idnits 2.17.1 draft-ietf-6tisch-architecture-29.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 2558 has weird spacing: '...atteyne for h...' == Line 2562 has weird spacing: '...ajosana who l...' == Line 2566 has weird spacing: '... Pister for c...' == Line 2569 has weird spacing: '...Vucinic for t...' == Line 2572 has weird spacing: '...hardson for h...' == (6 more instances...) -- The document date (27 August 2020) is 1339 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-44) exists of draft-ietf-roll-useofrplinfo-40 == Outdated reference: A later version (-30) exists of draft-ietf-roll-unaware-leaves-18 == Outdated reference: A later version (-18) exists of draft-ietf-6tisch-msf-17 -- Obsolete informational reference (is this intentional?): RFC 6347 (Obsoleted by RFC 9147) -- Obsolete informational reference (is this intentional?): RFC 6830 (Obsoleted by RFC 9300, RFC 9301) == Outdated reference: A later version (-45) exists of draft-ietf-anima-bootstrapping-keyinfra-43 == Outdated reference: A later version (-18) exists of draft-ietf-roll-aodv-rpl-08 == Outdated reference: A later version (-34) exists of draft-ietf-roll-dao-projection-10 == Outdated reference: A later version (-24) exists of draft-ietf-anima-constrained-voucher-08 Summary: 0 errors (**), 0 flaws (~~), 14 warnings (==), 3 comments (--). 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 27 August 2020 5 Expires: 28 February 2021 7 An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4 8 draft-ietf-6tisch-architecture-29 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 28 February 2021. 35 Copyright Notice 37 Copyright (c) 2020 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 . . . . . . . . . . . . . 16 60 3.4. Scheduling TSCH . . . . . . . . . . . . . . . . . . . . . 17 61 3.5. Distributed vs. Centralized Routing . . . . . . . . . . . 18 62 3.6. Forwarding Over TSCH . . . . . . . . . . . . . . . . . . 19 63 3.7. 6TiSCH Stack . . . . . . . . . . . . . . . . . . . . . . 20 64 3.8. Communication Paradigms and Interaction Models . . . . . 22 65 4. Architecture Components . . . . . . . . . . . . . . . . . . . 23 66 4.1. 6LoWPAN (and RPL) . . . . . . . . . . . . . . . . . . . . 23 67 4.1.1. RPL-Unaware Leaves and 6LoWPAN ND . . . . . . . . . . 23 68 4.1.2. 6LBR and RPL Root . . . . . . . . . . . . . . . . . . 24 69 4.2. Network Access and Addressing . . . . . . . . . . . . . . 24 70 4.2.1. Join Process . . . . . . . . . . . . . . . . . . . . 25 71 4.2.2. Registration . . . . . . . . . . . . . . . . . . . . 27 72 4.3. TSCH and 6top . . . . . . . . . . . . . . . . . . . . . . 28 73 4.3.1. 6top . . . . . . . . . . . . . . . . . . . . . . . . 28 74 4.3.2. Scheduling Functions and the 6top protocol . . . . . 30 75 4.3.3. 6top and RPL Objective Function operations . . . . . 31 76 4.3.4. Network Synchronization . . . . . . . . . . . . . . . 32 77 4.3.5. Slotframes and CDU matrix . . . . . . . . . . . . . . 33 78 4.3.6. Distributing the reservation of cells . . . . . . . . 34 79 4.4. Schedule Management Mechanisms . . . . . . . . . . . . . 35 80 4.4.1. Static Scheduling . . . . . . . . . . . . . . . . . . 35 81 4.4.2. Neighbor-to-neighbor Scheduling . . . . . . . . . . . 36 82 4.4.3. Remote Monitoring and Schedule Management . . . . . . 37 83 4.4.4. Hop-by-hop Scheduling . . . . . . . . . . . . . . . . 39 84 4.5. On Tracks . . . . . . . . . . . . . . . . . . . . . . . . 39 85 4.5.1. General Behavior of Tracks . . . . . . . . . . . . . 40 86 4.5.2. Serial Track . . . . . . . . . . . . . . . . . . . . 40 87 4.5.3. Complex Track with Replication and Elimination . . . 41 88 4.5.4. DetNet End-to-end Path . . . . . . . . . . . . . . . 41 89 4.5.5. Cell Reuse . . . . . . . . . . . . . . . . . . . . . 42 90 4.6. Forwarding Models . . . . . . . . . . . . . . . . . . . . 43 91 4.6.1. Track Forwarding . . . . . . . . . . . . . . . . . . 43 92 4.6.2. IPv6 Forwarding . . . . . . . . . . . . . . . . . . . 46 93 4.6.3. Fragment Forwarding . . . . . . . . . . . . . . . . . 47 94 4.7. Advanced 6TiSCH Routing . . . . . . . . . . . . . . . . . 48 95 4.7.1. Packet Marking and Handling . . . . . . . . . . . . . 48 96 4.7.2. Replication, Retries and Elimination . . . . . . . . 49 98 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 52 99 6. Security Considerations . . . . . . . . . . . . . . . . . . . 52 100 6.1. Availability of Remote Services . . . . . . . . . . . . . 52 101 6.2. Selective Jamming . . . . . . . . . . . . . . . . . . . . 52 102 6.3. MAC-Layer Security . . . . . . . . . . . . . . . . . . . 53 103 6.4. Time Synchronization . . . . . . . . . . . . . . . . . . 53 104 6.5. Validating ASN . . . . . . . . . . . . . . . . . . . . . 54 105 6.6. Network Keying and Rekeying . . . . . . . . . . . . . . . 55 106 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 56 107 7.1. Contributors . . . . . . . . . . . . . . . . . . . . . . 56 108 7.2. Special Thanks . . . . . . . . . . . . . . . . . . . . . 57 109 7.3. And Do not Forget . . . . . . . . . . . . . . . . . . . . 58 110 8. Normative References . . . . . . . . . . . . . . . . . . . . 58 111 9. Informative References . . . . . . . . . . . . . . . . . . . 62 112 Appendix A. Related Work In Progress . . . . . . . . . . . . . . 69 113 A.1. Unchartered IETF work items . . . . . . . . . . . . . . . 69 114 A.1.1. 6TiSCH Zerotouch security . . . . . . . . . . . . . . 69 115 A.1.2. 6TiSCH Track Setup . . . . . . . . . . . . . . . . . 69 116 A.1.3. Using BIER in a 6TiSCH Network . . . . . . . . . . . 70 117 A.2. External (non-IETF) work items . . . . . . . . . . . . . 70 118 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 71 120 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 457 (E)ARO: (Extended) Address Registration Option 459 (E)DAR: (Extended) Duplicate Address Request 461 (E)DAC: (Extended) Duplicate Address Confirmation 463 DAD: Duplicate Address Detection 465 DODAG: Destination-Oriented Directed Acyclic Graph 467 LLN: Low-Power and Lossy Network (a typical IoT network) 469 NA: Neighbor Advertisement 471 NCE: Neighbor Cache Entry 473 ND: Neighbor Discovery 475 NDP: Neighbor Discovery Protocol 477 PCE: Path Computation Element 479 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], 505 "Terms Used in Routing for Low-Power and Lossy Networks (LLNs)" 506 [RFC7102], 508 and RPL "Objective Function Zero for the Routing Protocol for 509 Low-Power and Lossy Networks (RPL)" [RFC6552], and "RPL: IPv6 510 Routing Protocol for Low-Power and Lossy Networks" [RFC6550]. 512 Other terms in use in LLNs are found in "Terminology for 513 Constrained-Node Networks" [RFC7228]. 515 Readers are expected to be familiar with all the terms and concepts 516 that are discussed in 518 * "Neighbor Discovery for IP version 6" [RFC4861], and "IPv6 519 Stateless Address Autoconfiguration" [RFC4862]. 521 In addition, readers would benefit from reading: 523 * "Problem Statement and Requirements for IPv6 over Low-Power 524 Wireless Personal Area Network (6LoWPAN) Routing" [RFC6606], 526 * "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. 997 Management mechanisms for the TSCH schedule at Link-Layer (one-hop), 998 Network-layer (multihop along a Track), and Application-layer (remote 999 control) are discussed in Section 4.4. Link-Layer frame forwarding 1000 interactions are discussed in Section 4.6, and Network-layer Packet 1001 routing is addressed in Section 4.7. 1003 4. Architecture Components 1005 4.1. 6LoWPAN (and RPL) 1007 A RPL DODAG is formed of a Root, a collection of routers, and leaves 1008 that are hosts. Hosts are nodes which do not forward packets that 1009 they did not generate. RPL-aware leaves will participate to RPL to 1010 advertise their own addresses, whereas RPL-unaware leaves depend on a 1011 connected RPL router to do so. RPL interacts with 6LoWPAN ND at 1012 multiple levels, in particular at the Root and in the RPL-unaware 1013 leaves. 1015 4.1.1. RPL-Unaware Leaves and 6LoWPAN ND 1017 RPL needs a set of information to advertise a leaf node through a 1018 Destination Advertisement Object (DAO) message and establish 1019 reachability. 1021 "Routing for RPL Leaves" [RUL-DRAFT] details the basic interaction of 1022 6LoWPAN ND and RPL and enables a plain 6LN that supports [RFC8505] to 1023 obtain return connectivity via the RPL network as an RPL-unaware 1024 leaf. The leaf indicates that it requires reachability services for 1025 the Registered Address from a Routing Registrar by setting a 'R' flag 1026 in the Extended Address Registration Option [RFC8505], and it 1027 provides a TID that maps to a sequence number in section 7 of RPL 1028 [RFC6550]. 1030 [RUL-DRAFT] also enables the leaf to signal the RPL InstanceID that 1031 it wants to participate to using the Opaque field of the EARO. On 1032 the backbone, the InstanceID is expected to be mapped to an overlay 1033 that matches the RPL Instance, e.g., a Virtual LAN (VLAN) or a 1034 virtual routing and forwarding (VRF) instance. 1036 Though at the time of this writing the above specification enables a 1037 model where the separation is possible, this architecture recommends 1038 to collocate the functions of 6LBR and RPL Root. 1040 4.1.2. 6LBR and RPL Root 1042 With the 6LowPAN ND [RFC6775], information on the 6LBR is 1043 disseminated via an Authoritative Border Router Option (ABRO) in RA 1044 messages. [RFC8505] extends [RFC6775] to enable a registration for 1045 routing and proxy ND. The capability to support [RFC8505] is 1046 indicated in the 6LoWPAN Capability Indication Option (6CIO). The 1047 discovery and liveliness of the RPL Root are obtained through RPL 1048 [RFC6550] itself. 1050 When 6LoWPAN ND is coupled with RPL, the 6LBR and RPL Root 1051 functionalities are co-located in order that the address of the 6LBR 1052 be indicated by RPL DIO messages and to associate the unique ID from 1053 the EDAR/EDAC [RFC8505] exchange with the state that is maintained by 1054 RPL. 1056 Section 7 of [RUL-DRAFT] specifies how the DAO messages are used to 1057 reconfirm the registration, thus eliminating a duplication of 1058 functionality between DAO and EDAR/EDAC messages, as illustrated in 1059 Figure 7. [RUL-DRAFT] also provides the protocol elements that are 1060 needed when the 6LBR and RPL Root functionalities are not co-located. 1062 Even though the Root of the RPL network is integrated with the 6LBR, 1063 it is logically separated from the Backbone Router (6BBR) that is 1064 used to connect the 6TiSCH LLN to the backbone. This way, the Root 1065 has all information from 6LoWPAN ND and RPL about the LLN devices 1066 attached to it. 1068 This architecture also expects that the Root of the RPL network 1069 (proxy-)registers the 6TiSCH nodes on their behalf to the 6BBR, for 1070 whatever operation the 6BBR performs on the backbone, such as ND 1071 proxy, or redistribution in a routing protocol. This relies on an 1072 extension of the 6LoWPAN ND registration described in [6BBR-DRAFT]. 1074 This model supports the movement of a 6TiSCH device across the Multi- 1075 Link Subnet, and allows the proxy registration of 6TiSCH nodes deep 1076 into the 6TiSCH LLN by the 6LBR / RPL Root. This is why in [RFC8505] 1077 the Registered Address is signaled in the Target Address field of the 1078 NS message as opposed to the IPv6 Source Address, which, in the case 1079 of a proxy registration, is that of the 6LBR / RPL Root itself. 1081 4.2. Network Access and Addressing 1082 4.2.1. Join Process 1084 A new device, called the pledge, undergoes the join protocol to 1085 become a node in a 6TiSCH network. This usually occurs only once 1086 when the device is first powered on. The pledge communicates with 1087 the Join Registrar/Coordinator (JRC) of the network through a Join 1088 Proxy (JP), a radio neighbor of the pledge. 1090 The JP is discovered though MAC layer beacons. When multiple JPs 1091 from possibly multiple networks are visible, trial and error till an 1092 acceptable position in the right network is obtained becomes 1093 ineffficient. [ENH-BEACON] adds a new subtype in the Information 1094 Element that was delegated to the IETF [RFC8137] and provides 1095 visibility on the network that can be joined and the willingness by 1096 the JP and the Root to be used by the pledge. 1098 The join protocol provides the following functionality: 1100 * Mutual authentication 1102 * Authorization 1104 * Parameter distribution to the pledge over a secure channel 1106 Minimal Security Framework for 6TiSCH [MIN-SECURITY] defines the 1107 minimal mechanisms required for this join process to occur in a 1108 secure manner. The specification defines the Constrained Join 1109 Protocol (CoJP) that is used to distribute the parameters to the 1110 pledge over a secure session established through OSCORE 1111 [I-D.ietf-core-object-security], and a secure configuration of the 1112 network stack. In the minimal setting with pre-shared keys (PSKs), 1113 CoJP allows the pledge to join after a single round-trip exchange 1114 with the JRC. The provisioning of the PSK to the pledge and the JRC 1115 needs to be done out of band, through a 'one-touch' bootstrapping 1116 process, which effectively enrolls the pledge into the domain managed 1117 by the JRC. 1119 In certain use cases, the 'one touch' bootstrapping is not feasible 1120 due to the operational constraints and the enrollment of the pledge 1121 into the domain needs to occur in-band. This is handled through a 1122 'zero-touch' extension of the Minimal Security Framework for 6TiSCH. 1123 Zero touch [I-D.ietf-6tisch-dtsecurity-zerotouch-join] extension 1124 leverages the 'Bootstrapping Remote Secure Key Infrastructures 1125 (BRSKI)' [[I-D.ietf-anima-bootstrapping-keyinfra] work to establish a 1126 shared secret between a pledge and the JRC without necessarily having 1127 them belong to a common (security) domain at join time. This happens 1128 through inter-domain communication occurring between the JRC of the 1129 network and the domain of the pledge, represented by a fourth entity, 1130 Manufacturer Authorized Signing Authority (MASA). Once the zero- 1131 touch exchange completes, the CoJP exchange defined in [MIN-SECURITY] 1132 is carried over the secure session established between the pledge and 1133 the JRC. 1135 Figure 5 depicts the join process and where a Link-Local Address 1136 (LLA) is used, versus a Global Unicast Address (GUA). 1138 6LoWPAN Node 6LR 6LBR Join Registrar MASA 1139 (pledge) (Join Proxy) (Root) /Coordinator (JRC) 1140 | | | | | 1141 | 6LoWPAN ND |6LoWPAN ND+RPL | IPv6 network |IPv6 network | 1142 | LLN link |Route-Over mesh|(the Internet)|(the Internet)| 1143 | | | | | 1144 | Layer-2 | | | | 1145 |enhanced beacon| | | | 1146 |<--------------| | | | 1147 | | | | | 1148 | NS (EARO) | | | | 1149 | (for the LLA) | | | | 1150 |-------------->| | | | 1151 | NA (EARO) | | | | 1152 |<--------------| | | | 1153 | | | | | 1154 | (Zero-touch | | | | 1155 | handshake) | (Zero-touch handshake) | (Zero-touch | 1156 | using LLA | using GUA | handshake) | 1157 |<------------->|<---------------------------->|<------------>| 1158 | | | | | 1159 | CoJP Join Req | | | | \ 1160 | using LLA | | | | | 1161 |-------------->| | | | | 1162 | | CoJP Join Request | | | 1163 | | using GUA | | | 1164 | |----------------------------->| | | C 1165 | | | | | | o 1166 | | CoJP Join Response | | | J 1167 | | using GUA | | | P 1168 | |<-----------------------------| | | 1169 |CoJP Join Resp | | | | | 1170 | using LLA | | | | | 1171 |<--------------| | | | / 1172 | | | | | 1174 Figure 5: Join process in a Multi-Link Subnet. Parentheses () 1175 denote optional exchanges. 1177 4.2.2. Registration 1179 Once the pledge successfully completes the CoJP protocol and becomes 1180 a network node, it obtains the network prefix from neighboring 1181 routers and registers its IPv6 addresses. As detailed in 1182 Section 4.1, the combined 6LoWPAN ND 6LBR and Root of the RPL network 1183 learn information such as the device Unique ID (from 6LoWPAN ND) and 1184 the updated Sequence Number (from RPL), and perform 6LoWPAN ND proxy 1185 registration to the 6BBR of behalf of the LLN nodes. 1187 Figure 6 illustrates the initial IPv6 signaling that enables a 6LN to 1188 form a global address and register it to a 6LBR using 6LoWPAN ND 1189 [RFC8505], is then carried over RPL to the RPL Root, and then to the 1190 6BBR. This flow happens just once when the address is created and 1191 first registered. 1193 6LoWPAN Node 6LR 6LBR 6BBR 1194 (RPL leaf) (router) (Root) 1195 | | | | 1196 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 1197 | LLN link |Route-Over mesh|Ethernet/serial| Backbone 1198 | | | | 1199 | RS (mcast) | | | 1200 |-------------->| | | 1201 |-----------> | | | 1202 |------------------> | | 1203 | RA (unicast) | | | 1204 |<--------------| | | 1205 | | | | 1206 | NS(EARO) | | | 1207 |-------------->| | | 1208 | 6LoWPAN ND | Extended DAR | | 1209 | |-------------->| | 1210 | | | NS(EARO) | 1211 | | |-------------->| 1212 | | | | NS-DAD 1213 | | | |------> 1214 | | | | (EARO) 1215 | | | | 1216 | | | NA(EARO) | 1217 | | |<--------------| 1218 | | Extended DAC | | 1219 | |<--------------| | 1220 | NA(EARO) | | | 1221 |<--------------| | | 1222 | | | | 1224 Figure 6: Initial Registration Flow over Multi-Link Subnet 1226 Figure 7 illustrates the repeating IPv6 signaling that enables a 6LN 1227 to keep a global address alive and registered to its 6LBR using 1228 6LoWPAN ND to the 6LR, RPL to the RPL Root, and then 6LoWPAN ND again 1229 to the 6BBR, which avoids repeating the Extended DAR/DAC flow across 1230 the network when RPL can suffice as a keep-alive mechanism. 1232 6LoWPAN Node 6LR 6LBR 6BBR 1233 (RPL leaf) (router) (Root) 1234 | | | | 1235 | 6LoWPAN ND |6LoWPAN ND+RPL | 6LoWPAN ND | IPv6 ND 1236 | LLN link |Route-Over mesh| ant IPv6 link | Backbone 1237 | | | 1238 | | | | 1239 | NS(EARO) | | | 1240 |-------------->| | | 1241 | NA(EARO) | | | 1242 |<--------------| | | 1243 | | DAO | | 1244 | |-------------->| | 1245 | | DAO-ACK | | 1246 | |<--------------| | 1247 | | | NS(EARO) | 1248 | | |-------------->| 1249 | | | NA(EARO) | 1250 | | |<--------------| 1251 | | | | 1252 | | | | 1254 Figure 7: Next Registration Flow over Multi-Link Subnet 1256 As the network builds up, a node should start as a leaf to join the 1257 RPL network, and may later turn into both a RPL-capable router and a 1258 6LR, so as to accept leaf nodes to recursively join the network. 1260 4.3. TSCH and 6top 1262 4.3.1. 6top 1264 6TiSCH expects a high degree of scalability together with a 1265 distributed routing functionality based on RPL. To achieve this 1266 goal, the spectrum must be allocated in a way that allows for spatial 1267 reuse between zones that will not interfere with one another. In a 1268 large and spatially distributed network, a 6TiSCH node is often in a 1269 good position to determine usage of the spectrum in its vicinity. 1271 With 6TiSCH, the abstraction of an IPv6 link is implemented as a pair 1272 of bundles of cells, one in each direction. IP Links are only 1273 enabled between RPL parents and children. The 6TiSCH operation is 1274 optimal when the size of a bundle is such that both the energy wasted 1275 in idle listening and the packet drops due to congestion loss are 1276 minimized, while packets are forwarded within an acceptable latency. 1278 Use cases for distributed routing are often associated with a 1279 statistical distribution of best-effort traffic with variable needs 1280 for bandwidth on each individual link. The 6TiSCH operation can 1281 remain optimal if RPL parents can adjust dynamically, and with enough 1282 reactivity to match the variations of best-effort traffic, the amount 1283 of bandwidth that is used to communicate between themselves and their 1284 children, in both directions. In turn, the agility to fulfill the 1285 needs for additional cells improves when the number of interactions 1286 with other devices and the protocol latencies are minimized. 1288 6top is a logical link control sitting between the IP layer and the 1289 TSCH MAC layer, which provides the link abstraction that is required 1290 for IP operations. The 6top protocol, 6P, which is specified in 1291 [RFC8480], is one of the services provided by 6top. In particular, 1292 the 6top services are available over a management API that enables an 1293 external management entity to schedule cells and slotframes, and 1294 allows the addition of complementary functionality, for instance a 1295 Scheduling Function that manages a dynamic schedule management based 1296 on observed resource usage as discussed in Section 4.4.2. For this 1297 purpose, the 6TiSCH architecture differentiates "soft" cells and 1298 "hard" cells. 1300 4.3.1.1. Hard Cells 1302 "Hard" cells are cells that are owned and managed by a separate 1303 scheduling entity (e.g., a PCE) that specifies the slotOffset/ 1304 channelOffset of the cells to be added/moved/deleted, in which case 1305 6top can only act as instructed, and may not move hard cells in the 1306 TSCH schedule on its own. 1308 4.3.1.2. Soft Cells 1310 In contrast, "soft" cells are cells that 6top can manage locally. 1311 6top contains a monitoring process which monitors the performance of 1312 cells, and can add, remove soft cells in the TSCH schedule to adapt 1313 to the traffic needs, or move one when it performs poorly. To 1314 reserve a soft cell, the higher layer does not indicate the exact 1315 slotOffset/channelOffset of the cell to add, but rather the resulting 1316 bandwidth and QoS requirements. When the monitoring process triggers 1317 a cell reallocation, the two neighbor devices communicating over this 1318 cell negotiate its new position in the TSCH schedule. 1320 4.3.2. Scheduling Functions and the 6top protocol 1322 In the case of soft cells, the cell management entity that controls 1323 the dynamic attribution of cells to adapt to the dynamics of variable 1324 rate flows is called a Scheduling Function (SF). 1326 There may be multiple SFs with more or less aggressive reaction to 1327 the dynamics of the network. 1329 An SF may be seen as divided between an upper bandwidth adaptation 1330 logic that is not aware of the particular technology that is used to 1331 obtain and release bandwidth, and an underlying service that maps 1332 those needs in the actual technology, which means mapping the 1333 bandwidth onto cells in the case of TSCH using the 6top protocol as 1334 illustrated in Figure 8. 1336 +------------------------+ +------------------------+ 1337 | Scheduling Function | | Scheduling Function | 1338 | Bandwidth adaptation | | Bandwidth adaptation | 1339 +------------------------+ +------------------------+ 1340 | Scheduling Function | | Scheduling Function | 1341 | TSCH mapping to cells | | TSCH mapping to cells | 1342 +------------------------+ +------------------------+ 1343 | 6top cells negotiation | <- 6P -> | 6top cells negotiation | 1344 +------------------------+ +------------------------+ 1345 Device A Device B 1347 Figure 8: SF/6P stack in 6top 1349 The SF relies on 6top services that implement the 6top Protocol (6P) 1350 [RFC8480] to negotiate the precise cells that will be allocated or 1351 freed based on the schedule of the peer. It may be for instance that 1352 a peer wants to use a particular time slot that is free in its 1353 schedule, but that timeslot is already in use by the other peer for a 1354 communication with a third party on a different cell. 6P enables the 1355 peers to find an agreement in a transactional manner that ensures the 1356 final consistency of the nodes state. 1358 [MSF] is one of the possible scheduling functions. MSF uses the 1359 rendez-vous slot from [RFC8180] for network discovery, neighbor 1360 discovery, and any other broadcast. 1362 For basic unicast communication with any neighbor, each node uses a 1363 receive cell at a well-known slotOffset/channelOffset, derived from a 1364 hash of their own MAC address. Nodes can reach any neighbor by 1365 installing a transmit (shared) cell with slotOffset/channelOffset 1366 derived from the neighbor's MAC address. 1368 For child-parent links, MSF continuously monitors the load to/from 1369 parents and children. It then uses 6P to install/remove unicast 1370 cells whenever the current schedule appears to be under-/over- 1371 provisioned. 1373 4.3.3. 6top and RPL Objective Function operations 1375 An implementation of a RPL [RFC6550] Objective Function (OF), such as 1376 the RPL Objective Function Zero (OF0) [RFC6552] that is used in the 1377 Minimal 6TiSCH Configuration [RFC8180] to support RPL over a static 1378 schedule, may leverage, for its internal computation, the information 1379 maintained by 6top. 1381 An OF may require metrics about reachability, such as the Expected 1382 Transmission Count (ETX) metric [RFC6551]. 6top creates and 1383 maintains an abstract neighbor table, and this state may be leveraged 1384 to feed an OF and/or store OF information as well. A neighbor table 1385 entry may contain a set of statistics with respect to that specific 1386 neighbor. 1388 The neighbor information may include the time when the last packet 1389 has been received from that neighbor, a set of cell quality metrics, 1390 e.g., received signal strength indication (RSSI) or link quality 1391 indicator (LQI), the number of packets sent to the neighbor or the 1392 number of packets received from it. This information can be made 1393 available through 6top management APIs and used for instance to 1394 compute a Rank Increment that will determine the selection of the 1395 preferred parent. 1397 6top provides statistics about the underlying layer so the OF can be 1398 tuned to the nature of the TSCH MAC layer. 6top also enables the RPL 1399 OF to influence the MAC behavior, for instance by configuring the 1400 periodicity of IEEE Std. 802.15.4 Extended Beacons (EBs). By 1401 augmenting the EB periodicity, it is possible to change the network 1402 dynamics so as to improve the support of devices that may change 1403 their point of attachment in the 6TiSCH network. 1405 Some RPL control messages, such as the DODAG Information Object (DIO) 1406 are ICMPv6 messages that are broadcast to all neighbor nodes. With 1407 6TiSCH, the broadcast channel requirement is addressed by 6top by 1408 configuring TSCH to provide a broadcast channel, as opposed to, for 1409 instance, piggybacking the DIO messages in Layer-2 Enhanced Beacons 1410 (EBs), which would produce undue timer coupling among layers, packet 1411 size issues and could conflict with the policy of production networks 1412 where EBs are mostly eliminated to conserve energy. 1414 4.3.4. Network Synchronization 1416 Nodes in a TSCH network must be time synchronized. A node keeps 1417 synchronized to its time source neighbor through a combination of 1418 frame-based and acknowledgment-based synchronization. To maximize 1419 battery life and network throughput, it is advisable that RPL ICMP 1420 discovery and maintenance traffic (governed by the trickle timer) be 1421 somehow coordinated with the transmission of time synchronization 1422 packets (especially with enhanced beacons). 1424 This could be achieved through an interaction of the 6top sublayer 1425 and the RPL objective Function, or could be controlled by a 1426 management entity. 1428 Time distribution requires a loop-free structure. Nodes taken in a 1429 synchronization loop will rapidly desynchronize from the network and 1430 become isolated. 6TiSCH uses a RPL DAG with a dedicated global 1431 Instance for the purpose of time synchronization. That Instance is 1432 referred to as the Time Synchronization Global Instance (TSGI). The 1433 TSGI can be operated in either of the 3 modes that are detailed in 1434 section 3.1.3 of RPL [RFC6550], "Instances, DODAGs, and DODAG 1435 Versions". Multiple uncoordinated DODAGs with independent Roots may 1436 be used if all the Roots share a common time source such as the 1437 Global Positioning System (GPS). 1439 In the absence of a common time source, the TSGI should form a single 1440 DODAG with a virtual Root. A backbone network is then used to 1441 synchronize and coordinate RPL operations between the backbone 1442 routers that act as sinks for the LLN. Optionally, RPL's periodic 1443 operations may be used to transport the network synchronization. 1444 This may mean that 6top would need to trigger (override) the trickle 1445 timer if no other traffic has occurred for such a time that nodes may 1446 get out of synchronization. 1448 A node that has not joined the TSGI advertises a MAC level Join 1449 Priority of 0xFF to notify its neighbors that is not capable of 1450 serving as time parent. A node that has joined the TSGI advertises a 1451 MAC level Join Priority set to its DAGRank() in that Instance, where 1452 DAGRank() is the operation specified in section 3.5.1 of [RFC6550], 1453 "Rank Comparison". 1455 The provisioning of a RPL Root is out of scope for both RPL and this 1456 Architecture, whereas RPL enables to propagate configuration 1457 information down the DODAG. This applies to the TSGI as well; a Root 1458 is configured or obtains by unspecified means the knowledge of the 1459 RPLInstanceID for the TSGI. The Root advertises its DagRank in the 1460 TSGI, that must be less than 0xFF, as its Join Priority in its IEEE 1461 Std. 802.15.4 Extended Beacons (EB). 1463 A node that reads a Join Priority of less than 0xFF should join the 1464 neighbor with the lesser Join Priority and use it as time parent. If 1465 the node is configured to serve as time parent, then the node should 1466 join the TSGI, obtain a Rank in that Instance and start advertising 1467 its own DagRank in the TSGI as its Join Priority in its EBs. 1469 4.3.5. Slotframes and CDU matrix 1471 6TiSCH enables IPv6 best effort (stochastic) transmissions over a MAC 1472 layer that is also capable of scheduled (deterministic) 1473 transmissions. A window of time is defined around the scheduled 1474 transmission where the medium must, as much as practically feasible, 1475 be free of contending energy to ensure that the medium is free of 1476 contending packets when time comes for a scheduled transmission. One 1477 simple way to obtain such a window is to format time and frequencies 1478 in cells of transmission of equal duration. This is the method that 1479 is adopted in IEEE Std. 802.15.4 TSCH as well as the Long Term 1480 Evolution (LTE) of cellular networks. 1482 The 6TiSCH architecture defines a global concept that is called a 1483 Channel Distribution and Usage (CDU) matrix to describe that 1484 formatting of time and frequencies, 1486 A CDU matrix is defined centrally as part of the network definition. 1487 It is a matrix of cells with a height equal to the number of 1488 available channels (indexed by ChannelOffsets) and a width (in 1489 timeslots) that is the period of the network scheduling operation 1490 (indexed by slotOffsets) for that CDU matrix. There are different 1491 models for scheduling the usage of the cells, which place the 1492 responsibility of avoiding collisions either on a central controller 1493 or on the devices themselves, at an extra cost in terms of energy to 1494 scan for free cells (more in Section 4.4). 1496 The size of a cell is a timeslot duration, and values of 10 to 15 1497 milliseconds are typical in 802.15.4 TSCH to accommodate for the 1498 transmission of a frame and an ack, including the security validation 1499 on the receive side which may take up to a few milliseconds on some 1500 device architecture. 1502 A CDU matrix iterates over and over with a well-known channel 1503 rotation called the hopping sequence. In a given network, there 1504 might be multiple CDU matrices that operate with different width, so 1505 they have different durations and represent different periodic 1506 operations. It is recommended that all CDU matrices in a 6TiSCH 1507 domain operate with the same cell duration and are aligned, so as to 1508 reduce the chances of interferences from the Slotted ALOHA 1509 operations. The knowledge of the CDU matrices is shared between all 1510 the nodes and used in particular to define slotframes. 1512 A slotframe is a MAC-level abstraction that is common to all nodes 1513 and contains a series of timeslots of equal length and precedence. 1514 It is characterized by a slotframe_ID, and a slotframe_size. A 1515 slotframe aligns to a CDU matrix for its parameters, such as number 1516 and duration of timeslots. 1518 Multiple slotframes can coexist in a node schedule, i.e., a node can 1519 have multiple activities scheduled in different slotframes. A 1520 slotframe is associated with a priority that may be related to the 1521 precedence of different 6TiSCH topologies. The slotframes may be 1522 aligned to different CDU matrices and thus have different width. 1523 There is typically one slotframe for scheduled traffic that has the 1524 highest precedence and one or more slotframe(s) for RPL traffic. The 1525 timeslots in the slotframe are indexed by the SlotOffset; the first 1526 cell is at SlotOffset 0. 1528 When a packet is received from a higher layer for transmission, 6top 1529 inserts that packet in the outgoing queue which matches the packet 1530 best (Differentiated Services [RFC2474] can therefore be used). At 1531 each scheduled transmit slot, 6top looks for the frame in all the 1532 outgoing queues that best matches the cells. If a frame is found, it 1533 is given to the TSCH MAC for transmission. 1535 4.3.6. Distributing the reservation of cells 1537 The 6TiSCH architecture introduces the concept of chunks 1538 (Section 2.1) to distribute the allocation of the spectrum for a 1539 whole group of cells at a time. The CDU matrix is formatted into a 1540 set of chunks, possibly as illustrated in Figure 9, each of the 1541 chunks identified uniquely by a chunk-ID. The knowledge of this 1542 formatting is shared between all the nodes in a 6TiSCH network. It 1543 could be conveyed during the join process, or codified into a profile 1544 document, or obtained using some other mechanism. This is as opposed 1545 to static scheduling that refers to the pre-programmed mechanism that 1546 is specified in [RFC8180] and pre-exists to the distribution of the 1547 chunk formatting. 1549 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1550 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1551 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1552 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1553 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1554 ... 1555 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1556 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1557 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1558 0 1 2 3 4 5 6 M 1560 Figure 9: CDU matrix Partitioning in Chunks 1562 The 6TiSCH Architecture envisions a protocol that enables chunk 1563 ownership appropriation whereby a RPL parent discovers a chunk that 1564 is not used in its interference domain, claims the chunk, and then 1565 defends it in case another RPL parent would attempt to appropriate it 1566 while it is in use. The chunk is the basic unit of ownership that is 1567 used in that process. 1569 As a result of the process of chunk ownership appropriation, the RPL 1570 parent has exclusive authority to decide which cell in the 1571 appropriated chunk can be used by which node in its interference 1572 domain. In other words, it is implicitly delegated the right to 1573 manage the portion of the CDU matrix that is represented by the 1574 chunk. 1576 Initially, those cells are added to the heap of free cells, then 1577 dynamically placed into existing bundles, in new bundles, or 1578 allocated opportunistically for one transmission. 1580 Note that a PCE is expected to have precedence in the allocation, so 1581 that a RPL parent would only be able to obtain portions that are not 1582 in-use by the PCE. 1584 4.4. Schedule Management Mechanisms 1586 6TiSCH uses 4 paradigms to manage the TSCH schedule of the LLN nodes: 1587 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1588 and scheduling management, and Hop-by-hop scheduling. Multiple 1589 mechanisms are defined that implement the associated Interaction 1590 Models, and can be combined and used in the same LLN. Which 1591 mechanism(s) to use depends on application requirements. 1593 4.4.1. Static Scheduling 1595 In the simplest instantiation of a 6TiSCH network, a common fixed 1596 schedule may be shared by all nodes in the network. Cells are 1597 shared, and nodes contend for slot access in a slotted ALOHA manner. 1599 A static TSCH schedule can be used to bootstrap a network, as an 1600 initial phase during implementation, or as a fall-back mechanism in 1601 case of network malfunction. This schedule is pre-established, for 1602 instance decided by a network administrator based on operational 1603 needs. It can be pre-configured into the nodes, or, more commonly, 1604 learned by a node when joining the network using standard IEEE Std. 1605 802.15.4 Information Elements (IE). Regardless, the schedule remains 1606 unchanged after the node has joined a network. RPL is used on the 1607 resulting network. This "minimal" scheduling mechanism that 1608 implements this paradigm is detailed in [RFC8180]. 1610 4.4.2. Neighbor-to-neighbor Scheduling 1612 In the simplest instantiation of a 6TiSCH network described in 1613 Section 4.4.1, nodes may expect a packet at any cell in the schedule 1614 and will waste energy idle listening. In a more complex 1615 instantiation of a 6TiSCH network, a matching portion of the schedule 1616 is established between peers to reflect the observed amount of 1617 transmissions between those nodes. The aggregation of the cells 1618 between a node and a peer forms a bundle that the 6top layer uses to 1619 implement the abstraction of a link for IP. The bandwidth on that 1620 link is proportional to the number of cells in the bundle. 1622 If the size of a bundle is configured to fit an average amount of 1623 bandwidth, peak traffic is dropped. If the size is configured to 1624 allow for peak emissions, energy is be wasted idle listening. 1626 As discussed in more details in Section 4.3, the 6top Protocol 1627 [RFC8480] specifies the exchanges between neighbor nodes to reserve 1628 soft cells to transmit to one another, possibly under the control of 1629 a Scheduling Function (SF). Because this reservation is done without 1630 global knowledge of the schedule of other nodes in the LLN, 1631 scheduling collisions are possible. 1633 And as discussed in Section 4.3.2, an optional Scheduling Function 1634 (SF) is used to monitor bandwidth usage and perform requests for 1635 dynamic allocation by the 6top sublayer. The SF component is not 1636 part of the 6top sublayer. It may be collocated on the same device 1637 or may be partially or fully offloaded to an external system. The 1638 "6TiSCH Minimal Scheduling Function (MSF)" [MSF] provides a simple 1639 scheduling function that can be used by default by devices that 1640 support dynamic scheduling of soft cells. 1642 Monitoring and relocation is done in the 6top layer. For the upper 1643 layer, the connection between two neighbor nodes appears as a number 1644 of cells. Depending on traffic requirements, the upper layer can 1645 request 6top to add or delete a number of cells scheduled to a 1646 particular neighbor, without being responsible for choosing the exact 1647 slotOffset/channelOffset of those cells. 1649 4.4.3. Remote Monitoring and Schedule Management 1651 Remote monitoring and Schedule Management refers to a DetNet/SDN 1652 model whereby an NME and a scheduling entity, associated with a PCE, 1653 reside in a central controller and interact with the 6top layer to 1654 control IPv6 Links and Tracks (Section 4.5) in a 6TiSCH network. The 1655 composite centralized controller can assign physical resources (e.g., 1656 buffers and hard cells) to a particular Track to optimize the 1657 reliability within a bounded latency for a well-specified flow. 1659 The work at the 6TiSCH WG focused on non-deterministic traffic and 1660 did not provide the generic data model that is necessary for the 1661 controller to monitor and manage resources of the 6top sublayer. 1662 This is deferred to future work, see Appendix A.1.2. 1664 With respect to Centralized routing and scheduling, it is envisioned 1665 that the related component of the 6TiSCH Architecture would be an 1666 extension of the DetNet Architecture [RFC8655], which studies Layer-3 1667 aspects of Deterministic Networks, and covers networks that span 1668 multiple Layer-2 domains. 1670 The DetNet architecture is a form of Software Defined Networking 1671 (SDN) Architecture and is composed of three planes, a (User) 1672 Application Plane, a Controller Plane (where the PCE operates), and a 1673 Network Plane which can represent a 6TiSCH LLN. 1675 Software-Defined Networking (SDN): Layers and Architecture 1676 Terminology [RFC7426] proposes a generic representation of the SDN 1677 architecture that is reproduced in Figure 10. 1679 o--------------------------------o 1680 | | 1681 | +-------------+ +----------+ | 1682 | | Application | | Service | | 1683 | +-------------+ +----------+ | 1684 | Application Plane | 1685 o---------------Y----------------o 1686 | 1687 *-----------------------------Y---------------------------------* 1688 | Network Services Abstraction Layer (NSAL) | 1689 *------Y------------------------------------------------Y-------* 1690 | | 1691 | Service Interface | 1692 | | 1693 o------Y------------------o o---------------------Y------o 1694 | | Control Plane | | Management Plane | | 1695 | +----Y----+ +-----+ | | +-----+ +----Y----+ | 1696 | | Service | | App | | | | App | | Service | | 1697 | +----Y----+ +--Y--+ | | +--Y--+ +----Y----+ | 1698 | | | | | | | | 1699 | *----Y-----------Y----* | | *---Y---------------Y----* | 1700 | | Control Abstraction | | | | Management Abstraction | | 1701 | | Layer (CAL) | | | | Layer (MAL) | | 1702 | *----------Y----------* | | *----------Y-------------* | 1703 | | | | | | 1704 o------------|------------o o------------|---------------o 1705 | | 1706 | CP | MP 1707 | Southbound | Southbound 1708 | Interface | Interface 1709 | | 1710 *------------Y---------------------------------Y----------------* 1711 | Device and resource Abstraction Layer (DAL) | 1712 *------------Y---------------------------------Y----------------* 1713 | | | | 1714 | o-------Y----------o +-----+ o--------Y----------o | 1715 | | Forwarding Plane | | App | | Operational Plane | | 1716 | o------------------o +-----+ o-------------------o | 1717 | Network Device | 1718 +---------------------------------------------------------------+ 1720 Figure 10: SDN Layers and Architecture Terminology per RFC 7426 1722 The PCE establishes end-to-end Tracks of hard cells, which are 1723 described in more details in Section 4.6.1. 1725 The DetNet work is expected to enable end to end Deterministic Path 1726 across heterogeneous network. This can be for instance a 6TiSCH LLN 1727 and an Ethernet Backbone. 1729 This model fits the 6TiSCH extended configuration, whereby a 6BBR 1730 federates multiple 6TiSCH LLN in a single subnet over a backbone that 1731 can be, for instance, Ethernet or Wi-Fi. In that model, 6TiSCH 6BBRs 1732 synchronize with one another over the backbone, so as to ensure that 1733 the multiple LLNs that form the IPv6 subnet stay tightly 1734 synchronized. 1736 If the Backbone is Deterministic, then the Backbone Router ensures 1737 that the end-to-end deterministic behavior is maintained between the 1738 LLN and the backbone. It is the responsibility of the PCE to compute 1739 a deterministic path and to end across the TSCH network and an IEEE 1740 Std. 802.1 TSN Ethernet backbone, and that of DetNet to enable end- 1741 to-end deterministic forwarding. 1743 4.4.4. Hop-by-hop Scheduling 1745 A node can reserve a Track (Section 4.5) to one or more 1746 destination(s) that are multiple hops away by installing soft cells 1747 at each intermediate node. This forms a Track of soft cells. A 1748 Track Scheduling Function above the 6top sublayer of each node on the 1749 Track is needed to monitor these soft cells and trigger relocation 1750 when needed. 1752 This hop-by-hop reservation mechanism is expected to be similar in 1753 essence to [RFC3209] and/or [RFC4080]/[RFC5974]. The protocol for a 1754 node to trigger hop-by-hop scheduling is not yet defined. 1756 4.5. On Tracks 1758 The architecture introduces the concept of a Track, which is a 1759 directed path from a source 6TiSCH node to one or more destination 1760 6TiSCH node(s) across a 6TiSCH LLN. 1762 A Track is the 6TiSCH instantiation of the concept of a Deterministic 1763 Path as described in [RFC8655]. Constrained resources such as memory 1764 buffers are reserved for that Track in intermediate 6TiSCH nodes to 1765 avoid loss related to limited capacity. A 6TiSCH node along a Track 1766 not only knows which bundles of cells it should use to receive 1767 packets from a previous hop, but also knows which bundle(s) it should 1768 use to send packets to its next hop along the Track. 1770 4.5.1. General Behavior of Tracks 1772 A Track is associated with Layer-2 bundles of cells with related 1773 schedules and logical relationships and that ensure that a packet 1774 that is injected in a Track will progress in due time all the way to 1775 destination. 1777 Multiple cells may be scheduled in a Track for the transmission of a 1778 single packet, in which case the normal operation of IEEE Std. 1779 802.15.4 Automatic Repeat-reQuest (ARQ) can take place; the 1780 acknowledgment may be omitted in some cases, for instance if there is 1781 no scheduled cell for a possible retry. 1783 There are several benefits for using a Track to forward a packet from 1784 a source node to the destination node. 1786 1. Track forwarding, as further described in Section 4.6.1, is a 1787 Layer-2 forwarding scheme, which introduces less process delay 1788 and overhead than Layer-3 forwarding scheme. Therefore, LLN 1789 Devices can save more energy and resource, which is critical for 1790 resource constrained devices. 1792 2. Since channel resources, i.e., bundles of cells, have been 1793 reserved for communications between 6TiSCH nodes of each hop on 1794 the Track, the throughput and the maximum latency of the traffic 1795 along a Track are guaranteed and the jitter is maintained small. 1797 3. By knowing the scheduled time slots of incoming bundle(s) and 1798 outgoing bundle(s), 6TiSCH nodes on a Track could save more 1799 energy by staying in sleep state during in-active slots. 1801 4. Tracks are protected from interfering with one another if a cell 1802 is scheduled to belong to at most one Track, and congestion loss 1803 is avoided if at most one packet can be presented to the MAC to 1804 use that cell. Tracks enhance the reliability of transmissions 1805 and thus further improve the energy consumption in LLN Devices by 1806 reducing the chances of retransmission. 1808 4.5.2. Serial Track 1810 A Serial (or simple) Track is the 6TiSCH version of a circuit; a 1811 bundle of cells that are programmed to receive (RX-cells) is uniquely 1812 paired to a bundle of cells that are set to transmit (TX-cells), 1813 representing a Layer-2 forwarding state which can be used regardless 1814 of the network layer protocol. A Serial Track is thus formed end-to- 1815 end as a succession of paired bundles, a receive bundle from the 1816 previous hop and a transmit bundle to the next hop along the Track. 1818 For a given iteration of the device schedule, the effective channel 1819 of the cell is obtained by following in a loop a well-known hopping 1820 sequence that started at Epoch time at the channelOffset of the cell, 1821 which results in a rotation of the frequency that used for 1822 transmission. The bundles may be computed so as to accommodate both 1823 variable rates and retransmissions, so they might not be fully used 1824 in the iteration of the schedule. 1826 4.5.3. Complex Track with Replication and Elimination 1828 The art of Deterministic Networks already include Packet Replication 1829 and Elimination techniques. Example standards include the Parallel 1830 Redundancy Protocol (PRP) and the High-availability Seamless 1831 Redundancy (HSR) [IEC62439]. Similarly, and as opposed to a Serial 1832 Track that is a sequence of nodes and links, a Complex Track is 1833 shaped as a directed acyclic graph towards one or more destination(s) 1834 to support multi-path forwarding and route around failures. 1836 A Complex Track may branch off over non congruent branches for the 1837 purpose of multicasting, and/or redundancy, in which case it 1838 reconverges later down the path. This enables the Packet 1839 Replication, Elimination and Ordering Functions (PREOF) defined by 1840 Detnet. Packet ARQ, Replication, Elimination and Overhearing (PAREO) 1841 adds radio-specific capabilities of Layer-2 ARQ and promiscuous 1842 listening to redundant transmissions to compensate for the lossiness 1843 of the medium and meet industrial expectations of a Reliable and 1844 Available Wireless network. Combining PAREO and PREOF, a Track may 1845 extend beyond the 6TiSCH network in a larger DetNet network. 1847 In the art of TSCH, a path does not necessarily support PRE but it is 1848 almost systematically multi-path. This means that a Track is 1849 scheduled so as to ensure that each hop has at least two forwarding 1850 solutions, and the forwarding decision is to try the preferred one 1851 and use the other in case of Layer-2 transmission failure as detected 1852 by ARQ. Similarly, at each 6TiSCH hop along the Track, the PCE may 1853 schedule more than one timeslot for a packet, so as to support 1854 Layer-2 retries (ARQ). It is also possible that the field device 1855 only uses the second branch if sending over the first branch fails. 1857 4.5.4. DetNet End-to-end Path 1859 Ultimately, DetNet should enable to extend a Track beyond the 6TiSCH 1860 LLN as illustrated in Figure 11. In that example, a Track that is 1861 laid out from a field device in a 6TiSCH network to an IoT gateway 1862 that is located on an 802.1 Time-Sensitive Networking (TSN) backbone. 1863 A 6TiSCH-Aware DetNet Service Layer handles the Packet Replication, 1864 Elimination, and Ordering Functions over the DODAG that forms a 1865 Track. 1867 The Replication function in the 6TiSCH Node sends a copy of each 1868 packet over two different branches, and the PCE schedules each hop of 1869 both branches so that the two copies arrive in due time at the 1870 gateway. In case of a loss on one branch, hopefully the other copy 1871 of the packet still makes it in due time. If two copies make it to 1872 the IoT gateway, the Elimination function in the gateway ignores the 1873 extra packet and presents only one copy to upper layers. 1875 +-=-=-+ 1876 | IoT | 1877 | G/W | 1878 +-=-=-+ 1879 ^ <=== Elimination 1880 Track branch | | 1881 +-=-=-=-+ +-=-=-=-=+ Subnet Backbone 1882 | | 1883 +-=|-=+ +-=|-=+ 1884 | | | Backbone | | | Backbone 1885 o | | | router | | | router 1886 +-=/-=+ +-=|-=+ 1887 o / o o-=-o-=-=/ o 1888 o o-=-o-=/ o o o o o 1889 o \ / o o LLN o 1890 o v <=== Replication 1891 o 1893 Figure 11: Example End-to-End DetNet Track 1895 4.5.5. Cell Reuse 1897 The 6TiSCH architecture provides means to avoid waste of cells as 1898 well as overflows in the transmit bundle of a Track, as follows: 1900 A TX-cell that is not needed for the current iteration may be reused 1901 opportunistically on a per-hop basis for routed packets. When all of 1902 the frame that were received for a given Track are effectively 1903 transmitted, any available TX-cell for that Track can be reused for 1904 upper layer traffic for which the next-hop router matches the next 1905 hop along the Track. In that case, the cell that is being used is 1906 effectively a TX-cell from the Track, but the short address for the 1907 destination is that of the next-hop router. 1909 It results in a frame that is received in a RX-cell of a Track with a 1910 destination MAC address set to this node as opposed to the broadcast 1911 MAC address must be extracted from the Track and delivered to the 1912 upper layer. Note that a frame with an unrecognized destination MAC 1913 address is dropped at the lower MAC layer and thus is not received at 1914 the 6top sublayer. 1916 On the other hand, it might happen that there are not enough TX-cells 1917 in the transmit bundle to accommodate the Track traffic, for instance 1918 if more retransmissions are needed than provisioned. In that case, 1919 and if the frame transports an IPv6 packet, then it can be placed for 1920 transmission in the bundle that is used for Layer-3 traffic towards 1921 the next hop along the Track. The MAC address should be set to the 1922 next-hop MAC address to avoid confusion. 1924 It results in a frame that is received over a Layer-3 bundle may be 1925 in fact associated to a Track. In a classical IP link such as an 1926 Ethernet, off-Track traffic is typically in excess over reservation 1927 to be routed along the non-reserved path based on its QoS setting. 1928 But with 6TiSCH, since the use of the Layer-3 bundle may be due to 1929 transmission failures, it makes sense for the receiver to recognize a 1930 frame that should be re-Tracked, and to place it back on the 1931 appropriate bundle if possible. . A frame is re-Tracked by 1932 scheduling it for transmission over the transmit bundle associated to 1933 the Track, with the destination MAC address set to broadcast. 1935 4.6. Forwarding Models 1937 By forwarding, this document means the per-packet operation that 1938 allows to deliver a packet to a next hop or an upper layer in this 1939 node. Forwarding is based on pre-existing state that was installed 1940 as a result of a routing computation Section 4.7. 6TiSCH supports 1941 three different forwarding model:(G-MPLS) Track Forwarding, 1942 (classical) IPv6 Forwarding and (6LoWPAN) Fragment Forwarding. 1944 4.6.1. Track Forwarding 1946 Forwarding along a Track can be seen as a Generalized Multi-protocol 1947 Label Switching (G-MPLS) operation in that the information used to 1948 switch a frame is not an explicit label, but rather related to other 1949 properties of the way the packet was received, a particular cell in 1950 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1951 Layer-2 security) accepts a frame, that frame can be switched 1952 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1953 fragment, or a frame from an alternate protocol such as WirelessHART 1954 or ISA100.11a. 1956 A data frame that is forwarded along a Track normally has a 1957 destination MAC address that is set to broadcast - or a multicast 1958 address depending on MAC support. This way, the MAC layer in the 1959 intermediate nodes accepts the incoming frame and 6top switches it 1960 without incurring a change in the MAC header. In the case of IEEE 1961 Std. 802.15.4, this means effectively broadcast, so that along the 1962 Track the short address for the destination of the frame is set to 1963 0xFFFF. 1965 There are 2 modes for a Track, an IPv6 native mode and a protocol- 1966 independant 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. 1978 The flow follows a Track which identification is done using a RPL 1979 Instance (see section 3.1.3 of [RFC6550]), signaled in a RPL Packet 1980 Information (more in section 11.2.2.1 of [RFC6550]) and the 1981 destination address in the case of a local instance. One or more 1982 flows may be placed in a same Track and the Track identification 1983 (TrackID) may be placed in an IP-in-IP encapsulation. The forwarding 1984 operation is based on the Track and does not depend on the flow 1985 therein. 1987 The Track identification is validated at egress before restoring the 1988 destination MAC address (DMAC) and punting to the upper layer. 1990 Figure 12 illustrates the Track Forwarding operation which happens at 1991 the 6top sublayer, below IP. 1993 | Packet flowing across the network ^ 1994 +--------------+ | | 1995 | IPv6 | | | 1996 +--------------+ | | 1997 | 6LoWPAN HC | | | 1998 +--------------+ ingress egress 1999 | 6top | sets +----+ +----+ restores 2000 +--------------+ DMAC to | | | | DMAC to 2001 | TSCH MAC | brdcst | | | | dest 2002 +--------------+ | | | | | | 2003 | LLN PHY | +-------+ +--...-----+ +-------+ 2004 +--------------+ 2005 Ingress Relay Relay Egress 2006 Stack Layer Node Node Node Node 2008 Figure 12: Track Forwarding, Native Mode 2010 4.6.1.2. Tunnel Mode 2012 In tunnel mode, the frames originate from an arbitrary protocol over 2013 a compatible MAC that may or may not be synchronized with the 6TiSCH 2014 network. An example of this would be a router with a dual radio that 2015 is capable of receiving and sending WirelessHART or ISA100.11a frames 2016 with the second radio, by presenting itself as an access Point or a 2017 Backbone Router, respectively. In that mode, some entity (e.g., PCE) 2018 can coordinate with a WirelessHART Network Manager or an ISA100.11a 2019 System Manager to specify the flows that are transported. 2021 +--------------+ 2022 | IPv6 | 2023 +--------------+ 2024 | 6LoWPAN HC | 2025 +--------------+ set restore 2026 | 6top | +DMAC+ +DMAC+ 2027 +--------------+ to|brdcst to|nexthop 2028 | TSCH MAC | | | | | 2029 +--------------+ | | | | 2030 | LLN PHY | +-------+ +--...-----+ +-------+ 2031 +--------------+ | ingress egress | 2032 | | 2033 +--------------+ | | 2034 | LLN PHY | | | 2035 +--------------+ | Packet flowing across the network | 2036 | TSCH MAC | | | 2037 +--------------+ | DMAC = | DMAC = 2038 |ISA100/WiHART | | nexthop v nexthop 2039 +--------------+ 2040 Source Ingress Egress Destination 2041 Stack Layer Node Node Node Node 2043 Figure 13: Track Forwarding, Tunnel Mode 2045 In that case, the TrackID that identifies the Track at the ingress 2046 6TiSCH router is derived from the RX-cell. The DMAC is set to this 2047 node but the TrackID indicates that the frame must be tunneled over a 2048 particular Track so the frame is not passed to the upper layer. 2049 Instead, the DMAC is forced to broadcast and the frame is passed to 2050 the 6top sublayer for switching. 2052 At the egress 6TiSCH router, the reverse operation occurs. Based on 2053 tunneling information of the Track, which may for instance indicate 2054 that the tunneled datagram is an IP packet, the datagram is passed to 2055 the appropriate Link-Layer with the destination MAC restored. 2057 4.6.1.3. Tunneling Information 2059 Tunneling information coming with the Track configuration provides 2060 the destination MAC address of the egress endpoint as well as the 2061 tunnel mode and specific data depending on the mode, for instance a 2062 service access point for frame delivery at egress. 2064 If the tunnel egress point does not have a MAC address that matches 2065 the configuration, the Track installation fails. 2067 If the Layer-3 destination address belongs to the tunnel termination, 2068 then it is possible that the IPv6 address of the destination is 2069 compressed at the 6LoWPAN sublayer based on the MAC address. 2070 Restoring the wrong MAC address at the egress would then also result 2071 in the wrong IP address in the packet after decompression. For that 2072 reason, a packet can be injected in a Track only if the destination 2073 MAC address is effectively that of the tunnel egress point. It is 2074 thus mandatory for the ingress router to validate that the MAC 2075 address that was used at the 6LoWPAN sublayer for compression matches 2076 that of the tunnel egress point before it overwrites it to broadcast. 2077 The 6top sublayer at the tunnel egress point reverts that operation 2078 to the MAC address obtained from the tunnel information. 2080 4.6.2. IPv6 Forwarding 2082 As the packets are routed at Layer-3, traditional QoS and Active 2083 Queue Management (AQM) operations are expected to prioritize flows. 2085 | Packet flowing across the network ^ 2086 +--------------+ | | 2087 | IPv6 | | +-QoS+ +-QoS+ | 2088 +--------------+ | | | | | | 2089 | 6LoWPAN HC | | | | | | | 2090 +--------------+ | | | | | | 2091 | 6top | | | | | | | 2092 +--------------+ | | | | | | 2093 | TSCH MAC | | | | | | | 2094 +--------------+ | | | | | | 2095 | LLN PHY | +-------+ +--...-----+ +-------+ 2096 +--------------+ 2097 Source Ingress Egress Destination 2098 Stack Layer Node Router Router Node 2100 Figure 14: IP Forwarding 2102 4.6.3. Fragment Forwarding 2104 Considering that per section 4 of [RFC4944] 6LoWPAN packets can be as 2105 large as 1280 bytes (the IPv6 minimum MTU), and that the non-storing 2106 mode of RPL implies Source Routing that requires space for routing 2107 headers, and that a IEEE Std. 802.15.4 frame with security may carry 2108 in the order of 80 bytes of effective payload, an IPv6 packet might 2109 be fragmented into more than 16 fragments at the 6LoWPAN sublayer. 2111 This level of fragmentation is much higher than that traditionally 2112 experienced over the Internet with IPv4 fragments, where 2113 fragmentation is already known as harmful. 2115 In the case to a multihop route within a 6TiSCH network, Hop-by-Hop 2116 recomposition occurs at each hop to reform the packet and route it. 2117 This creates additional latency and forces intermediate nodes to 2118 store a portion of a packet for an undetermined time, thus impacting 2119 critical resources such as memory and battery. 2121 [MIN-FRAG] describes a framework for forwarding fragments end-to-end 2122 across a 6TiSCH route-over mesh. Within that framework, 2123 [I-D.ietf-lwig-6lowpan-virtual-reassembly] details a virtual 2124 reassembly buffer mechanism whereby the datagram tag in the 6LoWPAN 2125 Fragment is used as a label for switching at the 6LoWPAN sublayer. 2127 Building on this technique, [RECOV-FRAG] introduces a new format for 2128 6LoWPAN fragments that enables the selective recovery of individual 2129 fragments, and allows for a degree of flow control based on an 2130 Explicit Congestion Notification. 2132 | Packet flowing across the network ^ 2133 +--------------+ | | 2134 | IPv6 | | +----+ +----+ | 2135 +--------------+ | | | | | | 2136 | 6LoWPAN HC | | learn learn | 2137 +--------------+ | | | | | | 2138 | 6top | | | | | | | 2139 +--------------+ | | | | | | 2140 | TSCH MAC | | | | | | | 2141 +--------------+ | | | | | | 2142 | LLN PHY | +-------+ +--...-----+ +-------+ 2143 +--------------+ 2144 Source Ingress Egress Destination 2145 Stack Layer Node Router Router Node 2147 Figure 15: Forwarding First Fragment 2149 In that model, the first fragment is routed based on the IPv6 header 2150 that is present in that fragment. The 6LoWPAN sublayer learns the 2151 next hop selection, generates a new datagram tag for transmission to 2152 the next hop, and stores that information indexed by the incoming MAC 2153 address and datagram tag. The next fragments are then switched based 2154 on that stored state. 2156 | Packet flowing across the network ^ 2157 +--------------+ | | 2158 | IPv6 | | | 2159 +--------------+ | | 2160 | 6LoWPAN HC | | replay replay | 2161 +--------------+ | | | | | | 2162 | 6top | | | | | | | 2163 +--------------+ | | | | | | 2164 | TSCH MAC | | | | | | | 2165 +--------------+ | | | | | | 2166 | LLN PHY | +-------+ +--...-----+ +-------+ 2167 +--------------+ 2168 Source Ingress Egress Destination 2169 Stack Layer Node Router Router Node 2171 Figure 16: Forwarding Next Fragment 2173 A bitmap and an ECN echo in the end-to-end acknowledgment enable the 2174 source to resend the missing fragments selectively. The first 2175 fragment may be resent to carve a new path in case of a path failure. 2176 The ECN echo set indicates that the number of outstanding fragments 2177 should be reduced. 2179 4.7. Advanced 6TiSCH Routing 2181 4.7.1. Packet Marking and Handling 2183 All packets inside a 6TiSCH domain must carry the RPLInstanceID that 2184 identifies the 6TiSCH topology (e.g., a Track) that is to be used for 2185 routing and forwarding that packet. The location of that information 2186 must be the same for all packets forwarded inside the domain. 2188 For packets that are routed by a PCE along a Track, the tuple formed 2189 by the IPv6 destination address and a local RPLInstanceID in the 2190 packet forms the TrackID that identify uniquely the Track and 2191 associated transmit bundle. 2193 For packets that are routed by RPL, that information is the 2194 RPLInstanceID which is carried in the RPL Packet Information (RPI), 2195 as discussed in section 11.2 of [RFC6550], "Loop Avoidance and 2196 Detection". The RPI is transported by a RPL option in the IPv6 Hop- 2197 By-Hop Header [RFC6553]. 2199 A compression mechanism for the RPL packet artifacts that integrates 2200 the compression of IP-in-IP encapsulation and the Routing Header type 2201 3 [RFC6554] with that of the RPI in a 6LoWPAN dispatch/header type is 2202 specified in [RFC8025] and [RFC8138]. 2204 Either way, the method and format used for encoding the RPLInstanceID 2205 is generalized to all 6TiSCH topological Instances, which include 2206 both RPL Instances and Tracks. 2208 4.7.2. Replication, Retries and Elimination 2210 6TiSCH supports the PREOF operations of elimination and reordering of 2211 packets along a complex Track, but has no requirement about whether a 2212 sequence number is tagged in the packet for that purpose. With 2213 6TiSCH, the schedule can tell when multiple receive timeslots 2214 correspond to copies of a same packet, in which case the receiver may 2215 avoid listening to the extra copies once it had received one instance 2216 of the packet. 2218 The semantics of the configuration will enable correlated timeslots 2219 to be grouped for transmit (and respectively receive) with a 'OR' 2220 relations, and then a 'AND' relation would be configurable between 2221 groups. The semantics is that if the transmit (and respectively 2222 receive) operation succeeded in one timeslot in a 'OR' group, then 2223 all the other timeslots in the group are ignored. Now, if there are 2224 at least two groups, the 'AND' relation between the groups indicates 2225 that one operation must succeed in each of the groups. 2227 On the transmit side, timeslots provisioned for retries along a same 2228 branch of a Track are placed a same 'OR' group. The 'OR' relation 2229 indicates that if a transmission is acknowledged, then 2230 retransmissions of that packet should not be attempted for remaining 2231 timeslots in that group. There are as many 'OR' groups as there are 2232 branches of the Track departing from this node. Different 'OR' 2233 groups are programmed for the purpose of replication, each group 2234 corresponding to one branch of the Track. The 'AND' relation between 2235 the groups indicates that transmission over any of branches must be 2236 attempted regardless of whether a transmission succeeded in another 2237 branch. It is also possible to place cells to different next-hop 2238 routers in a same 'OR' group. This allows to route along multi-path 2239 Tracks, trying one next-hop and then another only if sending to the 2240 first fails. 2242 On the receive side, all timeslots are programmed in a same 'OR' 2243 group. Retries of a same copy as well as converging branches for 2244 elimination are converged, meaning that the first successful 2245 reception is enough and that all the other timeslots can be ignored. 2246 A 'AND' group denotes different packets that must all be received and 2247 transmitted over the associated transmit groups within their 2248 respected 'AND' or 'OR' rules. 2250 As an example say that we have a simple network as represented in 2251 Figure 17, and we want to enable PREOF between an ingress node I and 2252 an egress node E. 2254 +-+ +-+ 2255 -- |A| ------ |C| -- 2256 / +-+ +-+ \ 2257 / \ 2258 +-+ +-+ 2259 |I| |E| 2260 +-+ +-+ 2261 \ / 2262 \ +-+ +-+ / 2263 -- |B| ------- |D| -- 2264 +-+ +-+ 2266 Figure 17: Scheduling PREOF on a Simple Network 2268 The assumption for this particular problem is that a 6TiSCH node has 2269 a single radio, so it cannot perform 2 receive and/or transmit 2270 operations at the same time, even on 2 different channels. 2272 Say we have 6 possible channels, and at least 10 timeslots per 2273 slotframe. Figure 18 shows a possible schedule whereby each 2274 transmission is retried 2 or 3 times, and redundant copies are 2275 forwarded in parallel via A and C on the one hand, and B and D on the 2276 other, providing time diversity, spatial diversity though different 2277 physical paths, and frequency diversity. 2279 slotOffset 0 1 2 3 4 5 6 7 9 2280 +----+----+----+----+----+----+----+----+----+ 2281 channelOffset 0 | | | | | | |B->D| | | ... 2282 +----+----+----+----+----+----+----+----+----+ 2283 channelOffset 1 | |I->A| |A->C|B->D| | | | | ... 2284 +----+----+----+----+----+----+----+----+----+ 2285 channelOffset 2 |I->A| | |I->B| |C->E| |D->E| | ... 2286 +----+----+----+----+----+----+----+----+----+ 2287 channelOffset 3 | | | | |A->C| | | | | ... 2288 +----+----+----+----+----+----+----+----+----+ 2289 channelOffset 4 | | |I->B| | |B->D| | |D->E| ... 2290 +----+----+----+----+----+----+----+----+----+ 2291 channelOffset 5 | | |A->C| | | |C->E| | | ... 2292 +----+----+----+----+----+----+----+----+----+ 2294 Figure 18: Example Global Schedule 2296 This translates in a different slotframe for every node that provides 2297 the waking and sleeping times, and the channelOffset to be used when 2298 awake. Figure 19 shows the corresponding slotframe for node A. 2300 slotOffset 0 1 2 3 4 5 6 7 9 2301 +----+----+----+----+----+----+----+----+----+ 2302 operation |rcv |rcv |xmit|xmit|xmit|none|none|none|none| ... 2303 +----+----+----+----+----+----+----+----+----+ 2304 channelOffset | 2 | 1 | 5 | 1 | 3 |N/A |N/A |N/A |N/A | ... 2305 +----+----+----+----+----+----+----+----+----+ 2307 Figure 19: Example Slotframe for Node A 2309 The logical relationship between the timeslots is given by the 2310 following table: 2312 +------+---------------------+------------------------+ 2313 | Node | rcv slotOffset | xmit slotOffset | 2314 +------+---------------------+------------------------+ 2315 | I | N/A | (0 OR 1) AND (2 OR 3) | 2316 | A | (0 OR 1) | (2 OR 3 OR 4) | 2317 | B | (2 OR 3) | (4 OR 5 OR 6) | 2318 | C | (2 OR 3 OR 4) | (5 OR 6) | 2319 | D | (4 OR 5 OR 6) | (7 OR 8) | 2320 | E | (5 OR 6 OR 7 OR 8) | N/A | 2321 +------+---------------------+------------------------+ 2322 Figure 20 2324 5. IANA Considerations 2326 This document does not require IANA action. 2328 6. Security Considerations 2330 The "Minimal Security Framework for 6TiSCH" [MIN-SECURITY] was 2331 optimized for Low-Power and TSCH operations. The reader is 2332 encouraged to review the Security Considerations section of that 2333 document, which discusses 6TiSCH security issues in more details. 2335 6.1. Availability of Remote Services 2337 The operation of 6TiSCH Tracks inherits its high level operation from 2338 DetNet and is subject to the observations in section 5 of [RFC8655]. 2339 The installation and the maintenance of the 6TiSCH Tracks depends on 2340 the availability of a controller with a PCE to compute and push them 2341 in the network. When that connectivity is lost, existing Tracks may 2342 continue to operate until the end of their lifetime, but cannot be 2343 removed or updated, and new Tracks cannot be installed. 2345 In a LLN, the communication with a remote PCE may be slow and 2346 unreactive to rapid changes in the condition of the wireless 2347 communication. An attacker may introduce extra delay by selectively 2348 jamming some packets or some flows. The expectation is that the 2349 6TiSCH Tracks enable enough redundancy to maintain the critical 2350 traffic in operation while new routes are calculated and programmed 2351 into the network. 2353 As with DetNet in general, the communication with the PCE must be 2354 secured and should be protected against DoS attacks, including delay 2355 injection and blackholing attacks, and secured as discussed in the 2356 security considerations defined for Abstraction and Control of 2357 Traffic Engineered Networks (ACTN) in Section 9 of [RFC8453], which 2358 applies equally to DetNet and 6TiSCH. In a similar manner, the 2359 communication with the JRC must be secured and should be protected 2360 against DoS attacks when possible. 2362 6.2. Selective Jamming 2364 The Hopping Sequence of a TSCH network is well-known, meaning that if 2365 a rogue manages to identify a cell of a particular flow, then it may 2366 to selectively jam that cell, without impacting any other traffic. 2367 This attack can be performed at the PHY layer without any knowledge 2368 of the Layer-2 keys, and is very hard to detect and diagnose because 2369 only one flow is impacted. 2371 [I-D.tiloca-6tisch-robust-scheduling] proposes a method to obfuscate 2372 the hopping sequence and make it harder to perpetrate that particular 2373 attack. 2375 6.3. MAC-Layer Security 2377 This architecture operates on IEEE Std. 802.15.4 and expects the 2378 Link-Layer security to be enabled at all times between connected 2379 devices, except for the very first step of the device join process, 2380 where a joining device may need some initial, unsecured exchanges so 2381 as to obtain its initial key material. In a typical deployment, all 2382 joined nodes use the same keys and rekeying needs to be global. 2384 The 6TISCH Architecture relies on the join process to deny 2385 authorization of invalid nodes and preserve the integrity of the 2386 network keys. A rogue that managed to access the network can perform 2387 a large variety of attacks from DoS to injecting forged packets and 2388 routing information. "Zero-trust" properties would be highly 2389 desirable but are mostly not available at the time of this writing. 2390 [AP-ND] is a notable exception that protects the ownership of IPv6 2391 addresses and prevents a rogue node with L2 access from stealing and 2392 injecting traffic on behalf of a legitimate node. 2394 6.4. Time Synchronization 2396 Time Synchronization in TSCH induces another event horizon whereby a 2397 node will only communicate with another node if they are synchronized 2398 within a guard time. The pledge discovers the synchronization of the 2399 network based on the time of reception of the beacon. If an attacker 2400 synchronizes a pledge outside of the guard time of the legitimate 2401 nodes then the pledge will never see a legitimate beacon and may not 2402 discover the attack. 2404 As discussed in [RFC8655], measures must be taken to protect the time 2405 synchronization, and for 6TiSCH this includes ensuring that the 2406 Absolute Slot Number (ASN), which is the node's sense of time, is not 2407 compromised. Once installed and as long as the node is synchronized 2408 to the network, ASN is implicit in the transmissions. 2410 IEEE Std. 802.15.4 [IEEE802154] specifies that in a TSCH network, the 2411 nonce that is used for the computation of the Message Integrity Code 2412 (MIC) to secure Link-Layer frames is composed of the address of the 2413 source of the frame and of the ASN. The standard assumes that the 2414 ASN is distributed securely by other means. The ASN is not passed 2415 explicitly in the data frames and does not constitute a complete 2416 anti-replay protection. It results that upper layer protocols must 2417 provide a way to detect duplicates and cope with them. 2419 If the receiver and the sender have a different sense of ASN, the MIC 2420 will not validate and the frame will be dropped. In that sense, TSCH 2421 induces an event horizon whereby only nodes that have a common sense 2422 of ASN can talk to one another in an authenticated manner. With 2423 6TiSCH, the pledge discovers a tentative ASN in beacons from nodes 2424 that have already joined the network. But even if the beacon can be 2425 authenticated, the ASN cannot be trusted as it could be a replay by 2426 an attacker and thus could announce an ASN that represents a time in 2427 the past. If the pledge uses an ASN that is learned from a replayed 2428 beacon for an encrypted transmission, a nonce-reuse attack becomes 2429 possible and the network keys may be compromised. 2431 6.5. Validating ASN 2433 After obtaining the tentative ASN, a pledge that wishes to join the 2434 6TiSCH network must use a join protocol to obtain its security keys. 2435 The join protocol used in 6TiSCH is the Constrained Join Protocol 2436 (CoJP). In the minimal setting defined in [MIN-SECURITY], the 2437 authentication requires a pre-shared key, based on which a secure 2438 session is derived. The CoJP exchange may also be preceded with a 2439 zero-touch handshake [I-D.ietf-6tisch-dtsecurity-zerotouch-join] in 2440 order to enable pledge joining based on certificates and/or inter- 2441 domain communication. 2443 As detailed in Section 4.2.1, a Join Proxy (JP) helps the pledge for 2444 the join procedure by relaying the link-scope Join Request over the 2445 IP network to a Join Registrar/Coordinator (JRC) that can 2446 authenticate the pledge and validate that it is attached to the 2447 appropriate network. As a result of the CoJP exchange, the pledge is 2448 in possession of a Link-Layer material including keys and a short 2449 address, and if the ASN is known to be correct, all traffic can now 2450 be secured using CCM* [CCMstar] at the Link-Layer. 2452 The authentication steps must be such that they cannot be replayed by 2453 an attacker, and they must not depend on the tentative ASN being 2454 valid. During the authentication, the keying material that the 2455 pledge obtains from the JRC does not provide protection against 2456 spoofed ASN. Once the pledge has obtained the keys to use in the 2457 network, it may still need to verify the ASN. If the nonce used in 2458 the Layer-2 security derives from the extended (MAC-64) address, then 2459 replaying the ASN alone cannot enable a nonce-reuse attack unless the 2460 same node is lost its state with a previous ASN. But if the nonce 2461 derives from the short address (e.g., assigned by the JRC) then the 2462 JRC must ensure that it never assigns short addresses that were 2463 already given to this or other nodes with the same keys. In other 2464 words, the network must be rekeyed before the JRC runs out of short 2465 addresses. 2467 6.6. Network Keying and Rekeying 2469 Section 4.2.1 provides an overview of the CoJP process described in 2470 [MIN-SECURITY] by which an LLN can be assembled in the field, having 2471 been provisioned in a lab. 2472 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] is future work that 2473 preceeds and then leverages the CoJP protocol using the 2474 [I-D.ietf-anima-constrained-voucher] constrained profile of 2475 [I-D.ietf-anima-bootstrapping-keyinfra] (BRSKI). This later work 2476 requires a yet-to-be standardized Lighweight Authenticated Key 2477 Exchange protocol. 2479 The CoJP protocol results in distribution of a network-wide key that 2480 is to be used with [IEEE802154] security. The details of use are 2481 described in [MIN-SECURITY] sections 9.2 and 9.3.2. 2483 The BRSKI mechanism may lead to the use of the CoJP protocol, in 2484 which case it also results in distribution of a network-wide key. 2485 Alternatively the BRSKI mechanism may be followed by use of 2486 [I-D.ietf-ace-coap-est] to enroll certificates for each device. In 2487 that case, the certificates may be used with an [IEEE802154] key 2488 agreement protocol. The description of this mechanism, while 2489 conceptually straight forward still has significant standardization 2490 hurdles to pass. 2492 [MIN-SECURITY] section 9.2 describes a mechanism to change (rekey) 2493 the network. There are a number of reasons to initiate a network 2494 rekey: to remove unwanted (corrupt/malicious) nodes, to recover 2495 unused 2-byte short addresses, or due to limits in encryption 2496 algorithms. For all of the mechanisms that distribute a network-wide 2497 key, rekeying is also needed on a periodic basis. In more details: 2499 * The mechanism described in [MIN-SECURITY] section 9.2 requires 2500 advance communication between the JRC and every one of the nodes 2501 before the key change. Given that many nodes may be sleepy, this 2502 operation may take a significant amount of time, and may consume a 2503 significant portion of the available bandwidth. As such, network- 2504 wide rekeys in order to exclude nodes that have become malicious 2505 will not be particularly quick. If a rekey is already in 2506 progress, but the unwanted node has not yet been updated, then it 2507 is possible to to just continue the operation. If the unwanted 2508 node has already received the update, then the rekey operation 2509 will need to be restarted. 2511 * The cryptographic mechanisms used by IEEE Std. 802.15.4 include 2512 the 2-byte short address in the calculation of the context. A 2513 nonce-reuse attack may become feasible if a short address is 2514 reassigned to another node while the same network-wide keys are in 2515 operation. A network that gains and loses nodes on a regular 2516 basis is likely to reach the 65536 limit of the 2-byte (16-bit) 2517 short addresses, even if the network has only a few thousand 2518 nodes. Network planners should consider the need to rekey the 2519 network on a periodic basis in order to recover 2-byte addresses. 2520 The rekey can update the short addresses for active nodes if 2521 desired, but there is actually no need to do this as long as the 2522 key has been changed. 2524 * With TSCH as it stands at the time of this writing, the ASN will 2525 wrap after 2^40 timeslot durations, which means with the default 2526 values around 350 years. Wrapping ASN is not expected to happen 2527 within the lifetime of most LLNs. Yet, should the ASN wrap, the 2528 network must be rekeyed to avoid a nonce-reuse attack. 2530 * Many cipher algorithms have some suggested limits on how many 2531 bytes should be encrypted with that algorithm before a new key is 2532 used. These numbers are typically in the many to hundreds of 2533 gigabytes of data. On very fast backbone networks this becomes an 2534 important concern. On LLNs with typical data rates in the 2535 kilobits/second, this concern is significantly less. With IEEE 2536 Std. 802.15.4 as it stands at the time of this writing, the ASN 2537 will wrap before the limits of the current L2 crypto (AES-CCM-128) 2538 are reached, so the problem should never occur. 2540 * In any fashion, if the LLN is expected to operate continuously for 2541 decades then the operators are advised to plan for the need to 2542 rekey. 2544 Except for urgent rekeys caused by malicious nodes, the rekey 2545 operation described in [MIN-SECURITY] can be done as a background 2546 task and can be done incrementally. It is a make-before-break 2547 mechanism. The switch over to the new key is not signaled by time, 2548 but rather by observation that the new key is in use. As such, the 2549 update can take as long as needed, or occur in as short a time as 2550 practical. 2552 7. Acknowledgments 2554 7.1. Contributors 2556 The co-authors of this document are listed below: 2558 Thomas Watteyne for his contribution to the whole design, in 2559 particular on TSCH and security, and to the open source community 2560 with openWSN that he created. 2562 Xavier Vilajosana who lead the design of the minimal support with 2563 RPL and contributed deeply to the 6top design and the G-MPLS 2564 operation of Track switching; 2566 Kris Pister for creating TSCH and his continuing guidance through 2567 the elaboration of this design; 2569 Malisa Vucinic for the work on the one-touch join process and his 2570 contribution to the Security Design Team; 2572 Michael Richardson for his leadership role in the Security Design 2573 Team and his contribution throughout this document; 2575 Tero Kivinen for his contribution to the security work in general 2576 and the security section in particular. 2578 Maria Rita Palattella for managing the Terminology document merged 2579 into this through the work of 6TiSCH; 2581 Simon Duquennoy for his contribution to the open source community 2582 with the 6TiSCH implementaton of contiki, and for his contribution 2583 to MSF and autonomous unicast cells. 2585 Qin Wang who lead the design of the 6top sublayer and contributed 2586 related text that was moved and/or adapted in this document; 2588 Rene Struik for the security section and his contribution to the 2589 Security Design Team; 2591 Robert Assimiti for his breakthrough work on RPL over TSCH and 2592 initial text and guidance; 2594 7.2. Special Thanks 2596 Special thanks to Jonathan Simon, Giuseppe Piro, Subir Das and 2597 Yoshihiro Ohba for their deep contribution to the initial security 2598 work, to Yasuyuki Tanaka for his work on implementation and 2599 simulation that tremendously helped build a robust system, to Diego 2600 Dujovne for starting and leading the SF0 effort and to Tengfei Chang 2601 for evolving it in the MSF. 2603 Special thanks also to Pat Kinney, Charlie Perkins and Bob Heile for 2604 their support in maintaining the connection active and the design in 2605 line with work happening at IEEE 802.15. 2607 Special thanks to Ted Lemon who was the INT Area A-D while this 2608 document was initiated for his great support and help throughout, and 2609 to Suresh Krishnan who took over with that kind efficiency of his 2610 till publication. 2612 Also special thanks to Ralph Droms who performed the first INT Area 2613 Directorate review, that was very deep and thorough and radically 2614 changed the orientations of this document, and then to Eliot Lear and 2615 Carlos Pignataro who help finalize this document in preparation to 2616 the IESG reviews, and to Gorry Fairhurst, David Mandelberg, Qin Wu, 2617 Francis Dupont, Eric Vyncke, Mirja Kuhlewind, Roman Danyliw, Benjamin 2618 Kaduk and Andrew Malis, who contributed to the final shaping of this 2619 document through the IESG review procedure. 2621 7.3. And Do not Forget 2623 This document is the result of multiple interactions, in particular 2624 during the 6TiSCH (bi)Weekly Interim call, relayed through the 6TiSCH 2625 mailing list at the IETF, over the course of more than 5 years. 2627 The authors wish to thank in arbitrary order: Alaeddine Weslati, 2628 Chonggang Wang, Georgios Exarchakos, Zhuo Chen, Georgios 2629 Papadopoulos, Eric Levy-Abegnoli, Alfredo Grieco, Bert Greevenbosch, 2630 Cedric Adjih, Deji Chen, Martin Turon, Dominique Barthel, Elvis 2631 Vogli, Geraldine Texier, Guillaume Gaillard, Herman Storey, Kazushi 2632 Muraoka, Ken Bannister, Kuor Hsin Chang, Laurent Toutain, Maik 2633 Seewald, Michael Behringer, Nancy Cam Winget, Nicola Accettura, 2634 Nicolas Montavont, Oleg Hahm, Patrick Wetterwald, Paul Duffy, Peter 2635 van der Stock, Rahul Sen, Pieter de Mil, Pouria Zand, Rouhollah 2636 Nabati, Rafa Marin-Lopez, Raghuram Sudhaakar, Sedat Gormus, Shitanshu 2637 Shah, Steve Simlo, Tina Tsou, Tom Phinney, Xavier Lagrange, Ines 2638 Robles and Samita Chakrabarti for their participation and various 2639 contributions. 2641 8. Normative References 2643 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 2644 DOI 10.17487/RFC0768, August 1980, 2645 . 2647 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2648 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2649 DOI 10.17487/RFC4861, September 2007, 2650 . 2652 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2653 Address Autoconfiguration", RFC 4862, 2654 DOI 10.17487/RFC4862, September 2007, 2655 . 2657 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2658 "Transmission of IPv6 Packets over IEEE 802.15.4 2659 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 2660 . 2662 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 2663 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 2664 DOI 10.17487/RFC6282, September 2011, 2665 . 2667 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 2668 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 2669 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 2670 Low-Power and Lossy Networks", RFC 6550, 2671 DOI 10.17487/RFC6550, March 2012, 2672 . 2674 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 2675 and D. Barthel, "Routing Metrics Used for Path Calculation 2676 in Low-Power and Lossy Networks", RFC 6551, 2677 DOI 10.17487/RFC6551, March 2012, 2678 . 2680 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 2681 Protocol for Low-Power and Lossy Networks (RPL)", 2682 RFC 6552, DOI 10.17487/RFC6552, March 2012, 2683 . 2685 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 2686 Power and Lossy Networks (RPL) Option for Carrying RPL 2687 Information in Data-Plane Datagrams", RFC 6553, 2688 DOI 10.17487/RFC6553, March 2012, 2689 . 2691 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 2692 Routing Header for Source Routes with the Routing Protocol 2693 for Low-Power and Lossy Networks (RPL)", RFC 6554, 2694 DOI 10.17487/RFC6554, March 2012, 2695 . 2697 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 2698 Bormann, "Neighbor Discovery Optimization for IPv6 over 2699 Low-Power Wireless Personal Area Networks (6LoWPANs)", 2700 RFC 6775, DOI 10.17487/RFC6775, November 2012, 2701 . 2703 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 2704 Application Protocol (CoAP)", RFC 7252, 2705 DOI 10.17487/RFC7252, June 2014, 2706 . 2708 [RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power 2709 Wireless Personal Area Network (6LoWPAN) Paging Dispatch", 2710 RFC 8025, DOI 10.17487/RFC8025, November 2016, 2711 . 2713 [RFC8137] Kivinen, T. and P. Kinney, "IEEE 802.15.4 Information 2714 Element for the IETF", RFC 8137, DOI 10.17487/RFC8137, May 2715 2017, . 2717 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 2718 "IPv6 over Low-Power Wireless Personal Area Network 2719 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 2720 April 2017, . 2722 [RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal 2723 IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) 2724 Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180, 2725 May 2017, . 2727 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2728 (IPv6) Specification", STD 86, RFC 8200, 2729 DOI 10.17487/RFC8200, July 2017, 2730 . 2732 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 2733 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 2734 DOI 10.17487/RFC8480, November 2018, 2735 . 2737 [RFC8453] Ceccarelli, D., Ed. and Y. Lee, Ed., "Framework for 2738 Abstraction and Control of TE Networks (ACTN)", RFC 8453, 2739 DOI 10.17487/RFC8453, August 2018, 2740 . 2742 [RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C. 2743 Perkins, "Registration Extensions for IPv6 over Low-Power 2744 Wireless Personal Area Network (6LoWPAN) Neighbor 2745 Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018, 2746 . 2748 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 2749 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 2750 2014, . 2752 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 2753 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 2754 Internet of Things (IoT): Problem Statement", RFC 7554, 2755 DOI 10.17487/RFC7554, May 2015, 2756 . 2758 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2759 Constrained-Node Networks", RFC 7228, 2760 DOI 10.17487/RFC7228, May 2014, 2761 . 2763 [RFC5889] Baccelli, E., Ed. and M. Townsley, Ed., "IP Addressing 2764 Model in Ad Hoc Networks", RFC 5889, DOI 10.17487/RFC5889, 2765 September 2010, . 2767 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 2768 "Deterministic Networking Architecture", RFC 8655, 2769 DOI 10.17487/RFC8655, October 2019, 2770 . 2772 [MIN-SECURITY] 2773 Vucinic, M., Simon, J., Pister, K., and M. Richardson, 2774 "Constrained Join Protocol (CoJP) for 6TiSCH", Work in 2775 Progress, Internet-Draft, draft-ietf-6tisch-minimal- 2776 security-15, 10 December 2019, 2777 . 2780 [6BBR-DRAFT] 2781 Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6 2782 Backbone Router", Work in Progress, Internet-Draft, draft- 2783 ietf-6lo-backbone-router-20, 23 March 2020, 2784 . 2787 [RECOV-FRAG] 2788 Thubert, P., "6LoWPAN Selective Fragment Recovery", Work 2789 in Progress, Internet-Draft, draft-ietf-6lo-fragment- 2790 recovery-21, 23 March 2020, . 2793 [MIN-FRAG] Watteyne, T., Thubert, P., and C. Bormann, "On Forwarding 2794 6LoWPAN Fragments over a Multihop IPv6 Network", Work in 2795 Progress, Internet-Draft, draft-ietf-6lo-minimal-fragment- 2796 15, 23 March 2020, . 2799 [AP-ND] Thubert, P., Sarikaya, B., Sethi, M., and R. Struik, 2800 "Address Protected Neighbor Discovery for Low-power and 2801 Lossy Networks", Work in Progress, Internet-Draft, draft- 2802 ietf-6lo-ap-nd-23, 30 April 2020, 2803 . 2805 [USEofRPLinfo] 2806 Robles, I., Richardson, M., and P. Thubert, "Using RPI 2807 Option Type, Routing Header for Source Routes and IPv6-in- 2808 IPv6 encapsulation in the RPL Data Plane", Work in 2809 Progress, Internet-Draft, draft-ietf-roll-useofrplinfo-40, 2810 25 June 2020, . 2813 [RUL-DRAFT] 2814 Thubert, P. and M. Richardson, "Routing for RPL Leaves", 2815 Work in Progress, Internet-Draft, draft-ietf-roll-unaware- 2816 leaves-18, 12 June 2020, . 2819 [ENH-BEACON] 2820 Dujovne, D. and M. Richardson, "IEEE 802.15.4 Information 2821 Element encapsulation of 6TiSCH Join and Enrollment 2822 Information", Work in Progress, Internet-Draft, draft- 2823 ietf-6tisch-enrollment-enhanced-beacon-14, 21 February 2824 2020, . 2827 [MSF] Chang, T., Vucinic, M., Vilajosana, X., Duquennoy, S., and 2828 D. Dujovne, "6TiSCH Minimal Scheduling Function (MSF)", 2829 Work in Progress, Internet-Draft, draft-ietf-6tisch-msf- 2830 17, 3 August 2020, 2831 . 2833 9. Informative References 2835 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 2836 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 2837 . 2839 [RFC6275] Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility 2840 Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July 2841 2011, . 2843 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2844 "Definition of the Differentiated Services Field (DS 2845 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2846 DOI 10.17487/RFC2474, December 1998, 2847 . 2849 [RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol 2850 Extensions for IPv6 Inter-Domain Routing", RFC 2545, 2851 DOI 10.17487/RFC2545, March 1999, 2852 . 2854 [RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. 2855 Thubert, "Network Mobility (NEMO) Basic Support Protocol", 2856 RFC 3963, DOI 10.17487/RFC3963, January 2005, 2857 . 2859 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 2860 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 2861 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 2862 . 2864 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2865 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2866 2006, . 2868 [RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between 2869 Information Models and Data Models", RFC 3444, 2870 DOI 10.17487/RFC3444, January 2003, 2871 . 2873 [RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S. Van den 2874 Bosch, "Next Steps in Signaling (NSIS): Framework", 2875 RFC 4080, DOI 10.17487/RFC4080, June 2005, 2876 . 2878 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 2879 over Low-Power Wireless Personal Area Networks (6LoWPANs): 2880 Overview, Assumptions, Problem Statement, and Goals", 2881 RFC 4919, DOI 10.17487/RFC4919, August 2007, 2882 . 2884 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, 2885 DOI 10.17487/RFC4903, June 2007, 2886 . 2888 [RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS 2889 Signaling Layer Protocol (NSLP) for Quality-of-Service 2890 Signaling", RFC 5974, DOI 10.17487/RFC5974, October 2010, 2891 . 2893 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2894 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2895 January 2012, . 2897 [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The 2898 Locator/ID Separation Protocol (LISP)", RFC 6830, 2899 DOI 10.17487/RFC6830, January 2013, 2900 . 2902 [RFC7426] Haleplidis, E., Ed., Pentikousis, K., Ed., Denazis, S., 2903 Hadi Salim, J., Meyer, D., and O. Koufopavlou, "Software- 2904 Defined Networking (SDN): Layers and Architecture 2905 Terminology", RFC 7426, DOI 10.17487/RFC7426, January 2906 2015, . 2908 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 2909 Statement and Requirements for IPv6 over Low-Power 2910 Wireless Personal Area Network (6LoWPAN) Routing", 2911 RFC 6606, DOI 10.17487/RFC6606, May 2012, 2912 . 2914 [I-D.ietf-roll-rpl-industrial-applicability] 2915 Phinney, T., Thubert, P., and R. Assimiti, "RPL 2916 applicability in industrial networks", Work in Progress, 2917 Internet-Draft, draft-ietf-roll-rpl-industrial- 2918 applicability-02, 21 October 2013, 2919 . 2922 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] 2923 Richardson, M., "6tisch Zero-Touch Secure Join protocol", 2924 Work in Progress, Internet-Draft, draft-ietf-6tisch- 2925 dtsecurity-zerotouch-join-04, 8 July 2019, 2926 . 2929 [I-D.ietf-core-object-security] 2930 Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 2931 "Object Security for Constrained RESTful Environments 2932 (OSCORE)", Work in Progress, Internet-Draft, draft-ietf- 2933 core-object-security-16, 6 March 2019, 2934 . 2937 [I-D.ietf-manet-aodvv2] 2938 Perkins, C., Ratliff, S., Dowdell, J., Steenbrink, L., and 2939 V. Mercieca, "Ad Hoc On-demand Distance Vector Version 2 2940 (AODVv2) Routing", Work in Progress, Internet-Draft, 2941 draft-ietf-manet-aodvv2-16, 4 May 2016, 2942 . 2944 [RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases", 2945 RFC 8578, DOI 10.17487/RFC8578, May 2019, 2946 . 2948 [I-D.ietf-detnet-ip] 2949 Varga, B., Farkas, J., Berger, L., Fedyk, D., and S. 2950 Bryant, "DetNet Data Plane: IP", Work in Progress, 2951 Internet-Draft, draft-ietf-detnet-ip-07, 3 July 2020, 2952 . 2954 [I-D.ietf-anima-bootstrapping-keyinfra] 2955 Pritikin, M., Richardson, M., Eckert, T., Behringer, M., 2956 and K. Watsen, "Bootstrapping Remote Secure Key 2957 Infrastructures (BRSKI)", Work in Progress, Internet- 2958 Draft, draft-ietf-anima-bootstrapping-keyinfra-43, 7 2959 August 2020, . 2962 [I-D.ietf-roll-aodv-rpl] 2963 Anamalamudi, S., Zhang, M., Perkins, C., Anand, S., and B. 2964 Liu, "AODV based RPL Extensions for Supporting Asymmetric 2965 P2P Links in Low-Power and Lossy Networks", Work in 2966 Progress, Internet-Draft, draft-ietf-roll-aodv-rpl-08, 7 2967 May 2020, 2968 . 2970 [I-D.ietf-lwig-6lowpan-virtual-reassembly] 2971 Bormann, C. and T. Watteyne, "Virtual reassembly buffers 2972 in 6LoWPAN", Work in Progress, Internet-Draft, draft-ietf- 2973 lwig-6lowpan-virtual-reassembly-02, 9 March 2020, 2974 . 2977 [I-D.ietf-roll-dao-projection] 2978 Thubert, P., Jadhav, R., and M. Gillmore, "Root initiated 2979 routing state in RPL", Work in Progress, Internet-Draft, 2980 draft-ietf-roll-dao-projection-10, 11 May 2020, 2981 . 2984 [I-D.rahul-roll-mop-ext] 2985 Jadhav, R. and P. Thubert, "RPL Mode of Operation 2986 extension", Work in Progress, Internet-Draft, draft-rahul- 2987 roll-mop-ext-01, 9 June 2019, 2988 . 2990 [I-D.selander-ace-cose-ecdhe] 2991 Selander, G., Mattsson, J., and F. Palombini, "Ephemeral 2992 Diffie-Hellman Over COSE (EDHOC)", Work in Progress, 2993 Internet-Draft, draft-selander-ace-cose-ecdhe-14, 11 2994 September 2019, . 2997 [I-D.thubert-roll-bier] 2998 Thubert, P., "RPL-BIER", Work in Progress, Internet-Draft, 2999 draft-thubert-roll-bier-02, 24 July 2018, 3000 . 3002 [I-D.thubert-bier-replication-elimination] 3003 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 3004 TE extensions for Packet Replication and Elimination 3005 Function (PREF) and OAM", Work in Progress, Internet- 3006 Draft, draft-thubert-bier-replication-elimination-03, 3 3007 March 2018, . 3010 [I-D.thubert-6lo-bier-dispatch] 3011 Thubert, P., Brodard, Z., Jiang, H., and G. Texier, "A 3012 6loRH for BitStrings", Work in Progress, Internet-Draft, 3013 draft-thubert-6lo-bier-dispatch-06, 28 January 2019, 3014 . 3017 [I-D.thubert-6man-unicast-lookup] 3018 Thubert, P. and E. Levy-Abegnoli, "IPv6 Neighbor Discovery 3019 Unicast Lookup", Work in Progress, Internet-Draft, draft- 3020 thubert-6man-unicast-lookup-00, 29 July 2019, 3021 . 3024 [I-D.pthubert-raw-problem-statement] 3025 Thubert, P. and G. Papadopoulos, "Reliable and Available 3026 Wireless Problem Statement", Work in Progress, Internet- 3027 Draft, draft-pthubert-raw-problem-statement-04, 23 October 3028 2019, . 3031 [I-D.tiloca-6tisch-robust-scheduling] 3032 Tiloca, M., Duquennoy, S., and G. Dini, "Robust Scheduling 3033 against Selective Jamming in 6TiSCH Networks", Work in 3034 Progress, Internet-Draft, draft-tiloca-6tisch-robust- 3035 scheduling-02, 10 June 2019, . 3038 [I-D.ietf-ace-coap-est] 3039 Stok, P., Kampanakis, P., Richardson, M., and S. Raza, 3040 "EST over secure CoAP (EST-coaps)", Work in Progress, 3041 Internet-Draft, draft-ietf-ace-coap-est-18, 6 January 3042 2020, 3043 . 3045 [I-D.ietf-anima-constrained-voucher] 3046 Richardson, M., Stok, P., and P. Kampanakis, "Constrained 3047 Voucher Artifacts for Bootstrapping Protocols", Work in 3048 Progress, Internet-Draft, draft-ietf-anima-constrained- 3049 voucher-08, 13 July 2020, . 3052 [IEEE802154] 3053 IEEE standard for Information Technology, "IEEE Std. 3054 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 3055 and Physical Layer (PHY) Specifications for Low-Rate 3056 Wireless Personal Area Networks". 3058 [CCMstar] Struik, R., "Formal Specification of the CCM* Mode of 3059 Operation", September 2004, . 3063 [IEEE802154e] 3064 IEEE standard for Information Technology, "IEEE standard 3065 for Information Technology, IEEE Std. 802.15.4, Part. 3066 15.4: Wireless Medium Access Control (MAC) and Physical 3067 Layer (PHY) Specifications for Low-Rate Wireless Personal 3068 Area Networks, June 2011 as amended by IEEE Std. 3069 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area 3070 Networks (LR-WPANs) Amendment 1: MAC sublayer", April 3071 2012. 3073 [WirelessHART] 3074 www.hartcomm.org, "Industrial Communication Networks - 3075 Wireless Communication Network and Communication Profiles 3076 - WirelessHART - IEC 62591", 2010. 3078 [HART] www.hartcomm.org, "Highway Addressable remote Transducer, 3079 a group of specifications for industrial process and 3080 control devices administered by the HART Foundation". 3082 [ISA100.11a] 3083 ISA/ANSI, "Wireless Systems for Industrial Automation: 3084 Process Control and Related Applications - ISA100.11a-2011 3085 - IEC 62734", 2011, . 3088 [ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation", 3089 . 3091 [TEAS] IETF, "Traffic Engineering Architecture and Signaling", 3092 . 3094 [ANIMA] IETF, "Autonomic Networking Integrated Model and 3095 Approach", 3096 . 3098 [PCE] IETF, "Path Computation Element", 3099 . 3101 [CCAMP] IETF, "Common Control and Measurement Plane", 3102 . 3104 [AMI] US Department of Energy, "Advanced Metering Infrastructure 3105 and Customer Systems", 2006, 3106 . 3109 [S-ALOHA] Roberts, L. G., "ALOHA Packet System With and Without 3110 Slots and Capture", doi 10.1145/1024916.1024920, April 3111 1975, . 3113 [IEC62439] IEC, "Industrial communication networks - High 3114 availability automation networks - Part 3: Parallel 3115 Redundancy Protocol (PRP) and High-availability Seamless 3116 Redundancy (HSR) - IEC62439-3", 2012, 3117 . 3119 Appendix A. Related Work In Progress 3121 This document has been incremented as the work progressed following 3122 the evolution of the WG charter and the availability of dependent 3123 work. The intent was to publish when the WG concludes on the covered 3124 items. At the time of publishing the following specification are 3125 still in progress and may affect the evolution of the stack in a 3126 6TiSCH-aware node. 3128 A.1. Unchartered IETF work items 3130 A.1.1. 6TiSCH Zerotouch security 3132 The security model and in particular the zerotouch join process 3133 [I-D.ietf-6tisch-dtsecurity-zerotouch-join] depends on the ANIMA 3134 [ANIMA] Bootstrapping Remote Secure Key Infrastructures (BRSKI) 3135 [I-D.ietf-anima-bootstrapping-keyinfra] to enable zero-touch security 3136 provisionning; for highly constrained nodes, a minimal model based on 3137 pre-shared keys (PSK) is also available. As written to this day, it 3138 also depends on a number of documents in progress as CORE, and on 3139 "Ephemeral Diffie-Hellman Over COSE (EDHOC)" 3140 [I-D.selander-ace-cose-ecdhe], which is being considered for adoption 3141 at the LAKE WG. 3143 A.1.2. 6TiSCH Track Setup 3145 ROLL is now standardizing a reactive routing protocol based on RPL 3146 [I-D.ietf-roll-aodv-rpl] The need of a reactive routing protocol to 3147 establish on-demand constraint-optimized routes and a reservation 3148 protocol to establish Layer-3 Tracks is being discussed at 6TiSCH but 3149 not chartered for. 3151 At the time of this writing, there is new work planned in the IETF to 3152 provide limited deterministic networking capabilities for wireless 3153 networks with a focus on forwarding behaviors to react quickly and 3154 locally to the changes as described in 3155 [I-D.pthubert-raw-problem-statement]. 3157 ROLL is also standardizing an extension to RPL to setup centrally- 3158 computed routes [I-D.ietf-roll-dao-projection] 3160 The 6TiSCH Architecture should thus inherit from the DetNet [RFC8655] 3161 architecture and thus depends on it. The Path Computation Element 3162 (PCE) should be a core component of that architecture. An extension 3163 to RPL or to TEAS [TEAS] will be required to expose the 6TiSCH node 3164 capabilities and the network peers to the PCE, possibly in 3165 combination with [I-D.rahul-roll-mop-ext]. A protocol such as a 3166 lightweight PCEP or an adaptation of CCAMP [CCAMP] G-MPLS formats and 3167 procedures could be used in combination to 3168 [I-D.ietf-roll-dao-projection] to install the Tracks, as computed by 3169 the PCE, to the 6TiSCH nodes. 3171 A.1.3. Using BIER in a 6TiSCH Network 3173 ROLL is actively working on Bit Index Explicit Replication (BIER) as 3174 a method to compress both the dataplane packets and the routing 3175 tables in storing mode [I-D.thubert-roll-bier]. 3177 BIER could also be used in the context of the DetNet service layer. 3178 BIER-TE-based OAM, Replication and Elimination 3179 [I-D.thubert-bier-replication-elimination] leverages BIER Traffic 3180 Engineering (TE) to control in the data plane the DetNet Replication 3181 and Elimination activities, and to provide traceability on links 3182 where replication and loss happen, in a manner that is abstract to 3183 the forwarding information. 3185 a 6loRH for BitStrings [I-D.thubert-6lo-bier-dispatch] proposes a 3186 6LoWPAN compression for the BIER Bitstring based on 6LoWPAN Routing 3187 Header [RFC8138]. 3189 A.2. External (non-IETF) work items 3191 The current charter positions 6TiSCH on IEEE Std. 802.15.4 only. 3192 Though most of the design should be portable on other link types, 3193 6TiSCH has a strong dependency on IEEE Std. 802.15.4 and its 3194 evolution. The impact of changes to TSCH on this Architecture should 3195 be minimal to non-existent, but deeper work such as 6top and security 3196 may be impacted. A 6TiSCH Interest Group at the IEEE maintains the 3197 synchronization and helps foster work at the IEEE should 6TiSCH 3198 demand it. 3200 Work is being proposed at IEEE (802.15.12 PAR) for an LLC that would 3201 logically include the 6top sublayer. The interaction with the 6top 3202 sublayer and the Scheduling Functions described in this document are 3203 yet to be defined. 3205 ISA100 [ISA100] Common Network Management (CNM) is another external 3206 work of interest for 6TiSCH. The group, referred to as ISA100.20, 3207 defines a Common Network Management framework that should enable the 3208 management of resources that are controlled by heterogeneous 3209 protocols such as ISA100.11a [ISA100.11a], WirelessHART 3210 [WirelessHART], and 6TiSCH. Interestingly, the establishment of 3211 6TiSCH Deterministic paths, called Tracks, are also in scope, and 3212 ISA100.20 is working on requirements for DetNet. 3214 Author's Address 3216 Pascal Thubert (editor) 3217 Cisco Systems, Inc 3218 Building D 3219 45 Allee des Ormes - BP1200 3220 06254 Mougins - Sophia Antipolis 3221 France 3223 Phone: +33 497 23 26 34 3224 Email: pthubert@cisco.com