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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: Standards Track October 18, 2018 5 Expires: April 21, 2019 7 An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4 8 draft-ietf-6tisch-architecture-15 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 https://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 April 21, 2019. 35 Copyright Notice 37 Copyright (c) 2018 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 (https://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 2.1. BCP 14 . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 2.2. References . . . . . . . . . . . . . . . . . . . . . . . 4 56 2.3. Subset of a 6LoWPAN Glossary . . . . . . . . . . . . . . 5 57 3. High Level Architecture . . . . . . . . . . . . . . . . . . . 6 58 3.1. 6TiSCH Stack . . . . . . . . . . . . . . . . . . . . . . 6 59 3.2. TSCH: A Deterministic MAC Layer . . . . . . . . . . . . . 8 60 3.3. Scheduling TSCH . . . . . . . . . . . . . . . . . . . . . 9 61 3.4. Routing and Forwarding Over TSCH . . . . . . . . . . . . 10 62 3.5. A Non-Broadcast Multi-Access Radio Mesh Network . . . . . 12 63 3.6. A Multi-Link Subnet Model . . . . . . . . . . . . . . . . 14 64 3.7. Join Process and Registration . . . . . . . . . . . . . . 15 65 3.8. Dependencies on Work In Progress . . . . . . . . . . . . 18 66 4. Architecture Components . . . . . . . . . . . . . . . . . . . 20 67 4.1. 6LoWPAN (and RPL) . . . . . . . . . . . . . . . . . . . . 20 68 4.1.1. RPL Leaf Support in 6LoWPAN ND . . . . . . . . . . . 20 69 4.1.2. RPL Root And 6LBR . . . . . . . . . . . . . . . . . . 21 70 4.2. TSCH and 6top . . . . . . . . . . . . . . . . . . . . . . 22 71 4.2.1. 6top . . . . . . . . . . . . . . . . . . . . . . . . 22 72 4.2.2. Scheduling Functions and the 6P protocol . . . . . . 22 73 4.2.3. 6top and RPL Objective Function operations . . . . . 23 74 4.2.4. Network Synchronization . . . . . . . . . . . . . . . 24 75 4.2.5. SlotFrames and Priorities . . . . . . . . . . . . . . 25 76 4.2.6. Distributing the reservation of cells . . . . . . . . 26 77 4.3. Communication Paradigms and Interaction Models . . . . . 28 78 4.4. Schedule Management Mechanisms . . . . . . . . . . . . . 29 79 4.4.1. Static Scheduling . . . . . . . . . . . . . . . . . . 29 80 4.4.2. Neighbor-to-neighbor Scheduling . . . . . . . . . . . 30 81 4.4.3. Remote Monitoring and Schedule Management . . . . . . 30 82 4.4.4. Hop-by-hop Scheduling . . . . . . . . . . . . . . . . 33 83 4.5. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 33 84 4.5.1. General Behavior of Tracks . . . . . . . . . . . . . 33 85 4.5.2. Serial Track . . . . . . . . . . . . . . . . . . . . 34 86 4.5.3. Complex Track with Replication and Elimination . . . 35 87 4.5.4. DetNet End-to-end Path . . . . . . . . . . . . . . . 35 88 4.5.5. Cell Reuse . . . . . . . . . . . . . . . . . . . . . 36 89 4.6. Forwarding Models . . . . . . . . . . . . . . . . . . . . 37 90 4.6.1. Track Forwarding . . . . . . . . . . . . . . . . . . 37 91 4.6.2. Fragment Forwarding . . . . . . . . . . . . . . . . . 40 92 4.6.3. IPv6 Forwarding . . . . . . . . . . . . . . . . . . . 41 93 4.7. Centralized vs. Distributed Routing . . . . . . . . . . . 42 94 4.7.1. Packet Marking and Handling . . . . . . . . . . . . . 42 95 4.7.2. Replication, Retries and Elimination . . . . . . . . 43 96 4.7.3. Differentiated Services Per-Hop-Behavior . . . . . . 44 97 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44 98 6. Security Considerations . . . . . . . . . . . . . . . . . . . 44 99 6.1. Join Process Highlights . . . . . . . . . . . . . . . . . 45 100 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 47 101 7.1. Contributors . . . . . . . . . . . . . . . . . . . . . . 47 102 7.2. Special Thanks . . . . . . . . . . . . . . . . . . . . . 48 103 7.3. And Do not Forget . . . . . . . . . . . . . . . . . . . . 48 104 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 49 105 8.1. Normative References . . . . . . . . . . . . . . . . . . 49 106 8.2. Informative References . . . . . . . . . . . . . . . . . 50 107 8.3. Other Informative References . . . . . . . . . . . . . . 56 108 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 57 110 1. Introduction 112 Wireless Networks enable a wide variety of devices of any size to get 113 interconnected, often at a very low marginal cost per device, at any 114 distance ranging from Near Field to interplanetary, and in 115 circumstances where wiring may be impractical, for instance on fast- 116 moving or rotating devices. 118 In the other hand, Deterministic Networks enable traffic that is 119 highly sensitive to jitter, quite sensitive to latency, and with a 120 high degree of operational criticality so that loss should be 121 minimized at all times. Applications that need such networks are 122 presented in [I-D.ietf-detnet-use-cases]. They include Professional 123 Media and Operation Technology (OT) Industrial Automation Control 124 Systems (IACS). 126 The Medium access Control (MAC) of IEEE Std 802.15.4 [IEEE802154] has 127 evolved with the IEEE Std 802.15.4e Timeslotted Channel Hopping 128 (TSCH) [RFC7554] mode to provide deterministic properties on wireless 129 networks. TSCH was initially introduced with the IEEE Std 802.15.4e 130 amendment [IEEE802154e] of the IEEE Std 802.15.4 standard and 131 constituted a part of the standard from that day. For all practical 132 purpose, this document is expected to be insensitive to the revisions 133 of the IEEE Std 802.15.4 standard, which is thus referenced undated. 135 Proven Deterministic Networking standards for use in Process Control, 136 including ISA100.11a [ISA100.11a] and WirelessHART [WirelessHART], 137 have demonstrated the capabilities of the IEEE Std 802.15.4 TSCH MAC 138 for high reliability against interference, low-power consumption on 139 well-known flows, and its applicability for Traffic Engineering (TE) 140 from a central controller. 142 In order to enable the convergence of IT and OT in LLN environments, 143 6TiSCH ports the IETF suite of protocol that are defined for such 144 environments over the TSCH MAC. 6TiSCH also provides large scaling 145 capabilities, which, in a number of scenarios, require the addition 146 of a high speed and reliable backbone and the use of IP version 6 147 (IPv6). The 6TiSCH Architecture introduces an IPv6 Multi-Link subnet 148 model that is composed of a federating backbone and a number of IEEE 149 Std 802.15.4 TSCH low-power wireless networks attached and 150 synchronized by Backbone Routers. 152 The architecture defines mechanisms to establish and maintain routing 153 and scheduling in a centralized, distributed, or mixed fashion, for 154 use in multiple OT environments. It is applicable in particular to 155 industrial control systems, building automation that leverage 156 distributed routing to address multipath over a large number of hops, 157 in-vehicle command and control that can be as demanding as industrial 158 applications, commercial automation and asset Tracking with mobile 159 scenarios, home automation and domotics which become more reliable 160 and thus provide a better user experience, and resource management 161 (energy, water, etc.). 163 2. Terminology 165 2.1. BCP 14 167 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 168 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 169 "OPTIONAL" in this document are to be interpreted as described in BCP 170 14 [RFC2119][RFC8174] when, and only when, they appear in all 171 capitals, as shown here. 173 2.2. References 175 The draft uses domain-specific terminology defined or referenced in: 177 "Terms Used in IPv6 over the TSCH mode of IEEE 802.15.4e" 178 [I-D.ietf-6tisch-terminology], 180 "Neighbor Discovery Optimization for Low-power and Lossy Networks" 181 [RFC6775], 183 "Registration Extensions for 6LoWPAN Neighbor Discovery" 184 [I-D.ietf-6lo-rfc6775-update], and 186 "Terms Used in Routing for Low-Power and Lossy Networks (LLNs)" 187 [RFC7102]. 189 Other terms in use in LLNs are found in "Terminology for Constrained- 190 Node Networks" [RFC7228]. 192 Readers are expected to be familiar with all the terms and concepts 193 that are discussed in 194 o "Neighbor Discovery for IP version 6" [RFC4861], 196 o "IPv6 Stateless Address Autoconfiguration" [RFC4862], 198 o "Problem Statement and Requirements for IPv6 over Low-Power 199 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606]. 201 The draft also conforms to the terms and models described in 202 [RFC3444] and [RFC5889] and uses the vocabulary and the concepts 203 defined in [RFC4291] for the IPv6 Architecture and refers [RFC4080] 204 for reservation 206 In addition, readers would benefit from reading: 208 o "Multi-Link Subnet Issues" [RFC4903], 210 o "Mobility Support in IPv6" [RFC6275], 212 o "RPL applicability in industrial networks" 213 [I-D.ietf-roll-rpl-industrial-applicability], 215 o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 216 Overview, Assumptions, Problem Statement, and Goals" [RFC4919]. 218 o "Optimistic Duplicate Address Detection" [RFC4429], 220 o "Neighbor Discovery Proxies (ND Proxy)" [RFC4389], 222 o "FCFS SAVI: First-Come, First-Served Source Address Validation 223 Improvement for Locally Assigned IPv6 Addresses" [RFC6620], and 225 o "Optimistic Duplicate Address Detection" [RFC4429] 227 prior to this specification for a clear understanding of the art in 228 ND-proxying and binding. 230 2.3. Subset of a 6LoWPAN Glossary 232 This document often uses the following acronyms: 234 6BBR: 6LoWPAN Backbone Router (proxy for the registration) 236 6LBR: 6LoWPAN Border Router (authoritative on DAD) 238 6LN: 6LoWPAN Node 240 6LR: 6LoWPAN Router (relay to the registration process) 241 6CIO: Capability Indication Option 243 (E)ARO: (Extended) Address Registration Option 245 (E)DAR: (Extended) Duplicate Address Request 247 (E)DAC: (Extended) Duplicate Address Confirmation 249 DAD: Duplicate Address Detection 251 DODAG: Destination-Oriented Directed Acyclic Graph 253 LLN: Low-Power and Lossy Network (a typical IoT network) 255 NA: Neighbor Advertisement 257 NCE: Neighbor Cache Entry 259 ND: Neighbor Discovery 261 NDP: Neighbor Discovery Protocol 263 NS: Neighbor Solicitation 265 ROVR: Registration Ownership Verifier (pronounced rover) 267 RPL: IPv6 Routing Protocol for LLNs (pronounced ripple) 269 RA: Router Advertisement 271 RS: Router Solicitation 273 TSCH: Timeslotted Channel Hopping 275 TID: Transaction ID (a sequence counter in the EARO) 277 3. High Level Architecture 279 3.1. 6TiSCH Stack 281 The 6TiSCH architecture presents a reference stack that is 282 implemented and interop tested by a conjunction of opensource, IETF 283 and ETSI efforts. One goal is to help other bodies to adopt the 284 stack as a whole, making the effort to move to an IPv6-based IOT 285 stack easier. Now, for a particular, environment, some of the 286 choices that are made in this architecture may not be relevant. For 287 instance, RPL is not required for star topologies and mesh-under 288 Layer-2 routed networks, and the 6LoWPAN compression may not be 289 sufficient for ultra-constrained cases such as some Low Power Wide 290 Area (LPWA) networks. In such cases, it is perfectly doable to adopt 291 a subset of the selection that is presented hereafter and then select 292 alternate components to complete the solution wherever needed. 294 The IETF proposes multiple techniques for implementing functions 295 related to routing, transport or security. In order to control the 296 complexity of the possible deployments and device interactions, and 297 to limit the size of the resulting object code, the architecture 298 limits the possible variations of the stack and recommends a number 299 of base elements for LLN applications. In particular, UDP [RFC0768] 300 [RFC8200] and the Constrained Application Protocol [RFC7252] (CoAP) 301 are used as the transport / binding of choice for applications and 302 management as opposed to TCP and HTTP. 304 The resulting protocol stack is represented below: 306 +-----+-----+ 307 | COMI | 308 +-----+-----+-----+------+-------+-----+ 309 | CoAP/OSCORE | 6LoWPAN ND | RPL | 310 +-----+-----+-----+------+-------+-----+ 311 | UDP | ICMPv6 | 312 +-----+-----+-----+-----+-------+------+ 313 | IPv6 | 314 +--------------------------------------+----------------------+ 315 | 6LoWPAN HC / 6LoRH HC | Scheduling Functions | 316 +--------------------------------------+----------------------+ 317 | 6top (to be IEEE Std 802.15.12) inc. 6top protocol | 318 +-------------------------------------------------------------+ 319 | IEEE Std 802.15.4 TSCH | 320 +-------------------------------------------------------------+ 322 Figure 1: 6TiSCH Protocol Stack 324 RPL is the routing protocol of choice for LLNs. So far, there was no 325 identified need to define a 6TiSCH specific Objective Function. The 326 Minimal 6TiSCH Configuration [RFC8180] describes the operation of RPL 327 over a static schedule used in a slotted aloha fashion, whereby all 328 active slots may be used for emission or reception of both unicast 329 and multicast frames. 331 The 6LoWPAN Header Compression [RFC6282] is used to compress the IPv6 332 and UDP headers, whereas the 6LoWPAN Routing Header (6LoRH) [RFC8138] 333 is used to compress the RPL artifacts in the IPv6 data packets, 334 including the RPL Packet Information (RPI), the IP-in-IP 335 encapsulation to/from the RPL root, and the Source Route Header (SRH) 336 in non-storing mode. 338 6TiSCH has adopted the general direction of CoAP Management Interface 339 (COMI) [I-D.ietf-core-comi] for the management of devices. 341 The Datagram Transport Layer Security (DTLS) [RFC6347] sitting either 342 under CoAP or over CoAP so as to traverse proxies, as well as Object 343 Security for Constrained RESTful Environments (OSCORE) 344 [I-D.ietf-core-object-security], are examples of protocol that could 345 be used to protect application payload, and OSCORE is used in 346 particular by the "Minimal Security Framework for 6TiSCH" 347 [I-D.ietf-6tisch-minimal-security] for the the Join Process. 349 An overview of the the initial steps of a device in a network can be 350 found in Section 3.7; the security aspects of the join process are 351 further detailed in Section 6. 353 The 6TiSCH Operation sublayer (6top) [I-D.wang-6tisch-6top-sublayer] 354 is a sublayer of a Logical Link Control (LLC) that provides the 355 abstraction of an IP link over a TSCH MAC and schedules packets over 356 TSCH cells,as further discussed in the next sections. 358 3.2. TSCH: A Deterministic MAC Layer 360 Though at a different time scale (several orders of magnitude), both 361 IEEE Std 802.1TSN and IEEE Std 802.15.4TSCH standards provide 362 Deterministic capabilities to the point that a packet that pertains 363 to a certain flow may traverse a network from node to node following 364 a very precise schedule, as a train that enters and then leaves 365 intermediate stations at precise times along its path. With TSCH, 366 time is formatted into timeslots, and individual communication cells 367 are allocated to unicast or broadcast communication at the MAC level. 368 The time-slotted operation reduces collisions, saves energy, and 369 enables to more closely engineer the network for deterministic 370 properties. The channel hopping aspect is a simple and efficient 371 technique to combat multipath fading and external interference (for 372 example by Wi-Fi emitters). 374 6TiSCH builds on the IEEE Std 802.15.4TSCH MAC and inherits its 375 advanced capabilities to enable them in multiple environments where 376 they can be leveraged to improve automated operations. The 6TiSCH 377 Architecture also inherits the capability to perform a centralized 378 route computation to achieve deterministic properties, though it 379 relies on the IETF DetNet Architecture 380 [I-D.ietf-detnet-architecture], and IETF components such as the Path 381 Computation Element (PCE) [PCE], for the protocol aspects. 383 On top of this inheritance, 6TiSCH adds capabilities for distributed 384 routing and scheduling operations based on the RPL routing protocol 385 and capabilities to negotiate schedule adjustments between peers. 386 These distributed routing and scheduling operations simplify the 387 deployment of TSCH networks and enable wireless solutions in a larger 388 variety of use cases from operational technology in general. 389 Examples of such use-cases in industrial environments include plant 390 setup and decommissioning, as well as monitoring of lots of lesser 391 importance measurements such as corrosion and events. RPL also 392 enables mobile use cases such as mobile workers and cranes, as 393 presented in [I-D.ietf-roll-rpl-industrial-applicability]. 395 3.3. Scheduling TSCH 397 A scheduling operation attributes cells in a Time-Division- 398 Multiplexing (TDM) / Frequency-Division Multiplexing (FDM) matrix 399 called the Channel distribution/usage (CDU) to either individual 400 transmissions or as multi-access shared resources (see the 6TiSCH 401 Terminology [I-D.ietf-6tisch-terminology] for more on these terms). 402 Scheduling effectively enables multiple communications at a same time 403 in a same interference domain using different channels; but a node 404 equipped with a single radio can only transmit or receive on one 405 channel at any given point of time. 407 From the standpoint of a 6TiSCH node (at the MAC layer), its schedule 408 is the collection of the times at which it must wake up for 409 transmission, and the channels to which it should either send or 410 listen at those times. The schedule is expressed as one or more 411 slotframes that repeat over and over. Slotframes may collide and 412 require a device to wake at a same time, in which case a priority 413 indicates which slotframe is actually activated. 415 The 6top sublayer hides the complexity of the schedule to the upper 416 layers. The Link that IP may utilize between the 6TiSCH node and a 417 peer may in fact be composed of a pair of cell bundles, one to 418 receive and one to transmit. Some of the cells may be shared, in 419 which case the 6top sublayer must perform some arbitration. 421 The 6TiSCH architecture identifies four ways a schedule can be 422 managed and CDU cells can be allocated: Static Scheduling, Neighbor- 423 to-Neighbor Scheduling, Remote Monitoring and Schedule Management, 424 and Hop-by-hop Scheduling. 426 Static Scheduling: This refers to the minimal 6TiSCH operation 427 whereby a static schedule is configured for the whole network for 428 use in a slotted-aloha fashion. The static schedule is 429 distributed through the native methods in the TSCH MAC layer. 430 This operation leverages RPL to maintain a loopless graph for 431 routing and time distribution. It is specified in the Minimal 432 6TiSCH Configuration [RFC8180] specification. and does not 433 preclude other scheduling operations to co-exist on a same 6TiSCH 434 network. 436 Neighbor-to-Neighbor Scheduling: This refers to the dynamic 437 adaptation of the bandwidth of the Links that are used for IPv6 438 traffic between adjacent routers. Scheduling Functions such as 439 the "6TiSCH Minimal Scheduling Function (MSF)" 440 [I-D.ietf-6tisch-msf] influence the operation of the MAC layer to 441 add, update and remove cells in peers schedule, using the "6top 442 Protocol (6P)" [I-D.ietf-6tisch-6top-protocol] for the negotiation 443 of the MAC resources. 445 Remote Monitoring and Schedule Management: This refers to the 446 central computation of a schedule and the capability to forward a 447 frame based on the cell of arrival. In that case, the related 448 portion of the device schedule as well as other device resources 449 are managed by an abstract Network Management Entity (NME), which 450 may cooperate with the PCE in order to minimize the interaction 451 with and the load on the constrained device. This model is the 452 TSCH adaption of the "DetNet Architecture" 453 [I-D.ietf-detnet-architecture], and it enables Traffic Engineering 454 with deterministic properties. 456 Hop-by-hop Scheduling: This refers to the possibility to reserves 457 cells along a path for a particular flow using a distributed 458 mechanism. 460 It is not expected that all use cases will require all those 461 mechanisms. Static Scheduling with minimal configuration one is the 462 only one that is expected in all implementations, since it provides a 463 simple and solid basis for convergecast routing and time 464 distribution. 466 A deeper dive in those mechanisms can be found in Section 4.4. 468 3.4. Routing and Forwarding Over TSCH 470 6TiSCH leverages the RPL routing protocol for interoperable 471 distributed routing operations. RPL is applicable to Static 472 Scheduling and Neighbor-to-Neighbor Scheduling. The architecture 473 also supports a centralized routing model for Remote Monitoring and 474 Schedule Management. It is expected that a routing protocol that is 475 more optimized for point-to-point routing than RPL [RFC6550], such as 476 the "Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks" 477 [I-D.ietf-roll-aodv-rpl] (AODV-RPL), which derives from the Ad Hoc 478 On-demand Distance Vector Routing (AODV) [I-D.ietf-manet-aodvv2] will 479 be selected for Hop-by-hop Scheduling. 481 The 6TiSCH architecture supports three different forwarding models, 482 the classical IPv6 Forwarding, where the node selects a feasible 483 successor at Layer-3 on a per packet basis and based on its routing 484 table, G-MPLS Track Forwarding, which switches a frame received at a 485 particular Timeslot into another Timeslot at Layer-2, and 6LoWPAN 486 Fragment Forwarding, which allows to forward individual 6loWPAN 487 fragments along the route set by the first fragment. 489 IPv6 Forwarding: This is the classical IP forwarding model, with a 490 Routing Information Based (RIB) that is installed by the RPL 491 routing protocol and used to select a feasible successor per 492 packet. The packet is placed on an outgoing Link, that the 6top 493 layer maps into a (Layer-3) bundle of cells, and scheduled for 494 transmission based on QoS parameters. On top of RPL, this model 495 also applies to any routing protocol which may be operated in the 496 6TiSCH network, and corresponds to all the distributed scheduling 497 models, Static, Neighbor-to-Neighbor and Hop-by-Hop Scheduling. 499 G-MPLS Track Forwarding: This model corresponds to the Remote 500 Monitoring and Schedule Management. In this model, A central 501 controller (hosting a PCE) computes and installs the schedules in 502 the devices per flow. The incoming (Layer-2) bundle of cells from 503 the previous node along the path determines the outgoing (Layer-2) 504 bundle towards the next hop for that flow as determined by the 505 PCE. The programmed sequence for bundles is called a Track and 506 can assume shapes that are more complex than a simple direct 507 sequence of nodes. 509 6LoWPAN Fragment Forwarding: This is an hybrid model that derives 510 from IPv6 forwarding for the case where packets must be fragmented 511 at the 6LoWPAN sublayer. The first fragment is forwarded like any 512 IPv6 packet and leaves a state in the intermediate hops to enable 513 forwarding of the next fragments that do not have a IP header 514 without the need to recompose the packet at every hop. 516 This can be broadly summarized in the following table: 518 +---------------------+------------+-----------------------------------+ 519 | Forwarding Model | Routing | Scheduling | 520 +=====================+============+===================================+ 521 |G-MPLS Track Fwrding | PCE |Remote Monitoring and Schedule Mgt | 522 +---------------------+------------+-----------------------------------+ 523 | | | Static (Minimal Configuration) | 524 + classical IPv6 + RPL +-----------------------------------+ 525 | / | | Neighbor-to-Neighbor (SF+6P) | 526 + 6LoWPAN Fragment F. +------------+-----------------------------------+ 527 | |Reactive P2P| Hop-by-Hop (TBD) | 528 +---------------------+------------+-----------------------------------+ 530 Figure 2: Routing, Forwarding and Scheduling 532 3.5. A Non-Broadcast Multi-Access Radio Mesh Network 534 A 6TiSCH network is an IPv6 [RFC8200] subnet which, in its basic 535 configuration, is a single Low Power Lossy Network (LLN) operating 536 over a synchronized TSCH-based mesh. 538 Inside a 6TiSCH LLN, nodes rely on 6LoWPAN Header Compression 539 (6LoWPAN HC) [RFC6282] to encode IPv6 packets. From the perspective 540 of the network layer, a single LLN interface (typically an IEEE Std 541 802.15.4-compliant radio) may be seen as a collection of Links with 542 different capabilities for unicast or multicast services. 544 6TiSCH nodes are not necessarily reachable from one another at 545 Layer-2 and an LLN may span over multiple links. This effectively 546 forms an homogeneous non-broadcast multi-access (NBMA) subnet, which 547 is beyond the scope of existing IPv6 ND methods. Extensions to IPv6 548 ND have to be introduced. 550 Within that subnet, neighbor devices are discovered with 6LoWPAN 551 Neighbor Discovery [RFC6775] (6LoWPAN ND), whereas RPL [RFC6550] 552 enables routing in the so called Route Over fashion, either in 553 storing (stateful) or non-storing (stateless, with routing headers) 554 mode. 556 ---+-------- ............ ------------ 557 | External Network | 558 | +-----+ 559 +-----+ | NME | 560 | | LLN Border | | 561 | | router +-----+ 562 +-----+ 563 o o o 564 o o o o o 565 o o 6LoWPAN + RPL o o 566 o o o o 567 o o 569 Figure 3: Basic Configuration of a 6TiSCH Network 571 6TiSCH nodes join the mesh by attaching to nodes that are already 572 members of the mesh. Some nodes act as routers for 6LoWPAN ND and 573 RPL operations, as detailed in Section 4.1. Security aspects of the 574 join process by which a device obtains access to the network are 575 discussed in Section 6. 577 With TSCH, devices are time-synchronized at the MAC level. The use 578 of a particular RPL Instance for time synchronization is discussed in 579 Section 4.2.4. With this mechanism, the time synchronization starts 580 at the RPL root and follows the RPL DODAGs with no timing loop. 582 RPL forms Destination Oriented Directed Acyclic Graphs (DODAGs) 583 within Instances of the protocol, each Instance being associated with 584 an Objective Function (OF) to form a routing topology. A particular 585 6TiSCH node, the LLN Border Router (LBR), acts as RPL root, 6LoWPAN 586 HC terminator, and Border Router for the LLN to the outside. The LBR 587 is usually powered. More on RPL Instances can be found in section 588 3.1 of RPL [RFC6550], in particular "3.1.2. RPL Identifiers" and 589 "3.1.3. Instances, DODAGs, and DODAG Versions". RPL adds artifacts 590 in the data packets that are compressed with a 6LoWPAN addition 6LoRH 591 [RFC8138]. 593 Additional routing and scheduling protocols may be deployed to 594 establish on-demand Peer-to-Peer routes with particular 595 characteristics inside the 6TiSCH network. This may be achieved in a 596 centralized fashion by a PCE [PCE] that programs both the routes and 597 the schedules inside the 6TiSCH nodes, or by in a distributed fashion 598 using a reactive routing protocol and a Hop-by-Hop scheduling 599 protocol. 601 A Backbone Router may be connected to the node that acts as RPL root 602 and / or 6LoWPAN 6LBR and provides connectivity to the larger campus 603 / factory plant network over a high speed backbone or a back-haul 604 link. A Backbone Router may perform proxy IPv6 Neighbor Discovery 605 (ND) [RFC4861] operations over the backbone on behalf of the 6TiSCH 606 nodes so they can share a same IPv6 subnet and appear to be connected 607 to the same backbone as classical devices. A Backbone Router may 608 alternatively redistribute the registration in a routing protocol 609 such as OSPF [RFC5340] or BGP [RFC2545], or inject them in a mobility 610 protocol such as MIPv6 [RFC6275], NEMO [RFC3963], or LISP [RFC6830]. 612 This architecture expects that a 6LoWPAN node can connect as a leaf 613 to a RPL network, where the leaf support is the minimal functionality 614 to connect as a host to a RPL network without the need to participate 615 to the full routing protocol. The architecture also expects that a 616 6LoWPAN node that is not aware at all of the RPL protocol may also 617 connect as a host but the specifications for this to happen are not 618 available at the time of this writing. 620 3.6. A Multi-Link Subnet Model 622 An extended configuration of the subnet comprises multiple LLNs. The 623 LLNs are interconnected and synchronized over a backbone, that can be 624 wired or wireless. The backbone can be a classical IPv6 network, 625 with Neighbor Discovery operating as defined in [RFC4861] and 626 [RFC4862]. This architecture requires work to standardize the the 627 registration of 6LoWPAN nodes to the Backbone Routers. 629 In the extended configuration, a Backbone Router (6BBR) operates as 630 described in [I-D.ietf-6lo-backbone-router]. The 6BBR performs ND 631 proxy operations between the registered devices and the classical ND 632 devices that are located over the backbone. 6TiSCH 6BBRs synchronize 633 with one another over the backbone, so as to ensure that the multiple 634 LLNs that form the IPv6 subnet stay tightly synchronized. 636 ---+-------- ............ ------------ 637 | External Network | 638 | +-----+ 639 | +-----+ | NME | 640 +-----+ | +-----+ | | 641 | | Router | | PCE | +-----+ 642 | | +--| | 643 +-----+ +-----+ 644 | | 645 | Subnet Backbone | 646 +--------------------+------------------+ 647 | | | 648 +-----+ +-----+ +-----+ 649 | | Backbone | | Backbone | | Backbone 650 o | | router | | router | | router 651 +-----+ +-----+ +-----+ 652 o o o o o 653 o o o o o o o o o o o 654 o o o LLN o o o o 655 o o o o o o o o o o o o 657 Figure 4: Extended Configuration of a 6TiSCH Network 659 As detailed in Section 4.1 the 6LoWPAN ND 6LBR and the root of the 660 RPL network need to be collocated and share information about the 661 devices that is learned through either protocol but not both. The 662 combined RPL root and 6LBR may be collocated with the 6BBR, or 663 directly attached to the 6BBR. In the latter case, it leverages the 664 extended registration process defined in 665 [I-D.ietf-6lo-backbone-router] to proxy the 6LoWPAN ND registration 666 to the 6BBR on behalf of the LLN nodes, so that the 6BBR may in turn 667 perform proxy classical ND operations over the backbone. 669 If the Backbone is Deterministic (such as defined by the Time 670 Sensitive Networking WG at IEEE), then the Backbone Router ensures 671 that the end-to-end deterministic behavior is maintained between the 672 LLN and the backbone. The DetNet Architecture 673 [I-D.ietf-detnet-architecture] studies Layer-3 aspects of 674 Deterministic Networks, and covers networks that span multiple 675 Layer-2 domains. 677 3.7. Join Process and Registration 679 As detailed in Section 6, a node that wishes to join the 6TiSCH 680 network with a preshared key (PSK) performs the role of the pledge in 681 the 6TiSCH Join Protocol (6JP) [I-D.ietf-6tisch-minimal-security] 682 protocol. In order to join, the pledge is helped by a Join Proxy 683 (JP) that relays the link-scope 6JP Join request over the IP network 684 to the Join Registrar/Coordinator (JRC) that can authenticate the 685 pledge and validate that it is attached to the appropriate network. 686 As a result of this exchange the pledge is in possession of a link- 687 layer material including a key and a short address, and all traffic 688 is secured at the link-layer . 690 Figure 5 illustrates that very initial step. 692 6LoWPAN Node 6LR 6LBR Join Registrar 693 (pledge) (Join Proxy) (root) /Coordinator (JRC) 694 | | | | 695 | 6LoWPAN ND |6LoWPAN ND+RPL | IPv6 network | 696 | LLN link |Route-Over mesh| (the Internet)| 697 | | | | 698 | Layer-2 | | | 699 |enhanced beacon| | | 700 |<--------------| | | 701 <-----------------| | | 702 | <------------| | | 703 | | | | 704 | 6JP Join Req | | | 705 | Link Local @ | | | 706 |-------------->| | | 707 | | 6JP Join Request | 708 | | Global Unicast @ | 709 | |------------------------------>| 710 | | | | 711 | | 6JP Join Response | 712 | | Global Unicast @ | 713 | |<------------------------------| 714 | 6JP Join Resp | | | 715 | Link Local @ | | | 716 |<--------------| | | 717 | | | | 719 Figure 5: (Re-)Registration Flow over Multi-Link Subnet 721 As detailed in Section 4.1, the combined 6LoWPAN ND 6LBR and root of 722 the RPL network learn information such as the device Unique ID (from 723 6LoWPAN ND) and the updated Sequence Number (from RPL), and perform 724 6LoWPAN ND proxy registration to the 6BBR of behalf of the LLN nodes. 726 Figure 6 illustrates the initial IPv6 signaling that eables a 6LN to 727 form a global address and register it to a 6LBR using 6LoWPAN ND 728 [I-D.ietf-6lo-rfc6775-update], is then carried over RPL to the RPL 729 root, and then to the 6BBR. 731 6LoWPAN Node 6LR 6LBR 6BBR 732 (RPL leaf) (router) (root) 733 | | | | 734 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 735 | LLN link |Route-Over mesh| ant IPv6 link | Backbone 736 | | | | 737 | IPv6 ND RS | | | 738 |-------------->| | | 739 |-----------> | | | 740 |------------------> | | 741 | IPv6 ND RA | | | 742 |<--------------| | | 743 | | | | 744 | NS(EARO) | | | 745 |-------------->| | | 746 | 6LoWPAN ND | Extended DAR | | 747 | |-------------->| | 748 | | | NS(EARO) | 749 | | |-------------->| 750 | | | | DAD (once) 751 | | | |------> 752 | | | | 753 | | | NA(EARO) | 754 | | |<--------------| 755 | | Extended DAC | | 756 | |<--------------| | 757 | NA(EARO) | | | 758 |<--------------| | | 759 | | | | 761 Figure 6: Initial Registration Flow over Multi-Link Subnet 763 Figure 7 illustrates the repeating IPv6 signaling that enables a 6LN 764 to keep a global address alive and registered to its 6LBR using 765 6LoWPAN ND [I-D.ietf-6lo-rfc6775-update], using 6LoWPAN ND ot the 766 6LR, RPL to the RPL root, and then 6LoWPAN ND again to the 6BBR. 768 6LoWPAN Node 6LR 6LBR 6BBR 769 (RPL leaf) (router) (root) 770 | | | | 771 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 772 | LLN link |Route-Over mesh| ant IPv6 link | Backbone 773 | | | | 774 | | | | 775 | | | | 776 | NS(EARO) | | | 777 |-------------->| | | 778 | NA(EARO) | | | 779 |<--------------| | | 780 | | DAO | | 781 | |-------------->| | 782 | | DAO-ACK | | 783 | |<--------------| | 784 | | | NS(EARO) | 785 | | |-------------->| 786 | | | NA(EARO) | 787 | | |<--------------| 788 | | | | 789 | | | | 791 Figure 7: Next Registration Flow over Multi-Link Subnet 793 As the network builds up, a node should start as a leaf to join the 794 RPL network, and may later turn into both a RPL-capable router and a 795 6LR, so as to accept leaf nodes to recursively join the network. 797 3.8. Dependencies on Work In Progress 799 In order to control the complexity and the size of the 6TiSCH work, 800 the architecture and the associated IETF work are staged and the WG 801 is expected to recharter multiple times. This document is 802 incremented as the work progresses following the evolution of the WG 803 charter and the availability of dependent work. The intent is to 804 publish when the WG concludes. 806 At the time of this writing: 808 o The architecture of the operation of RPL over a dynamic schedule 809 is being studied at 6TISCH as the second iteration of the charter. 811 o The need of a reactive routing protocol to establish on-demand 812 constraint-optimized routes and a reservation protocol to 813 establish Layer-3 Tracks is being discussed at 6TiSCH but not 814 chartered for. 816 o The components and protocols that are required to implement this 817 stage of architecture are being standardized at the IETF. An 818 Update to 6LoWPAN ND [I-D.ietf-6lo-rfc6775-update] covers the 819 evolution of 6LoWPAN Neighbor Discovery that is needed to 820 implement the Backbone Router [I-D.ietf-6lo-backbone-router]. In 821 addition the protection of registered addresses against 822 impersonation and take over can be guaranteed by Address Protected 823 Neighbor Discovery for Low-power and Lossy Networks 824 [I-D.ietf-6lo-ap-nd]. 826 o The work on centralized Track computation is deferred to a 827 subsequent iteration of the 6TiSCH charter. The idea at the time 828 of this writing is that 6TiSCH will apply the concepts of 829 Deterministic Networking on a Layer-3 network. The 6TiSCH 830 Architecture should thus inherit from the DetNet 831 [I-D.ietf-detnet-architecture] architecture and thus depends on 832 it. The Path Computation Element (PCE) should be a core component 833 of that architecture. Around the PCE, a protocol such as an 834 extension to a TEAS [TEAS] protocol will be required to expose the 835 6TiSCH node capabilities and the network peers to the PCE, and a 836 protocol such as a lightweight PCEP or an adaptation of CCAMP 837 [CCAMP] G-MPLS formats and procedures will be used to publish the 838 Tracks, as computed by the PCE, to the 6TiSCH nodes. 840 o BIER-TE-based OAM, Replication and Elimination 841 [I-D.thubert-bier-replication-elimination] leverages Bit Index 842 Explicit Replication - Traffic Engineering to control in the data 843 plane the DetNet Replication and Elimination activities, and to 844 provide traceability on links where replication and loss happen, 845 in a manner that is abstract to the forwarding information, 846 whereas a 6loRH for BitStrings [I-D.thubert-6lo-bier-dispatch] 847 proposes a 6LoWPAN compression for the BIER Bitstring based on 848 6LoWPAN Routing Header [RFC8138]. 850 o The security model and in particular the join process depends on 851 the ANIMA [ANIMA] Bootstrapping Remote Secure Key Infrastructures 852 (BRSKI) [I-D.ietf-anima-bootstrapping-keyinfra] in order to enable 853 zero-touch security provisionning; for highly constrained nodes, a 854 minimal model based on pre-shared keys (PSK) is also available. 856 o The current charter positions 6TiSCH on IEEE Std 802.15.4 only. 857 Though most of the design should be portable on other link types, 858 6TiSCH has a strong dependency on IEEE Std 802.15.4 and its 859 evolution. At the time of this writing, a revision of the IEEE 860 Std 802.15.4 standard is expected early 2016. That revision 861 should integrate TSCH as well as other amendments and fixes into 862 the main specification. The impact on this Architecture should be 863 minimal to non-existent, but deeper work such as 6top and security 864 may be impacted. A 6TiSCH Interest Group was formed at IEEE to 865 maintain the synchronization and help foster work at the IEEE 866 should 6TiSCH demand it. 868 o Work is being proposed at IEEE (802.15.12 PAR) for an LLC that 869 would logically include the 6top sublayer. The interaction with 870 the 6top sublayer and the Scheduling Functions described in this 871 document are yet to be defined. 873 o ISA100 [ISA100] Common Network Management (CNM) is another 874 external work of interest for 6TiSCH. The group, referred to as 875 ISA100.20, defines a Common Network Management framework that 876 should enable the management of resources that are controlled by 877 heterogeneous protocols such as ISA100.11a [ISA100.11a], 878 WirelessHART [WirelessHART], and 6TiSCH. Interestingly, the 879 establishment of 6TiSCH Deterministic paths, called Tracks, are 880 also in scope, and ISA100.20 is working on requirements for 881 DetNet. 883 4. Architecture Components 885 4.1. 6LoWPAN (and RPL) 887 4.1.1. RPL Leaf Support in 6LoWPAN ND 889 RPL needs a set of information in order to advertise a leaf node 890 through a DAO message and establish reachability. 892 At the bare minimum the leaf device must provide a sequence number 893 that matches the RPL specification in section 7. Section 5.3 of 894 [I-D.ietf-6lo-backbone-router], on the Extended Address Registration 895 Option (EARO), already incorporates that addition with a new field in 896 the option called the Transaction ID. 898 If for some reason the node is aware of RPL topologies, then 899 providing the RPL InstanceID for the instances to which the node 900 wishes to participate would be a welcome addition. In the absence of 901 such information, the RPL router must infer the proper instanceID 902 from external rules and policies. 904 On the backbone, the InstanceID is expected to be mapped onto a an 905 overlay that matches the instanceID, for instance a VLANID. 907 This architecture leverages [I-D.ietf-6lo-backbone-router] that 908 extends 6LoWPAN ND [RFC6775] to carry the counter as an abstract 909 Transaction ID (TID). 911 4.1.2. RPL Root And 6LBR 913 With [RFC6775], information on the 6LBR is disseminated via an 914 Authoritative Border Router Option (ABRO) in RA messages. The 915 discovery and liveliness of the RPL root are obtained through the RPL 916 protocol [RFC6550]. The capability to support the update to RFC6775 917 [I-D.ietf-6lo-rfc6775-update] is indicated in the 6LoWPAN Capability 918 Indication Option (6CIO). 920 "Routing for RPL Leaves" [I-D.thubert-roll-unaware-leaves] details 921 the basic interaction of 6LoWPAN ND and RPL and enables a plain 6LN 922 that supports [I-D.ietf-6lo-rfc6775-update] to obtain return 923 connectivity via the RPL network as a non-RPL-aware leaf. Though the 924 above specification enables a model where the separation is possible, 925 this architecture recommends to collocate the functions of LBR and 926 RPL root. 928 When 6LoWPAN ND is coupled with RPL, the 6LBR and RPL root 929 functionalities are co-located in order that the address of the 6LBR 930 be indicated by RPL DIO messages and to associate the unique ID from 931 the DAR/DAC exchange with the state that is maintained by RPL. The 932 DAR/DAC exchange becomes a preamble to the DAO messages that are used 933 from then on to reconfirm the registration, thus eliminating a 934 duplication of functionality between DAO and DAR messages. 936 Even though the root of the RPL network is integrated with the 6LBR, 937 it is logically separated from the Backbone Router (6BBR) that is 938 used to connect the 6TiSCH LLN to the backbone. This way, the root 939 has all information from 6LoWPAN ND and RPL about the LLN devices 940 attached to it. 942 This architecture also expects that the root of the RPL network 943 (proxy-)registers the 6TiSCH nodes on their behalf to the 6BBR, for 944 whatever operation the 6BBR performs on the backbone, such as ND 945 proxy, or redistribution in a routing protocol. This relies on an 946 extension of the 6LoWPAN ND registration described in 947 [I-D.ietf-6lo-backbone-router]. 949 This model supports the movement of a 6TiSCH device across the Multi- 950 Link Subnet, and allows the proxy registration of 6TiSCH nodes deep 951 into the 6TiSCH LLN by the 6LBR / RPL root. This requires an 952 alteration from [RFC6775] whereby the Target Address of the NS 953 message is registered as opposed to the Source, which, in the case of 954 a proxy registration, is that of the 6LBR / RPL root itself. 956 4.2. TSCH and 6top 958 4.2.1. 6top 960 6top is a logical link control sitting between the IP layer and the 961 TSCH MAC layer, which provides the link abstraction that is required 962 for IP operations. The 6top operations are specified in 963 [I-D.ietf-6tisch-6top-protocol]. In particular, 6top provides a 964 management interface that enables an external management entity to 965 schedule cells and slotFrames, and allows the addition of 966 complementary functionality, for instance to support a dynamic 967 schedule management based on observed resource usage as discussed in 968 Section 4.4.2. 970 The 6top data model and management interfaces are further discussed 971 in Section 4.4.3. 973 4.2.1.1. Hard Cells 975 The architecture defines "soft" cells and "hard" cells. "Hard" cells 976 are owned and managed by an separate scheduling entity (e.g. a PCE) 977 that specifies the slotOffset/channelOffset of the cells to be 978 added/moved/deleted, in which case 6top can only act as instructed, 979 and may not move hard cells in the TSCH schedule on its own. 981 4.2.1.2. Soft Cells 983 6top contains a monitoring process which monitors the performance of 984 cells, and can move a cell in the TSCH schedule when it performs 985 poorly. This is only applicable to cells which are marked as "soft". 986 To reserve a soft cell, the higher layer does not indicate the exact 987 slotOffset/channelOffset of the cell to add, but rather the resulting 988 bandwidth and QoS requirements. When the monitoring process triggers 989 a cell reallocation, the two neighbor devices communicating over this 990 cell negotiate its new position in the TSCH schedule. 992 4.2.2. Scheduling Functions and the 6P protocol 994 In the case of soft cells, the cell management entity that controls 995 the dynamic attribution of cells to adapt to the dynamics of variable 996 rate flows is called a Scheduling Function (SF). There may be 997 multiple SFs with more or less aggressive reaction to the dynamics of 998 the network. The "6TiSCH Minimal Scheduling Function (MSF)" 999 [I-D.ietf-6tisch-msf] provides a simple scheduling function that can 1000 be used by default by devices that support dynamic scheduling of soft 1001 cells. 1003 The SF may be seen as divided between an upper bandwidth adaptation 1004 logic that is not aware of the particular technology that is used to 1005 obtain and release bandwidth, and an underlying service that maps 1006 those needs in the actual technology, which means mapping the 1007 bandwidth onto cells in the case of TSCH. 1009 +------------------------+ +------------------------+ 1010 | Scheduling Function | | Scheduling Function | 1011 | Bandwidth adaptation | | Bandwidth adaptation | 1012 +------------------------+ +------------------------+ 1013 | Scheduling Function | | Scheduling Function | 1014 | TSCH mapping to cells | | TSCH mapping to cells | 1015 +------------------------+ +------------------------+ 1016 | 6top cells negotiation | <- 6P -> | 6top cells negotiation | 1017 +------------------------+ +------------------------+ 1018 Device A Device B 1020 Figure 8: SF/6P stack in 6top 1022 The SF relies on 6top services that implement the 6top Protocol (6P) 1023 [I-D.ietf-6tisch-6top-protocol] to negotiate the precise cells that 1024 will be allocated or freed based on the schedule of the peer. It may 1025 be for instance that a peer wants to use a particular time slot that 1026 is free in its schedule, but that timeslot is already in use by the 1027 other peer for a communication with a third party on a different 1028 cell. The 6P protocol enables the peers to find an agreement in a 1029 transactional manner that ensures the final consistency of the nodes 1030 state. 1032 4.2.3. 6top and RPL Objective Function operations 1034 An implementation of a RPL [RFC6550] Objective Function (OF), such as 1035 the RPL Objective Function Zero (OF0) [RFC6552] that is used in the 1036 Minimal 6TiSCH Configuration [RFC8180] to support RPL over a static 1037 schedule, may leverage, for its internal computation, the information 1038 maintained by 6top. 1040 Most OFs require metrics about reachability, such as the ETX. 6top 1041 creates and maintains an abstract neighbor table, and this state may 1042 be leveraged to feed an OF and/or store OF information as well. In 1043 particular, 6top creates and maintains an abstract neighbor table. A 1044 neighbor table entry contains a set of statistics with respect to 1045 that specific neighbor including the time when the last packet has 1046 been received from that neighbor, a set of cell quality metrics (e.g. 1047 RSSI or LQI), the number of packets sent to the neighbor or the 1048 number of packets received from it. This information can be obtained 1049 through 6top management APIs as detailed in the 6top sublayer 1050 specification [I-D.wang-6tisch-6top-sublayer] and used for instance 1051 to compute a Rank Increment that will determine the selection of the 1052 preferred parent. 1054 6top provides statistics about the underlying layer so the OF can be 1055 tuned to the nature of the TSCH MAC layer. 6top also enables the RPL 1056 OF to influence the MAC behaviour, for instance by configuring the 1057 periodicity of IEEE Std 802.15.4 Extended Beacons (EB's). By 1058 augmenting the EB periodicity, it is possible to change the network 1059 dynamics so as to improve the support of devices that may change 1060 their point of attachment in the 6TiSCH network. 1062 Some RPL control messages, such as the DODAG Information Object (DIO) 1063 are ICMPv6 messages that are broadcast to all neighbor nodes. With 1064 6TiSCH, the broadcast channel requirement is addressed by 6top by 1065 configuring TSCH to provide a broadcast channel, as opposed to, for 1066 instance, piggybacking the DIO messages in Enhance Beacons. 1067 Consideration was given towards finding a way to embed the Route 1068 Advertisements and the RPL DIO messages (both of which are multicast) 1069 into the IEEE Std 802.15.4 Enhanced Beacons. It was determined that 1070 this produced undue timer coupling among layers, that the resulting 1071 packet size was potentially too large, and required it is not yet 1072 clear that there is any need for Enhanced Beacons in a production 1073 network. 1075 4.2.4. Network Synchronization 1077 Nodes in a TSCH network must be time synchronized. A node keeps 1078 synchronized to its time source neighbor through a combination of 1079 frame-based and acknowledgment-based synchronization. In order to 1080 maximize battery life and network throughput, it is advisable that 1081 RPL ICMP discovery and maintenance traffic (governed by the trickle 1082 timer) be somehow coordinated with the transmission of time 1083 synchronization packets (especially with enhanced beacons). This 1084 could be achieved through an interaction of the 6top sublayer and the 1085 RPL objective Function, or could be controlled by a management 1086 entity. 1088 Time distribution requires a loop-less structure. Nodes taken in a 1089 synchronization loop will rapidly desynchronize from the network and 1090 become isolated. It is expected that a RPL DAG with a dedicated 1091 global Instance is deployed for the purpose of time synchronization. 1092 That Instance is referred to as the Time Synchronization Global 1093 Instance (TSGI). The TSGI can be operated in either of the 3 modes 1094 that are detailed in section 3.1.3 of RPL [RFC6550], "Instances, 1095 DODAGs, and DODAG Versions". Multiple uncoordinated DODAGs with 1096 independent roots may be used if all the roots share a common time 1097 source such as the Global Positioning System (GPS). In the absence 1098 of a common time source, the TSGI should form a single DODAG with a 1099 virtual root. A backbone network is then used to synchronize and 1100 coordinate RPL operations between the backbone routers that act as 1101 sinks for the LLN. Optionally, RPL's periodic operations may be used 1102 to transport the network synchronization. This may mean that 6top 1103 would need to trigger (override) the trickle timer if no other 1104 traffic has occurred for such a time that nodes may get out of 1105 synchronization. 1107 A node that has not joined the TSGI advertises a MAC level Join 1108 Priority of 0xFF to notify its neighbors that is not capable of 1109 serving as time parent. A node that has joined the TSGI advertises a 1110 MAC level Join Priority set to its DAGRank() in that Instance, where 1111 DAGRank() is the operation specified in section 3.5.1 of [RFC6550], 1112 "Rank Comparison". 1114 A root is configured or obtains by some external means the knowledge 1115 of the RPLInstanceID for the TSGI. The root advertises its DagRank 1116 in the TSGI, that must be less than 0xFF, as its Join Priority (JP) 1117 in its IEEE Std 802.15.4 Extended Beacons (EB). We'll note that the 1118 JP is now specified between 0 and 0x3F leaving 2 bits in the octet 1119 unused in the IEEE Std 802.15.4e specification. After consultation 1120 with IEEE authors, it was asserted that 6TiSCH can make a full use of 1121 the octet to carry an integer value up to 0xFF. 1123 A node that reads a Join Priority of less than 0xFF should join the 1124 neighbor with the lesser Join Priority and use it as time parent. If 1125 the node is configured to serve as time parent, then the node should 1126 join the TSGI, obtain a Rank in that Instance and start advertising 1127 its own DagRank in the TSGI as its Join Priority in its EBs. 1129 4.2.5. SlotFrames and Priorities 1131 6TiSCH enables in essence the capability to use IPv6 over a MAC layer 1132 that enables to schedule some of the transmissions. In order to 1133 ensure that the medium is free of contending packets when time 1134 arrives for a scheduled transmission, a window of time is defined 1135 around the scheduled transmission time where the medium must be free 1136 of contending energy. 1138 One simple way to obtain such a window is to format time and 1139 frequencies in cells of transmission of equal duration. This is the 1140 method that is adopted in IEEE Std 802.15.4 TSCH as well as the Long 1141 Term Evolution (LTE) of cellular networks. 1143 In order to describe that formatting of time and frequencies, the 1144 6TiSCH architecture defines a global concept that is called a Channel 1145 Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of 1146 cells with an height equal to the number of available channels 1147 (indexed by ChannelOffsets) and a width (in timeslots) that is the 1148 period of the network scheduling operation (indexed by slotOffsets) 1149 for that CDU matrix. The size of a cell is a timeslot duration, and 1150 values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to 1151 accommodate for the transmission of a frame and an ack, including the 1152 security validation on the receive side which may take up to a few 1153 milliseconds on some device architecture. 1155 A CDU matrix iterates over and over with a pseudo-random rotation 1156 from an epoch time. In a given network, there might be multiple CDU 1157 matrices that operate with different width, so they have different 1158 durations and represent different periodic operations. It is 1159 recommended that all CDU matrices in a 6TiSCH domain operate with the 1160 same cell duration and are aligned, so as to reduce the chances of 1161 interferences from slotted-aloha operations. The knowledge of the 1162 CDU matrices is shared between all the nodes and used in particular 1163 to define slotFrames. 1165 A slotFrame is a MAC-level abstraction that is common to all nodes 1166 and contains a series of timeslots of equal length and precedence. 1167 It is characterized by a slotFrame_ID, and a slotFrame_size. A 1168 slotFrame aligns to a CDU matrix for its parameters, such as number 1169 and duration of timeslots. 1171 Multiple slotFrames can coexist in a node schedule, i.e., a node can 1172 have multiple activities scheduled in different slotFrames, based on 1173 the precedence of the 6TiSCH topologies. The slotFrames may be 1174 aligned to different CDU matrices and thus have different width. 1175 There is typically one slotFrame for scheduled traffic that has the 1176 highest precedence and one or more slotFrame(s) for RPL traffic. The 1177 timeslots in the slotFrame are indexed by the SlotOffset; the first 1178 cell is at SlotOffset 0. 1180 When a packet is received from a higher layer for transmission, 6top 1181 inserts that packet in the outgoing queue which matches the packet 1182 best (Differentiated Services [RFC2474] can therefore be used). At 1183 each scheduled transmit slot, 6top looks for the frame in all the 1184 outgoing queues that best matches the cells. If a frame is found, it 1185 is given to the TSCH MAC for transmission. 1187 4.2.6. Distributing the reservation of cells 1189 6TiSCH expects a high degree of scalability together with a 1190 distributed routing functionality based on RPL. To achieve this 1191 goal, the spectrum must be allocated in a way that allows for spatial 1192 reuse between zones that will not interfere with one another. In a 1193 large and spatially distributed network, a 6TiSCH node is often in a 1194 good position to determine usage of spectrum in its vicinity. 1196 Use cases for distributed routing are often associated with a 1197 statistical distribution of best-effort traffic with variable needs 1198 for bandwidth on each individual link. With 6TiSCH, the abstraction 1199 of an IPv6 link is implemented as a pair of bundles of cells, one in 1200 each direction; the size of a bundle is optimal when both the energy 1201 wasted idle listening and the packet drops due to congestion loss are 1202 minimized. This can be maintained if the number of cells in a bundle 1203 is adapted dynamically, and with enough reactivity, to match the 1204 variations of best-effort traffic. In turn, the agility to fulfill 1205 the needs for additional cells improves when the number of 1206 interactions with other devices and the protocol latencies are 1207 minimized. 1209 6TiSCH limits that interaction to RPL parents that will only 1210 negotiate with other RPL parents, and performs that negotiation by 1211 groups of cells as opposed to individual cells. The 6TiSCH 1212 architecture allows RPL parents to adjust dynamically, and 1213 independently from the PCE, the amount of bandwidth that is used to 1214 communicate between themselves and their children, in both 1215 directions; to that effect, an allocation mechanism enables a RPL 1216 parent to obtain the exclusive use of a portion of a CDU matrix 1217 within its interference domain. Note that a PCE is expected to have 1218 precedence in the allocation, so that a RPL parent would only be able 1219 to obtain portions that are not in-use by the PCE. 1221 The 6TiSCH architecture introduces the concept of chunks 1222 [I-D.ietf-6tisch-terminology]) to operate such spectrum distribution 1223 for a whole group of cells at a time. The CDU matrix is formatted 1224 into a set of chunks, each of them identified uniquely by a chunk-ID. 1225 The knowledge of this formatting is shared between all the nodes in a 1226 6TiSCH network. 6TiSCH also defines the process of chunk ownership 1227 appropriation whereby a RPL parent discovers a chunk that is not used 1228 in its interference domain (e.g lack of energy detected in reference 1229 cells in that chunk); then claims the chunk, and then defends it in 1230 case another RPL parent would attempt to appropriate it while it is 1231 in use. The chunk is the basic unit of ownership that is used in 1232 that process. 1234 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1235 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1236 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1237 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1238 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1239 ... 1240 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1241 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1242 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1243 0 1 2 3 4 5 6 M 1245 Figure 9: CDU matrix Partitioning in Chunks 1247 As a result of the process of chunk ownership appropriation, the RPL 1248 parent has exclusive authority to decide which cell in the 1249 appropriated chunk can be used by which node in its interference 1250 domain. In other words, it is implicitly delegated the right to 1251 manage the portion of the CDU matrix that is represented by the 1252 chunk. The RPL parent may thus orchestrate which transmissions occur 1253 in any of the cells in the chunk, by allocating cells from the chunk 1254 to any form of communication (unicast, multicast) in any direction 1255 between itself and its children. Initially, those cells are added to 1256 the heap of free cells, then dynamically placed into existing 1257 bundles, in new bundles, or allocated opportunistically for one 1258 transmission. 1260 The appropriation of a chunk can also be requested explicitly by the 1261 PCE to any node. In that case, the node still may need to perform 1262 the appropriation process to validate that no other node has claimed 1263 that chunk already. After a successful appropriation, the PCE owns 1264 the cells in that chunk, and may use them as hard cells to set up 1265 Tracks. 1267 4.3. Communication Paradigms and Interaction Models 1269 [I-D.ietf-6tisch-terminology] defines the terms of Communication 1270 Paradigms and Interaction Models, which can be placed in parallel to 1271 the Information Models and Data Models that are defined in [RFC3444]. 1273 A Communication Paradigms would be an abstract view of a protocol 1274 exchange, and would come with an Information Model for the 1275 information that is being exchanged. In contrast, an Interaction 1276 Models would be more refined and could point on standard operation 1277 such as a Representational state transfer (REST) "GET" operation and 1278 would match a Data Model for the data that is provided over the 1279 protocol exchange. 1281 section 2.1.3 of [I-D.ietf-roll-rpl-industrial-applicability] and 1282 next sections discuss application-layer paradigms, such as Source- 1283 sink (SS) that is a Multipeer to Multipeer (MP2MP) model primarily 1284 used for alarms and alerts, Publish-subscribe (PS, or pub/sub) that 1285 is typically used for sensor data, as well as Peer-to-peer (P2P) and 1286 Peer-to-multipeer (P2MP) communications. Additional considerations 1287 on Duocast and its N-cast generalization are also provided. Those 1288 paradigms are frequently used in industrial automation, which is a 1289 major use case for IEEE Std 802.15.4 TSCH wireless networks with 1290 [ISA100.11a] and [WirelessHART], that provides a wireless access to 1291 [HART] applications and devices. 1293 This specification focuses on Communication Paradigms and Interaction 1294 Models for packet forwarding and TSCH resources (cells) management. 1295 Management mechanisms for the TSCH schedule at Link-layer (one-hop), 1296 Network-layer (multithop along a Track), and Application-layer 1297 (remote control) are discussed in Section 4.4. Link-layer frame 1298 forwarding interactions are discussed in Section 4.6, and Network- 1299 layer Packet routing is addressed in Section 4.7. 1301 4.4. Schedule Management Mechanisms 1303 6TiSCH uses 4 paradigms to manage the TSCH schedule of the LLN nodes: 1304 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1305 and scheduling management, and Hop-by-hop scheduling. Multiple 1306 mechanisms are defined that implement the associated Interaction 1307 Models, and can be combined and used in the same LLN. Which 1308 mechanism(s) to use depends on application requirements. 1310 4.4.1. Static Scheduling 1312 In the simplest instantiation of a 6TiSCH network, a common fixed 1313 schedule may be shared by all nodes in the network. Cells are 1314 shared, and nodes contend for slot access in a slotted aloha manner. 1316 A static TSCH schedule can be used to bootstrap a network, as an 1317 initial phase during implementation, or as a fall-back mechanism in 1318 case of network malfunction. This schedule is pre-established, for 1319 instance decided by a network administrator based on operational 1320 needs. It can be pre-configured into the nodes, or, more commonly, 1321 learned by a node when joining the network using standard IEEE Std 1322 802.15.4 Information Elements (IE). Regardless, the schedule remains 1323 unchanged after the node has joined a network. RPL is used on the 1324 resulting network. This "minimal" scheduling mechanism that 1325 implements this paradigm is detailed in [RFC8180]. 1327 4.4.2. Neighbor-to-neighbor Scheduling 1329 In the simplest instantiation of a 6TiSCH network described in 1330 Section 4.4.1, nodes may expect a packet at any cell in the schedule 1331 and will waste energy idle listening. In a more complex 1332 instantiation of a 6TiSCH network, a matching portion of the schedule 1333 is established between peers to reflect the observed amount of 1334 transmissions between those nodes. The aggregation of the cells 1335 between a node and a peer forms a bundle that the 6top layer uses to 1336 implement the abstraction of a link for IP. The bandwidth on that 1337 link is proportional to the number of cells in the bundle. 1339 If the size of a bundle is configured to fit an average amount of 1340 bandwidth, peak traffic is dropped. If the size is configured to 1341 allow for peak emissions, energy is be wasted idle listening. 1343 The 6top Protocol [I-D.ietf-6tisch-6top-protocol] specifies the 1344 exchanges between neighbor nodes to reserve soft cells to transmit to 1345 one another. Because this reservation is done without global 1346 knowledge of the schedule of other nodes in the LLN, scheduling 1347 collisions are possible. An optional Scheduling Function (SF) such 1348 as MSF [I-D.ietf-6tisch-msf] is used to monitor bandwidth usage and 1349 perform requests for dynamic allocation by the 6top sublayer. The SF 1350 component is not part of the 6top sublayer. It may be collocated on 1351 the same device or may be partially or fully offloaded to an external 1352 system. 1354 Monitoring and relocation is done in the 6top layer. For the upper 1355 layer, the connection between two neighbor nodes appears as an number 1356 of cells. Depending on traffic requirements, the upper layer can 1357 request 6top to add or delete a number of cells scheduled to a 1358 particular neighbor, without being responsible for choosing the exact 1359 slotOffset/channelOffset of those cells. 1361 4.4.3. Remote Monitoring and Schedule Management 1363 The work at the 6TiSCH WG is focused on non-deterministic traffic and 1364 does not provide the generic data model that would be necessary to 1365 monitor and manage resources of the 6top sublayer. It is recognized 1366 that CoAP can be appropriate to interact with the 6top layer of a 1367 node that is multiple hops away across a 6TiSCH mesh. 1369 The entity issuing the CoAP requests can be a central scheduling 1370 entity (e.g. a PCE), a node multiple hops away with the authority to 1371 modify the TSCH schedule (e.g. the head of a local cluster), or a 1372 external device monitoring the overall state of the network (e.g. 1373 NME). It is also possible that a mapping entity on the backbone 1374 transforms a non-CoAP protocol such as PCEP into the RESTful 1375 interfaces that the 6TiSCH devices support. 1377 With respect to Centralized routing and scheduling, it is envisionned 1378 that the related component of the 6TiSCH Architecture would be an 1379 extension of the Deterministic Networking Architecture 1380 [I-D.ietf-detnet-architecture], which studies Layer-3 aspects of 1381 Deterministic Networks, and covers networks that span multiple 1382 Layer-2 domains. The DetNet architecture is a form of SDN 1383 Architecture and is composed of three planes, a (User) Application 1384 Plane, a Controller Plane (where the PCE operates), and a Network 1385 Plane which in our case is the 6TiSCH LLN. The generic SDN 1386 architecture is discussed in Software-Defined Networking (SDN): 1387 Layers and Architecture Terminology [RFC7426] and is represented 1388 below: 1390 SDN Layers and Architecture Terminology per RFC 7426 1392 o--------------------------------o 1393 | | 1394 | +-------------+ +----------+ | 1395 | | Application | | Service | | 1396 | +-------------+ +----------+ | 1397 | Application Plane | 1398 o---------------Y----------------o 1399 | 1400 *-----------------------------Y---------------------------------* 1401 | Network Services Abstraction Layer (NSAL) | 1402 *------Y------------------------------------------------Y-------* 1403 | | 1404 | Service Interface | 1405 | | 1406 o------Y------------------o o---------------------Y------o 1407 | | Control Plane | | Management Plane | | 1408 | +----Y----+ +-----+ | | +-----+ +----Y----+ | 1409 | | Service | | App | | | | App | | Service | | 1410 | +----Y----+ +--Y--+ | | +--Y--+ +----Y----+ | 1411 | | | | | | | | 1412 | *----Y-----------Y----* | | *---Y---------------Y----* | 1413 | | Control Abstraction | | | | Management Abstraction | | 1414 | | Layer (CAL) | | | | Layer (MAL) | | 1415 | *----------Y----------* | | *----------Y-------------* | 1416 | | | | | | 1417 o------------|------------o o------------|---------------o 1418 | | 1419 | CP | MP 1420 | Southbound | Southbound 1421 | Interface | Interface 1422 | | 1423 *------------Y---------------------------------Y----------------* 1424 | Device and resource Abstraction Layer (DAL) | 1425 *------------Y---------------------------------Y----------------* 1426 | | | | 1427 | o-------Y----------o +-----+ o--------Y----------o | 1428 | | Forwarding Plane | | App | | Operational Plane | | 1429 | o------------------o +-----+ o-------------------o | 1430 | Network Device | 1431 +---------------------------------------------------------------+ 1433 Figure 10 1435 The PCE establishes end-to-end Tracks of hard cells, which are 1436 described in more details in Section 4.6.1. The DetNet work is 1437 expected to enable end to end Deterministic Path across heterogeneous 1438 network (e.g. a 6TiSCH LLN and an Ethernet Backbone). This model 1439 fits the 6TiSCH extended configuration, whereby a 6BBR federates 1440 multiple 6TiSCH LLN in a single subnet over a backbone that can be, 1441 for instance, Ethernet or Wi-Fi. In that model, 6TiSCH 6BBRs 1442 synchronize with one another over the backbone, so as to ensure that 1443 the multiple LLNs that form the IPv6 subnet stay tightly 1444 synchronized. 1446 If the Backbone is Deterministic, then the Backbone Router ensures 1447 that the end-to-end deterministic behavior is maintained between the 1448 LLN and the backbone. It is the responsibility of the PCE to compute 1449 a deterministic path and to end across the TSCH network and an IEEE 1450 Std 802.1 TSN Ethernet backbone, and that of DetNet to enable end-to- 1451 end deterministic forwarding. 1453 4.4.4. Hop-by-hop Scheduling 1455 A node can reserve a Track (Section 4.5) to a destination node 1456 multiple hops away by installing soft cells at each intermediate 1457 node. This forms a Track of soft cells. It is the responsibility of 1458 the 6top sublayer of each node on the Track to monitor these soft 1459 cells and trigger relocation when needed. 1461 This hop-by-hop reservation mechanism is expected to be similar in 1462 essence to [RFC3209] and/or [RFC4080]/[RFC5974]. The protocol for a 1463 node to trigger hop-by-hop scheduling is not yet defined. 1465 4.5. On Tracks 1467 4.5.1. General Behavior of Tracks 1469 The architecture introduces the concept of a Track, which is a 1470 directed path from a source 6TiSCH node to a destination 6TiSCH node 1471 across a 6TiSCH LLN. A Track is the 6TiSCH instantiation of the 1472 concept of a Deterministic Path as described in 1473 [I-D.ietf-detnet-architecture]. Constrained resources such as memory 1474 buffers are reserved for that Track in intermediate 6TiSCH nodes to 1475 avoid loss related to limited capacity. A 6TiSCH node along a Track 1476 not only knows which bundles of cells it should use to receive 1477 packets from a previous hop, but also knows which bundle(s) it should 1478 use to send packets to its next hop along the Track. 1480 A Track is composed of bundles of cells with related schedules and 1481 logical relationships and that ensure that a packet that is injected 1482 in a Track will progress in due time all the way to destination. 1483 Multiple cells may be scheduled in a Track for the transmission of a 1484 single packet, in which case the normal operation of IEEE Std 1485 802.15.4 Automatic Repeat-reQuest (ARQ) can take place; the 1486 acknowledgment may be omitted in some cases, for instance if there is 1487 no scheduled cell for a possible retry. 1489 There are several benefits for using a Track to forward a packet from 1490 a source node to the destination node. 1492 1. Track forwarding, as further described in Section 4.6.1, is a 1493 Layer-2 forwarding scheme, which introduces less process delay 1494 and overhead than Layer-3 forwarding scheme. Therefore, LLN 1495 Devices can save more energy and resource, which is critical for 1496 resource constrained devices. 1498 2. Since channel resources, i.e. bundles of cells, have been 1499 reserved for communications between 6TiSCH nodes of each hop on 1500 the Track, the throughput and the maximum latency of the traffic 1501 along a Track are guaranteed and the jitter is maintained small. 1503 3. By knowing the scheduled time slots of incoming bundle(s) and 1504 outgoing bundle(s), 6TiSCH nodes on a Track could save more 1505 energy by staying in sleep state during in-active slots. 1507 4. Tracks are protected from interfering with one another if a cell 1508 belongs to at most one Track, and congestion loss is avoided if 1509 at most one packet can be presented to the MAC to use that cell. 1510 Tracks enhance the reliability of transmissions and thus further 1511 improve the energy consumption in LLN Devices by reducing the 1512 chances of retransmission. 1514 4.5.2. Serial Track 1516 A Serial (or simple) Track is the 6TiSCH version of a circuit; a 1517 bundle of cells that are programmed to receive (RX-cells) is uniquely 1518 paired to a bundle of cells that are set to transmit (TX-cells), 1519 representing a Layer-2 forwarding state which can be used regardless 1520 of the network layer protocol. 1522 A Serial Track is thus formed end-to-end as a succession of paired 1523 bundles, a receive bundle from the previous hop and a transmit bundle 1524 to the next hop along the Track. For a given iteration of the device 1525 schedule, the effective channel of the cell is obtained by adding a 1526 pseudo-random number to the channelOffset of the cell, which results 1527 in a rotation of the frequency that used for transmission. 1529 The bundles may be computed so as to accommodate both variable rates 1530 and retransmissions, so they might not be fully used at a given 1531 iteration of the schedule. 1533 4.5.3. Complex Track with Replication and Elimination 1535 As opposed to a Serial Track that is a sequence of nodes and links, a 1536 Complex Track is shaped as a directed acyclic graph towards a 1537 destination to support multi-path forwarding and route around 1538 failures. 1540 A Complex Track may also branch off and rejoin, for the purpose of 1541 the DetNet Packet Replication and Elimination (PRE), over non 1542 congruent branches. PRE may be used to complement Layer-2 ARQ to 1543 meet industrial expectations in Packet Delivery Ratio (PDR), in 1544 particular when the Track extends beyond the 6TiSCH network in a 1545 larger DetNet network. 1547 The art of Deterministic Networks already include PRE techniques. 1548 Example standards include the Parallel Redundancy Protocol (PRP) and 1549 the High-availability Seamless Redundancy (HSR) [IEC62439]. 1551 At each 6TiSCH hop along the Track, the PCE may schedule more than 1552 one timeslot for a packet, so as to support Layer-2 retries (ARQ). 1553 It is also possible that the field device only uses the second branch 1554 if sending over the first branch fails. 1556 In the art of TSCH, a path does not necessarily support PRE but it is 1557 almost systematically multi-path. This means that a Track is 1558 scheduled so as to ensure that each hop has at least two forwarding 1559 solutions, and the forwarding decision is to try the preferred one 1560 and use the other in case of Layer-2 transmission failure as detected 1561 by ARQ. 1563 4.5.4. DetNet End-to-end Path 1565 Ultimately, DetNet should enable to extend a Track beyond the 6TiSCH 1566 LLN. Figure 11 illustrates a Track that is laid out from a field 1567 device in a 6TiSCH network to an IoT gateway that is located on an 1568 802.1 Time-Sensitive Networking (TSN) backbone. 1570 +-=-=-+ 1571 | IoT | 1572 | G/W | 1573 +-=-=-+ 1574 ^ <=== Elimination 1575 | | 1576 Track branch | | 1577 +-=-=-=-+ +-=-=-=-=+ Subnet Backbone 1578 | | 1579 +-=|-=+ +-=|-=+ 1580 | | | Backbone | | | Backbone 1581 o | | | router | | | router 1582 +-=/-=+ +-=|-=+ 1583 o / o o-=-o-=-=/ o 1584 o o-=-o-=/ o o o o o 1585 o \ / o o LLN o 1586 o v <=== Replication 1587 o 1589 Figure 11: End-to-End deterministic Track 1591 The Replication function in the 6TiSCH Node sends a copy of each 1592 packet over two different branches, and the PCE schedules each hop of 1593 both branches so that the two copies arrive in due time at the 1594 gateway. In case of a loss on one branch, hopefully the other copy 1595 of the packet still makes it in due time. If two copies make it to 1596 the IoT gateway, the Elimination function in the gateway ignores the 1597 extra packet and presents only one copy to upper layers. 1599 4.5.5. Cell Reuse 1601 The 6TiSCH architecture provides means to avoid waste of cells as 1602 well as overflows in the transmit bundle pof a Track, as follows: 1604 In one hand, a TX-cell that is not needed for the current 1605 iteration may be reused opportunistically on a per-hop basis for 1606 routed packets. When all of the frame that were received for a 1607 given Track are effectively transmitted, any available TX-cell for 1608 that Track can be reused for upper layer traffic for which the 1609 next-hop router matches the next hop along the Track. In that 1610 case, the cell that is being used is effectively a TX-cell from 1611 the Track, but the short address for the destination is that of 1612 the next-hop router. It results that a frame that is received in 1613 a RX-cell of a Track with a destination MAC address set to this 1614 node as opposed to broadcast must be extracted from the Track and 1615 delivered to the upper layer (a frame with an unrecognized 1616 destination MAC address is dropped at the lower MAC layer and thus 1617 is not received at the 6top sublayer). 1619 On the other hand, it might happen that there are not enough TX- 1620 cells in the transmit bundle to accommodate the Track traffic, for 1621 instance if more retransmissions are needed than provisioned. In 1622 that case, the frame can be placed for transmission in the bundle 1623 that is used for Layer-3 traffic towards the next hop along the 1624 Track as long as it can be routed by the upper layer, that is, 1625 typically, if the frame transports an IPv6 packet. The MAC 1626 address should be set to the next-hop MAC address to avoid 1627 confusion. It results that a frame that is received over a 1628 Layer-3 bundle may be in fact associated to a Track. In a 1629 classical IP link such as an Ethernet, off-Track traffic is 1630 typically in excess over reservation to be routed along the non- 1631 reserved path based on its QoS setting. But with 6TiSCH, since 1632 the use of the Layer-3 bundle may be due to transmission failures, 1633 it makes sense for the receiver to recognize a frame that should 1634 be re-Tracked, and to place it back on the appropriate bundle if 1635 possible. A frame should be re-Tracked if the Per-Hop-Behavior 1636 group indicated in the Differentiated Services Field of the IPv6 1637 header is set to Deterministic Forwarding, as discussed in 1638 Section 4.7.1. A frame is re-Tracked by scheduling it for 1639 transmission over the transmit bundle associated to the Track, 1640 with the destination MAC address set to broadcast. 1642 4.6. Forwarding Models 1644 By forwarding, this specification means the per-packet operation that 1645 allows to deliver a packet to a next hop or an upper layer in this 1646 node. Forwarding is based on pre-existing state that was installed 1647 as a result of a routing computation Section 4.7. 6TiSCH supports 1648 three different forwarding model, G-MPLS Track Forwarding (TF), 1649 6LoWPAN Fragment Forwarding (FF) and IPv6 Forwarding (6F). 1651 4.6.1. Track Forwarding 1653 Forwarding along a Track can be seen as a Generalized Multi-protocol 1654 Label Switching (G-MPLS) operation in that the information used to 1655 switch a frame is not an explicit label, but rather related to other 1656 properties of the way the packet was received, a particular cell in 1657 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1658 Layer-2 security) accepts a frame, that frame can be switched 1659 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1660 fragment, or a frame from an alternate protocol such as WirelessHART 1661 or ISA100.11a. 1663 A data frame that is forwarded along a Track normally has a 1664 destination MAC address that is set to broadcast - or a multicast 1665 address depending on MAC support. This way, the MAC layer in the 1666 intermediate nodes accepts the incoming frame and 6top switches it 1667 without incurring a change in the MAC header. In the case of IEEE 1668 Std 802.15.4, this means effectively broadcast, so that along the 1669 Track the short address for the destination of the frame is set to 1670 0xFFFF. 1672 There are 2 modes for a Track, transport mode and tunnel mode. 1674 4.6.1.1. Transport Mode 1676 In transport mode, the Protocol Data Unit (PDU) is associated with 1677 flow-dependant meta-data that refers uniquely to the Track, so the 1678 6top sublayer can place the frame in the appropriate cell without 1679 ambiguity. In the case of IPv6 traffic, this flow identification is 1680 transported in the Flow Label of the IPv6 header. Associated with 1681 the source IPv6 address, the Flow Label forms a globally unique 1682 identifier for that particular Track that is validated at egress 1683 before restoring the destination MAC address (DMAC) and punting to 1684 the upper layer. 1686 | ^ 1687 +--------------+ | | 1688 | IPv6 | | | 1689 +--------------+ | | 1690 | 6LoWPAN HC | | | 1691 +--------------+ ingress egress 1692 | 6top | sets +----+ +----+ restores 1693 +--------------+ dmac to | | | | dmac to 1694 | TSCH MAC | brdcst | | | | self 1695 +--------------+ | | | | | | 1696 | LLN PHY | +-------+ +--...-----+ +-------+ 1697 +--------------+ 1699 Track Forwarding, Transport Mode 1701 4.6.1.2. Tunnel Mode 1703 In tunnel mode, the frames originate from an arbitrary protocol over 1704 a compatible MAC that may or may not be synchronized with the 6TiSCH 1705 network. An example of this would be a router with a dual radio that 1706 is capable of receiving and sending WirelessHART or ISA100.11a frames 1707 with the second radio, by presenting itself as an access Point or a 1708 Backbone Router, respectively. 1710 In that mode, some entity (e.g. PCE) can coordinate with a 1711 WirelessHART Network Manager or an ISA100.11a System Manager to 1712 specify the flows that are to be transported transparently over the 1713 Track. 1715 +--------------+ 1716 | IPv6 | 1717 +--------------+ 1718 | 6LoWPAN HC | 1719 +--------------+ set restore 1720 | 6top | +dmac+ +dmac+ 1721 +--------------+ to|brdcst to|nexthop 1722 | TSCH MAC | | | | | 1723 +--------------+ | | | | 1724 | LLN PHY | +-------+ +--...-----+ +-------+ 1725 +--------------+ | ingress egress | 1726 | | 1727 +--------------+ | | 1728 | LLN PHY | | | 1729 +--------------+ | | 1730 | TSCH MAC | | | 1731 +--------------+ | dmac = | dmac = 1732 |ISA100/WiHART | | nexthop v nexthop 1733 +--------------+ 1735 Figure 12: Track Forwarding, Tunnel Mode 1737 In that case, the flow information that identifies the Track at the 1738 ingress 6TiSCH router is derived from the RX-cell. The dmac is set 1739 to this node but the flow information indicates that the frame must 1740 be tunneled over a particular Track so the frame is not passed to the 1741 upper layer. Instead, the dmac is forced to broadcast and the frame 1742 is passed to the 6top sublayer for switching. 1744 At the egress 6TiSCH router, the reverse operation occurs. Based on 1745 metadata associated to the Track, the frame is passed to the 1746 appropriate link layer with the destination MAC restored. 1748 4.6.1.3. Tunnel Metadata 1750 Metadata coming with the Track configuration is expected to provide 1751 the destination MAC address of the egress endpoint as well as the 1752 tunnel mode and specific data depending on the mode, for instance a 1753 service access point for frame delivery at egress. If the tunnel 1754 egress point does not have a MAC address that matches the 1755 configuration, the Track installation fails. 1757 In transport mode, if the final Layer-3 destination is the tunnel 1758 termination, then it is possible that the IPv6 address of the 1759 destination is compressed at the 6LoWPAN sublayer based on the MAC 1760 address. It is thus mandatory at the ingress point to validate that 1761 the MAC address that was used at the 6LoWPAN sublayer for compression 1762 matches that of the tunnel egress point. For that reason, the node 1763 that injects a packet on a Track checks that the destination is 1764 effectively that of the tunnel egress point before it overwrites it 1765 to broadcast. The 6top sublayer at the tunnel egress point reverts 1766 that operation to the MAC address obtained from the tunnel metadata. 1768 4.6.2. Fragment Forwarding 1770 Considering that 6LoWPAN packets can be as large as 1280 bytes (the 1771 IPv6 MTU), and that the non-storing mode of RPL implies Source 1772 Routing that requires space for routing headers, and that a IEEE Std 1773 802.15.4 frame with security may carry in the order of 80 bytes of 1774 effective payload, an IPv6 packet might be fragmented into more than 1775 16 fragments at the 6LoWPAN sublayer. 1777 This level of fragmentation is much higher than that traditionally 1778 experienced over the Internet with IPv4 fragments, where 1779 fragmentation is already known as harmful. 1781 In the case to a multihop route within a 6TiSCH network, Hop-by-Hop 1782 recomposition occurs at each hop in order to reform the packet and 1783 route it. This creates additional latency and forces intermediate 1784 nodes to store a portion of a packet for an undetermined time, thus 1785 impacting critical resources such as memory and battery. 1787 [I-D.ietf-6lo-minimal-fragment] describes a framework for 1788 forwarding fragments end-to-end across a 6TiSCH route-over mesh. 1789 Within that framework, [I-D.ietf-lwig-6lowpan-virtual-reassembly] 1790 details a virtual reassembly buffer mechanism whereby the datagram 1791 tag in the 6LoWPAN Fragment is used as a label for switching at the 1792 6LoWPAN sublayer. Building on this technique, 1793 [I-D.ietf-6lo-fragment-recovery] introduces a new format for 6LoWPAN 1794 fragments that enables the selective recovery of individual 1795 fragments, and allows for a degree of flow control based on an 1796 Explicit Congestion Notification. 1798 | ^ 1799 +--------------+ | | 1800 | IPv6 | | +----+ +----+ | 1801 +--------------+ | | | | | | 1802 | 6LoWPAN HC | | learn learn | 1803 +--------------+ | | | | | | 1804 | 6top | | | | | | | 1805 +--------------+ | | | | | | 1806 | TSCH MAC | | | | | | | 1807 +--------------+ | | | | | | 1808 | LLN PHY | +-------+ +--...-----+ +-------+ 1809 +--------------+ 1811 Figure 13: Forwarding First Fragment 1813 In that model, the first fragment is routed based on the IPv6 header 1814 that is present in that fragment. The 6LoWPAN sublayer learns the 1815 next hop selection, generates a new datagram tag for transmission to 1816 the next hop, and stores that information indexed by the incoming MAC 1817 address and datagram tag. The next fragments are then switched based 1818 on that stored state. 1820 | ^ 1821 +--------------+ | | 1822 | IPv6 | | | 1823 +--------------+ | | 1824 | 6LoWPAN HC | | replay replay | 1825 +--------------+ | | | | | | 1826 | 6top | | | | | | | 1827 +--------------+ | | | | | | 1828 | TSCH MAC | | | | | | | 1829 +--------------+ | | | | | | 1830 | LLN PHY | +-------+ +--...-----+ +-------+ 1831 +--------------+ 1833 Figure 14: Forwarding Next Fragment 1835 A bitmap and an ECN echo in the end-to-end acknowledgment enable the 1836 source to resend the missing fragments selectively. The first 1837 fragment may be resent to carve a new path in case of a path failure. 1838 The ECN echo set indicates that the number of outstanding fragments 1839 should be reduced. 1841 4.6.3. IPv6 Forwarding 1843 As the packets are routed at Layer-3, traditional QoS and Active 1844 Queue Management (AQM) operations are expected to prioritize flows; 1845 the application of Differentiated Services is further discussed in 1846 [I-D.svshah-tsvwg-lln-diffserv-recommendations]. 1848 | ^ 1849 +--------------+ | | 1850 | IPv6 | | +-QoS+ +-QoS+ | 1851 +--------------+ | | | | | | 1852 | 6LoWPAN HC | | | | | | | 1853 +--------------+ | | | | | | 1854 | 6top | | | | | | | 1855 +--------------+ | | | | | | 1856 | TSCH MAC | | | | | | | 1857 +--------------+ | | | | | | 1858 | LLN PHY | +-------+ +--...-----+ +-------+ 1859 +--------------+ 1861 Figure 15: IP Forwarding 1863 4.7. Centralized vs. Distributed Routing 1865 6TiSCH supports a mixed model of centralized routes and distributed 1866 routes. Centralized routes can for example be computed by a entity 1867 such as a PCE. Distributed routes are computed by RPL. 1869 Both methods may inject routes in the Routing Tables of the 6TiSCH 1870 routers. In either case, each route is associated with a 6TiSCH 1871 topology that can be a RPL Instance topology or a Track. The 6TiSCH 1872 topology is indexed by a Instance ID, in a format that reuses the 1873 RPLInstanceID as defined in RPL [RFC6550]. 1875 Both RPL and PCE rely on shared sources such as policies to define 1876 Global and Local RPLInstanceIDs that can be used by either method. 1877 It is possible for centralized and distributed routing to share a 1878 same topology. Generally they will operate in different slotFrames, 1879 and centralized routes will be used for scheduled traffic and will 1880 have precedence over distributed routes in case of conflict between 1881 the slotFrames. 1883 4.7.1. Packet Marking and Handling 1885 All packets inside a 6TiSCH domain must carry the Instance ID that 1886 identifies the 6TiSCH topology that is to be used for routing and 1887 forwarding that packet. The location of that information must be the 1888 same for all packets forwarded inside the domain. 1890 For packets that are routed by a PCE along a Track, the tuple formed 1891 by the IPv6 source address and a local RPLInstanceID in the packet 1892 identify uniquely the Track and associated transmit bundle. 1894 For packets that are routed by RPL, that information is the 1895 RPLInstanceID which is carried in the RPL Packet Information, as 1896 discussed in section 11.2 of [RFC6550], "Loop Avoidance and 1897 Detection". 1899 The RPL Packet Information (RPI) is carried in IPv6 packets as a RPL 1900 option in the IPv6 Hop-By-Hop Header [RFC6553]. 1902 A compression mechanism for the RPL packet artifacts that integrates 1903 the compression of IP-in-IP encapsulation and the Routing Header type 1904 3 [RFC6554] with that of the RPI in a 6LoWPAN dispatch/header type is 1905 specified in [RFC8025] and [RFC8138]. 1907 Either way, the method and format used for encoding the RPLInstanceID 1908 is generalized to all 6TiSCH topological Instances, which include 1909 both RPL Instances and Tracks. 1911 4.7.2. Replication, Retries and Elimination 1913 6TiSCH expects elimination and replication of packets along a complex 1914 Track, but has no position about how the sequence numbers would be 1915 tagged in the packet. 1917 As it goes, 6TiSCH expects that timeSlots corresponding to copies of 1918 a same packet along a Track are correlated by configuration, and does 1919 not need to process the sequence numbers. 1921 The semantics of the configuration will enable correlated timeSlots 1922 to be grouped for transmit (and respectively receive) with a 'OR' 1923 relations, and then a 'AND' relation would be configurable between 1924 groups. The semantics is that if the transmit (and respectively 1925 receive) operation succeeded in one timeSlot in a 'OR' group, then 1926 all the other timeSLots in the group are ignored. Now, if there are 1927 at least two groups, the 'AND' relation between the groups indicates 1928 that one operation must succeed in each of the groups. 1930 On the transmit side, timeSlots provisioned for retries along a same 1931 branch of a Track are placed a same 'OR' group. The 'OR' relation 1932 indicates that if a transmission is acknowledged, then further 1933 transmissions should not be attempted for timeSlots in that group. 1934 There are as many 'OR' groups as there are branches of the Track 1935 departing from this node. Different 'OR' groups are programmed for 1936 the purpose of replication, each group corresponding to one branch of 1937 the Track. The 'AND' relation between the groups indicates that 1938 transmission over any of branches must be attempted regardless of 1939 whether a transmission succeeded in another branch. It is also 1940 possible to place cells to different next-hop routers in a same 'OR' 1941 group. This allows to route along multi-path tracks, trying one 1942 next-hop and then another only if sending to the first fails. 1944 On the receive side, all timeSlots are programmed in a same 'OR' 1945 group. Retries of a same copy as well as converging branches for 1946 elimination are converged, meaning that the first successful 1947 reception is enough and that all the other timeSlots can be ignored. 1949 4.7.3. Differentiated Services Per-Hop-Behavior 1951 Additionally, an IP packet that is sent along a Track uses the 1952 Differentiated Services Per-Hop-Behavior Group called Deterministic 1953 Forwarding, as described in 1954 [I-D.svshah-tsvwg-deterministic-forwarding]. 1956 5. IANA Considerations 1958 This specification does not require IANA action. 1960 6. Security Considerations 1962 This architecture operates on IEEE Std 802.15.4 and expects link- 1963 layer security to be enabled at all times between connected devices, 1964 except for the very first step of the device join process, where a 1965 joining device may need some initial, unsecured exchanges so as to 1966 obtain its initial key material. 1968 The Minimal Security Framework for 6TiSCH 1969 [I-D.ietf-6tisch-minimal-security] describes the minimal mechanisms 1970 required to support secure enrollment of a pledge to a 6TiSCH network 1971 based on PSK. The specification enables to establish of link-layer 1972 keys, typically used in combination with a variation of Counter with 1973 CBC-MAC (CCM) [RFC3610], and set up a secure end-to-end session 1974 between the joining node (called the pledge) and the join registrar/ 1975 coordinator (JRC) in charge of authenticating the node via a Join 1976 Proxy (JP). It can also be used to obtain a link layer short address 1977 as a side effect. The 6TiSCH Joined Process (6JP) uses shared slots 1978 which are a constrained resource, so it is optimized to limit the 1979 number of messages to the strict minimum. As an example, Neighbor 1980 Discovery between the pledge and the JP can be skipped when the IPv6 1981 Link Local addresses that are used derive from the node's EUI-64 1982 address. 1984 The "6tisch Zero-Touch Secure Join protocol" 1985 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] wraps the minimal 1986 security draft with a flow inspired from ANIMA "Bootstrapping Remote 1987 Secure Key Infrastructures (BRSKI)" 1988 [I-D.ietf-anima-bootstrapping-keyinfra]. 1990 6.1. Join Process Highlights 1992 The BRSKI architecture specifies three logical elements to describe 1993 the join process: 1995 Pledge: Node that wishes to become part of the network; 1997 Join Registrar/Coordinator (JRC) : An entity that arbitrates network 1998 access and hands out network parameters (such as keying 1999 material); 2001 Join Proxy (JP), a one-hop (radio) neighbor of the joining node that 2002 acts as proxy network node and may provide connectivity with 2003 the JRC. 2005 The join protocol consists of three major activities: 2007 Device Authentication: The Pledge and the JP mutually authenticate 2008 each other and establish a shared key, so as to ensure on-going 2009 authenticated communications. This may involve a server as a 2010 third party. 2012 Authorization: The JP decides on whether/how to authorize a Pledge 2013 (if denied, this may result in loss of bandwidth). Conversely, 2014 the Pledge decides on whether/how to authorize the network (if 2015 denied, it will not join the network). Authorization decisions 2016 may involve other nodes in the network. 2018 Configuration/Parameterization: The JP distributes configuration 2019 information to the Pledge, such as scheduling information, IP 2020 address assignment information, and network policies. This may 2021 originate from other network devices, for which the JP may act 2022 as proxy. This step may also include distribution of 2023 information from the Pledge to the JP and other nodes in the 2024 network and, more generally, synchronization of information 2025 between these entities. 2027 The device joining process is depicted in Figure 16, where it is 2028 assumed that devices have access to certificates and where entities 2029 have access to the root CA keys of their communicating parties 2030 (initial set-up requirement). Under these assumptions, the 2031 authentication step of the device joining process does not require 2032 online involvement of a third party. Mutual authentication is 2033 performed between the Pledge and the JP using their certificates, 2034 which also results in a shared key between these two entities. 2036 The JP assists the Pledge in mutual authentication with a remote 2037 server node (primarily via provision of a communication path with the 2038 server), which also results in a shared (end-to-end) key between 2039 those two entities. The server node may be a JRC that arbitrages the 2040 network authorization of the Pledge (where the JP will deny bandwidth 2041 if authorization is not successful); it may distribute network- 2042 specific configuration parameters (including network-wide keys) to 2043 the Pledge. In its turn, the Pledge may distribute and synchronize 2044 information (including, e.g., network statistics) to the server node 2045 and, if so desired, also to the JP. The actual decision of the 2046 Pledge to become part of the network may depend on authorization of 2047 the network itself. 2049 The server functionality is a role which may be implemented with one 2050 (centralized) or multiple devices (distributed). In either case, 2051 mutual authentication is established with each physical server entity 2052 with which a role is implemented. 2054 Note that in the above description, the JP does not solely act as a 2055 relay node, thereby allowing it to first filter traffic to be relayed 2056 based on cryptographic authentication criteria - this provides first- 2057 level access control and mitigates certain types of denial-of-service 2058 attacks on the network at large. 2060 Depending on more detailed insight in cost/benefit trade-offs, this 2061 process might be complemented by a more "relaxed" mechanism, where 2062 the JP acts as a relay node only. The final architecture will 2063 provide mechanisms to also cover cases where the initial set-up 2064 requirements are not met or where some other out-of-sync behavior 2065 occurs; it will also suggest some optimizations in case JRC-related 2066 information is already available with the JP (via caching of 2067 information). 2069 When a device rejoins the network in the same authorization domain, 2070 the authorization step could be omitted if the server distributes the 2071 authorization state for the device to the JP when the device 2072 initially joined the network. However, this generally still requires 2073 the exchange of updated configuration information, e.g., related to 2074 time schedules and bandwidth allocation. 2076 {joining node} {neighbor} {server, etc.} Example: 2077 +---------+ +---------+ +---------+ 2078 | Joining | | Join | +--| CA |certificate 2079 | Node | |Assistant| | +---------+ issuance 2080 +---------+ +---------+ | +---------+ 2081 | | +--|Authoriz.| membership 2082 |<----Beaconing------| | +---------+ test (JRC) 2083 | | | +---------+ 2084 |<--Authentication-->| +--| Routing | IP address 2085 | |<--Authorization-->| +--------- assignment 2086 |<-------------------| | +---------+ 2087 | | +--| Gateway | backbone, 2088 |------------------->| | +---------+ cloud 2089 | |<--Configuration-->| +---------+ 2090 |<-------------------| +--|Bandwidth| PCE 2091 +---------+ schedule 2092 . . . 2093 . . . 2095 Figure 16: Network joining, with only authorization by third party 2097 7. Acknowledgments 2099 7.1. Contributors 2101 The co-authors of this document are listed below: 2103 Robert Assimiti for his breakthrough work on RPL over TSCH and 2104 initial text and guidance; 2106 Kris Pister for creating it all and his continuing guidance through 2107 the elaboration of this design; 2109 Michael Richardson for his leadership role in the Security Design 2110 Team and his contribution throughout this document; 2112 Rene Struik for the security section and his contribution to the 2113 Security Design Team; 2115 Malisa Vucinic for the work on the one-touch join process and his 2116 contribution to the Security Design Team; 2118 Xavier Vilajosana who lead the design of the minimal support with 2119 RPL and contributed deeply to the 6top design and the G-MPLS 2120 operation of Track switching; 2122 Qin Wang who lead the design of the 6top sublayer and contributed 2123 related text that was moved and/or adapted in this document; 2125 Thomas Watteyne for his contribution to the whole design, in 2126 particular on TSCH and security. 2128 7.2. Special Thanks 2130 Special thanks to Tero Kivinen, Jonathan Simon, Giuseppe Piro, Subir 2131 Das and Yoshihiro Ohba for their deep contribution to the initial 2132 security work, to Diego Dujovne for starting and leading the SF0 2133 effort and to Tengfei Chang for evolving it in the MSF. 2135 Special thanks also to Pat Kinney for his support in maintaining the 2136 connection active and the design in line with work happening at IEEE 2137 Std 802.15.4. 2139 Special thanks to Ted Lemon who was the INT Area A-D while this 2140 specification was developed for his great support and help 2141 throughout. 2143 Also special thanks to Ralph Droms who performed the first INT Area 2144 Directorate review, that was very deep and through and radically 2145 changed the orientations of this document. 2147 7.3. And Do not Forget 2149 This specification is the result of multiple interactions, in 2150 particular during the 6TiSCH (bi)Weekly Interim call, relayed through 2151 the 6TiSCH mailing list at the IETF. 2153 The authors wish to thank: Alaeddine Weslati, Chonggang Wang, 2154 Georgios Exarchakos, Zhuo Chen, Alfredo Grieco, Bert Greevenbosch, 2155 Cedric Adjih, Deji Chen, Martin Turon, Dominique Barthel, Elvis 2156 Vogli, Geraldine Texier, Malisa Vucinic, Guillaume Gaillard, Herman 2157 Storey, Kazushi Muraoka, Ken Bannister, Kuor Hsin Chang, Laurent 2158 Toutain, Maik Seewald, Maria Rita Palattella, Michael Behringer, 2159 Nancy Cam Winget, Nicola Accettura, Nicolas Montavont, Oleg Hahm, 2160 Patrick Wetterwald, Paul Duffy, Peter van der Stock, Rahul Sen, 2161 Pieter de Mil, Pouria Zand, Rouhollah Nabati, Rafa Marin-Lopez, 2162 Raghuram Sudhaakar, Sedat Gormus, Shitanshu Shah, Steve Simlo, 2163 Tengfei Chang, Tina Tsou, Tom Phinney, Xavier Lagrange, Ines Robles 2164 and Samita Chakrabarti for their participation and various 2165 contributions. 2167 8. References 2169 8.1. Normative References 2171 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2172 DOI 10.17487/RFC0768, August 1980, 2173 . 2175 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2176 Requirement Levels", BCP 14, RFC 2119, 2177 DOI 10.17487/RFC2119, March 1997, 2178 . 2180 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2181 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2182 DOI 10.17487/RFC4861, September 2007, 2183 . 2185 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2186 Address Autoconfiguration", RFC 4862, 2187 DOI 10.17487/RFC4862, September 2007, 2188 . 2190 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 2191 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 2192 DOI 10.17487/RFC6282, September 2011, 2193 . 2195 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 2196 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 2197 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 2198 Low-Power and Lossy Networks", RFC 6550, 2199 DOI 10.17487/RFC6550, March 2012, 2200 . 2202 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 2203 Protocol for Low-Power and Lossy Networks (RPL)", 2204 RFC 6552, DOI 10.17487/RFC6552, March 2012, 2205 . 2207 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 2208 Power and Lossy Networks (RPL) Option for Carrying RPL 2209 Information in Data-Plane Datagrams", RFC 6553, 2210 DOI 10.17487/RFC6553, March 2012, 2211 . 2213 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 2214 Routing Header for Source Routes with the Routing Protocol 2215 for Low-Power and Lossy Networks (RPL)", RFC 6554, 2216 DOI 10.17487/RFC6554, March 2012, 2217 . 2219 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 2220 Bormann, "Neighbor Discovery Optimization for IPv6 over 2221 Low-Power Wireless Personal Area Networks (6LoWPANs)", 2222 RFC 6775, DOI 10.17487/RFC6775, November 2012, 2223 . 2225 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 2226 Application Protocol (CoAP)", RFC 7252, 2227 DOI 10.17487/RFC7252, June 2014, 2228 . 2230 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 2231 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 2232 RFC 8025, DOI 10.17487/RFC8025, November 2016, 2233 . 2235 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 2236 "IPv6 over Low-Power Wireless Personal Area Network 2237 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 2238 April 2017, . 2240 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2241 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2242 May 2017, . 2244 [RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal 2245 IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) 2246 Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180, 2247 May 2017, . 2249 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2250 (IPv6) Specification", STD 86, RFC 8200, 2251 DOI 10.17487/RFC8200, July 2017, 2252 . 2254 8.2. Informative References 2256 [I-D.ietf-6lo-ap-nd] 2257 Thubert, P., Sarikaya, B., and M. Sethi, "Address 2258 Protected Neighbor Discovery for Low-power and Lossy 2259 Networks", draft-ietf-6lo-ap-nd-07 (work in progress), 2260 September 2018. 2262 [I-D.ietf-6lo-backbone-router] 2263 Thubert, P. and C. Perkins, "IPv6 Backbone Router", draft- 2264 ietf-6lo-backbone-router-07 (work in progress), September 2265 2018. 2267 [I-D.ietf-6lo-fragment-recovery] 2268 Thubert, P., "6LoWPAN Selective Fragment Recovery", draft- 2269 ietf-6lo-fragment-recovery-00 (work in progress), 2270 September 2018. 2272 [I-D.ietf-6lo-rfc6775-update] 2273 Thubert, P., Nordmark, E., Chakrabarti, S., and C. 2274 Perkins, "Registration Extensions for 6LoWPAN Neighbor 2275 Discovery", draft-ietf-6lo-rfc6775-update-21 (work in 2276 progress), June 2018. 2278 [I-D.ietf-6tisch-6top-protocol] 2279 Wang, Q., Vilajosana, X., and T. Watteyne, "6TiSCH 2280 Operation Sublayer Protocol (6P)", draft-ietf-6tisch-6top- 2281 protocol-12 (work in progress), June 2018. 2283 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] 2284 Richardson, M. and B. Damm, "6tisch Zero-Touch Secure Join 2285 protocol", draft-ietf-6tisch-dtsecurity-zerotouch-join-02 2286 (work in progress), April 2018. 2288 [I-D.ietf-6tisch-minimal-security] 2289 Vucinic, M., Simon, J., Pister, K., and M. Richardson, 2290 "Minimal Security Framework for 6TiSCH", draft-ietf- 2291 6tisch-minimal-security-06 (work in progress), May 2018. 2293 [I-D.ietf-6tisch-msf] 2294 Chang, T., Vucinic, M., Vilajosana, X., Duquennoy, S., and 2295 D. Dujovne, "6TiSCH Minimal Scheduling Function (MSF)", 2296 draft-ietf-6tisch-msf-00 (work in progress), August 2018. 2298 [I-D.ietf-6tisch-terminology] 2299 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang, 2300 "Terms Used in IPv6 over the TSCH mode of IEEE 802.15.4e", 2301 draft-ietf-6tisch-terminology-10 (work in progress), March 2302 2018. 2304 [I-D.ietf-anima-bootstrapping-keyinfra] 2305 Pritikin, M., Richardson, M., Behringer, M., Bjarnason, 2306 S., and K. Watsen, "Bootstrapping Remote Secure Key 2307 Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- 2308 keyinfra-16 (work in progress), June 2018. 2310 [I-D.ietf-core-comi] 2311 Veillette, M., Stok, P., Pelov, A., and A. Bierman, "CoAP 2312 Management Interface", draft-ietf-core-comi-03 (work in 2313 progress), June 2018. 2315 [I-D.ietf-core-object-security] 2316 Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 2317 "Object Security for Constrained RESTful Environments 2318 (OSCORE)", draft-ietf-core-object-security-15 (work in 2319 progress), August 2018. 2321 [I-D.ietf-detnet-architecture] 2322 Finn, N., Thubert, P., Varga, B., and J. Farkas, 2323 "Deterministic Networking Architecture", draft-ietf- 2324 detnet-architecture-08 (work in progress), September 2018. 2326 [I-D.ietf-detnet-use-cases] 2327 Grossman, E., "Deterministic Networking Use Cases", draft- 2328 ietf-detnet-use-cases-19 (work in progress), October 2018. 2330 [I-D.ietf-lwig-6lowpan-virtual-reassembly] 2331 Bormann, C. and T. Watteyne, "Virtual reassembly buffers 2332 in 6LoWPAN", draft-ietf-lwig-6lowpan-virtual-reassembly-00 2333 (work in progress), July 2018. 2335 [I-D.ietf-manet-aodvv2] 2336 Perkins, C., Ratliff, S., Dowdell, J., Steenbrink, L., and 2337 V. Mercieca, "Ad Hoc On-demand Distance Vector Version 2 2338 (AODVv2) Routing", draft-ietf-manet-aodvv2-16 (work in 2339 progress), May 2016. 2341 [I-D.ietf-roll-aodv-rpl] 2342 Anamalamudi, S., Zhang, M., Sangi, A., Perkins, C., Anand, 2343 S., and B. Liu, "Asymmetric AODV-P2P-RPL in Low-Power and 2344 Lossy Networks (LLNs)", draft-ietf-roll-aodv-rpl-04 (work 2345 in progress), July 2018. 2347 [I-D.ietf-roll-rpl-industrial-applicability] 2348 Phinney, T., Thubert, P., and R. Assimiti, "RPL 2349 applicability in industrial networks", draft-ietf-roll- 2350 rpl-industrial-applicability-02 (work in progress), 2351 October 2013. 2353 [I-D.svshah-tsvwg-deterministic-forwarding] 2354 Shah, S. and P. Thubert, "Deterministic Forwarding PHB", 2355 draft-svshah-tsvwg-deterministic-forwarding-04 (work in 2356 progress), August 2015. 2358 [I-D.svshah-tsvwg-lln-diffserv-recommendations] 2359 Shah, S. and P. Thubert, "Differentiated Service Class 2360 Recommendations for LLN Traffic", draft-svshah-tsvwg-lln- 2361 diffserv-recommendations-04 (work in progress), February 2362 2015. 2364 [I-D.thubert-6lo-bier-dispatch] 2365 Thubert, P., Brodard, Z., Jiang, H., and G. Texier, "A 2366 6loRH for BitStrings", draft-thubert-6lo-bier-dispatch-05 2367 (work in progress), July 2018. 2369 [I-D.thubert-bier-replication-elimination] 2370 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 2371 TE extensions for Packet Replication and Elimination 2372 Function (PREF) and OAM", draft-thubert-bier-replication- 2373 elimination-03 (work in progress), March 2018. 2375 [I-D.thubert-roll-unaware-leaves] 2376 Thubert, P., "Routing for RPL Leaves", draft-thubert-roll- 2377 unaware-leaves-05 (work in progress), May 2018. 2379 [I-D.wang-6tisch-6top-sublayer] 2380 Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer 2381 (6top)", draft-wang-6tisch-6top-sublayer-04 (work in 2382 progress), November 2015. 2384 [I-D.ietf-6lo-minimal-fragment] 2385 Watteyne, T., Bormann, C., and P. Thubert, "LLN Minimal 2386 Fragment Forwarding", draft-ietf-6lo-minimal- 2387 fragment-00 (work in progress), October 2018. 2389 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2390 "Definition of the Differentiated Services Field (DS 2391 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2392 DOI 10.17487/RFC2474, December 1998, 2393 . 2395 [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol 2396 Extensions for IPv6 Inter-Domain Routing", RFC 2545, 2397 DOI 10.17487/RFC2545, March 1999, 2398 . 2400 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2401 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2402 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2403 . 2405 [RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between 2406 Information Models and Data Models", RFC 3444, 2407 DOI 10.17487/RFC3444, January 2003, 2408 . 2410 [RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with 2411 CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September 2412 2003, . 2414 [RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. 2415 Thubert, "Network Mobility (NEMO) Basic Support Protocol", 2416 RFC 3963, DOI 10.17487/RFC3963, January 2005, 2417 . 2419 [RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 2420 Bosch, "Next Steps in Signaling (NSIS): Framework", 2421 RFC 4080, DOI 10.17487/RFC4080, June 2005, 2422 . 2424 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2425 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2426 2006, . 2428 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2429 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2430 2006, . 2432 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2433 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 2434 . 2436 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 2437 DOI 10.17487/RFC4903, June 2007, 2438 . 2440 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2441 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2442 Overview, Assumptions, Problem Statement, and Goals", 2443 RFC 4919, DOI 10.17487/RFC4919, August 2007, 2444 . 2446 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2447 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2448 . 2450 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 2451 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 2452 September 2010, . 2454 [RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS 2455 Signaling Layer Protocol (NSLP) for Quality-of-Service 2456 Signaling", RFC 5974, DOI 10.17487/RFC5974, October 2010, 2457 . 2459 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2460 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2461 2011, . 2463 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2464 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2465 January 2012, . 2467 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 2468 Statement and Requirements for IPv6 over Low-Power 2469 Wireless Personal Area Network (6LoWPAN) Routing", 2470 RFC 6606, DOI 10.17487/RFC6606, May 2012, 2471 . 2473 [RFC6620] Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS 2474 SAVI: First-Come, First-Served Source Address Validation 2475 Improvement for Locally Assigned IPv6 Addresses", 2476 RFC 6620, DOI 10.17487/RFC6620, May 2012, 2477 . 2479 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 2480 Locator/ID Separation Protocol (LISP)", RFC 6830, 2481 DOI 10.17487/RFC6830, January 2013, 2482 . 2484 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 2485 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2486 2014, . 2488 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2489 Constrained-Node Networks", RFC 7228, 2490 DOI 10.17487/RFC7228, May 2014, 2491 . 2493 [RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S., 2494 Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software- 2495 Defined Networking (SDN): Layers and Architecture 2496 Terminology", RFC 7426, DOI 10.17487/RFC7426, January 2497 2015, . 2499 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 2500 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 2501 Internet of Things (IoT): Problem Statement", RFC 7554, 2502 DOI 10.17487/RFC7554, May 2015, 2503 . 2505 8.3. Other Informative References 2507 [ACE] IETF, "Authentication and Authorization for Constrained 2508 Environments", 2509 . 2511 [ANIMA] IETF, "Autonomic Networking Integrated Model and 2512 Approach", 2513 . 2515 [CCAMP] IETF, "Common Control and Measurement Plane", 2516 . 2518 [DETNET] IETF, "Deterministic Networking", 2519 . 2521 [DICE] IETF, "DTLS In Constrained Environments", 2522 . 2524 [HART] www.hartcomm.org, "Highway Addressable remote Transducer, 2525 a group of specifications for industrial process and 2526 control devices administered by the HART Foundation". 2528 [IEC62439] 2529 IEC, "Industrial communication networks - High 2530 availability automation networks - Part 3: Parallel 2531 Redundancy Protocol (PRP) and High-availability Seamless 2532 Redundancy (HSR) - IEC62439-3", 2012, 2533 . 2535 [IEEE802.1TSNTG] 2536 IEEE Standards Association, "IEEE 802.1 Time-Sensitive 2537 Networks Task Group", March 2013, 2538 . 2540 [IEEE802154] 2541 IEEE standard for Information Technology, "IEEE Std. 2542 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 2543 and Physical Layer (PHY) Specifications for Low-Rate 2544 Wireless Personal Area Networks". 2546 [IEEE802154e] 2547 IEEE standard for Information Technology, "IEEE standard 2548 for Information Technology, IEEE Std. 802.15.4, Part. 2549 15.4: Wireless Medium Access Control (MAC) and Physical 2550 Layer (PHY) Specifications for Low-Rate Wireless Personal 2551 Area Networks, June 2011 as amended by IEEE Std. 2552 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area 2553 Networks (LR-WPANs) Amendment 1: MAC sublayer", April 2554 2012. 2556 [ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation", 2557 . 2559 [ISA100.11a] 2560 ISA/ANSI, "Wireless Systems for Industrial Automation: 2561 Process Control and Related Applications - ISA100.11a-2011 2562 - IEC 62734", 2011, . 2565 [PCE] IETF, "Path Computation Element", 2566 . 2568 [TEAS] IETF, "Traffic Engineering Architecture and Signaling", 2569 . 2571 [WirelessHART] 2572 www.hartcomm.org, "Industrial Communication Networks - 2573 Wireless Communication Network and Communication Profiles 2574 - WirelessHART - IEC 62591", 2010. 2576 Author's Address 2578 Pascal Thubert (editor) 2579 Cisco Systems, Inc 2580 Building D 2581 45 Allee des Ormes - BP1200 2582 MOUGINS - Sophia Antipolis 06254 2583 FRANCE 2585 Phone: +33 497 23 26 34 2586 Email: pthubert@cisco.com