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Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 5988 (Obsoleted by RFC 8288) == Outdated reference: A later version (-14) exists of draft-ietf-core-interfaces-03 == Outdated reference: A later version (-28) exists of draft-ietf-core-resource-directory-04 == Outdated reference: A later version (-05) exists of draft-koster-core-coap-pubsub-02 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CoRE Working Group T. Zotti 3 Internet-Draft Philips Research 4 Intended status: Informational P. van der Stok 5 Expires: March 31, 2016 Consultant 6 E. Dijk 7 Philips Research 8 September 28, 2015 10 Sleepy CoAP Nodes 11 draft-zotti-core-sleepy-nodes-04 13 Abstract 15 Control networks rely on application protocols like CoAP to enable 16 RESTful communications in constrained environments. Many of these 17 networks make use of "Sleepy Nodes": battery powered devices that 18 switch off their (radio) interface during most of the time to 19 conserve battery energy. As a result of this, Sleepy Nodes cannot be 20 reached most of the time. This fact prevents using normal 21 communication patterns as specified in the CoRE group, since the 22 server-model is not applicable to these devices. This document 23 discusses and specifies an architecture to support Sleepy Nodes such 24 as battery-powered sensors in mesh networks with the goal of 25 proposing a standardisation solution for Sleepy Node proxies. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at http://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on March 31, 2016. 44 Copyright Notice 46 Copyright (c) 2015 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (http://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Problem statement . . . . . . . . . . . . . . . . . . . . 3 63 1.2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 4 64 1.3. Requirements Language . . . . . . . . . . . . . . . . . . 4 65 1.4. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 5 66 2. Use cases and architecture . . . . . . . . . . . . . . . . . 5 67 2.1. Node interactions and use cases . . . . . . . . . . . . . 6 68 2.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 9 69 2.3. Example contents . . . . . . . . . . . . . . . . . . . . 10 70 3. Design motivation . . . . . . . . . . . . . . . . . . . . . . 10 71 4. Interactions involving Resource Directory . . . . . . . . . . 10 72 5. Synchronize interface . . . . . . . . . . . . . . . . . . . . 12 73 5.1. Sleepy Node discovers proxy . . . . . . . . . . . . . . . 12 74 5.2. Registration at a Proxy . . . . . . . . . . . . . . . . . 12 75 5.3. De-registration at a Proxy . . . . . . . . . . . . . . . 15 76 5.4. Initialization of delegated resource . . . . . . . . . . 16 77 5.5. Sleepy Node updates delegated resource at Proxy . . . . . 17 78 5.6. Sleepy Node READs resource updates from Proxy . . . . . . 18 79 6. Delegate Interface . . . . . . . . . . . . . . . . . . . . . 18 80 6.1. Discovering Endpoint discovers Sleepy Node at Proxy . . . 19 81 6.2. Proxy REPORTs events to Endpoint . . . . . . . . . . . . 20 82 6.3. A Node WRITEs to Sleepy Node via Proxy . . . . . . . . . 21 83 6.4. A Node READs information from Sleepy Node via Proxy . . . 22 84 7. Direct Interface . . . . . . . . . . . . . . . . . . . . . . 22 85 7.1. Sleepy Node REPORTs events directly to Destination Node . 22 86 7.2. A Sleepy Node READs information from a Server Node . . . 23 87 8. Realization with PubSub broker . . . . . . . . . . . . . . . 23 88 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 89 10. Security Considerations . . . . . . . . . . . . . . . . . . . 24 90 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24 91 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 24 92 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 93 13.1. Normative References . . . . . . . . . . . . . . . . . . 25 94 13.2. Informative References . . . . . . . . . . . . . . . . . 25 95 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 97 1. Introduction 99 Control networks rely on application protocols such as CoAP to enable 100 RESTful communications in constrained environments. Many of these 101 networks feature "Sleepy Nodes": battery-powered nodes which switch 102 on/off their communication interface to conserve battery energy. As 103 a result of this, Sleepy Nodes cannot be reached most of the time. 104 This fact prevents using normal communication patterns as specified 105 by the CoRE group, since the server model is clearly not applicable 106 to the most energy constrained devices. 108 This document discusses and specifies an architecture to support 109 Sleepy Nodes such as battery-powered sensors in wireless networks. 110 The proposed solution makes use of a Proxy Node to which a Sleepy 111 Node delegates part of its communication tasks while it is not 112 accessible in the wireless network. Direct interactions between 113 Sleepy Nodes and non-Sleepy Nodes are only possible, when the Sleepy 114 Node initiates the communication. 116 Earlier related documents treating the Sleepy Node subject are the 117 CoRE mirror server [I-D.vial-core-mirror-server] and the Publish- 118 Subscribe in the Constrained Application Protocol (CoAP) 119 [I-D.koster-core-coap-pubsub]. Both documents describe the 120 interfaces to the proxy accompanying the Sleepy Node. Both make use 121 of the observe option discussed in [I-D.ietf-core-observe]. This 122 document describes the roles of the nodes communicating with the 123 Sleepy Node and/or its proxy. The draft describes the differences 124 between the concepts supporting the Sleepy Node, and the concepts 125 underlying the PubSub paradigm. 127 The draft relies heavily on the concepts introduced by the Resource 128 Directory [I-D.ietf-core-resource-directory], and describes how the 129 Sleepy Node profits of the introduction of a Resource Directory into 130 the network. 132 The issues that need to be addressed to provide support for Sleepy 133 Nodes in Control networks are summarized in Section 1.1. Section 2 134 provides a set of use case descriptions that introduce communication 135 patterns to be used in home and building control scenarios. 136 Section 4, Section 5,Section 6, and Section 7 specify interfaces to 137 support each of these scenarios. Many interface specifications and 138 examples are taken over from [I-D.vial-core-mirror-server]. 140 1.1. Problem statement 142 During typical operation, a Sleepy Node has its radio disabled and 143 the CPU may be in a sleeping state. If an external event occurs 144 (e.g. person walks into the room activating a presence sensor), the 145 CPU and radio are powered back on and they send out a message to 146 another node, or to a group of nodes. After sending this message, 147 the radio and CPU are powered off again, and the Sleepy Node sleeps 148 until the next external event or until a predefined time period has 149 passed. The main problems when introducing Sleepy Nodes into a 150 wireless network are as follows: 152 Problem 1: How to contact a Sleepy Node that has its radio turned off 153 most of the time for: 155 - Writing configuration settings. 157 - Reading out sensor data, settings or log data. 159 - Configuring additional event destination nodes or node groups. 161 Problem 2: How to discover a Sleepy Node and its services, while the 162 node is asleep: 164 - Direct node discovery (CoAP GET /.well-known/core as defined in 165 [RFC7252]) does not find the node with high probability. 167 - Mechanisms may be needed to provide, as the result of node 168 discovery, the IP address of a Proxy instead of the IP address of 169 the node directly. 171 Problem 3: How a Sleepy Node can convey data to a node or groups of 172 nodes, with good reliability and minimal energy consumption. 174 1.2. Assumptions 176 The solution architecture specified here assumes that a Sleepy Node 177 has enough energy to perform bidirectional communication during its 178 normal operational state. This solution may be applicable also to 179 extreme low-power devices such as solar powered sensors as long as 180 they have enough energy to perform commissioning and the initial 181 registration steps. These installation operations may require, in 182 some cases, an additional source of power. Since a Sleepy Node is 183 unreachable for relatively long periods of times, the data exchanges 184 in the interaction model are always initiated by a Sleepy Node when 185 its sleep period ends. 187 1.3. Requirements Language 189 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 190 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 191 document are to be interpreted as described in [RFC2119]. 193 This document assumes readers are familiar with the terms and 194 concepts discussed in [RFC7252],[RFC5988], 195 [I-D.ietf-core-resource-directory], 196 [I-D.ietf-core-interfaces],[I-D.ietf-core-observe] and 197 [I-D.vial-core-mirror-server]. 199 In addition, this document makes use of the following additional 200 terminology: 202 Sleepy Node: a battery-powered node which does the on/off switching 203 of its communication interface with the purpose of conserving battery 204 energy 206 Sleeping/Asleep: A Sleepy Node being in a "sleeping state" i.e. its 207 network interface is switched off and a Sleepy Node is not able to 208 send or receive messages. 210 Awake/Not Sleeping: A Sleepy Node being in an "awake state" i.e. its 211 network interface is switched on and the Sleepy Node is able to send 212 or receive messages. 214 Wake up reporting duration: the duration between a wake up from a 215 Sleepy Node and the next wake up and report of the same Node. 217 Proxy: any node that is configured to, or selected to, perform 218 communication tasks on behalf of one or more Sleepy Nodes. 220 Regular Node: any node in the network which is not a Proxy or a 221 Sleepy Node. 223 1.4. Acronyms 225 This Internet-Draft contains the following acronyms: 227 DTLS: Datagram Transport Layer Security 229 EP: Endpoint 231 MC: Multicast 233 RD: Resource Directory 235 2. Use cases and architecture 237 To describe the application viewpoint of the solution, we introduce 238 some example scenarios for the various interactions shown in 239 Figure 1. The figure assigns the following roles taken up by a 240 regular node: 242 o Reading Node: any regular node that reads information from the 243 Sleepy Node. 245 o Configuring Node: any regular node that writes information/ 246 configuration into Sleepy Node(s). Examples of configuration are 247 new thresholds for a sensor or a new value for the wake-up cycle 248 time. 250 o Discovering Node: any regular node that performs discovery of the 251 nodes in a network, including Sleepy Nodes. 253 o Destination Node: any regular node or node in a group that 254 receives a message that is generated by the Sleepy Node. 256 o Server Node: an optional server that the Sleepy Node knows about, 257 or is told about, which is used to fetch 258 information/configuration/firmware updates/etc. 260 o Discovery Server: an optional server that enables nodes to 261 discover all the devices in the network, including Sleepy Nodes, 262 and query their capabilities. For example, a Resource Directory 263 server as defined in [I-D.ietf-core-resource-directory] or a DNS- 264 SD server as defined in [RFC6763]. For the rest of this document 265 the discovery server is a Resource Directory. Specifically, the 266 functionalities of the Resource Directory related to the 267 architecture presented in this Internet-Draft are described in 268 more details in Section 4. 270 o Delegated resource is the copy at the Proxy of a resource present 271 in the Sleepy Node. 273 2.1. Node interactions and use cases 274 +------------+ +-------------+ 275 | Discovery | <-DISCOVERY-| Discovering | 276 | server | | Node | 277 | (Optional) | +-------------+ 278 +------------+ | 279 | 280 .--DISCOVERY--' +---------+ 281 | | Reading | 282 | .---| Node | 283 v | +---------+ 284 +---------+ +-----------+ | 285 | Sleepy |---REPORT(A)-->| |<--READ--' +-------------+ 286 | Node |---READ------->| Proxy |<--WRITE---| Configuring | 287 | |---WRITE------>| | | Node | 288 +---------+ +-----------+ +-------------+ 289 | | | +-------------+ 290 | | '---REPORT(B)->| Destination | 291 | '-----DIRECT REPORT---------------------->| Node | 292 | +-------------+ 293 | +-----------+ 294 '------------READ--------------------------->| Server | 295 | Node | 296 +-----------+ 298 Figure 1: Interaction model for Sleepy Nodes in IP-based networks 300 The interactions visualized in Figure 1 are discussed and motivated 301 with their use cases. The arrows in the figure indicate that the 302 initiative for an interaction is taken by the source of the arrow. 304 DISCOVERY Interaction: a Discovering Node discovers Sleepy Node(s)via 305 Proxy or Discovery Server; for example: 307 - A Discovering Node wants to discover given services related to a 308 group of deployed sensors by sending a multicast to /.well-known/ 309 core. It gets responses for the sleeping sensors from the Proxy 310 nodes. 312 - During commissioning phase, a discovering node queries a 313 Discovery Server to find all the proxies providing a given 314 service. 316 REPORT Interaction: On request of a Destination Node or because of 317 configuration settings which have instructed the Node to do so, a 318 Node sends a sequence of event notifications to destination Node(s), 319 (A) directly or (B) via Proxy; for example: 321 - A battery-powered sensor sends a notification with "battery low" 322 event directly to a designated Destination Node (REPORT(A)). 324 - A battery-powered occupancy sensor detects an event "people 325 present", switches on the radio and multicasts an "ON" command to 326 a group of lights (REPORT(A)). 328 - A battery-powered temperature sensor reports periodically the 329 room temperature to a proxy Node (REPORT(A)). The proxy node 330 reports to all associated HVAC destination nodes when the 331 temperature change deviates from a predefined range (REPORT(B)). 333 WRITE Interaction: A node sends a request to a proxy to set a value. 335 o A Sleepy Node WRITES to the proxy; for example: 337 - A battery-powered sensor wants to extend the registration 338 lifetime of its delegated resource at the Proxy. 340 o A configuring Node WRITEs information to a Proxy; for example: 342 - A configuring Node changes the reporting frequency of a 343 deployed sensor by contacting the Proxy node to which the 344 sensor is registered. 346 - Sensor firmware is upgraded. A configuring Node pushes 347 firmware data blocks to the Proxy, which pushes the blocks to 348 the Sleepy Node. 350 - A configuring Node adds a new subscription to an operational 351 sensor via the Proxy. From that moment on, the new Node 352 receives also the sensor events and status updates from the 353 sensor. 355 READ Interaction: A node sends a read request to a node that returns 356 a value. 358 o Sleepy Node sends a read request to a server Node; for example: 360 - A sensor (periodically) updates internal data tables by 361 fetching it from a predetermined remote node. 363 - A sensor (periodically) checks for new firmware with a remote 364 node. If new firmware is found, the sensor switches to a non- 365 sleepy operation mode, and fetches the data. 367 o A Sleepy Node sends a read request to its proxy; for example: 369 - A sensor (periodically) checks with his Proxy availability of 370 configuration updates or changes of its delegated resources 371 (e.g. a sensor may detect in this way that a configuring Node 372 has changed its name or modified its reporting frequency). 374 o A reading Node sends a read request to a proxy; for example: 376 - A Node (e.g. in the backend) requests the status of a 377 deployed sensor, e.g. asking the sensor state and/or firmware 378 version and/or battery status and/or its error log. The Proxy 379 returns this information. 381 - A Node requests a Proxy when a Sleepy sensor was 'last 382 active' (i.e. identified as being awake) in the network. 384 2.2. Architecture 386 The architecture associated with the support of Sleepy Nodes is 387 illustrated in Figure 2. Three High level interfaces are shown. 389 direct synchronize delegate 390 | | | 391 +----+ | +--------+ | +-------+ | +----+ 392 | EP |---|---| sleepy |---|---| proxy |---|---| EP | 393 +----+ | +--------+ | +-------+ | +----+ 394 | | | 396 Figure 2: Architecture of Sleepy Node support 398 o Direct interface: it allows the Sleepy Node to communicate 399 directly to endpoints (i.e. for sending or reading information). 400 The operations performed via this interface are always initiated 401 by the Sleepy Node when its sleep period ends. 403 o Delegate interface: via this interface the Proxy exposes the 404 values of delegated resources to interested endpoints on behalf of 405 the Sleepy Node. The same interface is used by endpoints which 406 want to communicate with the Sleepy Node (e.g. for reading or 407 writing information). 409 o Synchronize interface: used by Sleepy Node and Proxy to 410 synchronize values of delegated resources. Through this interface 411 operations as discovery of the Proxy, registration, initialization 412 and update of resources at the Proxy are performed, along with a 413 de-registration operation to explicitly remove resources already 414 registered to the Proxy. 416 The interfaces consist of a set of functions which together realize 417 the interactions described in Section 2.1. 419 Endpoints and the proxy communicate with a Resource Directory (RD) to 420 discover resources of the Sleepy Node and delegated resources on the 421 proxy (not shown in the Figure 2). 423 2.3. Example contents 425 The examples presented in this specification make use of a smart 426 temperature sensor the resources of which are defined below using 427 Link Format [RFC6690]. Three resources are dedicated to the Device 428 Description (manufacturer, model, name) and one contains the current 429 temperature in degree Celsius. 431 ;rt="ipso.dev.mfg";if="core.rp", 432 ;rt="ipso.dev.mdl";if="core.rp", 433 ;rt="ipso.dev.n";if="core.p", 434 ;rt="ucum.Cel";if="core.s" 436 3. Design motivation 438 The Sleepy Node stack features a CoAP interface, to make the Sleepy 439 Node part of the IP-based network. Adding CoAP with a transport 440 protocol increases the possibilities to configure the Sleepy Node 441 within the network. The increased energy consumption coming from the 442 overhead of the CoAP and IP headers can be acceptable in many cases. 444 The proxy and Sleepy Node make use of the /.well-known/core resource 445 to handle discovery during network initialization. Using the 446 Resource Directory during operation of the Sleepy Node reduces its 447 participation in the discovery traffic. 449 A Sleepy Node delegates its resources to a proxy. The proxy 450 functionality extends the functionality of the RD, because the proxy 451 handles the value of the resource, and the RD does not. A proxy may 452 support multiple Sleepy Nodes. A Sleepy Node may also delegate its 453 resources to multiple proxies. A node can select a proxy that 454 handles the resource of the Sleepy Node of choice. 456 The complexity of the discovery and delegation interfaces is 457 minimized by reusing the RD interface as much as possible. 459 4. Interactions involving Resource Directory 461 It is assumed that the Proxy has a resource type rt="core.sp", where 462 sp stands for sleepy proxy. 464 In order to become fully operational in a network and to communicate 465 over the functional interfaces shown in Figure 2, a Sleepy Node and 466 the Proxy need to perform operations via the Registration interface 467 of the RD: 469 - Discovery of Proxy via RD. The Sleepy Node MAY discover the 470 Proxy by sending a request to the RD to return all EP with 471 rt=core.sp. 473 - Register existence of Proxy. When a RD is present and a Sleepy 474 Node has registered itself to a Proxy (see Section 5.2), the Proxy 475 MUST register the Sleepy Node at the RD and MUST keep this 476 registration up-to-date. 478 - Register delegated resources. When a RD is present, the Proxy 479 MUST register the delegated resources at the RD and keep them up- 480 to date. 482 A Configuring Endpoint (often part of a so-called Commissioning Tool) 483 registers the services that are reported directly by the Sleepy Node 484 in the resource directory, by registering the resource type and the 485 multicast address. The multicast address can be associated with a 486 group as described in [I-D.ietf-core-resource-directory]. 488 A discovering Endpoint can discover one or more Sleepy Node resources 489 via the Resource Directory. 491 +-------------+ +-----------------+ 492 | Configuring | | Discovering |---. 493 | Endpoint | | Endpoint | | 494 +-------------+ +-----------------+ | 495 | | 496 | +------------+ | 497 .-Register MC------>| |<--Discover resources -. 498 | Resource | 499 | Directory |<--Register Proxy -----. 500 .-Proxy Discovery-->| |<--Register resources -. 501 | +------------+ | 502 | | 503 +---------+ +-----------+ | 504 | Sleepy | | Proxy |---------' 505 | Node | | | 506 +---------+ +-----------+ 508 Figure 3: Interactions involving Resource Directory 510 5. Synchronize interface 512 The functions of the synchronize interface implemented by the Proxy 513 are described in this section. 515 5.1. Sleepy Node discovers proxy 517 A Sleepy Node can discover the proxy in two ways: 519 - via the CoAP interface [RFC7390] by sending a multicast message 520 to discover an endpoint with rt=core.sp. 522 - via RD as already described in Section 4. 524 The following example shows a sleeping endpoint discovering a proxy 525 using this interface, thus learning that the base Proxy resource, 526 where the Sleepy Node resources are registered, is at /sp. 528 Sleepy Proxy 529 | | 530 | ----- GET /.well-known/core?rt=core.sp ------> | 531 | | 532 | | 533 | <---- 2.05 Content "; rt="core.sp" ------ | 534 | | 536 Req: GET coap://[ff02::1]/.well-known/core?rt=core.sp 537 Res: 2.05 Content 538 ;rt="core.sp" 540 The use of /sp is recommended and not compulsory. 542 5.2. Registration at a Proxy 544 Once a Sleepy Node has discovered a Proxy by means of one of the 545 procedures described in Section 5.1, the registration step can be 546 performed. To perform registration, a Sleepy Node sends to the Proxy 547 Node a CoAP POST request containing a description of the resources to 548 be delegated to the Proxy as the message payload in the CoRE Link 549 Format [RFC6690]. The description of the resource includes the 550 Sleepy Node identifier, its domain and the lifetime of the 551 registration. 553 Upon successful registration a Proxy creates a new delegated resource 554 or updates an existing delegated resource and returns its location. 555 The resources specified by the Sleepy Node during registration are 556 created with path that has as prefix the base Proxy resource path 557 (e.g. /sp). The registration interface MUST be implemented to be 558 idempotent, so that registering twice with the same endpoint 559 parameter does not create multiple delegated resources. The 560 delegated resource SHOULD implement the Interface Type CoRE Link List 561 defined in [I-D.ietf-core-interfaces]. A GET request on this 562 resource MUST return the list of delegated resources for the 563 corresponding Sleepy Node. 565 After successful registration, a Proxy SHOULD enable resource 566 discovery for the new resources by updating its "/.well-known/core" 567 resource. A Proxy MUST wait for the initial representation of a 568 resource before it can be visible during resource discovery. The top 569 level delegated resource MUST be published in "/.well-known/core" to 570 enable the discovery of the resources via RD as described in 571 Section 4. Resources of a delegated container SHOULD be discoverable 572 either directly in "/.well-known/core" or indirectly through gradual 573 reveal from the delegated resource. The Web Link of a delegated 574 resource MUST contain an "ep" attribute with the value of the End- 575 Point parameter received during registration. 577 A Proxy MAY be configured to register the Sleepy Node's resources in 578 a RD. In this case, a Sleepy Node MUST NOT register the resources in 579 a RD by itself since it is the responsibility of the Proxy to perform 580 the registration in the RD on behalf of the Sleepy Node. Since each 581 Sleepy Node may register resources with different lifetimes, a Proxy 582 MUST register the resources of a given Sleepy Node in a dedicated 583 path of the RD. 585 In case a Sleepy Node delegates its own resources to more than one 586 Proxy and each Proxy registers the Sleepy Node's resource in a RD, 587 the RD entries from the different Proxies for the same Sleepy Node 588 risk to overlap. 590 To avoid this problem, a Proxy MUST create its own resource path to 591 register the resources of a Sleepy Node on the RD. 593 The new path name is typically formed by concatenating the Proxy's 594 endpoint identifier with the path in use. This precaution ensures 595 that the ep identifier of a Sleepy Node is unique for each resource 596 path in the RD. 598 Implementation note: It is not recommended to reuse the value of the 599 ep parameter in the URI of the delegated resource. This parameter 600 may be a relatively long identifier to guarantee global uniqueness 601 (e.g. EUI64) and would generate inefficient URIs on the Proxy where 602 only a local handler is necessary. 604 The following example shows a Sleepy Node registering with a Proxy. 606 Sleepy Proxy 607 | | 608 | --- POST /sp?ep=0224e8fffe925dcf;rt=sensor " | 609 | | 610 | | 611 | <-- 2.01 Created Location: /sp/0 ----------------------- | 612 | | 614 Req: POST coap://sp.example.org/sp?ep=0224e8fffe925dcf;rt=sensor 615 Etag: 0x3f 616 Payload: 617 ;rt="ipso.dev.mfg";if="core.rp", 618 ;rt="ipso.dev.mdl";if="core.rp", 619 ;rt="ipso.dev.n";if="core.p", 620 ;rt="ucum.Cel";if="core.s" 622 Res: 2.01 Created 623 Location: /sp/0 625 The delegated resource has been created with path /sp/0 on the Proxy 626 in the example above. The path to the ep can be discovered as shown 627 below: 629 Req: GET coap://sp.example.org/.well-known/core 630 Res: 2.05 Content 631 ;rt="core.sp", 632 ;ep="0224e8fffe925dcf";rt="sensor" 634 A node can discover the delegated resources of the ep as shown below: 636 Req: GET coap://sp.example.org/sp/0 637 Res: 2.05 Content 638 Payload: 639 ;rt="ipso.dev.mfg";if="core.rp", 640 ;rt="ipso.dev.mdl";if="core.rp", 641 ;rt="ipso.dev.n";if="core.p", 642 ;rt="ucum.Cel";if="core.s" 644 Once the resources are registered in the Proxy, the Proxy registers 645 the delegated resources in the RD. 647 Proxy RD 648 | | 649 | --- POST /rd?ep=0224e8fffe925dcf " | 650 | | 651 | | 652 | <-- 2.01 Created Location: /rd/6534 ------------------- | 653 | | 655 Req: POST coap://rd.example.org/rd?ep=0224e8fffe925dcf 656 Etag: 0x6a 657 Payload: 658 ;rt="ipso.dev.mfg";if="core.rp", 659 ;rt="ipso.dev.mdl";if="core.rp", 660 ;rt="ipso.dev.n";if="core.p", 661 ;rt="ucum.Cel";if="core.s" 663 Res: 2.01 Created 664 Location: /rd/6534 666 5.3. De-registration at a Proxy 668 Sleepy Node resources in the Proxy are kept active for the period 669 indicated by the lifetime parameter. The Sleepy Node is responsible 670 for refreshing the delegated resource within this period using either 671 the registration or update function (see Section 5.5 of the 672 Synchronize interface). Once a delegated resource has expired, the 673 Proxy deletes all resources associated to that resource and updates 674 its "/.well-known/core" resource. When the Proxy resources are also 675 registered in a RD, the RD and delegated resources are supposed to 676 have the same lifetime. Consequently, when the delegated resource 677 expires, a Proxy MAY let the RD resource expire too instead of 678 explicitly deleting it. When the delegated resource is deleted by 679 means of explicit de-registration operation then also the RD resource 680 MUST be explicitly removed. 682 A Proxy could lose or delete the delegated resource associated to a 683 Sleepy Node without sending an explicit notification (e.g. after 684 reboot). A Sleepy Node SHOULD be able to detect this situation by 685 processing the response code while using the Sleepy Node Operation or 686 Update interface. Especially an error code "4.04 Not Found" SHOULD 687 cause the Sleepy Node to register again. A Sleepy Node MAY also 688 register with multiple proxies to alleviate the risk of interruption 689 of service. 691 5.4. Initialization of delegated resource 693 Once registration has been successfully performed, the Sleepy Node 694 must initialize the delegated resource. To send the initial contents 695 (e.g. values, device name, manufacturer name) of the delegated 696 resources to the Proxy, the Sleepy Node uses CoAP PUT repeatedly. 698 The basic interface is specified as follows: 700 Interaction: Sleepy -> Proxy 702 Method: PUT 704 URI Template: /{+location}{+resource}{?lt} 706 URI Template Variables: 708 location := This is the Location path returned by the Proxy as a 709 result of a successful registration. 711 resource := This is the relative path to a delegated resource 712 managed by the registered Sleepy Node. 714 lt := Lifetime (optional). The number of seconds by which the 715 lifetime of the whole delegated resource is extended. Range of 716 1-4294967295. If no lifetime is included, the current 717 remaining lifetime stays unchanged. 719 Request Content-Type: Defined at registration 721 Response Content-Type: Defined at registration for GET method. 722 application/link-format for PUT method if at least one of the 723 mutable resources has been updated since the last PUT request. 725 Etag: The Etag option MAY be included to allow clients to validate a 726 resource on multiple Proxies. 728 Success: 2.01 "Created", the request MUST include the initial 729 representation of the delegated resource. 731 Success: 2.04 "Changed", the request MUST include the new 732 representation of the delegated resource. 734 Success: 2.05 "Content", the response MUST include the current 735 representation of the delegated resource. 737 Failure: 4.00 "Bad Request". Malformed request. 739 Failure: 5.03 "Service Unavailable". Service could not perform the 740 operation. 742 The following example describes how a Sleepy Node can initialize the 743 resource containing its manufacturer name just after registration. 745 Sleepy Proxy 746 | | 747 | --- PUT /sp/0/dev/mfg "acme" ---------------> | 748 | | 749 | | 750 | <-- 2.01 Created ----------------------------- | 751 | | 753 Req: PUT /sp/0/dev/mfg 754 Payload: acme 755 Res: 2.01 Created 757 The example below shows how a Sleepy Node can indicate that it is 758 supposed to send a temperature value at least every hour to keep its 759 delegated resource active. 761 Sleepy Proxy 762 | | 763 | --- PUT /sp/0/sen/temp?lt=3600 "22" --------> | 764 | | 765 | | 766 | <-- 2.04 Changed ----------------------------- | 767 | | 769 Req: PUT /sp/0/sen/temp?lt=3600 770 Payload: 22 771 Res: 2.04 Changed 773 The use of repeated CoAP PUT can be avoided by writing all relevant 774 resources into the Proxy in one operation by means of the Batch 775 interface described in [I-D.ietf-core-interfaces]. After successful 776 initialization, a Proxy SHOULD enable resource discovery for the new 777 delegated resources by updating its /.well-known/core resource. 779 5.5. Sleepy Node updates delegated resource at Proxy 781 A Sleepy Node can update a delegated resource at the Proxy (REPORT A) 782 using standard CoAP PUT requests on the delegated resource as shown 783 in Section 5.4. 785 When a Sleepy Node sends a PUT request to update its resources, the 786 response MAY contain a link-format payload. The payload does not 787 directly relate to the target resource of the PUT request. Instead, 788 it is a list of web links to resources that have been modified by 789 clients since either the last PUT request or the last call to the 790 modification check interface (see Section 5.6). 792 5.6. Sleepy Node READs resource updates from Proxy 794 This function allows a Sleepy Node to retrieve a list of delegated 795 resources that have been modified at the Proxy by other nodes. The 796 interface format for GET is the same as the one specified for PUT in 797 Section 5.4. 799 A configuring Node (EP) can update a resource in the Proxy. The 800 Sleepy Node receives an indication of the changed resources as 801 specified in Section 5.5. 803 The Sleepy Node can send GET requests to its Proxy on each delegated 804 resource in order to receive their updated representation. The 805 example in Figure 4 shows a configuration node which changes the name 806 of a Sleepy Node at the Proxy. The Sleepy Node can then check and 807 read the modification in its resource. 809 Sleepy Proxy EP 810 | | <---PUT /sp/0/dev/n----| 811 | | Payload: Sensor1 | 812 Wake-up |---2.04 Changed-------->| 813 event | | 814 | | | 815 |--POST /sp/0/dev/.. -->| | 816 |<----2.04 Changed------| | 817 | Payload: | | 818 | | | 819 |---GET /sp/0/dev/n---->| | 820 |<-----2.05 Content-----| | 821 | Payload: Sensor1 | | 822 | | | 824 Figure 4: Example: A Sleepy Node READs resource updates from his 825 Proxy 827 6. Delegate Interface 829 This section details the functions belonging to the delegate 830 interface. 832 6.1. Discovering Endpoint discovers Sleepy Node at Proxy 834 Through this function, a Discovering Endpoint can discover one or 835 more Sleepy Node(s) at a Proxy. In case a Resource Directory is not 836 present, this is the only way to discover Sleepy Nodes. A CoAP 837 client discovers resources owned by the Sleepy Node but hosted on the 838 Proxy using typical mechanisms such as one or more GETs on the 839 resource /.well-known/core [RFC6690]. 841 Resource discovery between an Endpoint and a proxy or an Endpoint and 842 a RD needs special care to take into account the fact that resources 843 from a Sleepy Node might appear duplicated. EPs SHOULD employ 2-step 844 resource discovery by looking up Sleepy Nodes AND resource types to 845 detect duplicate resources. EPs MAY use single-step resource 846 discovery only if the Sleepy Node can register with no more than one 847 Proxy. An EP can use the "ep" link attribute as a filter on the 848 "/.well-known/core" resource to retrieve a list of endpoints and 849 detect duplicate Sleepy Nodes registered on multiple proxies. An EP 850 can use the "ep" type of lookup to do the same on a RD. The result 851 of endpoint discovery is then used to filter out duplicate resources 852 returned from simple resource discovery. 854 The following example shows a client discovering the Sleepy Nodes and 855 learning that the Sleepy Node 0224e8fffe925dcf is registered on two 856 Proxies. 858 EP proxy1 proxy2 859 | | | 860 | ----- GET /.well-known/core?ep=* ------->|------>| 861 | | | 862 | | | 863 | <---- 2.05 Content "..." --------| | 864 | | | 865 | <---- 2.05 Content "..." --------|-------| 867 Req: GET coap://[ff02::1]/.well-known/core?ep=* 868 Res: 2.05 Content 869 ;ep="0224e8fffe925dcf" 870 Res: 2.05 Content 871 ;ep="02004cfffe4f4f50" 872 ;ep="0224e8fffe925dcf" 874 From the previous exchange and the next resource discovery request, 875 the EP can infer that the resources coap://sp1/sp/0/sen/temp and 876 coap://sp2/sp/1/sen/temp actually come from the same Sleepy Node with 877 ep=0224e8fffe925dcf. 879 EP proxy1 proxy2 880 | | | 881 | - GET /.well-known/core?rt=ipso:ucum.Cel ->|------>| 882 | | | 883 | | | 884 | <---- 2.05 Content "..." ----------| | 885 | | | 886 | <---- 2.05 Content "..." ----------|-------| 888 Req: GET coap://[ff02::1]/.well-known/core?rt=ucum.Cel 889 &ep=0224e8fffe925dcf 890 Res: 2.05 Content 891 ;rt="ucum.Cel" 895 6.2. Proxy REPORTs events to Endpoint 897 This interface can be used by the Endpoint to receive event report 898 message to Proxy (REPORT A) which further notifies it to interested 899 Destination Endpoint(s)(REPORT B). This indirect reporting is useful 900 for a scalable solution, e.g. there may be many interested 901 subscribers but the Sleepy Node itself can only support a limited 902 number of subscribers given its limits on battery energy. A client 903 interested in the events related with a specific resource may send a 904 CoAP GET to the Proxy, to obtain the last published state. If a 905 Reading node is interested in receiving updates whenever the Sleepy 906 Node reports new event to its Proxy, it can use observe 907 [I-D.ietf-core-observe] at the Proxy for that specific resource. 909 A proxy using the CoAP protocol [RFC7252] SHOULD accept to establish 910 a CoAP observation relationship between the delegated resource and a 911 client as defined in [I-D.ietf-core-observe]. 913 A Sleepy Node may stop updating its delegated resources without 914 explicitly removing its delegated resource (e.g. transition to 915 another proxy after network unreachability detection). An Endpoint 916 can detect this situation when the corresponding delegated resource 917 has expired. Upon receipt of a response with error code 4.04 "Not 918 Found", an Endpoint SHOULD restart resource discovery to determine if 919 the resources are now delegated to another proxy. 921 The interface function is specified as follows: 923 Interaction: EP -> Proxy 925 Method: Defined at registration 926 URI Template: /{+location}{+resource} 928 URI Template Variables: 930 location := This is the Location path returned by the Proxy as a 931 result of a successful registration. 933 resource := This is the relative path to a delegated resource 934 managed by a Sleepy Node. 936 Content-Type: Defined at registration 938 In the example below an EP observes the changes of temperature 939 through the Proxy. 941 Sleepy Proxy EP 942 | | | 943 | | <- GET /sp/0/sen/temp - | 944 | | (observe) | 945 | | | 946 | | -- 2.05 Content "22" -> | 947 | | | 948 | - PUT /sp/0/sen/temp "23" -> | | 949 | | | 950 | <- 2.04 Changed ------------ | | 951 | | | 952 | | -- 2.05 Content "23" -> | 954 6.3. A Node WRITEs to Sleepy Node via Proxy 956 A Configuring Node uses CoAP PUT to write information (such as 957 configuration data) to the Proxy, where the information is destined 958 for a Sleepy Node. Upon change of a delegated resource, an internal 959 flag is set in the Proxy that the specific resource has changed. 960 Next time the Sleepy Node wakes up, the Sleepy Node checks the Proxy 961 for any modification of its delegated resources and reads those 962 changed resources using CoAP GET requests, as shown in Figure 4. The 963 allowed resources that a Configuring Node can write to, and the CoAP 964 Content-Format of those CoAP resources, is determined in the initial 965 registration phase. 967 The following example shows a commissioning tool (EP) changing the 968 name of a Sleepy Node through a Proxy. The Sleepy Node detects this 969 change right after updating its current temperature. 971 Sleepy Proxy EP 972 | | | 973 | | <-- PUT /sp/0/dev/n --- | 974 | | | 975 | | -- 2.04 Changed ------> | 976 | | | 977 | - PUT /sp/0/sen/temp ---> | | 978 | <- 2.04 Changed --------- | | 979 | Payload: --- | | 980 | | | 981 | - GET /sp/0/dev/n ------> | | 982 | | | 983 | <- 2.05 Content --------- | | 984 | | | 986 Req: PUT /sp/0/dev/n 987 Payload: "sensor-1" 988 Res: 2.04 Changed 990 Req: PUT /sp/0/sen/temp 991 Payload: "24" 992 Res: 2.04 Changed, Content-Type: application/link-format 993 Payload: "" 995 Req: GET /sp/0/dev/n 996 Res: 2.05 Content 997 Payload: "sensor-1" 999 6.4. A Node READs information from Sleepy Node via Proxy 1001 A Reading Node uses standard CoAP GET to read information of a Sleepy 1002 Node via a Proxy. However, not all information/resources from the 1003 Sleepy Node may be copied to the Proxy. In that case, the Reading 1004 Node cannot get direct access to resources that are not delegated to 1005 the Proxy. The strategy to follow in that case is to first WRITE to 1006 the Sleepy Node (via the Proxy, Section 6.3) a request for reporting 1007 this missing information; where the request can be fulfilled by the 1008 Sleepy Node the next time the Sleepy Node wakes up. 1010 7. Direct Interface 1012 This section details the functions belonging to the direct interface. 1014 7.1. Sleepy Node REPORTs events directly to Destination Node 1016 When the Sleepy Node needs to report an event to Destination nodes or 1017 groups of Destination nodes present in the subscribers list, it 1018 becomes Awake and then it can use standard CoAP POST unicast or 1019 multicast requests to report the event. 1021 TODO: MC example 1023 7.2. A Sleepy Node READs information from a Server Node 1025 A Sleepy Node while Awake uses standard CoAP GET to read any 1026 information from a Server Node. While the Sleepy Node awaits a CoAP 1027 response containing the requested information, it remains awake. To 1028 increase battery life of Sleepy Nodes, such an operation should not 1029 be performed frequently. 1031 8. Realization with PubSub broker 1033 The PubSub broker [I-D.koster-core-coap-pubsub] can be used to 1034 implement the REPORT function of the Sleepy Node proxy specified in 1035 this document. However, there are some differences to be taken into 1036 account: 1038 - The PubSub broker handles topics. In the case of the proxy the 1039 topics must be equated to resources. 1041 - Clients publish anonymously updates to a topic. In the case of 1042 the proxy, a delegated resource is bound to one given node that is 1043 allowed to update it. For the same functionality, the PubSub 1044 broker must restrict topic updates to one client only. The client 1045 linked to the topic must be visible to the clients which subscribe 1046 to the topic. 1048 In addition, some other functionality needs to be added to the PubSub 1049 broker to satisfy the interaction model shown in Figure 1: 1051 - the READ function from Sleepy Node to proxy is not covered by 1052 the PubSub broker. The PubSub broker needs to piggy-back a "check 1053 topic" on the confirmation of a publication by the proxy. The 1054 proxy can then perform a Read on the signalled topic. 1056 - The interaction "register resources" from proxy to Resource 1057 Directory, shown in Figure 3, is not part of the PubSub broker. 1059 9. IANA Considerations 1061 The new Resource Type (rt=) Link Target Attribute, 'core.sp' needs to 1062 be registered in the "Resource Type (rt=) Link Target Attribute 1063 Values" sub registry under the "Constrained RESTful Environments 1064 (CoRE) Parameters" registry. 1066 10. Security Considerations 1068 For the communication between Sleepy Node and Proxy it MAY be 1069 sufficient to use Layer 2 (MAC) security without the recommended use 1070 of DTLS. However, it must be ascertained that the Sleepy Node can 1071 communicate only with a given secured Proxy. A Sleepy Node may 1072 obtain the Layer 2 network key using the bootstrapping mechanism 1073 described in [I-D.kumar-6lo-selective-bootstrap]. DTLS MUST be used 1074 over link-layer security for further transport-layer protection of 1075 messages between Regular Nodes and Proxies in the network. There are 1076 no special adaptations needed of the DTLS handshake to support Sleepy 1077 Nodes. During the whole handshake, Sleepy Nodes are required to 1078 remain awake to avoid that, in case of small retransmission timers, 1079 the other node may think the handshake message was lost and starts 1080 retransmitting. In view of this, the only key point, therefore, is 1081 that DTLS handshakes are not performed frequently to save on battery 1082 power. Based on the DTLS authentication, also an authorization 1083 method could be implemented so that only authorized nodes can e.g. 1085 - Act as a Proxy for a Sleepy Node. (The Proxy shall be a trusted 1086 device given its important role of storing values of parameters 1087 for the delegated resources); 1089 - READ data from Sleepy Nodes; 1091 - WRITE data to Sleepy Nodes (via the Proxy); 1093 - Receive REPORTs from Sleepy Nodes (direct or via Proxy). 1095 11. Acknowledgements 1097 Much of the text and examples in this document are copied from 1098 [I-D.vial-core-mirror-server]. Matthieu Vial has generously 1099 authorized us to use his text. Rahman Akbar has pointed out the CoAP 1100 dependency of earlier versions. 1102 12. Changelog 1104 RFC editor, please delete this section before publication. 1106 From version 2 to version 3: 1108 Introduced interfaces and copied examples and text from mirror 1109 server draft. 1111 From version 3 to version 4: 1113 Comparison with PubSub Broker completed. 1115 Mistakes in examples removed. 1117 Less dependence on 6LowPAN networks. 1119 Added Design motivation section. 1121 13. References 1123 13.1. Normative References 1125 [I-D.ietf-core-observe] 1126 Hartke, K., "Observing Resources in CoAP", draft-ietf- 1127 core-observe-16 (work in progress), December 2014. 1129 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1130 Requirement Levels", BCP 14, RFC 2119, 1131 DOI 10.17487/RFC2119, March 1997, 1132 . 1134 [RFC5988] Nottingham, M., "Web Linking", RFC 5988, 1135 DOI 10.17487/RFC5988, October 2010, 1136 . 1138 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link 1139 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, 1140 . 1142 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1143 Application Protocol (CoAP)", RFC 7252, 1144 DOI 10.17487/RFC7252, June 2014, 1145 . 1147 [RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for 1148 the Constrained Application Protocol (CoAP)", RFC 7390, 1149 DOI 10.17487/RFC7390, October 2014, 1150 . 1152 13.2. Informative References 1154 [I-D.ietf-core-interfaces] 1155 Shelby, Z., Vial, M., and M. Koster, "CoRE Interfaces", 1156 draft-ietf-core-interfaces-03 (work in progress), July 1157 2015. 1159 [I-D.ietf-core-resource-directory] 1160 Shelby, Z., Koster, M., Bormann, C., and P. Stok, "CoRE 1161 Resource Directory", draft-ietf-core-resource-directory-04 1162 (work in progress), July 2015. 1164 [I-D.koster-core-coap-pubsub] 1165 Koster, M., Keranen, A., and J. Jimenez, "Publish- 1166 Subscribe Broker for the Constrained Application Protocol 1167 (CoAP)", draft-koster-core-coap-pubsub-02 (work in 1168 progress), July 2015. 1170 [I-D.kumar-6lo-selective-bootstrap] 1171 Kumar, S. and P. Stok, "Security Bootstrapping over IEEE 1172 802.15.4 in selective order", draft-kumar-6lo-selective- 1173 bootstrap-00 (work in progress), March 2015. 1175 [I-D.vial-core-mirror-server] 1176 Vial, M., "CoRE Mirror Server", draft-vial-core-mirror- 1177 server-01 (work in progress), April 2013. 1179 [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service 1180 Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, 1181 . 1183 Authors' Addresses 1185 Teresa Zotti 1186 Philips Research 1187 High Tech Campus 34 1188 Eindhoven 5656 AE 1189 The Netherlands 1191 Phone: +31 6 21175346 1192 Email: teresa.zotti@philips.com 1194 Peter van der Stok 1195 Consultant 1197 Phone: +31 492474673 1198 Email: consultancy@vanderstok.org 1200 Esko Dijk 1201 Philips Research 1202 High Tech Campus 34 1203 Eindhoven 5656 AE 1204 The Netherlands 1206 Phone: +31 6 55408986 1207 Email: esko.dijk@philips.com