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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 6TiSCH P. Thubert, Ed. 3 Internet-Draft Cisco 4 Intended status: Informational June 10, 2016 5 Expires: December 12, 2016 7 An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4 8 draft-ietf-6tisch-architecture-10 10 Abstract 12 This document describes a network architecture that provides low- 13 latency, low-jitter and high-reliability packet delivery. It 14 combines a high speed powered backbone and subnetworks using IEEE 15 802.15.4 time-slotted channel hopping (TSCH) to meet the requirements 16 of LowPower wireless deterministic applications. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on December 12, 2016. 35 Copyright Notice 37 Copyright (c) 2016 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 3. High Level Architecture . . . . . . . . . . . . . . . . . . . 4 55 3.1. 6TiSCH Stack . . . . . . . . . . . . . . . . . . . . . . 4 56 3.2. TSCH: A Deterministic MAC Layer . . . . . . . . . . . . . 6 57 3.3. Scheduling TSCH . . . . . . . . . . . . . . . . . . . . . 7 58 3.4. Routing and Forwarding Over TSCH . . . . . . . . . . . . 8 59 3.5. A Non-Broadcast Multi-Access Radio Mesh Network . . . . . 10 60 3.6. A Multi-Link Subnet Model . . . . . . . . . . . . . . . . 12 61 3.7. Join Process and Registration . . . . . . . . . . . . . . 13 62 3.8. Dependencies on Work In Progress . . . . . . . . . . . . 14 63 4. Deeper Dive . . . . . . . . . . . . . . . . . . . . . . . . . 16 64 4.1. 6LoWPAN (and RPL) . . . . . . . . . . . . . . . . . . . . 16 65 4.1.1. RPL Leaf Support in 6LoWPAN ND . . . . . . . . . . . 16 66 4.1.2. RPL Root And 6LBR . . . . . . . . . . . . . . . . . . 16 67 4.2. TSCH and 6top . . . . . . . . . . . . . . . . . . . . . . 17 68 4.2.1. 6top . . . . . . . . . . . . . . . . . . . . . . . . 17 69 4.2.2. Scheduling Functions and the 6P protocol . . . . . . 18 70 4.2.3. 6top and RPL Objective Function operations . . . . . 19 71 4.2.4. Network Synchronization . . . . . . . . . . . . . . . 20 72 4.2.5. SlotFrames and Priorities . . . . . . . . . . . . . . 21 73 4.2.6. Distributing the reservation of cells . . . . . . . . 22 74 4.3. Communication Paradigms and Interaction Models . . . . . 24 75 4.4. Schedule Management Mechanisms . . . . . . . . . . . . . 25 76 4.4.1. Static Scheduling . . . . . . . . . . . . . . . . . . 25 77 4.4.2. Neighbor-to-neighbor Scheduling . . . . . . . . . . . 25 78 4.4.3. Remote Monitoring and Schedule Management . . . . . . 26 79 4.4.4. Hop-by-hop Scheduling . . . . . . . . . . . . . . . . 29 80 4.5. Forwarding Models . . . . . . . . . . . . . . . . . . . . 29 81 4.5.1. Track Forwarding . . . . . . . . . . . . . . . . . . 29 82 4.5.2. Fragment Forwarding . . . . . . . . . . . . . . . . . 33 83 4.5.3. IPv6 Forwarding . . . . . . . . . . . . . . . . . . . 34 84 4.6. Centralized vs. Distributed Routing . . . . . . . . . . . 35 85 4.6.1. Packet Marking and Handling . . . . . . . . . . . . . 35 86 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36 87 6. Security Considerations . . . . . . . . . . . . . . . . . . . 36 88 6.1. Join Process Highlights . . . . . . . . . . . . . . . . . 36 89 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 90 7.1. Contributors . . . . . . . . . . . . . . . . . . . . . . 39 91 7.2. Special Thanks . . . . . . . . . . . . . . . . . . . . . 40 92 7.3. And Do not Forget . . . . . . . . . . . . . . . . . . . . 40 93 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 40 94 8.1. Normative References . . . . . . . . . . . . . . . . . . 41 95 8.2. Informative References . . . . . . . . . . . . . . . . . 43 96 8.3. Other Informative References . . . . . . . . . . . . . . 47 97 Appendix A. Personal submissions relevant to upcoming work . . . 48 98 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 49 100 1. Introduction 102 Wireless Networks enable a wide variety of devices of any size to get 103 interconnected, often at a very low marginal cost per device, at any 104 distance ranging from Near Field to interplanetary, and in 105 circumstances where wiring may be impractical, for instance on fast- 106 moving or rotating devices. 108 In the other hand, Deterministic Networks enable traffic that is 109 highly sensitive to jitter, quite sensitive to latency, and with a 110 high degree of operational criticality so that loss should be 111 minimized at all times. Applications that need such networks are 112 presented in [I-D.ietf-detnet-use-cases]. They include Professional 113 Media and Operation Technology (OT) Industrial Automation Control 114 Systems (IACS). 116 The Medium access Control (MAC) of IEEE802.15.4 [IEEE802154] has 117 evolved with the IEEE802.15.4e Timeslotted Channel Hopping (TSCH) 118 [RFC7554] mode to provide deterministic properties on wireless 119 networks. TSCH was initially introduced with the IEEE802.15.4e 120 amendment [IEEE802154e] of the IEEE802.15.4 standard and constituted 121 a part of the standard from that day. For all practical purpose, 122 this document is expected to be insensitive to the revisions of the 123 IEEE802.15.4 standard, which is thus referenced undated. 125 Proven Deterministic Networking standards for use in Process Control, 126 including ISA100.11a [ISA100.11a] and WirelessHART [WirelessHART], 127 have demonstrated the capabilities of the IEEE802.15.4 TSCH MAC for 128 high reliability against interference, low-power consumption on well- 129 known flows, and its applicability for Traffic Engineering (TE) from 130 a central controller. 132 In order to enable the convergence of IT and OT in LLN environments, 133 6TiSCH ports the IETF suite of protocol that are defined for such 134 environments over the TSCH MAC. 6TiSCH also provides large scaling 135 capabilities, which, in a number of scenarios, require the addition 136 of a high speed and reliable backbone and the use of IP version 6 137 (IPv6). The 6TiSCH Architecture introduces an IPv6 Multi-Link subnet 138 model that is composed of a federating backbone and a number of 139 IEEE802.15.4 TSCH low-power wireless networks attached and 140 synchronized by Backbone Routers. 142 The architecture defines mechanisms to establish and maintain routing 143 and scheduling in a centralized, distributed, or mixed fashion, for 144 use in multiple OT environments. It is applicable in particular to 145 industrial control systems, building automation that leverage 146 distributed routing to address multipath over a large number of hops, 147 in-vehicle command and control that can be as demanding as industrial 148 applications, commercial automation and asset Tracking with mobile 149 scenarios, home automation and domotics which become more reliable 150 and thus provide a better user experience, and resource management 151 (energy, water, etc.). 153 2. Terminology 155 The draft uses domain-specific terminology defined or referenced in 156 [I-D.ietf-6tisch-terminology], [I-D.ietf-6lo-backbone-router], and 157 [I-D.ietf-roll-rpl-industrial-applicability]. 159 Readers are expected to be familiar with all the terms and concepts 160 that are discussed in "Neighbor Discovery for IP version 6" 161 [RFC4861], "IPv6 over Low-Power Wireless Personal Area Networks 162 (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals" 163 [RFC4919], and Neighbor Discovery Optimization for Low-power and 164 Lossy Networks [RFC6775] where the 6LoWPAN Router (6LR) and the 165 6LoWPAN Border Router (6LBR) are introduced. 167 Readers may benefit from reading the "RPL: IPv6 Routing Protocol for 168 Low-Power and Lossy Networks" [RFC6550] specification; "Multi-Link 169 Subnet Issues" [RFC4903]; "Mobility Support in IPv6" [RFC6275]; 170 "Neighbor Discovery Proxies (ND Proxy)" [RFC4389]; "IPv6 Stateless 171 Address Autoconfiguration" [RFC4862]; "FCFS SAVI: First-Come, First- 172 Served Source Address Validation Improvement for Locally Assigned 173 IPv6 Addresses" [RFC6620]; and "Optimistic Duplicate Address 174 Detection" [RFC4429] prior to this specification for a clear 175 understanding of the art in ND-proxying and binding. 177 The draft also conforms to the terms and models described in 178 [RFC3444] and [RFC5889] and uses the vocabulary and the concepts 179 defined in [RFC4291] for the IPv6 Architecture and refers [RFC4080] 180 for reservation signaling and [RFC5191] for authentication. 182 3. High Level Architecture 184 3.1. 6TiSCH Stack 186 The 6TiSCH architecture presents a reference stack that is 187 implemented and interop tested by a conjunction of opensource, IETF 188 and ETSI efforts. One goal is to help other bodies to adopt the 189 stack as a whole, making the effort to move to an IPv6-based IOT 190 stack easier. Now, for a particular, environment, some of the 191 choices that are made in this architecture may not be relevant. For 192 instance, RPL is not required for star topologies and mesh-under 193 layer-2 routed networks, and the 6LoWPAN compression may not be 194 sufficient for ultra-constrained cases such as some Low Power Wide 195 Area (LPWA) networks. In such cases, it is perfectly doable to adopt 196 a subset of the selection that is presented hereafter and then select 197 alternate components to complete the solution wherever needed. 199 The IETF proposes multiple techniques for implementing functions 200 related to routing, transport or security. In order to control the 201 complexity of the possible deployments and device interactions, and 202 to limit the size of the resulting object code, the architecture 203 limits the possible variations of the stack and recommends a number 204 of base elements for LLN applications. In particular, UDP [RFC0768] 205 [RFC2460] and the Constrained Application Protocol [RFC7252] (CoAP) 206 are used as the transport / binding of choice for applications and 207 management as opposed to TCP and HTTP. 209 The resulting stack is represented below: 211 +-----+-----+-----+------+-------+-----+ 212 | (COMI) |(PANA)|6LoWPAN| RPL | 213 | CoAP / DTLS | | ND | | 214 +-----+-----+-----+------+-------+-----+ 215 | UDP | ICMP | 216 +-----+-----+-----+-----+-------+------+-----+ 217 | IPv6 | 218 +-------------------------------------------+ 219 | 6LoWPAN adaptation and compression (HC) | 220 +-------------------------------------------+ 221 | 6top | 222 +-------------------------------------------+ 223 | IEEE802.15.4 TSCH | 224 +-------------------------------------------+ 226 Figure 1: 6TiSCH Protocol Stack 228 RPL is the routing protocol of choice for LLNs. So far, there was no 229 identified need to define a 6TiSCH specific Objective Function. The 230 Minimal 6TiSCH Configuration [I-D.ietf-6tisch-minimal] describes the 231 operation of RPL over a static schedule used in a slotted aloha 232 fashion, whereby all active slots may be used for emission or 233 reception of both unicast and multicast frames. 235 The 6LoWPAN Header Compression [RFC6282] is used to compress the IPv6 236 and UDP headers, whereas the 6LoWPAN Routing Header 237 [I-D.ietf-roll-routing-dispatch] is used to compress the RPL 238 artifacts in the IPv6 data packets, including the RPL Packet 239 Information (RPI), the IP-in-IP encapsulation to/from the RPL root, 240 and the Source Route Header (SRH) in non-storing mode. 242 6TiSCH has adopted the general direction of CoAP Management Interface 243 (COMI) [I-D.vanderstok-core-comi] for the management of devices. 244 This is leveraged for instance for the implementation of the generic 245 data model for the 6top sublayer management interface 246 [I-D.ietf-6tisch-6top-interface]. The proposed implementation is 247 based on CoAP and CBOR, and specified in 6TiSCH Resource Management 248 and Interaction using CoAP [I-D.ietf-6tisch-coap]. 250 The Datagram Transport Layer Security (DTLS) [RFC6347] is represented 251 as an example of a protocol that could be used to protect CoAP 252 datagrams, but the exact stack is not determined at the time of this 253 writing.. 255 Similarly, the Protocol for Carrying Authentication for Network 256 access (PANA) [RFC5191] is represented as an example of a protocol 257 that could be leveraged to secure the join process, as a Layer-3 258 alternate to IEEE802.1x/EAP. Regardless, the security model ensures 259 that, prior to a join process, packets from a untrusted device are 260 controlled in volume and in reachability. In particular, a PANA 261 stack should be separated from the main protocol stack to avoid 262 attacks during the join process that is introduced in Section 3.7. 263 An overview of the security aspects of the join process can be found 264 in Section 6. 266 The 6TiSCH Operation sublayer (6top) [I-D.wang-6tisch-6top-sublayer] 267 is a sublayer of a Logical Link Control (LLC) that provides the 268 abstraction of an IP link over a TSCH MAC and schedules packets over 269 TSCH cells,as further discussed in the next sections. 271 3.2. TSCH: A Deterministic MAC Layer 273 Though at a different time scale (several orders of magnitude), both 274 IEEE802.1TSN and IEEE802.15.4TSCH standards provide Deterministic 275 capabilities to the point that a packet that pertains to a certain 276 flow may traverse a network from node to node following a very 277 precise schedule, as a train that enters and then leaves intermediate 278 stations at precise times along its path. With TSCH, time is 279 formatted into timeslots, and individual communication cells are 280 allocated to unicast or broadcast communication at the MAC level. 281 The time-slotted operation reduces collisions, saves energy, and 282 enables to more closely engineer the network for deterministic 283 properties. The channel hopping aspect is a simple and efficient 284 technique to combat multipath fading and external interference (for 285 example by Wi-Fi emitters). 287 6TiSCH builds on the IEEE802.15.4TSCH MAC and inherits its advanced 288 capabilities to enable them in multiple environments where they can 289 be leveraged to improve automated operations. The 6TiSCH 290 Architecture also inherits the capability to perform a centralized 291 route computation to achieve deterministic properties, though it 292 relies on the IETF DetNet Architecture 293 [I-D.finn-detnet-architecture], and IETF components such as the Path 294 Computation Element (PCE) [PCE], for the protocol aspects. 296 On top of this inheritance, 6TiSCH adds capabilities for distributed 297 routing and scheduling operations based on the RPL routing protocol 298 and capabilities to negotiate schedule adjustments between peers. 299 These distributed routing and scheduling operations simplify the 300 deployment of TSCH networks and enable wireless solutions in a larger 301 variety of use cases from operational technology in general. 302 Examples of such use-cases in industrial environments include plant 303 setup and decommissioning, as well as monitoring of lots of lesser 304 importance measurements such as corrosion and events. RPL also 305 enables mobile use cases such as mobile workers and cranes, as 306 presented in [I-D.ietf-roll-rpl-industrial-applicability]. 308 3.3. Scheduling TSCH 310 A scheduling operation attributes cells in a Time-Division- 311 Multiplexing (TDM) / Frequency-Division Multiplexing (FDM) matrix 312 called the Channel distribution/usage (CDU) to either individual 313 transmissions or as multi-access shared resources (see the 6TiSCH 314 Terminology [I-D.ietf-6tisch-terminology] for more on these terms). 315 Scheduling effectively enables multiple communications at a same time 316 in a same interference domain using different channels; but a node 317 equipped with a single radio can only transmit or receive on one 318 channel at any given point of time. 320 From the standpoint of a 6TiSCH node (at the MAC layer), its schedule 321 is the collection of the times at which it must wake up for 322 transmission, and the channels to which it should either send or 323 listen at those times. The schedule is expressed as one or more 324 slotframes that repeat over and over. Slotframes may collision and 325 require a device to wake at a same time, in which case a priority 326 indicates which slotframe is actually activated. 328 The 6top sublayer hides the complexity of the schedule to the upper 329 layers. The Link that IP may utilize between the 6TiSCH node and a 330 peer may in fact be composed of a pair of cell bundles, one to 331 receive and one to transmit. Some of the cells may be shared, in 332 which case the 6top sublayer must perform some arbitration. 334 The 6TiSCH architecture identifies four ways a schedule can be 335 managed and CDU cells can be allocated: Static Scheduling, Neighbor- 336 to-Neighbor Scheduling, Remote Monitoring and Schedule Management, 337 and Hop-by-hop Scheduling. 339 Static Scheduling: This refers to the minimal 6TiSCH operation 340 whereby a static schedule is configured for the whole network for 341 use in a slotted-aloha fashion. The static schedule is 342 distributed through the native methods in the TSCH MAC layer. 343 This operation leverages RPL to maintain a loopless graph for 344 routing and time distribution. It is specified in the Minimal 345 6TiSCH Configuration [I-D.ietf-6tisch-minimal] specification. and 346 does not preclude other scheduling operations to co-exist on a 347 same 6TiSCH network. 349 Neighbor-to-Neighbor Scheduling: This refers to the dynamic 350 adaptation of the bandwidth of the Links that are used for IPv6 351 traffic between adjacent routers. Scheduling Functions such as 352 SF0 [I-D.ietf-6tisch-6top-sf0] influence the operation of the 6top 353 sublayer [I-D.wang-6tisch-6top-sublayer] to add and remove cells 354 in peers schedule, using the 6top protocol 355 [I-D.ietf-6tisch-6top-protocol] for the negotiation on the MAC 356 resources. 358 Remote Monitoring and Schedule Management: This refers to the 359 central computation of a schedule and the capability to forward a 360 frame based on the cell of arrival. In that case, the related 361 portion of the device schedule as well as other device resources 362 are managed by an abstract Network Management Entity (NME), which 363 may cooperate with the PCE in order to minimize the interaction 364 with and the load on the constrained device. This model is the 365 TSCH adaption of the DetNet Architecture 366 [I-D.finn-detnet-architecture], and it enables Traffic Engineering 367 with deterministic properties. 369 Hop-by-hop Scheduling: This refers to the possibility to reserves 370 cells along a path for a particular flow using a distributed 371 mechanism. 373 It is not expected that all use cases will require all those 374 mechanisms. Static Scheduling with minimal configuration one is the 375 only one that is expected in all implementations, since it provides a 376 simple and solid basis for convergecast routing and time 377 distribution. 379 A deeper dive in those mechanisms can be found in Section 4.4. 381 3.4. Routing and Forwarding Over TSCH 383 6TiSCH leverages the RPL routing protocol for interoperable 384 distributed routing operations. RPL is applicable to Static 385 Scheduling and Neighbor-to-Neighbor Scheduling. The architecture 386 also supports a centralized routing model for Remote Monitoring and 387 Schedule Management. It is expected that a routing protocol that is 388 more optimized for point-to-point routing than RPL, such as the 389 Reactive Discovery of Point-to-Point Routes in Low-Power and Lossy 390 Networks [RFC6997](P2P RPL), or the Ad Hoc On-demand Distance Vector 391 Routing (AODV) [I-D.ietf-manet-aodvv2] will be selected for Hop-by- 392 hop Scheduling. 394 The 6TiSCH architecture supports three different forwarding models, 395 the classical IPv6 Forwarding, where the node selects a feasible 396 successor at Layer-3 on a per packet basis and based on its routing 397 table, G-MPLS Track Forwarding, which switches a frame received at a 398 particular Timeslot into another Timeslot at Layer-2, and 6LoWPAN 399 Fragment Forwarding, which allows to forward individual 6loWPAN 400 fragments along the route set by the first fragment. 402 IPv6 Forwarding: This is the classical IP forwarding model, with a 403 Routing Information Based (RIB) that is installed by the RPL 404 routing protocol and used to select a feasible successor per 405 packet. The packet is placed on an outgoing Link, that the 6top 406 layer maps into a (Layer-3) bundle of cells, and scheduled for 407 transmission based on QoS parameters. On top of RPL, this model 408 also applies to any routing protocol which may be operated in the 409 6TiSCH network, and corresponds to all the distributed scheduling 410 models, Static, Neighbor-to-Neighbor and Hop-by-Hop Scheduling. 412 G-MPLS Track Forwarding: This model corresponds to the Remote 413 Monitoring and Schedule Management. In this model, A central 414 controller (hosting a PCE) computes and installs the schedules in 415 the devices per flow. The incoming (Layer-2) bundle of cells from 416 the previous node along the path determines the outgoing (Layer-2) 417 bundle towards the next hop for that flow as determined by the 418 PCE. The programmed sequence for bundles is called a Track and 419 can assume shapes that are more complex than a simple direct 420 sequence of nodes. 422 6LoWPAN Fragment Forwarding: This is an hybrid model that derives 423 from IPv6 forwarding for the case where packets must be fragmented 424 at the 6LoWPAN sublayer. The first fragment is forwarded like any 425 IPv6 packet and leaves a state in the intermediate hops to enable 426 forwarding of the next fragments that do not have a IP header 427 without the need to recompose the packet at every hop. 429 This can be broadly summarized in the following table: 431 +---------------------+------------+-----------------------------------+ 432 | Forwarding Model | Routing | Scheduling | 433 +=====================+============+===================================+ 434 |G-MPLS Track Fwrding | PCE |Remote Monitoring and Schedule Mgt | 435 +---------------------+------------+-----------------------------------+ 436 | | | Static (Minimal Configuration) | 437 + classical IPv6 + RPL +-----------------------------------+ 438 | / | | Neighbor-to-Neighbor (SF0) | 439 + 6LoWPAN Fragment F. +------------+-----------------------------------+ 440 | |Reactive P2P| Hop-by-Hop (TBD) | 441 +---------------------+------------+-----------------------------------+ 443 Figure 2: Routing, Forwarding and Scheduling 445 3.5. A Non-Broadcast Multi-Access Radio Mesh Network 447 A 6TiSCH network is an IPv6 [RFC2460] subnet which, in its basic 448 configuration, is a single Low Power Lossy Network (LLN) operating 449 over a synchronized TSCH-based mesh. 451 Inside a 6TiSCH LLN, nodes rely on 6LoWPAN Header Compression 452 (6LoWPAN HC) [RFC6282] to encode IPv6 packets. From the perspective 453 of the network layer, a single LLN interface (typically an 454 IEEE802.15.4-compliant radio) may be seen as a collection of Links 455 with different capabilities for unicast or multicast services. 457 6TiSCH nodes are not necessarily reachable from one another at 458 Layer-2 and an LLN may span over multiple links. This effectively 459 forms an homogeneous non-broadcast multi-access (NBMA) subnet, which 460 is beyond the scope of existing IPv6 ND methods. Extensions to IPv6 461 ND have to be introduced. 463 Within that subnet, neighbor devices are discovered with 6LoWPAN 464 Neighbor Discovery [RFC6775] (6LoWPAN ND), whereas RPL [RFC6550] 465 enables routing in the so called Route Over fashion, either in 466 storing (stateful) or non-storing (stateless, with routing headers) 467 mode. 469 ---+-------- ............ ------------ 470 | External Network | 471 | +-----+ 472 +-----+ | NME | 473 | | LLN Border | | 474 | | router +-----+ 475 +-----+ 476 o o o 477 o o o o o 478 o o 6LoWPAN + RPL o o 479 o o o o 480 o o 482 Figure 3: Basic Configuration of a 6TiSCH Network 484 6TiSCH nodes join the mesh by attaching to nodes that are already 485 members of the mesh. Some nodes act as routers for 6LoWPAN ND and 486 RPL operations, as detailed in Section 4.1. Security aspects of the 487 join process by which a device obtains access to the network are 488 discussed in Section 6. 490 With TSCH, devices are time-synchronized at the MAC level. The use 491 of a particular RPL Instance for time synchronization is discussed in 492 Section 4.2.4. With this mechanism, the time synchronization starts 493 at the RPL root and follows the RPL DODAGs with no timing loop. 495 RPL forms Destination Oriented Directed Acyclic Graphs (DODAGs) 496 within Instances of the protocol, each Instance being associated with 497 an Objective Function (OF) to form a routing topology. A particular 498 6TiSCH node, the LLN Border Router (LBR), acts as RPL root, 6LoWPAN 499 HC terminator, and Border Router for the LLN to the outside. The LBR 500 is usually powered. More on RPL Instances can be found in section 501 3.1 of RPL [RFC6550], in particular "3.1.2. RPL Identifiers" and 502 "3.1.3. Instances, DODAGs, and DODAG Versions". RPL adds artifacts 503 in the data packets that are compressed with a 6LoWPAN addition 6LoRH 504 [I-D.ietf-roll-routing-dispatch]. 506 Additional routing and scheduling protocols may be deployed to 507 establish on-demand Peer-to-Peer routes with particular 508 characteristics inside the 6TiSCH network. This may be achieved in a 509 centralized fashion by a PCE [PCE] that programs both the routes and 510 the schedules inside the 6TiSCH nodes, or by in a distributed fashion 511 using a reactive routing protocol and a Hop-by-Hop scheduling 512 protocol. 514 A Backbone Router may be connected to the node that acts as RPL root 515 and / or 6LoWPAN 6LBR and provides connectivity to the larger campus 516 / factory plant network over a high speed backbone or a back-haul 517 link. A Backbone Router may perform proxy IPv6 Neighbor Discovery 518 (ND) [RFC4861] operations over the backbone on behalf of the 6TiSCH 519 nodes so they can share a same IPv6 subnet and appear to be connected 520 to the same backbone as classical devices. A Backbone Router may 521 alternatively redistribute the registration in a routing protocol 522 such as OSPF [RFC5340] or BGP [RFC2545], or inject them in a mobility 523 protocol such as MIPv6 [RFC6275], NEMO [RFC3963], or LISP [RFC6830]. 525 This architecture expects that a 6LoWPAN node can connect as a leaf 526 to a RPL network, where the leaf support is the minimal functionality 527 to connect as a host to a RPL network without the need to participate 528 to the full routing protocol. The architecture also expects that a 529 6LoWPAN node that is not aware at all of the RPL protocol may also 530 connect as a host but the specifications for this to happen are not 531 available at the time of this writing. 533 3.6. A Multi-Link Subnet Model 535 An extended configuration of the subnet comprises multiple LLNs. The 536 LLNs are interconnected and synchronized over a backbone, that can be 537 wired or wireless. The backbone can be a classical IPv6 network, 538 with Neighbor Discovery operating as defined in [RFC4861] and 539 [RFC4862]. This architecture requires work to standardize the the 540 registration of 6LoWPAN nodes to the Backbone Routers. 542 In the extended configuration, a Backbone Router (6BBR) operates as 543 described in [I-D.ietf-6lo-backbone-router]. The 6BBR performs ND 544 proxy operations between the registered devices and the classical ND 545 devices that are located over the backbone. 6TiSCH 6BBRs synchronize 546 with one another over the backbone, so as to ensure that the multiple 547 LLNs that form the IPv6 subnet stay tightly synchronized. 549 ---+-------- ............ ------------ 550 | External Network | 551 | +-----+ 552 | +-----+ | NME | 553 +-----+ | +-----+ | | 554 | | Router | | PCE | +-----+ 555 | | +--| | 556 +-----+ +-----+ 557 | | 558 | Subnet Backbone | 559 +--------------------+------------------+ 560 | | | 561 +-----+ +-----+ +-----+ 562 | | Backbone | | Backbone | | Backbone 563 o | | router | | router | | router 564 +-----+ +-----+ +-----+ 565 o o o o o 566 o o o o o o o o o o o 567 o o o LLN o o o o 568 o o o o o o o o o o o o 570 Figure 4: Extended Configuration of a 6TiSCH Network 572 As detailed in Section 4.1 the 6LoWPAN ND 6LBR and the root of the 573 RPL network need to be collocated and share information about the 574 devices that is learned through either protocol but not both. The 575 combined RPL root and 6LBR may be collocated with the 6BBR, or 576 directly attached to the 6BBR. In the latter case, it leverages the 577 extended registration process defined in 578 [I-D.ietf-6lo-backbone-router] to proxy the 6LoWPAN ND registration 579 to the 6BBR on behalf of the LLN nodes, so that the 6BBR may in turn 580 perform proxy classical ND operations over the backbone. 582 If the Backbone is Deterministic (such as defined by the Time 583 Sensitive Networking WG at IEEE), then the Backbone Router ensures 584 that the end-to-end deterministic behavior is maintained between the 585 LLN and the backbone. The DetNet Architecture 586 [I-D.finn-detnet-architecture] studies Layer-3 aspects of 587 Deterministic Networks, and covers networks that span multiple 588 Layer-2 domains. 590 3.7. Join Process and Registration 592 As detailed in Section 4.1 the combined 6LoWPAN ND 6LBR and root of 593 the RPL network learn information such as the device Unique ID (from 594 6LoWPAN ND) and the updated Sequence Number (from RPL), and perform 595 6LoWPAN ND proxy registration to the 6BBR of behalf of the LLN nodes. 596 Figure 5 illustrates the periodic signaling that starts at the leaf 597 node with 6LoWPAN ND, is then carried over RPL to the RPL root, and 598 then to the 6BBR. Efficient ND being an adaptation of 6LoWPAN ND, it 599 makes sense to keep those two homogeneous in the way they use the 600 source and the target addresses in the Neighbor Solicitation (NS) 601 messages for registration, as well as in the options that they use 602 for that process. 604 6LoWPAN Node 6LR 6LBR 6BBR 605 (RPL leaf) (router) (root) 606 | | | | 607 | 6LoWPAN ND |6LoWPAN ND+RPL | Efficient ND | IPv6 ND 608 | LLN link |Route-Over mesh| IPv6 link | Backbone 609 | | | | 610 | NS(ARO) | | | 611 |-------------->| | | 612 | 6LoWPAN ND | DAR (then DAO)| | 613 | |-------------->| | 614 | | | NS(ARO) | 615 | | |-------------->| 616 | | | | DAD 617 | | | |------> 618 | | | | 619 | | | NA(ARO) | 620 | | |<--------------| 621 | | DAC | | 622 | |<--------------| | 623 | NA(ARO) | | | 624 |<--------------| | | 626 Figure 5: (Re-)Registration Flow over Multi-Link Subnet 628 As the network builds up, a node should start as a leaf to join the 629 RPL network, and may later turn into both a RPL-capable router and a 630 6LR, so as to accept leaf nodes to recursively join the network. 632 3.8. Dependencies on Work In Progress 634 In order to control the complexity and the size of the 6TiSCH work, 635 the architecture and the associated IETF work are staged and the WG 636 is expected to recharter multiple times. This document is 637 incremented as the work progresses following the evolution of the WG 638 charter and the availability of dependent work. The intent is to 639 publish when the WG concludes. 641 At the time of this writing: 643 o The architecture of the operation of RPL over a dynamic schedule 644 is being studied at 6TISCH as the second iteration of the charter. 646 o The need of a reactive routing protocol to establish on-demand 647 constraint-optimized routes and a reservation protocol to 648 establish Layer-3 Tracks is being discussed at 6TiSCH but not 649 chartered for. 651 o the components and protocols that are required to implement this 652 stage of architecture are not fully available from the IETF. In 653 particular, the requirements on an evolution of 6LoWPAN Neighbor 654 Discovery that are needed to implement the Backbone Router as 655 covered by this stage of the architecture are detailed in 656 [I-D.thubert-6lo-rfc6775-update-reqs], and a number of those 657 requirements are fulfilled in [I-D.ietf-6lo-backbone-router]. 659 o The work on centralized Track computation is deferred to a 660 subsequent iteration of the 6TiSCH charter. The idea at the time 661 of this writing is that 6TiSCH will apply the concepts of 662 Deterministic Networking on a Layer-3 network. The 6TiSCH 663 Architecture should thus inherit from the DetNet 664 [I-D.finn-detnet-architecture] architecture and thus depends on 665 it. The Path Computation Element (PCE) should be a core component 666 of that architecture. Around the PCE, a protocol such as an 667 extension to a TEAS [TEAS] protocol will be required to expose the 668 6TiSCH node capabilities and the network peers to the PCE, and a 669 protocol such as a lightweight PCEP or an adaptation of CCAMP 670 [CCAMP] G-MPLS formats and procedures will be used to publish the 671 Tracks, as computed by the PCE, to the 6TiSCH nodes. 673 o The security model and in particular the join process are being 674 discussed at 6lo and 6TiSCH. PANA is presented in Section 3.1 as 675 a candidate of choice for the join process but alternatives are 676 discussed. Work resulting from [ACE] could be considered as well. 677 Related contributions are presented in Appendix A. 679 o The current charter positions 6TiSCH on IEEE802.15.4 only. Though 680 most of the design should be portable on other link types, 6TiSCH 681 has a strong dependency on IEEE802.15.4 and its evolution. At the 682 time of this writing, a revision of the IEEE802.15.4 standard is 683 expected early 2016. That revision should integrate TSCH as well 684 as other amendments and fixes into the main specification. The 685 impact on this Architecture should be minimal to non-existent, but 686 deeper work such as 6top and security may be impacted. A 6TiSCH 687 Interest Group was formed at IEEE to maintain the synchronization 688 and help foster work at the IEEE should 6TiSCH demand it. 690 o Work is being proposed at IEEE (802.15.12 PAR) for an LLC that 691 would logically include the 6top sublayer. The interaction with 692 the 6top sublayer and the Scheduling Functions described in this 693 document are yet to be defined. 695 o ISA100 [ISA100] Common Network Management (CNM) is another 696 external work of interest for 6TiSCH. The group, referred to as 697 ISA100.20, defines a Common Network Management framework that 698 should enable the management of resources that are controlled by 699 heterogeneous protocols such as ISA100.11a [ISA100.11a], 700 WirelessHART [WirelessHART], and 6TiSCH. Interestingly, the 701 establishment of 6TiSCH Deterministic paths, called Tracks, are 702 also in scope, and ISA100.20 is working on requirements for 703 DetNet. 705 4. Deeper Dive 707 4.1. 6LoWPAN (and RPL) 709 4.1.1. RPL Leaf Support in 6LoWPAN ND 711 RPL needs a set of information in order to advertise a leaf node 712 through a DAO message and establish reachability. 714 At the bare minimum the leaf device must provide a sequence number 715 that matches the RPL specification in section 7. Section 5.3 of 716 [I-D.ietf-6lo-backbone-router], on the Extended Address Registration 717 Option (EARO), already incorporates that addition with a new field in 718 the option called the Transaction ID. 720 If for some reason the node is aware of RPL topologies, then 721 providing the RPL InstanceID for the instances to which the node 722 wishes to participate would be a welcome addition. In the absence of 723 such information, the RPL router must infer the proper instanceID 724 from external rules and policies. 726 On the backbone, the InstanceID is expected to be mapped onto a an 727 overlay that matches the instanceID, for instance a VLANID. 729 This architecture leverages [I-D.ietf-6lo-backbone-router] that 730 extends 6LoWPAN ND [RFC6775] to carry the counter as an abstract 731 Transaction ID (TID). 733 4.1.2. RPL Root And 6LBR 735 6LoWPAN ND is unclear on how the 6LBR is discovered, and how the 736 liveliness of the 6LBR is asserted over time. On the other hand, the 737 discovery and liveliness of the RPL root are obtained through the RPL 738 protocol. This architecture suggests to collocate these functions by 739 default, in which case the discovery of the 6LBR is automatic for RPL 740 leaves. 742 When 6LoWPAN ND is coupled with RPL, the 6LBR and RPL root 743 functionalities are co-located in order that the address of the 6LBR 744 be indicated by RPL DIO messages and to associate the unique ID from 745 the DAR/DAC exchange with the state that is maintained by RPL. The 746 DAR/DAC exchange becomes a preamble to the DAO messages that are used 747 from then on to reconfirm the registration, thus eliminating a 748 duplication of functionality between DAO and DAR messages. 750 Even though the root of the RPL network is integrated with the 6LBR, 751 it is logically separated from the Backbone Router (6BBR) that is 752 used to connect the 6TiSCH LLN to the backbone. This way, the root 753 has all information from 6LoWPAN ND and RPL about the LLN devices 754 attached to it. 756 This architecture also expects that the root of the RPL network 757 (proxy-)registers the 6TiSCH nodes on their behalf to the 6BBR, for 758 whatever operation the 6BBR performs on the backbone, such as ND 759 proxy, or redistribution in a routing protocol. This relies on an 760 extension of the 6LoWPAN ND registration described in 761 [I-D.ietf-6lo-backbone-router]. 763 This model supports the movement of a 6TiSCH device across the Multi- 764 Link Subnet, and allows the proxy registration of 6TiSCH nodes deep 765 into the 6TiSCH LLN by the 6LBR / RPL root. This requires an 766 alteration from [RFC6775] whereby the Target Address of the NS 767 message is registered as opposed to the Source, which, in the case of 768 a proxy registration, is that of the 6LBR / RPL root itself. 770 4.2. TSCH and 6top 772 4.2.1. 6top 774 6top is a logical link control sitting between the IP layer and the 775 TSCH MAC layer, which provides the link abstraction that is required 776 for IP operations. The 6top operations are specified in 777 [I-D.ietf-6tisch-6top-protocol]. In particular, 6top provides a 778 management interface that enables an external management entity to 779 schedule cells and slotFrames, and allows the addition of 780 complementary functionality, for instance to support a dynamic 781 schedule management based on observed resource usage as discussed in 782 Section 4.4.2. 784 The 6top data model and management interfaces are further discussed 785 in Section 4.4.3. 787 4.2.1.1. Hard Cells 789 The architecture defines "soft" cells and "hard" cells. "Hard" cells 790 are owned and managed by an separate scheduling entity (e.g. a PCE) 791 that specifies the slotOffset/channelOffset of the cells to be 792 added/moved/deleted, in which case 6top can only act as instructed, 793 and may not move hard cells in the TSCH schedule on its own. 795 4.2.1.2. Soft Cells 797 6top contains a monitoring process which monitors the performance of 798 cells, and can move a cell in the TSCH schedule when it performs 799 poorly. This is only applicable to cells which are marked as "soft". 800 To reserve a soft cell, the higher layer does not indicate the exact 801 slotOffset/channelOffset of the cell to add, but rather the resulting 802 bandwidth and QoS requirements. When the monitoring process triggers 803 a cell reallocation, the two neighbor devices communicating over this 804 cell negotiate its new position in the TSCH schedule. 806 4.2.2. Scheduling Functions and the 6P protocol 808 In the case of soft cells, the cell management entity that controls 809 the dynamic attribution of cells to adapt to the dynamics of variable 810 rate flows is called a Scheduling Function (SF). There may be 811 multiple SFs with more or less aggressive reaction to the dynamics of 812 the network. The 6TiSCH 6top Scheduling Function Zero (SF0) 813 [I-D.ietf-6tisch-6top-sf0] provides a simple scheduling function that 814 can be used by default by devices that support dynamic scheduling of 815 soft cells. 817 The SF may be seen as divided between an upper bandwidth adaptation 818 logic that is not aware of the particular technology that is used to 819 obtain and release bandwidth, and an underlying service that maps 820 those needs in the actual technology, which means mapping the 821 bandwidth onto cells in the case of TSCH. 823 +------------------------+ +------------------------+ 824 | Scheduling Function | | Scheduling Function | 825 | Bandwidth adaptation | | Bandwidth adaptation | 826 +------------------------+ +------------------------+ 827 | Scheduling Function | | Scheduling Function | 828 | TSCH mapping to cells | | TSCH mapping to cells | 829 +------------------------+ +------------------------+ 830 | 6top cells negotiation | <- 6P -> | 6top cells negotiation | 831 +------------------------+ +------------------------+ 832 Device A Device B 834 Figure 6: SF/6P stack in 6top 836 The SF relies on 6top services that implement the 6top Protocol (6P) 837 [I-D.ietf-6tisch-6top-protocol] to negotiate the precise cells that 838 will be allocated or freed based on the schedule of the peer. It may 839 be for instance that a peer wants to use a particular time slot that 840 is free in its schedule, but that timeslot is already in use by the 841 other peer for a communication with a third party on a different 842 cell. The 6P protocol enables the peers to find an agreement in a 843 transactional manner that ensures the final consistency of the nodes 844 state. 846 4.2.3. 6top and RPL Objective Function operations 848 An implementation of a RPL [RFC6550] Objective Function (OF), such as 849 the RPL Objective Function Zero (OF0) [RFC6552] that is used in the 850 Minimal 6TiSCH Configuration [I-D.ietf-6tisch-minimal] to support RPL 851 over a static schedule, may leverage, for its internal computation, 852 the information maintained by 6top. 854 Most OFs require metrics about reachability, such as the ETX. 6top 855 creates and maintains an abstract neighbor table, and this state may 856 be leveraged to feed an OF and/or store OF information as well. In 857 particular, 6top creates and maintains an abstract neighbor table. A 858 neighbor table entry contains a set of statistics with respect to 859 that specific neighbor including the time when the last packet has 860 been received from that neighbor, a set of cell quality metrics (e.g. 861 RSSI or LQI), the number of packets sent to the neighbor or the 862 number of packets received from it. This information can be obtained 863 through 6top management APIs as detailed in the 6top sublayer 864 specification [I-D.wang-6tisch-6top-sublayer] and used for instance 865 to compute a Rank Increment that will determine the selection of the 866 preferred parent. 868 6top provides statistics about the underlying layer so the OF can be 869 tuned to the nature of the TSCH MAC layer. 6top also enables the RPL 870 OF to influence the MAC behaviour, for instance by configuring the 871 periodicity of IEEE802.15.4 Extended Beacons (EB's). By augmenting 872 the EB periodicity, it is possible to change the network dynamics so 873 as to improve the support of devices that may change their point of 874 attachment in the 6TiSCH network. 876 Some RPL control messages, such as the DODAG Information Object (DIO) 877 are ICMPv6 messages that are broadcast to all neighbor nodes. With 878 6TiSCH, the broadcast channel requirement is addressed by 6top by 879 configuring TSCH to provide a broadcast channel, as opposed to, for 880 instance, piggybacking the DIO messages in Enhance Beacons. 881 Consideration was given towards finding a way to embed the Route 882 Advertisements and the RPL DIO messages (both of which are multicast) 883 into the IEEE802.15.4 Enhanced Beacons. It was determined that this 884 produced undue timer coupling among layers, that the resulting packet 885 size was potentially too large, and required it is not yet clear that 886 there is any need for Enhanced Beacons in a production network. 888 4.2.4. Network Synchronization 890 Nodes in a TSCH network must be time synchronized. A node keeps 891 synchronized to its time source neighbor through a combination of 892 frame-based and acknowledgment-based synchronization. In order to 893 maximize battery life and network throughput, it is advisable that 894 RPL ICMP discovery and maintenance traffic (governed by the trickle 895 timer) be somehow coordinated with the transmission of time 896 synchronization packets (especially with enhanced beacons). This 897 could be achieved through an interaction of the 6top sublayer and the 898 RPL objective Function, or could be controlled by a management 899 entity. 901 Time distribution requires a loop-less structure. Nodes taken in a 902 synchronization loop will rapidly desynchronize from the network and 903 become isolated. It is expected that a RPL DAG with a dedicated 904 global Instance is deployed for the purpose of time synchronization. 905 That Instance is referred to as the Time Synchronization Global 906 Instance (TSGI). The TSGI can be operated in either of the 3 modes 907 that are detailed in section 3.1.3 of RPL [RFC6550], "Instances, 908 DODAGs, and DODAG Versions". Multiple uncoordinated DODAGs with 909 independent roots may be used if all the roots share a common time 910 source such as the Global Positioning System (GPS). In the absence 911 of a common time source, the TSGI should form a single DODAG with a 912 virtual root. A backbone network is then used to synchronize and 913 coordinate RPL operations between the backbone routers that act as 914 sinks for the LLN. Optionally, RPL's periodic operations may be used 915 to transport the network synchronization. This may mean that 6top 916 would need to trigger (override) the trickle timer if no other 917 traffic has occurred for such a time that nodes may get out of 918 synchronization. 920 A node that has not joined the TSGI advertises a MAC level Join 921 Priority of 0xFF to notify its neighbors that is not capable of 922 serving as time parent. A node that has joined the TSGI advertises a 923 MAC level Join Priority set to its DAGRank() in that Instance, where 924 DAGRank() is the operation specified in section 3.5.1 of [RFC6550], 925 "Rank Comparison". 927 A root is configured or obtains by some external means the knowledge 928 of the RPLInstanceID for the TSGI. The root advertises its DagRank 929 in the TSGI, that must be less than 0xFF, as its Join Priority (JP) 930 in its IEEE802.15.4 Extended Beacons (EB). We'll note that the JP is 931 now specified between 0 and 0x3F leaving 2 bits in the octet unused 932 in the IEEE802.15.4e specification. After consultation with IEEE 933 authors, it was asserted that 6TiSCH can make a full use of the octet 934 to carry an integer value up to 0xFF. 936 A node that reads a Join Priority of less than 0xFF should join the 937 neighbor with the lesser Join Priority and use it as time parent. If 938 the node is configured to serve as time parent, then the node should 939 join the TSGI, obtain a Rank in that Instance and start advertising 940 its own DagRank in the TSGI as its Join Priority in its EBs. 942 4.2.5. SlotFrames and Priorities 944 6TiSCH enables in essence the capability to use IPv6 over a MAC layer 945 that enables to schedule some of the transmissions. In order to 946 ensure that the medium is free of contending packets when time 947 arrives for a scheduled transmission, a window of time is defined 948 around the scheduled transmission time where the medium must be free 949 of contending energy. 951 One simple way to obtain such a window is to format time and 952 frequencies in cells of transmission of equal duration. This is the 953 method that is adopted in IEEE802.15.4 TSCH as well as the Long Term 954 Evolution (LTE) of cellular networks. 956 In order to describe that formatting of time and frequencies, the 957 6TiSCH architecture defines a global concept that is called a Channel 958 Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of 959 cells with an height equal to the number of available channels 960 (indexed by ChannelOffsets) and a width (in timeslots) that is the 961 period of the network scheduling operation (indexed by slotOffsets) 962 for that CDU matrix. The size of a cell is a timeslot duration, and 963 values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to 964 accommodate for the transmission of a frame and an ack, including the 965 security validation on the receive side which may take up to a few 966 milliseconds on some device architecture. 968 A CDU matrix iterates over and over with a pseudo-random rotation 969 from an epoch time. In a given network, there might be multiple CDU 970 matrices that operate with different width, so they have different 971 durations and represent different periodic operations. It is 972 recommended that all CDU matrices in a 6TiSCH domain operate with the 973 same cell duration and are aligned, so as to reduce the chances of 974 interferences from slotted-aloha operations. The knowledge of the 975 CDU matrices is shared between all the nodes and used in particular 976 to define slotFrames. 978 A slotFrame is a MAC-level abstraction that is common to all nodes 979 and contains a series of timeslots of equal length and precedence. 980 It is characterized by a slotFrame_ID, and a slotFrame_size. A 981 slotFrame aligns to a CDU matrix for its parameters, such as number 982 and duration of timeslots. 984 Multiple slotFrames can coexist in a node schedule, i.e., a node can 985 have multiple activities scheduled in different slotFrames, based on 986 the precedence of the 6TiSCH topologies. The slotFrames may be 987 aligned to different CDU matrices and thus have different width. 988 There is typically one slotFrame for scheduled traffic that has the 989 highest precedence and one or more slotFrame(s) for RPL traffic. The 990 timeslots in the slotFrame are indexed by the SlotOffset; the first 991 cell is at SlotOffset 0. 993 When a packet is received from a higher layer for transmission, 6top 994 inserts that packet in the outgoing queue which matches the packet 995 best (Differentiated Services [RFC2474] can therefore be used). At 996 each scheduled transmit slot, 6top looks for the frame in all the 997 outgoing queues that best matches the cells. If a frame is found, it 998 is given to the TSCH MAC for transmission. 1000 4.2.6. Distributing the reservation of cells 1002 6TiSCH expects a high degree of scalability together with a 1003 distributed routing functionality based on RPL. To achieve this 1004 goal, the spectrum must be allocated in a way that allows for spatial 1005 reuse between zones that will not interfere with one another. In a 1006 large and spatially distributed network, a 6TiSCH node is often in a 1007 good position to determine usage of spectrum in its vicinity. 1009 Use cases for distributed routing are often associated with a 1010 statistical distribution of best-effort traffic with variable needs 1011 for bandwidth on each individual link. With 6TiSCH, the abstraction 1012 of an IPv6 link is implemented as a pair of bundles of cells, one in 1013 each direction; the size of a bundle is optimal when both the energy 1014 wasted idle listening and the packet drops due to congestion loss are 1015 minimized. This can be maintained if the number of cells in a bundle 1016 is adapted dynamically, and with enough reactivity, to match the 1017 variations of best-effort traffic. In turn, the agility to fulfill 1018 the needs for additional cells improves when the number of 1019 interactions with other devices and the protocol latencies are 1020 minimized. 1022 6TiSCH limits that interaction to RPL parents that will only 1023 negotiate with other RPL parents, and performs that negotiation by 1024 groups of cells as opposed to individual cells. The 6TiSCH 1025 architecture allows RPL parents to adjust dynamically, and 1026 independently from the PCE, the amount of bandwidth that is used to 1027 communicate between themselves and their children, in both 1028 directions; to that effect, an allocation mechanism enables a RPL 1029 parent to obtain the exclusive use of a portion of a CDU matrix 1030 within its interference domain. Note that a PCE is expected to have 1031 precedence in the allocation, so that a RPL parent would only be able 1032 to obtain portions that are not in-use by the PCE. 1034 The 6TiSCH architecture introduces the concept of chunks 1035 [I-D.ietf-6tisch-terminology]) to operate such spectrum distribution 1036 for a whole group of cells at a time. The CDU matrix is formatted 1037 into a set of chunks, each of them identified uniquely by a chunk-ID. 1038 The knowledge of this formatting is shared between all the nodes in a 1039 6TiSCH network. 6TiSCH also defines the process of chunk ownership 1040 appropriation whereby a RPL parent discovers a chunk that is not used 1041 in its interference domain (e.g lack of energy detected in reference 1042 cells in that chunk); then claims the chunk, and then defends it in 1043 case another RPL parent would attempt to appropriate it while it is 1044 in use. The chunk is the basic unit of ownership that is used in 1045 that process. 1047 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1048 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1049 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1050 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1051 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1052 ... 1053 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1054 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1055 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1056 0 1 2 3 4 5 6 M 1058 Figure 7: CDU matrix Partitioning in Chunks 1060 As a result of the process of chunk ownership appropriation, the RPL 1061 parent has exclusive authority to decide which cell in the 1062 appropriated chunk can be used by which node in its interference 1063 domain. In other words, it is implicitly delegated the right to 1064 manage the portion of the CDU matrix that is represented by the 1065 chunk. The RPL parent may thus orchestrate which transmissions occur 1066 in any of the cells in the chunk, by allocating cells from the chunk 1067 to any form of communication (unicast, multicast) in any direction 1068 between itself and its children. Initially, those cells are added to 1069 the heap of free cells, then dynamically placed into existing 1070 bundles, in new bundles, or allocated opportunistically for one 1071 transmission. 1073 The appropriation of a chunk can also be requested explicitly by the 1074 PCE to any node. In that case, the node still may need to perform 1075 the appropriation process to validate that no other node has claimed 1076 that chunk already. After a successful appropriation, the PCE owns 1077 the cells in that chunk, and may use them as hard cells to set up 1078 Tracks. 1080 4.3. Communication Paradigms and Interaction Models 1082 [I-D.ietf-6tisch-terminology] defines the terms of Communication 1083 Paradigms and Interaction Models, which can be placed in parallel to 1084 the Information Models and Data Models that are defined in [RFC3444]. 1086 A Communication Paradigms would be an abstract view of a protocol 1087 exchange, and would come with an Information Model for the 1088 information that is being exchanged. In contrast, an Interaction 1089 Models would be more refined and could point on standard operation 1090 such as a Representational state transfer (REST) "GET" operation and 1091 would match a Data Model for the data that is provided over the 1092 protocol exchange. 1094 section 2.1.3 of [I-D.ietf-roll-rpl-industrial-applicability] and 1095 next sections discuss application-layer paradigms, such as Source- 1096 sink (SS) that is a Multipeer to Multipeer (MP2MP) model primarily 1097 used for alarms and alerts, Publish-subscribe (PS, or pub/sub) that 1098 is typically used for sensor data, as well as Peer-to-peer (P2P) and 1099 Peer-to-multipeer (P2MP) communications. Additional considerations 1100 on Duocast and its N-cast generalization are also provided. Those 1101 paradigms are frequently used in industrial automation, which is a 1102 major use case for IEEE802.15.4 TSCH wireless networks with 1103 [ISA100.11a] and [WirelessHART], that provides a wireless access to 1104 [HART] applications and devices. 1106 This specification focuses on Communication Paradigms and Interaction 1107 Models for packet forwarding and TSCH resources (cells) management. 1108 Management mechanisms for the TSCH schedule at Link-layer (one-hop), 1109 Network-layer (multithop along a Track), and Application-layer 1110 (remote control) are discussed in Section 4.4. Link-layer frame 1111 forwarding interactions are discussed in Section 4.5, and Network- 1112 layer Packet routing is addressed in Section 4.6. 1114 4.4. Schedule Management Mechanisms 1116 6TiSCH uses 4 paradigms to manage the TSCH schedule of the LLN nodes: 1117 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1118 and scheduling management, and Hop-by-hop scheduling. Multiple 1119 mechanisms are defined that implement the associated Interaction 1120 Models, and can be combined and used in the same LLN. Which 1121 mechanism(s) to use depends on application requirements. 1123 4.4.1. Static Scheduling 1125 In the simplest instantiation of a 6TiSCH network, a common fixed 1126 schedule may be shared by all nodes in the network. Cells are 1127 shared, and nodes contend for slot access in a slotted aloha manner. 1129 A static TSCH schedule can be used to bootstrap a network, as an 1130 initial phase during implementation, or as a fall-back mechanism in 1131 case of network malfunction. This schedule is pre-established, for 1132 instance decided by a network administrator based on operational 1133 needs. It can be pre-configured into the nodes, or, more commonly, 1134 learned by a node when joining the network using standard 1135 IEEE802.15.4 Information Elements (IE). Regardless, the schedule 1136 remains unchanged after the node has joined a network. RPL is used 1137 on the resulting network. This "minimal" scheduling mechanism that 1138 implements this paradigm is detailed in [I-D.ietf-6tisch-minimal]. 1140 4.4.2. Neighbor-to-neighbor Scheduling 1142 In the simplest instantiation of a 6TiSCH network described in 1143 Section 4.4.1, nodes may expect a packet at any cell in the schedule 1144 and will waste energy idle listening. In a more complex 1145 instantiation of a 6TiSCH network, a matching portion of the schedule 1146 is established between peers to reflect the observed amount of 1147 transmissions between those nodes. The aggregation of the cells 1148 between a node and a peer forms a bundle that the 6top layer uses to 1149 implement the abstraction of a link for IP. The bandwidth on that 1150 link is proportional to the number of cells in the bundle. 1152 If the size of a bundle is configured to fit an average amount of 1153 bandwidth, peak traffic is dropped. If the size is configured to 1154 allow for peak emissions, energy is be wasted idle listening. 1156 The 6top sublayer [I-D.wang-6tisch-6top-sublayer] defines a protocol 1157 for neighbor nodes to reserve soft cells to transmit to one another. 1159 Because this reservation is done without global knowledge of the 1160 schedule of nodes in the LLN, scheduling collisions are possible. 1161 6top defines a monitoring process which continuously Tracks the 1162 packet delivery ratio of soft cells. It uses these statistics to 1163 trigger the reallocation of a soft cell in the schedule, using a 1164 negotiation protocol between the neighbors nodes communicating over 1165 that cell. 1167 In the most efficient instantiations of a 6TiSCH network, the size of 1168 the bundles that implement the links may be changed dynamically in 1169 order to adapt to the need of end-to-end flows routed by RPL. An 1170 optional Scheduling Function (SF) such as SF0 1171 [I-D.ietf-6tisch-6top-sf0] is used to monitor bandwidth usage and 1172 perform requests for dynamic allocation by the 6top sublayer. The SF 1173 component is not part of the 6top sublayer. It may be collocated on 1174 the same device or may be partially or fully offloaded to an external 1175 system. 1177 Monitoring and relocation is done in the 6top layer. For the upper 1178 layer, the connection between two neighbor nodes appears as an number 1179 of cells. Depending on traffic requirements, the upper layer can 1180 request 6top to add or delete a number of cells scheduled to a 1181 particular neighbor, without being responsible for choosing the exact 1182 slotOffset/channelOffset of those cells. 1184 4.4.3. Remote Monitoring and Schedule Management 1186 The 6top interface document [I-D.ietf-6tisch-6top-interface] 1187 specifies the generic data model that can be used to monitor and 1188 manage resources of the 6top sublayer. Abstract methods are 1189 suggested for use by a management entity in the device. The data 1190 model also enables remote control operations on the 6top sublayer. 1192 The capability to interact with the node 6top sublayer from multiple 1193 hops away can be leveraged for monitoring, scheduling, or a 1194 combination of thereof. The architecture supports variations on the 1195 deployment model, and focuses on the flows rather than whether there 1196 is a proxy or a translation operation en-route. 1198 [I-D.ietf-6tisch-coap] defines an mapping of the 6top set of 1199 commands, which is described in [I-D.ietf-6tisch-6top-interface], to 1200 CoAP resources. This allows an entity to interact with the 6top 1201 layer of a node that is multiple hops away in a RESTful fashion. 1203 The entity issuing the CoAP requests can be a central scheduling 1204 entity (e.g. a PCE), a node multiple hops away with the authority to 1205 modify the TSCH schedule (e.g. the head of a local cluster), or a 1206 external device monitoring the overall state of the network (e.g. 1208 NME). It is also possible that a mapping entity on the backbone 1209 transforms a non-CoAP protocol such as PCEP into the RESTful 1210 interfaces that the 6TiSCH devices support. 1212 With respect to Centralized routing and scheduling, the 6TiSCH 1213 Architecture is (expected to be) be an extension of the detnet work 1214 Deterministic Networking Architecture [I-D.finn-detnet-architecture], 1215 which studies Layer-3 aspects of Deterministic Networks, and covers 1216 networks that span multiple Layer-2 domains. The DetNet architecture 1217 is a form of SDN Architecture and is composed of three planes, a 1218 (User) Application Plane, a Controller Plane (where the PCE 1219 operates), and a Network Plane which in our case is the 6TiSCH LLN. 1220 The generic SDN architecture is discussed in Software-Defined 1221 Networking (SDN): Layers and Architecture Terminology [RFC7426] and 1222 is represented below: 1224 SDN Layers and Architecture Terminology per RFC 7426 1226 o--------------------------------o 1227 | | 1228 | +-------------+ +----------+ | 1229 | | Application | | Service | | 1230 | +-------------+ +----------+ | 1231 | Application Plane | 1232 o---------------Y----------------o 1233 | 1234 *-----------------------------Y---------------------------------* 1235 | Network Services Abstraction Layer (NSAL) | 1236 *------Y------------------------------------------------Y-------* 1237 | | 1238 | Service Interface | 1239 | | 1240 o------Y------------------o o---------------------Y------o 1241 | | Control Plane | | Management Plane | | 1242 | +----Y----+ +-----+ | | +-----+ +----Y----+ | 1243 | | Service | | App | | | | App | | Service | | 1244 | +----Y----+ +--Y--+ | | +--Y--+ +----Y----+ | 1245 | | | | | | | | 1246 | *----Y-----------Y----* | | *---Y---------------Y----* | 1247 | | Control Abstraction | | | | Management Abstraction | | 1248 | | Layer (CAL) | | | | Layer (MAL) | | 1249 | *----------Y----------* | | *----------Y-------------* | 1250 | | | | | | 1251 o------------|------------o o------------|---------------o 1252 | | 1253 | CP | MP 1254 | Southbound | Southbound 1255 | Interface | Interface 1256 | | 1257 *------------Y---------------------------------Y----------------* 1258 | Device and resource Abstraction Layer (DAL) | 1259 *------------Y---------------------------------Y----------------* 1260 | | | | 1261 | o-------Y----------o +-----+ o--------Y----------o | 1262 | | Forwarding Plane | | App | | Operational Plane | | 1263 | o------------------o +-----+ o-------------------o | 1264 | Network Device | 1265 +---------------------------------------------------------------+ 1267 Figure 8 1269 The PCE establishes end-to-end Tracks of hard cells, which are 1270 described in more details in Section 4.5.1. The DetNet work is 1271 expected to enable end to end Deterministic Path across heterogeneous 1272 network (e.g. a 6TiSCH LLN and an Ethernet Backbone). This model 1273 fits the 6TiSCH extended configuration, whereby a 6BBR federates 1274 multiple 6TiSCH LLN in a single subnet over a backbone that can be, 1275 for instance, Ethernet or Wi-Fi. In that model, 6TiSCH 6BBRs 1276 synchronize with one another over the backbone, so as to ensure that 1277 the multiple LLNs that form the IPv6 subnet stay tightly 1278 synchronized. 1280 If the Backbone is Deterministic, then the Backbone Router ensures 1281 that the end-to-end deterministic behavior is maintained between the 1282 LLN and the backbone. It is the responsibility of the PCE to compute 1283 a deterministic path and to end across the TSCH network and an 1284 IEEE802.1 TSN Ethernet backbone, and that of DetNet to enable end-to- 1285 end deterministic forwarding. 1287 4.4.4. Hop-by-hop Scheduling 1289 A node can reserve a Track to a destination node multiple hops away 1290 by installing soft cells at each intermediate node. This forms a 1291 Track of soft cells. It is the responsibility of the 6top sublayer 1292 of each node on the Track to monitor these soft cells and trigger 1293 relocation when needed. 1295 This hop-by-hop reservation mechanism is expected to be similar in 1296 essence to [RFC3209] and/or [RFC4080]/[RFC5974]. The protocol for a 1297 node to trigger hop-by-hop scheduling is not yet defined. 1299 4.5. Forwarding Models 1301 By forwarding, this specification means the per-packet operation that 1302 allows to deliver a packet to a next hop or an upper layer in this 1303 node. Forwarding is based on pre-existing state that was installed 1304 as a result of a routing computation Section 4.6. 6TiSCH supports 1305 three different forwarding model, G-MPLS Track Forwarding (TF), 1306 6LoWPAN Fragment Forwarding (FF) and IPv6 Forwarding (6F). 1308 4.5.1. Track Forwarding 1310 A Track is a directional path between a source and a destination. In 1311 a Track cell, the normal operation of IEEE802.15.4 Automatic Repeat- 1312 reQuest (ARQ) usually happens, though the acknowledgment may be 1313 omitted in some cases, for instance if there is no scheduled cell for 1314 a retry. 1316 Track Forwarding is the simplest and fastest. A bundle of cells set 1317 to receive (RX-cells) is uniquely paired to a bundle of cells that 1318 are set to transmit (TX-cells), representing a layer-2 forwarding 1319 state that can be used regardless of the network layer protocol. 1321 This model can effectively be seen as a Generalized Multi-protocol 1322 Label Switching (G-MPLS) operation in that the information used to 1323 switch a frame is not an explicit label, but rather related to other 1324 properties of the way the packet was received, a particular cell in 1325 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1326 Layer-2 security) accepts a frame, that frame can be switched 1327 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1328 fragment, or a frame from an alternate protocol such as WirelessHART 1329 or ISA100.11a. 1331 A data frame that is forwarded along a Track normally has a 1332 destination MAC address that is set to broadcast - or a multicast 1333 address depending on MAC support. This way, the MAC layer in the 1334 intermediate nodes accepts the incoming frame and 6top switches it 1335 without incurring a change in the MAC header. In the case of 1336 IEEE802.15.4, this means effectively broadcast, so that along the 1337 Track the short address for the destination of the frame is set to 1338 0xFFFF. 1340 A Track is thus formed end-to-end as a succession of paired bundles, 1341 a receive bundle from the previous hop and a transmit bundle to the 1342 next hop along the Track, and a cell in such a bundle belongs to at 1343 most one Track. For a given iteration of the device schedule, the 1344 effective channel of the cell is obtained by adding a pseudo-random 1345 number to the channelOffset of the cell, which results in a rotation 1346 of the frequency that used for transmission. The bundles may be 1347 computed so as to accommodate both variable rates and 1348 retransmissions, so they might not be fully used at a given iteration 1349 of the schedule. The 6TiSCH architecture provides additional means 1350 to avoid waste of cells as well as overflows in the transmit bundle, 1351 as follows: 1353 In one hand, a TX-cell that is not needed for the current iteration 1354 may be reused opportunistically on a per-hop basis for routed 1355 packets. When all of the frame that were received for a given Track 1356 are effectively transmitted, any available TX-cell for that Track can 1357 be reused for upper layer traffic for which the next-hop router 1358 matches the next hop along the Track. In that case, the cell that is 1359 being used is effectively a TX-cell from the Track, but the short 1360 address for the destination is that of the next-hop router. It 1361 results that a frame that is received in a RX-cell of a Track with a 1362 destination MAC address set to this node as opposed to broadcast must 1363 be extracted from the Track and delivered to the upper layer (a frame 1364 with an unrecognized MAC address is dropped at the lower MAC layer 1365 and thus is not received at the 6top sublayer). 1367 On the other hand, it might happen that there are not enough TX-cells 1368 in the transmit bundle to accommodate the Track traffic, for instance 1369 if more retransmissions are needed than provisioned. In that case, 1370 the frame can be placed for transmission in the bundle that is used 1371 for layer-3 traffic towards the next hop along the Track as long as 1372 it can be routed by the upper layer, that is, typically, if the frame 1373 transports an IPv6 packet. The MAC address should be set to the 1374 next-hop MAC address to avoid confusion. It results that a frame 1375 that is received over a layer-3 bundle may be in fact associated to a 1376 Track. In a classical IP link such as an Ethernet, off-Track traffic 1377 is typically in excess over reservation to be routed along the non- 1378 reserved path based on its QoS setting. But with 6TiSCH, since the 1379 use of the layer-3 bundle may be due to transmission failures, it 1380 makes sense for the receiver to recognize a frame that should be re- 1381 Tracked, and to place it back on the appropriate bundle if possible. 1382 A frame should be re-Tracked if the Per-Hop-Behavior group indicated 1383 in the Differentiated Services Field in the IPv6 header is set to 1384 Deterministic Forwarding, as discussed in Section 4.6.1. A frame is 1385 re-Tracked by scheduling it for transmission over the transmit bundle 1386 associated to the Track, with the destination MAC address set to 1387 broadcast. 1389 There are 2 modes for a Track, transport mode and tunnel mode. 1391 4.5.1.1. Transport Mode 1393 In transport mode, the Protocol Data Unit (PDU) is associated with 1394 flow-dependant meta-data that refers uniquely to the Track, so the 1395 6top sublayer can place the frame in the appropriate cell without 1396 ambiguity. In the case of IPv6 traffic, this flow identification is 1397 transported in the Flow Label of the IPv6 header. Associated with 1398 the source IPv6 address, the Flow Label forms a globally unique 1399 identifier for that particular Track that is validated at egress 1400 before restoring the destination MAC address (DMAC) and punting to 1401 the upper layer. 1403 | ^ 1404 +--------------+ | | 1405 | IPv6 | | | 1406 +--------------+ | | 1407 | 6LoWPAN HC | | | 1408 +--------------+ ingress egress 1409 | 6top | sets +----+ +----+ restores 1410 +--------------+ dmac to | | | | dmac to 1411 | TSCH MAC | brdcst | | | | self 1412 +--------------+ | | | | | | 1413 | LLN PHY | +-------+ +--...-----+ +-------+ 1414 +--------------+ 1416 Track Forwarding, Transport Mode 1418 4.5.1.2. Tunnel Mode 1420 In tunnel mode, the frames originate from an arbitrary protocol over 1421 a compatible MAC that may or may not be synchronized with the 6TiSCH 1422 network. An example of this would be a router with a dual radio that 1423 is capable of receiving and sending WirelessHART or ISA100.11a frames 1424 with the second radio, by presenting itself as an access Point or a 1425 Backbone Router, respectively. 1427 In that mode, some entity (e.g. PCE) can coordinate with a 1428 WirelessHART Network Manager or an ISA100.11a System Manager to 1429 specify the flows that are to be transported transparently over the 1430 Track. 1432 +--------------+ 1433 | IPv6 | 1434 +--------------+ 1435 | 6LoWPAN HC | 1436 +--------------+ set restore 1437 | 6top | +dmac+ +dmac+ 1438 +--------------+ to|brdcst to|nexthop 1439 | TSCH MAC | | | | | 1440 +--------------+ | | | | 1441 | LLN PHY | +-------+ +--...-----+ +-------+ 1442 +--------------+ | ingress egress | 1443 | | 1444 +--------------+ | | 1445 | LLN PHY | | | 1446 +--------------+ | | 1447 | TSCH MAC | | | 1448 +--------------+ | dmac = | dmac = 1449 |ISA100/WiHART | | nexthop v nexthop 1450 +--------------+ 1452 Figure 9: Track Forwarding, Tunnel Mode 1454 In that case, the flow information that identifies the Track at the 1455 ingress 6TiSCH router is derived from the RX-cell. The dmac is set 1456 to this node but the flow information indicates that the frame must 1457 be tunneled over a particular Track so the frame is not passed to the 1458 upper layer. Instead, the dmac is forced to broadcast and the frame 1459 is passed to the 6top sublayer for switching. 1461 At the egress 6TiSCH router, the reverse operation occurs. Based on 1462 metadata associated to the Track, the frame is passed to the 1463 appropriate link layer with the destination MAC restored. 1465 4.5.1.3. Tunnel Metadata 1467 Metadata coming with the Track configuration is expected to provide 1468 the destination MAC address of the egress endpoint as well as the 1469 tunnel mode and specific data depending on the mode, for instance a 1470 service access point for frame delivery at egress. If the tunnel 1471 egress point does not have a MAC address that matches the 1472 configuration, the Track installation fails. 1474 In transport mode, if the final layer-3 destination is the tunnel 1475 termination, then it is possible that the IPv6 address of the 1476 destination is compressed at the 6LoWPAN sublayer based on the MAC 1477 address. It is thus mandatory at the ingress point to validate that 1478 the MAC address that was used at the 6LoWPAN sublayer for compression 1479 matches that of the tunnel egress point. For that reason, the node 1480 that injects a packet on a Track checks that the destination is 1481 effectively that of the tunnel egress point before it overwrites it 1482 to broadcast. The 6top sublayer at the tunnel egress point reverts 1483 that operation to the MAC address obtained from the tunnel metadata. 1485 4.5.2. Fragment Forwarding 1487 Considering that 6LoWPAN packets can be as large as 1280 bytes (the 1488 IPv6 MTU), and that the non-storing mode of RPL implies Source 1489 Routing that requires space for routing headers, and that a 1490 IEEE802.15.4 frame with security may carry in the order of 80 bytes 1491 of effective payload, an IPv6 packet might be fragmented into more 1492 than 16 fragments at the 6LoWPAN sublayer. 1494 This level of fragmentation is much higher than that traditionally 1495 experienced over the Internet with IPv4 fragments, where 1496 fragmentation is already known as harmful. 1498 In the case to a multihop route within a 6TiSCH network, Hop-by-Hop 1499 recomposition occurs at each hop in order to reform the packet and 1500 route it. This creates additional latency and forces intermediate 1501 nodes to store a portion of a packet for an undetermined time, thus 1502 impacting critical resources such as memory and battery. 1504 [I-D.thubert-roll-forwarding-frags] describes a mechanism whereby the 1505 datagram tag in the 6LoWPAN Fragment is used as a label for switching 1506 at the 6LoWPAN sublayer. The draft allows for a degree of flow 1507 control based on an Explicit Congestion Notification, as well as end- 1508 to-end individual fragment recovery. 1510 | ^ 1511 +--------------+ | | 1512 | IPv6 | | +----+ +----+ | 1513 +--------------+ | | | | | | 1514 | 6LoWPAN HC | | learn learn | 1515 +--------------+ | | | | | | 1516 | 6top | | | | | | | 1517 +--------------+ | | | | | | 1518 | TSCH MAC | | | | | | | 1519 +--------------+ | | | | | | 1520 | LLN PHY | +-------+ +--...-----+ +-------+ 1521 +--------------+ 1523 Figure 10: Forwarding First Fragment 1525 In that model, the first fragment is routed based on the IPv6 header 1526 that is present in that fragment. The 6LoWPAN sublayer learns the 1527 next hop selection, generates a new datagram tag for transmission to 1528 the next hop, and stores that information indexed by the incoming MAC 1529 address and datagram tag. The next fragments are then switched based 1530 on that stored state. 1532 | ^ 1533 +--------------+ | | 1534 | IPv6 | | | 1535 +--------------+ | | 1536 | 6LoWPAN HC | | replay replay | 1537 +--------------+ | | | | | | 1538 | 6top | | | | | | | 1539 +--------------+ | | | | | | 1540 | TSCH MAC | | | | | | | 1541 +--------------+ | | | | | | 1542 | LLN PHY | +-------+ +--...-----+ +-------+ 1543 +--------------+ 1545 Figure 11: Forwarding Next Fragment 1547 A bitmap and an ECN echo in the end-to-end acknowledgment enable the 1548 source to resend the missing fragments selectively. The first 1549 fragment may be resent to carve a new path in case of a path failure. 1550 The ECN echo set indicates that the number of outstanding fragments 1551 should be reduced. 1553 4.5.3. IPv6 Forwarding 1555 As the packets are routed at Layer-3, traditional QoS and RED 1556 operations are expected to prioritize flows; the application of 1557 Differentiated Services is further discussed in 1558 [I-D.svshah-tsvwg-lln-diffserv-recommendations]. 1560 | ^ 1561 +--------------+ | | 1562 | IPv6 | | +-QoS+ +-QoS+ | 1563 +--------------+ | | | | | | 1564 | 6LoWPAN HC | | | | | | | 1565 +--------------+ | | | | | | 1566 | 6top | | | | | | | 1567 +--------------+ | | | | | | 1568 | TSCH MAC | | | | | | | 1569 +--------------+ | | | | | | 1570 | LLN PHY | +-------+ +--...-----+ +-------+ 1571 +--------------+ 1573 Figure 12: IP Forwarding 1575 4.6. Centralized vs. Distributed Routing 1577 6TiSCH supports a mixed model of centralized routes and distributed 1578 routes. Centralized routes can for example be computed by a entity 1579 such as a PCE. Distributed routes are computed by RPL. 1581 Both methods may inject routes in the Routing Tables of the 6TiSCH 1582 routers. In either case, each route is associated with a 6TiSCH 1583 topology that can be a RPL Instance topology or a Track. The 6TiSCH 1584 topology is indexed by a Instance ID, in a format that reuses the 1585 RPLInstanceID as defined in RPL [RFC6550]. 1587 Both RPL and PCE rely on shared sources such as policies to define 1588 Global and Local RPLInstanceIDs that can be used by either method. 1589 It is possible for centralized and distributed routing to share a 1590 same topology. Generally they will operate in different slotFrames, 1591 and centralized routes will be used for scheduled traffic and will 1592 have precedence over distributed routes in case of conflict between 1593 the slotFrames. 1595 4.6.1. Packet Marking and Handling 1597 All packets inside a 6TiSCH domain must carry the Instance ID that 1598 identifies the 6TiSCH topology that is to be used for routing and 1599 forwarding that packet. The location of that information must be the 1600 same for all packets forwarded inside the domain. 1602 For packets that are routed by a PCE along a Track, the tuple formed 1603 by the IPv6 source address and a local RPLInstanceID in the packet 1604 identify uniquely the Track and associated transmit bundle. 1606 Additionally, an IP packet that is sent along a Track uses the 1607 Differentiated Services Per-Hop-Behavior Group called Deterministic 1608 Forwarding, as described in 1609 [I-D.svshah-tsvwg-deterministic-forwarding]. 1611 For packets that are routed by RPL, that information is the 1612 RPLInstanceID which is carried in the RPL Packet Information, as 1613 discussed in section 11.2 of [RFC6550], "Loop Avoidance and 1614 Detection". 1616 The RPL Packet Information (RPI) is carried in IPv6 packets as a RPL 1617 option in the IPv6 Hop-By-Hop Header [RFC6553]. 1619 A compression mechanism for the RPL packet artifacts that integrates 1620 the compression of IP-in-IP encapsulation and the Routing Header type 1621 3 [RFC6554] with that of the RPI in a 6LoWPAN dispatch/header type is 1622 concurrently being evaluated as [I-D.ietf-roll-routing-dispatch]. 1624 Either way, the method and format used for encoding the RPLInstanceID 1625 is generalized to all 6TiSCH topological Instances, which include 1626 both RPL Instances and Tracks. 1628 5. IANA Considerations 1630 This specification does not require IANA action. 1632 6. Security Considerations 1634 This architecture operates on IEEE802.15.4 and expects link-layer 1635 security to be enabled at all times between connected devices, except 1636 for the very first step of the device join process, where a joining 1637 device may need some initial, unsecured exchanges so as to obtain its 1638 initial key material. Work has already started at the 6TiSCH 1639 Security Design Team and an overview of the current state of that 1640 work is presented in Section 6.1. 1642 Future work on 6TiSCH security and will examine in deeper detail how 1643 to secure transactions end-to-end, and to maintain the security 1644 posture of a device over its lifetime. The result of that work will 1645 be described in a subsequent volume of this architecture. 1647 6.1. Join Process Highlights 1649 The architecture specifies three logical elements to describe the 1650 join process: 1652 Joining Node (JN): Node that wishes to become part of the network; 1653 Join Coordination Entity (JCE) : A Join Coordination Entity (JCE) 1654 that arbitrates network access and hands out network parameters 1655 (such as keying material); 1657 Join Assistant (JA), a one-hop (radio) neighbor of the joining node 1658 that acts as proxy network node and may provide connectivity 1659 with the JCE. 1661 The join protocol consists of three major activities: 1663 Device Authentication: The JN and the JA mutually authenticate each 1664 other and establish a shared key, so as to ensure on-going 1665 authenticated communications. This may involve a server as a 1666 third party. 1668 Authorization: The JA decides on whether/how to authorize a JN (if 1669 denied, this may result in loss of bandwidth). Conversely, the 1670 JN decides on whether/how to authorize the network (if denied, 1671 it will not join the network). Authorization decisions may 1672 involve other nodes in the network. 1674 Configuration/Parameterization: The JA distributes configuration 1675 information to the JN, such as scheduling information, IP 1676 address assignment information, and network policies. This may 1677 originate from other network devices, for which the JA may act 1678 as proxy. This step may also include distribution of 1679 information from the JN to the JA and other nodes in the 1680 network and, more generally, synchronization of information 1681 between these entities. 1683 The device joining process is depicted in Figure 13, where it is 1684 assumed that devices have access to certificates and where entities 1685 have access to the root CA keys of their communicating parties 1686 (initial set-up requirement). Under these assumptions, the 1687 authentication step of the device joining process does not require 1688 online involvement of a third party. Mutual authentication is 1689 performed between the JN and the JA using their certificates, which 1690 also results in a shared key between these two entities. 1692 The JA assists the JN in mutual authentication with a remote server 1693 node (primarily via provision of a communication path with the 1694 server), which also results in a shared (end-to-end) key between 1695 those two entities. The server node may be a JCE that arbitrages the 1696 network authorization of the JN (where the JA will deny bandwidth if 1697 authorization is not successful); it may distribute network-specific 1698 configuration parameters (including network-wide keys) to the JN. In 1699 its turn, the JN may distribute and synchronize information 1700 (including, e.g., network statistics) to the server node and, if so 1701 desired, also to the JA. The actual decision of the JN to become 1702 part of the network may depend on authorization of the network 1703 itself. 1705 The server functionality is a role which may be implemented with one 1706 (centralized) or multiple devices (distributed). In either case, 1707 mutual authentication is established with each physical server entity 1708 with which a role is implemented. 1710 Note that in the above description, the JA does not solely act as a 1711 relay node, thereby allowing it to first filter traffic to be relayed 1712 based on cryptographic authentication criteria - this provides first- 1713 level access control and mitigates certain types of denial-of-service 1714 attacks on the network at large. 1716 Depending on more detailed insight in cost/benefit trade-offs, this 1717 process might be complemented by a more "relaxed" mechanism, where 1718 the JA acts as a relay node only. The final architecture will 1719 provide mechanisms to also cover cases where the initial set-up 1720 requirements are not met or where some other out-of-sync behavior 1721 occurs; it will also suggest some optimizations in case JCE-related 1722 information is already available with the JA (via caching of 1723 information). 1725 When a device rejoins the network in the same authorization domain, 1726 the authorization step could be omitted if the server distributes the 1727 authorization state for the device to the JA when the device 1728 initially joined the network. However, this generally still requires 1729 the exchange of updated configuration information, e.g., related to 1730 time schedules and bandwidth allocation. 1732 {joining node} {neighbor} {server, etc.} Example: 1733 +---------+ +---------+ +---------+ 1734 | Joining | | Join | +--| CA |certificate 1735 | Node | |Assistant| | +---------+ issuance 1736 +---------+ +---------+ | +---------+ 1737 | | +--|Authoriz.| membership 1738 |<----Beaconing------| | +---------+ test (JCE) 1739 | | | +---------+ 1740 |<--Authentication-->| +--| Routing | IP address 1741 | |<--Authorization-->| +--------- assignment 1742 |<-------------------| | +---------+ 1743 | | +--| Gateway | backbone, 1744 |------------------->| | +---------+ cloud 1745 | |<--Configuration-->| +---------+ 1746 |<-------------------| +--|Bandwidth| PCE 1747 +---------+ schedule 1748 . . . 1749 . . . 1751 Figure 13: Network joining, with only authorization by third party 1753 7. Acknowledgments 1755 7.1. Contributors 1757 The co-authors of this document are listed below: 1759 Robert Assimiti for his breakthrough work on RPL over TSCH and 1760 initial text and guidance. 1762 Kris Pister for creating it all and his continuing guidance through 1763 the elaboration of this design. 1765 Michael Richardson for his leadership role in the Security Design 1766 Team and his contribution throughout this document. 1768 Rene Struik for the security section and his contribution to the 1769 Security Design Team. 1771 Xavier Vilajosana who lead the design of the minimal support with 1772 RPL and contributed deeply to the 6top design and the G-MPLS 1773 operation of Track switching. 1775 Qin Wang who lead the design of the 6top sublayer and contributed 1776 related text that was moved and/or adapted in this document. 1778 Thomas Watteyne for his contribution to the whole design, in 1779 particular on TSCH and security. 1781 7.2. Special Thanks 1783 Special thanks to Tero Kivinen, Jonathan Simon, Giuseppe Piro, Subir 1784 Das and Yoshihiro Ohba for their deep contribution to the initial 1785 security work, and to Diego Dujovne for starting and leading the SF0 1786 effort. 1788 Special thanks also to Pat Kinney for his support in maintaining the 1789 connection active and the design in line with work happening at 1790 IEEE802.15.4. 1792 Special thanks to Ted Lemon who was the INT Area A-D while this 1793 specification was developed for his great support and help 1794 throughout. 1796 Also special thanks to Ralph Droms who performed the first INT Area 1797 Directorate review, that was very deep and through and radically 1798 changed the orientations of this document. 1800 7.3. And Do not Forget 1802 This specification is the result of multiple interactions, in 1803 particular during the 6TiSCH (bi)Weekly Interim call, relayed through 1804 the 6TiSCH mailing list at the IETF. 1806 The authors wish to thank: Alaeddine Weslati, Chonggang Wang, 1807 Georgios Exarchakos, Zhuo Chen, Alfredo Grieco, Bert Greevenbosch, 1808 Cedric Adjih, Deji Chen, Martin Turon, Dominique Barthel, Elvis 1809 Vogli, Geraldine Texier, Malisa Vucinic, Guillaume Gaillard, Herman 1810 Storey, Kazushi Muraoka, Ken Bannister, Kuor Hsin Chang, Laurent 1811 Toutain, Maik Seewald, Maria Rita Palattella, Michael Behringer, 1812 Nancy Cam Winget, Nicola Accettura, Nicolas Montavont, Oleg Hahm, 1813 Patrick Wetterwald, Paul Duffy, Peter van der Stock, Rahul Sen, 1814 Pieter de Mil, Pouria Zand, Rouhollah Nabati, Rafa Marin-Lopez, 1815 Raghuram Sudhaakar, Sedat Gormus, Shitanshu Shah, Steve Simlo, 1816 Tengfei Chang, Tina Tsou, Tom Phinney, Xavier Lagrange, Ines Robles 1817 and Samita Chakrabarti for their participation and various 1818 contributions. 1820 8. References 1821 8.1. Normative References 1823 [I-D.finn-detnet-architecture] 1824 Finn, N., Thubert, P., and M. Teener, "Deterministic 1825 Networking Architecture", draft-finn-detnet- 1826 architecture-04 (work in progress), March 2016. 1828 [I-D.ietf-6lo-backbone-router] 1829 Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo- 1830 backbone-router-01 (work in progress), March 2016. 1832 [I-D.ietf-6tisch-minimal] 1833 Vilajosana, X. and K. Pister, "Minimal 6TiSCH 1834 Configuration", draft-ietf-6tisch-minimal-15 (work in 1835 progress), February 2016. 1837 [I-D.ietf-6tisch-terminology] 1838 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, 1839 "Terminology in IPv6 over the TSCH mode of IEEE 1840 802.15.4e", draft-ietf-6tisch-terminology-07 (work in 1841 progress), March 2016. 1843 [I-D.ietf-roll-routing-dispatch] 1844 Thubert, P., Bormann, C., Toutain, L., and R. Cragie, 1845 "6LoWPAN Routing Header", draft-ietf-roll-routing- 1846 dispatch-00 (work in progress), March 2016. 1848 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 1849 DOI 10.17487/RFC0768, August 1980, 1850 . 1852 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1853 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1854 December 1998, . 1856 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1857 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1858 DOI 10.17487/RFC4861, September 2007, 1859 . 1861 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1862 Address Autoconfiguration", RFC 4862, 1863 DOI 10.17487/RFC4862, September 2007, 1864 . 1866 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1867 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1868 DOI 10.17487/RFC6282, September 2011, 1869 . 1871 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1872 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1873 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1874 Low-Power and Lossy Networks", RFC 6550, 1875 DOI 10.17487/RFC6550, March 2012, 1876 . 1878 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 1879 and D. Barthel, "Routing Metrics Used for Path Calculation 1880 in Low-Power and Lossy Networks", RFC 6551, 1881 DOI 10.17487/RFC6551, March 2012, 1882 . 1884 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 1885 Protocol for Low-Power and Lossy Networks (RPL)", 1886 RFC 6552, DOI 10.17487/RFC6552, March 2012, 1887 . 1889 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1890 Power and Lossy Networks (RPL) Option for Carrying RPL 1891 Information in Data-Plane Datagrams", RFC 6553, 1892 DOI 10.17487/RFC6553, March 2012, 1893 . 1895 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1896 Routing Header for Source Routes with the Routing Protocol 1897 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1898 DOI 10.17487/RFC6554, March 2012, 1899 . 1901 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1902 Bormann, "Neighbor Discovery Optimization for IPv6 over 1903 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1904 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1905 . 1907 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 1908 Application Protocol (CoAP)", RFC 7252, 1909 DOI 10.17487/RFC7252, June 2014, 1910 . 1912 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 1913 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 1914 Internet of Things (IoT): Problem Statement", RFC 7554, 1915 DOI 10.17487/RFC7554, May 2015, 1916 . 1918 8.2. Informative References 1920 [I-D.ietf-6tisch-6top-interface] 1921 Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer 1922 (6top) Interface", draft-ietf-6tisch-6top-interface-04 1923 (work in progress), July 2015. 1925 [I-D.ietf-6tisch-6top-protocol] 1926 Wang, Q. and X. Vilajosana, "6top Protocol (6P)", draft- 1927 ietf-6tisch-6top-protocol-00 (work in progress), April 1928 2016. 1930 [I-D.ietf-6tisch-6top-sf0] 1931 Dujovne, D., Grieco, L., Palattella, M., and N. Accettura, 1932 "6TiSCH 6top Scheduling Function Zero (SF0)", draft-ietf- 1933 6tisch-6top-sf0-00 (work in progress), May 2016. 1935 [I-D.ietf-6tisch-coap] 1936 Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and 1937 Interaction using CoAP", draft-ietf-6tisch-coap-03 (work 1938 in progress), March 2015. 1940 [I-D.ietf-detnet-use-cases] 1941 Grossman, E., Gunther, C., Thubert, P., Wetterwald, P., 1942 Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y., 1943 Varga, B., Farkas, J., Goetz, F., and J. Schmitt, 1944 "Deterministic Networking Use Cases", draft-ietf-detnet- 1945 use-cases-09 (work in progress), March 2016. 1947 [I-D.ietf-manet-aodvv2] 1948 Perkins, C., Ratliff, S., Dowdell, J., Steenbrink, L., and 1949 V. Mercieca, "Ad Hoc On-demand Distance Vector Version 2 1950 (AODVv2) Routing", draft-ietf-manet-aodvv2-16 (work in 1951 progress), May 2016. 1953 [I-D.ietf-roll-rpl-industrial-applicability] 1954 Phinney, T., Thubert, P., and R. Assimiti, "RPL 1955 applicability in industrial networks", draft-ietf-roll- 1956 rpl-industrial-applicability-02 (work in progress), 1957 October 2013. 1959 [I-D.richardson-6tisch-security-architecture] 1960 Richardson, M., "security architecture for 6top: 1961 requirements and structure", draft-richardson-6tisch- 1962 security-architecture-02 (work in progress), April 2014. 1964 [I-D.struik-6tisch-security-architecture-elements] 1965 Struik, R., Ohba, Y., and S. Das, "6TiSCH Security 1966 Architectural Elements, Desired Protocol Properties, and 1967 Framework", draft-struik-6tisch-security-architecture- 1968 elements-01 (work in progress), October 2014. 1970 [I-D.svshah-tsvwg-deterministic-forwarding] 1971 Shah, S. and P. Thubert, "Deterministic Forwarding PHB", 1972 draft-svshah-tsvwg-deterministic-forwarding-04 (work in 1973 progress), August 2015. 1975 [I-D.svshah-tsvwg-lln-diffserv-recommendations] 1976 Shah, S. and P. Thubert, "Differentiated Service Class 1977 Recommendations for LLN Traffic", draft-svshah-tsvwg-lln- 1978 diffserv-recommendations-04 (work in progress), February 1979 2015. 1981 [I-D.thubert-6lo-rfc6775-update-reqs] 1982 Thubert, P. and P. Stok, "Requirements for an update to 1983 6LoWPAN ND", draft-thubert-6lo-rfc6775-update-reqs-07 1984 (work in progress), April 2016. 1986 [I-D.thubert-roll-forwarding-frags] 1987 Thubert, P. and J. Hui, "LLN Fragment Forwarding and 1988 Recovery", draft-thubert-roll-forwarding-frags-02 (work in 1989 progress), September 2013. 1991 [I-D.vanderstok-core-comi] 1992 Stok, P. and A. Bierman, "CoAP Management Interface", 1993 draft-vanderstok-core-comi-09 (work in progress), March 1994 2016. 1996 [I-D.wang-6tisch-6top-sublayer] 1997 Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer 1998 (6top)", draft-wang-6tisch-6top-sublayer-04 (work in 1999 progress), November 2015. 2001 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2002 "Definition of the Differentiated Services Field (DS 2003 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2004 DOI 10.17487/RFC2474, December 1998, 2005 . 2007 [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol 2008 Extensions for IPv6 Inter-Domain Routing", RFC 2545, 2009 DOI 10.17487/RFC2545, March 1999, 2010 . 2012 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2013 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2014 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2015 . 2017 [RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between 2018 Information Models and Data Models", RFC 3444, 2019 DOI 10.17487/RFC3444, January 2003, 2020 . 2022 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 2023 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 2024 2003, . 2026 [RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. 2027 Thubert, "Network Mobility (NEMO) Basic Support Protocol", 2028 RFC 3963, DOI 10.17487/RFC3963, January 2005, 2029 . 2031 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2032 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2033 DOI 10.17487/RFC3971, March 2005, 2034 . 2036 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2037 RFC 3972, DOI 10.17487/RFC3972, March 2005, 2038 . 2040 [RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 2041 Bosch, "Next Steps in Signaling (NSIS): Framework", 2042 RFC 4080, DOI 10.17487/RFC4080, June 2005, 2043 . 2045 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2046 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2047 2006, . 2049 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2050 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2051 2006, . 2053 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2054 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 2055 . 2057 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 2058 DOI 10.17487/RFC4903, June 2007, 2059 . 2061 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2062 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2063 Overview, Assumptions, Problem Statement, and Goals", 2064 RFC 4919, DOI 10.17487/RFC4919, August 2007, 2065 . 2067 [RFC5191] Forsberg, D., Ohba, Y., Ed., Patil, B., Tschofenig, H., 2068 and A. Yegin, "Protocol for Carrying Authentication for 2069 Network Access (PANA)", RFC 5191, DOI 10.17487/RFC5191, 2070 May 2008, . 2072 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2073 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2074 . 2076 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 2077 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 2078 September 2010, . 2080 [RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS 2081 Signaling Layer Protocol (NSLP) for Quality-of-Service 2082 Signaling", RFC 5974, DOI 10.17487/RFC5974, October 2010, 2083 . 2085 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2086 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2087 2011, . 2089 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2090 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2091 January 2012, . 2093 [RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS 2094 SAVI: First-Come, First-Served Source Address Validation 2095 Improvement for Locally Assigned IPv6 Addresses", 2096 RFC 6620, DOI 10.17487/RFC6620, May 2012, 2097 . 2099 [RFC6655] McGrew, D. and D. Bailey, "AES-CCM Cipher Suites for 2100 Transport Layer Security (TLS)", RFC 6655, 2101 DOI 10.17487/RFC6655, July 2012, 2102 . 2104 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 2105 Locator/ID Separation Protocol (LISP)", RFC 6830, 2106 DOI 10.17487/RFC6830, January 2013, 2107 . 2109 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 2110 J. Martocci, "Reactive Discovery of Point-to-Point Routes 2111 in Low-Power and Lossy Networks", RFC 6997, 2112 DOI 10.17487/RFC6997, August 2013, 2113 . 2115 [RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S., 2116 Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software- 2117 Defined Networking (SDN): Layers and Architecture 2118 Terminology", RFC 7426, DOI 10.17487/RFC7426, January 2119 2015, . 2121 8.3. Other Informative References 2123 [ACE] IETF, "Authentication and Authorization for Constrained 2124 Environments", . 2127 [CCAMP] IETF, "Common Control and Measurement Plane", 2128 . 2130 [DETNET] IETF, "Deterministic Networking", 2131 . 2133 [DICE] IETF, "DTLS In Constrained Environments", 2134 . 2136 [HART] www.hartcomm.org, "Highway Addressable remote Transducer, 2137 a group of specifications for industrial process and 2138 control devices administered by the HART Foundation". 2140 [IEC62439] 2141 IEC, "Industrial communication networks - High 2142 availability automation networks - Part 3: Parallel 2143 Redundancy Protocol (PRP) and High-availability Seamless 2144 Redundancy (HSR) - IEC62439-3", 2012, 2145 . 2147 [IEEE802.1TSNTG] 2148 IEEE Standards Association, "IEEE 802.1 Time-Sensitive 2149 Networks Task Group", March 2013, 2150 . 2152 [IEEE802154] 2153 IEEE standard for Information Technology, "IEEE std. 2154 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 2155 and Physical Layer (PHY) Specifications for Low-Rate 2156 Wireless Personal Area Networks". 2158 [IEEE802154e] 2159 IEEE standard for Information Technology, "IEEE standard 2160 for Information Technology, IEEE std. 802.15.4, Part. 2161 15.4: Wireless Medium Access Control (MAC) and Physical 2162 Layer (PHY) Specifications for Low-Rate Wireless Personal 2163 Area Networks, June 2011 as amended by IEEE std. 2164 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area 2165 Networks (LR-WPANs) Amendment 1: MAC sublayer", April 2166 2012. 2168 [ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation", 2169 . 2171 [ISA100.11a] 2172 ISA/ANSI, "Wireless Systems for Industrial Automation: 2173 Process Control and Related Applications - ISA100.11a-2011 2174 - IEC 62734", 2011, . 2177 [PCE] IETF, "Path Computation Element", 2178 . 2180 [TEAS] IETF, "Traffic Engineering Architecture and Signaling", 2181 . 2183 [WirelessHART] 2184 www.hartcomm.org, "Industrial Communication Networks - 2185 Wireless Communication Network and Communication Profiles 2186 - WirelessHART - IEC 62591", 2010. 2188 Appendix A. Personal submissions relevant to upcoming work 2190 This document covers a portion of the total work that is needed to 2191 cover the full 6TiSCH architecture. Missing portions at this time 2192 include Deterministic Networking with Track Forwarding, Dynamic 2193 Scheduling, and Security. 2195 [I-D.richardson-6tisch-security-architecture] elaborates on the 2196 potential use of 802.1AR certificates, and some options for the join 2197 process are presented in more details. 2199 [I-D.struik-6tisch-security-architecture-elements] describes 6TiSCH 2200 security architectural elements with high level requirements and the 2201 security framework that are relevant for the design of the 6TiSCH 2202 security solution. 2204 Author's Address 2206 Pascal Thubert (editor) 2207 Cisco Systems, Inc 2208 Building D 2209 45 Allee des Ormes - BP1200 2210 MOUGINS - Sophia Antipolis 06254 2211 FRANCE 2213 Phone: +33 497 23 26 34 2214 Email: pthubert@cisco.com