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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 Systems 4 Intended status: Informational 29 October 2019 5 Expires: 1 May 2020 7 An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4 8 draft-ietf-6tisch-architecture-28 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 1 May 2020. 35 Copyright Notice 37 Copyright (c) 2019 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 (https://trustee.ietf.org/ 42 license-info) in effect on the date of publication of this document. 43 Please review these documents carefully, as they describe your rights 44 and restrictions with respect to this document. Code Components 45 extracted from this document must include Simplified BSD License text 46 as described in Section 4.e of the Trust Legal Provisions and are 47 provided without warranty as described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 53 2.1. New Terms . . . . . . . . . . . . . . . . . . . . . . . . 5 54 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 10 55 2.3. Related Documents . . . . . . . . . . . . . . . . . . . . 11 56 3. High Level Architecture . . . . . . . . . . . . . . . . . . . 12 57 3.1. A Non-Broadcast Multi-Access Radio Mesh Network . . . . . 12 58 3.2. A Multi-Link Subnet Model . . . . . . . . . . . . . . . . 14 59 3.3. TSCH: A Deterministic MAC Layer . . . . . . . . . . . . . 15 60 3.4. Scheduling TSCH . . . . . . . . . . . . . . . . . . . . . 16 61 3.5. Distributed vs. Centralized Routing . . . . . . . . . . . 17 62 3.6. Forwarding Over TSCH . . . . . . . . . . . . . . . . . . 18 63 3.7. 6TiSCH Stack . . . . . . . . . . . . . . . . . . . . . . 19 64 3.8. Communication Paradigms and Interaction Models . . . . . 21 65 4. Architecture Components . . . . . . . . . . . . . . . . . . . 22 66 4.1. 6LoWPAN (and RPL) . . . . . . . . . . . . . . . . . . . . 22 67 4.1.1. RPL-Unaware Leaves and 6LoWPAN ND . . . . . . . . . . 22 68 4.1.2. 6LBR and RPL Root . . . . . . . . . . . . . . . . . . 23 69 4.2. Network Access and Addressing . . . . . . . . . . . . . . 23 70 4.2.1. Join Process . . . . . . . . . . . . . . . . . . . . 24 71 4.2.2. Registration . . . . . . . . . . . . . . . . . . . . 26 72 4.3. TSCH and 6top . . . . . . . . . . . . . . . . . . . . . . 27 73 4.3.1. 6top . . . . . . . . . . . . . . . . . . . . . . . . 27 74 4.3.2. Scheduling Functions and the 6top protocol . . . . . 29 75 4.3.3. 6top and RPL Objective Function operations . . . . . 30 76 4.3.4. Network Synchronization . . . . . . . . . . . . . . . 31 77 4.3.5. Slotframes and CDU matrix . . . . . . . . . . . . . . 32 78 4.3.6. Distributing the reservation of cells . . . . . . . . 33 79 4.4. Schedule Management Mechanisms . . . . . . . . . . . . . 34 80 4.4.1. Static Scheduling . . . . . . . . . . . . . . . . . . 34 81 4.4.2. Neighbor-to-neighbor Scheduling . . . . . . . . . . . 35 82 4.4.3. Remote Monitoring and Schedule Management . . . . . . 36 83 4.4.4. Hop-by-hop Scheduling . . . . . . . . . . . . . . . . 38 84 4.5. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 38 85 4.5.1. General Behavior of Tracks . . . . . . . . . . . . . 39 86 4.5.2. Serial Track . . . . . . . . . . . . . . . . . . . . 39 87 4.5.3. Complex Track with Replication and 88 Elimination . . . . . . . . . . . . . . . . . . . . . 40 89 4.5.4. DetNet End-to-end Path . . . . . . . . . . . . . . . 40 90 4.5.5. Cell Reuse . . . . . . . . . . . . . . . . . . . . . 41 91 4.6. Forwarding Models . . . . . . . . . . . . . . . . . . . . 42 92 4.6.1. Track Forwarding . . . . . . . . . . . . . . . . . . 42 93 4.6.2. IPv6 Forwarding . . . . . . . . . . . . . . . . . . . 45 94 4.6.3. Fragment Forwarding . . . . . . . . . . . . . . . . . 45 95 4.7. Advanced 6TiSCH Routing . . . . . . . . . . . . . . . . . 47 96 4.7.1. Packet Marking and Handling . . . . . . . . . . . . . 47 97 4.7.2. Replication, Retries and Elimination . . . . . . . . 48 98 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 99 6. Security Considerations . . . . . . . . . . . . . . . . . . . 50 100 6.1. Availability of Remote Services . . . . . . . . . . . . . 50 101 6.2. Selective Jamming . . . . . . . . . . . . . . . . . . . . 51 102 6.3. MAC-Layer Security . . . . . . . . . . . . . . . . . . . 51 103 6.4. Time Synchronization . . . . . . . . . . . . . . . . . . 52 104 6.5. Validating ASN . . . . . . . . . . . . . . . . . . . . . 52 105 6.6. Network Keying and Rekeying . . . . . . . . . . . . . . . 53 106 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 55 107 7.1. Contributors . . . . . . . . . . . . . . . . . . . . . . 55 108 7.2. Special Thanks . . . . . . . . . . . . . . . . . . . . . 56 109 7.3. And Do not Forget . . . . . . . . . . . . . . . . . . . . 56 110 8. Normative References . . . . . . . . . . . . . . . . . . . . 57 111 9. Informative References . . . . . . . . . . . . . . . . . . . 61 112 Appendix A. Related Work In Progress . . . . . . . . . . . . . . 67 113 A.1. Unchartered IETF work items . . . . . . . . . . . . . . . 67 114 A.1.1. 6TiSCH Zerotouch security . . . . . . . . . . . . . . 67 115 A.1.2. 6TiSCH Track Setup . . . . . . . . . . . . . . . . . 67 116 A.1.3. Using BIER in a 6TiSCH Network . . . . . . . . . . . 68 117 A.2. External (non-IETF) work items . . . . . . . . . . . . . 68 118 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 69 120 1. Introduction 122 Wireless Networks enable a wide variety of devices of any size to get 123 interconnected, often at a very low marginal cost per device, at any 124 range, and in circumstances where wiring may be impractical, for 125 instance on fast-moving or rotating devices. 127 On the other hand, Deterministic Networking maximizes the packet 128 delivery ratio within a bounded latency so as to enable mission- 129 critical machine-to-machine (M2M) operations. Applications that need 130 such networks are presented in [RFC8578]. The considered 131 applications include Professional Media, Industrial Automation 132 Control Systems (IACS), building automation, in-vehicle command and 133 control, commercial automation and asset tracking with mobile 134 scenarios, as well as gaming, drones and edge robotic control, and 135 home automation applications. 137 The Timeslotted Channel Hopping (TSCH) [RFC7554] mode of the IEEE 138 Std. 802.15.4 [IEEE802154] Medium Access Control (MAC) was introduced 139 with the IEEE Std. 802.15.4e [IEEE802154e] amendment and is now 140 retrofitted in the main standard. For all practical purposes, this 141 document is expected to be insensitive to the revisions of that 142 standard, which is thus referenced without a date. TSCH is both a 143 Time-Division Multiplexing and a Frequency-Division Multiplexing 144 technique whereby a different channel can be used for each 145 transmission, and that allows to schedule transmissions for 146 deterministic operations, and applies to the slower and most energy 147 constrained wireless use cases. 149 The scheduled operation provides for a more reliable experience which 150 can be used to monitor and manage resources, e.g., energy and water, 151 in a more efficient fashion. 153 Proven Deterministic Networking standards for use in Process Control, 154 including ISA100.11a [ISA100.11a] and WirelessHART [WirelessHART], 155 have demonstrated the capabilities of the IEEE Std. 802.15.4 TSCH MAC 156 for high reliability against interference, low-power consumption on 157 well-known flows, and its applicability for Traffic Engineering (TE) 158 from a central controller. 160 To enable the convergence of Information Technology (IT) and 161 Operational Technology (OT) in Low-Power Lossy Networks (LLNs), the 162 6TiSCH Architecture supports an IETF suite of protocols over the IEEE 163 Std. 802.15.4 TSCH MAC to provide IP connectivity for energy and 164 otherwise constrained wireless devices. 166 The 6TiSCH Architecture relies on IPv6 [RFC8200] and the use of 167 routing to provide large scaling capabilities. The addition of a 168 high-speed federating backbone adds yet another degree of scalability 169 to the design. The backbone is typically a Layer-2 transit Link such 170 as an Ethernet bridged network, but it can also be a more complex 171 routed structure. 173 The 6TiSCH Architecture introduces an IPv6 Multi-Link subnet model 174 that is composed of a federating backbone and a number of IEEE Std. 175 802.15.4 TSCH low-power wireless networks federated and synchronized 176 by Backbone Routers. If the backbone is a Layer-2 transit Link then 177 the Backbone Routers can operate as an IPv6 Neighbor Discovery (IPv6 178 ND) [RFC4861] proxy. 180 The 6TiSCH Architecture leverages 6LoWPAN [RFC4944] to adapt IPv6 to 181 the constrained media and RPL [RFC6550] for the distributed routing 182 operations. 184 Centralized routing refers to a model where routes are computed and 185 resources are allocated from a central controller. This is 186 particularly helpful to schedule deterministic multihop 187 transmissions. In contrast, Distributed Routing refers to a model 188 that relies on concurrent peer to peer protocol exchanges for TSCH 189 resource allocation and routing operations. 191 The architecture defines mechanisms to establish and maintain routing 192 and scheduling in a centralized, distributed, or mixed fashion, for 193 use in multiple OT environments. It is applicable in particular to 194 highly scalable solutions such as used in Advanced Metering 195 Infrastructure [AMI] solutions that leverage distributed routing to 196 enable multipath forwarding over large LLN meshes. 198 2. Terminology 200 2.1. New Terms 202 The draft does not reuse terms from the IEEE Std. 802.15.4 203 [IEEE802154] standard such as "path" or "link" which bear a meaning 204 that is quite different from classical IETF parlance. 206 This document adds the following terms: 208 6TiSCH (IPv6 over the TSCH mode of IEEE 802.15.4): 6TiSCH defines an 209 adaptation sublayer for IPv6 over TSCH called 6top, a set of 210 protocols for setting up a TSCH schedule in distributed approach, 211 and a security solution. 6TiSCH may be extended in the future for 212 other MAC/PHY pairs providing a service similar to TSCH. 214 6top (6TiSCH Operation Sublayer): The next higher layer of the IEEE 215 Std. 802.15.4 TSCH MAC layer. 6top provides the abstraction of an 216 IP link over a TSCH MAC, schedules packets over TSCH cells, and 217 exposes a management interface to schedule TSCH cells. 219 6P (6top Protocol): The protocol defined in [RFC8480]. 6P enables 220 Layer-2 peers to allocate, move or deallocate cells in their 221 respective schedules to communicate. 6P operates at the 6top 222 layer. 224 6P Transaction: A 2-way or 3-way sequence of 6P messages used by 225 Layer-2 peers to modify their communication schedule. 227 ASN (Absolute Slot Number): Defined in [IEEE802154], the ASN is the 228 total number of timeslots that have elapsed since the Epoch Time 229 when the TSCH network started. Incremented by one at each 230 timeslot. It is wide enough to not roll over in practice. 232 bundle: A group of equivalent scheduled cells, i.e., cells 233 identified by different [slotOffset, channelOffset], which are 234 scheduled for a same purpose, with the same neighbor, with the 235 same flags, and the same slotframe. The size of the bundle refers 236 to the number of cells it contains. For a given slotframe length, 237 the size of the bundle translates directly into bandwidth. A 238 bundle is a local abstraction that represents a half-duplex link 239 for either sending or receiving, with bandwidth that amounts to 240 the sum of the cells in the bundle. 242 Layer-2 vs. Layer-3 bundle: Bundles are associated for either 243 Layer-2 (switching) or Layer-3 (routing) forwarding operations. A 244 pair of Layer-3 bundles (one for each direction) maps to an IP 245 Link with a neighbor, whereas a set of Layer-2 bundles (of an 246 "arbitrary" cardinality and direction) corresponds to the relation 247 of one or more incoming bundle(s) from the previous-hop 248 neighbor(s) with one or more outgoing bundle(s) to the next-hop 249 neighbor(s) along a Track as part of the switching role, which may 250 include replication and elimination. 252 CCA (Clear Channel Assessment): A mechanism defined in [IEEE802154] 253 whereby nodes listen to the channel before sending to detect 254 ongoing transmissions from other parties. Because the network is 255 synchronized, CCA cannot be used to detect colliding transmissions 256 within the same network, but it can be used to detect other radio 257 networks in vicinity. 259 cell: A unit of transmission resource in the CDU matrix, a cell is 260 identified by a slotOffset and a channelOffset. A cell can be 261 scheduled or unscheduled. 263 Channel Distribution/Usage (CDU) matrix: : A matrix of cells (i,j) 264 representing the spectrum (channel) distribution among the 265 different nodes in the 6TiSCH network. The CDU matrix has width 266 in timeslots, equal to the period of the network scheduling 267 operation, and height equal to the number of available channels. 268 Every cell (i,j) in the CDU, identified by (slotOffset, 269 channelOffset), belongs to a specific chunk. 271 channelOffset: Identifies a row in the TSCH schedule. The number of 272 channelOffset values is bounded by the number of available 273 frequencies. The channelOffset translates into a frequency with a 274 function that depends on the absolute time when the communication 275 takes place, resulting in a channel hopping operation. 277 chunk: A well-known list of cells, distributed in time and 278 frequency, within a CDU matrix. A chunk represents a portion of a 279 CDU matrix. The partition of the CDU matrix in chunks is globally 280 known by all the nodes in the network to support the appropriation 281 process, which is a negotiation between nodes within an 282 interference domain. A node that manages to appropriate a chunk 283 gets to decide which transmissions will occur over the cells in 284 the chunk within its interference domain, i.e., a parent node will 285 decide when the cells within the appropriated chunk are used and 286 by which node, among its children. 288 CoJP (Constrained Join Protocol): The Constrained Join Protocol 289 (CoJP) enables a pledge to securely join a 6TiSCH network and 290 obtain network parameters over a secure channel. Minimal Security 291 Framework for 6TiSCH [MIN-SECURITY] defines the minimal CoJP setup 292 with pre-shared keys defined. In that mode, CoJP can operate with 293 a single round trip exchange. 295 dedicated cell: A cell that is reserved for a given node to transmit 296 to a specific neighbor. 298 deterministic network: The generic concept of deterministic network 299 is defined in the "DetNet Architecture" [RFC8655] document. When 300 applied to 6TiSCH, it refers to the reservation of Tracks which 301 guarantees an end-to-end latency and optimizes the Packet Delivery 302 Ratio (PDR) for well-characterized flows. 304 distributed cell reservation: A reservation of a cell done by one or 305 more in-network entities. 307 distributed Track reservation: A reservation of a Track done by one 308 or more in-network entities. 310 EB (Enhanced Beacon): A special frame defined in [IEEE802154] used 311 by a node, including the JP, to announce the presence of the 312 network. It contains enough information for a pledge to 313 synchronize to the network. 315 hard cell: A scheduled cell which the 6top sublayer may not 316 relocate. 318 hopping sequence: Ordered sequence of frequencies, identified by a 319 Hopping_Sequence_ID, used for channel hopping when translating the 320 channelOffset value into a frequency. 322 IE (Information Element): Type-Length-Value containers placed at the 323 end of the MAC header, used to pass data between layers or 324 devices. Some IE identifiers are managed by the IEEE 325 [IEEE802154]. Some IE identifiers are managed by the IETF 326 [RFC8137], and [ENH-BEACON] uses one subtype to support the 327 selection of the Join Proxy. 329 join process: The overall process that includes the discovery of the 330 network by pledge(s) and the execution of the join protocol. 332 join protocol: The protocol that allows the pledge to join the 333 network. The join protocol encompasses authentication, 334 authorization and parameter distribution. The join protocol is 335 executed between the pledge and the JRC. 337 joined node: The new device, after having completed the join 338 process, often just called a node. 340 JP (Join Proxy): Node already part of the 6TiSCH network that serves 341 as a relay to provide connectivity between the pledge and the JRC. 342 The JP announces the presence of the network by regularly sending 343 EB frames. 345 JRC (Join Registrar/Coordinator): Central entity responsible for the 346 authentication, authorization and configuration of the pledge. 348 link: A communication facility or medium over which nodes can 349 communicate at the Link-Layer, the layer immediately below IP. In 350 6TiSCH, the concept is implemented as a collection of Layer-3 351 bundles. Note: the IETF parlance for the term "Link" is adopted, 352 as opposed to the IEEE Std. 802.15.4 terminology. 354 Operational Technology: OT refers to technology used in automation, 355 for instance in industrial control networks. The convergence of 356 IT and OT is the main object of the Industrial Internet of Things 357 (IIOT). 359 pledge: A new device that attempts to join a 6TiSCH network. 361 (to) relocate a cell: The action operated by the 6top sublayer of 362 changing the slotOffset and/or channelOffset of a soft cell. 364 (to) schedule a cell: The action of turning an unscheduled cell into 365 a scheduled cell. 367 scheduled cell: A cell which is assigned a neighbor MAC address 368 (broadcast address is also possible), and one or more of the 369 following flags: TX, RX, Shared and Timekeeping. A scheduled cell 370 can be used by the IEEE Std. 802.15.4 TSCH implementation to 371 communicate. A scheduled cell can either be a hard or a soft 372 cell. 374 SF (6top Scheduling Function): The cell management entity that adds 375 or deletes cells dynamically based on application networking 376 requirements. The cell negotiation with a neighbor is done using 377 6P. 379 SFID (6top Scheduling Function Identifier): A 4-bit field 380 identifying an SF. 382 shared cell: A cell marked with both the "TX" and "shared" flags. 383 This cell can be used by more than one transmitter node. A back- 384 off algorithm is used to resolve contention. 386 slotframe: A collection of timeslots repeating in time, analogous to 387 a superframe in that it defines periods of communication 388 opportunities. It is characterized by a slotframe_ID, and a 389 slotframe_size. Multiple slotframes can coexist in a node's 390 schedule, i.e., a node can have multiple activities scheduled in 391 different slotframes, based on the priority of its packets/traffic 392 flows. The timeslots in the Slotframe are indexed by the 393 SlotOffset; the first timeslot is at SlotOffset 0. 395 slotOffset: A column in the TSCH schedule, i.e., the number of 396 timeslots since the beginning of the current iteration of the 397 slotframe. 399 soft cell: A scheduled cell which the 6top sublayer can relocate. 401 time source neighbor: A neighbor that a node uses as its time 402 reference, and to which it needs to keep its clock synchronized. 404 timeslot: A basic communication unit in TSCH which allows a 405 transmitter node to send a frame to a receiver neighbor, and that 406 receiver neighbor to optionally send back an acknowledgment. 408 Track: A Track is a Directed Acyclic Graph (DAG) that is used as a 409 complex multi-hop path to the destination(s) of the path. In the 410 case of unicast traffic, the Track is a Destination Oriented DAG 411 (DODAG) where the Root of the DODAG is the destination of the 412 unicast traffic. A Track enables replication, elimination and 413 reordering functions on the way (more on those functions in 414 [RFC8655]. A Track reservation locks physical resources such as 415 cells and buffers in every node along the DODAG. A Track is 416 associated with a owner that can be for instance the destination 417 of the Track. 419 TrackID: A TrackID is either globally unique, or locally unique to 420 the Track owner, in which case the identification of the owner 421 must be provided together with the TrackID to provide a full 422 reference to the Track. If the Track owner is the destination of 423 the Track then the destination IP address of packets along the 424 Track can be used as identification of the owner and a local 425 InstanceID [RFC6550] can be used as TrackID. In that case, a RPL 426 Packet Information [RFC6550] in an IPv6 packet can unambiguously 427 identify the Track and can be expressed in a compressed form using 428 [RFC8138]. 430 TSCH: A medium access mode of the IEEE Std. 802.15.4 [IEEE802154] 431 standard which uses time synchronization to achieve ultra-low- 432 power operation, and channel hopping to enable high reliability. 434 TSCH Schedule: A matrix of cells, each cell indexed by a slotOffset 435 and a channelOffset. The TSCH schedule contains all the scheduled 436 cells from all slotframes and is sufficient to qualify the 437 communication in the TSCH network. The number of channelOffset 438 values (the "height" of the matrix) is equal to the number of 439 available frequencies. 441 Unscheduled Cell: A cell which is not used by the IEEE Std. 802.15.4 442 TSCH implementation. 444 2.2. Abbreviations 446 This document uses the following abbreviations: 448 6BBR: 6LoWPAN Backbone Router (router with a proxy ND function) 450 6LBR: 6LoWPAN Border Router (authoritative on DAD) 452 6LN: 6LoWPAN Node 454 6LR: 6LoWPAN Router (relay to the registration process) 456 6CIO: Capability Indication Option 458 (E)ARO: (Extended) Address Registration Option 460 (E)DAR: (Extended) Duplicate Address Request 462 (E)DAC: (Extended) Duplicate Address Confirmation 464 DAD: Duplicate Address Detection 466 DODAG: Destination-Oriented Directed Acyclic Graph 468 LLN: Low-Power and Lossy Network (a typical IoT network) 470 NA: Neighbor Advertisement 472 NCE: Neighbor Cache Entry 474 ND: Neighbor Discovery 476 NDP: Neighbor Discovery Protocol 478 PCE: Path Computation Element 480 NME: Network Management Entity 481 ROVR: Registration Ownership Verifier (pronounced rover) 483 RPL: IPv6 Routing Protocol for LLNs (pronounced ripple) 485 RA: Router Advertisement 487 RS: Router Solicitation 489 TSCH: timeslotted Channel Hopping 491 TID: Transaction ID (a sequence counter in the EARO) 493 2.3. Related Documents 495 The draft also conforms to the terms and models described in 496 [RFC3444] and [RFC5889] and uses the vocabulary and the concepts 497 defined in [RFC4291] for the IPv6 Architecture and refers [RFC4080] 498 for reservation 500 The draft uses domain-specific terminology defined or referenced in: 502 6LoWPAN ND "Neighbor Discovery Optimization for Low-power and 503 Lossy Networks" [RFC6775] and "Registration Extensions for 6LoWPAN 504 Neighbor Discovery" [RFC8505], 506 "Terms Used in Routing for Low-Power and Lossy Networks (LLNs)" 507 [RFC7102], 509 and RPL "Objective Function Zero for the Routing Protocol for 510 Low-Power and Lossy Networks (RPL)" [RFC6552], and "RPL: IPv6 511 Routing Protocol for Low-Power and Lossy Networks" [RFC6550]. 513 Other terms in use in LLNs are found in "Terminology for 514 Constrained-Node Networks" [RFC7228]. 516 Readers are expected to be familiar with all the terms and concepts 517 that are discussed in 519 * "Neighbor Discovery for IP version 6" [RFC4861], and "IPv6 520 Stateless Address Autoconfiguration" [RFC4862]. 522 In addition, readers would benefit from reading: 524 * "Problem Statement and Requirements for IPv6 over Low-Power 525 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 527 * "Multi-Link Subnet Issues" [RFC4903], and 528 * "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): 529 Overview, Assumptions, Problem Statement, and Goals" [RFC4919] 531 prior to this specification for a clear understanding of the art in 532 ND-proxying and binding. 534 3. High Level Architecture 536 3.1. A Non-Broadcast Multi-Access Radio Mesh Network 538 A 6TiSCH network is an IPv6 [RFC8200] subnet which, in its basic 539 configuration illustrated in Figure 1, is a single Low-Power Lossy 540 Network (LLN) operating over a synchronized TSCH-based mesh. 542 ---+-------- ............ ------------ 543 | External Network | 544 | +-----+ 545 +-----+ | NME | 546 | | LLN Border | PCE | 547 | | router (6LBR) +-----+ 548 +-----+ 549 o o o 550 o o o o o 551 o o 6LoWPAN + RPL o o 552 o o o o 554 Figure 1: Basic Configuration of a 6TiSCH Network 556 Inside a 6TiSCH LLN, nodes rely on 6LoWPAN Header Compression 557 (6LoWPAN HC) [RFC6282] to encode IPv6 packets. From the perspective 558 of the network layer, a single LLN interface (typically an IEEE Std. 559 802.15.4-compliant radio) may be seen as a collection of Links with 560 different capabilities for unicast or multicast services. 562 6TiSCH nodes join a mesh network by attaching to nodes that are 563 already members of the mesh (see Section 4.2.1). The security 564 aspects of the join process are further detailed in Section 6. In a 565 mesh network, 6TiSCH nodes are not necessarily reachable from one 566 another at Layer-2 and an LLN may span over multiple links. 568 This forms a homogeneous non-broadcast multi-access (NBMA) subnet, 569 which is beyond the scope of IPv6 Neighbor Discovery (IPv6 ND) 570 [RFC4861][RFC4862]. 6LoWPAN Neighbor Discovery (6LoWPAN ND) 571 [RFC6775][RFC8505] specifies extensions to IPv6 ND that enable ND 572 operations in this type of subnet that can be protected against 573 address theft and impersonation with [AP-ND]. 575 Once it has joined the 6TiSCH network, a node acquires IPv6 Addresses 576 and register them using 6LoWPAN ND. This guarantees that the 577 addresses are unique and protects the address ownership over the 578 subnet, more in Section 4.2.2. 580 Within the NBMA subnet, RPL [RFC6550] enables routing in the so- 581 called Route Over fashion, either in storing (stateful) or non- 582 storing (stateless, with routing headers) mode. From there, some 583 nodes can act as routers for 6LoWPAN ND and RPL operations, as 584 detailed in Section 4.1. 586 With TSCH, devices are time-synchronized at the MAC level. The use 587 of a particular RPL Instance for time synchronization is discussed in 588 Section 4.3.4. With this mechanism, the time synchronization starts 589 at the RPL Root and follows the RPL loopless routing topology. 591 RPL forms Destination Oriented Directed Acyclic Graphs (DODAGs) 592 within Instances of the protocol, each Instance being associated with 593 an Objective Function (OF) to form a routing topology. A particular 594 6TiSCH node, the LLN Border Router (6LBR), acts as RPL Root, 6LoWPAN 595 HC terminator, and Border Router for the LLN to the outside. The 596 6LBR is usually powered. More on RPL Instances can be found in 597 section 3.1 of RPL [RFC6550], in particular "3.1.2. RPL Identifiers" 598 and "3.1.3. Instances, DODAGs, and DODAG Versions". RPL adds 599 artifacts in the data packets that are compressed with a 6LoWPAN 600 addition 6LoRH [RFC8138]. 602 Additional routing and scheduling protocols may be deployed to 603 establish on-demand Peer-to-Peer routes with particular 604 characteristics inside the 6TiSCH network. This may be achieved in a 605 centralized fashion by a Path Computation Element (PCE) [PCE] that 606 programs both the routes and the schedules inside the 6TiSCH nodes, 607 or by in a distributed fashion using a reactive routing protocol and 608 a Hop-by-Hop scheduling protocol. 610 This architecture expects that a 6LoWPAN node can connect as a leaf 611 to a RPL network, where the leaf support is the minimal functionality 612 to connect as a host to a RPL network without the need to participate 613 to the full routing protocol. The architecture also expects that a 614 6LoWPAN node that is not aware at all of the RPL protocol may also 615 connect as described in [RUL-DRAFT]. 617 3.2. A Multi-Link Subnet Model 619 An extended configuration of the subnet comprises multiple LLNs as 620 illustrated in Figure 2. In the extended configuration, a Routing 621 Registrar [RFC8505] may be connected to the node that acts as RPL 622 Root and / or 6LoWPAN 6LBR and provides connectivity to the larger 623 campus / factory plant network over a high-speed backbone or a back- 624 haul link. The Routing registrar may perform IPv6 ND proxy 625 operations, or redistribute the registration in a routing protocol 626 such as OSPF [RFC5340] or BGP [RFC2545], or inject a route in a 627 mobility protocol such as MIPv6 [RFC6275], NEMO [RFC3963], or LISP 628 [RFC6830]. 630 Multiple LLNs can be interconnected and possibly synchronized over a 631 backbone, which can be wired or wireless. The backbone can operate 632 with IPv6 ND [RFC4861][RFC4862] procedures or an hybrid of IPv6 ND 633 and 6LoWPAN ND [RFC6775][RFC8505][AP-ND]. 635 | 636 +-----+ +-----+ +-----+ 637 (default) | | (Optional) | | | | IPv6 638 Router | | 6LBR | | | | Node 639 +-----+ +-----+ +-----+ 640 | Backbone side | | 641 --------+---+--------------------+-+---------------+------+--- 642 | | | 643 +-----------+ +-----------+ +-----------+ 644 | Routing | | Routing | | Routing | 645 | Registrar | | Registrar | | Registrar | 646 +-----------+ +-----------+ +-----------+ 647 o Wireless side o o o o 648 o o o o o o o o o o o o o o 649 o 6TiSCH o 6TiSCH o o o o 6TiSCH o 650 o o LLN o o o o LLN o o LLN o 651 o o o o o o o o o o o o o o 653 Figure 2: Extended Configuration of a 6TiSCH Network 655 A Routing Registrar that performs proxy IPv6 ND operations over the 656 backbone on behalf of the 6TiSCH nodes is called a Backbone Router 657 (6BBR) [6BBR-DRAFT]. The 6BBRs are placed along the wireless edge of 658 a Backbone, and federate multiple wireless links to form a single 659 MultiLink Subnet. The 6BBRs synchronize with one another over the 660 backbone, so as to ensure that the multiple LLNs that form the IPv6 661 subnet stay tightly synchronized. 663 The use of multicast can also be reduced on the backbone with a 664 registrar that would contribute to Duplicate Address Detection as 665 well as Address Lookup using only unicast request/response exchanges. 666 [I-D.thubert-6man-unicast-lookup] is a proposed method that presents 667 an example of how to this could be achieved with an extension of 668 [RFC8505], using an optional 6LBR as a SubNet-level registrar, as 669 illustrated in Figure 2. 671 As detailed in Section 4.1 the 6LBR that serves the LLN and the Root 672 of the RPL network need to share information about the devices that 673 are learned through either 6LoWPAN ND or RPL but not both. The 674 preferred way of achieving this is to collocate/combine them. The 675 combined RPL Root and 6LBR may be collocated with the 6BBR, or 676 directly attached to the 6BBR. In the latter case, it leverages the 677 extended registration process defined in [RFC8505] to proxy the 678 6LoWPAN ND registration to the 6BBR on behalf of the LLN nodes, so 679 that the 6BBR may in turn perform proxy classical ND operations over 680 the backbone. 682 The DetNet Architecture [RFC8655] studies Layer-3 aspects of 683 Deterministic Networks, and covers networks that span multiple 684 Layer-2 domains. If the Backbone is Deterministic (such as defined 685 by the Time Sensitive Networking WG at IEEE), then the Backbone 686 Router ensures that the end-to-end deterministic behavior is 687 maintained between the LLN and the backbone. 689 3.3. TSCH: A Deterministic MAC Layer 691 Though at a different time scale (several orders of magnitude), both 692 IEEE Std. 802.1TSN and IEEE Std. 802.15.4 TSCH standards provide 693 Deterministic capabilities to the point that a packet that pertains 694 to a certain flow may traverse a network from node to node following 695 a precise schedule, as a train that enters and then leaves 696 intermediate stations at precise times along its path. 698 With TSCH, time is formatted into timeslots, and individual 699 communication cells are allocated to unicast or broadcast 700 communication at the MAC level. The time-slotted operation reduces 701 collisions, saves energy, and enables to more closely engineer the 702 network for deterministic properties. The channel hopping aspect is 703 a simple and efficient technique to combat multipath fading and co- 704 channel interference. 706 6TiSCH builds on the IEEE Std. 802.15.4 TSCH MAC and inherits its 707 advanced capabilities to enable them in multiple environments where 708 they can be leveraged to improve automated operations. The 6TiSCH 709 Architecture also inherits the capability to perform a centralized 710 route computation to achieve deterministic properties, though it 711 relies on the IETF DetNet Architecture [RFC8655], and IETF components 712 such as the PCE [PCE], for the protocol aspects. 714 On top of this inheritance, 6TiSCH adds capabilities for distributed 715 routing and scheduling operations based on the RPL routing protocol 716 and capabilities to negotiate schedule adjustments between peers. 717 These distributed routing and scheduling operations simplify the 718 deployment of TSCH networks and enable wireless solutions in a larger 719 variety of use cases from operational technology in general. 720 Examples of such use-cases in industrial environments include plant 721 setup and decommissioning, as well as monitoring of lots of lesser 722 importance measurements such as corrosion and events and mobile 723 workers accessing local devices. 725 3.4. Scheduling TSCH 727 A scheduling operation attributes cells in a Time-Division- 728 Multiplexing (TDM) / Frequency-Division Multiplexing (FDM) matrix 729 called the Channel distribution/usage (CDU) to either individual 730 transmissions or as multi-access shared resources. The CDU matrix 731 can be formatted in chunks that can be allocated exclusively to 732 particular nodes to enable distributed scheduling without collision. 733 More in Section 4.3.5. 735 From the standpoint of a 6TiSCH node (at the MAC layer), its schedule 736 is the collection of the timeslots at which it must wake up for 737 transmission, and the channels to which it should either send or 738 listen at those times. The schedule is expressed as one or more 739 slotframes that repeat over and over. Slotframes may collide and 740 require a device to wake up at a same time, in which case the 741 slotframe with the highest priority is actionable. 743 The 6top sublayer (see Section 4.3 for more) hides the complexity of 744 the schedule from the upper layers. The Link abstraction that IP 745 traffic utilizes is composed of a pair of Layer-3 cell bundles, one 746 to receive and one to transmit. Some of the cells may be shared, in 747 which case the 6top sublayer must perform some arbitration. 749 Scheduling enables multiple communications at a same time in a same 750 interference domain using different channels; but a node equipped 751 with a single radio can only either transmit or receive on one 752 channel at any point of time. Scheduled cells that fulfil the same 753 role, e.g., receive IP packets from a peer, are grouped in bundles. 755 The 6TiSCH architecture identifies four ways a schedule can be 756 managed and CDU cells can be allocated: Static Scheduling, Neighbor- 757 to-Neighbor Scheduling, Centralized (or Remote) Monitoring and 758 Schedule Management, and Hop-by-hop Scheduling. 760 Static Scheduling: This refers to the minimal 6TiSCH operation 761 whereby a static schedule is configured for the whole network for 762 use in a Slotted ALOHA [S-ALOHA] fashion. The static schedule is 763 distributed through the native methods in the TSCH MAC layer and 764 does not preclude other scheduling operations to co-exist on a 765 same 6TiSCH network. A static schedule is necessary for basic 766 operations such as the join process and for interoperability 767 during the network formation, which is specified as part of the 768 Minimal 6TiSCH Configuration [RFC8180]. 770 Neighbor-to-Neighbor Scheduling: This refers to the dynamic 771 adaptation of the bandwidth of the Links that are used for IPv6 772 traffic between adjacent peers. Scheduling Functions such as the 773 "6TiSCH Minimal Scheduling Function (MSF)" [MSF] influence the 774 operation of the MAC layer to add, update and remove cells in its 775 own, and its peer's schedules using 6P [RFC8480], for the 776 negotiation of the MAC resources. 778 Centralized (or Remote) Monitoring and Schedule Management: This 779 refers to the central computation of a schedule and the capability 780 to forward a frame based on the cell of arrival. In that case, 781 the related portion of the device schedule as well as other device 782 resources are managed by an abstract Network Management Entity 783 (NME), which may cooperate with the PCE to minimize the 784 interaction with and the load on the constrained device. This 785 model is the TSCH adaption of the DetNet Architecture [RFC8655], 786 and it enables Traffic Engineering with deterministic properties. 788 Hop-by-hop Scheduling: This refers to the possibility to reserves 789 cells along a path for a particular flow using a distributed 790 mechanism. 792 It is not expected that all use cases will require all those 793 mechanisms. Static Scheduling with minimal configuration one is the 794 only one that is expected in all implementations, since it provides a 795 simple and solid basis for convergecast routing and time 796 distribution. 798 A deeper dive in those mechanisms can be found in Section 4.4. 800 3.5. Distributed vs. Centralized Routing 802 6TiSCH enables a mixed model of centralized routes and distributed 803 routes. Centralized routes can for example be computed by an entity 804 such as a PCE. 6TiSCH leverages the RPL [RFC6550] routing protocol 805 for interoperable distributed routing operations. 807 Both methods may inject routes in the Routing Tables of the 6TiSCH 808 routers. In either case, each route is associated with a 6TiSCH 809 topology that can be a RPL Instance topology or a Track. The 6TiSCH 810 topology is indexed by a RPLInstanceID, in a format that reuses the 811 RPLInstanceID as defined in RPL. 813 RPL [RFC6550] is applicable to Static Scheduling and Neighbor-to- 814 Neighbor Scheduling. The architecture also supports a centralized 815 routing model for Remote Monitoring and Schedule Management. It is 816 expected that a routing protocol that is more optimized for point-to- 817 point routing than RPL [RFC6550], such as the Asymmetric AODV-P2P-RPL 818 in Low-Power and Lossy Networks" [I-D.ietf-roll-aodv-rpl] AODV-RPL), 819 which derives from the Ad Hoc On-demand Distance Vector Routing 820 (AODV) [I-D.ietf-manet-aodvv2] will be selected for Hop-by-hop 821 Scheduling. 823 Both RPL and PCE rely on shared sources such as policies to define 824 Global and Local RPLInstanceIDs that can be used by either method. 825 It is possible for centralized and distributed routing to share a 826 same topology. Generally they will operate in different slotframes, 827 and centralized routes will be used for scheduled traffic and will 828 have precedence over distributed routes in case of conflict between 829 the slotframes. 831 3.6. Forwarding Over TSCH 833 The 6TiSCH architecture supports three different forwarding models. 834 One is the classical IPv6 Forwarding, where the node selects a 835 feasible successor at Layer-3 on a per packet basis and based on its 836 routing table. The second derives from Generic MPLS (G-MPLS) for so- 837 called Track Forwarding, whereby a frame received at a particular 838 timeslot can be switched into another timeslot at Layer-2 without 839 regard to the upper layer protocol. The third model is the 6LoWPAN 840 Fragment Forwarding, which allows to forward individual 6loWPAN 841 fragments along a route that is setup by the first fragment. 843 In more details: 845 IPv6 Forwarding: This is the classical IP forwarding model, with a 846 Routing Information Based (RIB) that is installed by the RPL 847 routing protocol and used to select a feasible successor per 848 packet. The packet is placed on an outgoing Link, that the 6top 849 layer maps into a (Layer-3) bundle of cells, and scheduled for 850 transmission based on QoS parameters. Besides RPL, this model 851 also applies to any routing protocol which may be operated in the 852 6TiSCH network, and corresponds to all the distributed scheduling 853 models, Static, Neighbor-to-Neighbor and Hop-by-Hop Scheduling. 855 G-MPLS Track Forwarding: This model corresponds to the Remote 856 Monitoring and Schedule Management. In this model, a central 857 controller (hosting a PCE) computes and installs the schedules in 858 the devices per flow. The incoming (Layer-2) bundle of cells from 859 the previous node along the path determines the outgoing (Layer-2) 860 bundle towards the next hop for that flow as determined by the 861 PCE. The programmed sequence for bundles is called a Track and 862 can assume DAG shapes that are more complex than a simple direct 863 sequence of nodes. 865 6LoWPAN Fragment Forwarding: This is a hybrid model that derives 866 from IPv6 forwarding for the case where packets must be fragmented 867 at the 6LoWPAN sublayer. The first fragment is forwarded like any 868 IPv6 packet and leaves a state in the intermediate hops to enable 869 forwarding of the next fragments that do not have a IP header 870 without the need to recompose the packet at every hop. 872 A deeper dive on these operations can be found in Section 4.6. 874 The following table summarizes how the forwarding models apply to the 875 various routing and scheduling possibilities: 877 +-------------------+------------+----------------------------------+ 878 | Forwarding Model | Routing | Scheduling | 879 +===================+============+==================================+ 880 | | | Static (Minimal Configuration) | 881 + classical IPv6 + RPL +----------------------------------+ 882 | / | | Neighbor-to-Neighbor (SF+6P) | 883 + 6LoWPAN Fragment +------------+----------------------------------+ 884 | | Reactive | Hop-by-Hop (AODV-RPL) | 885 +-------------------+------------+----------------------------------+ 886 |G-MPLS Track Fwding| PCE |Remote Monitoring and Schedule Mgt| 887 +-------------------+------------+----------------------------------+ 889 Figure 3 891 3.7. 6TiSCH Stack 893 The IETF proposes multiple techniques for implementing functions 894 related to routing, transport or security. 896 The 6TiSCH architecture limits the possible variations of the stack 897 and recommends a number of base elements for LLN applications to 898 control the complexity of possible deployments and device 899 interactions, and to limit the size of the resulting object code. In 900 particular, UDP [RFC0768], IPv6 [RFC8200] and the Constrained 901 Application Protocol [RFC7252] (CoAP) are used as the transport / 902 binding of choice for applications and management as opposed to TCP 903 and HTTP. 905 The resulting protocol stack is represented in Figure 4: 907 +--------+--------+ 908 | Applis | CoJP | 909 +--------+--------+--------------+-----+ 910 | CoAP / OSCORE | 6LoWPAN ND | RPL | 911 +-----------------+--------------+-----+ 912 | UDP | ICMPv6 | 913 +-----------------+--------------------+ 914 | IPv6 | 915 +--------------------------------------+----------------------+ 916 | 6LoWPAN HC / 6LoRH HC | Scheduling Functions | 917 +--------------------------------------+----------------------+ 918 | 6top inc. 6top protocol | 919 +-------------------------------------------------------------+ 920 | IEEE Std. 802.15.4 TSCH | 921 +-------------------------------------------------------------+ 923 Figure 4: 6TiSCH Protocol Stack 925 RPL is the routing protocol of choice for LLNs. So far, there was no 926 identified need to define a 6TiSCH specific Objective Function. The 927 Minimal 6TiSCH Configuration [RFC8180] describes the operation of RPL 928 over a static schedule used in a Slotted ALOHA fashion [S-ALOHA], 929 whereby all active slots may be used for emission or reception of 930 both unicast and multicast frames. 932 The 6LoWPAN Header Compression [RFC6282] is used to compress the IPv6 933 and UDP headers, whereas the 6LoWPAN Routing Header (6LoRH) [RFC8138] 934 is used to compress the RPL artifacts in the IPv6 data packets, 935 including the RPL Packet Information (RPI), the IP-in-IP 936 encapsulation to/from the RPL Root, and the Source Route Header (SRH) 937 in non-storing mode. "When to use RFC 6553, 6554 and IPv6-in-IPv6" 938 [USEofRPLinfo] provides the details on when headers or encapsulation 939 are needed. 941 The Object Security for Constrained RESTful Environments (OSCORE) 942 [I-D.ietf-core-object-security], is leveraged by the Constrained Join 943 Protocol (CoJP) and is expected to be the primary protocol for the 944 protection of the application payload as well. The application 945 payload may also be protected by the Datagram Transport Layer 946 Security (DTLS) [RFC6347] sitting either under CoAP or over CoAP so 947 it can traverse proxies. 949 The 6TiSCH Operation sublayer (6top) is a sublayer of a Logical Link 950 Control (LLC) that provides the abstraction of an IP link over a TSCH 951 MAC and schedules packets over TSCH cells, as further discussed in 952 the next sections, providing in particular dynamic cell allocation 953 with the 6top Protocol (6P) [RFC8480]. 955 The reference stack presented in this document was implemented and 956 interop-tested by a conjunction of opensource, IETF and ETSI efforts. 957 One goal is to help other bodies to adopt the stack as a whole, 958 making the effort to move to an IPv6-based IoT stack easier. 960 For a particular environment, some of the choices that are made in 961 this architecture may not be relevant. For instance, RPL is not 962 required for star topologies and mesh-under Layer-2 routed networks, 963 and the 6LoWPAN compression may not be sufficient for ultra- 964 constrained cases such as some Low-Power Wide Area (LPWA) networks. 965 In such cases, it is perfectly doable to adopt a subset of the 966 selection that is presented hereafter and then select alternate 967 components to complete the solution wherever needed. 969 3.8. Communication Paradigms and Interaction Models 971 Section 2.1 provides the terms of Communication Paradigms and 972 Interaction Models, in relation with "On the Difference between 973 Information Models and Data Models" [RFC3444]. A Communication 974 Paradigm would be an abstract view of a protocol exchange, and would 975 come with an Information Model for the information that is being 976 exchanged. In contrast, an Interaction Model would be more refined 977 and could point to standard operation such as a Representational 978 state transfer (REST) "GET" operation and would match a Data Model 979 for the data that is provided over the protocol exchange. 981 Section 2.1.3 of [I-D.ietf-roll-rpl-industrial-applicability] and 982 next sections discuss application-layer paradigms, such as Source- 983 sink (SS) that is a Multipeer to Multipeer (MP2MP) model primarily 984 used for alarms and alerts, Publish-subscribe (PS, or pub/sub) that 985 is typically used for sensor data, as well as Peer-to-peer (P2P) and 986 Peer-to-multipeer (P2MP) communications. 988 Additional considerations on Duocast - one sender, two receivers for 989 redundancy - and its N-cast generalization are also provided. Those 990 paradigms are frequently used in industrial automation, which is a 991 major use case for IEEE Std. 802.15.4 TSCH wireless networks with 992 [ISA100.11a] and [WirelessHART], that provides a wireless access to 993 [HART] applications and devices. 995 This document focuses on Communication Paradigms and Interaction 996 Models for packet forwarding and TSCH resources (cells) management. 998 Management mechanisms for the TSCH schedule at Link-Layer (one-hop), 999 Network-layer (multihop along a Track), and Application-layer (remote 1000 control) are discussed in Section 4.4. Link-Layer frame forwarding 1001 interactions are discussed in Section 4.6, and Network-layer Packet 1002 routing is addressed in Section 4.7. 1004 4. Architecture Components 1006 4.1. 6LoWPAN (and RPL) 1008 A RPL DODAG is formed of a Root, a collection of routers, and leaves 1009 that are hosts. Hosts are nodes which do not forward packets that 1010 they did not generate. RPL-aware leaves will participate to RPL to 1011 advertise their own addresses, whereas RPL-unaware leaves depend on a 1012 connected RPL router to do so. RPL interacts with 6LoWPAN ND at 1013 multiple levels, in particular at the Root and in the RPL-unaware 1014 leaves. 1016 4.1.1. RPL-Unaware Leaves and 6LoWPAN ND 1018 RPL needs a set of information to advertise a leaf node through a 1019 Destination Advertisement Object (DAO) message and establish 1020 reachability. 1022 "Routing for RPL Leaves" [RUL-DRAFT] details the basic interaction of 1023 6LoWPAN ND and RPL and enables a plain 6LN that supports [RFC8505] to 1024 obtain return connectivity via the RPL network as an RPL-unaware 1025 leaf. The leaf indicates that it requires reachability services for 1026 the Registered Address from a Routing Registrar by setting a 'R' flag 1027 in the Extended Address Registration Option [RFC8505], and it 1028 provides a TID that maps to a sequence number in section 7 of RPL 1029 [RFC6550]. 1031 [RUL-DRAFT] also enables the leaf to signal the RPL InstanceID that 1032 it wants to participate to using the Opaque field of the EARO. On 1033 the backbone, the InstanceID is expected to be mapped to an overlay 1034 that matches the RPL Instance, e.g., a Virtual LAN (VLAN) or a 1035 virtual routing and forwarding (VRF) instance. 1037 Though at the time of this writing the above specification enables a 1038 model where the separation is possible, this architecture recommends 1039 to collocate the functions of 6LBR and RPL Root. 1041 4.1.2. 6LBR and RPL Root 1043 With the 6LowPAN ND [RFC6775], information on the 6LBR is 1044 disseminated via an Authoritative Border Router Option (ABRO) in RA 1045 messages. [RFC8505] extends [RFC6775] to enable a registration for 1046 routing and proxy ND. The capability to support [RFC8505] is 1047 indicated in the 6LoWPAN Capability Indication Option (6CIO). The 1048 discovery and liveliness of the RPL Root are obtained through RPL 1049 [RFC6550] itself. 1051 When 6LoWPAN ND is coupled with RPL, the 6LBR and RPL Root 1052 functionalities are co-located in order that the address of the 6LBR 1053 be indicated by RPL DIO messages and to associate the unique ID from 1054 the EDAR/EDAC [RFC8505] exchange with the state that is maintained by 1055 RPL. 1057 Section 7 of [RUL-DRAFT] specifies how the DAO messages are used to 1058 reconfirm the registration, thus eliminating a duplication of 1059 functionality between DAO and EDAR/EDAC messages, as illustrated in 1060 Figure 7. [RUL-DRAFT] also provides the protocol elements that are 1061 needed when the 6LBR and RPL Root functionalities are not co-located. 1063 Even though the Root of the RPL network is integrated with the 6LBR, 1064 it is logically separated from the Backbone Router (6BBR) that is 1065 used to connect the 6TiSCH LLN to the backbone. This way, the Root 1066 has all information from 6LoWPAN ND and RPL about the LLN devices 1067 attached to it. 1069 This architecture also expects that the Root of the RPL network 1070 (proxy-)registers the 6TiSCH nodes on their behalf to the 6BBR, for 1071 whatever operation the 6BBR performs on the backbone, such as ND 1072 proxy, or redistribution in a routing protocol. This relies on an 1073 extension of the 6LoWPAN ND registration described in [6BBR-DRAFT]. 1075 This model supports the movement of a 6TiSCH device across the Multi- 1076 Link Subnet, and allows the proxy registration of 6TiSCH nodes deep 1077 into the 6TiSCH LLN by the 6LBR / RPL Root. This is why in [RFC8505] 1078 the Registered Address is signaled in the Target Address field of the 1079 NS message as opposed to the IPv6 Source Address, which, in the case 1080 of a proxy registration, is that of the 6LBR / RPL Root itself. 1082 4.2. Network Access and Addressing 1083 4.2.1. Join Process 1085 A new device, called the pledge, undergoes the join protocol to 1086 become a node in a 6TiSCH network. This usually occurs only once 1087 when the device is first powered on. The pledge communicates with 1088 the Join Registrar/Coordinator (JRC) of the network through a Join 1089 Proxy (JP), a radio neighbor of the pledge. 1091 The JP is discovered though MAC layer beacons. When multiple JPs 1092 from possibly multiple networks are visible, trial and error till an 1093 acceptable position in the right network is obtained becomes 1094 ineffficient. [ENH-BEACON] adds a new subtype in the Information 1095 Element that was delegated to the IETF [RFC8137] and provides 1096 visibility on the network that can be joined and the willingness by 1097 the JP and the Root to be used by the pledge. 1099 The join protocol provides the following functionality: 1101 * Mutual authentication 1103 * Authorization 1105 * Parameter distribution to the pledge over a secure channel 1107 Minimal Security Framework for 6TiSCH [MIN-SECURITY] defines the 1108 minimal mechanisms required for this join process to occur in a 1109 secure manner. The specification defines the Constrained Join 1110 Protocol (CoJP) that is used to distribute the parameters to the 1111 pledge over a secure session established through OSCORE 1112 [I-D.ietf-core-object-security], and a secure configuration of the 1113 network stack. In the minimal setting with pre-shared keys (PSKs), 1114 CoJP allows the pledge to join after a single round-trip exchange 1115 with the JRC. The provisioning of the PSK to the pledge and the JRC 1116 needs to be done out of band, through a 'one-touch' bootstrapping 1117 process, which effectively enrolls the pledge into the domain managed 1118 by the JRC. 1120 In certain use cases, the 'one touch' bootstrapping is not feasible 1121 due to the operational constraints and the enrollment of the pledge 1122 into the domain needs to occur in-band. This is handled through a 1123 'zero-touch' extension of the Minimal Security Framework for 6TiSCH. 1124 Zero touch [I-D.ietf-6tisch-dtsecurity-zerotouch-join] extension 1125 leverages the 'Bootstrapping Remote Secure Key Infrastructures 1126 (BRSKI)' [[I-D.ietf-anima-bootstrapping-keyinfra] work to establish a 1127 shared secret between a pledge and the JRC without necessarily having 1128 them belong to a common (security) domain at join time. This happens 1129 through inter-domain communication occurring between the JRC of the 1130 network and the domain of the pledge, represented by a fourth entity, 1131 Manufacturer Authorized Signing Authority (MASA). Once the zero- 1132 touch exchange completes, the CoJP exchange defined in [MIN-SECURITY] 1133 is carried over the secure session established between the pledge and 1134 the JRC. 1136 Figure 5 depicts the join process and where a Link-Local Address 1137 (LLA) is used, versus a Global Unicast Address (GUA). 1139 6LoWPAN Node 6LR 6LBR Join Registrar MASA 1140 (pledge) (Join Proxy) (Root) /Coordinator (JRC) 1141 | | | | | 1142 | 6LoWPAN ND |6LoWPAN ND+RPL | IPv6 network |IPv6 network | 1143 | LLN link |Route-Over mesh|(the Internet)|(the Internet)| 1144 | | | | | 1145 | Layer-2 | | | | 1146 |enhanced beacon| | | | 1147 |<--------------| | | | 1148 | | | | | 1149 | NS (EARO) | | | | 1150 | (for the LLA) | | | | 1151 |-------------->| | | | 1152 | NA (EARO) | | | | 1153 |<--------------| | | | 1154 | | | | | 1155 | (Zero-touch | | | | 1156 | handshake) | (Zero-touch handshake) | (Zero-touch | 1157 | using LLA | using GUA | handshake) | 1158 |<------------->|<---------------------------->|<------------>| 1159 | | | | | 1160 | CoJP Join Req | | | | \ 1161 | using LLA | | | | | 1162 |-------------->| | | | | 1163 | | CoJP Join Request | | | 1164 | | using GUA | | | 1165 | |----------------------------->| | | C 1166 | | | | | | o 1167 | | CoJP Join Response | | | J 1168 | | using GUA | | | P 1169 | |<-----------------------------| | | 1170 |CoJP Join Resp | | | | | 1171 | using LLA | | | | | 1172 |<--------------| | | | / 1173 | | | | | 1175 Figure 5: Join process in a Multi-Link Subnet. Parentheses () 1176 denote optional exchanges. 1178 4.2.2. Registration 1180 Once the pledge successfully completes the CoJP protocol and becomes 1181 a network node, it obtains the network prefix from neighboring 1182 routers and registers its IPv6 addresses. As detailed in 1183 Section 4.1, the combined 6LoWPAN ND 6LBR and Root of the RPL network 1184 learn information such as the device Unique ID (from 6LoWPAN ND) and 1185 the updated Sequence Number (from RPL), and perform 6LoWPAN ND proxy 1186 registration to the 6BBR of behalf of the LLN nodes. 1188 Figure 6 illustrates the initial IPv6 signaling that enables a 6LN to 1189 form a global address and register it to a 6LBR using 6LoWPAN ND 1190 [RFC8505], is then carried over RPL to the RPL Root, and then to the 1191 6BBR. This flow happens just once when the address is created and 1192 first registered. 1194 6LoWPAN Node 6LR 6LBR 6BBR 1195 (RPL leaf) (router) (Root) 1196 | | | | 1197 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 1198 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 1199 | | | | 1200 | RS (mcast) | | | 1201 |-------------->| | | 1202 |-----------> | | | 1203 |------------------> | | 1204 | RA (unicast) | | | 1205 |<--------------| | | 1206 | | | | 1207 | NS(EARO) | | | 1208 |-------------->| | | 1209 | 6LoWPAN ND | Extended DAR | | 1210 | |-------------->| | 1211 | | | NS(EARO) | 1212 | | |-------------->| 1213 | | | | NS-DAD 1214 | | | |------> 1215 | | | | (EARO) 1216 | | | | 1217 | | | NA(EARO) | 1218 | | |<--------------| 1219 | | Extended DAC | | 1220 | |<--------------| | 1221 | NA(EARO) | | | 1222 |<--------------| | | 1223 | | | | 1225 Figure 6: Initial Registration Flow over Multi-Link Subnet 1227 Figure 7 illustrates the repeating IPv6 signaling that enables a 6LN 1228 to keep a global address alive and registered to its 6LBR using 1229 6LoWPAN ND to the 6LR, RPL to the RPL Root, and then 6LoWPAN ND again 1230 to the 6BBR, which avoids repeating the Extended DAR/DAC flow across 1231 the network when RPL can suffice as a keep-alive mechanism. 1233 6LoWPAN Node 6LR 6LBR 6BBR 1234 (RPL leaf) (router) (Root) 1235 | | | | 1236 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 1237 | LLN link |Route-Over mesh| ant IPv6 link | Backbone 1238 | | | 1239 | | | | 1240 | NS(EARO) | | | 1241 |-------------->| | | 1242 | NA(EARO) | | | 1243 |<--------------| | | 1244 | | DAO | | 1245 | |-------------->| | 1246 | | DAO-ACK | | 1247 | |<--------------| | 1248 | | | NS(EARO) | 1249 | | |-------------->| 1250 | | | NA(EARO) | 1251 | | |<--------------| 1252 | | | | 1253 | | | | 1255 Figure 7: Next Registration Flow over Multi-Link Subnet 1257 As the network builds up, a node should start as a leaf to join the 1258 RPL network, and may later turn into both a RPL-capable router and a 1259 6LR, so as to accept leaf nodes to recursively join the network. 1261 4.3. TSCH and 6top 1263 4.3.1. 6top 1265 6TiSCH expects a high degree of scalability together with a 1266 distributed routing functionality based on RPL. To achieve this 1267 goal, the spectrum must be allocated in a way that allows for spatial 1268 reuse between zones that will not interfere with one another. In a 1269 large and spatially distributed network, a 6TiSCH node is often in a 1270 good position to determine usage of the spectrum in its vicinity. 1272 With 6TiSCH, the abstraction of an IPv6 link is implemented as a pair 1273 of bundles of cells, one in each direction. IP Links are only 1274 enabled between RPL parents and children. The 6TiSCH operation is 1275 optimal when the size of a bundle is such that both the energy wasted 1276 in idle listening and the packet drops due to congestion loss are 1277 minimized, while packets are forwarded within an acceptable latency. 1279 Use cases for distributed routing are often associated with a 1280 statistical distribution of best-effort traffic with variable needs 1281 for bandwidth on each individual link. The 6TiSCH operation can 1282 remain optimal if RPL parents can adjust dynamically, and with enough 1283 reactivity to match the variations of best-effort traffic, the amount 1284 of bandwidth that is used to communicate between themselves and their 1285 children, in both directions. In turn, the agility to fulfill the 1286 needs for additional cells improves when the number of interactions 1287 with other devices and the protocol latencies are minimized. 1289 6top is a logical link control sitting between the IP layer and the 1290 TSCH MAC layer, which provides the link abstraction that is required 1291 for IP operations. The 6top protocol, 6P, which is specified in 1292 [RFC8480], is one of the services provided by 6top. In particular, 1293 the 6top services are available over a management API that enables an 1294 external management entity to schedule cells and slotframes, and 1295 allows the addition of complementary functionality, for instance a 1296 Scheduling Function that manages a dynamic schedule management based 1297 on observed resource usage as discussed in Section 4.4.2. For this 1298 purpose, the 6TiSCH architecture differentiates "soft" cells and 1299 "hard" cells. 1301 4.3.1.1. Hard Cells 1303 "Hard" cells are cells that are owned and managed by a separate 1304 scheduling entity (e.g., a PCE) that specifies the slotOffset/ 1305 channelOffset of the cells to be added/moved/deleted, in which case 1306 6top can only act as instructed, and may not move hard cells in the 1307 TSCH schedule on its own. 1309 4.3.1.2. Soft Cells 1311 In contrast, "soft" cells are cells that 6top can manage locally. 1312 6top contains a monitoring process which monitors the performance of 1313 cells, and can add, remove soft cells in the TSCH schedule to adapt 1314 to the traffic needs, or move one when it performs poorly. To 1315 reserve a soft cell, the higher layer does not indicate the exact 1316 slotOffset/channelOffset of the cell to add, but rather the resulting 1317 bandwidth and QoS requirements. When the monitoring process triggers 1318 a cell reallocation, the two neighbor devices communicating over this 1319 cell negotiate its new position in the TSCH schedule. 1321 4.3.2. Scheduling Functions and the 6top protocol 1323 In the case of soft cells, the cell management entity that controls 1324 the dynamic attribution of cells to adapt to the dynamics of variable 1325 rate flows is called a Scheduling Function (SF). 1327 There may be multiple SFs with more or less aggressive reaction to 1328 the dynamics of the network. 1330 An SF may be seen as divided between an upper bandwidth adaptation 1331 logic that is not aware of the particular technology that is used to 1332 obtain and release bandwidth, and an underlying service that maps 1333 those needs in the actual technology, which means mapping the 1334 bandwidth onto cells in the case of TSCH using the 6top protocol as 1335 illustrated in Figure 8. 1337 +------------------------+ +------------------------+ 1338 | Scheduling Function | | Scheduling Function | 1339 | Bandwidth adaptation | | Bandwidth adaptation | 1340 +------------------------+ +------------------------+ 1341 | Scheduling Function | | Scheduling Function | 1342 | TSCH mapping to cells | | TSCH mapping to cells | 1343 +------------------------+ +------------------------+ 1344 | 6top cells negotiation | <- 6P -> | 6top cells negotiation | 1345 +------------------------+ +------------------------+ 1346 Device A Device B 1348 Figure 8: SF/6P stack in 6top 1350 The SF relies on 6top services that implement the 6top Protocol (6P) 1351 [RFC8480] to negotiate the precise cells that will be allocated or 1352 freed based on the schedule of the peer. It may be for instance that 1353 a peer wants to use a particular time slot that is free in its 1354 schedule, but that timeslot is already in use by the other peer for a 1355 communication with a third party on a different cell. 6P enables the 1356 peers to find an agreement in a transactional manner that ensures the 1357 final consistency of the nodes state. 1359 [MSF] is one of the possible scheduling functions. MSF uses the 1360 rendez-vous slot from [RFC8180] for network discovery, neighbor 1361 discovery, and any other broadcast. 1363 For basic unicast communication with any neighbor, each node uses a 1364 receive cell at a well-known slotOffset/channelOffset, derived from a 1365 hash of their own MAC address. Nodes can reach any neighbor by 1366 installing a transmit (shared) cell with slotOffset/channelOffset 1367 derived from the neighbor's MAC address. 1369 For child-parent links, MSF continuously monitors the load to/from 1370 parents and children. It then uses 6P to install/remove unicast 1371 cells whenever the current schedule appears to be under-/over- 1372 provisioned. 1374 4.3.3. 6top and RPL Objective Function operations 1376 An implementation of a RPL [RFC6550] Objective Function (OF), such as 1377 the RPL Objective Function Zero (OF0) [RFC6552] that is used in the 1378 Minimal 6TiSCH Configuration [RFC8180] to support RPL over a static 1379 schedule, may leverage, for its internal computation, the information 1380 maintained by 6top. 1382 An OF may require metrics about reachability, such as the Expected 1383 Transmission Count (ETX) metric [RFC6551]. 6top creates and 1384 maintains an abstract neighbor table, and this state may be leveraged 1385 to feed an OF and/or store OF information as well. A neighbor table 1386 entry may contain a set of statistics with respect to that specific 1387 neighbor. 1389 The neighbor information may include the time when the last packet 1390 has been received from that neighbor, a set of cell quality metrics, 1391 e.g., received signal strength indication (RSSI) or link quality 1392 indicator (LQI), the number of packets sent to the neighbor or the 1393 number of packets received from it. This information can be made 1394 available through 6top management APIs and used for instance to 1395 compute a Rank Increment that will determine the selection of the 1396 preferred parent. 1398 6top provides statistics about the underlying layer so the OF can be 1399 tuned to the nature of the TSCH MAC layer. 6top also enables the RPL 1400 OF to influence the MAC behavior, for instance by configuring the 1401 periodicity of IEEE Std. 802.15.4 Extended Beacons (EBs). By 1402 augmenting the EB periodicity, it is possible to change the network 1403 dynamics so as to improve the support of devices that may change 1404 their point of attachment in the 6TiSCH network. 1406 Some RPL control messages, such as the DODAG Information Object (DIO) 1407 are ICMPv6 messages that are broadcast to all neighbor nodes. With 1408 6TiSCH, the broadcast channel requirement is addressed by 6top by 1409 configuring TSCH to provide a broadcast channel, as opposed to, for 1410 instance, piggybacking the DIO messages in Layer-2 Enhanced Beacons 1411 (EBs), which would produce undue timer coupling among layers, packet 1412 size issues and could conflict with the policy of production networks 1413 where EBs are mostly eliminated to conserve energy. 1415 4.3.4. Network Synchronization 1417 Nodes in a TSCH network must be time synchronized. A node keeps 1418 synchronized to its time source neighbor through a combination of 1419 frame-based and acknowledgment-based synchronization. To maximize 1420 battery life and network throughput, it is advisable that RPL ICMP 1421 discovery and maintenance traffic (governed by the trickle timer) be 1422 somehow coordinated with the transmission of time synchronization 1423 packets (especially with enhanced beacons). 1425 This could be achieved through an interaction of the 6top sublayer 1426 and the RPL objective Function, or could be controlled by a 1427 management entity. 1429 Time distribution requires a loop-free structure. Nodes taken in a 1430 synchronization loop will rapidly desynchronize from the network and 1431 become isolated. 6TiSCH uses a RPL DAG with a dedicated global 1432 Instance for the purpose of time synchronization. That Instance is 1433 referred to as the Time Synchronization Global Instance (TSGI). The 1434 TSGI can be operated in either of the 3 modes that are detailed in 1435 section 3.1.3 of RPL [RFC6550], "Instances, DODAGs, and DODAG 1436 Versions". Multiple uncoordinated DODAGs with independent Roots may 1437 be used if all the Roots share a common time source such as the 1438 Global Positioning System (GPS). 1440 In the absence of a common time source, the TSGI should form a single 1441 DODAG with a virtual Root. A backbone network is then used to 1442 synchronize and coordinate RPL operations between the backbone 1443 routers that act as sinks for the LLN. Optionally, RPL's periodic 1444 operations may be used to transport the network synchronization. 1445 This may mean that 6top would need to trigger (override) the trickle 1446 timer if no other traffic has occurred for such a time that nodes may 1447 get out of synchronization. 1449 A node that has not joined the TSGI advertises a MAC level Join 1450 Priority of 0xFF to notify its neighbors that is not capable of 1451 serving as time parent. A node that has joined the TSGI advertises a 1452 MAC level Join Priority set to its DAGRank() in that Instance, where 1453 DAGRank() is the operation specified in section 3.5.1 of [RFC6550], 1454 "Rank Comparison". 1456 The provisioning of a RPL Root is out of scope for both RPL and this 1457 Architecture, whereas RPL enables to propagate configuration 1458 information down the DODAG. This applies to the TSGI as well; a Root 1459 is configured or obtains by unspecified means the knowledge of the 1460 RPLInstanceID for the TSGI. The Root advertises its DagRank in the 1461 TSGI, that must be less than 0xFF, as its Join Priority in its IEEE 1462 Std. 802.15.4 Extended Beacons (EB). 1464 A node that reads a Join Priority of less than 0xFF should join the 1465 neighbor with the lesser Join Priority and use it as time parent. If 1466 the node is configured to serve as time parent, then the node should 1467 join the TSGI, obtain a Rank in that Instance and start advertising 1468 its own DagRank in the TSGI as its Join Priority in its EBs. 1470 4.3.5. Slotframes and CDU matrix 1472 6TiSCH enables IPv6 best effort (stochastic) transmissions over a MAC 1473 layer that is also capable of scheduled (deterministic) 1474 transmissions. A window of time is defined around the scheduled 1475 transmission where the medium must, as much as practically feasible, 1476 be free of contending energy to ensure that the medium is free of 1477 contending packets when time comes for a scheduled transmission. One 1478 simple way to obtain such a window is to format time and frequencies 1479 in cells of transmission of equal duration. This is the method that 1480 is adopted in IEEE Std. 802.15.4 TSCH as well as the Long Term 1481 Evolution (LTE) of cellular networks. 1483 The 6TiSCH architecture defines a global concept that is called a 1484 Channel Distribution and Usage (CDU) matrix to describe that 1485 formatting of time and frequencies, 1487 A CDU matrix is defined centrally as part of the network definition. 1488 It is a matrix of cells with a height equal to the number of 1489 available channels (indexed by ChannelOffsets) and a width (in 1490 timeslots) that is the period of the network scheduling operation 1491 (indexed by slotOffsets) for that CDU matrix. There are different 1492 models for scheduling the usage of the cells, which place the 1493 responsibility of avoiding collisions either on a central controller 1494 or on the devices themselves, at an extra cost in terms of energy to 1495 scan for free cells (more in Section 4.4). 1497 The size of a cell is a timeslot duration, and values of 10 to 15 1498 milliseconds are typical in 802.15.4 TSCH to accommodate for the 1499 transmission of a frame and an ack, including the security validation 1500 on the receive side which may take up to a few milliseconds on some 1501 device architecture. 1503 A CDU matrix iterates over and over with a well-known channel 1504 rotation called the hopping sequence. In a given network, there 1505 might be multiple CDU matrices that operate with different width, so 1506 they have different durations and represent different periodic 1507 operations. It is recommended that all CDU matrices in a 6TiSCH 1508 domain operate with the same cell duration and are aligned, so as to 1509 reduce the chances of interferences from the Slotted ALOHA 1510 operations. The knowledge of the CDU matrices is shared between all 1511 the nodes and used in particular to define slotframes. 1513 A slotframe is a MAC-level abstraction that is common to all nodes 1514 and contains a series of timeslots of equal length and precedence. 1515 It is characterized by a slotframe_ID, and a slotframe_size. A 1516 slotframe aligns to a CDU matrix for its parameters, such as number 1517 and duration of timeslots. 1519 Multiple slotframes can coexist in a node schedule, i.e., a node can 1520 have multiple activities scheduled in different slotframes. A 1521 slotframe is associated with a priority that may be related to the 1522 precedence of different 6TiSCH topologies. The slotframes may be 1523 aligned to different CDU matrices and thus have different width. 1524 There is typically one slotframe for scheduled traffic that has the 1525 highest precedence and one or more slotframe(s) for RPL traffic. The 1526 timeslots in the slotframe are indexed by the SlotOffset; the first 1527 cell is at SlotOffset 0. 1529 When a packet is received from a higher layer for transmission, 6top 1530 inserts that packet in the outgoing queue which matches the packet 1531 best (Differentiated Services [RFC2474] can therefore be used). At 1532 each scheduled transmit slot, 6top looks for the frame in all the 1533 outgoing queues that best matches the cells. If a frame is found, it 1534 is given to the TSCH MAC for transmission. 1536 4.3.6. Distributing the reservation of cells 1538 The 6TiSCH architecture introduces the concept of chunks 1539 (Section 2.1) to distribute the allocation of the spectrum for a 1540 whole group of cells at a time. The CDU matrix is formatted into a 1541 set of chunks, possibly as illustrated in Figure 9, each of the 1542 chunks identified uniquely by a chunk-ID. The knowledge of this 1543 formatting is shared between all the nodes in a 6TiSCH network. It 1544 could be conveyed during the join process, or codified into a profile 1545 document, or obtained using some other mechanism. This is as opposed 1546 to static scheduling that refers to the pre-programmed mechanism that 1547 is specified in [RFC8180] and pre-exists to the distribution of the 1548 chunk formatting. 1550 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1551 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1552 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1553 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1554 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1555 ... 1556 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1557 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1558 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1559 0 1 2 3 4 5 6 M 1561 Figure 9: CDU matrix Partitioning in Chunks 1563 The 6TiSCH Architecture envisions a protocol that enables chunk 1564 ownership appropriation whereby a RPL parent discovers a chunk that 1565 is not used in its interference domain, claims the chunk, and then 1566 defends it in case another RPL parent would attempt to appropriate it 1567 while it is in use. The chunk is the basic unit of ownership that is 1568 used in that process. 1570 As a result of the process of chunk ownership appropriation, the RPL 1571 parent has exclusive authority to decide which cell in the 1572 appropriated chunk can be used by which node in its interference 1573 domain. In other words, it is implicitly delegated the right to 1574 manage the portion of the CDU matrix that is represented by the 1575 chunk. 1577 Initially, those cells are added to the heap of free cells, then 1578 dynamically placed into existing bundles, in new bundles, or 1579 allocated opportunistically for one transmission. 1581 Note that a PCE is expected to have precedence in the allocation, so 1582 that a RPL parent would only be able to obtain portions that are not 1583 in-use by the PCE. 1585 4.4. Schedule Management Mechanisms 1587 6TiSCH uses 4 paradigms to manage the TSCH schedule of the LLN nodes: 1588 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1589 and scheduling management, and Hop-by-hop scheduling. Multiple 1590 mechanisms are defined that implement the associated Interaction 1591 Models, and can be combined and used in the same LLN. Which 1592 mechanism(s) to use depends on application requirements. 1594 4.4.1. Static Scheduling 1596 In the simplest instantiation of a 6TiSCH network, a common fixed 1597 schedule may be shared by all nodes in the network. Cells are 1598 shared, and nodes contend for slot access in a slotted ALOHA manner. 1600 A static TSCH schedule can be used to bootstrap a network, as an 1601 initial phase during implementation, or as a fall-back mechanism in 1602 case of network malfunction. This schedule is pre-established, for 1603 instance decided by a network administrator based on operational 1604 needs. It can be pre-configured into the nodes, or, more commonly, 1605 learned by a node when joining the network using standard IEEE Std. 1606 802.15.4 Information Elements (IE). Regardless, the schedule remains 1607 unchanged after the node has joined a network. RPL is used on the 1608 resulting network. This "minimal" scheduling mechanism that 1609 implements this paradigm is detailed in [RFC8180]. 1611 4.4.2. Neighbor-to-neighbor Scheduling 1613 In the simplest instantiation of a 6TiSCH network described in 1614 Section 4.4.1, nodes may expect a packet at any cell in the schedule 1615 and will waste energy idle listening. In a more complex 1616 instantiation of a 6TiSCH network, a matching portion of the schedule 1617 is established between peers to reflect the observed amount of 1618 transmissions between those nodes. The aggregation of the cells 1619 between a node and a peer forms a bundle that the 6top layer uses to 1620 implement the abstraction of a link for IP. The bandwidth on that 1621 link is proportional to the number of cells in the bundle. 1623 If the size of a bundle is configured to fit an average amount of 1624 bandwidth, peak traffic is dropped. If the size is configured to 1625 allow for peak emissions, energy is be wasted idle listening. 1627 As discussed in more details in Section 4.3, the 6top Protocol 1628 [RFC8480] specifies the exchanges between neighbor nodes to reserve 1629 soft cells to transmit to one another, possibly under the control of 1630 a Scheduling Function (SF). Because this reservation is done without 1631 global knowledge of the schedule of other nodes in the LLN, 1632 scheduling collisions are possible. 1634 And as discussed in Section 4.3.2, an optional Scheduling Function 1635 (SF) is used to monitor bandwidth usage and perform requests for 1636 dynamic allocation by the 6top sublayer. The SF component is not 1637 part of the 6top sublayer. It may be collocated on the same device 1638 or may be partially or fully offloaded to an external system. The 1639 "6TiSCH Minimal Scheduling Function (MSF)" [MSF] provides a simple 1640 scheduling function that can be used by default by devices that 1641 support dynamic scheduling of soft cells. 1643 Monitoring and relocation is done in the 6top layer. For the upper 1644 layer, the connection between two neighbor nodes appears as a number 1645 of cells. Depending on traffic requirements, the upper layer can 1646 request 6top to add or delete a number of cells scheduled to a 1647 particular neighbor, without being responsible for choosing the exact 1648 slotOffset/channelOffset of those cells. 1650 4.4.3. Remote Monitoring and Schedule Management 1652 Remote monitoring and Schedule Management refers to a DetNet/SDN 1653 model whereby an NME and a scheduling entity, associated with a PCE, 1654 reside in a central controller and interact with the 6top layer to 1655 control IPv6 Links and Tracks (Section 4.5) in a 6TiSCH network. The 1656 composite centralized controller can assign physical resources (e.g., 1657 buffers and hard cells) to a particular Track to optimize the 1658 reliability within a bounded latency for a well-specified flow. 1660 The work at the 6TiSCH WG focused on non-deterministic traffic and 1661 did not provide the generic data model that is necessary for the 1662 controller to monitor and manage resources of the 6top sublayer. 1663 This is deferred to future work, see Appendix A.1.2. 1665 With respect to Centralized routing and scheduling, it is envisioned 1666 that the related component of the 6TiSCH Architecture would be an 1667 extension of the DetNet Architecture [RFC8655], which studies Layer-3 1668 aspects of Deterministic Networks, and covers networks that span 1669 multiple Layer-2 domains. 1671 The DetNet architecture is a form of Software Defined Networking 1672 (SDN) Architecture and is composed of three planes, a (User) 1673 Application Plane, a Controller Plane (where the PCE operates), and a 1674 Network Plane which can represent a 6TiSCH LLN. 1676 Software-Defined Networking (SDN): Layers and Architecture 1677 Terminology [RFC7426] proposes a generic representation of the SDN 1678 architecture that is reproduced in Figure 10. 1680 o--------------------------------o 1681 | | 1682 | +-------------+ +----------+ | 1683 | | Application | | Service | | 1684 | +-------------+ +----------+ | 1685 | Application Plane | 1686 o---------------Y----------------o 1687 | 1688 *-----------------------------Y---------------------------------* 1689 | Network Services Abstraction Layer (NSAL) | 1690 *------Y------------------------------------------------Y-------* 1691 | | 1692 | Service Interface | 1693 | | 1694 o------Y------------------o o---------------------Y------o 1695 | | Control Plane | | Management Plane | | 1696 | +----Y----+ +-----+ | | +-----+ +----Y----+ | 1697 | | Service | | App | | | | App | | Service | | 1698 | +----Y----+ +--Y--+ | | +--Y--+ +----Y----+ | 1699 | | | | | | | | 1700 | *----Y-----------Y----* | | *---Y---------------Y----* | 1701 | | Control Abstraction | | | | Management Abstraction | | 1702 | | Layer (CAL) | | | | Layer (MAL) | | 1703 | *----------Y----------* | | *----------Y-------------* | 1704 | | | | | | 1705 o------------|------------o o------------|---------------o 1706 | | 1707 | CP | MP 1708 | Southbound | Southbound 1709 | Interface | Interface 1710 | | 1711 *------------Y---------------------------------Y----------------* 1712 | Device and resource Abstraction Layer (DAL) | 1713 *------------Y---------------------------------Y----------------* 1714 | | | | 1715 | o-------Y----------o +-----+ o--------Y----------o | 1716 | | Forwarding Plane | | App | | Operational Plane | | 1717 | o------------------o +-----+ o-------------------o | 1718 | Network Device | 1719 +---------------------------------------------------------------+ 1721 Figure 10: SDN Layers and Architecture Terminology per RFC 7426 1723 The PCE establishes end-to-end Tracks of hard cells, which are 1724 described in more details in Section 4.6.1. 1726 The DetNet work is expected to enable end to end Deterministic Path 1727 across heterogeneous network. This can be for instance a 6TiSCH LLN 1728 and an Ethernet Backbone. 1730 This model fits the 6TiSCH extended configuration, whereby a 6BBR 1731 federates multiple 6TiSCH LLN in a single subnet over a backbone that 1732 can be, for instance, Ethernet or Wi-Fi. In that model, 6TiSCH 6BBRs 1733 synchronize with one another over the backbone, so as to ensure that 1734 the multiple LLNs that form the IPv6 subnet stay tightly 1735 synchronized. 1737 If the Backbone is Deterministic, then the Backbone Router ensures 1738 that the end-to-end deterministic behavior is maintained between the 1739 LLN and the backbone. It is the responsibility of the PCE to compute 1740 a deterministic path and to end across the TSCH network and an IEEE 1741 Std. 802.1 TSN Ethernet backbone, and that of DetNet to enable end- 1742 to-end deterministic forwarding. 1744 4.4.4. Hop-by-hop Scheduling 1746 A node can reserve a Track (Section 4.5) to one or more 1747 destination(s) that are multiple hops away by installing soft cells 1748 at each intermediate node. This forms a Track of soft cells. A 1749 Track Scheduling Function above the 6top sublayer of each node on the 1750 Track is needed to monitor these soft cells and trigger relocation 1751 when needed. 1753 This hop-by-hop reservation mechanism is expected to be similar in 1754 essence to [RFC3209] and/or [RFC4080]/[RFC5974]. The protocol for a 1755 node to trigger hop-by-hop scheduling is not yet defined. 1757 4.5. On Tracks 1759 The architecture introduces the concept of a Track, which is a 1760 directed path from a source 6TiSCH node to one or more destination 1761 6TiSCH node(s) across a 6TiSCH LLN. 1763 A Track is the 6TiSCH instantiation of the concept of a Deterministic 1764 Path as described in [RFC8655]. Constrained resources such as memory 1765 buffers are reserved for that Track in intermediate 6TiSCH nodes to 1766 avoid loss related to limited capacity. A 6TiSCH node along a Track 1767 not only knows which bundles of cells it should use to receive 1768 packets from a previous hop, but also knows which bundle(s) it should 1769 use to send packets to its next hop along the Track. 1771 4.5.1. General Behavior of Tracks 1773 A Track is associated with Layer-2 bundles of cells with related 1774 schedules and logical relationships and that ensure that a packet 1775 that is injected in a Track will progress in due time all the way to 1776 destination. 1778 Multiple cells may be scheduled in a Track for the transmission of a 1779 single packet, in which case the normal operation of IEEE Std. 1780 802.15.4 Automatic Repeat-reQuest (ARQ) can take place; the 1781 acknowledgment may be omitted in some cases, for instance if there is 1782 no scheduled cell for a possible retry. 1784 There are several benefits for using a Track to forward a packet from 1785 a source node to the destination node. 1787 1. Track forwarding, as further described in Section 4.6.1, is a 1788 Layer-2 forwarding scheme, which introduces less process delay 1789 and overhead than Layer-3 forwarding scheme. Therefore, LLN 1790 Devices can save more energy and resource, which is critical for 1791 resource constrained devices. 1793 2. Since channel resources, i.e., bundles of cells, have been 1794 reserved for communications between 6TiSCH nodes of each hop on 1795 the Track, the throughput and the maximum latency of the traffic 1796 along a Track are guaranteed and the jitter is maintained small. 1798 3. By knowing the scheduled time slots of incoming bundle(s) and 1799 outgoing bundle(s), 6TiSCH nodes on a Track could save more 1800 energy by staying in sleep state during in-active slots. 1802 4. Tracks are protected from interfering with one another if a cell 1803 is scheduled to belong to at most one Track, and congestion loss 1804 is avoided if at most one packet can be presented to the MAC to 1805 use that cell. Tracks enhance the reliability of transmissions 1806 and thus further improve the energy consumption in LLN Devices by 1807 reducing the chances of retransmission. 1809 4.5.2. Serial Track 1811 A Serial (or simple) Track is the 6TiSCH version of a circuit; a 1812 bundle of cells that are programmed to receive (RX-cells) is uniquely 1813 paired to a bundle of cells that are set to transmit (TX-cells), 1814 representing a Layer-2 forwarding state which can be used regardless 1815 of the network layer protocol. A Serial Track is thus formed end-to- 1816 end as a succession of paired bundles, a receive bundle from the 1817 previous hop and a transmit bundle to the next hop along the Track. 1819 For a given iteration of the device schedule, the effective channel 1820 of the cell is obtained by following in a loop a well-known hopping 1821 sequence that started at Epoch time at the channelOffset of the cell, 1822 which results in a rotation of the frequency that used for 1823 transmission. The bundles may be computed so as to accommodate both 1824 variable rates and retransmissions, so they might not be fully used 1825 in the iteration of the schedule. 1827 4.5.3. Complex Track with Replication and Elimination 1829 The art of Deterministic Networks already include Packet Replication 1830 and Elimination techniques. Example standards include the Parallel 1831 Redundancy Protocol (PRP) and the High-availability Seamless 1832 Redundancy (HSR) [IEC62439]. Similarly, and as opposed to a Serial 1833 Track that is a sequence of nodes and links, a Complex Track is 1834 shaped as a directed acyclic graph towards one or more destination(s) 1835 to support multi-path forwarding and route around failures. 1837 A Complex Track may branch off over non congruent branches for the 1838 purpose of multicasting, and/or redundancy, in which case it 1839 reconverges later down the path. This enables the Packet 1840 Replication, Elimination and Ordering Functions (PREOF) defined by 1841 Detnet. Packet ARQ, Replication, Elimination and Overhearing (PAREO) 1842 adds radio-specific capabilities of Layer-2 ARQ and promiscuous 1843 listening to redundant transmissions to compensate for the lossiness 1844 of the medium and meet industrial expectations of a Reliable and 1845 Available Wireless network. Combining PAREO and PREOF, a Track may 1846 extend beyond the 6TiSCH network in a larger DetNet network. 1848 In the art of TSCH, a path does not necessarily support PRE but it is 1849 almost systematically multi-path. This means that a Track is 1850 scheduled so as to ensure that each hop has at least two forwarding 1851 solutions, and the forwarding decision is to try the preferred one 1852 and use the other in case of Layer-2 transmission failure as detected 1853 by ARQ. Similarly, at each 6TiSCH hop along the Track, the PCE may 1854 schedule more than one timeslot for a packet, so as to support 1855 Layer-2 retries (ARQ). It is also possible that the field device 1856 only uses the second branch if sending over the first branch fails. 1858 4.5.4. DetNet End-to-end Path 1860 Ultimately, DetNet should enable to extend a Track beyond the 6TiSCH 1861 LLN as illustrated in Figure 11. In that example, a Track that is 1862 laid out from a field device in a 6TiSCH network to an IoT gateway 1863 that is located on an 802.1 Time-Sensitive Networking (TSN) backbone. 1864 A 6TiSCH-Aware DetNet Service Layer handles the Packet Replication, 1865 Elimination, and Ordering Functions over the DODAG that forms a 1866 Track. 1868 The Replication function in the 6TiSCH Node sends a copy of each 1869 packet over two different branches, and the PCE schedules each hop of 1870 both branches so that the two copies arrive in due time at the 1871 gateway. In case of a loss on one branch, hopefully the other copy 1872 of the packet still makes it in due time. If two copies make it to 1873 the IoT gateway, the Elimination function in the gateway ignores the 1874 extra packet and presents only one copy to upper layers. 1876 +-=-=-+ 1877 | IoT | 1878 | G/W | 1879 +-=-=-+ 1880 ^ <=== Elimination 1881 Track branch | | 1882 +-=-=-=-+ +-=-=-=-=+ Subnet Backbone 1883 | | 1884 +-=|-=+ +-=|-=+ 1885 | | | Backbone | | | Backbone 1886 o | | | router | | | router 1887 +-=/-=+ +-=|-=+ 1888 o / o o-=-o-=-=/ o 1889 o o-=-o-=/ o o o o o 1890 o \ / o o LLN o 1891 o v <=== Replication 1892 o 1894 Figure 11: Example End-to-End DetNet Track 1896 4.5.5. Cell Reuse 1898 The 6TiSCH architecture provides means to avoid waste of cells as 1899 well as overflows in the transmit bundle of a Track, as follows: 1901 A TX-cell that is not needed for the current iteration may be reused 1902 opportunistically on a per-hop basis for routed packets. When all of 1903 the frame that were received for a given Track are effectively 1904 transmitted, any available TX-cell for that Track can be reused for 1905 upper layer traffic for which the next-hop router matches the next 1906 hop along the Track. In that case, the cell that is being used is 1907 effectively a TX-cell from the Track, but the short address for the 1908 destination is that of the next-hop router. 1910 It results in a frame that is received in a RX-cell of a Track with a 1911 destination MAC address set to this node as opposed to the broadcast 1912 MAC address must be extracted from the Track and delivered to the 1913 upper layer. Note that a frame with an unrecognized destination MAC 1914 address is dropped at the lower MAC layer and thus is not received at 1915 the 6top sublayer. 1917 On the other hand, it might happen that there are not enough TX-cells 1918 in the transmit bundle to accommodate the Track traffic, for instance 1919 if more retransmissions are needed than provisioned. In that case, 1920 and if the frame transports an IPv6 packet, then it can be placed for 1921 transmission in the bundle that is used for Layer-3 traffic towards 1922 the next hop along the Track. The MAC address should be set to the 1923 next-hop MAC address to avoid confusion. 1925 It results in a frame that is received over a Layer-3 bundle may be 1926 in fact associated to a Track. In a classical IP link such as an 1927 Ethernet, off-Track traffic is typically in excess over reservation 1928 to be routed along the non-reserved path based on its QoS setting. 1929 But with 6TiSCH, since the use of the Layer-3 bundle may be due to 1930 transmission failures, it makes sense for the receiver to recognize a 1931 frame that should be re-Tracked, and to place it back on the 1932 appropriate bundle if possible. . A frame is re-Tracked by 1933 scheduling it for transmission over the transmit bundle associated to 1934 the Track, with the destination MAC address set to broadcast. 1936 4.6. Forwarding Models 1938 By forwarding, this document means the per-packet operation that 1939 allows to deliver a packet to a next hop or an upper layer in this 1940 node. Forwarding is based on pre-existing state that was installed 1941 as a result of a routing computation Section 4.7. 6TiSCH supports 1942 three different forwarding model:(G-MPLS) Track Forwarding, 1943 (classical) IPv6 Forwarding and (6LoWPAN) Fragment Forwarding. 1945 4.6.1. Track Forwarding 1947 Forwarding along a Track can be seen as a Generalized Multi-protocol 1948 Label Switching (G-MPLS) operation in that the information used to 1949 switch a frame is not an explicit label, but rather related to other 1950 properties of the way the packet was received, a particular cell in 1951 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1952 Layer-2 security) accepts a frame, that frame can be switched 1953 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1954 fragment, or a frame from an alternate protocol such as WirelessHART 1955 or ISA100.11a. 1957 A data frame that is forwarded along a Track normally has a 1958 destination MAC address that is set to broadcast - or a multicast 1959 address depending on MAC support. This way, the MAC layer in the 1960 intermediate nodes accepts the incoming frame and 6top switches it 1961 without incurring a change in the MAC header. In the case of IEEE 1962 Std. 802.15.4, this means effectively broadcast, so that along the 1963 Track the short address for the destination of the frame is set to 1964 0xFFFF. 1966 There are 2 modes for a Track, native mode and tunnel mode. 1968 4.6.1.1. Native Mode 1970 In native mode, the Protocol Data Unit (PDU) is associated with flow- 1971 dependent meta-data that refers uniquely to the Track, so the 6top 1972 sublayer can place the frame in the appropriate cell without 1973 ambiguity. In the case of IPv6 traffic, this flow identification may 1974 be done using a 6-tuple as discussed in [I-D.ietf-detnet-ip]. In 1975 particular, implementations of this document should support 1976 identification of DetNet flows based on the IPv6 Flow Label field. 1977 The flow identification may also be done using a dedicated RPL 1978 Instance (see section 3.1.3 of [RFC6550]), signaled in a RPL Packet 1979 Information (more in section 11.2.2.1 of [RFC6550]). The flow 1980 identification is validated at egress before restoring the 1981 destination MAC address (DMAC) and punting to the upper layer. 1983 Figure 12 illustrates the Track Forwarding operation which happens at 1984 the 6top sublayer, below IP. 1986 | Packet flowing across the network ^ 1987 +--------------+ | | 1988 | IPv6 | | | 1989 +--------------+ | | 1990 | 6LoWPAN HC | | | 1991 +--------------+ ingress egress 1992 | 6top | sets +----+ +----+ restores 1993 +--------------+ DMAC to | | | | DMAC to 1994 | TSCH MAC | brdcst | | | | dest 1995 +--------------+ | | | | | | 1996 | LLN PHY | +-------+ +--...-----+ +-------+ 1997 +--------------+ 1998 Ingress Relay Relay Egress 1999 Stack Layer Node Node Node Node 2001 Figure 12: Track Forwarding, Native Mode 2003 4.6.1.2. Tunnel Mode 2005 In tunnel mode, the frames originate from an arbitrary protocol over 2006 a compatible MAC that may or may not be synchronized with the 6TiSCH 2007 network. An example of this would be a router with a dual radio that 2008 is capable of receiving and sending WirelessHART or ISA100.11a frames 2009 with the second radio, by presenting itself as an access Point or a 2010 Backbone Router, respectively. In that mode, some entity (e.g., PCE) 2011 can coordinate with a WirelessHART Network Manager or an ISA100.11a 2012 System Manager to specify the flows that are transported. 2014 +--------------+ 2015 | IPv6 | 2016 +--------------+ 2017 | 6LoWPAN HC | 2018 +--------------+ set restore 2019 | 6top | +DMAC+ +DMAC+ 2020 +--------------+ to|brdcst to|nexthop 2021 | TSCH MAC | | | | | 2022 +--------------+ | | | | 2023 | LLN PHY | +-------+ +--...-----+ +-------+ 2024 +--------------+ | ingress egress | 2025 | | 2026 +--------------+ | | 2027 | LLN PHY | | | 2028 +--------------+ | Packet flowing across the network | 2029 | TSCH MAC | | | 2030 +--------------+ | DMAC = | DMAC = 2031 |ISA100/WiHART | | nexthop v nexthop 2032 +--------------+ 2033 Source Ingress Egress Destination 2034 Stack Layer Node Node Node Node 2036 Figure 13: Track Forwarding, Tunnel Mode 2038 In that case, the flow information that identifies the Track at the 2039 ingress 6TiSCH router is derived from the RX-cell. The DMAC is set 2040 to this node but the flow information indicates that the frame must 2041 be tunneled over a particular Track so the frame is not passed to the 2042 upper layer. Instead, the DMAC is forced to broadcast and the frame 2043 is passed to the 6top sublayer for switching. 2045 At the egress 6TiSCH router, the reverse operation occurs. Based on 2046 tunneling information of the Track, which may for instance indicate 2047 that the tunneled datagram is an IP packet, the datagram is passed to 2048 the appropriate Link-Layer with the destination MAC restored. 2050 4.6.1.3. Tunneling Information 2052 Tunneling information coming with the Track configuration provides 2053 the destination MAC address of the egress endpoint as well as the 2054 tunnel mode and specific data depending on the mode, for instance a 2055 service access point for frame delivery at egress. 2057 If the tunnel egress point does not have a MAC address that matches 2058 the configuration, the Track installation fails. 2060 If the Layer-3 destination address belongs to the tunnel termination, 2061 then it is possible that the IPv6 address of the destination is 2062 compressed at the 6LoWPAN sublayer based on the MAC address. 2063 Restoring the wrong MAC address at the egress would then also result 2064 in the wrong IP address in the packet after decompression. For that 2065 reason, a packet can be injected in a Track only if the destination 2066 MAC address is effectively that of the tunnel egress point. It is 2067 thus mandatory for the ingress router to validate that the MAC 2068 address that was used at the 6LoWPAN sublayer for compression matches 2069 that of the tunnel egress point before it overwrites it to broadcast. 2070 The 6top sublayer at the tunnel egress point reverts that operation 2071 to the MAC address obtained from the tunnel information. 2073 4.6.2. IPv6 Forwarding 2075 As the packets are routed at Layer-3, traditional QoS and Active 2076 Queue Management (AQM) operations are expected to prioritize flows. 2078 | Packet flowing across the network ^ 2079 +--------------+ | | 2080 | IPv6 | | +-QoS+ +-QoS+ | 2081 +--------------+ | | | | | | 2082 | 6LoWPAN HC | | | | | | | 2083 +--------------+ | | | | | | 2084 | 6top | | | | | | | 2085 +--------------+ | | | | | | 2086 | TSCH MAC | | | | | | | 2087 +--------------+ | | | | | | 2088 | LLN PHY | +-------+ +--...-----+ +-------+ 2089 +--------------+ 2090 Source Ingress Egress Destination 2091 Stack Layer Node Router Router Node 2093 Figure 14: IP Forwarding 2095 4.6.3. Fragment Forwarding 2097 Considering that per section 4 of [RFC4944] 6LoWPAN packets can be as 2098 large as 1280 bytes (the IPv6 minimum MTU), and that the non-storing 2099 mode of RPL implies Source Routing that requires space for routing 2100 headers, and that a IEEE Std. 802.15.4 frame with security may carry 2101 in the order of 80 bytes of effective payload, an IPv6 packet might 2102 be fragmented into more than 16 fragments at the 6LoWPAN sublayer. 2104 This level of fragmentation is much higher than that traditionally 2105 experienced over the Internet with IPv4 fragments, where 2106 fragmentation is already known as harmful. 2108 In the case to a multihop route within a 6TiSCH network, Hop-by-Hop 2109 recomposition occurs at each hop to reform the packet and route it. 2111 This creates additional latency and forces intermediate nodes to 2112 store a portion of a packet for an undetermined time, thus impacting 2113 critical resources such as memory and battery. 2115 [MIN-FRAG] describes a framework for forwarding fragments end-to-end 2116 across a 6TiSCH route-over mesh. Within that framework, 2117 [I-D.ietf-lwig-6lowpan-virtual-reassembly] details a virtual 2118 reassembly buffer mechanism whereby the datagram tag in the 6LoWPAN 2119 Fragment is used as a label for switching at the 6LoWPAN sublayer. 2121 Building on this technique, [RECOV-FRAG] introduces a new format for 2122 6LoWPAN fragments that enables the selective recovery of individual 2123 fragments, and allows for a degree of flow control based on an 2124 Explicit Congestion Notification. 2126 | Packet flowing across the network ^ 2127 +--------------+ | | 2128 | IPv6 | | +----+ +----+ | 2129 +--------------+ | | | | | | 2130 | 6LoWPAN HC | | learn learn | 2131 +--------------+ | | | | | | 2132 | 6top | | | | | | | 2133 +--------------+ | | | | | | 2134 | TSCH MAC | | | | | | | 2135 +--------------+ | | | | | | 2136 | LLN PHY | +-------+ +--...-----+ +-------+ 2137 +--------------+ 2138 Source Ingress Egress Destination 2139 Stack Layer Node Router Router Node 2141 Figure 15: Forwarding First Fragment 2143 In that model, the first fragment is routed based on the IPv6 header 2144 that is present in that fragment. The 6LoWPAN sublayer learns the 2145 next hop selection, generates a new datagram tag for transmission to 2146 the next hop, and stores that information indexed by the incoming MAC 2147 address and datagram tag. The next fragments are then switched based 2148 on that stored state. 2150 | Packet flowing across the network ^ 2151 +--------------+ | | 2152 | IPv6 | | | 2153 +--------------+ | | 2154 | 6LoWPAN HC | | replay replay | 2155 +--------------+ | | | | | | 2156 | 6top | | | | | | | 2157 +--------------+ | | | | | | 2158 | TSCH MAC | | | | | | | 2159 +--------------+ | | | | | | 2160 | LLN PHY | +-------+ +--...-----+ +-------+ 2161 +--------------+ 2162 Source Ingress Egress Destination 2163 Stack Layer Node Router Router Node 2165 Figure 16: Forwarding Next Fragment 2167 A bitmap and an ECN echo in the end-to-end acknowledgment enable the 2168 source to resend the missing fragments selectively. The first 2169 fragment may be resent to carve a new path in case of a path failure. 2170 The ECN echo set indicates that the number of outstanding fragments 2171 should be reduced. 2173 4.7. Advanced 6TiSCH Routing 2175 4.7.1. Packet Marking and Handling 2177 All packets inside a 6TiSCH domain must carry the RPLInstanceID that 2178 identifies the 6TiSCH topology that is to be used for routing and 2179 forwarding that packet. The location of that information must be the 2180 same for all packets forwarded inside the domain. 2182 For packets that are routed by a PCE along a Track, the tuple formed 2183 by the IPv6 source address and a local RPLInstanceID in the packet 2184 identify uniquely the Track and associated transmit bundle. 2186 For packets that are routed by RPL, that information is the 2187 RPLInstanceID which is carried in the RPL Packet Information (RPI), 2188 as discussed in section 11.2 of [RFC6550], "Loop Avoidance and 2189 Detection". The RPI is transported by a RPL option in the IPv6 Hop- 2190 By-Hop Header [RFC6553]. 2192 A compression mechanism for the RPL packet artifacts that integrates 2193 the compression of IP-in-IP encapsulation and the Routing Header type 2194 3 [RFC6554] with that of the RPI in a 6LoWPAN dispatch/header type is 2195 specified in [RFC8025] and [RFC8138]. 2197 Either way, the method and format used for encoding the RPLInstanceID 2198 is generalized to all 6TiSCH topological Instances, which include 2199 both RPL Instances and Tracks. 2201 4.7.2. Replication, Retries and Elimination 2203 6TiSCH supports the PREOF operations of elimination and reordering of 2204 packets along a complex Track, but has no requirement about whether a 2205 sequence number is tagged in the packet for that purpose. With 2206 6TiSCH, the schedule can tell when multiple receive timeslots 2207 correspond to copies of a same packet, in which case the receiver may 2208 avoid listening to the extra copies once it had received one instance 2209 of the packet. 2211 The semantics of the configuration will enable correlated timeslots 2212 to be grouped for transmit (and respectively receive) with a 'OR' 2213 relations, and then a 'AND' relation would be configurable between 2214 groups. The semantics is that if the transmit (and respectively 2215 receive) operation succeeded in one timeslot in a 'OR' group, then 2216 all the other timeslots in the group are ignored. Now, if there are 2217 at least two groups, the 'AND' relation between the groups indicates 2218 that one operation must succeed in each of the groups. 2220 On the transmit side, timeslots provisioned for retries along a same 2221 branch of a Track are placed a same 'OR' group. The 'OR' relation 2222 indicates that if a transmission is acknowledged, then 2223 retransmissions of that packet should not be attempted for remaining 2224 timeslots in that group. There are as many 'OR' groups as there are 2225 branches of the Track departing from this node. Different 'OR' 2226 groups are programmed for the purpose of replication, each group 2227 corresponding to one branch of the Track. The 'AND' relation between 2228 the groups indicates that transmission over any of branches must be 2229 attempted regardless of whether a transmission succeeded in another 2230 branch. It is also possible to place cells to different next-hop 2231 routers in a same 'OR' group. This allows to route along multi-path 2232 Tracks, trying one next-hop and then another only if sending to the 2233 first fails. 2235 On the receive side, all timeslots are programmed in a same 'OR' 2236 group. Retries of a same copy as well as converging branches for 2237 elimination are converged, meaning that the first successful 2238 reception is enough and that all the other timeslots can be ignored. 2239 A 'AND' group denotes different packets that must all be received and 2240 transmitted over the associated transmit groups within their 2241 respected 'AND' or 'OR' rules. 2243 As an example say that we have a simple network as represented in 2244 Figure 17, and we want to enable PREOF between an ingress node I and 2245 an egress node E. 2247 +-+ +-+ 2248 -- |A| ------ |C| -- 2249 / +-+ +-+ \ 2250 / \ 2251 +-+ +-+ 2252 |I| |E| 2253 +-+ +-+ 2254 \ / 2255 \ +-+ +-+ / 2256 -- |B| ------- |D| -- 2257 +-+ +-+ 2259 Figure 17: Scheduling PREOF on a Simple Network 2261 The assumption for this particular problem is that a 6TiSCH node has 2262 a single radio, so it cannot perform 2 receive and/or transmit 2263 operations at the same time, even on 2 different channels. 2265 Say we have 6 possible channels, and at least 10 timeslots per 2266 slotframe. Figure 18 shows a possible schedule whereby each 2267 transmission is retried 2 or 3 times, and redundant copies are 2268 forwarded in parallel via A and C on the one hand, and B and D on the 2269 other, providing time diversity, spatial diversity though different 2270 physical paths, and frequency diversity. 2272 slotOffset 0 1 2 3 4 5 6 7 9 2273 +----+----+----+----+----+----+----+----+----+ 2274 channelOffset 0 | | | | | | |B->D| | | ... 2275 +----+----+----+----+----+----+----+----+----+ 2276 channelOffset 1 | |I->A| |A->C|B->D| | | | | ... 2277 +----+----+----+----+----+----+----+----+----+ 2278 channelOffset 2 |I->A| | |I->B| |C->E| |D->E| | ... 2279 +----+----+----+----+----+----+----+----+----+ 2280 channelOffset 3 | | | | |A->C| | | | | ... 2281 +----+----+----+----+----+----+----+----+----+ 2282 channelOffset 4 | | |I->B| | |B->D| | |D->E| ... 2283 +----+----+----+----+----+----+----+----+----+ 2284 channelOffset 5 | | |A->C| | | |C->E| | | ... 2285 +----+----+----+----+----+----+----+----+----+ 2287 Figure 18: Example Global Schedule 2289 This translates in a different slotframe for every node that provides 2290 the waking and sleeping times, and the channelOffset to be used when 2291 awake. Figure 19 shows the corresponding slotframe for node A. 2293 slotOffset 0 1 2 3 4 5 6 7 9 2294 +----+----+----+----+----+----+----+----+----+ 2295 operation |rcv |rcv |xmit|xmit|xmit|none|none|none|none| ... 2296 +----+----+----+----+----+----+----+----+----+ 2297 channelOffset | 2 | 1 | 5 | 1 | 3 |N/A |N/A |N/A |N/A | ... 2298 +----+----+----+----+----+----+----+----+----+ 2300 Figure 19: Example Slotframe for Node A 2302 The logical relationship between the timeslots is given by the 2303 following table: 2305 +------+---------------------+------------------------+ 2306 | Node | rcv slotOffset | xmit slotOffset | 2307 +------+---------------------+------------------------+ 2308 | I | N/A | (0 OR 1) AND (2 OR 3) | 2309 | A | (0 OR 1) | (2 OR 3 OR 4) | 2310 | B | (2 OR 3) | (4 OR 5 OR 6) | 2311 | C | (2 OR 3 OR 4) | (5 OR 6) | 2312 | D | (4 OR 5 OR 6) | (7 OR 8) | 2313 | E | (5 OR 6 OR 7 OR 8) | N/A | 2314 +------+---------------------+------------------------+ 2316 Figure 20 2318 5. IANA Considerations 2320 This document does not require IANA action. 2322 6. Security Considerations 2324 The "Minimal Security Framework for 6TiSCH" [MIN-SECURITY] was 2325 optimized for Low-Power and TSCH operations. The reader is 2326 encouraged to review the Security Considerations section of that 2327 document, which discusses 6TiSCH security issues in more details. 2329 6.1. Availability of Remote Services 2331 The operation of 6TiSCH Tracks inherits its high level operation from 2332 DetNet and is subject to the observations in section 5 of [RFC8655]. 2333 The installation and the maintenance of the 6TiSCH Tracks depends on 2334 the availability of a controller with a PCE to compute and push them 2335 in the network. When that connectivity is lost, existing Tracks may 2336 continue to operate until the end of their lifetime, but cannot be 2337 removed or updated, and new Tracks cannot be installed. 2339 In a LLN, the communication with a remote PCE may be slow and 2340 unreactive to rapid changes in the condition of the wireless 2341 communication. An attacker may introduce extra delay by selectively 2342 jamming some packets or some flows. The expectation is that the 2343 6TiSCH Tracks enable enough redundancy to maintain the critical 2344 traffic in operation while new routes are calculated and programmed 2345 into the network. 2347 As with DetNet in general, the communication with the PCE must be 2348 secured and should be protected against DoS attacks, including delay 2349 injection and blackholing attacks, and secured as discussed in the 2350 security considerations defined for Abstraction and Control of 2351 Traffic Engineered Networks (ACTN) in Section 9 of [RFC8453], which 2352 applies equally to DetNet and 6TiSCH. In a similar manner, the 2353 communication with the JRC must be secured and should be protected 2354 against DoS attacks when possible. 2356 6.2. Selective Jamming 2358 The Hopping Sequence of a TSCH network is well-known, meaning that if 2359 a rogue manages to identify a cell of a particular flow, then it may 2360 to selectively jam that cell, without impacting any other traffic. 2361 This attack can be performed at the PHY layer without any knowledge 2362 of the Layer-2 keys, and is very hard to detect and diagnose because 2363 only one flow is impacted. 2365 [I-D.tiloca-6tisch-robust-scheduling] proposes a method to obfuscate 2366 the hopping sequence and make it harder to perpetrate that particular 2367 attack. 2369 6.3. MAC-Layer Security 2371 This architecture operates on IEEE Std. 802.15.4 and expects the 2372 Link-Layer security to be enabled at all times between connected 2373 devices, except for the very first step of the device join process, 2374 where a joining device may need some initial, unsecured exchanges so 2375 as to obtain its initial key material. In a typical deployment, all 2376 joined nodes use the same keys and rekeying needs to be global. 2378 The 6TISCH Architecture relies on the join process to deny 2379 authorization of invalid nodes and preserve the integrity of the 2380 network keys. A rogue that managed to access the network can perform 2381 a large variety of attacks from DoS to injecting forged packets and 2382 routing information. "Zero-trust" properties would be highly 2383 desirable but are mostly not available at the time of this writing. 2384 [AP-ND] is a notable exception that protects the ownership of IPv6 2385 addresses and prevents a rogue node with L2 access from stealing and 2386 injecting traffic on behalf of a legitimate node. 2388 6.4. Time Synchronization 2390 Time Synchronization in TSCH induces another event horizon whereby a 2391 node will only communicate with another node if they are synchronized 2392 within a guard time. The pledge discovers the synchronization of the 2393 network based on the time of reception of the beacon. If an attacker 2394 synchronizes a pledge outside of the guard time of the legitimate 2395 nodes then the pledge will never see a legitimate beacon and may not 2396 discover the attack. 2398 As discussed in [RFC8655], measures must be taken to protect the time 2399 synchronization, and for 6TiSCH this includes ensuring that the 2400 Absolute Slot Number (ASN), which is the node's sense of time, is not 2401 compromised. Once installed and as long as the node is synchronized 2402 to the network, ASN is implicit in the transmissions. 2404 IEEE Std. 802.15.4 [IEEE802154] specifies that in a TSCH network, the 2405 nonce that is used for the computation of the Message Integrity Code 2406 (MIC) to secure Link-Layer frames is composed of the address of the 2407 source of the frame and of the ASN. The standard assumes that the 2408 ASN is distributed securely by other means. The ASN is not passed 2409 explicitly in the data frames and does not constitute a complete 2410 anti-replay protection. It results that upper layer protocols must 2411 provide a way to detect duplicates and cope with them. 2413 If the receiver and the sender have a different sense of ASN, the MIC 2414 will not validate and the frame will be dropped. In that sense, TSCH 2415 induces an event horizon whereby only nodes that have a common sense 2416 of ASN can talk to one another in an authenticated manner. With 2417 6TiSCH, the pledge discovers a tentative ASN in beacons from nodes 2418 that have already joined the network. But even if the beacon can be 2419 authenticated, the ASN cannot be trusted as it could be a replay by 2420 an attacker and thus could announce an ASN that represents a time in 2421 the past. If the pledge uses an ASN that is learned from a replayed 2422 beacon for an encrypted transmission, a nonce-reuse attack becomes 2423 possible and the network keys may be compromised. 2425 6.5. Validating ASN 2427 After obtaining the tentative ASN, a pledge that wishes to join the 2428 6TiSCH network must use a join protocol to obtain its security keys. 2429 The join protocol used in 6TiSCH is the Constrained Join Protocol 2430 (CoJP). In the minimal setting defined in [MIN-SECURITY], the 2431 authentication requires a pre-shared key, based on which a secure 2432 session is derived. The CoJP exchange may also be preceded with a 2433 zero-touch handshake [I-D.ietf-6tisch-dtsecurity-zerotouch-join] in 2434 order to enable pledge joining based on certificates and/or inter- 2435 domain communication. 2437 As detailed in Section 4.2.1, a Join Proxy (JP) helps the pledge for 2438 the join procedure by relaying the link-scope Join Request over the 2439 IP network to a Join Registrar/Coordinator (JRC) that can 2440 authenticate the pledge and validate that it is attached to the 2441 appropriate network. As a result of the CoJP exchange, the pledge is 2442 in possession of a Link-Layer material including keys and a short 2443 address, and if the ASN is known to be correct, all traffic can now 2444 be secured using CCM* [CCMstar] at the Link-Layer. 2446 The authentication steps must be such that they cannot be replayed by 2447 an attacker, and they must not depend on the tentative ASN being 2448 valid. During the authentication, the keying material that the 2449 pledge obtains from the JRC does not provide protection against 2450 spoofed ASN. Once the pledge has obtained the keys to use in the 2451 network, it may still need to verify the ASN. If the nonce used in 2452 the Layer-2 security derives from the extended (MAC-64) address, then 2453 replaying the ASN alone cannot enable a nonce-reuse attack unless the 2454 same node is lost its state with a previous ASN. But if the nonce 2455 derives from the short address (e.g., assigned by the JRC) then the 2456 JRC must ensure that it never assigns short addresses that were 2457 already given to this or other nodes with the same keys. In other 2458 words, the network must be rekeyed before the JRC runs out of short 2459 addresses. 2461 6.6. Network Keying and Rekeying 2463 Section 4.2.1 provides an overview of the CoJP process described in 2464 [MIN-SECURITY] by which an LLN can be assembled in the field, having 2465 been provisioned in a lab. 2466 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] is future work that 2467 preceeds and then leverages the CoJP protocol using the 2468 [I-D.ietf-anima-constrained-voucher] constrained profile of 2469 [I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI). This later work 2470 requires a yet-to-be standardized Lighweight Authenticated Key 2471 Exchange protocol. 2473 The CoJP protocol results in distribution of a network-wide key that 2474 is to be used with [IEEE802154] security. The details of use are 2475 described in [MIN-SECURITY] sections 9.2 and 9.3.2. 2477 The BRSKI mechanism may lead to the use of the CoJP protocol, in 2478 which case it also results in distribution of a network-wide key. 2479 Alternatively the BRSKI mechanism may be followed by use of 2480 [I-D.ietf-ace-coap-est] to enroll certificates for each device. In 2481 that case, the certificates may be used with an [IEEE802154] key 2482 agreement protocol. The description of this mechanism, while 2483 conceptually straight forward still has significant standardization 2484 hurdles to pass. 2486 [MIN-SECURITY] section 9.2 describes a mechanism to change (rekey) 2487 the network. There are a number of reasons to initiate a network 2488 rekey: to remove unwanted (corrupt/malicious) nodes, to recover 2489 unused 2-byte short addresses, or due to limits in encryption 2490 algorithms. For all of the mechanisms that distribute a network-wide 2491 key, rekeying is also needed on a periodic basis. In more details: 2493 * The mechanism described in [MIN-SECURITY] section 9.2 requires 2494 advance communication between the JRC and every one of the nodes 2495 before the key change. Given that many nodes may be sleepy, this 2496 operation may take a significant amount of time, and may consume a 2497 significant portion of the available bandwidth. As such, network- 2498 wide rekeys in order to exclude nodes that have become malicious 2499 will not be particularly quick. If a rekey is already in 2500 progress, but the unwanted node has not yet been updated, then it 2501 is possible to to just continue the operation. If the unwanted 2502 node has already received the update, then the rekey operation 2503 will need to be restarted. 2505 * The cryptographic mechanisms used by IEEE Std. 802.15.4 include 2506 the 2-byte short address in the calculation of the context. A 2507 nonce-reuse attack may become feasible if a short address is 2508 reassigned to another node while the same network-wide keys are in 2509 operation. A network that gains and loses nodes on a regular 2510 basis is likely to reach the 65536 limit of the 2-byte (16-bit) 2511 short addresses, even if the network has only a few thousand 2512 nodes. Network planners should consider the need to rekey the 2513 network on a periodic basis in order to recover 2-byte addresses. 2514 The rekey can update the short addresses for active nodes if 2515 desired, but there is actually no need to do this as long as the 2516 key has been changed. 2518 * With TSCH as it stands at the time of this writing, the ASN will 2519 wrap after 2^40 timeslot durations, which means with the default 2520 values around 350 years. Wrapping ASN is not expected to happen 2521 within the lifetime of most LLNs. Yet, should the ASN wrap, the 2522 network must be rekeyed to avoid a nonce-reuse attack. 2524 * Many cipher algorithms have some suggested limits on how many 2525 bytes should be encrypted with that algorithm before a new key is 2526 used. These numbers are typically in the many to hundreds of 2527 gigabytes of data. On very fast backbone networks this becomes an 2528 important concern. On LLNs with typical data rates in the 2529 kilobits/second, this concern is significantly less. With IEEE 2530 Std. 802.15.4 as it stands at the time of this writing, the ASN 2531 will wrap before the limits of the current L2 crypto (AES-CCM-128) 2532 are reached, so the problem should never occur. 2534 * In any fashion, if the LLN is expected to operate continuously for 2535 decades then the operators are advised to plan for the need to 2536 rekey. 2538 Except for urgent rekeys caused by malicious nodes, the rekey 2539 operation described in [MIN-SECURITY] can be done as a background 2540 task and can be done incrementally. It is a make-before-break 2541 mechanism. The switch over to the new key is not signaled by time, 2542 but rather by observation that the new key is in use. As such, the 2543 update can take as long as needed, or occur in as short a time as 2544 practical. 2546 7. Acknowledgments 2548 7.1. Contributors 2550 The co-authors of this document are listed below: 2552 Thomas Watteyne for his contribution to the whole design, in 2553 particular on TSCH and security, and to the open source community 2554 with openWSN that he created. 2556 Xavier Vilajosana who lead the design of the minimal support with 2557 RPL and contributed deeply to the 6top design and the G-MPLS 2558 operation of Track switching; 2560 Kris Pister for creating TSCH and his continuing guidance through 2561 the elaboration of this design; 2563 Malisa Vucinic for the work on the one-touch join process and his 2564 contribution to the Security Design Team; 2566 Michael Richardson for his leadership role in the Security Design 2567 Team and his contribution throughout this document; 2569 Tero Kivinen for his contribution to the security work in general 2570 and the security section in particular. 2572 Maria Rita Palattella for managing the Terminology document merged 2573 into this through the work of 6TiSCH; 2575 Simon Duquennoy for his contribution to the open source community 2576 with the 6TiSCH implementaton of contiki, and for his contribution 2577 to MSF and autonomous unicast cells. 2579 Qin Wang who lead the design of the 6top sublayer and contributed 2580 related text that was moved and/or adapted in this document; 2582 Rene Struik for the security section and his contribution to the 2583 Security Design Team; 2585 Robert Assimiti for his breakthrough work on RPL over TSCH and 2586 initial text and guidance; 2588 7.2. Special Thanks 2590 Special thanks to Jonathan Simon, Giuseppe Piro, Subir Das and 2591 Yoshihiro Ohba for their deep contribution to the initial security 2592 work, to Yasuyuki Tanaka for his work on implementation and 2593 simulation that tremendously helped build a robust system, to Diego 2594 Dujovne for starting and leading the SF0 effort and to Tengfei Chang 2595 for evolving it in the MSF. 2597 Special thanks also to Pat Kinney, Charlie Perkins and Bob Heile for 2598 their support in maintaining the connection active and the design in 2599 line with work happening at IEEE 802.15. 2601 Special thanks to Ted Lemon who was the INT Area A-D while this 2602 document was initiated for his great support and help throughout, and 2603 to Suresh Krishnan who took over with that kind efficiency of his 2604 till publication. 2606 Also special thanks to Ralph Droms who performed the first INT Area 2607 Directorate review, that was very deep and thorough and radically 2608 changed the orientations of this document, and then to Eliot Lear and 2609 Carlos Pignataro who help finalize this document in preparation to 2610 the IESG reviews, and to Gorry Fairhurst, David Mandelberg, Qin Wu, 2611 Francis Dupont, Eric Vyncke, Mirja Kuhlewind, Roman Danyliw, Benjamin 2612 Kaduk and Andrew Malis, who contributed to the final shaping of this 2613 document through the IESG review procedure. 2615 7.3. And Do not Forget 2617 This document is the result of multiple interactions, in particular 2618 during the 6TiSCH (bi)Weekly Interim call, relayed through the 6TiSCH 2619 mailing list at the IETF, over the course of more than 5 years. 2621 The authors wish to thank in arbitrary order: Alaeddine Weslati, 2622 Chonggang Wang, Georgios Exarchakos, Zhuo Chen, Georgios 2623 Papadopoulos, Eric Levy-Abegnoli, Alfredo Grieco, Bert Greevenbosch, 2624 Cedric Adjih, Deji Chen, Martin Turon, Dominique Barthel, Elvis 2625 Vogli, Geraldine Texier, Guillaume Gaillard, Herman Storey, Kazushi 2626 Muraoka, Ken Bannister, Kuor Hsin Chang, Laurent Toutain, Maik 2627 Seewald, Michael Behringer, Nancy Cam Winget, Nicola Accettura, 2628 Nicolas Montavont, Oleg Hahm, Patrick Wetterwald, Paul Duffy, Peter 2629 van der Stock, Rahul Sen, Pieter de Mil, Pouria Zand, Rouhollah 2630 Nabati, Rafa Marin-Lopez, Raghuram Sudhaakar, Sedat Gormus, Shitanshu 2631 Shah, Steve Simlo, Tina Tsou, Tom Phinney, Xavier Lagrange, Ines 2632 Robles and Samita Chakrabarti for their participation and various 2633 contributions. 2635 8. Normative References 2637 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2638 DOI 10.17487/RFC0768, August 1980, 2639 . 2641 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2642 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2643 DOI 10.17487/RFC4861, September 2007, 2644 . 2646 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2647 Address Autoconfiguration", RFC 4862, 2648 DOI 10.17487/RFC4862, September 2007, 2649 . 2651 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2652 "Transmission of IPv6 Packets over IEEE 802.15.4 2653 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 2654 . 2656 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 2657 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 2658 DOI 10.17487/RFC6282, September 2011, 2659 . 2661 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 2662 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 2663 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 2664 Low-Power and Lossy Networks", RFC 6550, 2665 DOI 10.17487/RFC6550, March 2012, 2666 . 2668 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 2669 and D. Barthel, "Routing Metrics Used for Path Calculation 2670 in Low-Power and Lossy Networks", RFC 6551, 2671 DOI 10.17487/RFC6551, March 2012, 2672 . 2674 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 2675 Protocol for Low-Power and Lossy Networks (RPL)", 2676 RFC 6552, DOI 10.17487/RFC6552, March 2012, 2677 . 2679 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 2680 Power and Lossy Networks (RPL) Option for Carrying RPL 2681 Information in Data-Plane Datagrams", RFC 6553, 2682 DOI 10.17487/RFC6553, March 2012, 2683 . 2685 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 2686 Routing Header for Source Routes with the Routing Protocol 2687 for Low-Power and Lossy Networks (RPL)", RFC 6554, 2688 DOI 10.17487/RFC6554, March 2012, 2689 . 2691 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 2692 Bormann, "Neighbor Discovery Optimization for IPv6 over 2693 Low-Power Wireless Personal Area Networks (6LoWPANs)", 2694 RFC 6775, DOI 10.17487/RFC6775, November 2012, 2695 . 2697 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 2698 Application Protocol (CoAP)", RFC 7252, 2699 DOI 10.17487/RFC7252, June 2014, 2700 . 2702 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 2703 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 2704 RFC 8025, DOI 10.17487/RFC8025, November 2016, 2705 . 2707 [RFC8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information 2708 Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May 2709 2017, . 2711 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 2712 "IPv6 over Low-Power Wireless Personal Area Network 2713 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 2714 April 2017, . 2716 [RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal 2717 IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) 2718 Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180, 2719 May 2017, . 2721 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2722 (IPv6) Specification", STD 86, RFC 8200, 2723 DOI 10.17487/RFC8200, July 2017, 2724 . 2726 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 2727 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 2728 DOI 10.17487/RFC8480, November 2018, 2729 . 2731 [RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for 2732 Abstraction and Control of TE Networks (ACTN)", RFC 8453, 2733 DOI 10.17487/RFC8453, August 2018, 2734 . 2736 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 2737 Perkins, "Registration Extensions for IPv6 over Low-Power 2738 Wireless Personal Area Network (6LoWPAN) Neighbor 2739 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 2740 . 2742 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 2743 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2744 2014, . 2746 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 2747 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 2748 Internet of Things (IoT): Problem Statement", RFC 7554, 2749 DOI 10.17487/RFC7554, May 2015, 2750 . 2752 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2753 Constrained-Node Networks", RFC 7228, 2754 DOI 10.17487/RFC7228, May 2014, 2755 . 2757 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 2758 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 2759 September 2010, . 2761 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 2762 "Deterministic Networking Architecture", RFC 8655, 2763 DOI 10.17487/RFC8655, October 2019, 2764 . 2766 [MIN-SECURITY] 2767 Vucinic, M., Simon, J., Pister, K., and M. Richardson, 2768 "Minimal Security Framework for 6TiSCH", Work in Progress, 2769 Internet-Draft, draft-ietf-6tisch-minimal-security-12, 29 2770 July 2019, . 2773 [6BBR-DRAFT] 2774 Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 2775 Backbone Router", Work in Progress, Internet-Draft, draft- 2776 ietf-6lo-backbone-router-13, 26 September 2019, 2777 . 2780 [RECOV-FRAG] 2781 Thubert, P., "6LoWPAN Selective Fragment Recovery", Work 2782 in Progress, Internet-Draft, draft-ietf-6lo-fragment- 2783 recovery-05, 22 July 2019, . 2786 [MIN-FRAG] Watteyne, T., Bormann, C., and P. Thubert, "6LoWPAN 2787 Fragment Forwarding", Work in Progress, Internet-Draft, 2788 draft-ietf-6lo-minimal-fragment-04, 2 September 2019, 2789 . 2792 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 2793 "Address Protected Neighbor Discovery for Low-power and 2794 Lossy Networks", Work in Progress, Internet-Draft, draft- 2795 ietf-6lo-ap-nd-12, 10 April 2019, 2796 . 2798 [USEofRPLinfo] 2799 Robles, I., Richardson, M., and P. Thubert, "Using RPL 2800 Option Type, Routing Header for Source Routes and IPv6-in- 2801 IPv6 encapsulation in the RPL Data Plane", Work in 2802 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-31, 2803 7 August 2019, . 2806 [RUL-DRAFT] 2807 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 2808 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 2809 leaves-04, 9 September 2019, . 2812 [ENH-BEACON] 2813 Dujovne, D. and M. Richardson, "IEEE802.15.4 Informational 2814 Element encapsulation of 6tisch Join and Enrollment 2815 Information", Work in Progress, Internet-Draft, draft- 2816 ietf-6tisch-enrollment-enhanced-beacon-05, 16 September 2817 2019, . 2820 [MSF] Chang, T., Vucinic, M., Vilajosana, X., Duquennoy, S., and 2821 D. Dujovne, "6TiSCH Minimal Scheduling Function (MSF)", 2822 Work in Progress, Internet-Draft, draft-ietf-6tisch-msf- 2823 07, 17 October 2019, 2824 . 2826 9. Informative References 2828 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2829 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2830 . 2832 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2833 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2834 2011, . 2836 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2837 "Definition of the Differentiated Services Field (DS 2838 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2839 DOI 10.17487/RFC2474, December 1998, 2840 . 2842 [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol 2843 Extensions for IPv6 Inter-Domain Routing", RFC 2545, 2844 DOI 10.17487/RFC2545, March 1999, 2845 . 2847 [RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. 2848 Thubert, "Network Mobility (NEMO) Basic Support Protocol", 2849 RFC 3963, DOI 10.17487/RFC3963, January 2005, 2850 . 2852 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2853 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2854 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2855 . 2857 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2858 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2859 2006, . 2861 [RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between 2862 Information Models and Data Models", RFC 3444, 2863 DOI 10.17487/RFC3444, January 2003, 2864 . 2866 [RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 2867 Bosch, "Next Steps in Signaling (NSIS): Framework", 2868 RFC 4080, DOI 10.17487/RFC4080, June 2005, 2869 . 2871 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2872 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2873 Overview, Assumptions, Problem Statement, and Goals", 2874 RFC 4919, DOI 10.17487/RFC4919, August 2007, 2875 . 2877 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 2878 DOI 10.17487/RFC4903, June 2007, 2879 . 2881 [RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS 2882 Signaling Layer Protocol (NSLP) for Quality-of-Service 2883 Signaling", RFC 5974, DOI 10.17487/RFC5974, October 2010, 2884 . 2886 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2887 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2888 January 2012, . 2890 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 2891 Locator/ID Separation Protocol (LISP)", RFC 6830, 2892 DOI 10.17487/RFC6830, January 2013, 2893 . 2895 [RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S., 2896 Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software- 2897 Defined Networking (SDN): Layers and Architecture 2898 Terminology", RFC 7426, DOI 10.17487/RFC7426, January 2899 2015, . 2901 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 2902 Statement and Requirements for IPv6 over Low-Power 2903 Wireless Personal Area Network (6LoWPAN) Routing", 2904 RFC 6606, DOI 10.17487/RFC6606, May 2012, 2905 . 2907 [I-D.ietf-roll-rpl-industrial-applicability] 2908 Phinney, T., Thubert, P., and R. Assimiti, "RPL 2909 applicability in industrial networks", Work in Progress, 2910 Internet-Draft, draft-ietf-roll-rpl-industrial- 2911 applicability-02, 21 October 2013, 2912 . 2915 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] 2916 Richardson, M., "6tisch Zero-Touch Secure Join protocol", 2917 Work in Progress, Internet-Draft, draft-ietf-6tisch- 2918 dtsecurity-zerotouch-join-04, 8 July 2019, 2919 . 2922 [I-D.ietf-core-object-security] 2923 Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 2924 "Object Security for Constrained RESTful Environments 2925 (OSCORE)", Work in Progress, Internet-Draft, draft-ietf- 2926 core-object-security-16, 6 March 2019, 2927 . 2930 [I-D.ietf-manet-aodvv2] 2931 Perkins, C., Ratliff, S., Dowdell, J., Steenbrink, L., and 2932 V. Mercieca, "Ad Hoc On-demand Distance Vector Version 2 2933 (AODVv2) Routing", Work in Progress, Internet-Draft, 2934 draft-ietf-manet-aodvv2-16, 4 May 2016, 2935 . 2937 [RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases", 2938 RFC 8578, DOI 10.17487/RFC8578, May 2019, 2939 . 2941 [I-D.ietf-detnet-ip] 2942 Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A., 2943 Bryant, S., and J. Korhonen, "DetNet Data Plane: IP", Work 2944 in Progress, Internet-Draft, draft-ietf-detnet-ip-01, 1 2945 July 2019, 2946 . 2948 [I-D.ietf-anima-bootstrapping-keyinfra] 2949 Pritikin, M., Richardson, M., Eckert, T., Behringer, M., 2950 and K. Watsen, "Bootstrapping Remote Secure Key 2951 Infrastructures (BRSKI)", Work in Progress, Internet- 2952 Draft, draft-ietf-anima-bootstrapping-keyinfra-28, 19 2953 September 2019, . 2956 [I-D.ietf-roll-aodv-rpl] 2957 Anamalamudi, S., Zhang, M., Perkins, C., Anand, S., and B. 2958 Liu, "Asymmetric AODV-P2P-RPL in Low-Power and Lossy 2959 Networks (LLNs)", Work in Progress, Internet-Draft, draft- 2960 ietf-roll-aodv-rpl-07, 12 April 2019, 2961 . 2963 [I-D.ietf-lwig-6lowpan-virtual-reassembly] 2964 Bormann, C. and T. Watteyne, "Virtual reassembly buffers 2965 in 6LoWPAN", Work in Progress, Internet-Draft, draft-ietf- 2966 lwig-6lowpan-virtual-reassembly-01, 11 March 2019, 2967 . 2970 [I-D.ietf-roll-dao-projection] 2971 Thubert, P., Jadhav, R., Gillmore, M., and J. Pylakutty, 2972 "Root initiated routing state in RPL", Work in Progress, 2973 Internet-Draft, draft-ietf-roll-dao-projection-06, 24 May 2974 2019, . 2977 [I-D.rahul-roll-mop-ext] 2978 Jadhav, R. and P. Thubert, "RPL Mode of Operation 2979 extension", Work in Progress, Internet-Draft, draft-rahul- 2980 roll-mop-ext-01, 9 June 2019, 2981 . 2983 [I-D.selander-ace-cose-ecdhe] 2984 Selander, G., Mattsson, J., and F. Palombini, "Ephemeral 2985 Diffie-Hellman Over COSE (EDHOC)", Work in Progress, 2986 Internet-Draft, draft-selander-ace-cose-ecdhe-14, 11 2987 September 2019, . 2990 [I-D.thubert-roll-bier] 2991 Thubert, P., "RPL-BIER", Work in Progress, Internet-Draft, 2992 draft-thubert-roll-bier-02, 24 July 2018, 2993 . 2995 [I-D.thubert-bier-replication-elimination] 2996 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 2997 TE extensions for Packet Replication and Elimination 2998 Function (PREF) and OAM", Work in Progress, Internet- 2999 Draft, draft-thubert-bier-replication-elimination-03, 3 3000 March 2018, . 3003 [I-D.thubert-6lo-bier-dispatch] 3004 Thubert, P., Brodard, Z., Jiang, H., and G. Texier, "A 3005 6loRH for BitStrings", Work in Progress, Internet-Draft, 3006 draft-thubert-6lo-bier-dispatch-06, 28 January 2019, 3007 . 3010 [I-D.thubert-6man-unicast-lookup] 3011 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 3012 Unicast Lookup", Work in Progress, Internet-Draft, draft- 3013 thubert-6man-unicast-lookup-00, 29 July 2019, 3014 . 3017 [I-D.pthubert-raw-problem-statement] 3018 Thubert, P. and G. Papadopoulos, "Reliable and Available 3019 Wireless Problem Statement", Work in Progress, Internet- 3020 Draft, draft-pthubert-raw-problem-statement-03, 8 October 3021 2019, . 3024 [I-D.tiloca-6tisch-robust-scheduling] 3025 Tiloca, M., Duquennoy, S., and G. Dini, "Robust Scheduling 3026 against Selective Jamming in 6TiSCH Networks", Work in 3027 Progress, Internet-Draft, draft-tiloca-6tisch-robust- 3028 scheduling-02, 10 June 2019, . 3031 [I-D.ietf-ace-coap-est] 3032 Stok, P., Kampanakis, P., Richardson, M., and S. Raza, 3033 "EST over secure CoAP (EST-coaps)", Work in Progress, 3034 Internet-Draft, draft-ietf-ace-coap-est-15, 1 October 3035 2019, 3036 . 3038 [I-D.ietf-anima-constrained-voucher] 3039 Richardson, M., Stok, P., and P. Kampanakis, "Constrained 3040 Voucher Artifacts for Bootstrapping Protocols", Work in 3041 Progress, Internet-Draft, draft-ietf-anima-constrained- 3042 voucher-05, 8 July 2019, . 3045 [IEEE802154] 3046 IEEE standard for Information Technology, "IEEE Std. 3047 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 3048 and Physical Layer (PHY) Specifications for Low-Rate 3049 Wireless Personal Area Networks", October 2019. 3051 [CCMstar] Struik, R., "Formal Specification of the CCM* Mode of 3052 Operation", September 2004, . 3056 [IEEE802154e] 3057 IEEE standard for Information Technology, "IEEE standard 3058 for Information Technology, IEEE Std. 802.15.4, Part. 3059 15.4: Wireless Medium Access Control (MAC) and Physical 3060 Layer (PHY) Specifications for Low-Rate Wireless Personal 3061 Area Networks, June 2011 as amended by IEEE Std. 3062 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area 3063 Networks (LR-WPANs) Amendment 1: MAC sublayer", April 3064 2012. 3066 [WirelessHART] 3067 www.hartcomm.org, "Industrial Communication Networks - 3068 Wireless Communication Network and Communication Profiles 3069 - WirelessHART - IEC 62591", 2010. 3071 [HART] www.hartcomm.org, "Highway Addressable remote Transducer, 3072 a group of specifications for industrial process and 3073 control devices administered by the HART Foundation", 3074 October 2019. 3076 [ISA100.11a] 3077 ISA/ANSI, "Wireless Systems for Industrial Automation: 3078 Process Control and Related Applications - ISA100.11a-2011 3079 - IEC 62734", 2011, . 3082 [ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation", 3083 October 2019, . 3085 [TEAS] IETF, "Traffic Engineering Architecture and Signaling", 3086 October 2019, 3087 . 3089 [ANIMA] IETF, "Autonomic Networking Integrated Model and 3090 Approach", October 2019, 3091 . 3093 [PCE] IETF, "Path Computation Element", October 2019, 3094 . 3096 [CCAMP] IETF, "Common Control and Measurement Plane", October 3097 2019, 3098 . 3100 [AMI] US Department of Energy, "Advanced Metering Infrastructure 3101 and Customer Systems", 2006, 3102 . 3105 [S-ALOHA] Roberts, L. G., "ALOHA Packet System With and Without 3106 Slots and Capture", doi 10.1145/1024916.1024920, April 3107 1975, . 3109 [IEC62439] IEC, "Industrial communication networks - High 3110 availability automation networks - Part 3: Parallel 3111 Redundancy Protocol (PRP) and High-availability Seamless 3112 Redundancy (HSR) - IEC62439-3", 2012, 3113 . 3115 Appendix A. Related Work In Progress 3117 This document has been incremented as the work progressed following 3118 the evolution of the WG charter and the availability of dependent 3119 work. The intent was to publish when the WG concludes on the covered 3120 items. At the time of publishing the following specification are 3121 still in progress and may affect the evolution of the stack in a 3122 6TiSCH-aware node. 3124 A.1. Unchartered IETF work items 3126 A.1.1. 6TiSCH Zerotouch security 3128 The security model and in particular the zerotouch join process 3129 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] depends on the ANIMA 3130 [ANIMA] Bootstrapping Remote Secure Key Infrastructures (BRSKI) 3131 [I-D.ietf-anima-bootstrapping-keyinfra] to enable zero-touch security 3132 provisionning; for highly constrained nodes, a minimal model based on 3133 pre-shared keys (PSK) is also available. As written to this day, it 3134 also depends on a number of documents in progress as CORE, and on 3135 "Ephemeral Diffie-Hellman Over COSE (EDHOC)" 3136 [I-D.selander-ace-cose-ecdhe], which is being considered for adoption 3137 at the LAKE WG. 3139 A.1.2. 6TiSCH Track Setup 3141 ROLL is now standardizing a reactive routing protocol based on RPL 3142 [I-D.ietf-roll-aodv-rpl] The need of a reactive routing protocol to 3143 establish on-demand constraint-optimized routes and a reservation 3144 protocol to establish Layer-3 Tracks is being discussed at 6TiSCH but 3145 not chartered for. 3147 At the time of this writing, there is new work planned in the IETF to 3148 provide limited deterministic networking capabilities for wireless 3149 networks with a focus on forwarding behaviors to react quickly and 3150 locally to the changes as described in 3151 [I-D.pthubert-raw-problem-statement]. 3153 ROLL is also standardizing an extension to RPL to setup centrally- 3154 computed routes [I-D.ietf-roll-dao-projection] 3156 The 6TiSCH Architecture should thus inherit from the DetNet [RFC8655] 3157 architecture and thus depends on it. The Path Computation Element 3158 (PCE) should be a core component of that architecture. An extension 3159 to RPL or to TEAS [TEAS] will be required to expose the 6TiSCH node 3160 capabilities and the network peers to the PCE, possibly in 3161 combination with [I-D.rahul-roll-mop-ext]. A protocol such as a 3162 lightweight PCEP or an adaptation of CCAMP [CCAMP] G-MPLS formats and 3163 procedures could be used in combination to 3164 [I-D.ietf-roll-dao-projection] to install the Tracks, as computed by 3165 the PCE, to the 6TiSCH nodes. 3167 A.1.3. Using BIER in a 6TiSCH Network 3169 ROLL is actively working on Bit Index Explicit Replication (BIER) as 3170 a method to compress both the dataplane packets and the routing 3171 tables in storing mode [I-D.thubert-roll-bier]. 3173 BIER could also be used in the context of the DetNet service layer. 3174 BIER-TE-based OAM, Replication and Elimination 3175 [I-D.thubert-bier-replication-elimination] leverages BIER Traffic 3176 Engineering (TE) to control in the data plane the DetNet Replication 3177 and Elimination activities, and to provide traceability on links 3178 where replication and loss happen, in a manner that is abstract to 3179 the forwarding information. 3181 a 6loRH for BitStrings [I-D.thubert-6lo-bier-dispatch] proposes a 3182 6LoWPAN compression for the BIER Bitstring based on 6LoWPAN Routing 3183 Header [RFC8138]. 3185 A.2. External (non-IETF) work items 3187 The current charter positions 6TiSCH on IEEE Std. 802.15.4 only. 3188 Though most of the design should be portable on other link types, 3189 6TiSCH has a strong dependency on IEEE Std. 802.15.4 and its 3190 evolution. The impact of changes to TSCH on this Architecture should 3191 be minimal to non-existent, but deeper work such as 6top and security 3192 may be impacted. A 6TiSCH Interest Group at the IEEE maintains the 3193 synchronization and helps foster work at the IEEE should 6TiSCH 3194 demand it. 3196 Work is being proposed at IEEE (802.15.12 PAR) for an LLC that would 3197 logically include the 6top sublayer. The interaction with the 6top 3198 sublayer and the Scheduling Functions described in this document are 3199 yet to be defined. 3201 ISA100 [ISA100] Common Network Management (CNM) is another external 3202 work of interest for 6TiSCH. The group, referred to as ISA100.20, 3203 defines a Common Network Management framework that should enable the 3204 management of resources that are controlled by heterogeneous 3205 protocols such as ISA100.11a [ISA100.11a], WirelessHART 3206 [WirelessHART], and 6TiSCH. Interestingly, the establishment of 3207 6TiSCH Deterministic paths, called Tracks, are also in scope, and 3208 ISA100.20 is working on requirements for DetNet. 3210 Author's Address 3212 Pascal Thubert (editor) 3213 Cisco Systems, Inc 3214 Building D, 45 Allee des Ormes - BP1200 3215 06254 Mougins - Sophia Antipolis 3216 France 3218 Phone: +33 497 23 26 34 3219 Email: pthubert@cisco.com