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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'RFC5246' is defined on line 1166, but no explicit reference was found in the text == Unused Reference: 'RFC6347' is defined on line 1189, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-dice-profile' is defined on line 1265, but no explicit reference was found in the text == Unused Reference: 'I-D.keoh-dice-multicast-security' is defined on line 1270, but no explicit reference was found in the text == Unused Reference: 'I-D.kumar-dice-dtls-relay' is defined on line 1276, but no explicit reference was found in the text == Unused Reference: 'I-D.richardson-6tisch--security-6top' is defined on line 1281, but no explicit reference was found in the text ** Downref: Normative reference to an Experimental RFC: RFC 4764 ** Obsolete normative reference: RFC 5246 (Obsoleted by RFC 8446) ** Downref: Normative reference to an Informational RFC: RFC 5548 ** Downref: Normative reference to an Informational RFC: RFC 5673 ** Downref: Normative reference to an Informational RFC: RFC 5826 ** Downref: Normative reference to an Informational RFC: RFC 5867 ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Downref: Normative reference to an Experimental RFC: RFC 6997 ** Downref: Normative reference to an Experimental RFC: RFC 6998 ** Downref: Normative reference to an Informational RFC: RFC 7102 ** Downref: Normative reference to an Informational RFC: RFC 7416 == Outdated reference: A later version (-12) exists of draft-ietf-roll-trickle-mcast-11 -- Possible downref: Non-RFC (?) normative reference: ref. 'IEEE802.15.4' -- Possible downref: Non-RFC (?) normative reference: ref. 'G.9959' == Outdated reference: A later version (-17) exists of draft-ietf-dice-profile-10 == Outdated reference: A later version (-05) exists of draft-richardson-6tisch--security-6top-04 Summary: 11 errors (**), 0 flaws (~~), 11 warnings (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Roll A. Brandt 3 Internet-Draft Sigma Designs 4 Intended status: Standards Track E. Baccelli 5 Expires: October 28, 2015 INRIA 6 R. Cragie 7 ARM Ltd. 8 P. van der Stok 9 Consultant 10 April 26, 2015 12 Applicability Statement: The use of the RPL protocol suite in Home 13 Automation and Building Control 14 draft-ietf-roll-applicability-home-building-10 16 Abstract 18 The purpose of this document is to provide guidance in the selection 19 and use of protocols from the RPL protocol suite to implement the 20 features required for control in building and home environments. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on October 28, 2015. 39 Copyright Notice 41 Copyright (c) 2015 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (http://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 57 1.1. Relationship to other documents . . . . . . . . . . . . . 4 58 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 59 1.3. Required Reading . . . . . . . . . . . . . . . . . . . . 5 60 1.4. Out of scope requirements . . . . . . . . . . . . . . . . 5 61 2. Deployment Scenario . . . . . . . . . . . . . . . . . . . . . 5 62 2.1. Network Topologies . . . . . . . . . . . . . . . . . . . 6 63 2.2. Traffic Characteristics . . . . . . . . . . . . . . . . . 7 64 2.2.1. General . . . . . . . . . . . . . . . . . . . . . . . 8 65 2.2.2. Source-sink (SS) communication paradigm . . . . . . . 8 66 2.2.3. Publish-subscribe (PS, or pub/sub)) communication 67 paradigm . . . . . . . . . . . . . . . . . . . . . . 9 68 2.2.4. Peer-to-peer (P2P) communication paradigm . . . . . . 9 69 2.2.5. Peer-to-multipeer (P2MP) communication paradigm . . . 9 70 2.2.6. Additional considerations: Duocast and N-cast . . . . 10 71 2.2.7. RPL applicability per communication paradigm . . . . 10 72 2.3. Layer-2 applicability . . . . . . . . . . . . . . . . . . 11 73 3. Using RPL to meet Functional Requirements . . . . . . . . . . 12 74 4. RPL Profile . . . . . . . . . . . . . . . . . . . . . . . . . 12 75 4.1. RPL Features . . . . . . . . . . . . . . . . . . . . . . 13 76 4.1.1. RPL Instances . . . . . . . . . . . . . . . . . . . . 13 77 4.1.2. Storing vs. Non-Storing Mode . . . . . . . . . . . . 13 78 4.1.3. DAO Policy . . . . . . . . . . . . . . . . . . . . . 14 79 4.1.4. Path Metrics . . . . . . . . . . . . . . . . . . . . 14 80 4.1.5. Objective Function . . . . . . . . . . . . . . . . . 14 81 4.1.6. DODAG Repair . . . . . . . . . . . . . . . . . . . . 14 82 4.1.7. Multicast . . . . . . . . . . . . . . . . . . . . . . 14 83 4.1.8. Security . . . . . . . . . . . . . . . . . . . . . . 15 84 4.1.9. P2P communications . . . . . . . . . . . . . . . . . 16 85 4.1.10. IPv6 address configuration . . . . . . . . . . . . . 16 86 4.2. Layer 2 features . . . . . . . . . . . . . . . . . . . . 16 87 4.2.1. Specifics about layer-2 . . . . . . . . . . . . . . . 16 88 4.2.2. Services provided at layer-2 . . . . . . . . . . . . 16 89 4.2.3. 6LowPAN options assumed . . . . . . . . . . . . . . . 17 90 4.2.4. Mesh Link Establishment (MLE) and other things . . . 17 91 4.3. Recommended Configuration Defaults and Ranges . . . . . . 17 92 4.3.1. Trickle parameters . . . . . . . . . . . . . . . . . 17 93 4.3.2. Other Parameters . . . . . . . . . . . . . . . . . . 17 94 5. MPL Profile . . . . . . . . . . . . . . . . . . . . . . . . . 18 95 5.1. Recommended configuration Defaults and Ranges . . . . . . 18 96 5.1.1. Real-Time optimizations . . . . . . . . . . . . . . . 18 97 5.1.2. Trickle parameters . . . . . . . . . . . . . . . . . 18 98 5.1.3. Other parameters . . . . . . . . . . . . . . . . . . 19 99 6. Manageability Considerations . . . . . . . . . . . . . . . . 20 100 7. Security Considerations . . . . . . . . . . . . . . . . . . . 20 101 7.1. Security considerations during initial deployment . . . . 20 102 7.2. Security Considerations during incremental deployment . . 21 103 7.3. Security Considerations for P2P uses . . . . . . . . . . 22 104 7.4. MPL routing . . . . . . . . . . . . . . . . . . . . . . . 22 105 7.5. RPL Security features . . . . . . . . . . . . . . . . . . 22 106 8. Other related protocols . . . . . . . . . . . . . . . . . . . 22 107 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 108 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 109 11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 23 110 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 111 12.1. Normative References . . . . . . . . . . . . . . . . . . 25 112 12.2. Informative References . . . . . . . . . . . . . . . . . 27 113 Appendix A. RPL shortcomings in home and building deployments . 29 114 A.1. Risk of undesired long P2P routes . . . . . . . . . . . . 29 115 A.1.1. Traffic concentration at the root . . . . . . . . . . 29 116 A.1.2. Excessive battery consumption in source nodes . . . . 29 117 A.2. Risk of delayed route repair . . . . . . . . . . . . . . 29 118 A.2.1. Broken service . . . . . . . . . . . . . . . . . . . 30 119 Appendix B. Communication failures . . . . . . . . . . . . . . . 30 120 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 122 1. Introduction 124 The primary purpose of this document is to give guidance in the use 125 of the Routing Protocol for Low power and lossy networks (RPL) 126 protocol suite in two application domains: 128 o Home automation 130 o Building automation 132 The guidance is based on the features required by the requirements 133 documents "Home Automation Routing Requirements in Low-Power and 134 Lossy Networks" [RFC5826] and "Building Automation Routing 135 Requirements in Low-Power and Lossy Networks" [RFC5867] respectively. 136 The Advanced Metering Infrastructure is also considered where 137 appropriate. The applicability domains distinguish themselves in the 138 way they are operated, their performance requirements, and the most 139 likely network structures. An abstract set of distinct communication 140 paradigms is then used to frame the applicability domains. 142 Home automation and building automation application domains share a 143 substantial number of properties: 145 o In both domains, the network can be disconnected from the ISP and 146 must still continue to provide control to the occupants of the 147 home/building. Routing needs to be possible independent of the 148 existence of a border router 150 o Both domains are subject to unreliable links but require instant 151 and very reliable reactions. This has impact on routing because 152 of timeliness and multipath routing. 154 The differences between the two application domains mostly appear in 155 commissioning, maintenance and the user interface, which do not 156 typically affect routing. Therefore, the focus of this applicability 157 document is on reliability, timeliness, and local routing. 159 1.1. Relationship to other documents 161 The Routing Over Low power and Lossy networks (ROLL) working group 162 has specified a set of routing protocols for Low-Power and Lossy 163 Networks (LLN) [RFC6550]. This applicability text describes a subset 164 of those protocols and the conditions under which the subset is 165 appropriate and provides recommendations and requirements for the 166 accompanying parameter value ranges. 168 In addition, an extension document has been produced specifically to 169 provide a solution for reactive discovery of point-to-point routes in 170 LLNs [RFC6997]. The present applicability document provides 171 recommendations and requirements for the accompanying parameter value 172 ranges. 174 A common set of security threats are described in [RFC7416]. The 175 applicability statements complement the security threats document by 176 describing preferred security settings and solutions within the 177 applicability statement conditions. This applicability statement 178 recommends lighter weight security solutions appropriate for home and 179 building environments and indicates why these solutions are 180 appropriate. 182 1.2. Terminology 184 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 185 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 186 document are to be interpreted as described in [RFC2119]. 188 Additionally, this document uses terminology from [RFC6997], 189 [I-D.ietf-roll-trickle-mcast], [RFC7102], [IEEE802.15.4], and 190 [RFC6550]. 192 1.3. Required Reading 194 Applicable requirements are described in [RFC5826] and [RFC5867]. A 195 survey of the application field is described in [BCsurvey]. 197 1.4. Out of scope requirements 199 The considered network diameter is limited to a maximum diameter of 200 10 hops and a typical diameter of 5 hops, which captures the most 201 common cases in home automation and building control networks. 203 This document does not consider the applicability of Routing Protocol 204 for Low-Power and Lossy Networks (RPL)-related specifications for 205 urban and industrial applications [RFC5548], [RFC5673], which may 206 exhibit significantly larger network diameters. 208 2. Deployment Scenario 210 The use of communications networks in buildings is essential to 211 satisfy energy saving regulations. Environmental conditions of 212 buildings can be adapted to suit the comfort of the individuals 213 present inside. Consequently when no one is present, energy 214 consumption can be reduced. Cost is the main driving factor behind 215 deployment of wireless networking in buildings, especially in the 216 case of retrofitting, where wireless connectivity saves costs 217 incurred due to cabling and building modifications. 219 A typical home automation network is comprised of less than 100 220 nodes. Large building deployments may span 10,000 nodes but to 221 ensure uninterrupted service of light and air conditioning systems in 222 individual zones of the building, nodes are typically organized in 223 sub-networks. Each sub-network in a building automation deployment 224 typically contains tens to hundreds of nodes, and for critical 225 operations may operate independently from the other sub-networks. 227 The main purpose of the home or building automation network is to 228 provide control over light and heating/cooling resources. User 229 intervention via wall controllers is combined with movement, light 230 and temperature sensors to enable automatic adjustment of window 231 blinds, reduction of room temperature, etc. In general, the sensors 232 and actuators in a home or building typically have fixed physical 233 locations and will remain in the same home or building automation 234 network. 236 People expect an immediate and reliable response to their presence or 237 actions. For example, a light not switching on after entry into a 238 room may lead to confusion and a profound dissatisfaction with the 239 lighting product. 241 Monitoring of functional correctness is at least as important as 242 timely responses. Devices typically communicate their status 243 regularly and send alarm messages notifying a malfunction of 244 controlled equipment or network. 246 In building control, the infrastructure of the building management 247 network can be shared with the security/access, the Internet Protocol 248 (IP) telephony, and the fire/alarm networks. This approach has a 249 positive impact on the operation and cost of the network; however, 250 care should be taken to ensure that the availability of the building 251 management network does not become compromised beyond the ability for 252 critical functions to perform adequately. 254 In homes, the entertainment network for audio/video streaming and 255 gaming has different requirements, where the most important 256 requirement is the need for high bandwidth not typically needed for 257 home or building control. It is therefore expected that the 258 entertainment network in the home will mostly be separate from the 259 control network, which also lessens the impact on availability of the 260 control network 262 2.1. Network Topologies 264 In general, the home automation network or building control network 265 consists of wired and wireless sub-networks. In large buildings 266 especially, the wireless sub-networks can be connected to an IP 267 backbone network where all infrastructure services are located, such 268 as Domain Name System (DNS), automation servers, etc. 270 The wireless sub-network can be configured according to any of the 271 following topologies: 273 o A stand-alone network of 10-100 nodes without border router. This 274 typically occurs in the home with a stand-alone control network, 275 in low cost buildings, and during installation of high end control 276 systems in buildings. 278 o A connected network with one border router. This configuration 279 will happen in homes where home appliances are controlled from 280 outside the home, possibly via a smart phone, and in many building 281 control scenarios. 283 o A connected network with multiple border routers. This will 284 typically happen in installations of large buildings. 286 Many of the nodes are battery-powered and may be sleeping nodes which 287 wake up according to clock signals or external events. 289 In a building control network, for a large installation with multiple 290 border routers, sub-networks often overlap both geographically and 291 from a wireless coverage perspective. Due to two purposes of the 292 network, (i) direct control and (ii) monitoring, there may exist two 293 types of routing topologies in a given sub-network: (i) a tree-shaped 294 collection of routes spanning from a central building controller via 295 the border router, on to destination nodes in the sub-network; and/or 296 (ii) a flat, un-directed collection of intra-network routes between 297 functionally related nodes in the sub-network. 299 The majority of nodes in home and building automation networks are 300 typically class 0 devices [RFC7228], such as individual wall 301 switches. Only a few nodes (such as multi-purpose remote controls) 302 are more expensive Class 1 devices, which can afford more memory 303 capacity. 305 2.2. Traffic Characteristics 307 Traffic may enter the network originating from a central controller 308 or it may originate from an intra-network node. The majority of 309 traffic is light-weight point-to-point control style; e.g. Put-Ack 310 or Get-Response. There are however exceptions. Bulk data transfer 311 is used for firmware update and logging, where firmware updates enter 312 the network and logs leave the network. Group communication is used 313 for service discovery or to control groups of nodes, such as light 314 fixtures. 316 Often, there is a direct physical relation between a controlling 317 sensor and the controlled equipment. For example the temperature 318 sensor and room controller are located in the same room sharing the 319 same climate conditions. Consequently, the bulk of senders and 320 receivers are separated by a distance that allows one-hop direct path 321 communication. A graph of the communication will show several fully 322 connected subsets of nodes. However, due to interference, multipath 323 fading, reflection and other transmission mechanisms, the one-hop 324 direct path may be temporally disconnected. For reliability 325 purposes, it is therefore essential that alternative n-hop 326 communication routes exist for quick error recovery. (See Appendix B 327 for motivation.) 329 Looking over time periods of a day, the networks are very lightly 330 loaded. However, bursts of traffic can be generated by e.g. 331 incessant pushing of the button of a remote control, the occurrence 332 of a defect, and other unforeseen events. Under those conditions, 333 the timeliness must nevertheless be maintained. Therefore, measures 334 are necessary to remove any unnecessary traffic. Short routes are 335 preferred. Long multi-hop routes via the border router, should be 336 avoided whenever possible. 338 Group communication is essential for lighting control. For example, 339 once the presence of a person is detected in a given room, lighting 340 control applies to that room only and no other lights should be 341 dimmed, or switched on/off. In many cases, this means that a 342 multicast message with a 1-hop and 2-hop radius would suffice to 343 control the required lights. The same argument holds for Heating, 344 Ventilating, and Air Conditioning (HVAC) and other climate control 345 devices. To reduce network load, it is advisable that messages to 346 the lights in a room are not distributed any further in the mesh than 347 necessary based on intended receivers. 349 An example of an office surface is shown in [office-light], and the 350 current use of wireless lighting control products is shown in 351 [occuswitch]. 353 2.2.1. General 355 Whilst air conditioning and other environmental-control applications 356 may accept response delays of tens of seconds or longer, alarm and 357 light control applications may be regarded as soft real-time systems. 358 A slight delay is acceptable, but the perceived quality of service 359 degrades significantly if response times exceed 250 ms. If the light 360 does not turn on at short notice, a user may activate the controls 361 again, thus causing a sequence of commands such as 362 Light{on,off,on,off,..} or Volume{up,up,up,up,up,...}. In addition 363 the repetitive sending of commands creates an unnecessary loading of 364 the network, which in turn increases the bad responsiveness of the 365 network. 367 2.2.2. Source-sink (SS) communication paradigm 369 This paradigm translates to many sources sending messages to the same 370 sink, sometimes reachable via the border router. As such, source- 371 sink (SS) traffic can be present in home and building networks. The 372 traffic may be generated by environmental sensors (often present in a 373 wireless sub-network) which push periodic readings to a central 374 server. The readings may be used for pure logging, or more often, 375 processed to adjust light, heating and ventilation. Alarm sensors 376 may also generate SS style traffic. The central server in a home 377 automation network will be connected mostly to a wired network 378 segment of the home network, although it is likely that cloud 379 services will also be used. The central server in a building 380 automation network may be connected to a backbone or be placed 381 outside the building. 383 With regards to message latency, most SS transmissions can tolerate 384 worst-case delays measured in tens of seconds. Fire detectors, 385 however, represent an exception; For example, special provisions with 386 respect to the location of the Fire detectors and the smoke dampers 387 need to be put in place to meet the stringent delay requirements 388 measured in seconds. 390 2.2.3. Publish-subscribe (PS, or pub/sub)) communication paradigm 392 This paradigm translates to a number of devices expressing their 393 interest for a service provided by a server device. For example, a 394 server device can be a sensor delivering temperature readings on the 395 basis of delivery criteria, like changes in acquisition value or age 396 of the latest acquisition. In building automation networks, this 397 paradigm may be closely related to the SS paradigm given that 398 servers, which are connected to the backbone or outside the building, 399 can subscribe to data collectors that are present at strategic places 400 in the building automation network. The use of PS will probably 401 differ significantly from installation to installation. 403 2.2.4. Peer-to-peer (P2P) communication paradigm 405 This paradigm translates to a device transferring data to another 406 device often connected to the same sub-network. Peer-to-peer (P2P) 407 traffic is a common traffic type in home automation networks. Most 408 building automation networks rely on P2P traffic, described in the 409 next paragraph. Other building automation networks rely on P2P 410 control traffic between controls and a local controller box for 411 advanced group control. A local controller box can be further 412 connected to service control boxes, thus generating more SS or PS 413 traffic. 415 P2P traffic is typically generated by remote controls and wall 416 controllers which push control messages directly to light or heat 417 sources. P2P traffic has a stringent requirement for low latency 418 since P2P traffic often carries application messages that are invoked 419 by humans. As mentioned in Section 2.2.1 application messages should 420 be delivered within a few hundred milliseconds - even when 421 connections fail momentarily. 423 2.2.5. Peer-to-multipeer (P2MP) communication paradigm 425 This paradigm translates to a device sending a message as many times 426 as there are destination devices. Peer-to-multipeer (P2MP) traffic 427 is common in home and building automation networks. Often, a 428 thermostat in a living room responds to temperature changes by 429 sending temperature acquisitions to several fans and valves 430 consecutively. This paradigm is also closely related to the PS 431 paradigm in the case where a single server device has multiple 432 subscribers. 434 2.2.6. Additional considerations: Duocast and N-cast 436 This paradigm translates to a device sending a message to many 437 destinations in one network transfer invocation. Multicast is well 438 suited for lighting where a presence sensor sends a presence message 439 to a set of lighting devices. Multicast increases the probability 440 that the message is delivered within the strict time constraints. 441 The recommended multicast algorithm (e.g. 442 [I-D.ietf-roll-trickle-mcast]) assures that messages are delivered to 443 ALL intended destinations. 445 2.2.7. RPL applicability per communication paradigm 447 In the case of the SS paradigm applied to a wireless sub-network to a 448 server reachable via a border router, the use of RPL [RFC6550] in 449 non-storing mode is appropriate. Given the low resources of the 450 devices, source routing will be used from the border router to the 451 destination in the wireless sub-network for messages generated 452 outside the mesh network. No specific timing constraints are 453 associated with the SS type messages so network repair does not 454 violate the operational constraints. When no SS traffic takes place, 455 it is good practice to load only RPL code enabling P2P mode of 456 operation [RFC6997] to reduce the code size and satisfy memory 457 requirements. 459 P2P-RPL [RFC6997] is required for all P2P and P2MP traffic taking 460 place between nodes within a wireless sub-network (excluding the 461 border router) to assure responsiveness. Source and destination 462 devices are typically physically close based on room layout. 463 Consequently, most P2P and P2MP traffic is 1-hop or 2-hop traffic. 464 Appendix A explains why P2P-RPL is preferable to RPL for this type of 465 communication. Appendix B explains why reliability measures such as 466 multi-path routing are necessary even when 1-hop communication 467 dominates. 469 Additional advantages of P2P-RPL for home and building automation 470 networks are, for example: 472 o Individual wall switches are typically inexpensive class 0 devices 473 [RFC7228] with extremely low memory capacities. Multi-purpose 474 remote controls for use in a home environment typically have more 475 memory but such devices are asleep when there is no user activity. 476 P2P-RPL reactive discovery allows a node to wake up and find new 477 routes within a few seconds while memory constrained nodes only 478 have to keep routes to relevant targets. 480 o The reactive discovery features of P2P-RPL ensure that commands 481 are normally delivered within the 250 ms time window. When 482 connectivity needs to be restored, discovery is typically 483 completed within seconds. In most cases, an alternative (earlier 484 discovered) route will work and route rediscovery is not 485 necessary. 487 o Broadcast storms typically associated with route discovery for Ad 488 hoc On-Demand Distance Vector (AODV) [RFC3561] are less disruptive 489 for P2P-RPL. P2P-RPL has a "STOP" bit which is set by the target 490 of a route discovery to notify all other nodes that no more 491 Directed Acyclic Graph (DAG) Information Option (DIO) messages 492 should be forwarded for this temporary DAG. Something looking 493 like a broadcast storm may happen when no target is responding 494 however, in this case, the Trickle suppression mechanism kicks in, 495 limiting the number of DIO forwards in dense networks. 497 Due to the limited memory of the majority of devices, P2P-RPL SHOULD 498 be deployed with source routing in non-storing mode as explained in 499 Section 4.1.2. 501 Multicast with Multicast Protocol for Low power and Lossy Networks 502 (MPL) [I-D.ietf-roll-trickle-mcast] is preferably deployed for N-cast 503 over the wireless network. Configuration constraints that are 504 necessary to meet reliability and timeliness with MPL are discussed 505 in Section 4.1.7. 507 2.3. Layer-2 applicability 509 This document applies to [IEEE802.15.4] and [G.9959] which are 510 adapted to IPv6 by the adaption layers [RFC4944] and [RFC7428]. 511 Other layer-2 technologies, accompanied by an "IP over Foo" 512 specification, are also relevant provided there is no frame size 513 issue, and there are link layer acknowledgements. 515 The above mentioned adaptation layers leverage on the compression 516 capabilities of [RFC6554] and [RFC6282]. Header compression allows 517 small IP packets to fit into a single layer 2 frame even when source 518 routing is used. A network diameter limited to 5 hops helps to 519 achieve this even while using source routing. 521 Dropped packets are often experienced in the targeted environments. 522 Internet Control Message Protocol (ICMP), User Datagram Protocol 523 (UDP) and even Transmission Control Protocol (TCP) flows may benefit 524 from link layer unicast acknowledgments and retransmissions. Link 525 layer unicast acknowledgments SHOULD be enabled when [IEEE802.15.4] 526 or [G.9959] is used with RPL and P2P-RPL. 528 3. Using RPL to meet Functional Requirements 530 Several features required by [RFC5826], [RFC5867] challenge the P2P 531 paths provided by RPL. Appendix A reviews these challenges. In some 532 cases, a node may need to spontaneously initiate the discovery of a 533 path towards a desired destination that is neither the root of a DAG, 534 nor a destination originating Destination Advertisement Object (DAO) 535 signalling. Furthermore, P2P paths provided by RPL are not 536 satisfactory in all cases because they involve too many intermediate 537 nodes before reaching the destination. 539 P2P-RPL [RFC6997] SHOULD be used in home automation and building 540 control networks, as point-to-point style traffic is substantial and 541 route repair needs to be completed within seconds. P2P-RPL provides 542 a reactive mechanism for quick, efficient and root-independent route 543 discovery/repair. The use of P2P-RPL furthermore allows data traffic 544 to avoid having to go through a central region around the root of the 545 tree, and drastically reduces path length [SOFT11] [INTEROP12]. 546 These characteristics are desirable in home and building automation 547 networks because they substantially decrease unnecessary network 548 congestion around the root of the tree. 550 When more reliability is required, P2P-RPL enables the establishment 551 of multiple independent paths. For 1-hop destinations this means 552 that one 1-hop communication and a second 2-hop communication take 553 place via a neighbouring node. Such a pair of redundant 554 communication paths can be achieved by using MPL where the source is 555 a MPL forwarder, while a second MPL forwarder is 1 hop away from both 556 the source and the destination node. When the source multicasts the 557 message, it may be received by both the destination and the 2nd 558 forwarder. The 2nd forwarder forwards the message to the 559 destination, thus providing two routes from sender to destination. 561 To provide more reliability with multiple paths, P2P-RPL can maintain 562 two independent P2P source routes per destination, at the source. 563 Good practice is to use the paths alternately to assess their 564 existence. When one P2P path has failed (possibly only temporarily), 565 as described in Appendix B, the alternative P2P path can be used 566 without discarding the failed path. The failed P2P path, unless 567 proven to work again, can be safely discarded after a timeout 568 (typically 15 minutes). A new route discovery is done when the 569 number of P2P paths is exhausted due to persistent link failures. 571 4. RPL Profile 573 P2P-RPL SHOULD be used in home automation and building control 574 networks. Its reactive discovery allows for low application response 575 times even when on-the-fly route repair is needed. Non-storing mode 576 SHOULD be used to reduce memory consumption in repeaters with 577 constrained memory when source routing is used. 579 4.1. RPL Features 581 An important constraint on the application of RPL is the presence of 582 sleeping nodes. 584 For example, in a stand-alone network, the master node (or 585 coordinator) providing the logical layer-2 identifier and unique node 586 identifiers to connected nodes may be a remote control which returns 587 to sleep once new nodes have been added. Due to the absence of the 588 border router, there may be no global routable prefixes at all. 589 Likewise, there may be no authoritative always-on root node since 590 there is no border router to host this function. 592 In a network with a border router and many sleeping nodes, there may 593 be battery powered sensors and wall controllers configured to contact 594 other nodes in response to events and then return to sleep. Such 595 nodes may never detect the announcement of new prefixes via 596 multicast. 598 In each of the above mentioned constrained deployments, a link layer 599 node (e.g. coordinator or master) SHOULD assume the role of 600 authoritative root node, transmitting unicast Router Advertisement 601 (RA) messages with a Unique Local Address (ULA) prefix information 602 option to nodes during the joining process to prepare the nodes for a 603 later operational phase, where a border router is added. 605 A border router SHOULD be designed to be aware of sleeping nodes in 606 order to support the distribution of updated global prefixes to such 607 sleeping nodes. 609 4.1.1. RPL Instances 611 When operating P2P-RPL on a stand-alone basis, there is no 612 authoritative root node maintaining a permanent RPL Direction- 613 Oriented Directed Acyclic Graph (DODAG). A node MUST be able to join 614 at least one RPL instance, as a new, temporary instance is created 615 during each P2P-RPL route discovery operation. A node MAY be 616 designed to join multiple RPL instances. 618 4.1.2. Storing vs. Non-Storing Mode 620 Non-storing mode MUST be used to cope with the extremely constrained 621 memory of a majority of nodes in the network (such as individual 622 light switches). 624 4.1.3. DAO Policy 626 Nodes send DAO messages to establish downward paths from the root to 627 themselves. DAO messages are not acknowledged in networks composed 628 of battery operated field devices in order to minimize the power 629 consumption overhead associated with path discovery. The DAO 630 messages build up a source route because the nodes MUST be in non- 631 storing mode. 633 If devices in LLNs participate in multiple RPL instances and DODAGs, 634 both the RPLInstance ID and the DODAGID SHOULD be included in the 635 DAO. 637 4.1.4. Path Metrics 639 Expected Transmission Count (ETX) is the RECOMMENDED metric. 640 [RFC6551] provides other options. 642 Packets from asymmetric and/or unstable channels SHOULD be deleted at 643 layer 2. 645 4.1.5. Objective Function 647 Objective Function 0 (OF0) MUST be the Objective Function. Other 648 Objective Functions MAY be used when dictated by circumstances. 650 4.1.6. DODAG Repair 652 Since P2P-RPL only creates DODAGs on a temporary basis during route 653 repair or route discovery, there is no need to repair DODAGs. 655 For SS traffic, local repair is sufficient. The accompanying process 656 is known as poisoning and is described in Section 8.2.2.5 of 657 [RFC6550]. Given that the majority of nodes in the building do not 658 physically move around, creating new DODAGs should not happen 659 frequently. 661 4.1.7. Multicast 663 Commercial lighting deployments may have a need for multicast to 664 distribute commands to a group of lights in a timely fashion. 665 Several mechanisms exist for achieving such functionality; 666 [I-D.ietf-roll-trickle-mcast] is the RECOMMENDED protocol for home 667 and building deployments. This section relies heavily on the 668 conclusions of [RT-MPL]. 670 At reception of a packet, the MPL forwarder starts a series of 671 consecutive trickle timer intervals, where the first interval has a 672 minimum size of Imin. Each consecutive interval is twice as long as 673 the former with a maximum value of Imax. There is a maximum number 674 of intervals given by max_expiration. For each interval of length I, 675 a time t is randomly chosen in the period [I/2, I]. For a given 676 packet, p, MPL counts the number of times it receives p during the 677 period [0, t] in a counter c. At time t, MPL re-broadcasts p when c 678 < k, where k is a predefined constant with a value k > 0. 680 The density of forwarders and the frequency of message generation are 681 important aspects to obtain timeliness during control operations. A 682 high frequency of message generation can be expected when a remote 683 control button is incessantly pressed, or when alarm situations 684 arise. 686 Guaranteeing timeliness is intimately related to the density of the 687 MPL routers. In ideal circumstances the message is propagated as a 688 single wave through the network, such that the maximum delay is 689 related to the number of hops times the smallest repetition interval 690 of MPL. Each forwarder that receives the message passes the message 691 on to the next hop by repeating the message. When several copies of 692 a message reach the forwarder, it is specified that the copy need not 693 be repeated. Repetition of the message can be inhibited by a small 694 value of k. To assure timeliness, the value of k should be chosen 695 high enough to make sure that messages are repeated at the first 696 arrival of the message in the forwarder. However, a network that is 697 too dense leads to a saturation of the medium that can only be 698 prevented by selecting a low value of k. Consequently, timeliness is 699 assured by choosing a relatively high value of k but assuring at the 700 same time a low enough density of forwarders to reduce the risk of 701 medium saturation. Depending on the reliability of the network 702 channels, it is advisable to choose the network such that at least 2 703 forwarders per hop repeat messages to the same set of destinations. 705 There are no rules about selecting forwarders for MPL. In buildings 706 with central management tools, the forwarders can be selected, but in 707 the home is not possible to automatically configure the forwarder 708 topology at the time of writing this document. 710 4.1.8. Security 712 RPL MAY use unsecured messages to reduce message size. If there is a 713 single node that uses unsecured RPL messages, link-layer security 714 MUST be present.(see Section 7). If RPL is used with secured 715 messages [RFC6550], the following RPL security parameter values 716 SHOULD be used: 718 o Counter Time Flag: T = '0': Do not use timestamp in the Counter 719 Field. Counters based on timestamps are typically more applicable 720 to industrial networks where strict timing synchronization between 721 nodes is often implemented. Home and building networks typically 722 do not implement such strict timing synchronization therefore a 723 monotonically increasing counter is more appropriate. 725 o Algorithm = '0': Use Counter with Cipher Block Chaining Message 726 Authentication Code (CBC-MAC Mode) (CCM) with Advanced Encryption 727 Standard (AES)-128. This is the only assigned mode at present 729 o Key Identifier Mode; KIM = '10': Use group key, Key Source 730 present, Key Index present. Given the relatively confined 731 perimeter of a home or building network, a group key is usually 732 sufficient to protect RPL messages sent between nodes. The use of 733 the Key Source field allows multiple group keys to be used within 734 the network. 736 o Security Level; LVL = 0: Use MAC-32.This is recommended as 737 integrity protection for RPL messages is the basic requirement. 738 Encryption is unlikely to be necessary given the relatively non- 739 confidential nature of RPL message payloads. 741 4.1.9. P2P communications 743 [RFC6997] MUST be used to accommodate P2P traffic, which is typically 744 substantial in home and building automation networks. 746 4.1.10. IPv6 address configuration 748 Assigned IP addresses MUST be routable and unique within the routing 749 domain [RFC5889]. 751 4.2. Layer 2 features 753 No particular requirements exist for layer 2 but for the ones cited 754 in the IP over Foo RFCs. (See Section 2.3) 756 4.2.1. Specifics about layer-2 758 Not applicable 760 4.2.2. Services provided at layer-2 762 Not applicable 764 4.2.3. 6LowPAN options assumed 766 Not applicable 768 4.2.4. Mesh Link Establishment (MLE) and other things 770 Not applicable 772 4.3. Recommended Configuration Defaults and Ranges 774 The following sections describe the recommended parameter values for 775 P2P-RPL and Trickle. 777 4.3.1. Trickle parameters 779 Trickle is used to distribute network parameter values to all nodes 780 without stringent time restrictions. The recommended Trickle 781 parameter values are: 783 o DIOIntervalMin 4 = 16 ms 785 o DIOIntervalDoublings 14 787 o DIORedundancyConstant 1 789 When a node sends a changed DIO, this is an inconsistency and forces 790 the receiving node to respond within Imin. So when something happens 791 which affects the DIO, the change is ideally communicated to a node, 792 n hops away, within n times Imin. Often, dependent on the node 793 density, packets are lost, or not sent, leading to larger delays. 795 In general we can expect DIO changes to propagate within 1 to 3 796 seconds within the envisaged networks. 798 When nothing happens, the DIO sending interval increases to 4.37 799 minutes, thus drastically reducing the network load. When a node 800 does not receive DIO messages during more than 10 minutes it can 801 safely conclude the connection with other nodes has been lost. 803 4.3.2. Other Parameters 805 This section discusses the P2P-RPL parameters. 807 P2P-RPL [RFC6997] provides the features requested by [RFC5826] and 808 [RFC5867]. P2P-RPL uses a subset of the frame formats and features 809 defined for RPL [RFC6550] but may be combined with RPL frame flows in 810 advanced deployments. 812 The recommended parameter values for P2P-RPL are: 814 o MinHopRankIncrease 1 816 o MaxRankIncrease 0 818 o MaxRank 6 820 o Objective function: OF0 822 5. MPL Profile 824 MPL is used to distribute values to groups of devices. Using MPL, 825 based on the Trickle algorithm, timeliness should also be guaranteed. 826 A deadline of 200 ms needs to be met when human action is followed by 827 an immediately observable action such as switching on lights. The 828 deadline needs to be met in a building where the number of hops from 829 seed to destination varies between 1 and 10. 831 5.1. Recommended configuration Defaults and Ranges 833 5.1.1. Real-Time optimizations 835 When the network is heavily loaded, MAC delays contribute 836 significantly to the end to end delays when MPL intervals between 10 837 to 100 ms are used to meet the 200 ms deadline. It is possible to 838 set the number of buffers in the MAC to 1 and set the number of Back- 839 off repetitions to 1. The number of MPL repetitions compensates for 840 the reduced probability of transmission per MAC invocation [RT-MPL]. 842 In addition, end to end delays and message losses are reduced, by 843 adding a real-time layer between MPL and MAC to throw away the 844 earliest messages (exploiting the MPL message numbering) and favour 845 the most recent ones. 847 5.1.2. Trickle parameters 849 This section proposes values for the Trickle parameters used by MPL 850 for the distribution of packets that need to meet a 200 ms deadline. 851 The probability of meeting the deadline is increased by (1) choosing 852 a small Imin value,(2) reducing the number of MPL intervals thus 853 reducing the load, and (3) reducing the number of MPL forwarders to 854 also reduce the load. 856 The consequence of this approach is that the value of k can be larger 857 than 1 because network load reduction is already guaranteed by the 858 network configuration. 860 Under the condition that the density of MPL repeaters can be limited, 861 it is possible to choose low MPL repeat intervals (Imin) connected to 862 k values such that k>1. The minimum value of k is related to: 864 o Value of Imin. The length of Imin determines the number of 865 packets that can be received within the listening period of Imin. 867 o Number of repeaters receiving the broadcast message from the same 868 forwarder or seed. These repeaters repeat within the same Imin 869 interval, thus increasing the c counter. 871 Within the first MPL interval a limited number, q, of messages can be 872 transmitted. Assuming a 3 ms transmission interval, q is given by q 873 = Imin/3. Assuming that at most q message copies can reach a given 874 forwarder within the first repeat interval of length Imin, the 875 related MPL parameter values are suggested in the following sections. 877 5.1.2.1. Imin 879 The recommended value is Imin = 10 to 50 ms. 881 When Imin is chosen much smaller, the interference between the copies 882 leads to significant losses given that q is much smaller than the 883 number of repeated packets. With much larger intervals the 884 probability that the deadline will be met decreases with increasing 885 hop count. 887 5.1.2.2. Imax 889 The recommended value is Imax = 100 to 400 ms. 891 The value of Imax is less important than the value of max_expiration. 892 Given an Imin value of 10 ms, the 3rd MPL interval has a value of 893 10*2*2 = 40 ms. When Imin has a value of 40 ms, the 3rd interval has 894 a value of 160 ms. Given that more than 3 intervals are unnecessary, 895 the Imax does not contribute much to the performance. 897 5.1.3. Other parameters 899 Other parameters are the k parameter and the max_expiration 900 parameter. 902 k > q (see condition above). Under this condition and for small 903 Imin, a value of k=2 or k=3 is usually sufficient to minimize the 904 losses of packets in the first repeat interval. 906 max_expiration = 2 - 4. Higher values lead to more network load 907 while generating copies which will probably not meet their deadline. 909 6. Manageability Considerations 911 At this moment it is not clear how homenets will be managed. 912 Consequently it is not clear which tools will be used and which 913 parameters must be exposed for management. 915 In building control, management is mandatory. It is expected that 916 installations will be managed using the set of currently available 917 tools(including IETF tools like Management Information Base (MIB) 918 modules, NETCONF modules, Dynamic Host Configuration Protocol (DHCP) 919 and others) with large differences between the ways an installation 920 is managed. 922 7. Security Considerations 924 This section refers to the security considerations of [RFC6997], 925 [RFC6550], [I-D.ietf-roll-trickle-mcast], and the counter measures 926 discussed in sections 6 and 7 of [RFC7416]. 928 Communications network security is based on providing integrity 929 protection and encryption to messages. This can be applied at 930 various layers in the network protocol stack based on using various 931 credentials and a network identity. 933 The credentials which are relevant in the case of RPL are: (i) the 934 credential used at the link layer in the case where link layer 935 security is applied (see Section 7.1) or (ii) the credential used for 936 securing RPL messages. In both cases, the assumption is that the 937 credential is a shared key. Therefore, there MUST be a mechanism in 938 place which allows secure distribution of a shared key and 939 configuration of network identity. Both MAY be done using: (i) pre- 940 installation using an out-of-band method, (ii) delivered securely 941 when a device is introduced into the network or (iii) delivered 942 securely by a trusted neighbouring device. The shared key MUST be 943 stored in a secure fashion which makes it difficult to be read by an 944 unauthorized party. 946 This document mandates that a layer-2 mechanism be used during 947 initial and incremental deployment. Please see the following 948 sections. 950 7.1. Security considerations during initial deployment 952 Wireless mesh networks are typically secured at the link layer in 953 order to prevent unauthorized parties from accessing the information 954 exchanged over the links. It is good practice to create a network of 955 nodes which share the same keys for link layer security and exclude 956 nodes sending unsecured messages. With per-message data origin 957 authentication, it is possible to prevent unauthorized nodes joining 958 the mesh. 960 At initial deployment the network is secured by consecutively 961 securing nodes at the link layer, thus building a network of secured 962 nodes. The Protocol for carrying Authentication for Network Access 963 (PANA) [RFC5191] [RFC6345] with an Extensible Authentication Protocol 964 (EAP) provides a framework for network access and delivery of common 965 link keys. Several versions of EAP exist. ZigBee specifies the use 966 of EAP-TLS [RFC5216] (see section 5 of [ZigBeeIP]. Wi-SUN HAN (Home 967 Area Network) uses EAP-PSK [RFC4764] (see section 5.6 of [WI-SUN]), 968 which also looks promising for building control at this moment. 970 This document does not specify a multicast security solution. 971 Networks deployed with this specification will depend upon layer-2 972 security to prevent outsiders from sending multicast traffic. It is 973 recognized that this does not protect this control traffic from 974 impersonation by already trusted devices. This is an area for a 975 future specification. 977 For building control an installer will probably use an installation 978 tool that establishes a secure communication path with the joining 979 node. It is recognized that the recommendations for initial 980 deployment of Section 7 and Section 7.1 do not cover all building 981 requirements such as selecting the node-to-secure independent of 982 network topology. 984 In the home, nodes can be visually inspected by the home owner and a 985 simple procedure, e.g. pushing buttons simultaneously on an already 986 secured device and an unsecured joining device is usually sufficient 987 to ensure that the unsecured joining device is authenticated and 988 configured securely, and paired appropriately. 990 This recommendation is in line with the countermeasures described in 991 section 6.1.1 of [RFC7416]. 993 7.2. Security Considerations during incremental deployment 995 Normally, the network remains secure by not allowing the addition of 996 new nodes. If a new node needs to be added to the network, the 997 network is usually configured to allow the new node to join via an 998 assisting node in the manner described in Section 7.1. If an 999 existing node becomes lost, it is usually possible to re-key all 1000 other existing nodes to isolate the lost node to ensure that, should 1001 it be found again, it has to re-join as if it were a new node. 1003 7.3. Security Considerations for P2P uses 1005 Refer to the security considerations of [RFC6997]. 1007 7.4. MPL routing 1009 The routing of MPL is determined by the enabling of the interfaces 1010 for specified Multicast addresses. The specification of these 1011 addresses can be done via a Constrained Application Protocol (CoAP) 1012 application as specified in [RFC7390]. An alternative is the 1013 creation of a MPL MIB and use of Simple Network Management Protocol 1014 (SNMP)v3 [RFC3411] or equivalent techniques to specify the Multicast 1015 addresses in the MIB. The application of security measures for the 1016 specification of the multicast addresses assures that the routing of 1017 MPL packets is secured. 1019 7.5. RPL Security features 1021 This section follows the structure of section 7, "RPL security 1022 features" of [RFC7416], where a thorough analysis of security threats 1023 and proposed counter measures relevant to RPL and MPL are done. 1025 In accordance with section 7.1 of [RFC7416], "Confidentiality 1026 features", a secured RPL protocol implements payload protection, as 1027 explained in Section 7 of this document. The attributes key-length 1028 and life-time of the keys depend on operational conditions, 1029 maintenance and installation procedures. 1031 Section 7.1 and Section 7.2 of this document recommend link-layer 1032 measures to assure integrity in accordance with section 7.2 of 1033 [RFC7416], "Integrity features". 1035 The provision of multiple paths recommended in section 7.3 1036 "Availability features" of [RFC7416] is also recommended from a 1037 reliability point of view. Randomly choosing paths MAY be supported. 1039 Key management discussed in section 7.4, "Key Management" of 1040 [RFC7416], is not standardized and discussions continue. 1042 Section 7.5, "Considerations on Matching Application Domain Needs" of 1043 [RFC7416] applies as such. 1045 8. Other related protocols 1047 Application and transport protocols used in home and building 1048 automation domains are expected to mostly consist in CoAP over UDP, 1049 or equivalents. Typically, UDP is used for IP transport to keep down 1050 the application response time and bandwidth overhead. CoAP is used 1051 at the application layer to reduce memory footprint and bandwidth 1052 requirements. 1054 9. IANA Considerations 1056 No considerations for IANA pertain to this document. 1058 10. Acknowledgements 1060 This document reflects discussions and remarks from several 1061 individuals including (in alphabetical order): Stephen Farrell, Mukul 1062 Goyal, Sandeep Kumar, Jerry Martocci, Catherine Meadows, Yoshira 1063 Ohba, Charles Perkins, Yvonne-Anne Pignolet, Michael Richardson, Ines 1064 Robles, Zach Shelby, and Meral Sherazipour. 1066 11. Changelog 1068 RFC editor, please delete this section before publication. 1070 Changes from version 0 to version 1. 1072 o Adapted section structure to template. 1074 o Standardized the reference syntax. 1076 o Section 2.2, moved everything concerning algorithms to section 1077 2.2.7, and adapted text in 2.2.1-2.2.6. 1079 o Added MPL parameter text to section 4.1.7 and section 4.3.1. 1081 o Replaced all TODO sections with text. 1083 o Consistent use of border router, monitoring, home- and building 1084 network. 1086 o Reformulated security aspects with references to other 1087 publications. 1089 o MPL and RPL parameter values introduced. 1091 Changes from version 1 to version 2. 1093 o Clarified common characteristics of control in home and building. 1095 o Clarified failure behaviour of point to point communication in 1096 appendix. 1098 o Changed examples, more hvac and less lighting. 1100 o Clarified network topologies. 1102 o replaced reference to smart_object paper by reference to I-D.roll- 1103 security-threats 1105 o Added a concise definition of secure delivery and secure storage 1107 o text about securing network with PANA 1109 Changes from version 2 to version 3. 1111 o Changed security section to follow the structure of security 1112 threats draft. 1114 o Added text to DODAG repair sub-section 1116 Changes from version 3 to version 4. 1118 o Renumbered sections and moved text to conform to applicability 1119 template 1121 o Extended MPL parameter value text 1123 o Added references to building control products 1125 Changes from version 4 to version 5. 1127 o Large editing effort to streamline text 1129 o Rearranged Normative and Informative references 1131 o Replaced RFC2119 terminology by non-normative terminology 1133 o Rearranged text of section 7, 7.1, and 7.2 to agree with the 1134 intention of section 7.2 1136 Changes from version 5 to version 6. 1138 o Issues #162 - #166 addressed 1140 Changes from version 6 to version 6. 1142 o Text of section 7.1 edited for better security coverage. 1144 12. References 1146 12.1. Normative References 1148 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1149 Requirement Levels", BCP 14, RFC 2119, March 1997. 1151 [RFC4764] Bersani, F. and H. Tschofenig, "The EAP-PSK Protocol: A 1152 Pre-Shared Key Extensible Authentication Protocol (EAP) 1153 Method", RFC 4764, January 2007. 1155 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 1156 "Transmission of IPv6 Packets over IEEE 802.15.4 1157 Networks", RFC 4944, September 2007. 1159 [RFC5191] Forsberg, D., Ohba, Y., Patil, B., Tschofenig, H., and A. 1160 Yegin, "Protocol for Carrying Authentication for Network 1161 Access (PANA)", RFC 5191, May 2008. 1163 [RFC5216] Simon, D., Aboba, B., and R. Hurst, "The EAP-TLS 1164 Authentication Protocol", RFC 5216, March 2008. 1166 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1167 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1169 [RFC5548] Dohler, M., Watteyne, T., Winter, T., and D. Barthel, 1170 "Routing Requirements for Urban Low-Power and Lossy 1171 Networks", RFC 5548, May 2009. 1173 [RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney, 1174 "Industrial Routing Requirements in Low-Power and Lossy 1175 Networks", RFC 5673, October 2009. 1177 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation 1178 Routing Requirements in Low-Power and Lossy Networks", RFC 1179 5826, April 2010. 1181 [RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen, 1182 "Building Automation Routing Requirements in Low-Power and 1183 Lossy Networks", RFC 5867, June 2010. 1185 [RFC6282] Hui, J. and P. Thubert, "Compression Format for IPv6 1186 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1187 September 2011. 1189 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1190 Security Version 1.2", RFC 6347, January 2012. 1192 [RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R., 1193 Levis, P., Pister, K., Struik, R., Vasseur, JP., and R. 1194 Alexander, "RPL: IPv6 Routing Protocol for Low-Power and 1195 Lossy Networks", RFC 6550, March 2012. 1197 [RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D. 1198 Barthel, "Routing Metrics Used for Path Calculation in 1199 Low-Power and Lossy Networks", RFC 6551, March 2012. 1201 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1202 Routing Header for Source Routes with the Routing Protocol 1203 for Low-Power and Lossy Networks (RPL)", RFC 6554, March 1204 2012. 1206 [RFC6997] Goyal, M., Baccelli, E., Philipp, M., Brandt, A., and J. 1207 Martocci, "Reactive Discovery of Point-to-Point Routes in 1208 Low-Power and Lossy Networks", RFC 6997, August 2013. 1210 [RFC6998] Goyal, M., Baccelli, E., Brandt, A., and J. Martocci, "A 1211 Mechanism to Measure the Routing Metrics along a Point-to- 1212 Point Route in a Low-Power and Lossy Network", RFC 6998, 1213 August 2013. 1215 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1216 Lossy Networks", RFC 7102, January 2014. 1218 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1219 and M. Richardson, "A Security Threat Analysis for the 1220 Routing Protocol for Low-Power and Lossy Networks (RPLs)", 1221 RFC 7416, January 2015. 1223 [I-D.ietf-roll-trickle-mcast] 1224 Hui, J. and R. Kelsey, "Multicast Protocol for Low power 1225 and Lossy Networks (MPL)", draft-ietf-roll-trickle- 1226 mcast-11 (work in progress), November 2014. 1228 [IEEE802.15.4] 1229 "IEEE 802.15.4 - Standard for Local and metropolitan area 1230 networks -- Part 15.4: Low-Rate Wireless Personal Area 1231 Networks", . 1233 [G.9959] "ITU-T G.9959 Short range narrow-band digital 1234 radiocommunication transceivers - PHY and MAC layer 1235 specifications", . 1237 12.2. Informative References 1239 [RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An 1240 Architecture for Describing Simple Network Management 1241 Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, 1242 December 2002. 1244 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 1245 Demand Distance Vector (AODV) Routing", RFC 3561, July 1246 2003. 1248 [RFC5889] Baccelli, E. and M. Townsley, "IP Addressing Model in Ad 1249 Hoc Networks", RFC 5889, September 2010. 1251 [RFC6345] Duffy, P., Chakrabarti, S., Cragie, R., Ohba, Y., and A. 1252 Yegin, "Protocol for Carrying Authentication for Network 1253 Access (PANA) Relay Element", RFC 6345, August 2011. 1255 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1256 Constrained-Node Networks", RFC 7228, May 2014. 1258 [RFC7390] Rahman, A. and E. Dijk, "Group Communication for the 1259 Constrained Application Protocol (CoAP)", RFC 7390, 1260 October 2014. 1262 [RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets 1263 over ITU-T G.9959 Networks", RFC 7428, February 2015. 1265 [I-D.ietf-dice-profile] 1266 Tschofenig, H. and T. Fossati, "A TLS/DTLS Profile for the 1267 Internet of Things", draft-ietf-dice-profile-10 (work in 1268 progress), March 2015. 1270 [I-D.keoh-dice-multicast-security] 1271 Keoh, S., Kumar, S., Garcia-Morchon, O., Dijk, E., and A. 1272 Rahman, "DTLS-based Multicast Security in Constrained 1273 Environments", draft-keoh-dice-multicast-security-08 (work 1274 in progress), July 2014. 1276 [I-D.kumar-dice-dtls-relay] 1277 Kumar, S., Keoh, S., and O. Garcia-Morchon, "DTLS Relay 1278 for Constrained Environments", draft-kumar-dice-dtls- 1279 relay-02 (work in progress), October 2014. 1281 [I-D.richardson-6tisch--security-6top] 1282 Richardson, M., "6tisch secure join using 6top", draft- 1283 richardson-6tisch--security-6top-04 (work in progress), 1284 November 2014. 1286 [SOFT11] Baccelli, E., Phillip, M., and M. Goyal, "The P2P-RPL 1287 Routing Protocol for IPv6 Sensor Networks: Testbed 1288 Experiments", Proceedings of the Conference on Software 1289 Telecommunications and Computer Networks, Split, Croatia,, 1290 September 2011. 1292 [INTEROP12] 1293 Baccelli, E., Phillip, M., Brandt, A., Valev , H., and J. 1294 Buron , "Report on P2P-RPL Interoperability Testing", 1295 RR-7864 INRIA Research Report RR-7864, January 2012. 1297 [RT-MPL] van der Stok, P., "Real-Time multicast for wireless mesh 1298 networks using MPL", White paper, 1299 http://www.vanderstok.org/papers/Real-time-MPL.pdf, April 1300 2014. 1302 [occuswitch] 1303 Lighting, Philips., "OccuSwitch wireless", Brochure, http: 1304 //www.philipslightingcontrols.com/assets/cms/uploads/files 1305 /osw/MK_OSWNETBROC_5.pdf, May 2012. 1307 [office-light] 1308 Clanton and Associates, ., "A Life Cycle Cost Evaluation 1309 of Multiple Lighting Control Strategies", Wireless 1310 Lighting Control, http://www.daintree.net/wp- 1311 content/uploads/2014/02/ 1312 clanton_lighting_control_report_0411.pdf, February 2014. 1314 [RTN2011] Holtman, K. and P. van der Stok, "Real-time routing for 1315 low-latency 802.15.4 control networks", International 1316 Workshop on Real-Time Networks; Euromicro Conference on 1317 Real-Time Systems, July 2011. 1319 [MEAS] Holtman, K., "Connectivity loss in large scale IEEE 1320 802.15.4 network", Private Communication, November 2013. 1322 [BCsurvey] 1323 Kastner, W., Neugschwandtner, G., Soucek, S., and H. 1324 Newman, "Communication Systems for Building Automation and 1325 Control", Proceedings of the IEEE Vol 93, No 6, June 2005. 1327 [ZigBeeIP] 1328 ZigBee Alliance, ., "ZigBee IP specification", ZigBee 1329 document 095023r34, March 2014. 1331 [WI-SUN] ECHONET Lite, ., "Home network Communication Interface for 1332 ECHONET Lite (IEEE802.15.4/4 e/4g 920MHz-band Wireless)", 1333 Japanese TTC standard JJ-300.10, May 2014. 1335 Appendix A. RPL shortcomings in home and building deployments 1337 A.1. Risk of undesired long P2P routes 1339 The DAG, being a tree structure is formed from a root. If nodes 1340 residing in different branches have a need for communicating 1341 internally, DAG mechanisms provided in RPL [RFC6550] will propagate 1342 traffic towards the root, potentially all the way to the root, and 1343 down along another branch [RFC6998]. In a typical example two nodes 1344 could reach each other via just two router nodes but in unfortunate 1345 cases, RPL may send traffic three hops up and three hops down again. 1346 This leads to several undesired phenomena described in the following 1347 sections 1349 A.1.1. Traffic concentration at the root 1351 If many P2P data flows have to move up towards the root to get down 1352 again in another branch there is an increased risk of congestion the 1353 nearer to the root of the DAG the data flows. Due to the broadcast 1354 nature of RF systems any child node of the root is not just directing 1355 RF power downwards its sub-tree but just as much upwards towards the 1356 root; potentially jamming other MP2P traffic leaving the tree or 1357 preventing the root of the DAG from sending P2MP traffic into the DAG 1358 because the listen-before-talk link-layer protection kicks in. 1360 A.1.2. Excessive battery consumption in source nodes 1362 Battery-powered nodes originating P2P traffic depend on the route 1363 length. Long routes cause source nodes to stay awake for longer 1364 periods before returning to sleep. Thus, a longer route translates 1365 proportionally (more or less) into higher battery consumption. 1367 A.2. Risk of delayed route repair 1369 The RPL DAG mechanism uses DIO and DAO messages to monitor the health 1370 of the DAG. In rare occasions, changed radio conditions may render 1371 routes unusable just after a destination node has returned a DAO 1372 indicating that the destination is reachable. Given enough time, the 1373 next Trickle timer-controlled DIO/DAO update will eventually repair 1374 the broken routes, however this may not occur in a timely manner 1375 appropriate to the application. In an apparently stable DAG, 1376 Trickle-timer dynamics may reduce the update rate to a few times 1377 every hour. If a user issues an actuator command, e.g. light on in 1378 the time interval between the last DAO message was issued the 1379 destination module and the time one of the parents sends the next 1380 DIO, the destination cannot be reached. There is no mechanism in RPL 1381 to initiate restoration of connectivity in a reactive fashion. The 1382 consequence is a broken service in home and building applications. 1384 A.2.1. Broken service 1386 Experience from the telecom industry shows that if the voice delay 1387 exceeds 250ms, users start getting confused, frustrated and/or 1388 annoyed. In the same way, if the light does not turn on within the 1389 same period of time, a home control user will activate the controls 1390 again, causing a sequence of commands such as 1391 Light{on,off,off,on,off,..} or Volume{up,up,up,up,up,...}. Whether 1392 the outcome is nothing or some unintended response this is 1393 unacceptable. A controlling system must be able to restore 1394 connectivity to recover from the error situation. Waiting for an 1395 unknown period of time is not an option. While this issue was 1396 identified during the P2P analysis, it applies just as well to 1397 application scenarios where an IP application outside the LLN 1398 controls actuators, lights, etc. 1400 Appendix B. Communication failures 1402 Measurements on the connectivity between neighbouring nodes are 1403 discussed in [RTN2011] and [MEAS]. 1405 The work is motivated by the measurements in literature which affirm 1406 that the range of an antenna is not circle symmetric but that the 1407 signal strength of a given level follows an intricate pattern around 1408 the antenna, and there may be holes within the area delineated by an 1409 iso-strength line. It is reported that communication is not 1410 symmetric: reception of messages from node A by node B does not imply 1411 reception of messages from node B by node A. The quality of the 1412 signal fluctuates over time, and also the height of the antenna 1413 within a room can have consequences for the range. As function of 1414 the distance from the source, three regions are generally recognized: 1415 (1) a clear region with excellent signal quality, (2) a region with 1416 fluctuating signal quality, (3) a region without reception. In the 1417 text below it is shown that installation of meshes with neighbours in 1418 the clear region is not sufficient. 1420 [RTN2011] extends existing work by: 1422 o Observations over periods of at least a week, 1424 o Testing links that are in the clear region, 1426 o Observation in an office building during working hours, 1428 o Concentrating on one-hop and two-hop routes. 1430 Eight nodes were distributed over a surface of 30m2. All nodes are 1431 at one hop distance from each other and are situated in the clear 1432 region of each other. Each node sends messages to each of its 1433 neighbours, and repeats the message until it arrives. The latency of 1434 the message was measured over periods of at least a week. It is 1435 noticed that latencies longer than a second occurred without apparent 1436 reasons, but only during working days and never in the weekends. Bad 1437 periods could last for minutes. By sending messages via two paths: 1438 (1) one hop path directly, and (2) two hop path via a randomly chosen 1439 neighbour, the probability of delays larger than 100 ms decreased 1440 significantly. 1442 The conclusion is that even for 1-hop communication between not too 1443 distant "Line of Sight" nodes, there are periods of low reception in 1444 which communication deadlines of 200 ms are exceeded. It pays to 1445 send a second message over a 2-hop path to increase the reliability 1446 of timely message transfer. 1448 [MEAS] confirms that temporary bad reception by close neighbours can 1449 occur within other types of areas. Nodes were installed on the 1450 ceiling in a grid with a distance of 30-50 cm between nodes. 200 1451 nodes were distributed over an area of 10m x 5m. It clearly 1452 transpired that with increasing distance the probability of reception 1453 decreases. At the same time a few nodes furthest away from the 1454 sender had a high probability of message reception, while some close 1455 neighbours of the sender did not receive messages. The patterns of 1456 clear reception nodes evolved over time. 1458 The conclusion is that even for direct neighbours reception can 1459 temporarily be bad during periods of several minutes. For a reliable 1460 and timely communication it is imperative to have at least two 1461 communication paths available (e.g. two hop paths next to the 1-hop 1462 path for direct neighbours). 1464 Authors' Addresses 1466 Anders Brandt 1467 Sigma Designs 1469 Email: anders_Brandt@sigmadesigns.com 1471 Emmanuel Baccelli 1472 INRIA 1474 Email: Emmanuel.Baccelli@inria.fr 1475 Robert Cragie 1476 ARM Ltd. 1477 110 Fulbourn Road 1478 Cambridge CB1 9NJ 1479 UK 1481 Email: robert.cragie@gridmerge.com 1483 Peter van der Stok 1484 Consultant 1486 Email: consultancy@vanderstok.org