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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RAW P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Informational D. Cavalcanti 5 Expires: December 8, 2019 Intel 6 X. Vilajosana 7 Universitat Oberta de Catalunya 8 June 6, 2019 10 Reliable and Available Wireless Technologies 11 draft-thubert-raw-technologies-01 13 Abstract 15 This document presents a series of recent technologies that are 16 capable of time synchronization and scheduling of transmission, 17 making them suitable to carry time-sensitive flows with requirements 18 of both reliable delivery in bounded time, and availability at all 19 times, regardless of packet transmission or individual equipement 20 failures. 22 Status of This Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current Internet- 30 Drafts is at https://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six months 33 and may be updated, replaced, or obsoleted by other documents at any 34 time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 This Internet-Draft will expire on December 8, 2019. 39 Copyright Notice 41 Copyright (c) 2019 IETF Trust and the persons identified as the 42 document authors. All rights reserved. 44 This document is subject to BCP 78 and the IETF Trust's Legal 45 Provisions Relating to IETF Documents 46 (https://trustee.ietf.org/license-info) in effect on the date of 47 publication of this document. Please review these documents 48 carefully, as they describe your rights and restrictions with respect 49 to this document. Code Components extracted from this document must 50 include Simplified BSD License text as described in Section 4.e of 51 the Trust Legal Provisions and are provided without warranty as 52 described in the Simplified BSD License. 54 Table of Contents 56 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 57 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 58 3. On Scheduling . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3.1. Benefits of Scheduling on Wires . . . . . . . . . . . . . 4 60 3.2. Benefits of Scheduling on Wireless . . . . . . . . . . . 4 61 4. IEEE 802 standards . . . . . . . . . . . . . . . . . . . . . 5 62 4.1. IEEE 802.11 . . . . . . . . . . . . . . . . . . . . . . . 5 63 4.1.1. Provenance and Documents . . . . . . . . . . . . . . 5 64 4.1.2. 802.11ax High Efficiency (HE) . . . . . . . . . . . . 7 65 4.1.3. 802.11be Extreme High Throughput (EHT) . . . . . . . 10 66 4.1.4. 802.11ad and 802.11ay (mmWave operation) . . . . . . 11 67 4.2. IEEE 802.15.4 . . . . . . . . . . . . . . . . . . . . . . 12 68 4.2.1. Provenance and Documents . . . . . . . . . . . . . . 12 69 4.2.2. TimeSlotted Channel Hopping . . . . . . . . . . . . . 14 70 5. 3GPP standards . . . . . . . . . . . . . . . . . . . . . . . 16 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 73 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 75 9.1. Normative References . . . . . . . . . . . . . . . . . . 17 76 9.2. Informative References . . . . . . . . . . . . . . . . . 17 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 79 1. Introduction 81 When used in math or philosophy, the term "deterministic" generally 82 refers to a perfection where all aspect are understood and 83 predictable. A perfectly Deterministic Network would ensure that 84 every packet reach its destination following a predetermined path 85 along a predefined schedule to be delivered at the exact due time. 86 In a real and imperfect world, a Deterministic Network must highly 87 predictable, which is a combination of reliability and availability. 88 On the one hand the network must be reliable, meaning that it will 89 perform as expected for all packets and in particular that it will 90 always deliver the packet at the destination in due time. On the 91 other hand, the network must be available, meaning that it is 92 resilient to any single outage, whether the cause is a software, a 93 hardware or a transmission issue. 95 RAW (Reliable and Available Wireless) is an effort to provide 96 Deterministic Networking on across a path that include a wireless 97 physical layer. Making Wireless Reliable and Available is even more 98 challenging than it is with wires, due to the numerous causes of loss 99 in transmission that add up to the congestion losses and the delays 100 caused by overbooked shared resources. In order to maintain a 101 similar quality of service along a multihop path that is composed of 102 wired and wireless hops, additional methods that are specific to 103 wireless must be leveraged to combat the sources of loss that are 104 also specific to wireless. 106 Such wireless-specific methods include per-hop retransmissions (HARQ) 107 and P2MP overhearing whereby multiple receivers are scheduled to 108 receive the same transmission, which balances the adverse effects of 109 the transmission losses that are experienced when a radio is used as 110 pure P2P. 112 2. Terminology 114 This specification uses several terms that are uncommon on protocols 115 that ensure bets effort transmissions for stochastics flows, such as 116 found in the traditional Internet and other statistically multiplexed 117 packet networks. 119 Reliable: That consistently performs as expected, the expectation 120 for a network being to always deliver a packet in due time. 122 Available: That is exempt of unscheduled outage, the expectation for 123 a network being that the flow is maintained in the face of any 124 single breakage. 126 PAREO (functions): the wireless extension of DetNet PREOF. PAREO 127 functions include scheduled ARQ at selected hops, and expect 128 the use of new operations like overhearing where available. 130 Track: A DODAG oriented to a destination, and that enables Packet 131 ARQ, Replication, Elimination, and Ordering Functions. 133 ARQ: Automatic Repeat Request, enabling an acknowledged 134 transmission, which is the typical model at Layer-2 on a 135 wireless medium. 137 HARQ: Forward error correction, sending redundant coded data to help 138 the receiver recover transmission errors. 140 HARQ: Hybrid ARQ, a combination of FEC and ARQ. 142 3. On Scheduling 144 The operations of a Deterministic Network often rely on precisely 145 applying a tight schedule, in order to avoid collision loss and 146 guarantee the worst-case time of delivery. To achieve this, there 147 must be a shared sense of time throughout the network. The sense of 148 time is usually provided by the lower layer and is not in scope for 149 RAW. 151 3.1. Benefits of Scheduling on Wires 153 A network is reliable when the statistical effects that affect the 154 packet transmission are eliminated. This involves maintaining at all 155 time the amount of critical packets within the physical capabilities 156 of the hardware and that of the radio medium. This is achieved by 157 controlling the use of time-shared resources such as CPUs and 158 buffers, by shaping the flows and by scheduling the time of 159 transmission of the packets that compose the flow at every hop. 161 Equipment failure, such as an access point rebooting, a broken radio 162 adapter, or a permanent obstacle to the transmission, is a secondary 163 source of packet loss. When a breakage occurs, multiple packets are 164 lost in a row before the flows are rerouted or the system may 165 recover. This is not acceptable for critical applications such as 166 related to safety. A typical process control loop will tolerate an 167 occasional packet loss, but a loss of several packets in a row will 168 cause an emergency stop (e.g., after 4 packets lost, within a period 169 of 1 second). 171 Network Availability is obtained by making the transmission resilient 172 against hardware failures and radio transmission losses due to 173 uncontrolled events such as co-channel interferers, multipath fading 174 or moving obstacles. The best results are typically achieved by 175 pseudo randomly cumulating all forms of diversity, in the spatial 176 domain with replication and elimination, in the time domain with ARQ 177 and diverse scheduled transmissions, and in the frequency domain with 178 frequency hopping or channel hopping between frames. 180 3.2. Benefits of Scheduling on Wireless 182 In addition to the benefits listed in Section 3.1, scheduling 183 transmissions provides specific value to the wireless medium. 185 On the one hand, scheduling avoids collisions between scheduled 186 transmissions and can ensure both time and frequency diversity 187 between retries in order to defeat co-channel interference from un- 188 controlled transmitters as well as multipath fading. Transmissions 189 can be scheduled on multiple channels in parallel, which enables to 190 use the full available spectrum while avoiding the hidden terminal 191 problem, e.g., when the next packet in a same flow interferes on a 192 same channel with the previous one that progressed a few hops 193 farther. 195 On the other hand, scheduling optimizes the bandwidth usage: compared 196 to classical Collision Avoidance techniques, there is no blank time 197 related to inter-frame space (IFS) and exponential back-off in 198 scheduled operations. A minimal Clear Channel Assessment may be 199 needed to comply with the local regulations such as ETSI 300-328, but 200 that will not detect a collision when the senders are synchronized. 201 And because scheduling allows a time-sharing operation, there is no 202 limit to the ratio of isolated critical traffic. 204 Finally, scheduling plays a critical role to save energy. In IOT, 205 energy is the foremost concern, and synchronizing sender and listener 206 enables to always maintain them in deep sleep when there is no 207 scheduled transmission. This avoids idle listening and long 208 preambles and enables long sleep periods between traffic and 209 resynchronization, allowing battery-operated nodes to operate in a 210 mesh topology for multiple years. 212 4. IEEE 802 standards 214 With an active portfolio of nearly 1,300 standards and projects under 215 development, IEEE is a leading developer of industry standards in a 216 broad range of technologies that drive the functionality, 217 capabilities, and interoperability of products and services, 218 transforming how people live, work, and communicate. 220 The IEEE 802 LAN/MAN Standards Committee (SC) develops and maintains 221 networking standards and recommended practices for local, 222 metropolitan, and other area networks, using an open and accredited 223 process, and advocates them on a global basis. The most widely used 224 standards are for Ethernet, Bridging and Virtual Bridged LANs 225 Wireless LAN, Wireless PAN, Wireless MAN, Wireless Coexistence, Media 226 Independent Handover Services, and Wireless RAN. An individual 227 Working Group provides the focus for each area. Standards produced 228 by the IEEE 802 SC are freely available from the IEEE GET Program 229 after they have been published in PDF for six months. 231 4.1. IEEE 802.11 233 4.1.1. Provenance and Documents 235 The IEEE 802.11 LAN standards define the underlying MAC and PHY 236 layers for the Wi-Fi technology. Wi-Fi/802.11 is one of the most 237 successful wireless technologies, supporting many application 238 domains. While previous 802.11 generations, such as 802.11n and 239 802.11ac, have focused mainly on improving peak throughput, more 240 recent generations are also considering other performance vectors, 241 such as efficiency enhancements for dense environments in 802.11ax, 242 and latency and support for Time-Sensitive Networking (TSN) 243 capabilities in 802.11be. 245 IEEE 802.11 already supports some 802.1 TSN standards and it is 246 undergoing efforts to support for other 802.1 TSN capabilities 247 required to address the use cases that require time synchronization 248 and timeliness (bounded latency) guarantees with high reliability and 249 availability. The IEEE 802.11 working group has been working in 250 collaboration with the IEEE 802.1 group for several years extending 251 802.1 features over 802.11. As with any wireless media, 802.11 252 imposes new constraints and restrictions to TSN-grade QoS, and 253 tradeoffs between latency and reliability guarantees must be 254 considered as well as managed deployment requirements. An overview 255 of 802.1 TSN capabilities and their extensions to 802.11 are 256 discussed in [Cavalcanti_2019]. 258 Wi-Fi Alliance (WFA) is the worldwide network of companies that 259 drives global Wi-Fi adoption and evolution through thought 260 leadership, spectrum advocacy, and industry-wide collaboration. The 261 WFA work helps ensure that Wi-Fi devices and networks provide users 262 the interoperability, security, and reliability they have come to 263 expect. 265 The following IEEE 802.11 specifications/certifications are relevant 266 in the context of reliable and available wireless services and 267 support for time-sensitive networking capabilities: 269 Time Synchronization: IEEE802.11-2016 with IEEE802.1AS; WFA TimeSync 270 Certification. 272 Congestion Control: IEEE802.11-2016 Admission Control; WFA Admission 273 Control. 275 Security: WFA Wi-Fi Protected Access, WPA2 and WPA3. 277 Interoperating with IEEE802.1Q bridges: IEEE802.11ak. 279 Stream Reservation Protocol (part of IEEE802.1Qat): 280 AIEEE802.11-2016. 282 Scheduled channel access: IEEE802.11ad Enhancements for very 283 high throughput in the 60 GHz band [IEEE80211ad]. 285 802.11 Real-Time Applications: Topic Interest Group (TIG) 286 ReportDoc [IEEE_doc_11-18-2009-06]. 288 In addition, major amendments being developed by the IEEE802.11 289 Working Group include capabilities that can be used as the basis for 290 providing more reliable and predictable wireless connectivity and 291 support time-sensitive applications: 293 IEEE 802.11ax D4.0: Enhancements for High Efficiency (HE). [IEEE802 294 11ax] 296 IEEE 802.11be Extreme High Throughput (EHT). [IEEE80211be] 298 IEE 802.11ay Enhanced throughput for operation in license-exempt 299 bands above 45 GHz. [IEEE80211ay] 301 The main 802.11ax and 802.11be capabilities and their relevance to 302 RAW are discussed in the remainder of this document. 304 4.1.2. 802.11ax High Efficiency (HE) 306 4.1.2.1. General Characteristics 308 The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE802.11ax 309 amendment [IEEE80211ax], which includes new capabilities to increase 310 efficiency, control and reduce latency. Some of the new features 311 include higher order 1024-QAM modulation, support for uplink multi- 312 user MIMO, OFDMA, trigger-based access and Target Wake time (TWT) for 313 enhanced power savings. The OFDMA mode and trigger-based access 314 enable scheduled operation, which is a key capability required to 315 support deterministic latency and reliability for time-sensitive 316 flows. 802.11ax can operate in up to 160 MHz channels and it includes 317 support for operation in the new 6 GHz band, which is expected to be 318 open to unlicensed use by the FCC and other regulatory agencies 319 worldwide. 321 4.1.2.1.1. Multi-User OFDMA and Trigger-based Scheduled Access 323 802.11ax introduced a new orthogonal frequency-division multiple 324 access (OFDMA) mode in which multiple users can be scheduled across 325 the frequency domain. In this mode, the Access Point (AP) can 326 initiate multi-user (MU) Uplink (UL) transmissions in the same PHY 327 Protocol Data Unit (PPDU) by sending a trigger frame. This 328 centralized scheduling capability gives the AP much more control of 329 the channel, and it can remove contention between devices for uplink 330 transmissions, therefore reducing the randomness caused by CSMA-based 331 access between stations. The AP can also transmit simultaneously to 332 multiple users in the downlink direction by using a Downlink (DL) MU 333 OFDMA PPDU. In order to initiate a contention free Transmission 334 Opportunity (TXOP) using the OFDMA mode, the AP still follows the 335 typical listen before talk procedure to acquire the medium, which 336 ensures interoperability and compliance with unlicensed band access 337 rules. However, 802.11ax also includes a multi-user Enhanced 338 Distributed Channel Access (MU-EDCA) capability, which allows the AP 339 to get higher channel access priority. 341 4.1.2.1.2. Improved PHY Robustness 343 The 802.11ax PHY can operate with 0.8, 1.6 or 3.2 microsecond guard 344 interval (GI). The larger GI options provide better protection 345 against multipath, which is expected to be a challenge in industrial 346 environments. The possibility to operate with smaller resource units 347 (e.g. 2 MHz) enabled by OFDMA also helps reduce noise power and 348 improve SNR, leading to better packet error rate (PER) performance. 350 802.11ax supports beamforming as in 802.11ac, but introduces UL MU 351 MIMO, which helps improve reliability. The UL MU MIMO capability is 352 also enabled by the trigger based access operation in 802.11ax. 354 4.1.2.1.3. Support for 6GHz band 356 The 802.11ax specification [IEEE80211ax] includes support for 357 operation in the new 6 GHz band. Given the amount of new spectrum 358 available as well as the fact that no legacy 802.11 device (prior 359 802.11ax) will be able to operate in this new band, 802.11ax 360 operation in this new band can be even more efficient. 362 4.1.2.2. Applicability to deterministic flows 364 TSN capabilities, as defined by the IEEE 802.1 TSN standards, provide 365 the underlying mechanism for supporting deterministic flows in a 366 Local Area Network (LAN). The 802.11 working group has already 367 incorporated support for several TSN capabilities, so that time- 368 sensitive flow can experience precise time synchronization and 369 timeliness when operating over 802.11 links. TSN capabilities 370 supported over 802.11 (which also extends to 802.11ax), include: 372 1. 802.1AS based Time Synchronization (other time synchronization 373 techniques may also be used) 375 2. Interoperating with IEEE802.1Q bridges 377 3. Time-sensitive Traffic Stream identification 379 The exiting 802.11 TSN capabilities listed above, and the 802.11ax 380 OFDMA and scheduled access provide a new set of tools to better 381 server time-sensitive flows. However, it is important to understand 382 the tradeoffs and constraints associated with such capabilities, as 383 well as redundancy and diversity mechanisms that can be used to 384 provide more predictable and reliable performance. 386 4.1.2.2.1. 802.11 Managed network operation and admission control 388 Time-sensitive applications and TSN standards are expected to operate 389 under a managed network (e.g. industrial/enterprise network). Thus, 390 the Wi-Fi operation must also be carefully managed and integrated 391 with the overall TSN management framework, as defined in the IEEE 392 Std. 802.1Qcc specification [IEEE8021Qcc]. 394 Some of the random-access latency and interference from legacy/ 395 unmanaged devices can be minimized under a centralized management 396 mode as defined in IEEE Std. 802.1Qcc, in which admission control 397 procedures are enforced. 399 Existing traffic stream identification, configuration and admission 400 control procedures defined in IEEE Std. 802.11 QoS mechanism can be 401 re-used. However, given the high degree of determinism required by 402 many time-sensitive applications, additional capabilities to manage 403 interference and legacy devices within tight time-constraints need to 404 be explored. 406 4.1.2.2.2. Scheduling for bounded latency and diversity 408 As discussed earlier, the 802.11ax OFDMA mode introduces the 409 possibility of assigning different RUs (frequency resources) to users 410 within a PPDU. Several RU sizes are defined in the specification 411 (26, 52, 106, 242, 484, 996 subcarriers). In addition, the AP can 412 also decide on MCS and grouping of users within a given OFMDA PPDU. 413 Such flexibility can be leveraged to support time-sensitive 414 applications with bounded latency, especially in a managed network 415 where stations can be configured to operate under the control of the 416 AP. 418 As shown in [Cavalcanti_2019], it is possible to achieve latencies in 419 the order of 1msec with high reliability in an interference free 420 environment. Obviously, there are latency, reliability and capacity 421 tradeoffs to be considered. For instance, smaller Resource Units 422 (RU)s result in longer transmission durations, which may impact the 423 minimal latency that can be achieved, but the contention latency and 424 randomness elimination due to multi-user transmission is a major 425 benefit of the OFDMA mode. 427 The flexibility to dynamically assign RUs to each transmission also 428 enables the AP to provide frequency diversity, which can help 429 increase reliability. 431 4.1.3. 802.11be Extreme High Throughput (EHT) 433 4.1.3.1. General Characteristics 435 The 802.11be is the next major 802.11 amendment (after 802.11ax) for 436 operation in the 2.4, 5 and 6 GHz bands. 802.11be is expected to 437 include new PHY and MAC features and it is targeting extremely high 438 throughput (at least 30 Gbps), as well as enhancements to worst case 439 latency and jitter. It is also expected to improve the integration 440 with 802.1 TSN to support time-sensitive applications over Ethernet 441 and Wireless LANs. 443 The 802.11be Task Group started its operation in May 2019, therefore, 444 detailed information about specific features is not yet available. 445 Only high level candidate features have been discussed so far, 446 including: 448 1. 320MHz bandwidth and more efficient utilization of non- 449 contiguous spectrum. 451 2. Multi-band/multi-channel aggregation and operation. 453 3. 16 spatial streams and related MIMO enhancements. 455 4. Multi-Access Point (AP) Coordination. 457 5. Enhanced link adaptation and retransmission protocol, e.g. 458 Hybrid Automatic Repeat Request (HARQ). 460 6. Any required adaptations to regulatory rules for the 6 GHz 461 spectrum. 463 4.1.3.2. Applicability to deterministic flows 465 The 802.11 Real-Time Applications (RTA) Topic Interest Group (TIG) 466 provided detailed information on use cases, issues and potential 467 solution directions to improve support for time-sensitive 468 applications in 802.11. The RTA TIG report [IEEE_doc_11-18-2009-06] 469 was used as input to the 802.11be project scope. 471 Improvements for worst-case latency, jitter and reliability were the 472 main topics identified in the RTA report, which were motivated by 473 applications in gaming, industrial automation, robotics, etc. The 474 RTA report also highlighted the need to support additional TSN 475 capabilities, such as time-aware (802.1Qbv) shaping and packet 476 replication and elimination as defined in 802.1CB. 478 802.11be is expected to build on and enhance 802.11ax capabilities to 479 improve worst case latency and jitter. Some of the enhancement areas 480 are discussed next. 482 4.1.3.2.1. Enhanced scheduled operation for bounded latency 484 In addition to the throughput enhancements, 802.11be will leverage 485 the trigger-based scheduled operation enabled by 802.11ax to provide 486 efficient and more predictable medium access. 802.11be is expected to 487 include enhancements to reduce overhead and enable more efficient 488 operation in managed network deployments [IEEE_doc_11-19-0373-00]. 490 4.1.3.2.2. Multi-AP coordination 492 Multi-AP coordination is one of the main new candidate features in 493 802.11be. It can provide benefits in throughput and capacity and has 494 the potential to address some of the issues that impact worst case 495 latency and reliability. Multi-AP coordination is expected to 496 address the contention due to overlapping Basic Service Sets (OBSS), 497 which is one of the main sources of random latency variations. 498 802.11be can define methods to enable better coordination between 499 APs, for instance, in a managed network scenario, in order to reduce 500 latency due to unmanaged contention. 502 Several multi-AP coordination approaches have been discussed with 503 different levels of complexities and benefits, but specific 504 coordination methods have not yet been defined. 506 4.1.3.2.3. Multi-band operation 508 802.11be will introduce new features to improve operation over 509 multiple bands and channels. By leveraging multiple bands/channels, 510 802.11be can isolate time-sensitive traffic from network congestion, 511 one of the main causes of large latency variations. In a managed 512 802.11be network, it should be possible to steer traffic to certain 513 bands/channels to isolate time-sensitive traffic from other traffic 514 and help achieve bounded latency. 516 4.1.4. 802.11ad and 802.11ay (mmWave operation) 518 4.1.4.1. General Characteristics 520 The IEEE 802.11ad amendment defines PHY and MAC capabilities to 521 enable multi-Gbps throughput in the 60 GHz millimeter wave (mmWave) 522 band. The standard addresses the adverse mmWave signal propagation 523 characteristics and provides directional communication capabilities 524 that take advantage of beamforming to cope with increased 525 attenuation. An overview of the 802.11ad standard can be found in 526 [Nitsche_2015] . 528 The IEEE 802.11ay is currently developing enhancements to the 529 802.11ad standard to enable the next generation mmWave operation 530 targeting 100 Gbps throughput. Some of the main enhancements in 531 802.11ay include MIMO, channel bonding, improved channel access and 532 beamforming training. An overview of the 802.11ay capabilities can 533 be found in [Ghasempour_2017] 535 4.1.4.2. Applicability to deterministic flows 537 The high data rates achievable with 802.11ad and 802.11ay can 538 significantly reduce latency down to microsecond levels. Limited 539 interference from legacy and other unlicensed devices in 60 GHz is 540 also a benefit. However, directionality and short range typical in 541 mmWave operation impose new challenges such as the overhead required 542 for beam training and blockage issues, which impact both latency and 543 reliability. Therefore, it is important to understand the use case 544 and deployment conditions in order to properly apply and configure 545 802.11ad/ay networks for time sensitive applications. 547 The 802.11ad standard include a scheduled access mode in which 548 stations can be allocated contention-free service periods by a 549 central controller. This scheduling capability is also available in 550 802.11ay, and it is one of the mechanisms that can be used to provide 551 bounded latency to time-sensitive data flows. An analysis of the 552 theoretical latency bounds that can be achieved with 802.11ad service 553 periods is provided in [Cavalcanti_2019]. 555 4.2. IEEE 802.15.4 557 4.2.1. Provenance and Documents 559 The IEEE802.15.4 Task Group has been driving the development of low- 560 power low-cost radio technology. The Timeslotted Channel Hopping 561 mode, added to the 2015 revision of the IEEE802.15.4 standard 562 [IEEE802154], is targeted at the embedded and industrial world, where 563 reliability, energy consumption and cost drive the application space. 565 The IEEE802.15.4 physical layer has been designed to support 566 demanding low-power scenarios targeting the use of unlicensed bands, 567 both the 2.4 GHz and sub GHz Industrial, Scientific and Medical (ISM) 568 bands. This has imposed requirements in terms of frame size, data 569 rate and bandwidth to achieve reduced collision probability, reduced 570 packet error rate, and acceptable range with limited transmission 571 power. The PHY layer supports frames of up to 127 bytes. The Medium 572 Access Control (MAC) sublayer overhead is in the order of 10-20 573 bytes, leaving about 100 bytes to the upper layers. IEEE802.15.4 574 uses spread spectrum modulation such as the Direct Sequence Spread 575 Spectrum (DSSS). 577 IPv6 over TSCH is enabled by the work done at the 6TiSCH WG. 6TiSCH 578 has enabled best effort distributed scheduling to exploit the 579 deterministic access capabilities provided by TSCH. The group 580 designed the essential mechanisms to enable the management plane 581 operation while ensuring IPv6 is supported. Yet the charter did not 582 focus to providing a solution to establish end to end tracks while 583 meeting quality of service requirements. 6TiSCH, through the RFC8480 584 [RFC8480] defines the 6P protocol which provides a pairwise 585 negotiation mechanism to the control plane operation. The protocol 586 supports agreement on a schedule between neighbors, enabling 587 distributed scheduling. 6P goes hand-in-hand with a Scheduling 588 Function (SF), the policy that decides how to maintain cells and 589 trigger 6P transactions. The Minimal Scheduling Function (MSF) 590 [I-D.ietf-6tisch-msf] is the default SF defined by the 6TiSCH WG; 591 other standardized SFs can be defined in the future. MSF extends the 592 minimal schedule configuration, and is used to add child-parent links 593 according to the traffic load. 595 Time sensitive networking on low power constrained wireless networks 596 have been addressed by ISA100.11a and WirelessHART. TODO 598 The 6TiSCH architecture [I-D.ietf-6tisch-architecture] already 599 identified different models to schedule resources along tracks 600 exploiting the TSCH schedule structure however these models have not 601 been standardized. A Track, in the 6TiSCH architecture is considered 602 a directed path from a source 6TiSCH node to one or more 603 destination(s) 6TiSCH node(s) through the 6TiSCH network. A Track in 604 6TiSCH is the implementation of the deterministic path in the Detnet 605 architecture [I-D.ietf-detnet-architecture] . Along a Track, 6TiSCH 606 nodes reserve the resources to enable the efficient transmission of 607 packets while aiming to optimize certain properties such as 608 reliability and ensure small jitter or bounded latency. The track 609 structure enables Layer-2 forwarding schemes, reducing the overhead 610 of taking routing decisions at the Layer-3. Serial Tracks can be 611 understood as the concatenation of cells or bundles along a routing 612 path from a node towards a destination. The serial track concept is 613 analogous to the circuit concept where resources are chained through 614 the multi-hop topology. For example, A bundle of Tx Cells in a 615 particular node is paired to a bundle of Rx Cells in the next hop 616 node following a routing path. More complex approaches are described 617 in and complemented by extensions to the RPL routing protocol in 618 [I-D.ietf-roll-nsa-extension]. Reliability measures are for example 619 achieved by exploiting concepts such as Replication and Elimination. 620 In them, packets at origin are replicated and transmitted along 621 disjoint tracks. This redundancy measure exploiting track forwarding 622 increases energy consumption of the network nodes but improves 623 significantly the reliability of the network. 625 Useful References include: 627 1. IEEE Std 802.15.4: "IEEE Std. 802.15.4, Part. 15.4: Wireless 628 Medium Access Control (MAC) and Physical Layer (PHY) 629 Specifications for Low-Rate Wireless Personal Area Networks" 630 [IEEE802154]. The latest version at the time of this writing is 631 dated year 2015. 633 2. Morell, A. , Vilajosana, X. , Vicario, J. L. and Watteyne, T. 634 (2013), Label switching over IEEE802.15.4e networks. Trans. 635 Emerging Tel. Tech., 24: 458-475. doi:10.1002/ett.2650" 636 [morell13]. 638 3. De Armas, J., Tuset, P., Chang, T., Adelantado, F., Watteyne, 639 T., Vilajosana, X. (2016, September). Determinism through path 640 diversity: Why packet replication makes sense. In 2016 641 International Conference on Intelligent Networking and 642 Collaborative Systems (INCoS) (pp. 150-154). IEEE. [dearmas16]. 644 4. X. Vilajosana, T. Watteyne, M. Vucinic, T. Chang and K. S. 645 J. Pister, "6TiSCH: Industrial Performance for IPv6 Internet- 646 of-Things Networks," in Proceedings of the IEEE, vol. 107, no. 647 6, pp. 1153-1165, June 2019. [vilajosana19]. 649 4.2.2. TimeSlotted Channel Hopping 651 4.2.2.1. General Characteristics 653 As a core technique in IEEE802.15.4, TSCH splits time in multiple 654 time slots that repeat over time. The structure is referred as a 655 Slotframe. For each timeslot, a set of available frequencies can be 656 used, resulting in a matrix-like schedule (see Fig. Figure 1). 658 timeslot offset 659 | 0 1 2 3 4 | 0 1 2 3 4 | Nodes 660 +------------------------+------------------------+ +-----+ 661 | | | | | | | | | | | | C | 662 CH-1 | EB | | |C->B| | EB | | |C->B| | | | 663 | | | | | | | | | | | +-----+ 664 +-------------------------------------------------+ | 665 | | | | | | | | | | | | 666 CH-2 | | |B->C| |B->A| | |B->C| |B->A| +-----+ 667 | | | | | | | | | | | | B | 668 +-------------------------------------------------+ | | 669 ... +-----+ 670 | 671 +-------------------------------------------------+ | 672 | | | | | | | | | | | +-----+ 673 CH-15| |A->B| | | | |A->B| | | | | A | 674 | | | | | | | | | | | | | 675 +-------------------------------------------------+ +-----+ 676 ch. 677 offset 679 Figure 1: Slotframe example with scheduled cells between nodes A, B 680 and C 682 This schedule represents the possible communications of a node with 683 its neighbors, and is managed by a Scheduling Function such as The 684 Minimal Scheduling Function (MSF) [I-D.ietf-6tisch-msf]. Each cell 685 in the schedule is identified by its slotoffset and channeloffset 686 coordinates. A cell's timeslot offset indicates its position in 687 time, relative to the beginning of the slotframe. A cell's channel 688 offset is an index which maps to a frequency at each iteration of the 689 slotframe. Each packet exchanged between neighbors happens within 690 one cell. An Absolute Slot Number (ASN) indicates the number of 691 slots elapsed since the network started. It increments at every 692 slot. This is a 5 byte counter that can support networks running for 693 more than 300 years without wrapping (assuming a 10 ms timeslot). 694 Channel hopping provides increased reliability to multi-path fading 695 and external interference. It is handled by TSCH through a channel 696 hopping sequence referred as macHopSeq in the IEEE802.15.4 697 specification. 699 The Time-Frequency Division Multiple Access provided by TSCH enables 700 the orchestration of traffic flows, spreading them in time and 701 frequency, and hence enabling an efficient management of the 702 bandwidth utilization. Such efficient bandwidth utilization can be 703 combined to OFDM modulations also supported by the IEEE802.15.4 704 standard [IEEE802154] since the 2015 version. 706 In the RAW context, low power reliable networks should address non- 707 critical control scenarios such as Class 2 and monitoring scenarios 708 such as Class 4 defined by the RFC5673 [RFC5673]. As a low power 709 technology targeting industrial scenarios radio transducers provide 710 low data rates (typically between 50kbps to 250kbps) and robust 711 modulations to trade-off performance to reliability. TSCH networks 712 are organized in mesh topologies and connected to a backbone. 713 Latency in the mesh network is mainly influenced by propagation 714 aspects such as interference. ARQ methods and redundancy techniques 715 such as replication and elimination should be studied to provide the 716 needed performance to address deterministic scenarios. 718 4.2.2.2. Applicability to Deterministic Flows 720 Nodes in a TSCH network are tightly synchronized. This enables to 721 build the slotted structure an ensure efficient utilization of 722 resources thranks to proper scheduling policies. Scheduling is a key 723 to orchestrate the resources that different nodes in a track or path 724 are using. Slotframes can be split in resource blocks reserving the 725 needed capacity to certain needs. Periodic and bursty traffic can be 726 handled independently in the schedule, using active and reactive 727 policies and taking advantage of certain cell overprovision. Along a 728 track, resource blocks can be chained so nodes in previous hops 729 transmit their data before those that come later. This provides a 730 tight control to latency along a track. Redundancy is achieved in a 731 best effort manner by overprovision, giving time to the management 732 plane of the network to request more resources if needed. -time 733 synchronization - scheduling capabilities, discuss such things as 734 Resource Units, time slots or resource blocks. Can we reserve 735 periodic resources vs. ask each time, what precision can we get in 736 latency control. - diversity scenarios, what's available, - gap 737 analysis, e.g. discuss multihop, or what's missing how to do PAREO 738 features. 740 5. 3GPP standards 742 6. IANA Considerations 744 This specification does not require IANA action. 746 7. Security Considerations 748 Most RAW technologies integrate some authentication or encryption 749 mechanisms that were defined outside the IETF. 751 8. Acknowledgments 753 Many thanks to the participants of the RAW WG where a lot of the work 754 discussed here happened. 756 9. References 758 9.1. Normative References 760 [I-D.ietf-6tisch-architecture] 761 Thubert, P., "An Architecture for IPv6 over the TSCH mode 762 of IEEE 802.15.4", draft-ietf-6tisch-architecture-20 (work 763 in progress), March 2019. 765 [I-D.ietf-detnet-architecture] 766 Finn, N., Thubert, P., Varga, B., and J. Farkas, 767 "Deterministic Networking Architecture", draft-ietf- 768 detnet-architecture-13 (work in progress), May 2019. 770 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 771 Phinney, "Industrial Routing Requirements in Low-Power and 772 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 773 2009, . 775 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 776 (IPv6) Specification", STD 86, RFC 8200, 777 DOI 10.17487/RFC8200, July 2017, 778 . 780 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 781 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 782 DOI 10.17487/RFC8480, November 2018, 783 . 785 9.2. Informative References 787 [Cavalcanti_2019] 788 Dave Cavalcanti et al., "Extending Time Distribution and 789 Timeliness Capabilities over the Air to Enable Future 790 Wireless Industrial Automation Systems, the Proceedings of 791 IEEE", June 2019. 793 [dearmas16] 794 Jesica de Armas et al., "Determinism through path 795 diversity: Why packet replication makes sense", September 796 2016. 798 [Ghasempour_2017] 799 Yasaman Ghasempour et al., "802.11ay: Next-Generation 60 800 GHz Communications for 100 Gb/s Wi-Fi", December 2017. 802 [I-D.ietf-6tisch-msf] 803 Chang, T., Vucinic, M., Vilajosana, X., Duquennoy, S., and 804 D. Dujovne, "6TiSCH Minimal Scheduling Function (MSF)", 805 draft-ietf-6tisch-msf-03 (work in progress), April 2019. 807 [I-D.ietf-roll-nsa-extension] 808 Koutsiamanis, R., Papadopoulos, G., Montavont, N., and P. 809 Thubert, "RPL DAG Metric Container Node State and 810 Attribute object type extension", draft-ietf-roll-nsa- 811 extension-01 (work in progress), March 2019. 813 [IEEE80211] 814 "IEEE Standard 802.11 - IEEE Standard for Information 815 Technology - Telecommunications and information exchange 816 between systems Local and metropolitan area networks - 817 Specific requirements - Part 11: Wireless LAN Medium 818 Access Control (MAC) and Physical Layer (PHY) 819 Specifications.". 821 [IEEE80211ad] 822 "802.11ad: Enhancements for very high throughput in the 60 823 GHz band". 825 [IEEE80211ak] 826 "802.11ak: Enhancements for Transit Links Within Bridged 827 Networks", 2017. 829 [IEEE80211ax] 830 "802.11ax D4.0: Enhancements for High Efficiency WLAN". 832 [IEEE80211ay] 833 "802.11ay: Enhanced throughput for operation in license- 834 exempt bands above 45 GHz". 836 [IEEE80211be] 837 "802.11be: Extreme High Throughput". 839 [IEEE802154] 840 IEEE standard for Information Technology, "IEEE Std. 841 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 842 and Physical Layer (PHY) Specifications for Low-Rate 843 Wireless Personal Area Networks". 845 [IEEE8021Qat] 846 "802.1Qat: Stream Reservation Protocol". 848 [IEEE8021Qcc] 849 "802.1Qcc: IEEE Standard for Local and Metropolitan Area 850 Networks--Bridges and Bridged Networks -- Amendment 31: 851 Stream Reservation Protocol (SRP) Enhancements and 852 Performance Improvements". 854 [IEEE_doc_11-18-2009-06] 855 "802.11 Real-Time Applications (RTA) Topic Interest Group 856 (TIG) Report", November 2018. 858 [IEEE_doc_11-19-0373-00] 859 Kevin Stanton et Al., "Time-Sensitive Applications Support 860 in EHT", March 2019. 862 [morell13] 863 Antoni Morell et al., "Label switching over IEEE802.15.4e 864 networks", April 2013. 866 [Nitsche_2015] 867 Thomas Nitsche et al., "IEEE 802.11ad: directional 60 GHz 868 communication for multi-Gigabit-per-second Wi-Fi", 869 December 2014. 871 [vilajosana19] 872 Xavier Vilajosana et al., "6TiSCH: Industrial Performance 873 for IPv6 Internet-of-Things Networks", June 2019. 875 Authors' Addresses 877 Pascal Thubert (editor) 878 Cisco Systems, Inc 879 Building D 880 45 Allee des Ormes - BP1200 881 MOUGINS - Sophia Antipolis 06254 882 FRANCE 884 Phone: +33 497 23 26 34 885 Email: pthubert@cisco.com 886 Dave Cavalcanti 887 Intel Corporation 888 2111 NE 25th Ave 889 Hillsboro, OR 97124 890 USA 892 Phone: 503 712 5566 893 Email: dave.cavalcanti@intel.com 895 Xavier Vilajosana 896 Universitat Oberta de Catalunya 897 156 Rambla Poblenou 898 Barcelona, Catalonia 08018 899 Spain 901 Email: xvilajosana@uoc.edu