned location of the Registration Resource for further + operations, including refreshing the registration in order to extend + the lifetime and "keep-alive" the registration. When the lifetime of + the registration has expired, the RD SHOULD NOT respond to discovery + queries concerning this endpoint. The RD SHOULD continue to provide + access to the Registration Resource after a registration time-out + occurs in order to enable the registering endpoint to eventually + refresh the registration. The RD MAY eventually remove the + registration resource for the purpose of garbage collection and + remove it from any group it belongs to. If the Registration Resource + is removed, the corresponding endpoint will need to be re-registered. + + The Registration Resource may also be used to inspect the + registration resource using GET, update the registration, cancel the + registration using DELETE, do an endpoint lookup, or a group lookup. + + These operations are described below. + +A.1. Registration Update + + The update interface is used by the registering endpoint to refresh + or update its registration with an RD. To use the interface, the + registering endpoint sends a POST request to the registration + resource returned by the initial registration operation. + + An update MAY update the lifetime- or the context- registration + parameters "lt", "base" as in Section 5.3. Parameters that are not + being changed SHOULD NOT be included in an update. Adding parameters + that have not changed increases the size of the message but does not + have any other implications. Parameters MUST be included as query + parameters in an update operation as in Section 5.3. + + A registration update resets the timeout of the registration to the + (possibly updated) lifetime of the registration, independent of + whether a "lt" parameter was given. + + If the context of the registration is changed in an update explicitly + or implicitly, relative references submitted in the original + registration or later updates are resolved anew against the new + context (like in the original registration). + + The registration update operation only describes the use of POST with + an empty payload. Future standards might describe the semantics of + using content formats and payloads with the POST method to update the + links of a registration (see Appendix A.4). + + The update registration request interface is specified as follows: + + Interaction: EP -> RD + + Method: POST + + URI Template: {+location}{?lt,con,extra-attrs*} + + URI Template Variables: + + location := This is the Location 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, + the previous last lifetime set on a previous update or the + original registration (falling back to 90000) SHOULD be used. + + base := Base URI (optional). This parameter updates the context + established in the original registration to a new value. If + the parameter is set in an update, it is stored by the RD as + the new Base URI under which to interpret the links of the + registration, following the same restrictions as in the + registration. If the parameter is not set and was set + explicitly before, the previous Base URI value is kept + unmodified. If the parameter is not set and was not set + explicitly before either, the source address and source port of + the update request are stored as the Base URI. + + extra-attrs := Additional registration attributes (optional). As + with the registration, the RD processes them if it knows their + semantics. Otherwise, unknown attributes are stored as + endpoint attributes, overriding any previously stored endpoint + attributes of the same key. + + Content-Format: none (no payload) + + The following response codes are defined for this interface: + + Success: 2.04 "Changed" or 204 "No Content" if 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 + + If the registration update fails with a "Service Unavailable" + response and a Max-Age option or Retry-After header, the registering + endpoint SHOULD retry the operation after the time indicated. If the + registration fails in another way, including request timeouts, or if + the time indicated excedes the remaining lifetime, the registering + endpoint SHOULD attempt registration again. + + The following example shows the registering endpoint updates its + registration resource at an RD using this interface with the example + location value: /rd/4521. + + Req: POST /rd/4521 + + Res: 2.04 Changed + + The following example shows the registering endpoint updating its + registration resource at an RD using this interface with the example + location value: /rd/4521. The initial registration by the + registering endpoint set the following values: + + o endpoint name (ep)=endpoint1 + + o lifetime (lt)=500 + + o context (con)=coap://local-proxy-old.example.com:5683 + + o payload of Figure 7 + + The initial state of the Resource Directory is reflected in the + following request: + + Req: GET /rd-lookup/res?ep=endpoint1 + + Res: 2.01 Content + Payload: + ;ct=41; + rt="temperature"; anchor="coap://spurious.example.com:5683", + ;ct=41; + rt="light-lux"; if="sensor"; + anchor="coap://local-proxy-old.example.com:5683" + + The following example shows the registering endpoint changing the + context to "coaps://new.example.com:5684": + + Req: POST /rd/4521?con=coaps://new.example.com:5684 + + Res: 2.04 Changed + + The consecutive query returns: + + Req: GET /rd-lookup/res?ep=endpoint1 + + Res: 2.01 Content + Payload: + ;ct=41;rt="temperature"; + anchor="coap://spurious.example.com:5683", + ;ct=41;rt="light-lux"; + if="sensor"; anchor="coaps://new.example.com:5684", + +A.2. Registration Removal + + Although RD entries have soft state and will eventually timeout after + their lifetime, the registering endpoint SHOULD explicitly remove an + 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. + + Removed registrations are implicitly removed from the groups to which + they belong. + + The removal request interface is specified as follows: + + Interaction: EP -> RD + + Method: DELETE + + URI Template: {+location} + + URI Template Variables: + + location := This is the Location returned by the RD as a result + of a successful earlier registration. + + The following response 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 with example location value /rd/4521. + + Req: DELETE /rd/4521 + + Res: 2.02 Deleted + +A.3. Read Endpoint Links + + Some registering endpoints may wish to manage their links as a + collection, and may need to read the current set of links stored in + the registration resource, in order to determine link maintenance + operations. + + One or more links MAY be selected by using query filtering as + specified in [RFC6690] Section 4.1 + + If no links are selected, the Resource Directory SHOULD return an + empty payload. + + The read request interface is specified as follows: + + Interaction: EP -> RD + + Method: GET + + URI Template: {+location}{?href,rel,rt,if,ct} + + URI Template Variables: + + location := This is the Location returned by the RD as a result + of a successful earlier registration. + + href,rel,rt,if,ct := link relations and attributes specified in + the query in order to select particular links based on their + relations and attributes. "href" denotes the URI target of the + link. See [RFC6690] Sec. 4.1 + + The following response 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, with example location value /rd/4521 and example + registration payload of Figure 7. + + Req: GET /rd/4521 + + Res: 2.01 Content + Payload: + ;ct=41;rt="temperature-c";if="sensor"; + anchor="coap://spurious.example.com:5683", + ;ct=41;rt="light-lux";if="sensor" + +A.4. Update Endpoint Links + + An iPATCH (or PATCH) update ([RFC8132]) can add, remove or change the + links of a registration. + + Those operations are out of scope of this document, and will require + media types suitable for modifying sets of links. + +A.5. Endpoint and group lookup + + Endpoint and group lookups result in links to registration resources + and group resources, respectively. Endpoint registration resources + are annotated with their endpoint names (ep), sectors (d, if present) + and registration base URI (base) as well as a constant resource type + (rt="core.rd-ep"); the lifetime (lt) is not reported. Additional + endpoint attributes are added as link attributes to their endpoint + link unless their specification says otherwise. + + Group resources are annotated with their group names (gp), sector (d, + if present) and multicast address (base, if present) as well as a + constant resource type (rt="core.rd-gp"). + + Serializations derived from Link Format, SHOULD present links to + groups and endpoints in path-absolute form or, if required, as + absolute references. (This approach avoids the RFC6690 ambiguities.) + While Endpoint Lookup does expose the registration resources, the RD + does not need to make them accessible to clients. Clients SHOULD NOT + attempt to dereference or manipulate them. + + A Resource Directory can report endpoints or groups in lookup that + are not hosted at the same address. Lookup clients MUST be prepared + to see arbitrary URIs as registration or group resources in the + results and treat them as opaque identifiers; the precise semantics + of such links are left to future specifications. + + For groups, a Resource Directory as specified here does not provide a + lookup mechanism for the resources that can be accessed on a group's + multicast address (ie. no lookup will return links like + ";..." for a group registered + with "base=coap://[ff35...]"). Such an additional lookup interface + could be specified in an extension document. + + The following example shows a client performing an endpoint type (et) + lookup with the value oic.d.sensor (which is currently a registered + rt value): + + Req: GET /rd-lookup/ep?et=oic.d.sensor + + Res: 2.05 Content + ;base="coap://[2001:db8:3::127]:61616";ep="node5"; + et="oic.d.sensor";ct="40", + ;base="coap://[2001:db8:3::129]:61616";ep="node7"; + et="oic.d.sensor";ct="40";d="floor-3" + + The following example shows a client performing a group lookup for + all groups: + + Req: GET /rd-lookup/gp + + Res: 2.05 Content + ;gp="lights1";d="example.com"; + base="coap://[ff35:30:2001:db8::1]", + ;gp="lights2";d="example.com"; + base="coap://[ff35:30:2001:db8::2]" + + The following example shows a client performing a lookup for all + groups the endpoint "node1" belongs to: + + Req: GET /rd-lookup/gp?ep=node1 + + Res: 2.05 Content + ;gp="lights1" + +Appendix B. Web links and the Resource Directory Understanding the semantics of a link-format document and its URI references is a journey through different documents ([RFC3986] defining URIs, [RFC6690] defining link-format documents based on [RFC8288] which defines link headers, and [RFC7252] providing the transport). This appendix summarizes the mechanisms and semantics at play from an entry in ".well-known/core" to a resource lookup. This text is primarily aimed at people entering the field of Constrained Restful Environments from applications that previously did not use web mechanisms. -A.1. A simple example +B.1. A simple example Let's start this example with a very simple host, "2001:db8:f0::1". A client that follows classical CoAP Discovery ([RFC7252] Section 7), sends the following multicast request to learn about neighbours supporting resources with resource-type "temperature". The client sends a link-local multicast: GET coap://[ff02::fd]:5683/.well-known/core?rt=temperature RES 2.05 Content ;rt=temperature;ct=0 where the response is sent by the server, "[2001:db8:f0::1]:5683". While the client - on the practical or implementation side - can just go ahead and create a new request to "[2001:db8:f0::1]:5683" with Uri-Path: "temp", the full resolution steps without any shortcuts are: -A.1.1. Resolving the URIs +B.1.1. Resolving the URIs The client parses the single returned record. The link's target (sometimes called "href") is ""/temp"", which is a relative URI that needs resolving. As long as all involved links follow the - restrictions set forth for this document (see Appendix A.4), the base + restrictions set forth for this document (see Appendix B.4), the base URI to resolve this against the requested URI. The URI of the requested resource can be composed by following the steps of [RFC7252] section 6.5 (with an addition at the end of 8.2) into ""coap://[2001:db8:f0::1]/.well-known/core"". The record's target is resolved by replacing the path ""/.well-known/ core"" from the Base URI (section 5.2 [RFC3986]) with the relative target URI ""/temp"" into ""coap://[2001:db8:f0::1]/temp"". -A.1.2. Interpreting attributes and relations +B.1.2. Interpreting attributes and relations Some more information but the record's target can be obtained from the payload: the resource type of the target is "temperature", and its content type is text/plain (ct=0). A relation in a web link is a three-part statement that the context resource has a named relation to the target resource, like "_This page_ has _its table of contents_ at _/toc.html_". In [RFC6690] link-format documents, there is an implicit "host relation" specified with default parameter: rel="hosts". In our example, the context of the link is the URI of the requested document itself. A full English expression of the "host relation" is: '"coap://[2001:db8:f0::1]/.well-known/core" is hosting the resource "coap://[2001:db8:f0::1]/temp", which is of the resource type "temperature" and can be accessed using the text/plain content format.' -A.2. A slightly more complex example +B.2. A slightly more complex example Omitting the "rt=temperature" filter, the discovery query would have given some more records in the payload: ;rt=temperature;ct=0, ;rt=light-lux;ct=0, ;anchor="/sensors/temp";rel=alternate, ;anchor="/sensors/temp"; rel="describedby" @@ -2957,37 +3354,37 @@ the target and the document Base URI any more, but about the target and that address. Thus, the third record could be read as ""coap://[2001:db8:f0::1]/sensors/temp" has an alternate representation at "coap://[2001:db8:f0::1]/t"". The fourth record can be read as ""coap://[2001:db8:f0::1]/sensors/ temp" is described by "http://www.example.com/sensors/t123"". -A.3. Enter the Resource Directory +B.3. Enter the Resource Directory The resource directory tries to carry the semantics obtainable by classical CoAP discovery over to the resource lookup interface as faithfully as possible. For the following queries, we will assume that the simple host has used Simple Registration to register at the resource directory that was announced to it, sending this request from its UDP port "[2001:db8:f0::1]:6553": POST coap://[2001:db8:f01::ff]/.well-known/core?ep=simple-host1 The resource directory would have accepted the registration, and queried the simple host's ".well-known/core" by itself. As a result, the host is registered as an endpoint in the RD with the name - "simple-host1". The registration is active for 86400 seconds, and + "simple-host1". The registration is active for 90000 seconds, and the endpoint registration Base URI is ""coap://[2001:db8:f0::1]/"" because that is the address the registration was sent from (and no explicit "con=" was given). If the client now queries the RD as it would previously have issued a multicast request, it would go through the RD discovery steps by fetching "coap://[2001:db8:f0::ff]/.well-known/core?rt=core.rd- lookup-res", obtain "coap://[2001:db8:f0::ff]/rd-lookup/res" as the resource lookup endpoint, and issue a request to "coap://[2001:db8:f0::ff]/rd-lookup/res?rt=temperature" to receive @@ -3028,64 +3425,69 @@ Had the simple host registered with an explicit context (eg. "?ep=simple-host1&con=coap+tcp://simple-host1.example.com"), that context would have been used to resolve the relative anchor values instead, giving ;rt=temperature;ct=0; anchor="coap+tcp://simple-host1.example.com" and analogous records. -A.4. A note on differences between link-format and Link headers +B.4. A note on differences between link-format and Link headers While link-format and Link headers look very similar and are based on the same model of typed links, there are some differences between [RFC6690] and [RFC5988], which are dealt with differently: o "Resolving the target against the anchor": [RFC6690] Section 2.1 - states that the anchor of a link uses the Base URI against which - the term inside the angle brackets (the target) is resolved. - [RFC8288] Section B.2 describes that the anchor is immaterial to - the resolution of the target reference. + states that the anchor of a link is used as the Base URI against + which the term inside the angle brackets (the target) is resolved, + falling back to the resource's URI with paths stripped off (its + "Origin"). [RFC8288] Section B.2 describes that the anchor is + immaterial to the resolution of the target reference. + + RFC6690, in the same section, also states that absent anchors set + the context of the link to the target's URI with its path stripped + off, while according to [RFC8288] Section 3.2, the context is the + resource's base URI. In the context of a Resource Directory, the authors decided not to not let this become an issue by requiring that RFC6690 links be serialized in a way that either rule set can be applied and give the same results. Note that all examples of [RFC6690], [RFC8288] and this document comply with that rule. - Applications that would prefer to transport references with a - relative target and an absolute anchor are advised to use a - different serialization of the links. [I-D.ietf-core-links-json] - might provide such formats. + The Modernized Link Format is introduced in Appendix D to + formalize what it means to apply the ruleset of RFC8288 to Link + Format documents. o There is no percent encoding in link-format documents. A link-format document is a UTF-8 encoded string of Unicode characters and does not have percent encoding, while Link headers are practically ASCII strings that use percent encoding for non- - ASCII characters, stating the encoding explictly when required. + ASCII characters, stating the encoding explicitly when required. For example, while a Link header in a page about a Swedish city might read "Link: ;rel="live-environment-data"" a link-format document from the same source might describe the link as ";rel="live-environment-data"" Parsers and producers of link-format and header data need to be aware of this difference. -Appendix B. Syntax examples for Protocol Negotiation +Appendix C. Syntax examples for Protocol Negotiation [ This appendix should not show up in a published version of this document. ] The protocol negotiation that is being worked on in [I-D.silverajan-core-coap-protocol-negotiation] makes use of the Resource Directory. Until that document is update to use the latest resource-directory specification, here are some examples of protocol negotiation with @@ -3094,56 +3496,110 @@ An endpoint could register as follows from its address "[2001:db8:f1::2]:5683": Req: POST coap://rd.example.com/rd?ep=node1 &at=coap+tcp://[2001:db8:f1::2] Content-Format: 40 Payload: ;ct=0;rt="temperature";if="core.s" Res: 2.01 Created - Location: /rd/1234 + Location-Path: /rd/1234 An endpoint lookup would just reflect the registered attributes: Req: GET /rd-lookup/ep Res: 2.05 Content ;ep="node1";con="coap://[2001:db8:f1::2]:5683"; at="coap+tcp://[2001:db8:f1::2]" A UDP client would then see the following in a resource lookup: Req: GET /rd-lookup/res?rt=temperature Res: 2.05 Content -;ct=0;rt="temperature";if="core.s"; - anchor="coap://[2001:db8:f1::2]" + ;ct=0;rt="temperature"; + if="core.s"; anchor="coap://[2001:db8:f1::2]" while a TCP capable client could say: Req: GET /rd-lookup/res?rt=temperature&tt=tcp Res: 2.05 Content ;ct=0;rt="temperature"; if="core.s";anchor="coap+tcp://[2001:db8:f1::2]" -Authors' Addresses +Appendix D. Modernized Link Format parsing + + The CoRE Link Format as described in [RFC6690] is unsuitable for some + use cases of the Resource Directory, and their resolution scheme is + often misunderstood by developers familiar with [RFC8288]. + + For the correct application of base URIs, we describe the + interpretation of a Link Format document as a Modernized Link Format. + In Modernized Link Format, the document is processed as in Link + Format, with the exception of Section 2.1 of [RFC6690]: + + o The URI-reference inside angle brackets ("<>") describes the + target URI of the link. If it is a relative reference, it is + resolved against the base URI of the document. + + o The context of the link is expressed by the "anchor" parameter; if + it is a relative reference, it is resolved against the document's + base URI. In absence of the "anchor" attribute, the base URI is + the link's context. + + Content formats derived from [RFC6690] which inherit its resolution + rules, like JSON and CBOR link format of [I-D.ietf-core-links-json], + can be interpreted in analogy to that. + For where the Resource Directory is concerned, all common forms of + links (eg. all the examples of RFC6690) yield identical results. + When interpreting data read from ".well-known/core", differences in + interpretation only affect links where the absent anchor attribute + means "coap://host/" according to RFC6690 and "coap://host/.well- + known/core" according to Modernized Link format; those typically only + occur in conjunction with the vaguely defined implicit "hosts" + relationship. + +D.1. For endpoint developers + + When developing endpoints, ie. when generating documents that will be + submitted to a Resource Directory, the differences between Modernized + Link Format and RFC6690 can be ignored as long as all relative + references start with a slash, and any of the following applies: + + o There is no anchor attribute, and the context of the link does not + matter to the application. + + Example: ";ct=40" + + o The anchor is a relative reference. + + Example: ";anchor="/sensors/temp";rel="alternate" + + o The target is an absolute reference. + + Example: ";anchor="/sensors/ + temp";rel="describedby"" + +Authors' Addresses Zach Shelby ARM 150 Rose Orchard San Jose 95134 USA Phone: +1-408-203-9434 Email: zach.shelby@arm.com + Michael Koster SmartThings 665 Clyde Avenue Mountain View 94043 USA Phone: +1-707-502-5136 Email: Michael.Koster@smartthings.com Carsten Bormann