draft-ietf-core-resource-directory-09.txt		draft-ietf-core-resource-directory-10.txt
	CoRE Z. Shelby		CoRE Z. Shelby
	Internet-Draft ARM		Internet-Draft ARM
	Intended status: Standards Track M. Koster		Intended status: Standards Track M. Koster
	Expires: May 4, 2017 SmartThings		Expires: September 14, 2017 SmartThings
	C. Bormann		C. Bormann
	Universitaet Bremen TZI		Universitaet Bremen TZI
	P. van der Stok		P. van der Stok
	consultant		consultant
	October 31, 2016		March 13, 2017
	CoRE Resource Directory		CoRE Resource Directory
	draft-ietf-core-resource-directory-09		draft-ietf-core-resource-directory-10
	Abstract		Abstract
	In many M2M applications, direct discovery of resources is not		In many M2M applications, direct discovery of resources is not
	practical due to sleeping nodes, disperse networks, or networks where		practical due to sleeping nodes, disperse networks, or networks where
	multicast traffic is inefficient. These problems can be solved by		multicast traffic is inefficient. These problems can be solved by
	employing an entity called a Resource Directory (RD), which hosts		employing an entity called a Resource Directory (RD), which hosts
	descriptions of resources held on other servers, allowing lookups to		descriptions of resources held on other servers, allowing lookups to
	be performed for those resources. This document specifies the web		be performed for those resources. This document specifies the web
	interfaces that a Resource Directory supports in order for web		interfaces that a Resource Directory supports in order for web
	skipping to change at page 1, line 44 ¶		skipping to change at page 1, line 44 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on May 4, 2017.		This Internet-Draft will expire on September 14, 2017.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2017 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 5		3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 5
	3.1. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 6		3.1. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 6
	3.2. Use Case: Home and Building Automation . . . . . . . . . 7		3.2. Use Case: Home and Building Automation . . . . . . . . . 7
	3.3. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 7		3.3. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 7
	4. Finding a Directory Server . . . . . . . . . . . . . . . . . 8		4. Finding a Resource Directory . . . . . . . . . . . . . . . . 8
	4.1. Resource Directory Address Option (RDAO) . . . . . . . . 9		4.1. Resource Directory Address Option (RDAO) . . . . . . . . 9
	5. Simple Registration . . . . . . . . . . . . . . . . . . . . . 10		5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 10
	5.1. Simple publishing to Resource Directory Server . . . . . 11		5.1. Content Formats . . . . . . . . . . . . . . . . . . . . . 11
	5.2. Third-party registration . . . . . . . . . . . . . . . . 12		5.2. Base URI Discovery . . . . . . . . . . . . . . . . . . . 11
	6. Resource Directory Function Set . . . . . . . . . . . . . . . 12		5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 13
	6.1. Content Formats . . . . . . . . . . . . . . . . . . . . . 13		5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 16
	6.2. Discovery . . . . . . . . . . . . . . . . . . . . . . . . 13		5.3.2. Simple publishing to Resource Directory Server . . . 17
	6.3. Registration . . . . . . . . . . . . . . . . . . . . . . 15		5.3.3. Third-party registration . . . . . . . . . . . . . . 17
	6.4. Registration Update . . . . . . . . . . . . . . . . . . . 18		5.3.4. Plurality of link references in a Registration . . . 18
	6.5. Registration Removal . . . . . . . . . . . . . . . . . . 20		5.4. Operations on the Registration Resource . . . . . . . . . 18
	6.6. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 21		5.4.1. Registration Update . . . . . . . . . . . . . . . . . 19
	6.7. Update Endpoint Links . . . . . . . . . . . . . . . . . . 22		5.4.2. Registration Removal . . . . . . . . . . . . . . . . 21
	7. Group Function Set . . . . . . . . . . . . . . . . . . . . . 24		5.4.3. Read Endpoint Links . . . . . . . . . . . . . . . . . 22
	7.1. Register a Group . . . . . . . . . . . . . . . . . . . . 24		5.4.4. Update Endpoint Links . . . . . . . . . . . . . . . . 23
	7.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 26		6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 27
	8. RD Lookup Function Set . . . . . . . . . . . . . . . . . . . 27		6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 27
	9. New Link-Format Attributes . . . . . . . . . . . . . . . . . 32		6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 29
	9.1. Resource Instance attribute 'ins' . . . . . . . . . . . . 32		7. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 30
	9.2. Export attribute 'exp' . . . . . . . . . . . . . . . . . 33		8. Security Considerations . . . . . . . . . . . . . . . . . . . 35
	10. DNS-SD Mapping . . . . . . . . . . . . . . . . . . . . . . . 33		8.1. Endpoint Identification and Authentication . . . . . . . 35
	10.1. DNS-based Service discovery . . . . . . . . . . . . . . 33		8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 35
	10.2. mapping ins to <Instance> . . . . . . . . . . . . . . . 34		8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 36
	10.3. Mapping rt to <ServiceType> . . . . . . . . . . . . . . 35		9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
	10.4. Domain mapping . . . . . . . . . . . . . . . . . . . . . 35		9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 36
	10.5. TXT Record key=value strings . . . . . . . . . . . . . . 35		9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 36
	10.6. Importing resource links into DNS-SD . . . . . . . . . . 36		9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 36
	11. Security Considerations . . . . . . . . . . . . . . . . . . . 37		10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 37
	11.1. Endpoint Identification and Authentication . . . . . . . 37		10.1. Lighting Installation . . . . . . . . . . . . . . . . . 37
	11.2. Access Control . . . . . . . . . . . . . . . . . . . . . 37		10.1.1. Installation Characteristics . . . . . . . . . . . . 38
	11.3. Denial of Service Attacks . . . . . . . . . . . . . . . 37		10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 39
	12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38		10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 42
	12.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 38		10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 42
	12.2. Link Extension . . . . . . . . . . . . . . . . . . . . . 38		10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 44
	12.3. IPv6 ND Resource Directory Address Option . . . . . . . 38		10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 45
	12.4. RD Parameter Registry . . . . . . . . . . . . . . . . . 38		10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 46
	13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 39		11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 46
	13.1. Lighting Installation . . . . . . . . . . . . . . . . . 39		12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 46
	13.1.1. Installation Characteristics . . . . . . . . . . . . 40		13. References . . . . . . . . . . . . . . . . . . . . . . . . . 50
	13.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 41		13.1. Normative References . . . . . . . . . . . . . . . . . . 50
	13.1.3. DNS entries . . . . . . . . . . . . . . . . . . . . 44		13.2. Informative References . . . . . . . . . . . . . . . . . 51
	13.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 44		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
	13.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 45
	13.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 46
	13.2.3. Alternate Base URI . . . . . . . . . . . . . . . . . 48
	13.2.4. LWM2M Update Endpoint Registration . . . . . . . . . 48
	13.2.5. LWM2M De-Register Endpoint . . . . . . . . . . . . . 48
	14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 48
	15. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 49
	16. References . . . . . . . . . . . . . . . . . . . . . . . . . 52
	16.1. Normative References . . . . . . . . . . . . . . . . . . 52
	16.2. Informative References . . . . . . . . . . . . . . . . . 53
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54
	1. Introduction		1. Introduction
	The work on Constrained RESTful Environments (CoRE) aims at realizing		The work on Constrained RESTful Environments (CoRE) aims at realizing
	the REST architecture in a suitable form for the most constrained		the REST architecture in a suitable form for the most constrained
	nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and		nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and
	networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M)		networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M)
	applications such as smart energy and building automation.		applications such as smart energy and building automation.
	The discovery of resources offered by a constrained server is very		The discovery of resources offered by a constrained server is very
	skipping to change at page 5, line 11 ¶		skipping to change at page 4, line 48 ¶
	All groups within a domain are unique.		All groups within a domain are unique.
	Endpoint		Endpoint
	Endpoint (EP) is a term used to describe a web server or client in		Endpoint (EP) is a term used to describe a web server or client in
	[RFC7252]. In the context of this specification an endpoint is		[RFC7252]. In the context of this specification an endpoint is
	used to describe a web server that registers resources to the		used to describe a web server that registers resources to the
	Resource Directory. An endpoint is identified by its endpoint		Resource Directory. An endpoint is identified by its endpoint
	name, which is included during registration, and is unique within		name, which is included during registration, and is unique within
	the associated domain of the registration.		the associated domain of the registration.
			Context
			When registering links to a Resource Directory, the Context refers
			to the scheme, address, port, and base path for all the links
			registered on behalf of an endpoint, of the general form
			scheme://host:port/path/ where the client may explicitly set the
			scheme and host, and may supply the port and path as optional
			parameters. When the context of a registration is explicitly set,
			the URI resolution rules in [RFC3986] MUST be applied.
	Commissioning Tool		Commissioning Tool
	Commissioning Tool (CT) is a device that assists during the		Commissioning Tool (CT) is a device that assists during the
	installation of the network by assigning values to parameters,		installation of the network by assigning values to parameters,
	naming endpoints and groups, or adapting the installation to the		naming endpoints and groups, or adapting the installation to the
	needs of the applications.		needs of the applications.
	RDAO		RDAO
	Resource Directory Address Option.		Resource Directory Address Option.
	3. Architecture and Use Cases		3. Architecture and Use Cases
	The resource directory architecture is illustrated in Figure 1. A		The resource directory architecture is illustrated in Figure 1. A
	Resource Directory (RD) is used as a repository for Web Links		Resource Directory (RD) is used as a repository for Web Links
	[RFC5988] about resources hosted on other web servers, which are		[RFC5988] about resources hosted on other web servers, which are
	called endpoints (EP). An endpoint is a web server associated with a		called endpoints (EP). An endpoint is a web server associated with a
	scheme, IP address and port (called Context), thus a physical node		scheme, IP address and port (called Context), thus a physical node
	may host one or more endpoints. The RD implements a set of REST		may host one or more endpoints. The RD implements a set of REST
	interfaces for endpoints to register and maintain sets of Web Links		interfaces for endpoints to register and maintain sets of Web Links
	(called resource directory entries), and for clients to lookup		(called resource directory registration entries), and for clients to
	resources from the RD or maintain groups. Endpoints themselves can		lookup resources from the RD or maintain groups. Endpoints
	also act as clients. An RD can be logically segmented by the use of		themselves can also act as clients. An RD can be logically segmented
	Domains. The domain an endpoint is associated with can be defined by		by the use of Domains. The domain an endpoint is associated with can
	the RD or configured by an outside entity. This information		be defined by the RD or configured by an outside entity. This
	hierarchy is shown in Figure 2.		information hierarchy is shown in Figure 2.
	Endpoints are assumed to proactively register and maintain resource		A mechanism to discover an RD using CoRE Link Format [RFC6690] is
	directory entries on the RD, which are soft state and need to be		defined.
	periodically refreshed. An endpoint is provided with interfaces to
	register, update and remove a resource directory entry. Furthermore,		Endpoints proactively register and maintain resource directory
	a mechanism to discover an RD using the CoRE Link Format [RFC6690] is		registration entries on the RD, which are soft state and need to be
	defined. It is also possible for an RD to proactively discover Web		periodically refreshed.
	Links from endpoints and add them as resource directory entries. A
	lookup interface for discovering any of the Web Links held in the RD		An endpoint is provided with interfaces to register, update and
	is provided using the CoRE Link Format.		remove a resource directory registration entry. It is also possible
			for an RD to fetch Web Links from endpoints and add them as resource
			directory entries.
			At the first registration of a set of entries, a "registration
			resource" is created, the location of which is returned to the
			registering endpoint. The registering endpoint uses this
			registration resource to manage the contents of the registration
			entry.
			A lookup interface for discovering any of the Web Links held in the
			RD is provided using the CoRE Link Format.
	Registration Lookup, Group		Registration Lookup, Group
	Interface Interfaces		Interface Interfaces
	+----+ | |		+----+ | |
	| EP |---- | |		| EP |---- | |
	+----+ ---- | |		+----+ ---- | |
	--|- +------+ |		--|- +------+ |
	+----+ | ----| | | +--------+		+----+ | ----| | | +--------+
	| EP | ---------|-----| RD |----|-----| Client |		| EP | ---------|-----| RD |----|-----| Client |
	+----+ | ----| | | +--------+		+----+ | ----| | | +--------+
	skipping to change at page 7, line 41 ¶		skipping to change at page 7, line 44 ¶
	Home and commercial building automation systems can benefit from the		Home and commercial building automation systems can benefit from the
	use of M2M web services. The discovery requirements of these		use of M2M web services. The discovery requirements of these
	applications are demanding. Home automation usually relies on run-		applications are demanding. Home automation usually relies on run-
	time discovery to commission the system, whereas in building		time discovery to commission the system, whereas in building
	automation a combination of professional commissioning and run-time		automation a combination of professional commissioning and run-time
	discovery is used. Both home and building automation involve peer-		discovery is used. Both home and building automation involve peer-
	to-peer interactions between endpoints, and involve battery-powered		to-peer interactions between endpoints, and involve battery-powered
	sleeping devices.		sleeping devices.
	The exporting of resource information to other discovery systems is
	also important in these automation applications. In home automation
	there is a need to interact with other consumer electronics, which
	may already support DNS-SD, and in building automation DNS-SD in
	combination with resource directories can cover multiple buildings.
	3.3. Use Case: Link Catalogues		3.3. Use Case: Link Catalogues
	Resources may be shared through data brokers that have no knowledge		Resources may be shared through data brokers that have no knowledge
	beforehand of who is going to consume the data. Resource Directory		beforehand of who is going to consume the data. Resource Directory
	can be used to hold links about resources and services hosted		can be used to hold links about resources and services hosted
	anywhere to make them discoverable by a general class of		anywhere to make them discoverable by a general class of
	applications.		applications.
	For example, environmental and weather sensors that generate data for		For example, environmental and weather sensors that generate data for
	public consumption may provide the data to an intermediary server, or		public consumption may provide the data to an intermediary server, or
	broker. Sensor data are published to the intermediary upon changes		broker. Sensor data are published to the intermediary upon changes
	or at regular intervals. Descriptions of the sensors that resolve to		or at regular intervals. Descriptions of the sensors that resolve to
	links to sensor data may be published to a Resource Directory.		links to sensor data may be published to a Resource Directory.
	Applications wishing to consume the data can use the Resource		Applications wishing to consume the data can use RD Lookup to
	Directory lookup function set to discover and resolve links to the		discover and resolve links to the desired resources and endpoints.
	desired resources and endpoints. The Resource Directory service need		The Resource Directory service need not be coupled with the data
	not be coupled with the data intermediary service. Mapping of		intermediary service. Mapping of Resource Directories to data
	Resource Directories to data intermediaries may be many-to-many.		intermediaries may be many-to-many.
	Metadata in web-link compatible representations are supplied by		Metadata in web link formats like [RFC6690] are supplied by Resource
	Resource Directories, which may be internally stored as triples, or		Directories, which may be internally stored as triples, or relation/
	relation/attribute pairs providing metadata about resource links.		attribute pairs providing metadata about resource links. External
	External catalogs that are represented in other formats may be		catalogs that are represented in other formats may be converted to
	converted to common web linking formats for storage and access by		common web linking formats for storage and access by Resource
	Resource Directories. Since it is common practice for these to be		Directories. Since it is common practice for these to be URN
	URN encoded, simple and lossless structural transforms should		encoded, simple and lossless structural transforms should generally
	generally be sufficient to store external metadata in Resource		be sufficient to store external metadata in Resource Directories.
	Directories.
	The additional features of Resource Directory allow domains to be		The additional features of Resource Directory allow domains to be
	defined to enable access to a particular set of resources from		defined to enable access to a particular set of resources from
	particular applications. This provides isolation and protection of		particular applications. This provides isolation and protection of
	sensitive data when needed. Resource groups may defined to allow		sensitive data when needed. Resource groups may defined to allow
	batched reads from multiple resources.		batched reads from multiple resources.
	4. Finding a Directory Server		4. Finding a Resource Directory
	Endpoints that want to contact a directory server can obtain		Several mechanisms can be employed for discovering the RD, including
	candidate IP addresses for such servers in a number of ways.		assuming a default location (e.g. on an Edge Router in a LoWPAN),
			assigning an anycast address to the RD, using DHCP, or discovering
			the RD using .well-known/core and hyperlinks as specified in CoRE
			Link Format [RFC6690]. Endpoints that want to contact a Resource
			Directory can obtain candidate IP addresses for such servers in a
			number of ways.
	In a 6LoWPAN, good candidates can be taken from:		In a 6LoWPAN, good candidates can be taken from:
	o specific static configuration (e.g., anycast addresses), if any,		o specific static configuration (e.g., anycast addresses), if any,
	o the ABRO option of 6LoWPAN-ND [RFC6775],		o the ABRO option of 6LoWPAN-ND [RFC6775],
	o other ND options that happen to point to servers (such as RDNSS),		o other ND options that happen to point to servers (such as RDNSS),
	o DHCPv6 options that might be defined later.		o DHCPv6 options that might be defined later.
	o The IPv6 Neighbor Discovery Resource Directory Address Option		o The IPv6 Neighbor Discovery Resource Directory Address Option
	described in Section 4.1		described in Section 4.1
	In networks with more inexpensive use of multicast, the candidate IP		In networks with more inexpensive use of multicast, the candidate IP
	address may be a well-known multicast address, i.e. directory servers		address may be a well-known multicast address, i.e. directory servers
	are found by simply sending GET requests to that well-known multicast		are found by simply sending GET requests to that well-known multicast
	address (see Section 6.2).		address (see Section 5.2).
			Constrained nodes configured in large batches may be configured for
			an anycast address for the RD. Each target network environment in
			which some of these preconfigured nodes are to be brought up is then
			configured with a route for this anycast address that leads to an RD
			that is appropriate for the environment.
	As some of these sources are just (more or less educated) guesses,		As some of these sources are just (more or less educated) guesses,
	endpoints MUST make use of any error messages to very strictly rate-		endpoints MUST make use of any error messages to very strictly rate-
	limit requests to candidate IP addresses that don't work out. For		limit requests to candidate IP addresses that don't work out. For
	example, an ICMP Destination Unreachable message (and, in particular,		example, an ICMP Destination Unreachable message (and, in particular,
	the port unreachable code for this message) may indicate the lack of		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		a CoAP server on the candidate host, or a CoAP error response code
	such as 4.05 "Method Not Allowed" may indicate unwillingness of a		such as 4.05 "Method Not Allowed" may indicate unwillingness of a
	CoAP server to act as a directory server.		CoAP server to act as a directory server.
	skipping to change at page 10, line 32 ¶		skipping to change at page 10, line 32 ¶
	Type: 38		Type: 38
	Length: 8-bit unsigned integer. The length of		Length: 8-bit unsigned integer. The length of
	the option in units of 8 bytes.		the option in units of 8 bytes.
	Always 3.		Always 3.
	Valid Lifetime: 16-bit unsigned integer. The length of		Valid Lifetime: 16-bit unsigned integer. The length of
	time in units of 60 seconds (relative to		time in units of 60 seconds (relative to
	the time the packet is received) that		the time the packet is received) that
	this set of border router information is		this Resource Directory address is valid.
	valid. A value of all zero bits (0x0)		A value of all zero bits (0x0) indicates
	assumes a default value of 10,000		that this Resource Directory address
	(~one week).		is not valid anymore.
	Reserved: This field is unused. It MUST be		Reserved: This field is unused. It MUST be
	initialized to zero by the sender and		initialized to zero by the sender and
	MUST be ignored by the receiver.		MUST be ignored by the receiver.
	RD Address: IPv6 address of the RD.		RD Address: IPv6 address of the RD.
	Figure 3: Resource Directory Address Option		Figure 3: Resource Directory Address Option
	5. Simple Registration		5. Resource Directory
	Not all endpoints hosting resources are expected to know how to
	implement the Resource Directory Function Set (see Section 6) hence
	cannot register with a Resource Directory. Instead, simple endpoints
	can implement the generic Simple Directory Discovery approach
	described in this section. An RD implementing this specification
	MUST implement Simple Directory Discovery. However, there may be
	security reasons why this form of directory discovery would be
	disabled.
	This approach requires that the endpoint makes available the hosted
	resources that it wants to be discovered, as links on its "/.well-
	known/core" interface as specified in [RFC6690].
	The endpoint then finds one or more addresses of the directory server
	as described in Section 4.
	An endpoint can send (a selection of) hosted resources to a directory
	server for publication as described in Section 5.1.
	The directory server integrates the information it received this way
	into its resource directory. It MAY make the information available
	to further directories, if it can ensure that a loop does not form.
	The protocol used between directories to ensure loop-free operation
	is outside the scope of this document.
	5.1. Simple publishing to Resource Directory Server
	An endpoint that wants to make itself discoverable occasionally sends
	a POST request to the "/.well-known/core" URI of any candidate
	directory server that it finds. The body of the POST request is
	empty, which triggers the resource directory server to perform GET
	requests at the requesting server's default discovery URI to obtain
	the link-format payload to register.
	The endpoint MAY include registration parameters in the POST request
	as per Section 6.3.
	The following example shows an endpoint using simple publishing, by
	simply sending an empty POST to a resource directory.
	Req:(to RD server from [ff02::1])
	POST coap://rd.example.com/.well-known/core?lt=6000
	Content-Format: 40
	payload:
	(empty payload)
	Res: 2.04 Changed
	(later)
	Req: (from RD server to [ff02::1])
	GET coap://[ff02::1]/.well-known/core
	Accept: 40
	Res: 2.05 Content
	payload:
	</sen/temp>
	5.2. Third-party registration
	For some applications, even Simple Directory Discovery may be too
	taxing for certain very constrained devices, in particular if the
	security requirements become too onerous.
	In a controlled environment (e.g. building control), the Resource
	Directory can be filled by a third device, called 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 6.3.
	6. Resource Directory Function Set
	This section defines the REST interfaces between an RD and endpoints,		This section defines the required set of REST interfaces between a
	which is called the Resource Directory Function Set. Although the		Resource Directory (RD) and endpoints. Although the examples
	examples throughout this section assume the use of CoAP [RFC7252],		throughout this section assume the use of CoAP [RFC7252], these REST
	these REST interfaces can also be realized using HTTP [RFC7230]. In		interfaces can also be realized using HTTP [RFC7230]. In all
	all definitions in this section, both CoAP response codes (with dot		definitions in this section, both CoAP response codes (with dot
	notation) and HTTP response codes (without dot notation) are shown.		notation) and HTTP response codes (without dot notation) are shown.
	An RD implementing this specification MUST support the discovery,		An RD implementing this specification MUST support the discovery,
	registration, update, lookup, and removal interfaces defined in this		registration, update, lookup, and removal interfaces defined in this
	section.		section.
	Resource directory entries are designed to be easily exported to		5.1. Content Formats
	other discovery mechanisms such as DNS-SD. For that reason,
	parameters that would meaningfully be mapped to DNS SHOULD be limited
	to a maximum length of 63 bytes.
	6.1. Content Formats
	Resource Directory implementations using this specification MUST		Resource Directory implementations using this specification MUST
	support the application/link-format content format (ct=40).		support the application/link-format content format (ct=40).
	Resource Directories implementing this specification MAY support		Resource Directories implementing this specification MAY support
	additional content formats.		additional content formats.
	Any additional content format supported by a Resource Directory		Any additional content format supported by a Resource Directory
	implementing this specification MUST have an equivalent serialization		implementing this specification MUST have an equivalent serialization
	in the application/link-format content format.		in the application/link-format content format.
	6.2. Discovery		5.2. Base URI Discovery
	Before an endpoint can make use of an RD, it must first know the RD's		Before an endpoint can make use of an RD, it must first know the RD's
	address and port, and the path of its RD Function Set. There can be		address and port, and the base URI information for its REST API.
	several mechanisms for discovering the RD including assuming a		This section defines discovery of the RD and its base URI using the
	default location (e.g. on an Edge Router in a LoWPAN), by assigning		well-known interface of the CoRE Link Format [RFC6690]. It is
	an anycast address to the RD, using DHCP, or by discovering the RD		however expected that RDs will also be discoverable via other methods
	using the CoRE Link Format (see also Section 4). This section
	defines discovery of the RD using the well-known interface of the
	CoRE Link Format [RFC6690] as the required mechanism. It is however
	expected that RDs will also be discoverable via other methods
	depending on the deployment.		depending on the deployment.
	Discovery of the RD function set is performed by sending either a		Discovery of the RD base URI is performed by sending either a
	multicast or unicast GET request to "/.well-known/core" and including		multicast or unicast GET request to "/.well-known/core" and including
	a Resource Type (rt) parameter [RFC6690] with the value "core.rd" in		a Resource Type (rt) parameter [RFC6690] with the value "core.rd" in
	the query string. Likewise, a Resource Type parameter value of		the query string. Likewise, a Resource Type parameter value of
	"core.rd-lookup" is used to discover the RD Lookup Function Set.		"core.rd-lookup*" is used to discover the base URI for RD Lookup
	Upon success, the response will contain a payload with a link format		operations, and "core.gp" is used to discover the base URI for RD
	entry for each RD discovered, with the URL indicating the root		Group operations. Upon success, the response will contain a payload
	resource of the RD. When performing multicast discovery, the		with a link format entry for each RD function discovered, indicating
	multicast IP address used will depend on the scope required and the		the base URI of the RD function returned and the corresponding
	multicast capabilities of the network.		Resource Type. When performing multicast discovery, the multicast IP
			address used will depend on the scope required and the multicast
			capabilities of the network.
	A Resource Directory MAY provide hints about the content-formats it		A Resource Directory MAY provide hints about the content-formats it
	supports in the links it exposes or registers, using the "ct" link		supports in the links it exposes or registers, using the "ct" link
	attribute, as shown in the example below. Clients MAY use these		attribute, as shown in the example below. Clients MAY use these
	hints to select alternate content-formats for interaction with the		hints to select alternate content-formats for interaction with the
	Resource Directory.		Resource Directory.
	HTTP does not support multicast and consequently only unicast		HTTP does not support multicast and consequently only unicast
	discovery can be supported using HTTP. Links to Resource Directories		discovery can be supported using HTTP. Links to Resource Directories
	MAY be registered in other Resource Directories, and well-known entry		MAY be registered in other Resource Directories, and well-known entry
	skipping to change at page 14, line 24 ¶		skipping to change at page 12, line 20 ¶
	The discovery request interface is specified as follows:		The discovery request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	Method: GET		Method: GET
	URI Template: /.well-known/core{?rt}		URI Template: /.well-known/core{?rt}
	URI Template Variables:		URI Template Variables:
	rt := Resource Type (optional). MAY contain one or more of the		rt := Resource Type (optional). MAY contain one of the values
	values "core.rd", "core.rd-lookup", "core.rd-group" or		"core.rd", "core.rd-lookup*", "core.rd-lookup-d", "core.rd-
	"core.rd*"		lookup-res", "core.rd-lookup-ep", "core.rd-lookup-gp",
			"core.rd-group" or "core.rd*"
	Content-Format: application/link-format (if any)		Content-Format: application/link-format (if any)
	Content-Format: application/link-format+json (if any)		Content-Format: application/link-format+json (if any)
	Content-Format: application/link-format+cbor (if any)		Content-Format: application/link-format+cbor (if any)
	The following response codes are defined for this interface:		The following response codes are defined for this interface:
	Success: 2.05 "Content" with an application/link-format,		Success: 2.05 "Content" with an application/link-format,
	skipping to change at page 15, line 4 ¶		skipping to change at page 12, line 50 ¶
	Failure: 4.00 "Bad Request" is returned in case of a malformed		Failure: 4.00 "Bad Request" is returned in case of a malformed
	request for a unicast request.		request for a unicast request.
	Failure: No error response to a multicast request.		Failure: No error response to a multicast request.
	HTTP support : YES (Unicast only)		HTTP support : YES (Unicast only)
	The following example shows an endpoint discovering an RD using this		The following example shows an endpoint discovering an RD using this
	interface, thus learning that the base RD resource is, in this		interface, thus learning that the base RD resource is, in this
	example, at /rd and that the content_format delivered by the server		example, at /rd and that the content-format delivered by the server
	hosting the resource is application.xml (ct=40). Note that it is up		hosting the resource is application/link-format (ct=40). Note that
	to the RD to choose its base RD resource, although diagnostics and		it is up to the RD to choose its base RD resource, although
	debugging is facilitated by using the base paths specified here where		diagnostics and debugging is facilitated by using the base paths
	possible.		specified here where possible.
	Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*		Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*
	Res: 2.05 Content		Res: 2.05 Content
	</rd>;rt="core.rd";ct=40,		</rd>;rt="core.rd";ct=40,
	</rd-lookup>;rt="core.rd-lookup";ct=40,		</rd-lookup/ep>;rt="core.rd-lookup-ep";ct=40,
			</rd-lookup/res>;rt="core.rd-lookup-res";ct="40",
	</rd-group>;rt="core.rd-group";ct=40		</rd-group>;rt="core.rd-group";ct=40
	The following example shows the way of indicating that a client may		The following example shows the way of indicating that a client may
	request alternate content-formats. The Content-Format code attribute		request alternate content-formats. The Content-Format code attribute
	"ct" MAY include a space-separated sequence of Content-Format codes		"ct" MAY include a space-separated sequence of Content-Format codes
	as specified in Section 7.2.1 of [RFC7252], indicating that multiple		as specified in Section 7.2.1 of [RFC7252], indicating that multiple
	content-formats are available. The example below shows the required		content-formats are available. The example below shows the required
	Content-Format 40 (application/link-format) indicated as well as a		Content-Format 40 (application/link-format) indicated as well as a
	more application-specific content format (picked as 65225 in this		more application-specific content format (picked as 65225 in this
	example; this is in the experimental space, not an assigned value).		example; this is in the experimental space, not an assigned value).
	The base RD resource values /rd, /rd-lookup, and /rd-group are		The base RD resource values /rd, /rd-lookup, and /rd-group are
	example values.		example values.
	Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*		Req: GET coap://[ff02::1]/.well-known/core?rt=core.rd*
	Res: 2.05 Content		Res: 2.05 Content
	</rd>;rt="core.rd";ct="40 65225",		</rd>;rt="core.rd";ct="40 65225",
	</rd-lookup>;rt="core.rd-lookup";ct="40 65225",		</rd-lookup/res>;rt="core.rd-lookup-res";ct="40 65225",
			</rd-lookup/ep>;rt="core.rd-lookup-ep";ct="40 65225",
	</rd-group>;rt="core.rd-group";ct="40 65225"		</rd-group>;rt="core.rd-group";ct="40 65225"
	6.3. Registration		5.3. Registration
	After discovering the location of an RD Function Set, an endpoint MAY		After discovering the location of an RD, an endpoint MAY register its
	register its resources using the registration interface. This		resources using the registration interface. This interface accepts a
	interface accepts a POST from an endpoint containing the list of		POST from an endpoint containing the list of resources to be added to
	resources to be added to the directory as the message payload in the		the directory as the message payload in the CoRE Link Format
	CoRE Link Format [RFC6690], JSON CoRE Link Format (application/link-		[RFC6690], JSON CoRE Link Format (application/link-format+json), or
	format+json), or CBOR CoRE Link Format (application/link-format+cbor)		CBOR CoRE Link Format (application/link-format+cbor)
	[I-D.ietf-core-links-json], along with query string parameters		[I-D.ietf-core-links-json], along with query parameters indicating
	indicating the name of the endpoint, its domain and the lifetime of		the name of the endpoint, and optionally its domain and the lifetime
	the registration. All parameters except the endpoint name are		of the registration. It is expected that other specifications will
	optional. It is expected that other specifications will define		define further parameters (see Section 9.3). The RD then creates a
	further parameters (see Section 12.4). The RD then creates a new		new registration resource in the RD and returns its location. An
	resource or updates an existing resource in the RD and returns its		endpoint MUST use that location when refreshing registrations using
	location. An endpoint MUST use that location when refreshing		this interface. Endpoint resources in the RD are kept active for the
	registrations using this interface. Endpoint resources in the RD are		period indicated by the lifetime parameter. The endpoint is
	kept active for the period indicated by the lifetime parameter. The		responsible for refreshing the entry within this period using either
	endpoint is responsible for refreshing the entry within this period		the registration or update interface. The registration interface
	using either the registration or update interface. The registration		MUST be implemented to be idempotent, so that registering twice with
	interface MUST be implemented to be idempotent, so that registering		the same endpoint parameters ep and d does not create multiple RD
	twice with the same endpoint parameter does not create multiple RD
	entries. A new registration may be created at any time to supersede		entries. A new registration may be created at any time to supersede
	an existing registration, replacing the registration parameters and		an existing registration, replacing the registration parameters and
	links.		links.
	The registration request interface is specified as follows:		The registration request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	Method: POST		Method: POST
	URI Template: /{+rd}{?ep,d,et,lt,con}		URI Template: /{+rd}{?ep,d,et,lt,con}
	URI Template Variables:		URI Template Variables:
	rd := RD Function Set path (mandatory). This is the path of the		rd := RD Base URI path (mandatory). This is the path of the RD,
	RD Function Set, as obtained from discovery. The value "rd" is		as obtained from discovery. The value "rd" is recommended for
	recommended for this variable.		this variable.
	ep := Endpoint name (mandatory). The endpoint name is an		ep := Endpoint name (mandatory). The endpoint name is an
	identifier that MUST be unique within a domain. The maximum		identifier that MUST be unique within a domain. The maximum
	length of this parameter is 63 bytes.		length of this parameter is 63 bytes.
	d := Domain (optional). The domain to which this endpoint		d := Domain (optional). The domain to which this endpoint
	belongs. The maximum length of this parameter is 63 bytes.		belongs. The maximum length of this parameter is 63 bytes.
	When this parameter is elided, the RD MAY associate the		When this parameter is elided, the RD MAY associate the
	endpoint with a configured default domain. The domain value is		endpoint with a configured default domain.
	needed to export the endpoint to DNS-SD (see Section 10).
	et := Endpoint Type (optional). The semantic type of the		et := Endpoint Type (optional). The semantic type of the
	endpoint. This parameter SHOULD be less than 63 bytes.		endpoint. This parameter SHOULD be less than 63 bytes.
	lt := Lifetime (optional). Lifetime of the registration in		lt := Lifetime (optional). Lifetime of the registration in
	seconds. Range of 60-4294967295. If no lifetime is included,		seconds. Range of 60-4294967295. If no lifetime is included
	a default value of 86400 (24 hours) SHOULD be assumed.		in the initial registration, a default value of 86400 (24
			hours) SHOULD be assumed. If the lt parameter is not included
			in a registration refresh or update operation, the most
			recently supplied value SHALL be re-used.
	con := Context (optional). This parameter sets the scheme,		con := Context (optional). This parameter sets the scheme,
	address and port at which this server is available in the form		address and port at which this server is available in the form
	scheme://host:port. In the absence of this parameter the		scheme://host:port/path. In the absence of this parameter the
	scheme of the protocol, source IP address and source port of		scheme of the protocol, source address and source port of the
	the register request are assumed. This parameter is mandatory		register request are assumed. This parameter is mandatory when
	when the directory is filled by a third party such as an		the directory is filled by a third party such as an
	commissioning tool.		commissioning tool. When con is used, scheme and host are
			mandatory and port and path parameters are optional. If the
			endpoint uses an ephemeral port to register with, it MUST
			include the con: parameter in the registration to provide a
			valid network path. If the endpoint which is located behind a
			NAT gateway is registering with a Resource Directory which is
			on the network service side of the NAT gateway, the endpoint
			MUST use a persistent port for the outgoing registration in
			order to provide the NAT gateway with a valid network address
			for replies and incoming requests.
	Content-Format: application/link-format		Content-Format: application/link-format
	Content-Format: application/link-format+json		Content-Format: application/link-format+json
	Content-Format: application/link-format+cbor		Content-Format: application/link-format+cbor
	The following response codes are defined for this interface:		The following response codes are defined for this interface:
	Success: 2.01 "Created" or 201 "Created". The Location header MUST		Success: 2.01 "Created" or 201 "Created". The Location header
	be included with the new resource entry for the endpoint. This		option MUST be included in the response when a new registration
	Location MUST be a stable identifier generated by the RD as it is		resource is created. This Location MUST be a stable identifier
	used for all subsequent operations on this registration. The		generated by the RD as it is used for all subsequent operations on
	resource returned in the Location is for the purpose of updating		this registration resource. The registration resource location
	the lifetime of the registration and for maintaining the content		thus returned is for the purpose of updating the lifetime of the
	of the registered links, including updating and deleting links.		registration and for maintaining the content of the registered
			links, including updating and deleting links.
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
			Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the
			registration content with links resulting in plurality of
			references; see Section 5.3.4.
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	HTTP support: YES		HTTP support: YES
	The following example shows an endpoint with the name "node1"		The following example shows an endpoint with the name "node1"
	registering two resources to an RD using this interface. The		registering two resources to an RD using this interface. The
	location "/rd" is an example value of an RD base location.		location "/rd" is an example value of an RD base location.
	Req: POST coap://rd.example.com/rd?ep=node1		Req: POST coap://rd.example.com/rd?ep=node1
	Content-Format: 40		Content-Format: 40
	Payload:		Payload:
	</sensors/temp>;ct=41;rt="temperature-c";if="sensor",		</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
	</sensors/light>;ct=41;rt="light-lux";if="sensor"		</sensors/light>;ct=41;rt="light-lux";if="sensor"
	Res: 2.01 Created		Res: 2.01 Created
	Location: /rd/4521		Location: /rd/4521
			A Resource Directory may optionally support HTTP. Here is an example
			of the same registration operation above, when done using HTTP.
	Req: POST /rd?ep=node1 HTTP/1.1		Req: POST /rd?ep=node1 HTTP/1.1
	Host : example.com		Host : example.com
	Content-Type: application/link-format		Content-Type: application/link-format
	Payload:		Payload:
	</sensors/temp>;ct=41;rt="temperature-c";if="sensor",		</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
	</sensors/light>;ct=41;rt="light-lux";if="sensor"		</sensors/light>;ct=41;rt="light-lux";if="sensor"
	Res: 201 Created		Res: 201 Created
	Location: /rd/4521		Location: /rd/4521
	6.4. Registration Update		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
			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 endpoint then finds one or more addresses of the directory server
			as described in Section 4.
			An endpoint can send (a selection of) hosted resources to a directory
			server for publication as described in Section 5.3.2.
			The directory server integrates the information it received this way
			into its resource directory. It MAY make the information available
			to further directories, if it can ensure that a loop does not form.
			The protocol used between directories to ensure loop-free operation
			is outside the scope of this document.
			5.3.2. Simple publishing to Resource Directory Server
			An endpoint that wants to make itself discoverable occasionally sends
			a POST request to the "/.well-known/core" URI of any candidate
			directory server that it finds. The body of the POST request is
			empty, which triggers the resource directory server to perform GET
			requests at the requesting server's default discovery URI to obtain
			the link-format payload to register.
			The endpoint MUST include the endpoint name and MAY include the
			registration parameters d, lt, and et, in the POST request as per
			Section 5.3.
			The following example shows an endpoint using simple publishing, by
			simply sending an empty POST to a resource directory.
			Req:(to RD server from [ff02::1])
			POST coap://rd.example.com/.well-known/core?lt=6000;ep=node1
			Content-Format: 40
			payload:
			(empty payload)
			Res: 2.04 Changed
			(later)
			Req: (from RD server to [ff02::1])
			GET coap://[ff02::1]/.well-known/core
			Accept: 40
			Res: 2.05 Content
			payload:
			</sen/temp>
			5.3.3. Third-party registration
			For some applications, even Simple Directory Discovery may be too
			taxing for certain very constrained devices, in particular if the
			security requirements become too onerous.
			In a controlled environment (e.g. building control), the Resource
			Directory can be filled by a third device, called 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.
			5.3.4. Plurality of link references in a Registration
			Plurality of link references within a Registration (registration
			resource) is an indication of some error condition and should not be
			allowed.
			Plurality of link references exists if, and only if, two or more
			links in a Registration contain identical context, target, and
			relation values. This condition would be likely to arise if there
			were multiple co-ordinators or configuration tools, each with a
			different set of configuration values for the same resource.
			A Resource Directory SHOULD reject a registration, or an operation on
			a registration, which would result in a plurality of link references
			within the the context of the registration. There is no requirement
			in this document for a resource directory to check for plurality of
			reference between different registrations. Resource Directory
			operations which are rejected due to reference plurality SHOULD be
			returned the "Conflict" code, indicating that there is someting wrong
			with the request.
			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 lifetie and "keep-alive" the registration. If the lifetime of
			the registration expires, the RD SHOULD NOT respond to discovery
			queries with information from the endpoint. The RD SHOULD continue
			to provide access to the Registration Resource after a registration
			time-out occurs in order to enable the registering endpoint to
			eventually refresh the registration. The RD MAY eventually remove
			the registration resource for the purpose of resource recovery and
			garbage collection. If the Registration Resource is removed, the
			endpoint will need to re-register.
			The Registration Resource may also be used to inspect the
			registration resource using GET, update the registration link
			contents using PATCH, or cancel the registration using DELETE.
			These operations are described in this section.
			In accordance with Section 5.3.4, operations which would result in
			plural link references within the context of a registration resource
			SHOULD be rejected using the "Conflict" result code.
			5.4.1. Registration Update
	The update interface is used by an endpoint to refresh or update its		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		registration with an RD. To use the interface, the endpoint sends a
	POST request to the resource returned in the Location option in the		POST request to the registration resource returned in the Location
	response to the first registration.		header option in the response returned from the intial registration
			operation.
	An update MAY update the lifetime or context registration parameters		An update MAY update the lifetime or context registration parameters
	"lt", "con" as in Section 6.3 ) if they have changed since the last		"lt", "con" as in Section 5.3 ) if the previous settings are to be
	registration or update. Parameters that have not changed SHOULD NOT		retained. Parameters that are not being changed changed SHOULD NOT
	be included in an update. Adding parameters that have not changed		be included in an update. Adding parameters that have not changed
	increases the size of the message but does not have any other		increases the size of the message but does not have any other
	implications. Parameters MUST be included as query parameters in an		implications. Parameters MUST be included as query parameters in an
	update operation as in Section 6.3.		update operation as in Section 5.3.
	Upon receiving an update request, an RD MUST reset the timeout for		Upon receiving an update request, an RD MUST reset the timeout for
	that endpoint and update the scheme, IP address and port of the		that endpoint and update the scheme, IP address and port of the
	endpoint, using the source address of the update, or the context		endpoint, using the source address of the update, or the context
	("con") parameter if present. If the lifetime parameter "lt" is		("con") parameter if present. If the lifetime parameter "lt" is
	included in the received update request, the RD MUST update the		included in the received update request, the RD MUST update the
	lifetime of the registration and set the timeout equal to the new		lifetime of the registration and set the timeout equal to the new
	lifetime.		lifetime. If the lifetime parameter is not included in the
			registration update, the most recent setting is re-used for the next
			registration time-out period.
	An update MAY optionally add or replace links for the endpoint by		An update MAY optionally add or replace links for the endpoint by
	including those links in the payload of the update as a CoRE Link		including those links in the payload of the update as a CoRE Link
	Format document. A link is replaced only if both the target URI and		Format document. A link is replaced only if all of the target URI
	relation type match.		and relation type (if present) and anchor value (if present) match.
			If the link payload is included, it SHOULD be checked for reference
			plurality as described in Section 5.3.4 and rejected with a
			"Conflict" result if there are plural link references detected.
	In addition to the use of POST, as described in this section, there		In addition to the use of POST, as described in this section, there
	is an alternate way to add, replace, and delete links using PATCH as		is an alternate way to add, replace, and delete links using PATCH as
	described in Section 6.7.		described in Section 5.4.4.
	The update registration request interface is specified as follows:		The update registration request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	Method: POST		Method: POST
	URI Template: /{+location}{?lt,con}		URI Template: /{+location}{?lt,con}
	URI Template Variables:		URI Template Variables:
	location := This is the Location path returned by the RD as a		location := This is the Location path returned by the RD as a
	result of a successful earlier registration.		result of a successful earlier registration.
	lt := Lifetime (optional). Lifetime of the registration in		lt := Lifetime (optional). Lifetime of the registration in
	seconds. Range of 60-4294967295. If no lifetime is included,		seconds. Range of 60-4294967295. If no lifetime is included,
	a default value of 86400 (24 hours) SHOULD be assumed.		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 sets the scheme,		con := Context (optional). This parameter sets the scheme,
	address and port at which this server is available in the form		address and port at which this server is available in the form
	scheme://host:port. Optional. In the absence of this		scheme://host:port/path. In the absence of this parameter the
	parameter the scheme of the protocol, source IP address and		scheme of the protocol, source address and source port of the
	source port used to register are assumed. This parameter is		register request are assumed. This parameter is mandatory when
	compulsory when the directory is filled by a third party such		the directory is filled by a third party such as an
	as a commissioning tool.		commissioning tool. When con is used, scheme and host are
			mandatory and port and path parameters are optional.
	Content-Format: application/link-format (mandatory)		Content-Format: application/link-format (mandatory)
	Content-Format: application/link-format+json (optional)		Content-Format: application/link-format+json (optional)
	Content-Format: application/link-format+cbor (optional)		Content-Format: application/link-format+cbor (optional)
	The following response codes are defined for this interface:		The following response codes are defined for this interface:
	Success: 2.04 "Changed" or 204 "No Content" if the update was		Success: 2.04 "Changed" or 204 "No Content" if the update was
	successfully processed.		successfully processed.
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
	Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not		Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not
	exist (e.g. may have expired).		exist (e.g. may have expired).
			Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the
			registration content with links resulting in plurality of
			references; see Section 5.3.4.
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	HTTP support: YES		HTTP support: YES
	The following example shows an endpoint updating its registration at		The following example shows an endpoint updating its registration at
	an RD using this interface with the example location value: /rd/4521.		an RD using this interface with the example location value: /rd/4521.
	Req: POST /rd/4521		Req: POST /rd/4521
	Res: 2.04 Changed		Res: 2.04 Changed
	The following example shows an endpoint updating its registration		The following example shows an endpoint updating its registration
	with a new lifetime and context, changing an existing link, and		with a new lifetime and context, changing an existing link, and
	adding a new link using this interface with the example location		adding a new link using this interface with the example location
	skipping to change at page 20, line 4 ¶		skipping to change at page 21, line 22 ¶
	with a new lifetime and context, changing an existing link, and		with a new lifetime and context, changing an existing link, and
	adding a new link using this interface with the example location		adding a new link using this interface with the example location
	value /rd/4521. With the initial registration the client set the		value /rd/4521. With the initial registration the client set the
	following values:		following values:
	o lifetime (lt)=500		o lifetime (lt)=500
	o context (con)=coap://local-proxy-old.example.com:5683		o context (con)=coap://local-proxy-old.example.com:5683
	o resource= </sensors/temp>;ct=41;rt="foobar";if="sensor"		o resource= </sensors/temp>;ct=41;rt="foobar";if="sensor"
	Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683"		Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683"
	Content-Format: 40		Content-Format: 40
	Payload:		Payload:
	</sensors/temp>;ct=41;rt="temperature-f";if="sensor",		</sensors/temp>;ct=41;rt="temperature-f";if="sensor",
	</sensors/door>;ct=41;rt="door";if="sensor"		</sensors/door>;ct=41;rt="door";if="sensor"
	Res: 2.04 Changed		Res: 2.04 Changed
	6.5. Registration Removal		5.4.2. Registration Removal
	Although RD entries have soft state and will eventually timeout after		Although RD entries have soft state and will eventually timeout after
	their lifetime, an endpoint SHOULD explicitly remove its entry from		their lifetime, an endpoint SHOULD explicitly remove its entry from
	the RD if it knows it will no longer be available (for example on		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		shut-down). This is accomplished using a removal interface on the RD
	by performing a DELETE on the endpoint resource.		by performing a DELETE on the endpoint resource.
	The removal request interface is specified as follows:		The removal request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	skipping to change at page 21, line 9 ¶		skipping to change at page 22, line 27 ¶
	HTTP support: YES		HTTP support: YES
	The following examples shows successful removal of the endpoint from		The following examples shows successful removal of the endpoint from
	the RD with example location value /rd/4521.		the RD with example location value /rd/4521.
	Req: DELETE /rd/4521		Req: DELETE /rd/4521
	Res: 2.02 Deleted		Res: 2.02 Deleted
	6.6. Read Endpoint Links		5.4.3. Read Endpoint Links
	Some endpoints may wish to manage their links as a collection, and		Some endpoints may wish to manage their links as a collection, and
	may need to read the current set of links in order to determine link		may need to read the current set of links stored in the registration
	maintenance operations.		resource, in order to determine link maintenance operations.
	One or more links MAY be selected by using query filtering as		One or more links MAY be selected by using query filtering as
	specified in [RFC6690] Section 4.1		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:		The read request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	Method: GET		Method: GET
	URI Template: /{+location}{?href,rel,rt,if,ct}		URI Template: /{+location}{?href,rel,rt,if,ct}
	URI Template Variables:		URI Template Variables:
	skipping to change at page 22, line 14 ¶		skipping to change at page 23, line 37 ¶
	The following examples show successful read of the endpoint links		The following examples show successful read of the endpoint links
	from the RD, with example location value /rd/4521.		from the RD, with example location value /rd/4521.
	Req: GET /rd/4521		Req: GET /rd/4521
	Res: 2.01 Content		Res: 2.01 Content
	Payload:		Payload:
	</sensors/temp>;ct=41;rt="temperature-c";if="sensor",		</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
	</sensors/light>;ct=41;rt="light-lux";if="sensor"		</sensors/light>;ct=41;rt="light-lux";if="sensor"
	6.7. Update Endpoint Links		5.4.4. Update Endpoint Links
	[This section will be removed before or as a result of a working-
	group last-call if the PATCH methods do not achieve the same level of
	consensus as the present document.]
	A PATCH update adds, removes or changes links for the endpoint by		A PATCH update adds, removes or changes links for the endpoint by
	including link update information in the payload of the update as a		including link update information in the payload of the update as a
	merge-patch+json format [RFC7396] document.		merge-patch+json format [RFC7396] document.
			Other PATCH document formats may be used as appropriate for patching
			the array of objects format of a Registration Resource. In
			particular, a select-merge patch document format could combine the
			function of link selection query and link attribute replacement
			values.
	One or more links are selected for update by using query filtering as		One or more links are selected for update by using query filtering as
	specified in [RFC6690] Section 4.1		specified in [RFC6690] Section 4.1
	The query filter selects the links to be modified or deleted, by		The query filter selects the links to be modified or deleted, by
	matching the query parameter values to the values of the link		matching the query parameter values to the values of the link
	attributes.		attributes.
	When the query parameters are not present in the request, the payload		When the query parameters are not present in the request, the payload
	specifies links to be added to the target document. When the query		specifies links to be added to the target document. When the query
	parameters are present, the attribute names and values in the query		parameters are present, the attribute names and values in the query
	parameters select one or more links on which to apply the PATCH		parameters select one or more links on which to apply the PATCH
	operation.		operation.
	skipping to change at page 22, line 37 ¶		skipping to change at page 24, line 14 ¶
	The query filter selects the links to be modified or deleted, by		The query filter selects the links to be modified or deleted, by
	matching the query parameter values to the values of the link		matching the query parameter values to the values of the link
	attributes.		attributes.
	When the query parameters are not present in the request, the payload		When the query parameters are not present in the request, the payload
	specifies links to be added to the target document. When the query		specifies links to be added to the target document. When the query
	parameters are present, the attribute names and values in the query		parameters are present, the attribute names and values in the query
	parameters select one or more links on which to apply the PATCH		parameters select one or more links on which to apply the PATCH
	operation.		operation.
			If no links are selected by the query parameters, the PATCH operation
			SHOULD NOT update the state of any resource, and SHOULD return a
			reply of "Changed".
	If an attribute name specified in the PATCH document exists in any		If an attribute name specified in the PATCH document exists in any
	the set of selected links, all occurrences of the attribute value in		the set of selected links, all occurrences of the attribute value in
	the target document MUST be updated using the value from the PATCH		the target document MUST be updated using the value from the PATCH
	payload. If the attribute name is not present in any selected links,		payload. If the attribute name is not present in any selected links,
	the attribute MUST be added to the links.		the attribute MUST be added to the links.
			If the PATCH payload contains plural link references, or processing
			the PATCH payload would result in plural link references, the request
			SHOULD be rejected with a "Conflict" result.
			If the PATCH payload results in the modification of link target,
			context, or relation values, that is "href", "rel", or "anchor", the
			request SHOULD be rejected with a "Conflict" result code.
	The update request interface is specified as follows:		The update request interface is specified as follows:
	Interaction: EP -> RD		Interaction: EP -> RD
	Method: PATCH		Method: PATCH
	URI Template: /{+location}{?href,rel,rt,if,ct}		URI Template: /{+location}{?href,rel,rt,if,ct}
	URI Template Variables:		URI Template Variables:
	skipping to change at page 23, line 26 ¶		skipping to change at page 25, line 15 ¶
	Success: 2.04 "Changed" 0r 204 "No Content" in the update was		Success: 2.04 "Changed" 0r 204 "No Content" in the update was
	successfully processed.		successfully processed.
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
	Failure: 4.04 "Not Found" or 404 "Not Found". Registration resource		Failure: 4.04 "Not Found" or 404 "Not Found". Registration resource
	does not exist (e.g. may have expired).		does not exist (e.g. may have expired).
			Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the
			registration content with links resulting in plurality of
			references; see Section 5.3.4.
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	HTTP support: YES		HTTP support: YES
	The following examples show an endpoint adding </sensors/humid>,		The following examples show an endpoint adding </sensors/humid>,
	modifying </sensors/temp>, and removing </sensors/light> links in RD		modifying </sensors/temp>, and removing </sensors/light> links in RD
	using the Update Endpoint Links function with the example location		using the Update Endpoint Links function with the example location
	value /rd/4521.		value /rd/4521.
			The Registration Resource initial state is:
			Req: GET /rd/4521
			Res: 2.01 Content
			Payload:
			</sensors/temp>;ct=41;rt="temperature",
			</sensors/light>;ct=41;rt="light-lux";if="sensor"
	The following example shows an EP adding the link </sensors/		The following example shows an EP adding the link </sensors/
	humid>;ct=41;rt="humid-s";if="sensor" to the collection of links at		humid>;ct=41;rt="humid-s";if="sensor" to the collection of links at
	the location /rd/4521.		the location /rd/4521.
	Req: PATCH /rd/4521		Req: PATCH /rd/4521
	Payload:		Payload:
	[{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}]		[{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}]
	Content-Format:		Content-Format:
	application/merge-patch+json		application/merge-patch+json
	Res: 2.04 Changed		Res: 2.04 Changed
			Req: GET /rd/4521
			Res: 2.01 Content
			Payload:
			</sensors/temp>;ct=41;rt="temperature",
			</sensors/light>;ct=41;rt="light-lux";if="sensor",
			</sensors/humid>;ct=41;rt="humid-s";if="sensor"
	The following example shows an EP modifying all links at the example		The following example shows an EP modifying all links at the example
	location /rd/4521 which are identified by href="/sensors/temp", from		location /rd/4521 which are identified by href="/sensors/temp", from
	the initial link-value of </sensors/temp>;rt="temperature" to the new		the initial link-value of </sensors/temp>;rt="temperature" to the new
	link-value </sensors/temp>;rt="temperature-c";if="sensor" by changing		link-value </sensors/temp>;rt="temperature-c";if="sensor" by changing
	the value of the link attribute "rt" and adding the link attribute		the value of the link attribute "rt" and adding the link attribute
	if="sensor" using the PATCH operation with the supplied merge-		if="sensor" using the PATCH operation with the supplied merge-
	patch+json document payload.		patch+json document payload.
	Req: PATCH /rd/4521?href="/sensors/temp"		Req: PATCH /rd/4521?href=/sensors/temp
	Payload:		Payload:
	{"rt": "temperature-c", "if": "sensor"},		{"rt": "temperature-c", "if": "sensor"},
	Content-Format:		Content-Format:
	application/merge-patch+json		application/merge-patch+json
	Res: 2.04 Changed		Res: 2.04 Changed
			Req: GET /rd/4521
			Res: 2.01 Content
			Payload:
			</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
			</sensors/light>;ct=41;rt="light-lux";if="sensor",
			</sensors/humid>;ct=41;rt="humid-s";if="sensor"
	This example shows an EP removing all links at the example location		This example shows an EP removing all links at the example location
	/rd/4521 which are identified by href="/sensors/light".		/rd/4521 which are identified by href="/sensors/light".
	Req: PATCH /rd/4521?href="/sensors/light"		Req: PATCH /rd/4521?href=/sensors/light
	Payload:		Payload:
	{null}		{}
	Content-Format:		Content-Format:
	application/merge-patch+json		application/merge-patch+json
	Res: 2.04 Changed		Res: 2.04 Changed
			Req: GET /rd/4521
	7. Group Function Set		Res: 2.01 Content
			Payload:
			</sensors/temp>;ct=41;rt="temperature-c";if="sensor",
			</sensors/humid>;ct=41;rt="humid-s";if="sensor"
	This section defines a function set for the creation of groups of		6. RD Groups
	endpoints for the purpose of managing and looking up endpoints for
	group operations. The group function set is similar to the resource		This section defines the REST API for the creation, management, and
	directory function set, in that a group may be created or removed.		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		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		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		to make use of multicast requests with CoAP, a group MAY have a
	multicast address associated with it.		multicast address associated with it.
	7.1. Register a Group		6.1. Register a Group
	In order to create a group, a commissioning tool (CT) used to		In order to create a group, a commissioning tool (CT) used to
	configure groups, makes a request to the RD indicating the name of		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 domain the group
	belongs to, and optionally the multicast address of the group. The		belongs to, and optionally the multicast address of the group. The
	registration message includes the list of endpoints that belong to		registration message includes the list of endpoints that belong to
	that group.		that group.
	All the endpoints in the group MUST be registered with the RD before		All the endpoints in the group MUST be registered with the RD before
	registering a group. If an endpoint is not yet registered to the RD		registering a group. If an endpoint is not yet registered to the RD
	skipping to change at page 25, line 25 ¶		skipping to change at page 28, line 5 ¶
	The registration request interface is specified as follows:		The registration request interface is specified as follows:
	Interaction: CT -> RD		Interaction: CT -> RD
	Method: POST		Method: POST
	URI Template: /{+rd-group}{?gp,d,con}		URI Template: /{+rd-group}{?gp,d,con}
	URI Template Variables:		URI Template Variables:
	rd-group := RD Group Function Set path (mandatory). This is the		rd-group := RD Group Base URI path (mandatory). This is the path
	path of the RD Group Function Set. The value "rd-group" is		of the RD Group REST API. The value "rd-group" is recommended
	recommended for this variable.		for this variable.
	gp := Group Name (mandatory). The name of the group to be		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 domain. The maximum
	length of this parameter is 63 bytes.		length of this parameter is 63 bytes.
	d := Domain (optional). The domain to which this group belongs.		d := Domain (optional). The domain to which this group belongs.
	The maximum length of this parameter is 63 bytes. Optional.		The maximum length of this parameter is 63 bytes. Optional.
	When this parameter is elided, the RD MAY associate the		When this parameter is elided, the RD MAY associate the
	endpoint with a configured default domain. The domain value is		endpoint with a configured default domain.
	needed to export the endpoint to DNS-SD (see Section 10)
	con := Context (optional). This parameter is used to set the IP		con := Context (optional). This parameter sets the scheme,
	multicast address at which this server is available in the form		address and port at which this server is available in the form
	scheme://multicast-address:port. Optional. In the absence of		scheme://host:port/path. In the absence of this parameter the
	this parameter no multicast address is configured. This		scheme of the protocol, source address and source port of the
	parameter is compulsory when the directory is filled by a		register request are assumed. This parameter is mandatory when
	commissioning tool.		the directory is filled by a third party such as an
			commissioning tool. When con is used, scheme and host are
			mandatory and port and path parameters are optional.
	Content-Format: application/link-format		Content-Format: application/link-format
	Content-Format: application/link-format+json		Content-Format: application/link-format+json
	Content-Format: application/link-format+cbor		Content-Format: application/link-format+cbor
	The following response codes are defined for this interface:		The following response codes are defined for this interface:
	Success: 2.01 "Created" or 201 "Created". The Location header MUST		Success: 2.01 "Created" or 201 "Created". The Location header
	be included with the new group entry. This Location MUST be a		option MUST be returned in response to a successful group CREATE
	stable identifier generated by the RD as it is used for delete		operation. This Location MUST be a stable identifier generated by
	operations on this registration.		the RD as it is used for delete operations of the group
			registration resource.
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
	Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is not		Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is not
	registered in the RD (e.g. may have expired).		registered in the RD (e.g. may have expired).
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	skipping to change at page 26, line 34 ¶		skipping to change at page 29, line 17 ¶
	Req: POST coap://rd.example.com/rd-group?gp=lights		Req: POST coap://rd.example.com/rd-group?gp=lights
	Content-Format: 40		Content-Format: 40
	Payload:		Payload:
	<>;ep="node1",		<>;ep="node1",
	<>;ep="node2"		<>;ep="node2"
	Res: 2.01 Created		Res: 2.01 Created
	Location: /rd-group/12		Location: /rd-group/12
	Req: POST /rd-group?gp=lights HTTP/1.1		6.2. Group Removal
	Host: example.com
	Content-Type: application/link-format
	Payload:
	<>;ep="node1",
	<>;ep="node2"
	Res: 201 Created
	Location: /rd-group/12
	7.2. Group Removal
	A group can be removed simply by sending a removal message to the		A group can be removed simply by sending a removal message to the
	location returned when registering the group. Removing a group MUST		location of the group registration resource which was returned when
	NOT remove the endpoints of the group from the RD.		intially registering the group. Removing a group MUST NOT remove the
			endpoints of the group from the RD.
	The removal request interface is specified as follows:		The removal request interface is specified as follows:
	Interaction: CT -> RD		Interaction: CT -> RD
	Method: DELETE		Method: DELETE
	URI Template: /{+location}		URI Template: /{+location}
	URI Template Variables:		URI Template Variables:
	location := This is the Location path returned by the RD as a		location := This is the Location path returned by the RD as a
	result of a successful group registration.		result of a successful group registration.
	The following responses codes are defined for this interface:		The following responses codes are defined for this interface:
	skipping to change at page 27, line 26 ¶		skipping to change at page 30, line 4 ¶
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
	Failure: 4.04 "Not Found" or 404 "Not Found". Group does not exist.		Failure: 4.04 "Not Found" or 404 "Not Found". Group does not exist.
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	HTTP support: YES		HTTP support: YES
	The following examples shows successful removal of the group from the		The following examples shows successful removal of the group from the
	RD with the example location value /rd-group/12.		RD with the example location value /rd-group/12.
	Req: DELETE /rd-group/12		Req: DELETE /rd-group/12
	Res: 2.02 Deleted		Res: 2.02 Deleted
	8. RD Lookup Function Set		7. RD Lookup
	In order for an RD to be used for discovering resources registered		In order for an RD to be used for discovering resources registered
	with it, a lookup interface can be provided using this function set.		with it, an optional lookup interface may be provided. This lookup
	This lookup interface is defined as a default, and it is assumed that		interface is defined as a default, and it is assumed that RDs may
	RDs may also support lookups to return resource descriptions in		also support lookups to return resource descriptions in alternative
	alternative formats (e.g. Atom or HTML Link) or using more advanced		formats (e.g. Atom or HTML Link) or using more advanced interfaces
	interfaces (e.g. supporting context or semantic based lookup).		(e.g. supporting context or semantic based lookup).
	This function set allows lookups for domains, groups, endpoints and		RD Lookup allows lookups for domains, groups, endpoints and resources
	resources using attributes defined in the RD Function Set and for use		using attributes defined in this document and for use with the CoRE
	with the CoRE Link Format. The result of a lookup request is the		Link Format. The result of a lookup request is the list of links (if
	list of links (if any) corresponding to the type of lookup. Thus, a		any) corresponding to the type of lookup. Thus, a domain lookup MUST
	domain lookup MUST return a list of domains, a group lookup MUST		return a list of domains, a group lookup MUST return a list of
	return a list of groups, an endpoint lookup MUST return a list of		groups, an endpoint lookup MUST return a list of endpoints and a
	endpoints and a resource lookup MUST return a list of links to		resource lookup MUST return a list of links to resources.
	resources.
			RD Lookup does not expose registration resources directly, but
			returns link content from registration resource entries which satisfy
			RD Lookup queries.
			The lookup type is selected by a URI endpoint, which is indicated by
			a Resource Type as per Table 1 below:
			+-------------+--------------------+-----------+
			| Lookup Type | Resource Type | Mandatory |
			+-------------+--------------------+-----------+
			| Resource | core.rd-lookup-res | Mandatory |
			| Endpoint | core.rd-lookup-ep | Mandatory |
			| Domain | core.rd-lookup-d | Optional |
			| Group | core.rd-lookup-gp | Optional |
			+-------------+--------------------+-----------+
			Table 1: Lookup Types
	Each endpoint and resource lookup result returns respectively the		Each endpoint and resource lookup result returns respectively the
	scheme (IP address and port) followed by the path part of the URI of		scheme (IP address and port) followed by the path part of the URI of
	every endpoint and resource inside angle brackets ("<>") and followed		every endpoint and resource inside angle brackets ("<>") and followed
	by the other parameters.		by the other parameters.
	The target of these links SHOULD be the actual location of the		The target of these links SHOULD be the actual location of the
	domain, endpoint or resource, but MAY be an intermediate proxy e.g.		domain, endpoint or resource, but MAY be an intermediate proxy e.g.
	in the case of an HTTP lookup interface for CoAP endpoints.		in the case of an HTTP lookup interface for CoAP endpoints.
	skipping to change at page 28, line 42 ¶		skipping to change at page 31, line 37 ¶
	zero and page zero. Thus, specifying count of 10 and page of 0 will		zero and page zero. Thus, specifying count of 10 and page of 0 will
	return the first 10 links in the result set (links 0-9). Count = 10		return the first 10 links in the result set (links 0-9). Count = 10
	and page = 1 will return the next 'page' containing links 10-19, and		and page = 1 will return the next 'page' containing links 10-19, and
	so on.		so on.
	Multiple query parameters MAY be included in a lookup, all included		Multiple query parameters MAY be included in a lookup, all included
	parameters MUST match for a resource to be returned. The		parameters MUST match for a resource to be returned. The
	character'*' MAY be included at the end of a parameter value as a		character'*' MAY be included at the end of a parameter value as a
	wildcard operator.		wildcard operator.
	The rd-lookup interface MAY use any set of query parameters to match		RD Lookup requests MAY use any set of query parameters to match the
	the registered attributes and relations. In addition, this interface		registered attributes and relations. In addition, this interface MAY
	MAY be used with queries that specify domains, endpoints, and groups.		be used with queries that specify domains, endpoints, and groups.
	For example, a domain lookup filtering on groups would return a list		For example, a domain lookup filtering on groups would return a list
	of domains that contain the specified groups. An endpoint lookup		of domains that contain the specified groups. An endpoint lookup
	filtering on groups would return a list of endpoints that are in the		filtering on groups would return a list of endpoints that are in the
	specified groups.		specified groups.
	The lookup interface is specified as follows:		The lookup interface is specified as follows:
	Interaction: Client -> RD		Interaction: Client -> RD
	Method: GET		Method: GET
	URI Template: /{+rd-lookup-base}/{lookup-		URI Template: /{+rd-lookup-base}/{lookup-
	type}{?d,ep,gp,et,rt,page,count,resource-param}		type}{?d,res,ep,gp,et,rt,page,count,resource-param}
	URI Template Variables:		URI Template Variables:
	rd-lookup-base := RD Lookup Function Set path (mandatory). This		rd-lookup-base := RD Lookup Base URI path (mandatory). This is
	is the path of the RD Lookup Function Set. The recommended		the base path for RD Lookup requests. The recommended value
	value for this variable is: "rd-lookup".		for this variable is: "rd-lookup".
	lookup-type := ("d", "ep", "res", "gp") (mandatory) This variable		lookup-type := ("ep", "res") (mandatory), ("d","gp") (optional)
	is used to select the kind of lookup to perform (domain,		This variable is used to select the type of lookup to perform
	endpoint, resource, or group).		(endpoint, resource, domain, or group). The values are
			recommended defaults and MAY use other values as needed. The
			supported lookup-types SHOULD be listed in .well-known/core
			using the specified resource types.
	ep := Endpoint name (optional). Used for endpoint, group and		ep := Endpoint name (optional). Used for endpoint, group and
	resource lookups.		resource lookups.
	d := Domain (optional). Used for domain, group, endpoint and		d := Domain (optional). Used for domain, group, endpoint and
	resource lookups.		resource lookups.
	res := resource (optional). Used for domain, group, endpoint and		res := resource (optional). Used for domain, group, endpoint and
	resource lookups.		resource lookups.
	skipping to change at page 30, line 6 ¶		skipping to change at page 32, line 50 ¶
	all matching links in the result set. Link numbering starts		all matching links in the result set. Link numbering starts
	with zero.		with zero.
	rt := Resource type (optional). Used for group, endpoint and		rt := Resource type (optional). Used for group, endpoint and
	resource lookups.		resource lookups.
	et := Endpoint type (optional). Used for group, endpoint and		et := Endpoint type (optional). Used for group, endpoint and
	resource lookups.		resource lookups.
	resource-param := Link attribute parameters (optional). Any link		resource-param := Link attribute parameters (optional). Any link
	attribute as defined in Section 4.1 of [RFC6690], used for		target attribute as defined in Section 4.1 of [RFC6690], used
	resource lookups.		for resource lookups.
	Content-Format: application/link-format (optional)		Content-Format: application/link-format (optional)
	Content-Format: application/link-format+json (optional)		Content-Format: application/link-format+json (optional)
	Content-Format: application/link-format+cbor (optional)		Content-Format: application/link-format+cbor (optional)
	The following responses codes are defined for this interface:		The following responses codes are defined for this interface:
	Success: 2.05 "Content" or 200 "OK" with an "application/link-		Success: 2.05 "Content" or 200 "OK" with an "application/link-
	skipping to change at page 30, line 34 ¶		skipping to change at page 33, line 30 ¶
	Failure: No error response to a multicast request.		Failure: No error response to a multicast request.
	Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed		Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed
	request.		request.
	Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".		Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable".
	Service could not perform the operation.		Service could not perform the operation.
	HTTP support: YES		HTTP support: YES
	The examples in this section assume a CoAP host with IP address		The examples in this section assume CoAP hosts with a default CoAP
	FDFD::123 and a default CoAP port 61616. HTTP hosts are possible and		port 61616. HTTP hosts are possible and do not change the nature of
	do not change the nature of the examples.\		the examples.
	The following example shows a client performing a resource lookup		The following example shows a client performing a resource lookup
	with the example look-up location /rd-lookup/:		with the example look-up location /rd-lookup/:
	Req: GET /rd-lookup/res?rt=temperature		Req: GET /rd-lookup/res?rt=temperature
	Res: 2.05 Content		Res: 2.05 Content
	<coap://[FDFD::123]:61616/temp>;rt="temperature"		<coap://[FDFD::123]:61616/temp>;rt="temperature"
	The following example shows a client performing an endpoint type		The following example shows a client performing an endpoint type
	lookup:		lookup:
	Req: GET /rd-lookup/ep?et=power-node		Req: GET /rd-lookup/ep?et=power-node
	Res: 2.05 Content		Res: 2.05 Content
	<coap://[FDFD::123]:61616>;ep="node5",		<coap://[FDFD::127]:61616>;ep="node5",
	<coap://[FDFD::123]:61616>;ep="node7"		<coap://[FDFD::129]:61616>;ep="node7"
	The following example shows a client performing a domain lookup:		The following example shows a client performing a domain lookup:
	Req: GET /rd-lookup/d		Req: GET /rd-lookup/d
	Res: 2.05 Content		Res: 2.05 Content
	<>;d="domain1",		<>;d="domain1",
	<>;d="domain2"		<>;d="domain2"
	The following example shows a client performing a group lookup for		The following example shows a client performing a group lookup for
	skipping to change at page 31, line 35 ¶		skipping to change at page 34, line 27 ¶
	<>;gp="lights1";d="example.com"		<>;gp="lights1";d="example.com"
	<>;gp="lights2";d="ecample.com"		<>;gp="lights2";d="ecample.com"
	The following example shows a client performing a lookup for all		The following example shows a client performing a lookup for all
	endpoints in a particular group:		endpoints in a particular group:
	Req: GET /rd-lookup/ep?gp=lights1		Req: GET /rd-lookup/ep?gp=lights1
	Res: 2.05 Content		Res: 2.05 Content
	<coap://[FDFD::123]:61616>;ep="node1",		<coap://[FDFD::123]:61616>;ep="node1",
	<coap://[FDFD::123]:61616>;ep="node2"		<coap://[FDFD::124]:61616>;ep="node2"
	The following example shows a client performing a lookup for all		The following example shows a client performing a lookup for all
	groups an endpoint belongs to:		groups an endpoint belongs to:
	Req: GET /rd-lookup/gp?ep=node1		Req: GET /rd-lookup/gp?ep=node1
	Res: 2.05 Content		Res: 2.05 Content
	<>;gp="lights1"		<>;gp="lights1"
	The following example shows a client performing a paginated lookup		The following example shows a client performing a paginated lookup
	skipping to change at page 32, line 22 ¶		skipping to change at page 35, line 22 ¶
	Req: GET /rd-lookup/res?page=1&count=5		Req: GET /rd-lookup/res?page=1&count=5
	Res: 2.05 Content		Res: 2.05 Content
	<coap://[FDFD::123]:61616/res/5>;rt=sensor;ct=60		<coap://[FDFD::123]:61616/res/5>;rt=sensor;ct=60
	<coap://[FDFD::123]:61616/res/6>;rt=sensor;ct=60		<coap://[FDFD::123]:61616/res/6>;rt=sensor;ct=60
	<coap://[FDFD::123]:61616/res/7>;rt=sensor;ct=60		<coap://[FDFD::123]:61616/res/7>;rt=sensor;ct=60
	<coap://[FDFD::123]:61616/res/8>;rt=sensor;ct=60		<coap://[FDFD::123]:61616/res/8>;rt=sensor;ct=60
	<coap://[FDFD::123]:61616/res/9>;rt=sensor;ct=60		<coap://[FDFD::123]:61616/res/9>;rt=sensor;ct=60
	9. New Link-Format Attributes		8. Security Considerations
	When using the CoRE Link Format to describe resources being
	discovered by or posted to a resource directory service, additional
	information about those resources is useful. This specification
	defines the following new attributes for use in the CoRE Link Format
	[RFC6690]:
	link-extension = ( "ins" "=" (ptoken | quoted-string) )
	; The token or string is max 63 bytes
	link-extension = ( "exp" )
	9.1. Resource Instance attribute 'ins'
	The Resource Instance "ins" attribute is an identifier for this
	resource, which makes it possible to distinguish it from other
	similar resources. This attribute is similar in use to the
	<Instance> portion of a DNS-SD record (see Section 10.1, and SHOULD
	be unique across resources with the same Resource Type attribute in
	the domain it is used. A Resource Instance might be a descriptive
	string like "Ceiling Light, Room 3", a short ID like "AF39" or a
	unique UUID or iNumber. This attribute is used by a Resource
	Directory to distinguish between multiple instances of the same
	resource type within the directory.
	This attribute MUST be no more than 63 bytes in length. The resource
	identifier attribute MUST NOT appear more than once in a link
	description. This attribute MAY be used as a query parameter in the
	RD Lookup Function Set defined in Section 7.
	9.2. Export attribute 'exp'
	The Export "exp" attribute is used as a flag to indicate that a link
	description MAY be exported by a resource directory to external
	directories.
	The CoRE Link Format is used for many purposes between CoAP
	endpoints. Some are useful mainly locally, for example checking the
	observability of a resource before accessing it, determining the size
	of a resource, or traversing dynamic resource structures. However,
	other links are very useful to be exported to other directories, for
	example the entry point resource to a functional service. This
	attribute MAY be used as a query parameter in the RD Lookup Function
	Set defined in Section 7.
	10. DNS-SD Mapping
	CoRE Resource Discovery is intended to support fine-grained discovery
	of hosted resources, their attributes, and possibly other resource
	relations [RFC6690]. In contrast, service discovery generally refers
	to a coarse-grained resolution of an endpoint's IP address, port
	number, and protocol.
	Resource and service discovery are complementary in the case of large
	networks, where the latter can facilitate scaling. This document
	defines a mapping between CoRE Link Format attributes and DNS-Based
	Service Discovery [RFC6763] fields that permits discovery of CoAP
	services by either method.
	10.1. DNS-based Service discovery
	DNS-Based Service Discovery (DNS-SD) defines a conventional method of
	configuring DNS PTR, SRV, and TXT resource records to facilitate
	discovery of services (such as CoAP servers in a subdomain) using the
	existing DNS infrastructure. This section gives a brief overview of
	DNS-SD; see [RFC6763] for a detailed specification.
	DNS-SD service names are limited to 255 octets and are of the form:
	Service Name = <Instance>.<ServiceType>.<Domain>.
	The service name is the label of SRV/TXT resource records. The SRV
	RR specifies the host and the port of the endpoint. The TXT RR
	provides additional information in the form of key/value pairs.
	The <Domain> part of the service name is identical to the global (DNS
	subdomain) part of the authority in URIs that identify servers or
	groups of servers.
	The <ServiceType> part is composed of at least two labels. The first
	label of the pair is the application protocol name [RFC6335] preceded
	by an underscore character. The second label indicates the transport
	and is always "_udp" for UDP-based CoAP services. In cases where
	narrowing the scope of the search may be useful, these labels may be
	optionally preceded by a subtype name followed by the "_sub" label.
	An example of this more specific <ServiceType> is
	"light._sub._dali._udp".
	A default <Instance> part of the service name may be set at the
	factory or during the commissioning process. It SHOULD uniquely
	identify an instance of <ServiceType> within a <Domain>. Taken
	together, these three elements comprise a unique name for an SRV/ TXT
	record pair within the DNS subdomain.
	The granularity of a service name MAY be that of a host or group, or
	it could represent a particular resource within a CoAP server. The
	SRV record contains the host name (AAAA record name) and port of the
	service while protocol is part of the service name. In the case
	where a service name identifies a particular resource, the path part
	of the URI must be carried in a corresponding TXT record.
	A DNS TXT record is in practice limited to a few hundred octets in
	length, which is indicated in the resource record header in the DNS
	response message. The data consists of one or more strings
	comprising a key=value pair. By convention, the first pair is
	txtver=<number> (to support different versions of a service
	description).
	10.2. mapping ins to <Instance>
	The Resource Instance "ins" attribute maps to the <Instance> part of
	a DNS-SD service name. It is stored directly in the DNS as a single
	DNS label of canonical precomposed UTF-8 [RFC3629] "Net-Unicode"
	(Unicode Normalization Form C) [RFC5198] text. However, to the
	extent that the "ins" attribute may be chosen to match the DNS host
	name of a service, it SHOULD use the syntax defined in Section 3.5 of
	[RFC1034] and Section 2.1 of [RFC1123].
	The <Instance> part of the name of a service being offered on the
	network SHOULD be configurable by the user setting up the service, so
	that he or she may give it an informative name. However, the device
	or service SHOULD NOT require the user to configure a name before it
	can be used. A sensible choice of default name can allow the device
	or service to be accessed in many cases without any manual
	configuration at all. The default name should be short and
	descriptive, and MAY include a collision-resistant substring such as
	the lower bits of the device's MAC address, serial number,
	fingerprint, or other identifier in an attempt to make the name
	relatively unique.
	DNS labels are currently limited to 63 octets in length and the
	entire service name may not exceed 255 octets.
	10.3. Mapping rt to <ServiceType>
	The resource type "rt" attribute is mapped into the <ServiceType>
	part of a DNS-SD service name and SHOULD conform to the reg-rel-type
	production of the Link Format defined in Section 2 of [RFC6690]. The
	"rt" attribute MUST be composed of at least a single Net-Unicode text
	string, without underscore '_' or period '.' and limited to 15 octets
	in length, which represents the application protocol name. This
	string is mapped to the DNS-SD <ServiceType> by prepending an
	underscore and appending a period followed by the "_udp" label. For
	example, rt="dali" is mapped into "_dali._udp".
	The application protocol name may be optionally followed by a period
	and a service subtype name consisting of a Net-Unicode text string,
	without underscore or period and limited to 63 octets. This string
	is mapped to the DNS-SD <ServiceType> by appending a period followed
	by the "_sub" label and then appending a period followed by the
	service type label pair derived as in the previous paragraph. For
	example, rt="dali.light" is mapped into "light._sub._dali._udp".
	The resulting string is used to form labels for DNS-SD records which
	are stored directly in the DNS.
	10.4. Domain mapping
	DNS domains may be derived from the "d" attribute. The domain
	attribute may be suffixed with the zone name of the authoritative DNS
	server to generate the domain name. The "ep" attribute is prefixed
	to the domain name to generate the FQDN to be stored into DNS with an
	AAAA RR.
	10.5. TXT Record key=value strings
	A number of [RFC6763] key/value pairs are derived from link-format
	information, to be exported in the DNS-SD as key=value strings in a
	TXT record ([RFC6763], Section 6.3).
	The resource <URI> is exported as key/value pair "path=<URI>".
	The Interface Description "if" attribute is exported as key/value
	pair "if=<Interface Description>".
	The DNS TXT record can be further populated by importing any other
	resource description attributes as they share the same key=value
	format specified in Section 6 of [RFC6763].
	10.6. Importing resource links into DNS-SD
	Assuming the ability to query a Resource Directory or multicast a GET
	(?exp) over the local link, CoAP resource discovery may be used to
	populate the DNS-SD database in an automated fashion. CoAP resource
	descriptions (links) can be exported to DNS-SD for exposure to
	service discovery by using the Resource Instance attribute as the
	basis for a unique service name, composed with the Resource Type as
	the <ServiceType>, and registered in the correct <Domain>. The agent
	responsible for exporting records to the DNS zone file SHOULD be
	authenticated to the DNS server. The following example, using the
	example lookup location /rd-lookup, shows an agent discovering a
	resource to be exported:
	Req: GET /rd-lookup/res?exp
	Res: 2.05 Content
	<coap://[FDFD::1234]:5683/light/1>;
	exp;rt="dali.light";ins="Spot";
	d="office";ep="node1"
	The agent subsequently registers the following DNS-SD RRs, assuming a
	zone name "example.com" prefixed with "office":
	node1.office.example.com. IN AAAA FDFD::1234
	_dali._udp.office.example.com IN PTR
	Spot._dali._udp.office.example.com
	light._sub._dali._udp.example.com IN PTR
	Spot._dali._udp.office.example.com
	Spot._dali._udp.office.example.com IN SRV 0 0 5683
	node1.office.example.com.
	Spot._dali._udp.office.example.com IN TXT
	txtver=1;path=/light/1
	In the above figure the Service Name is chosen as
	Spot._dali._udp.office.example.com without the light._sub service
	prefix. An alternative Service Name would be:
	Spot.light._sub._dali._udp.office.example.com.
	11. Security Considerations
	The security considerations as described in Section 7 of [RFC5988]		The security considerations as described in Section 7 of [RFC5988]
	and Section 6 of [RFC6690] apply. The "/.well-known/core" resource		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		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		described in [RFC7252]. DTLS or TLS based security SHOULD be used on
	all resource directory interfaces defined in this document.		all resource directory interfaces defined in this document.
	11.1. Endpoint Identification and Authentication		8.1. Endpoint Identification and Authentication
	An Endpoint is determined to be unique by an RD by the Endpoint		An Endpoint is determined to be unique by an RD by the Endpoint
	identifier parameter included during Registration, and any associated		identifier parameter included during Registration, and any associated
	TLS or DTLS security bindings. An Endpoint MUST NOT be identified by		TLS or DTLS security bindings. An Endpoint MUST NOT be identified by
	its protocol, port or IP address as these may change over the		its protocol, port or IP address as these may change over the
	lifetime of an Endpoint.		lifetime of an Endpoint.
	Every operation performed by an Endpoint or Client on a resource		Every operation performed by an Endpoint or Client on a resource
	directory SHOULD be mutually authenticated using Pre-Shared Key, Raw		directory SHOULD be mutually authenticated using Pre-Shared Key, Raw
	Public Key or Certificate based security. Endpoints using a		Public Key or Certificate based security. Endpoints using a
	Certificate MUST include the Endpoint identifier as the Subject of		Certificate MUST include the Endpoint identifier as the Subject of
	the Certificate, and this identifier MUST be checked by a resource		the Certificate, and this identifier MUST be checked by a resource
	directory to match the Endpoint identifier included in the		directory to match the Endpoint identifier included in the
	Registration message.		Registration message.
	11.2. Access Control		8.2. Access Control
	Access control SHOULD be performed separately for the RD Function Set		Access control SHOULD be performed separately for the RD
	and the RD Lookup Function Set, as different endpoints may be		registration, Lookup, and group API base paths, as different
	authorized to register with an RD from those authorized to lookup		endpoints may be authorized to register with an RD from those
	endpoints from the RD. Such access control SHOULD be performed in as		authorized to lookup endpoints from the RD. Such access control
	fine-grained a level as possible. For example access control for		SHOULD be performed in as fine-grained a level as possible. For
	lookups could be performed either at the domain, endpoint or resource		example access control for lookups could be performed either at the
	level.		domain, endpoint or resource level.
	11.3. Denial of Service Attacks		8.3. Denial of Service Attacks
	Services that run over UDP unprotected are vulnerable to unknowingly		Services that run over UDP unprotected are vulnerable to unknowingly
	become part of a DDoS attack as UDP does not require return		become part of a DDoS attack as UDP does not require return
	routability check. Therefore, an attacker can easily spoof the		routability check. Therefore, an attacker can easily spoof the
	source IP of the target entity and send requests to such a service		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		which would then respond to the target entity. This can be used for
	large-scale DDoS attacks on the target. Especially, if the service		large-scale DDoS attacks on the target. Especially, if the service
	returns a response that is order of magnitudes larger than the		returns a response that is order of magnitudes larger than the
	request, the situation becomes even worse as now the attack can be		request, the situation becomes even worse as now the attack can be
	amplified. DNS servers have been widely used for DDoS amplification		amplified. DNS servers have been widely used for DDoS amplification
	attacks. There is also a danger that NTP Servers could become		attacks. There is also a danger that NTP Servers could become
	implicated in denial-of-service (DoS) attacks since they run on		implicated in denial-of-service (DoS) attacks since they run on
	unprotected UDP, there is no return routability check, and they can		unprotected UDP, there is no return routability check, and they can
	have a large amplification factor. The responses from the NTP server		have a large amplification factor. The responses from the NTP server
	were found to be 19 times larger than the request. A Resource		were found to be 19 times larger than the request. A Resource
	Directory (RD) which responds to wild-card lookups is potentially		Directory (RD) which responds to wild-card lookups is potentially
	vulnerable if run with CoAP over UDP. Since there is no return		vulnerable if run with CoAP over UDP. Since there is no return
	routability check and the responses can be significantly larger than		routability check and the responses can be significantly larger than
	requests, RDs can unknowingly become part of a DDoS amplification		requests, RDs can unknowingly become part of a DDoS amplification
	attack. Therefore, it is RECOMMENDED that implementations ensure		attack.
	return routability. This can be done, for example by responding to
	wild card lookups only over DTLS or TLS or TCP.
	12. IANA Considerations		9. IANA Considerations
	12.1. Resource Types		9.1. Resource Types
	"core.rd", "core.rd-group" and "core.rd-lookup" resource types need		"core.rd", "core.rd-group", "core.rd-lookup-ep", "core.rd-lookup-
			res", "core.rd-lookup-d", and "core.rd-lookup-gp" resource types need
	to be registered with the resource type registry defined by		to be registered with the resource type registry defined by
	[RFC6690].		[RFC6690].
	12.2. Link Extension		9.2. IPv6 ND Resource Directory Address Option
	The "exp" and "ins" attributes need to be registered when a future
	Web Linking link-extension registry is created (e.g. in RFC5988bis).
	12.3. IPv6 ND Resource Directory Address Option
	This document registers one new ND option type under the subregistry		This document registers one new ND option type under the subregistry
	"IPv6 Neighbor Discovery Option Formats":		"IPv6 Neighbor Discovery Option Formats":
	o Resource Directory address Option (38)		o Resource Directory address Option (38)
	12.4. RD Parameter Registry		9.3. RD Parameter Registry
	This specification defines a new sub-registry for registration and		This specification defines a new sub-registry for registration and
	lookup parameters called "RD Parameters" under "CoRE Parameters".		lookup parameters called "RD Parameters" under "CoRE Parameters".
	Although this specification defines a basic set of parameters, it is		Although this specification defines a basic set of parameters, it is
	expected that other standards that make use of this interface will		expected that other standards that make use of this interface will
	define new ones.		define new ones.
	Each entry in the registry must include the human readable name of		Each entry in the registry must include the human readable name of
	the parameter, the query parameter, validity requirements if any and		the parameter, the query parameter, validity requirements if any and
	a description. The query parameter MUST be a valid URI query key		a description. The query parameter MUST be a valid URI query key
	[RFC3986].		[RFC3986].
	Initial entries in this sub-registry are as follows:		Initial entries in this sub-registry are as follows:
	+-----------+-------+---------------+-------------------------------+		+----------+-------+---------------+--------------------------------+
	| Name | Query | Validity | Description |		| Name | Query | Validity | Description |
	+-----------+-------+---------------+-------------------------------+		+----------+-------+---------------+--------------------------------+
	| Endpoint | ep | | Name of the endpoint, max 63 |		| Endpoint | ep | | Name of the endpoint, max 63 |
	| Name | | | bytes |		| Name | | | bytes |
	| Lifetime | lt | 60-4294967295 | Lifetime of the registration |		| Lifetime | lt | 60-4294967295 | Lifetime of the registration |
	| | | | in seconds |		| | | | in seconds |
	| Domain | d | | Domain to which this endpoint |		| Domain | d | | Domain to which this endpoint |
	| | | | belongs |		| | | | belongs |
	| Endpoint | et | | Semantic name of the endpoint |		| Endpoint | et | | Semantic name of the endpoint |
	| Type | | | |		| Type | | | |
	| Context | con | URI | The scheme, address and port |		| Context | con | URI | The scheme, address and port |
	| | | | at which this server is |		| | | | at which this server is |
	| | | | available |		| | | | available |
	| Resource | res | | Name of the resource |		| Resource | res | | Name of the resource |
	| Name | | | |		| Name | | | |
	| Group | gp | | Name of a group in the RD |		| Group | gp | | Name of a group in the RD |
	| Name | | | |		| Name | | | |
	| Page | page | Integer | Used for pagination |		| Page | page | Integer | Used for pagination |
	| Count | count | Integer | Used for pagination |		| Count | count | Integer | Used for pagination |
	| Resource | ins | | Instance Identifier |		+----------+-------+---------------+--------------------------------+
	| Instance | | | |
	| Export | exp | | A link MAY be exported to |
	| | | | another Resource Directory |
	+-----------+-------+---------------+-------------------------------+
	Table 1: RD Parameters		Table 2: RD Parameters
	The IANA policy for future additions to the sub-registry is "Expert		The IANA policy for future additions to the sub-registry is "Expert
	Review" as described in [RFC5226].		Review" as described in [RFC5226].
	13. Examples		10. Examples
	13.1. Lighting Installation		Two examples are presented: a Lighting Installation example in
			Section 10.1 and a LWM2M example in Section 10.2.
			10.1. Lighting Installation
	This example shows a simplified lighting installation which makes use		This example shows a simplified lighting installation which makes use
	of the Resource Directory (RD) with a CoAP interface to facilitate		of the Resource Directory (RD) with a CoAP interface to facilitate
	the installation and start up of the application code in the lights		the installation and start up of the application code in the lights
	and sensors. In particular, the example leads to the definition of a		and sensors. In particular, the example leads to the definition of a
	group and the enabling of the corresponding multicast address. No		group and the enabling of the corresponding multicast address. No
	conclusions must be drawn on the realization of actual installation		conclusions must be drawn on the realization of actual installation
	or naming procedures, because the example only "emphasizes" some of		or naming procedures, because the example only "emphasizes" some of
	the issues that may influence the use of the RD and does not pretend		the issues that may influence the use of the RD and does not pretend
	to be normative. The example uses the recommended values for the		to be normative. The example uses the recommended values for the
	base resources: "/rd", "/rd-lookup", and "/rd-group".		base resources: "/rd", "/rd-lookup", and "/rd-group".
	13.1.1. Installation Characteristics		10.1.1. Installation Characteristics
	The example assumes that the installation is managed. That means		The example assumes that the installation is managed. That means
	that a Commissioning Tool (CT) is used to authorize the addition of		that a Commissioning Tool (CT) is used to authorize the addition of
	nodes, name them, and name their services. The CT can be connected		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		to the installation in many ways: the CT can be part of the
	installation network, connected by WiFi to the installation network,		installation network, connected by WiFi to the installation network,
	or connected via GPRS link, or other method.		or connected via GPRS link, or other method.
	It is assumed that there are two naming authorities for the		It is assumed that there are two naming authorities for the
	installation: (1) the network manager that is responsible for the		installation: (1) the network manager that is responsible for the
	skipping to change at page 40, line 39 ¶		skipping to change at page 38, line 45 ¶
	group of lamps consists of: middle and left lamps of luminary1 and		group of lamps consists of: middle and left lamps of luminary1 and
	right lamp of luminary2.		right lamp of luminary2.
	Before commissioning by the lighting manager, the network is		Before commissioning by the lighting manager, the network is
	installed and access to the interfaces is proven to work by the		installed and access to the interfaces is proven to work by the
	network manager.		network manager.
	At the moment of installation, the network under installation is not		At the moment of installation, the network under installation is not
	necessarily connected to the DNS infra structure. Therefore, SLAAC		necessarily connected to the DNS infra structure. Therefore, SLAAC
	IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in		IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in
	Table 2 below:		Table 3 below:
	+--------------------+--------------+		+--------------------+--------------+
	| Name | IPv6 address |		| Name | IPv6 address |
	+--------------------+--------------+		+--------------------+--------------+
	| luminary1 | FDFD::ABCD:1 |		| luminary1 | FDFD::ABCD:1 |
	| luminary2 | FDFD::ABCD:2 |		| luminary2 | FDFD::ABCD:2 |
	| Presence sensor | FDFD::ABCD:3 |		| Presence sensor | FDFD::ABCD:3 |
	| Resource directory | FDFD::ABCD:0 |		| Resource directory | FDFD::ABCD:0 |
	+--------------------+--------------+		+--------------------+--------------+
	Table 2: interface SLAAC addresses		Table 3: interface SLAAC addresses
	In Section 13.1.2 the use of resource directory during installation		In Section 10.1.2 the use of resource directory during installation
	is presented. In Section 13.1.3 the connection to DNS is discussed.		is presented.
	13.1.2. RD entries		10.1.2. RD entries
	It is assumed that access to the DNS infrastructure is not always		It is assumed that access to the DNS infrastructure is not always
	possible during installation. Therefore, the SLAAC addresses are		possible during installation. Therefore, the SLAAC addresses are
	used in this section.		used in this section.
	For discovery, the resource types (rt) of the devices are important.		For discovery, the resource types (rt) of the devices are important.
	The lamps in the luminaries have rt: light, and the presence sensor		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		has rt: p-sensor. The endpoints have names which are relevant to the
	light installation manager. In this case luminary1, luminary2, and		light installation manager. In this case luminary1, luminary2, and
	the presence sensor are located in room 2-4-015, where luminary1 is		the presence sensor are located in room 2-4-015, where luminary1 is
	located at the window and luminary2 and the presence sensor are		located at the window and luminary2 and the presence sensor are
	located at the door. The endpoint names reflect this physical		located at the door. The endpoint names reflect this physical
	location. The middle, left and right lamps are accessed via path		location. The middle, left and right lamps are accessed via path
	/light/middle, /light/left, and /light/right respectively. The		/light/middle, /light/left, and /light/right respectively. The
	identifiers relevant to the Resource Directory are shown in Table 3		identifiers relevant to the Resource Directory are shown in Table 4
	below:		below:
	+----------------+------------------+---------------+---------------+		+----------------+------------------+---------------+---------------+
	| Name | endpoint | resource path | resource type |		| Name | endpoint | resource path | resource type |
	+----------------+------------------+---------------+---------------+		+----------------+------------------+---------------+---------------+
	| luminary1 | lm_R2-4-015_wndw | /light/left | light |		| luminary1 | lm_R2-4-015_wndw | /light/left | light |
	| luminary1 | lm_R2-4-015_wndw | /light/middle | light |		| luminary1 | lm_R2-4-015_wndw | /light/middle | light |
	| luminary1 | lm_R2-4-015_wndw | /light/right | light |		| luminary1 | lm_R2-4-015_wndw | /light/right | light |
	| luminary2 | lm_R2-4-015_door | /light/left | light |		| luminary2 | lm_R2-4-015_door | /light/left | light |
	| luminary2 | lm_R2-4-015_door | /light/middle | light |		| luminary2 | lm_R2-4-015_door | /light/middle | light |
	| luminary2 | lm_R2-4-015_door | /light/right | light |		| luminary2 | lm_R2-4-015_door | /light/right | light |
	| Presence | ps_R2-4-015_door | /ps | p-sensor |		| Presence | ps_R2-4-015_door | /ps | p-sensor |
	| sensor | | | |		| sensor | | | |
	+----------------+------------------+---------------+---------------+		+----------------+------------------+---------------+---------------+
	Table 3: Resource Directory identifiers		Table 4: Resource Directory identifiers
	The CT inserts the endpoints of the luminaries and the sensor in the		The CT inserts the endpoints of the luminaries and the sensor in the
	RD using the Context parameter (con) to specify the interface		RD using the Context parameter (con) to specify the interface
	address:		address:
	Req: POST coap://[FDFD::ABCD:0]/rd		Req: POST coap://[FDFD::ABCD:0]/rd
	?ep=lm_R2-4-015_wndw&con=coap://[FDFD::ABCD:1]		?ep=lm_R2-4-015_wndw&con=coap://[FDFD::ABCD:1]
	Payload:		Payload:
	</light/left>;rt="light"; d="R2-4-015",		</light/left>;rt="light"; d="R2-4-015",
	</light/middle>;rt="light"; d="R2-4-015",		</light/middle>;rt="light"; d="R2-4-015",
	skipping to change at page 42, line 44 ¶		skipping to change at page 41, line 6 ¶
	because filtering on "ep" name is more awkward. The same domain name		because filtering on "ep" name is more awkward. The same domain name
	is communicated to the two luminaries and the presence sensor by the		is communicated to the two luminaries and the presence sensor by the
	CT.		CT.
	The group is specified in the RD. The Context parameter is set to		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		the site-local multicast address allocated to the group. In the POST
	in the example below, these two endpoints and the endpoint of the		in the example below, these two endpoints and the endpoint of the
	presence sensor are registered as members of the group.		presence sensor are registered as members of the group.
	Req: POST coap://[FDFD::ABCD:0]/rd-group		Req: POST coap://[FDFD::ABCD:0]/rd-group
	?gp=grp_R2-4-015;con="coap//[FF05::1]";exp;ins="grp1234"		?gp=grp_R2-4-015;con="coap//[FF05::1]"
	Payload:		Payload:
	<>ep=lm_R2-4-015_wndw,		<>ep=lm_R2-4-015_wndw,
	<>ep=lm_R2-4-015_door,		<>ep=lm_R2-4-015_door,
	<>ep=ps_R2-4-015_door		<>ep=ps_R2-4-015_door
	Res: 2.01 Created		Res: 2.01 Created
	Location: /rd-group/501		Location: /rd-group/501
	After the filling of the RD by the CT, the application in the		After the filling of the RD by the CT, the application in the
	luminaries can learn to which groups they belong, and enable their		luminaries can learn to which groups they belong, and enable their
	interface for the multicast address.		interface for the multicast address.
	The luminary, knowing its domain, queries the RD for the endpoint		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		with rt=light and d=R2-4-015. The RD returns all endpoints in the
	domain.		domain.
	Req: GET coap://[FDFD::ABCD:0]/rd-lookup/ep		Req: GET coap://[FDFD::ABCD:0]/rd-lookup/ep
	?d=R2-4-015;rt=light		?d=R2-4-015;rt=light
	skipping to change at page 44, line 5 ¶		skipping to change at page 42, line 16 ¶
	Content-Format: application/coap-group+json		Content-Format: application/coap-group+json
	{ "a": "[FF05::1]",		{ "a": "[FF05::1]",
	"n": "grp_R2-4-015"}		"n": "grp_R2-4-015"}
	Res: 2.01 Created		Res: 2.01 Created
	Location-Path: /coap-group/1		Location-Path: /coap-group/1
	Dependent on the situation, only the address, "a", or the name, "n",		Dependent on the situation, only the address, "a", or the name, "n",
	is specified in the coap-group resource.		is specified in the coap-group resource.
	13.1.3. DNS entries		10.2. OMA Lightweight M2M (LWM2M) Example
	It may be profitable to discover the light groups for applications,
	which are unaware ot the existence of the RD. An agent needs to
	query the RD to return all groups which are exported to be inserted
	into DNS.
	Req: GET /rd-lookup/gp?exp
	Res: 2.05 Content
	<coap://[FF05::1]/>;exp;gp="grp_R2-4-015;ins="grp1234";
	ep="lm_R2-4-015_wndw";
	ep="lm_R2-4-015_door
	The group with FQDN grp_R2-4-015.bc.example.com can be entered into
	the DNS by the agent. The accompanying instance name is grp1234.
	The <ServiceType> is chosen to be _group._udp. The agent enters the
	following RRs into the DNS.
	grp_R2-4-015.bc.example.com. IN AAAA FF05::1
	_group._udp.bc.example.com IN PTR
	grp1234._group._udp.bc.example.com
	grp1234._group._udp.bc.example.com IN SRV 0 0 5683
	grp_R2-4-015_door.bc.example.com.
	grp1234._group._udp.bc.example.com IN TXT
	txtver=1;path=/light/grp1
	From then on applications, not familiar with the existence of the RD,
	can use DNS to access the lighting group.
	13.2. OMA Lightweight M2M (LWM2M) Example
	This example shows how the OMA LWM2M specification makes use of		This example shows how the OMA LWM2M specification makes use of
	Resource Directory (RD).		Resource Directory (RD).
	OMA LWM2M is a profile for device services based on CoAP(OMA Name		OMA LWM2M is a profile for device services based on CoAP(OMA Name
	Authority). LWM2M defines a simple object model and a number of		Authority). LWM2M defines a simple object model and a number of
	abstract interfaces and operations for device management and device		abstract interfaces and operations for device management and device
	service enablement.		service enablement.
	An LWM2M server is an instance of an LWM2M middleware service layer,		An LWM2M server is an instance of an LWM2M middleware service layer,
	skipping to change at page 45, line 10 ¶		skipping to change at page 42, line 38 ¶
	defined by the LWM2M specification.		defined by the LWM2M specification.
	CoRE Resource Directory (RD) is used to provide the LWM2M		CoRE Resource Directory (RD) is used to provide the LWM2M
	Registration interface.		Registration interface.
	LWM2M does not provide for registration domains and does not		LWM2M does not provide for registration domains and does not
	currently use the rd-group or rd-lookup interfaces.		currently use the rd-group or rd-lookup interfaces.
	The LWM2M specification describes a set of interfaces and a resource		The LWM2M specification describes a set of interfaces and a resource
	model used between a LWM2M device and an LWM2M server. Other		model used between a LWM2M device and an LWM2M server. Other
	interfaces, proxies, applications, and function sets are currently		interfaces, proxies, and applications are currently out of scope for
	out of scope for LWM2M.		LWM2M.
	The location of the LWM2M Server and RD Function Set is provided by		The location of the LWM2M Server and RD base URI path is provided by
	the LWM2M Bootstrap process, so no dynamic discovery of the RD		the LWM2M Bootstrap process, so no dynamic discovery of the RD is
	function set is used. LWM2M Servers and endpoints are not required		used. LWM2M Servers and endpoints are not required to implement the
	to implement the ./well-known/core resource.		./well-known/core resource.
	13.2.1. The LWM2M Object Model		10.2.1. The LWM2M Object Model
	The OMA LWM2M object model is based on a simple 2 level class		The OMA LWM2M object model is based on a simple 2 level class
	hierarchy consisting of Objects and Resources.		hierarchy consisting of Objects and Resources.
	An LWM2M Resource is a REST endpoint, allowed to be a single value or		An LWM2M Resource is a REST endpoint, allowed to be a single value or
	an array of values of the same data type.		an array of values of the same data type.
	An LWM2M Object is a resource template and container type that		An LWM2M Object is a resource template and container type that
	encapsulates a set of related resources. An LWM2M Object represents		encapsulates a set of related resources. An LWM2M Object represents
	a specific type of information source; for example, there is a LWM2M		a specific type of information source; for example, there is a LWM2M
	skipping to change at page 45, line 50 ¶		skipping to change at page 43, line 29 ¶
	{/base-uri}{/object-id}{/object-instance}{/resource-id}{/resource-		{/base-uri}{/object-id}{/object-instance}{/resource-id}{/resource-
	instance}		instance}
	The five variables given here are strings. base-uri can also have		The five variables given here are strings. base-uri can also have
	the special value "undefined" (sometimes called "null" in RFC 6570).		the special value "undefined" (sometimes called "null" in RFC 6570).
	Each of the variables object-instance, resource-id, and resource-		Each of the variables object-instance, resource-id, and resource-
	instance can be the special value "undefined" only if the values		instance can be the special value "undefined" only if the values
	behind it in this sequence also are "undefined". As a special case,		behind it in this sequence also are "undefined". As a special case,
	object-instance can be "empty" (which is different from "undefined")		object-instance can be "empty" (which is different from "undefined")
	if resource-id is not "undefined". [_TEMPLATE_TODO]		if resource-id is not "undefined".
	base-uri := Base URI for LWM2M resources or "undefined" for default		base-uri := Base URI for LWM2M resources or "undefined" for default
	(empty) base URI		(empty) base URI
	object-id := OMNA (OMA Name Authority) registered object ID (0-65535)		object-id := OMNA (OMA Name Authority) registered object ID (0-65535)
	object-instance := Object instance identifier (0-65535) or		object-instance := Object instance identifier (0-65535) or
	"undefined"/"empty" (see above)) to refer to all instances of an		"undefined"/"empty" (see above)) to refer to all instances of an
	object ID		object ID
	resource-id := OMNA (OMA Name Authority) registered resource ID		resource-id := OMNA (OMA Name Authority) registered resource ID
	skipping to change at page 46, line 24 ¶		skipping to change at page 44, line 4 ¶
	(0-65535) or "undefined" to refer to all resources within an instance		(0-65535) or "undefined" to refer to all resources within an instance
	resource-instance := Resource instance identifier or "undefined" to		resource-instance := Resource instance identifier or "undefined" to
	refer to single instance of a resource		refer to single instance of a resource
	LWM2M IDs are 16 bit unsigned integers represented in decimal (no		LWM2M IDs are 16 bit unsigned integers represented in decimal (no
	leading zeroes except for the value 0) by URI format strings. For		leading zeroes except for the value 0) by URI format strings. For
	example, a LWM2M URI might be:		example, a LWM2M URI might be:
	/1/0/1		/1/0/1
	The base uri is empty, the Object ID is 1, the instance ID is 0, the		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		resource ID is 1, and the resource instance is "undefined". This
	example URI points to internal resource 1, which represents the		example URI points to internal resource 1, which represents the
	registration lifetime configured, in instance 0 of a type 1 object		registration lifetime configured, in instance 0 of a type 1 object
	(LWM2M Server Object).		(LWM2M Server Object).
	13.2.2. LWM2M Register Endpoint		10.2.2. LWM2M Register Endpoint
	LWM2M defines a registration interface based on the Resource		LWM2M defines a registration interface based on the REST API,
	Directory Function Set, described in Section 6. The URI of the LWM2M		described in Section 5. The base URI path of the LWM2M Resource
	Resource Directory function set is specified to be "/rd" as		Directory is specified to be "/rd" as recommended in Section 5.3.
	recommended in Section 6.3.
	LWM2M endpoints register object IDs, for example </1>, to indicate		LWM2M endpoints register object IDs, for example </1>, to indicate
	that a particular object type is supported, and register object		that a particular object type is supported, and register object
	instances, for example </1/0>, to indicate that a particular instance		instances, for example </1/0>, to indicate that a particular instance
	of that object type exists.		of that object type exists.
	Resources within the LWM2M object instance are not registered with		Resources within the LWM2M object instance are not registered with
	the RD, but may be discovered by reading the resource links from the		the RD, but may be discovered by reading the resource links from the
	object instance using GET with a CoAP Content-Format of application/		object instance using GET with a CoAP Content-Format of application/
	link-format. Resources may also be read as a structured object by		link-format. Resources may also be read as a structured object by
	performing a GET to the object instance with a Content-Format of		performing a GET to the object instance with a Content-Format of
	senml+json.		senml+json.
	When an LWM2M object or instance is registered, this indicates to the		When an LWM2M object or instance is registered, this indicates to the
	LWM2M server that the object and its resources are available for		LWM2M server that the object and its resources are available for
	management and service enablement (REST API) operations.		management and service enablement (REST API) operations.
	LWM2M endpoints may use the following RD registration parameters as		LWM2M endpoints may use the following RD registration parameters as
	defined in Table 1 :		defined in Table 2 :
	ep - Endpoint Name		ep - Endpoint Name
	lt - registration lifetime		lt - registration lifetime
	Endpoint Name is mandatory, all other registration parameters are		Endpoint Name is mandatory, all other registration parameters are
	optional.		optional.
	Additional optional LWM2M registration parameters are defined:		Additional optional LWM2M registration parameters are defined:
	+------------+-------+-------------------------------+--------------+		+------------+-------+-------------------------------+--------------+
	skipping to change at page 47, line 32 ¶		skipping to change at page 45, line 17 ¶
	+------------+-------+-------------------------------+--------------+		+------------+-------+-------------------------------+--------------+
	| Protocol | b | {"U",UQ","S","SQ","US","UQS"} | Available |		| Protocol | b | {"U",UQ","S","SQ","US","UQS"} | Available |
	| Binding | | | Protocols |		| Binding | | | Protocols |
	| | | | |		| | | | |
	| LWM2M | ver | 1.0 | Spec Version |		| LWM2M | ver | 1.0 | Spec Version |
	| Version | | | |		| Version | | | |
	| | | | |		| | | | |
	| SMS Number | sms | | MSISDN |		| SMS Number | sms | | MSISDN |
	+------------+-------+-------------------------------+--------------+		+------------+-------+-------------------------------+--------------+
	Table 4: LWM2M Additional Registration Parameters		Table 5: LWM2M Additional Registration Parameters
	The following RD registration parameters are not currently specified		The following RD registration parameters are not currently specified
	for use in LWM2M:		for use in LWM2M:
	et - Endpoint Type		et - Endpoint Type
	con - Context		con - Context
	The endpoint registration must include a payload containing links to		The endpoint registration must include a payload containing links to
	all supported objects and existing object instances, optionally		all supported objects and existing object instances, optionally
	including the appropriate link-format relations.		including the appropriate link-format relations.
	skipping to change at page 48, line 5 ¶		skipping to change at page 45, line 39 ¶
	Here is an example LWM2M registration payload:		Here is an example LWM2M registration payload:
	</1>,</1/0>,</3/0>,</5>		</1>,</1/0>,</3/0>,</5>
	This link format payload indicates that object ID 1 (LWM2M Server		This link format payload indicates that object ID 1 (LWM2M Server
	Object) is supported, with a single instance 0 existing, object ID 3		Object) is supported, with a single instance 0 existing, object ID 3
	(LWM2M Device object) is supported, with a single instance 0		(LWM2M Device object) is supported, with a single instance 0
	existing, and object 5 (LWM2M Firmware Object) is supported, with no		existing, and object 5 (LWM2M Firmware Object) is supported, with no
	existing instances.		existing instances.
	13.2.3. Alternate Base URI		10.2.3. LWM2M Update Endpoint Registration
	If the LWM2M endpoint exposes objects at a base URI other than the
	default empty base path, the endpoint must register the base URI
	using rt="oma.lwm2m". An example link payload using alternate base
	URI would be:
	</my_lwm2m>;rt="oma.lwm2m",</my_lwm2m/1>,<my_lwm2m/1/0>,<my_lwm2m/5>
	This link payload indicates that the lwm2m objects will be placed
	under the base URI "/my_lwm2m" and that object ID 1 (server) is
	supported, with a single instance 0 existing, and object 5 (firmware
	update) is supported.
	13.2.4. LWM2M Update Endpoint Registration
	An LWM2M Registration update proceeds as described in Section 6.4,		An LWM2M Registration update proceeds as described in Section 5.4.1,
	and adds some optional parameter updates:		and adds some optional parameter updates:
	lt - Registration Lifetime		lt - Registration Lifetime
	b - Protocol Binding		b - Protocol Binding
	sms - MSISDN		sms - MSISDN
	link payload - new or modified links		link payload - new or modified links
	A Registration update is also specified to be used to update the		A Registration update is also specified to be used to update the
	LWM2M server whenever the endpoint's UDP port or IP address are		LWM2M server whenever the endpoint's UDP port or IP address are
	changed.		changed.
	13.2.5. LWM2M De-Register Endpoint		10.2.4. LWM2M De-Register Endpoint
	LWM2M allows for de-registration using the delete method on the		LWM2M allows for de-registration using the delete method on the
	returned location from the initial registration operation. LWM2M de-		returned location from the initial registration operation. LWM2M de-
	registration proceeds as described in Section 6.5.		registration proceeds as described in Section 5.4.2.
	14. Acknowledgments		11. Acknowledgments
	Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders		Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders
	Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola and Linyi Tian have		Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola, Linyi Tian,
	provided helpful comments, discussions and ideas to improve and shape		Chistian Amsuss, and Jan Newmarch have provided helpful comments,
	this document. Section 9 is based on an earlier draft by Kerry Lynn.		discussions and ideas to improve and shape this document. Zach would
	Zach would also like to thank his colleagues from the EU FP7 SENSEI		also like to thank his colleagues from the EU FP7 SENSEI project,
	project, where many of the resource directory concepts were		where many of the resource directory concepts were originally
	originally developed.		developed.
	15. Changelog		12. Changelog
			changes from -09 to -10
			o removed "ins" and "exp" link-format extensions.
			o removed all text concerning DNS-SD.
			o removed inconsistency in RDAO text.
			o suggestions taken over from various sources
			o replaced "Function Set" with "REST API", "base URI", "base path"
			o moved simple registration to registration section
	changes from -08 to -09		changes from -08 to -09
	o clarified the "example use" of the base RD resource values /rd,		o clarified the "example use" of the base RD resource values /rd,
	/rd-lookup, and /rd-group.		/rd-lookup, and /rd-group.
	o changed "ins" ABNF notation.		o changed "ins" ABNF notation.
	o various editorial improvements, including in examples		o various editorial improvements, including in examples
	skipping to change at page 52, line 35 ¶		skipping to change at page 50, line 18 ¶
	o Added the concept of an RD Domain and a registration parameter for		o Added the concept of an RD Domain and a registration parameter for
	it.		it.
	o Recommended the Location returned from a registration to be		o Recommended the Location returned from a registration to be
	stable, allowing for endpoint and Domain information to be changed		stable, allowing for endpoint and Domain information to be changed
	during updates.		during updates.
	o Changed the lookup interface to accept endpoint and Domain as		o Changed the lookup interface to accept endpoint and Domain as
	query string parameters to control the scope of a lookup.		query string parameters to control the scope of a lookup.
	16. References		13. References
	16.1. Normative References		13.1. Normative References
	[I-D.ietf-core-links-json]		[I-D.ietf-core-links-json]
	Li, K., Rahman, A., and C. Bormann, "Representing CoRE		Li, K., Rahman, A., and C. Bormann, "Representing CoRE
	Formats in JSON and CBOR", draft-ietf-core-links-json-06		Formats in JSON and CBOR", draft-ietf-core-links-json-06
	(work in progress), July 2016.		(work in progress), July 2016.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	skipping to change at page 53, line 14 ¶		skipping to change at page 50, line 46 ¶
	[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an		[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 5226,		IANA Considerations Section in RFCs", BCP 26, RFC 5226,
	DOI 10.17487/RFC5226, May 2008,		DOI 10.17487/RFC5226, May 2008,
	<http://www.rfc-editor.org/info/rfc5226>.		<http://www.rfc-editor.org/info/rfc5226>.
	[RFC5988] Nottingham, M., "Web Linking", RFC 5988,		[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
	DOI 10.17487/RFC5988, October 2010,		DOI 10.17487/RFC5988, October 2010,
	<http://www.rfc-editor.org/info/rfc5988>.		<http://www.rfc-editor.org/info/rfc5988>.
	[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
	Cheshire, "Internet Assigned Numbers Authority (IANA)
	Procedures for the Management of the Service Name and
	Transport Protocol Port Number Registry", BCP 165,
	RFC 6335, DOI 10.17487/RFC6335, August 2011,
	<http://www.rfc-editor.org/info/rfc6335>.
	[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,		[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
	and D. Orchard, "URI Template", RFC 6570,		and D. Orchard, "URI Template", RFC 6570,
	DOI 10.17487/RFC6570, March 2012,		DOI 10.17487/RFC6570, March 2012,
	<http://www.rfc-editor.org/info/rfc6570>.		<http://www.rfc-editor.org/info/rfc6570>.
	[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link		[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
	Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,		Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
	<http://www.rfc-editor.org/info/rfc6690>.		<http://www.rfc-editor.org/info/rfc6690>.
	[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
	Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
	<http://www.rfc-editor.org/info/rfc6763>.
	[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,		[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
	DOI 10.17487/RFC7396, October 2014,		DOI 10.17487/RFC7396, October 2014,
	<http://www.rfc-editor.org/info/rfc7396>.		<http://www.rfc-editor.org/info/rfc7396>.
	16.2. Informative References		13.2. Informative References
	[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
	STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
	<http://www.rfc-editor.org/info/rfc1034>.
	[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
	Application and Support", STD 3, RFC 1123,
	DOI 10.17487/RFC1123, October 1989,
	<http://www.rfc-editor.org/info/rfc1123>.
	[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
	10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
	2003, <http://www.rfc-editor.org/info/rfc3629>.
	[RFC5198] Klensin, J. and M. Padlipsky, "Unicode Format for Network
	Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
	<http://www.rfc-editor.org/info/rfc5198>.
	[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.		[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
	Bormann, "Neighbor Discovery Optimization for IPv6 over		Bormann, "Neighbor Discovery Optimization for IPv6 over
	Low-Power Wireless Personal Area Networks (6LoWPANs)",		Low-Power Wireless Personal Area Networks (6LoWPANs)",
	RFC 6775, DOI 10.17487/RFC6775, November 2012,		RFC 6775, DOI 10.17487/RFC6775, November 2012,
	<http://www.rfc-editor.org/info/rfc6775>.		<http://www.rfc-editor.org/info/rfc6775>.
	[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer		[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
	Protocol (HTTP/1.1): Message Syntax and Routing",		Protocol (HTTP/1.1): Message Syntax and Routing",
	RFC 7230, DOI 10.17487/RFC7230, June 2014,		RFC 7230, DOI 10.17487/RFC7230, June 2014,
	skipping to change at page 54, line 30 ¶		skipping to change at page 51, line 36 ¶
	[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained		[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
	Application Protocol (CoAP)", RFC 7252,		Application Protocol (CoAP)", RFC 7252,
	DOI 10.17487/RFC7252, June 2014,		DOI 10.17487/RFC7252, June 2014,
	<http://www.rfc-editor.org/info/rfc7252>.		<http://www.rfc-editor.org/info/rfc7252>.
	[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for		[RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
	the Constrained Application Protocol (CoAP)", RFC 7390,		the Constrained Application Protocol (CoAP)", RFC 7390,
	DOI 10.17487/RFC7390, October 2014,		DOI 10.17487/RFC7390, October 2014,
	<http://www.rfc-editor.org/info/rfc7390>.		<http://www.rfc-editor.org/info/rfc7390>.
	Editorial Comments
	[_TEMPLATE_TODO] This text needs some help from an RFC 6570 expert.
	Authors' Addresses		Authors' Addresses
	Zach Shelby		Zach Shelby
	ARM		ARM
	150 Rose Orchard		150 Rose Orchard
	San Jose 95134		San Jose 95134
	USA		USA
	Phone: +1-408-203-9434		Phone: +1-408-203-9434
	Email: zach.shelby@arm.com		Email: zach.shelby@arm.com
End of changes. 139 change blocks.
	741 lines changed or deleted		603 lines changed or added
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