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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: 30 January 2022 Intel 6 X. Vilajosana 7 Universitat Oberta de Catalunya 8 C. Schmitt 9 Research Institute CODE, UniBwM 10 J. Farkas 11 Ericsson 12 29 July 2021 14 Reliable and Available Wireless Technologies 15 draft-ietf-raw-technologies-03 17 Abstract 19 This document presents a series of recent technologies that are 20 capable of time synchronization and scheduling of transmission, 21 making them suitable to carry time-sensitive flows with high 22 reliability and availability. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on 30 January 2022. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 48 license-info) in effect on the date of publication of this document. 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. Code Components 51 extracted from this document must include Simplified BSD License text 52 as described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 58 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 3. On Scheduling . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3.1. Benefits of Scheduling on Wires . . . . . . . . . . . . . 5 61 3.2. Benefits of Scheduling on Wireless . . . . . . . . . . . 5 62 4. IEEE 802.11 . . . . . . . . . . . . . . . . . . . . . . . . . 6 63 4.1. Provenance and Documents . . . . . . . . . . . . . . . . 6 64 4.2. 802.11ax High Efficiency (HE) . . . . . . . . . . . . . . 8 65 4.2.1. General Characteristics . . . . . . . . . . . . . . . 8 66 4.2.2. Applicability to deterministic flows . . . . . . . . 9 67 4.3. 802.11be Extreme High Throughput (EHT) . . . . . . . . . 11 68 4.3.1. General Characteristics . . . . . . . . . . . . . . . 11 69 4.3.2. Applicability to deterministic flows . . . . . . . . 12 70 4.4. 802.11ad and 802.11ay (mmWave operation) . . . . . . . . 13 71 4.4.1. General Characteristics . . . . . . . . . . . . . . . 13 72 4.4.2. Applicability to deterministic flows . . . . . . . . 13 73 5. IEEE 802.15.4 . . . . . . . . . . . . . . . . . . . . . . . . 14 74 5.1. Provenance and Documents . . . . . . . . . . . . . . . . 14 75 5.2. TimeSlotted Channel Hopping . . . . . . . . . . . . . . . 15 76 5.2.1. General Characteristics . . . . . . . . . . . . . . . 16 77 5.2.2. Applicability to Deterministic Flows . . . . . . . . 18 78 6. 5G . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 79 6.1. Provenance and Documents . . . . . . . . . . . . . . . . 31 80 6.2. General Characteristics . . . . . . . . . . . . . . . . . 33 81 6.3. Deployment and Spectrum . . . . . . . . . . . . . . . . . 34 82 6.4. Applicability to Deterministic Flows . . . . . . . . . . 35 83 6.4.1. System Architecture . . . . . . . . . . . . . . . . . 35 84 6.4.2. Overview of The Radio Protocol Stack . . . . . . . . 37 85 6.4.3. Radio (PHY) . . . . . . . . . . . . . . . . . . . . . 38 86 6.4.4. Scheduling and QoS (MAC) . . . . . . . . . . . . . . 40 87 6.4.5. Time-Sensitive Networking (TSN) Integration . . . . . 42 88 6.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 46 89 7. L-band Digital Aeronautical Communications System . . . . . . 47 90 7.1. Provenance and Documents . . . . . . . . . . . . . . . . 48 91 7.2. General Characteristics . . . . . . . . . . . . . . . . . 49 92 7.3. Deployment and Spectrum . . . . . . . . . . . . . . . . . 50 93 7.4. Applicability to Deterministic Flows . . . . . . . . . . 50 94 7.4.1. System Architecture . . . . . . . . . . . . . . . . . 51 95 7.4.2. Overview of The Radio Protocol Stack . . . . . . . . 51 96 7.4.3. Radio (PHY) . . . . . . . . . . . . . . . . . . . . . 52 97 7.4.4. Scheduling, Frame Structure and QoS (MAC) . . . . . . 53 98 7.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 55 99 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 56 100 9. Security Considerations . . . . . . . . . . . . . . . . . . . 56 101 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 56 102 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 56 103 12. Normative References . . . . . . . . . . . . . . . . . . . . 56 104 13. Informative References . . . . . . . . . . . . . . . . . . . 57 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 66 107 1. Introduction 109 When used in math or philosophy, the term "deterministic" generally 110 refers to a perfection where all aspect are understood and 111 predictable. A perfectly Deterministic Network would ensure that 112 every packet reach its destination following a predetermined path 113 along a predefined schedule to be delivered at the exact due time. 114 In a real and imperfect world, a Deterministic Network must highly 115 predictable, which is a combination of reliability and availability. 116 On the one hand the network must be reliable, meaning that it will 117 perform as expected for all packets and in particular that it will 118 always deliver the packet at the destination in due time. On the 119 other hand, the network must be available, meaning that it is 120 resilient to any single outage, whether the cause is a software, a 121 hardware or a transmission issue. 123 RAW (Reliable and Available Wireless) is an effort to provide 124 Deterministic Networking on across a path that include a wireless 125 physical layer. Making Wireless Reliable and Available is even more 126 challenging than it is with wires, due to the numerous causes of loss 127 in transmission that add up to the congestion losses and the delays 128 caused by overbooked shared resources. In order to maintain a 129 similar quality of service along a multihop path that is composed of 130 wired and wireless hops, additional methods that are specific to 131 wireless must be leveraged to combat the sources of loss that are 132 also specific to wireless. 134 Such wireless-specific methods include per-hop retransmissions (HARQ) 135 and P2MP overhearing whereby multiple receivers are scheduled to 136 receive the same transmission, which balances the adverse effects of 137 the transmission losses that are experienced when a radio is used as 138 pure P2P. Those methods are collectively referred to as PAREO 139 functions in the "Reliable and Available Wireless Architecture/ 140 Framework" [I-D.pthubert-raw-architecture]. 142 2. Terminology 144 This specification uses several terms that are uncommon on protocols 145 that ensure bets effort transmissions for stochastics flows, such as 146 found in the traditional Internet and other statistically multiplexed 147 packet networks. 149 ARQ: Automatic Repeat Request, enabling an acknowledged transmission 150 and retries. ARQ is a typical model at Layer-2 on a wireless 151 medium. It is typically avoided end-to-end on deterministic flows 152 because it introduces excessive indetermination in latency, but a 153 limited number of retries within a bounded time may be used over a 154 wireless link and yet respect end-to-end constraints. 156 Available: That is exempt of unscheduled outage, the expectation for 157 a network being that the flow is maintained in the face of any 158 single breakage. 160 Deterministic Networking We refer to section 2 of [RFC8557] for this 161 term. 163 FEC: Forward error correction, sending redundant coded data to help 164 the receiver recover transmission errors without the delays 165 incurred with ARQ. 167 HARQ: Hybrid ARQ, a combination of FEC and ARQ. 169 PCE: Path Computation Element. 171 PAREO (functions): the wireless extension of DetNet PREOF. PAREO 172 functions include scheduled ARQ at selected hops, and expect the 173 use of new operations like overhearing where available. 175 Reliable: That consistently performs as expected, the expectation 176 for a network being to always deliver a packet in due time. 178 Track: A DODAG oriented to a destination, and that enables Packet 179 ARQ, Replication, Elimination, and Ordering Functions. 181 3. On Scheduling 183 The operations of a Deterministic Network often rely on precisely 184 applying a tight schedule, in order to avoid collision loss and 185 guarantee the worst-case time of delivery. To achieve this, there 186 must be a shared sense of time throughout the network. The sense of 187 time is usually provided by the lower layer and is not in scope for 188 RAW. 190 3.1. Benefits of Scheduling on Wires 192 A network is reliable when the statistical effects that affect the 193 packet transmission are eliminated. This involves maintaining at all 194 time the amount of critical packets within the physical capabilities 195 of the hardware and that of the radio medium. This is achieved by 196 controlling the use of time-shared resources such as CPUs and 197 buffers, by shaping the flows and by scheduling the time of 198 transmission of the packets that compose the flow at every hop. 200 Equipment failure, such as an access point rebooting, a broken radio 201 adapter, or a permanent obstacle to the transmission, is a secondary 202 source of packet loss. When a breakage occurs, multiple packets are 203 lost in a row before the flows are rerouted or the system may 204 recover. This is not acceptable for critical applications such as 205 related to safety. A typical process control loop will tolerate an 206 occasional packet loss, but a loss of several packets in a row will 207 cause an emergency stop (e.g., after 4 packets lost, within a period 208 of 1 second). 210 Network Availability is obtained by making the transmission resilient 211 against hardware failures and radio transmission losses due to 212 uncontrolled events such as co-channel interferers, multipath fading 213 or moving obstacles. The best results are typically achieved by 214 pseudo randomly cumulating all forms of diversity, in the spatial 215 domain with replication and elimination, in the time domain with ARQ 216 and diverse scheduled transmissions, and in the frequency domain with 217 frequency hopping or channel hopping between frames. 219 3.2. Benefits of Scheduling on Wireless 221 In addition to the benefits listed in Section 3.1, scheduling 222 transmissions provides specific value to the wireless medium. 224 On the one hand, scheduling avoids collisions between scheduled 225 transmissions and can ensure both time and frequency diversity 226 between retries in order to defeat co-channel interference from un- 227 controlled transmitters as well as multipath fading. Transmissions 228 can be scheduled on multiple channels in parallel, which enables to 229 use the full available spectrum while avoiding the hidden terminal 230 problem, e.g., when the next packet in a same flow interferes on a 231 same channel with the previous one that progressed a few hops 232 farther. 234 On the other hand, scheduling optimizes the bandwidth usage: compared 235 to classical Collision Avoidance techniques, there is no blank time 236 related to inter-frame space (IFS) and exponential back-off in 237 scheduled operations. A minimal Clear Channel Assessment may be 238 needed to comply with the local regulations such as ETSI 300-328, but 239 that will not detect a collision when the senders are synchronized. 240 And because scheduling allows a time-sharing operation, there is no 241 limit to the ratio of isolated critical traffic. 243 Finally, scheduling plays a critical role to save energy. In IOT, 244 energy is the foremost concern, and synchronizing sender and listener 245 enables to always maintain them in deep sleep when there is no 246 scheduled transmission. This avoids idle listening and long 247 preambles and enables long sleep periods between traffic and 248 resynchronization, allowing battery-operated nodes to operate in a 249 mesh topology for multiple years. 251 4. IEEE 802.11 253 4.1. Provenance and Documents 255 With an active portfolio of nearly 1,300 standards and projects under 256 development, IEEE is a leading developer of industry standards in a 257 broad range of technologies that drive the functionality, 258 capabilities, and interoperability of products and services, 259 transforming how people live, work, and communicate. 261 The IEEE 802 LAN/MAN Standards Committee (SC) develops and maintains 262 networking standards and recommended practices for local, 263 metropolitan, and other area networks, using an open and accredited 264 process, and advocates them on a global basis. The most widely used 265 standards are for Ethernet, Bridging and Virtual Bridged LANs 266 Wireless LAN, Wireless PAN, Wireless MAN, Wireless Coexistence, Media 267 Independent Handover Services, and Wireless RAN. An individual 268 Working Group provides the focus for each area. Standards produced 269 by the IEEE 802 SC are freely available from the IEEE GET Program 270 after they have been published in PDF for six months. 272 The IEEE 802.11 Wireless LAN (WLAN) standards define the underlying 273 MAC and PHY layers for the Wi-Fi technology. Wi-Fi/802.11 is one of 274 the most successful wireless technologies, supporting many 275 application domains. While previous 802.11 generations, such as 276 802.11n and 802.11ac, have focused mainly on improving peak 277 throughput, more recent generations are also considering other 278 performance vectors, such as efficiency enhancements for dense 279 environments in 802.11ax, latency, reliability and enhancements 280 supporting Time-Sensitive Networking (TSN) capabilities in P802.11be. 282 IEEE std 802.11-2012 introduced support for TSN time synchronization 283 based on IEEE 802.1AS over 802.11 Timing Measurement protocol. IEEE 284 802.11-2016 extended the 802.1AS operation over 802.11 Fine Timing 285 Measurement (FTM), as well as the Stream Reservation Protocol (IEEE 286 802.1Qat). 802.11 WLANs can also be part of a 802.1Q bridged networks 287 with enhancements enabled by the 802.11ak amendment. Traffic 288 classification based on 802.1Q VLAN tags is also supported in 802.11. 289 Other 802.1 TSN capabilities such as 802.1Qbv and 802.1CB, which are 290 media agnostic, can already operate over 802.11. The IEEE Std. 291 802.11ax-2021 adds new scheduling capabilities that can enhance the 292 timeliness performance in the 802.11 MAC and achieve lower bounded 293 latency. The IEEE 802.11be is undergoing efforts to enhance the 294 support for 802.1 TSN capabilities especially related to worst-case 295 latency, reliability and availability. The IEEE 802.11 working group 296 has been working in collaboration with the IEEE 802.1 working group 297 for several years extending some 802.1 features over 802.11. As with 298 any wireless media, 802.11 imposes new constraints and restrictions 299 to TSN-grade QoS, and tradeoffs between latency and reliability 300 guarantees must be considered as well as managed deployment 301 requirements. An overview of 802.1 TSN capabilities and challenges 302 for their extensions to 802.11 are discussed in [Cavalcanti_2019]. 304 Wi-Fi Alliance (WFA) is the worldwide network of companies that 305 drives global Wi-Fi adoption and evolution through thought 306 leadership, spectrum advocacy, and industry-wide collaboration. The 307 WFA work helps ensure that Wi-Fi devices and networks provide users 308 the interoperability, security, and reliability they have come to 309 expect. 311 The following [IEEE Std. 802.11] specifications/certifications are 312 relevant in the context of reliable and available wireless services 313 and support for time-sensitive networking capabilities: 315 Time Synchronization: IEEE802.11-2016 with IEEE802.1AS; WFA TimeSync 316 Certification. 318 Congestion Control: IEEE802.11-2016 Admission Control; WFA Admission 319 Control. 321 Security: WFA Wi-Fi Protected Access, WPA2 and WPA3. 323 Interoperating with IEEE802.1Q bridges: [IEEE Std. 802.11ak]. 325 Stream Reservation Protocol (part of [IEEE Std. 802.1Qat]): AIEEE802 326 .11-2016 328 Scheduled channel access: IEEE802.11ad Enhancements for very high 329 throughput in the 60 GHz band [IEEE Std. 802.11ad]. 331 802.11 Real-Time Applications: Topic Interest Group (TIG) ReportDoc 332 [IEEE_doc_11-18-2009-06]. 334 In addition, major amendments being developed by the IEEE802.11 335 Working Group include capabilities that can be used as the basis for 336 providing more reliable and predictable wireless connectivity and 337 support time-sensitive applications: 339 IEEE 802.11ax D4.0: Enhancements for High Efficiency (HE). [IEEE 340 Std. 802.11ax] 342 IEEE 802.11be Extreme High Throughput (EHT). [IEEE 802.11be WIP] 344 IEE 802.11ay Enhanced throughput for operation in license-exempt 345 bands above 45 GHz. [IEEE Std. 802.11ay] 347 The main 802.11ax and 802.11be capabilities and their relevance to 348 RAW are discussed in the remainder of this document. 350 4.2. 802.11ax High Efficiency (HE) 352 4.2.1. General Characteristics 354 The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE802.11ax 355 amendment [IEEE Std. 802.11ax], which includes new capabilities to 356 increase efficiency, control and reduce latency. Some of the new 357 features include higher order 1024-QAM modulation, support for uplink 358 multi-user MIMO, OFDMA, trigger-based access and Target Wake time 359 (TWT) for enhanced power savings. The OFDMA mode and trigger-based 360 access enable the AP, after acquiring the channel for a given 361 duration, to schedule multi-user transmissions, which is a key 362 capability required to increase latency predictability and and 363 reliability for time-sensitive flows. 802.11ax can operate in up to 364 160 MHz channels and it includes support for operation in the new 6 365 GHz band, which is expected to be open to unlicensed use by the FCC 366 and other regulatory agencies worldwide. 368 4.2.1.1. Multi-User OFDMA and Trigger-based Scheduled Access 370 802.11ax introduced a new orthogonal frequency-division multiple 371 access (OFDMA) mode in which multiple users can be scheduled across 372 the frequency domain. In this mode, the Access Point (AP) can 373 initiate multi-user (MU) Uplink (UL) transmissions in the same PHY 374 Protocol Data Unit (PPDU) by sending a trigger frame. This 375 centralized scheduling capability gives the AP much more control of 376 the channel in its Basic Service Set (BSS) and it can remove 377 contention between associated stations for uplink transmissions, 378 therefore reducing the randomness caused by CSMA-based access between 379 stations within the same BSS. The AP can also transmit 380 simultaneously to multiple users in the downlink direction by using a 381 Downlink (DL) MU OFDMA PPDU. In order to initiate a contention free 382 Transmission Opportunity (TXOP) using the OFDMA mode, the AP still 383 follows the typical listen before talk procedure to acquire the 384 medium, which ensures interoperability and compliance with unlicensed 385 band access rules. However, 802.11ax also includes a multi-user 386 Enhanced Distributed Channel Access (MU-EDCA) capability, which 387 allows the AP to get higher channel access priority than other 388 devices in its BSS. 390 4.2.1.2. Improved PHY Robustness 392 The 802.11ax PHY can operate with 0.8, 1.6 or 3.2 microsecond guard 393 interval (GI). The larger GI options provide better protection 394 against multipath, which is expected to be a challenge in industrial 395 environments. The possibility to operate with smaller resource units 396 (e.g. 2 MHz) enabled by OFDMA also helps reduce noise power and 397 improve SNR, leading to better packet error rate (PER) performance. 399 802.11ax supports beamforming as in 802.11ac, but introduces UL MU 400 MIMO, which helps improve reliability. The UL MU MIMO capability is 401 also enabled by the trigger based access operation in 802.11ax. 403 4.2.1.3. Support for 6GHz band 405 The 802.11ax specification [IEEE Std. 802.11ax] includes support for 406 operation in the new 6 GHz band. Given the amount of new spectrum 407 available as well as the fact that no legacy 802.11 device (prior 408 802.11ax) will be able to operate in this new band, 802.11ax 409 operation in this new band can be even more efficient. 411 4.2.2. Applicability to deterministic flows 413 TSN capabilities, as defined by the IEEE 802.1 TSN standards, provide 414 the underlying mechanism for supporting deterministic flows in a 415 Local Area Network (LAN). The 802.11 working group has incorporated 416 support for absolute time synchronization to extend the TSN 802.1AS 417 protocol so that time-sensitive flow can experience precise time 418 synchronization when operating over 802.11 links. As IEEE 802.11 and 419 IEEE 802.1 TSN are both based on the IEEE 802 architecture, 802.11 420 devices can directly implement TSN capabilities without the need for 421 a gateway/translation protocol. Basic features required for 422 operation in a 802.1Q LAN are already enabled for 802.11. Some TSN 423 capabilities, such as 802.1Qbv, can already operate over the existing 424 802.11 MAC SAP [SUR2021]. Nevertheless, the IEEE 802.11 MAC/PHY 425 requires further extensions to improve the operation of IEEE 802.1 426 TSN features and achieve better performance metrics [CAL1287]. 428 TSN capabilities supported over 802.11 (which also extends to 429 802.11ax), include: 431 1. 802.1AS based Time Synchronization (other time synchronization 432 techniques may also be used) 434 2. Interoperating with IEEE802.1Q bridges as per IEEE 802.11ak 436 3. Time-sensitive Traffic Stream Identification and Classification 438 The exiting 802.11 TSN capabilities listed above, and the 802.11ax 439 OFDMA and AP-controlled access within a BSS provide a new set of 440 tools to better serve time-sensitive flows. However, it is important 441 to understand the tradeoffs and constraints associated with such 442 capabilities, as well as redundancy and diversity mechanisms that can 443 be used to provide more predictable and reliable performance. 445 4.2.2.1. 802.11 Managed network operation and admission control 447 Time-sensitive applications and TSN standards are expected to operate 448 under a managed network (e.g. industrial/enterprise network). Thus, 449 the Wi-Fi operation must also be carefully managed and integrated 450 with the overall TSN management framework, as defined in the 451 [IEEE8021Qcc] specification. 453 Some of the random-access latency and interference from legacy/ 454 unmanaged devices can be minimized under a centralized management 455 mode as defined in [IEEE8021Qcc]. 457 Existing traffic stream identification, configuration and admission 458 control procedures defined in [IEEE Std. 802.11] QoS mechanism can be 459 re-used. However, given the high degree of determinism required by 460 many time-sensitive applications, additional capabilities to manage 461 interference and legacy devices within tight time-constraints need to 462 be explored. 464 4.2.2.2. Scheduling for bounded latency and diversity 466 As discussed earlier, the [IEEE Std. 802.11ax] OFDMA mode introduces 467 the possibility of assigning different RUs (frequency resources) to 468 users within a PPDU. Several RU sizes are defined in the 469 specification (26, 52, 106, 242, 484, 996 subcarriers). In addition, 470 the AP can also decide on MCS and grouping of users within a given 471 OFMDA PPDU. Such flexibility can be leveraged to support time- 472 sensitive applications with bounded latency, especially in a managed 473 network where stations can be configured to operate under the control 474 of the AP, in a controlled environment (which contains only devices 475 operating on the unlicensed band installed by the facility owner and 476 where unexpected interference from other systems and/or radio access 477 technologies only sporadically happens), or in a deployment where 478 channel/link redundancy is used to minimize the impact of unmanaged 479 devices/interference. 481 When the network in lightly loaded, it is possible to achieve 482 latencies under 1 msec when Wi-Fi is operated in contention-based 483 (i.e., without OFDMA) mode. It is also has been shown that it is 484 possible to achieve 1 msec latencies in controlled environment with 485 higher efficiency when multi-user transmissions are used (enabled by 486 OFDMA operation) [Cavalcanti_2019]. Obviously, there are latency, 487 reliability and capacity tradeoffs to be considered. For instance, 488 smaller Resource Units (RU)s result in longer transmission durations, 489 which may impact the minimal latency that can be achieved, but the 490 contention latency and randomness elimination in an interference-free 491 environment due to multi-user transmission is a major benefit of the 492 OFDMA mode. 494 The flexibility to dynamically assign RUs to each transmission also 495 enables the AP to provide frequency diversity, which can help 496 increase reliability. 498 4.3. 802.11be Extreme High Throughput (EHT) 500 4.3.1. General Characteristics 502 The ongoing [IEEE 802.11be WIP] project is the next major 802.11 503 amendment (after [IEEE Std. 802.11ax-2021]) for operation in the 2.4, 504 5 and 6 GHz bands. 802.11be is expected to include new PHY and MAC 505 features and it is targeting extremely high throughput (at least 30 506 Gbps), as well as enhancements to worst case latency and jitter. It 507 is also expected to improve the integration with 802.1 TSN to support 508 time-sensitive applications over Ethernet and Wireless LANs. 510 The 802.11be Task Group started its operation in May 2019, therefore, 511 detailed information about specific features is not yet available. 512 Only high level candidate features have been discussed so far, 513 including: 515 1. 320MHz bandwidth and more efficient utilization of non-contiguous 516 spectrum. 518 2. Multi-band/multi-channel aggregation and operation. 520 3. 16 spatial streams and related MIMO enhancements. 522 4. Multi-Access Point (AP) Coordination. 524 5. Enhanced link adaptation and retransmission protocol, e.g. 525 Hybrid Automatic Repeat Request (HARQ). 527 6. Any required adaptations to regulatory rules for the 6 GHz 528 spectrum. 530 4.3.2. Applicability to deterministic flows 532 The 802.11 Real-Time Applications (RTA) Topic Interest Group (TIG) 533 provided detailed information on use cases, issues and potential 534 solution directions to improve support for time-sensitive 535 applications in 802.11. The RTA TIG report [IEEE_doc_11-18-2009-06] 536 was used as input to the 802.11be project scope. 538 Improvements for worst-case latency, jitter and reliability were the 539 main topics identified in the RTA report, which were motivated by 540 applications in gaming, industrial automation, robotics, etc. The 541 RTA report also highlighted the need to support additional TSN 542 capabilities, such as time-aware (802.1Qbv) shaping and packet 543 replication and elimination as defined in 802.1CB. 545 802.11be is expected to build on and enhance 802.11ax capabilities to 546 improve worst case latency and jitter. Some of the enhancement areas 547 are discussed next. 549 4.3.2.1. Enhanced scheduled operation for bounded latency 551 In addition to the throughput enhancements, 802.11be will leverage 552 the trigger-based scheduled operation enabled by 802.11ax to provide 553 efficient and more predictable medium access. 802.11be is expected to 554 include enhancements to reduce overhead and enable more efficient 555 operation in managed network deployments [IEEE_doc_11-19-0373-00]. 557 4.3.2.2. Multi-AP coordination 559 Multi-AP coordination is one of the main new candidate features in 560 802.11be. It can provide benefits in throughput and capacity and has 561 the potential to address some of the issues that impact worst case 562 latency and reliability. Multi-AP coordination is expected to 563 address the contention due to overlapping Basic Service Sets (OBSS), 564 which is one of the main sources of random latency variations. 565 802.11be can define methods to enable better coordination between 566 APs, for instance, in a managed network scenario, in order to reduce 567 latency due to unmanaged contention. 569 Several multi-AP coordination approaches have been discussed with 570 different levels of complexities and benefits, but specific 571 coordination methods have not yet been defined. 573 4.3.2.3. Multi-band operation 575 802.11be will introduce new features to improve operation over 576 multiple bands and channels. By leveraging multiple bands/channels, 577 802.11be can isolate time-sensitive traffic from network congestion, 578 one of the main causes of large latency variations. In a managed 579 802.11be network, it should be possible to steer traffic to certain 580 bands/channels to isolate time-sensitive traffic from other traffic 581 and help achieve bounded latency. 583 4.4. 802.11ad and 802.11ay (mmWave operation) 585 4.4.1. General Characteristics 587 The IEEE 802.11ad amendment defines PHY and MAC capabilities to 588 enable multi-Gbps throughput in the 60 GHz millimeter wave (mmWave) 589 band. The standard addresses the adverse mmWave signal propagation 590 characteristics and provides directional communication capabilities 591 that take advantage of beamforming to cope with increased 592 attenuation. An overview of the 802.11ad standard can be found in 593 [Nitsche_2015] . 595 The IEEE 802.11ay is currently developing enhancements to the 596 802.11ad standard to enable the next generation mmWave operation 597 targeting 100 Gbps throughput. Some of the main enhancements in 598 802.11ay include MIMO, channel bonding, improved channel access and 599 beamforming training. An overview of the 802.11ay capabilities can 600 be found in [Ghasempour_2017] 602 4.4.2. Applicability to deterministic flows 604 The high data rates achievable with 802.11ad and 802.11ay can 605 significantly reduce latency down to microsecond levels. Limited 606 interference from legacy and other unlicensed devices in 60 GHz is 607 also a benefit. However, directionality and short range typical in 608 mmWave operation impose new challenges such as the overhead required 609 for beam training and blockage issues, which impact both latency and 610 reliability. Therefore, it is important to understand the use case 611 and deployment conditions in order to properly apply and configure 612 802.11ad/ay networks for time sensitive applications. 614 The 802.11ad standard includes a scheduled access mode in which the 615 central controller, after contending and reserving the channel for a 616 dedicated period, can allocate to stations contention-free service 617 periods. This scheduling capability is also available in 802.11ay, 618 and it is one of the mechanisms that can be used to provide bounded 619 latency to time-sensitive data flows in interference-free scenarios. 620 An analysis of the theoretical latency bounds that can be achieved 621 with 802.11ad service periods is provided in [Cavalcanti_2019]. 623 5. IEEE 802.15.4 625 5.1. Provenance and Documents 627 The IEEE802.15.4 Task Group has been driving the development of low- 628 power low-cost radio technology. The IEEE802.15.4 physical layer has 629 been designed to support demanding low-power scenarios targeting the 630 use of unlicensed bands, both the 2.4 GHz and sub GHz Industrial, 631 Scientific and Medical (ISM) bands. This has imposed requirements in 632 terms of frame size, data rate and bandwidth to achieve reduced 633 collision probability, reduced packet error rate, and acceptable 634 range with limited transmission power. The PHY layer supports frames 635 of up to 127 bytes. The Medium Access Control (MAC) sublayer 636 overhead is in the order of 10-20 bytes, leaving about 100 bytes to 637 the upper layers. IEEE802.15.4 uses spread spectrum modulation such 638 as the Direct Sequence Spread Spectrum (DSSS). 640 The Timeslotted Channel Hopping (TSCH) mode was added to the 2015 641 revision of the IEEE802.15.4 standard [IEEE Std. 802.15.4]. TSCH is 642 targeted at the embedded and industrial world, where reliability, 643 energy consumption and cost drive the application space. 645 At the IETF, the 6TiSCH Working Group (WG) [TiSCH] deals with best 646 effort operation of IPv6 [RFC8200] over TSCH. 6TiSCH has enabled 647 distributed scheduling to exploit the deterministic access 648 capabilities provided by TSCH. The group designed the essential 649 mechanisms to enable the management plane operation while ensuring 650 IPv6 is supported. Yet the charter did not focus to providing a 651 solution to establish end to end Tracks while meeting quality of 652 service requirements. 6TiSCH, through the RFC8480 [RFC8480] defines 653 the 6P protocol which provides a pairwise negotiation mechanism to 654 the control plane operation. The protocol supports agreement on a 655 schedule between neighbors, enabling distributed scheduling. 6P goes 656 hand-in-hand with a Scheduling Function (SF), the policy that decides 657 how to maintain cells and trigger 6P transactions. The Minimal 658 Scheduling Function (MSF) [RFC9033] is the default SF defined by the 659 6TiSCH WG; other standardized SFs can be defined in the future. MSF 660 extends the minimal schedule configuration, and is used to add child- 661 parent links according to the traffic load. 663 Time sensitive networking on low power constrained wireless networks 664 have been partially addressed by ISA100.11a [ISA100.11a] and 665 WirelessHART [WirelessHART]. Both technologies involve a central 666 controller that computes redundant paths for industrial process 667 control traffic over a TSCH mesh. Moreover, ISA100.11a introduces 668 IPv6 capabilities with a Link-Local Address for the join process and 669 a global unicast addres for later exchanges, but the IPv6 traffic 670 typically ends at a local application gateway and the full power of 671 IPv6 for end-to-end communication is not enabled. Compared to that 672 state of the art, work at the IETF and in particular at RAW could 673 provide additional techniques such as optimized P2P routing, PAREO 674 functions, and end-to-end secured IPv6/CoAP connectivity. 676 The 6TiSCH architecture [RFC9030] identifies different models to 677 schedule resources along so-called Tracks (see Section 5.2.2.2) 678 exploiting the TSCH schedule structure however the focus at 6TiSCH is 679 on best effort traffic and the group was never chartered to produce 680 standard work related to Tracks. 682 Useful References include: 684 1. IEEE Std 802.15.4: "IEEE Std. 802.15.4, Part. 15.4: Wireless 685 Medium Access Control (MAC) and Physical Layer (PHY) 686 Specifications for Low-Rate Wireless Personal Area Networks" 687 [IEEE Std. 802.15.4]. The latest version at the time of this 688 writing is dated year 2015. 690 2. Morell, A. , Vilajosana, X. , Vicario, J. L. and Watteyne, T. 691 (2013), Label switching over IEEE802.15.4e networks. Trans. 692 Emerging Tel. Tech., 24: 458-475. doi:10.1002/ett.2650" 693 [morell13]. 695 3. De Armas, J., Tuset, P., Chang, T., Adelantado, F., Watteyne, T., 696 Vilajosana, X. (2016, September). Determinism through path 697 diversity: Why packet replication makes sense. In 2016 698 International Conference on Intelligent Networking and 699 Collaborative Systems (INCoS) (pp. 150-154). IEEE. [dearmas16]. 701 4. X. Vilajosana, T. Watteyne, M. Vucinic, T. Chang and K. S. 702 J. Pister, "6TiSCH: Industrial Performance for IPv6 Internet-of- 703 Things Networks," in Proceedings of the IEEE, vol. 107, no. 6, 704 pp. 1153-1165, June 2019. [vilajosana19]. 706 5.2. TimeSlotted Channel Hopping 707 5.2.1. General Characteristics 709 As a core technique in IEEE802.15.4, TSCH splits time in multiple 710 time slots that repeat over time. A set of timeslots constructs a 711 Slotframe (see Section 5.2.2.1.4). For each timeslot, a set of 712 available frequencies can be used, resulting in a matrix-like 713 schedule (see Figure 1). 715 timeslot offset 716 | 0 1 2 3 4 | 0 1 2 3 4 | Nodes 717 +------------------------+------------------------+ +-----+ 718 | | | | | | | | | | | | C | 719 CH-1 | EB | | |C->B| | EB | | |C->B| | | | 720 | | | | | | | | | | | +-----+ 721 +-------------------------------------------------+ | 722 | | | | | | | | | | | | 723 CH-2 | | |B->C| |B->A| | |B->C| |B->A| +-----+ 724 | | | | | | | | | | | | B | 725 +-------------------------------------------------+ | | 726 ... +-----+ 727 | 728 +-------------------------------------------------+ | 729 | | | | | | | | | | | +-----+ 730 CH-15| |A->B| | | | |A->B| | | | | A | 731 | | | | | | | | | | | | | 732 +-------------------------------------------------+ +-----+ 733 ch. 734 offset 736 Figure 1: Slotframe example with scheduled cells between nodes A, 737 B and C 739 This schedule represents the possible communications of a node with 740 its neighbors, and is managed by a Scheduling Function such as the 741 Minimal Scheduling Function (MSF) [RFC9033]. Each cell in the 742 schedule is identified by its slotoffset and channeloffset 743 coordinates. A cell's timeslot offset indicates its position in 744 time, relative to the beginning of the slotframe. A cell's channel 745 offset is an index which maps to a frequency at each iteration of the 746 slotframe. Each packet exchanged between neighbors happens within 747 one cell. The size of a cell is a timeslot duration, between 10 to 748 15 milliseconds. An Absolute Slot Number (ASN) indicates the number 749 of slots elapsed since the network started. It increments at every 750 slot. This is a 5 byte counter that can support networks running for 751 more than 300 years without wrapping (assuming a 10 ms timeslot). 752 Channel hopping provides increased reliability to multi-path fading 753 and external interference. It is handled by TSCH through a channel 754 hopping sequence referred as macHopSeq in the IEEE802.15.4 755 specification. 757 The Time-Frequency Division Multiple Access provided by TSCH enables 758 the orchestration of traffic flows, spreading them in time and 759 frequency, and hence enabling an efficient management of the 760 bandwidth utilization. Such efficient bandwidth utilization can be 761 combined to OFDM modulations also supported by the IEEE802.15.4 762 standard [IEEE Std. 802.15.4] since the 2015 version. 764 TSCH networks operate in ISM bands in which the spectrum is shared by 765 different coexisting technologies. Regulations such as FCC, ETSI and 766 ARIB impose duty cycle regulations to limit the use of the bands but 767 yet interference may constraint the probability to deliver a packet. 768 Part of these reliability challenges are addressed at the MAC 769 introducing redundancy and diversity, thanks to channel hopping, 770 scheduling and ARQ policies. Yet, the MAC layer operates with a 771 1-hop vision, being limited to local actions to mitigate 772 underperforming links. 774 In the RAW context, low power reliable networks should address non- 775 critical control scenarios such as Class 2 and monitoring scenarios 776 such as Class 4 defined by the RFC5673 [RFC5673]. As a low power 777 technology targeting industrial scenarios radio transducers provide 778 low data rates (typically between 50kbps to 250kbps) and robust 779 modulations to trade-off performance to reliability. TSCH networks 780 are organized in mesh topologies and connected to a backbone. 781 Latency in the mesh network is mainly influenced by propagation 782 aspects such as interference. ARQ methods and redundancy techniques 783 such as replication and elimination should be studied to provide the 784 needed performance to address deterministic scenarios. 786 5.2.2. Applicability to Deterministic Flows 788 Nodes in a TSCH network are tightly synchronized. This enables to 789 build the slotted structure and ensure efficient utilization of 790 resources thanks to proper scheduling policies. Scheduling is a key 791 to orchestrate the resources that different nodes in a Track or a 792 path are using. Slotframes can be split in resource blocks reserving 793 the needed capacity to certain flows. Periodic and bursty traffic 794 can be handled independently in the schedule, using active and 795 reactive policies and taking advantage of overprovisionned cells to 796 measu reth excursion. Along a Track, resource blocks can be chained 797 so nodes in previous hops transmit their data before the next packet 798 comes. This provides a tight control to latency along a Track. 799 Collision loss is avoided for best effort traffic by 800 overprovisionning resources, giving time to the management plane of 801 the network to dedicate more resources if needed. 803 5.2.2.1. Centralized Path Computation 805 In a controlled environment, a 6TiSCH device usually does not place a 806 request for bandwidth between itself and another device in the 807 network. Rather, an Operation Control System (OCS) invoked through 808 an Human/Machine Interface (HMI) iprovides the Traffic Specification, 809 in particular in terms of latency and reliability, and the end nodes, 810 to a Path Computation element (PCE). With this, the PCE computes a 811 Track between the end nodes and provisions every hop in the Track 812 with per-flow state that describes the per-hop operation for a given 813 packet, the corresponding timeSlots, and the flow identification to 814 recognize which packet is placed in which Track, sort out duplicates, 815 etc. In Figure 2, an example of Operational Control System and HMI 816 is depicted. 818 For a static configuration that serves a certain purpose for a long 819 period of time, it is expected that a node will be provisioned in one 820 shot with a full schedule, which incorporates the aggregation of its 821 behavior for multiple Tracks. The 6TiSCH Architecture expects that 822 the programing of the schedule is done over CoAP as discussed in 823 "6TiSCH Resource Management and Interaction using CoAP" 824 [I-D.ietf-6tisch-coap]. 826 But an Hybrid mode may be required as well whereby a single Track is 827 added, modified, or removed, for instance if it appears that a Track 828 does not perform as expected for, say, Packet Delivery Ratio (PDR). 829 For that case, the expectation is that a protocol that flows along a 830 Track (to be), in a fashion similar to classical Traffic Engineering 831 (TE) [CCAMP], may be used to update the state in the devices. 6TiSCH 832 provides means for a device to negotiate a timeSlot with a neighbor, 833 but in general that flow was not designed and no protocol was 834 selected and it is expected that DetNet will determine the 835 appropriate end-to-end protocols to be used in that case. 837 Stream Management Entity 839 Operational Control System and HMI 841 -+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 843 PCE PCE PCE PCE 845 -+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 847 --- 6TiSCH------6TiSCH------6TiSCH------6TiSCH-- 848 6TiSCH / Device Device Device Device \ 849 Device- - 6TiSCH 850 \ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device 851 ----Device------Device------Device------Device-- 853 Figure 2 855 5.2.2.1.1. Packet Marking and Handling 857 Section "Packet Marking and Handling" of [RFC9030] describes the 858 packet tagging and marking that is expected in 6TiSCH networks. 860 5.2.2.1.1.1. Tagging Packets for Flow Identification 862 For packets that are routed by a PCE along a Track, the tuple formed 863 by the IPv6 source address and a local RPLInstanceID is tagged in the 864 packets to identify uniquely the Track and associated transmit bundle 865 of timeSlots. 867 It results that the tagging that is used for a DetNet flow outside 868 the 6TiSCH LLN MUST be swapped into 6TiSCH formats and back as the 869 packet enters and then leaves the 6TiSCH network. 871 Note: The method and format used for encoding the RPLInstanceID at 872 6lo is generalized to all 6TiSCH topological Instances, which 873 includes Tracks. 875 5.2.2.1.1.2. Replication, Retries and Elimination 877 PRE establishes several paths in a network to provide redundancy and 878 parallel transmissions to bound the end-to-end delay. Considering 879 the scenario shown in Figure 3, many different paths are possible for 880 S to reach R. A simple way to benefit from this topology could be to 881 use the two independent paths via nodes A, C, E and via B, D, F. But 882 more complex paths are possible as well. 884 (A) (C) (E) 886 source (S) (R) (destination) 888 (B) (D) (F) 890 Figure 3: A Typical Ladder Shape with Two Parallel Paths Toward 891 the Destination 893 By employing a Packet Replication function, each node forwards a copy 894 of each data packet over two different branches. For instance, in 895 Figure 4, the source node S transmits the data packet to nodes A and 896 B, in two different timeslots within the same TSCH slotframe. 898 ===> (A) => (C) => (E) === 899 // \\// \\// \\ 900 source (S) //\\ //\\ (R) (destination) 901 \\ // \\ // \\ // 902 ===> (B) => (D) => (F) === 904 Figure 4: Packet Replication: S transmits twice the same data 905 packet, to its DP (A) and to its AP (B). 907 By employing Packet Elimination function once a node receives the 908 first copy of a data packet, it discards the subsequent copies. 909 Because the first copy that reaches a node is the one that matters, 910 it is the only copy that will be forwarded upward. 912 Considering that the wireless medium is broadcast by nature, any 913 neighbor of a transmitter may overhear a transmission. By employing 914 the Promiscuous Overhearing function, nodes will have multiple 915 opportunities to receive a given data packet. For instance, in 916 Figure 4, when the source node S transmits the data packet to node A, 917 node B may overhear this transmission. 919 6TiSCH expects elimination and replication of packets along a complex 920 Track, but has no position about how the sequence numbers would be 921 tagged in the packet. 923 As it goes, 6TiSCH expects that timeSlots corresponding to copies of 924 a same packet along a Track are correlated by configuration, and does 925 not need to process the sequence numbers. 927 The semantics of the configuration MUST enable correlated timeSlots 928 to be grouped for transmit (and respectively receive) with 929 a'OR'relations, and then a'AND'relation MUST be configurable between 930 groups. The semantics is that if the transmit (and respectively 931 receive) operation succeeded in one timeSlot in a'OR'group, then all 932 the other timeSLots in the group are ignored. Now, if there are at 933 least two groups, the'AND'relation between the groups indicates that 934 one operation must succeed in each of the groups. 936 On the transmit side, timeSlots provisioned for retries along a same 937 branch of a Track are placed a same'OR'group. The'OR'relation 938 indicates that if a transmission is acknowledged, then further 939 transmissions SHOULD NOT be attempted for timeSlots in that group. 940 There are as many'OR'groups as there are branches of the Track 941 departing from this node. Different'OR'groups are programmed for the 942 purpose of replication, each group corresponding to one branch of the 943 Track. The'AND'relation between the groups indicates that 944 transmission over any of branches MUST be attempted regardless of 945 whether a transmission succeeded in another branch. It is also 946 possible to place cells to different next-hop routers in a 947 same'OR'group. This allows to route along multi-path Tracks, trying 948 one next-hop and then another only if sending to the first fails. 950 On the receive side, all timeSlots are programmed in a same'OR'group. 951 Retries of a same copy as well as converging branches for elimination 952 are converged, meaning that the first successful reception is enough 953 and that all the other timeSlots can be ignored. 955 5.2.2.1.1.3. Differentiated Services Per-Hop-Behavior 957 Additionally, an IP packet that is sent along a Track uses the 958 Differentiated Services Per-Hop-Behavior Group called Deterministic 959 Forwarding, as described in 960 [I-D.svshah-tsvwg-deterministic-forwarding]. 962 5.2.2.1.2. Topology and capabilities 964 6TiSCH nodes are usually IoT devices, characterized by very limited 965 amount of memory, just enough buffers to store one or a few IPv6 966 packets, and limited bandwidth between peers. It results that a node 967 will maintain only a small number of peering information, and will 968 not be able to store many packets waiting to be forwarded. Peers can 969 be identified through MAC or IPv6 addresses. 971 Neighbors can be discovered over the radio using mechanism such as 972 Enhanced Beacons, but, though the neighbor information is available 973 in the 6TiSCH interface data model, 6TiSCH does not describe a 974 protocol to pro-actively push the neighborhood information to a PCE. 975 This protocol should be described and should operate over CoAP. The 976 protocol should be able to carry multiple metrics, in particular the 977 same metrics as used for RPL operations [RFC6551]. 979 The energy that the device consumes in sleep, transmit and receive 980 modes can be evaluated and reported. So can the amount of energy 981 that is stored in the device and the power that it can be scavenged 982 from the environment. The PCE SHOULD be able to compute Tracks that 983 will implement policies on how the energy is consumed, for instance 984 balance between nodes, ensure that the spent energy does not exceeded 985 the scavenged energy over a period of time, etc... 987 5.2.2.1.3. Schedule Management by a PCE 989 6TiSCH supports a mixed model of centralized routes and distributed 990 routes. Centralized routes can for example be computed by a entity 991 such as a PCE [PCE]. Distributed routes are computed by RPL 992 [RFC6550]. 994 Both methods may inject routes in the Routing Tables of the 6TiSCH 995 routers. In either case, each route is associated with a 6TiSCH 996 topology that can be a RPL Instance topology or a Track. The 6TiSCH 997 topology is indexed by a Instance ID, in a format that reuses the 998 RPLInstanceID as defined in RPL. 1000 Both RPL and PCE rely on shared sources such as policies to define 1001 Global and Local RPLInstanceIDs that can be used by either method. 1002 It is possible for centralized and distributed routing to share a 1003 same topology. Generally they will operate in different slotFrames, 1004 and centralized routes will be used for scheduled traffic and will 1005 have precedence over distributed routes in case of conflict between 1006 the slotFrames. 1008 5.2.2.1.4. SlotFrames and Priorities 1010 A slotFrame is the base object that a PCE needs to manipulate to 1011 program a schedule into an LLN node. Elaboration on that concept can 1012 be fond in section "SlotFrames and Priorities" of [RFC9030] 1014 IEEE802.15.4 TSCH avoids contention on the medium by formatting time 1015 and frequencies in cells of transmission of equal duration. In order 1016 to describe that formatting of time and frequencies, the 6TiSCH 1017 architecture defines a global concept that is called a Channel 1018 Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of 1019 cells with an height equal to the number of available channels 1020 (indexed by ChannelOffsets) and a width (in timeSlots) that is the 1021 period of the network scheduling operation (indexed by slotOffsets) 1022 for that CDU matrix. The size of a cell is a timeSlot duration, and 1023 values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to 1024 accommodate for the transmission of a frame and an acknowledgement, 1025 including the security validation on the receive side which may take 1026 up to a few milliseconds on some device architecture. 1028 The frequency used by a cell in the matrix rotates in a pseudo-random 1029 fashion, from an initial position at an epoch time, as the matrix 1030 iterates over and over. 1032 A CDU matrix is computed by the PCE, but unallocated timeSlots may be 1033 used opportunistically by the nodes for classical best effort IP 1034 traffic. The PCE has precedence in the allocation in case of a 1035 conflict. 1037 In a given network, there might be multiple CDU matrices that operate 1038 with different width, so they have different durations and represent 1039 different periodic operations. It is recommended that all CDU 1040 matrices in a 6TiSCH domain operate with the same cell duration and 1041 are aligned, so as to reduce the chances of interferences from 1042 slotted-aloha operations. The PCE MUST compute the CDU matrices and 1043 shared that knowledge with all the nodes. The matrices are used in 1044 particular to define slotFrames. 1046 A slotFrame is a MAC-level abstraction that is common to all nodes 1047 and contains a series of timeSlots of equal length and precedence. 1048 It is characterized by a slotFrame_ID, and a slotFrame_size. A 1049 slotFrame aligns to a CDU matrix for its parameters, such as number 1050 and duration of timeSlots. 1052 Multiple slotFrames can coexist in a node schedule, i.e., a node can 1053 have multiple activities scheduled in different slotFrames, based on 1054 the precedence of the 6TiSCH topologies. The slotFrames may be 1055 aligned to different CDU matrices and thus have different width. 1056 There is typically one slotFrame for scheduled traffic that has the 1057 highest precedence and one or more slotFrame(s) for RPL traffic. The 1058 timeSlots in the slotFrame are indexed by the SlotOffset; the first 1059 cell is at SlotOffset 0. 1061 The 6TiSCH architecture introduces the concept of chunks ([RFC9030]) 1062 to operate such spectrum distribution for a whole group of cells at a 1063 time. The CDU matrix is formatted into a set of chunks, each of them 1064 identified uniquely by a chunk-ID, see Figure 5. The PCE MUST 1065 compute the partitioning of CDU matrices into chunks and shared that 1066 knowledge with all the nodes in a 6TiSCH network. 1068 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1069 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1070 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1071 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1072 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1073 ... 1074 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1075 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1076 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1077 0 1 2 3 4 5 6 M 1079 Figure 5: CDU matrix Partitioning in Chunks 1081 The appropriation of a chunk can be requested explicitly by the PCE 1082 to any node. After a successful appropriation, the PCE owns the 1083 cells in that chunk, and may use them as hard cells to set up Tracks. 1084 Then again, 6TiSCH did not propose a method for chunk definition and 1085 a protocol for appropriation. This is to be done at RAW. 1087 5.2.2.2. 6TiSCH Tracks 1089 A Track at 6TiSCH is the application to wireless of the concept of a 1090 path in the "Detnet architecture" [RFC8655]. A Track can follow a 1091 simple sequence of relay nodes or can be structured as a more complex 1092 Destination Oriented Directed Acyclic Graph (DODAG) to a unicast 1093 destination. Along a Track, 6TiSCH nodes reserve the resources to 1094 enable the efficient transmission of packets while aiming to optimize 1095 certain properties such as reliability and ensure small jitter or 1096 bounded latency. The Track structure enables Layer-2 forwarding 1097 schemes, reducing the overhead of taking routing decisions at the 1098 Layer-3. 1100 Serial Tracks can be understood as the concatenation of cells or 1101 bundles along a routing path from a source towards a destination. 1102 The serial Track concept is analogous to the circuit concept where 1103 resources are chained through the multi-hop topology. For example, A 1104 bundle of Tx Cells in a particular node is paired to a bundle of Rx 1105 Cells in the next hop node following a routing path. 1107 Whereas scheduling ensures reliable delivery in bounded time along 1108 any Track, high availability requires the application of PAREO 1109 functions along a more complex DODAG Track structure. A DODAG has 1110 forking and joining nodes where the concepts such as Replication and 1111 Elimination can be exploited. Spatial redundancy increases the 1112 oveall energy consumption in the network but improves significantly 1113 the availability of the network as well as the packet delivery ratio. 1114 A Track may also branch off and rejoin, for the purpose of the so- 1115 called Packet Replication and Elimination (PRE), over non congruent 1116 branches. PRE may be used to complement layer-2 Automatic Repeat 1117 reQuest (ARQ) and receiver-end Ordering to form the PAREO functions. 1118 PAREO functions enable to meet industrial expectations in PDR within 1119 bounded delivery time over a Track that includes wireless links, even 1120 when the Track extends beyond the 6TiSCH network. 1122 +-----+ 1123 | IoT | 1124 | G/W | 1125 +-----+ 1126 ^ <---- Elimination 1127 | | 1128 Track branch | | 1129 +-------+ +--------+ Subnet Backbone 1130 | | 1131 +--|--+ +--|--+ 1132 | | | Backbone | | | Backbone 1133 o | | | router | | | router 1134 +--/--+ +--|--+ 1135 o / o o---o----/ o 1136 o o---o--/ o o o o o 1137 o \ / o o LLN o 1138 o v <---- Replication 1139 o 1141 Figure 6: End-to-End deterministic Track 1143 In the example above (see Figure 6), a Track is laid out from a field 1144 device in a 6TiSCH network to an IoT gateway that is located on a 1145 IEEE802.1 TSN backbone. 1147 The Replication function in the field device sends a copy of each 1148 packet over two different branches, and a PCE schedules each hop of 1149 both branches so that the two copies arrive in due time at the 1150 gateway. In case of a loss on one branch, hopefully the other copy 1151 of the packet still makes it in due time. If two copies make it to 1152 the IoT gateway, the Elimination function in the gateway ignores the 1153 extra packet and presents only one copy to upper layers. 1155 At each 6TiSCH hop along the Track, the PCE may schedule more than 1156 one timeSlot for a packet, so as to support Layer-2 retries (ARQ). 1157 It is also possible that the field device only uses the second branch 1158 if sending over the first branch fails. 1160 In current deployments, a TSCH Track does not necessarily support PRE 1161 but is systematically multi-path. This means that a Track is 1162 scheduled so as to ensure that each hop has at least two forwarding 1163 solutions, and the forwarding decision is to try the preferred one 1164 and use the other in case of Layer-2 transmission failure as detected 1165 by ARQ. 1167 Methods to implement complex Tracks are described in 1168 [I-D.papadopoulos-paw-pre-reqs] and complemented by extensions to the 1169 RPL routing protocol in [I-D.ietf-roll-nsa-extension] for best effort 1170 traffic, but a centralized routing technique such as promoted in 1171 DetNet is still missing. 1173 5.2.2.2.1. Track Scheduling Protocol 1175 Section "Schedule Management Mechanisms" of the 6TiSCH architecture 1176 describes 4 paradigms to manage the TSCH schedule of the LLN nodes: 1177 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1178 and scheduling management, and Hop-by-hop scheduling. The Track 1179 operation for DetNet corresponds to a remote monitoring and 1180 scheduling management by a PCE. 1182 Early work at 6TiSCH on a data model and a protocol to program the 1183 schedule in the 6TiSCH device was never concluded as the group 1184 focussed on best effort traffic. This work would be revived by RAW: 1186 The 6top interface document [RFC8480] (to be reopened at RAW) was 1187 intended to specify the generic data model that can be used to 1188 monitor and manage resources of the 6top sublayer. Abstract 1189 methods were suggested for use by a management entity in the 1190 device. The data model also enables remote control operations on 1191 the 6top sublayer. 1193 [I-D.ietf-6tisch-coap] (to be reopened at RAW) was intended to 1194 define a mapping of the 6top set of commands, which is described 1195 in RFC 8480, to CoAP resources. This allows an entity to interact 1196 with the 6top layer of a node that is multiple hops away in a 1197 RESTful fashion. 1199 [I-D.ietf-6tisch-coap] also defined a basic set CoAP resources and 1200 associated RESTful access methods (GET/PUT/POST/DELETE). The 1201 payload (body) of the CoAP messages is encoded using the CBOR 1202 format. The PCE commands are expected to be issued directly as 1203 CoAP requests or to be mapped back and forth into CoAP by a 1204 gateway function at the edge of the 6TiSCH network. For instance, 1205 it is possible that a mapping entity on the backbone transforms a 1206 non-CoAP protocol such as PCEP into the RESTful interfaces that 1207 the 6TiSCH devices support. 1209 5.2.2.2.2. Track Forwarding 1211 By forwarding, this specification means the per-packet operation that 1212 allows to deliver a packet to a next hop or an upper layer in this 1213 node. Forwarding is based on pre-existing state that was installed 1214 as a result of the routing computation of a Track by a PCE. The 1215 6TiSCH architecture supports three different forwarding model, G-MPLS 1216 Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and IPv6 1217 Forwarding (6F) which is the classical IP operation [RFC9030]. The 1218 DetNet case relates to the Track Forwarding operation under the 1219 control of a PCE. 1221 A Track is a unidirectional path between a source and a destination. 1222 In a Track cell, the normal operation of IEEE802.15.4 Automatic 1223 Repeat-reQuest (ARQ) usually happens, though the acknowledgment may 1224 be omitted in some cases, for instance if there is no scheduled cell 1225 for a retry. 1227 Track Forwarding is the simplest and fastest. A bundle of cells set 1228 to receive (RX-cells) is uniquely paired to a bundle of cells that 1229 are set to transmit (TX-cells), representing a layer-2 forwarding 1230 state that can be used regardless of the network layer protocol. 1231 This model can effectively be seen as a Generalized Multi-protocol 1232 Label Switching (G-MPLS) operation in that the information used to 1233 switch a frame is not an explicit label, but rather related to other 1234 properties of the way the packet was received, a particular cell in 1235 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1236 Layer-2 security) accepts a frame, that frame can be switched 1237 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1238 fragment, or a frame from an alternate protocol such as WirelessHART 1239 or ISA100.11a. 1241 A data frame that is forwarded along a Track normally has a 1242 destination MAC address that is set to broadcast - or a multicast 1243 address depending on MAC support. This way, the MAC layer in the 1244 intermediate nodes accepts the incoming frame and 6top switches it 1245 without incurring a change in the MAC header. In the case of 1246 IEEE802.15.4, this means effectively broadcast, so that along the 1247 Track the short address for the destination of the frame is set to 1248 0xFFFF. 1250 A Track is thus formed end-to-end as a succession of paired bundles, 1251 a receive bundle from the previous hop and a transmit bundle to the 1252 next hop along the Track, and a cell in such a bundle belongs to at 1253 most one Track. For a given iteration of the device schedule, the 1254 effective channel of the cell is obtained by adding a pseudo-random 1255 number to the channelOffset of the cell, which results in a rotation 1256 of the frequency that used for transmission. The bundles may be 1257 computed so as to accommodate both variable rates and 1258 retransmissions, so they might not be fully used at a given iteration 1259 of the schedule. The 6TiSCH architecture provides additional means 1260 to avoid waste of cells as well as overflows in the transmit bundle, 1261 as follows: 1263 In one hand, a TX-cell that is not needed for the current iteration 1264 may be reused opportunistically on a per-hop basis for routed 1265 packets. When all of the frame that were received for a given Track 1266 are effectively transmitted, any available TX-cell for that Track can 1267 be reused for upper layer traffic for which the next-hop router 1268 matches the next hop along the Track. In that case, the cell that is 1269 being used is effectively a TX-cell from the Track, but the short 1270 address for the destination is that of the next-hop router. It 1271 results that a frame that is received in a RX-cell of a Track with a 1272 destination MAC address set to this node as opposed to broadcast must 1273 be extracted from the Track and delivered to the upper layer (a frame 1274 with an unrecognized MAC address is dropped at the lower MAC layer 1275 and thus is not received at the 6top sublayer). 1277 On the other hand, it might happen that there are not enough TX-cells 1278 in the transmit bundle to accommodate the Track traffic, for instance 1279 if more retransmissions are needed than provisioned. In that case, 1280 the frame can be placed for transmission in the bundle that is used 1281 for layer-3 traffic towards the next hop along the Track as long as 1282 it can be routed by the upper layer, that is, typically, if the frame 1283 transports an IPv6 packet. The MAC address should be set to the 1284 next-hop MAC address to avoid confusion. It results that a frame 1285 that is received over a layer-3 bundle may be in fact associated to a 1286 Track. In a classical IP link such as an Ethernet, off-Track traffic 1287 is typically in excess over reservation to be routed along the non- 1288 reserved path based on its QoS setting. But with 6TiSCH, since the 1289 use of the layer-3 bundle may be due to transmission failures, it 1290 makes sense for the receiver to recognize a frame that should be re- 1291 Tracked, and to place it back on the appropriate bundle if possible. 1292 A frame should be re-Tracked if the Per-Hop-Behavior group indicated 1293 in the Differentiated Services Field in the IPv6 header is set to 1294 Deterministic Forwarding, as discussed in Section 5.2.2.1.1. A frame 1295 is re-Tracked by scheduling it for transmission over the transmit 1296 bundle associated to the Track, with the destination MAC address set 1297 to broadcast. 1299 There are 2 modes for a Track, transport mode and tunnel mode. 1301 5.2.2.2.2.1. Transport Mode 1303 In transport mode, the Protocol Data Unit (PDU) is associated with 1304 flow-dependant meta-data that refers uniquely to the Track, so the 1305 6top sublayer can place the frame in the appropriate cell without 1306 ambiguity. In the case of IPv6 traffic, this flow identification is 1307 transported in the Flow Label of the IPv6 header. Associated with 1308 the source IPv6 address, the Flow Label forms a globally unique 1309 identifier for that particular Track that is validated at egress 1310 before restoring the destination MAC address (DMAC) and punting to 1311 the upper layer. 1313 | ^ 1314 +--------------+ | | 1315 | IPv6 | | | 1316 +--------------+ | | 1317 | 6LoWPAN HC | | | 1318 +--------------+ ingress egress 1319 | 6top | sets +----+ +----+ restores 1320 +--------------+ dmac to | | | | dmac to 1321 | TSCH MAC | brdcst | | | | self 1322 +--------------+ | | | | | | 1323 | LLN PHY | +-------+ +--...-----+ +-------+ 1324 +--------------+ 1326 Figure 7: Track Forwarding, Transport Mode 1328 5.2.2.2.2.2. Tunnel Mode 1330 In tunnel mode, the frames originate from an arbitrary protocol over 1331 a compatible MAC that may or may not be synchronized with the 6TiSCH 1332 network. An example of this would be a router with a dual radio that 1333 is capable of receiving and sending WirelessHART or ISA100.11a frames 1334 with the second radio, by presenting itself as an Access Point or a 1335 Backbone Router, respectively. 1337 In that mode, some entity (e.g. PCE) can coordinate with a 1338 WirelessHART Network Manager or an ISA100.11a System Manager to 1339 specify the flows that are to be transported transparently over the 1340 Track. 1342 +--------------+ 1343 | IPv6 | 1344 +--------------+ 1345 | 6LoWPAN HC | 1346 +--------------+ set restore 1347 | 6top | +dmac+ +dmac+ 1348 +--------------+ to|brdcst to|nexthop 1349 | TSCH MAC | | | | | 1350 +--------------+ | | | | 1351 | LLN PHY | +-------+ +--...-----+ +-------+ 1352 +--------------+ | ingress egress | 1353 | | 1354 +--------------+ | | 1355 | LLN PHY | | | 1356 +--------------+ | | 1357 | TSCH MAC | | | 1358 +--------------+ | dmac = | dmac = 1359 |ISA100/WiHART | | nexthop v nexthop 1360 +--------------+ 1362 Figure 8: Track Forwarding, Tunnel Mode 1364 In that case, the flow information that identifies the Track at the 1365 ingress 6TiSCH router is derived from the RX-cell. The dmac is set 1366 to this node but the flow information indicates that the frame must 1367 be tunneled over a particular Track so the frame is not passed to the 1368 upper layer. Instead, the dmac is forced to broadcast and the frame 1369 is passed to the 6top sublayer for switching. 1371 At the egress 6TiSCH router, the reverse operation occurs. Based on 1372 metadata associated to the Track, the frame is passed to the 1373 appropriate link layer with the destination MAC restored. 1375 5.2.2.2.2.3. Tunnel Metadata 1377 Metadata coming with the Track configuration is expected to provide 1378 the destination MAC address of the egress endpoint as well as the 1379 tunnel mode and specific data depending on the mode, for instance a 1380 service access point for frame delivery at egress. If the tunnel 1381 egress point does not have a MAC address that matches the 1382 configuration, the Track installation fails. 1384 In transport mode, if the final layer-3 destination is the tunnel 1385 termination, then it is possible that the IPv6 address of the 1386 destination is compressed at the 6LoWPAN sublayer based on the MAC 1387 address. It is thus mandatory at the ingress point to validate that 1388 the MAC address that was used at the 6LoWPAN sublayer for compression 1389 matches that of the tunnel egress point. For that reason, the node 1390 that injects a packet on a Track checks that the destination is 1391 effectively that of the tunnel egress point before it overwrites it 1392 to broadcast. The 6top sublayer at the tunnel egress point reverts 1393 that operation to the MAC address obtained from the tunnel metadata. 1395 5.2.2.2.2.4. OAM 1397 An Overview of Operations, Administration, and Maintenance (OAM) 1398 Tools [RFC7276] provides an overwiew of the existing tooling for OAM 1399 [RFC6291]. Tracks are complex paths and new tooling is necessary to 1400 manage them, with respect to load control, timing, and the Packet 1401 Replication and Elimination Functions (PREF). 1403 An example of such tooling can be found in the context of BIER 1404 [RFC8279] and more specifically BIER Traffic Engineering 1405 [I-D.ietf-bier-te-arch] (BIER-TE): 1406 [I-D.thubert-bier-replication-elimination] leverages BIER-TE to 1407 control the process of PREF, and to provide traceability of these 1408 operations, in the deterministic dataplane, along a complex Track. 1409 For the 6TiSCH type of constrained environment, 1410 [I-D.thubert-6lo-bier-dispatch] enables an efficient encoding of the 1411 BIER bitmap within the 6LoRH framework. 1413 6. 5G 1415 6.1. Provenance and Documents 1417 The 3rd Generation Partnership Project (3GPP) incorporates many 1418 companies whose business is related to cellular network operation as 1419 well as network equipment and device manufacturing. All generations 1420 of 3GPP technologies provide scheduled wireless segments, primarily 1421 in licensed spectrum which is beneficial for reliability and 1422 availability. 1424 In 2016, the 3GPP started to design New Radio (NR) technology 1425 belonging to the fifth generation (5G) of cellular networks. NR has 1426 been designed from the beginning to not only address enhanced Mobile 1427 Broadband (eMBB) services for consumer devices such as smart phones 1428 or tablets but is also tailored for future Internet of Things (IoT) 1429 communication and connected cyber-physical systems. In addition to 1430 eMBB, requirement categories have been defined on Massive Machine- 1431 Type Communication (M-MTC) for a large number of connected devices/ 1432 sensors, and Ultra-Reliable Low-Latency Communication (URLLC) for 1433 connected control systems and critical communication as illustrated 1434 in Figure 9. It is the URLLC capabilities that make 5G a great 1435 candidate for reliable low-latency communication. With these three 1436 corner stones, NR is a complete solution supporting the connectivity 1437 needs of consumers, enterprises, and public sector for both wide area 1438 and local area, e.g. indoor deployments. A general overview of NR 1439 can be found in [TS38300]. 1441 enhanced 1442 Mobile Broadband 1443 ^ 1444 / \ 1445 / \ 1446 / \ 1447 / \ 1448 / 5G \ 1449 / \ 1450 / \ 1451 / \ 1452 +-----------------+ 1453 Massive Ultra-Reliable 1454 Machine-Type Low-Latency 1455 Communication Communication 1457 Figure 9: 5G Application Areas 1459 As a result of releasing the first NR specification in 2018 (Release 1460 15), it has been proven by many companies that NR is a URLLC-capable 1461 technology and can deliver data packets at 10^-5 packet error rate 1462 within 1ms latency budget [TR37910]. Those evaluations were 1463 consolidated and forwarded to ITU to be included in the [IMT2020] 1464 work. 1466 In order to understand communication requirements for automation in 1467 vertical domains, 3GPP studied different use cases [TR22804] and 1468 released technical specification with reliability, availability and 1469 latency demands for a variety of applications [TS22104]. 1471 As an evolution of NR, multiple studies have been conducted in scope 1472 of 3GPP Release 16 including the following two, focusing on radio 1473 aspects: 1475 1. Study on physical layer enhancements for NR ultra-reliable and 1476 low latency communication (URLLC) [TR38824]. 1478 2. Study on NR industrial Internet of Things (I-IoT) [TR38825]. 1480 In addition, several enhancements have been done on system 1481 architecture level which are reflected in System architecture for the 1482 5G System (5GS) [TS23501]. 1484 6.2. General Characteristics 1486 The 5G Radio Access Network (5G RAN) with its NR interface includes 1487 several features to achieve Quality of Service (QoS), such as a 1488 guaranteeably low latency or tolerable packet error rates for 1489 selected data flows. Determinism is achieved by centralized 1490 admission control and scheduling of the wireless frequency resources, 1491 which are typically licensed frequency bands assigned to a network 1492 operator. 1494 NR enables short transmission slots in a radio subframe, which 1495 benefits low-latency applications. NR also introduces mini-slots, 1496 where prioritized transmissions can be started without waiting for 1497 slot boundaries, further reducing latency. As part of giving 1498 priority and faster radio access to URLLC traffic, NR introduces 1499 preemption where URLLC data transmission can preempt ongoing non- 1500 URLLC transmissions. Additionally, NR applies very fast processing, 1501 enabling retransmissions even within short latency bounds. 1503 NR defines extra-robust transmission modes for increased reliability 1504 both for data and control radio channels. Reliability is further 1505 improved by various techniques, such as multi-antenna transmission, 1506 the use of multiple frequency carriers in parallel and packet 1507 duplication over independent radio links. NR also provides full 1508 mobility support, which is an important reliability aspect not only 1509 for devices that are moving, but also for devices located in a 1510 changing environment. 1512 Network slicing is seen as one of the key features for 5G, allowing 1513 vertical industries to take advantage of 5G networks and services. 1514 Network slicing is about transforming a Public Land Mobile Network 1515 (PLMN) from a single network to a network where logical partitions 1516 are created, with appropriate network isolation, resources, optimized 1517 topology and specific configuration to serve various service 1518 requirements. An operator can configure and manage the mobile 1519 network to support various types of services enabled by 5G, for 1520 example eMBB and URLLC, depending on the different customers' needs. 1522 Exposure of capabilities of 5G Systems to the network or applications 1523 outside the 3GPP domain have been added to Release 16 [TS23501]. Via 1524 exposure interfaces, applications can access 5G capabilities, e.g., 1525 communication service monitoring and network maintenance. 1527 For several generations of mobile networks, 3GPP has considered how 1528 the communication system should work on a global scale with billions 1529 of users, taking into account resilience aspects, privacy regulation, 1530 protection of data, encryption, access and core network security, as 1531 well as interconnect. Security requirements evolve as demands on 1532 trustworthiness increase. For example, this has led to the 1533 introduction of enhanced privacy protection features in 5G. 5G also 1534 employs strong security algorithms, encryption of traffic, protection 1535 of signaling and protection of interfaces. 1537 One particular strength of mobile networks is the authentication, 1538 based on well-proven algorithms and tightly coupled with a global 1539 identity management infrastructure. Since 3G, there is also mutual 1540 authentication, allowing the network to authenticate the device and 1541 the device to authenticate the network. Another strength is secure 1542 solutions for storage and distribution of keys fulfilling regulatory 1543 requirements and allowing international roaming. When connecting to 1544 5G, the user meets the entire communication system, where security is 1545 the result of standardization, product security, deployment, 1546 operations and management as well as incident handling capabilities. 1547 The mobile networks approach the entirety in a rather coordinated 1548 fashion which is beneficial for security. 1550 6.3. Deployment and Spectrum 1552 The 5G system allows deployment in a vast spectrum range, addressing 1553 use-cases in both wide-area as well as local networks. Furthermore, 1554 5G can be configured for public and non-public access. 1556 When it comes to spectrum, NR allows combining the merits of many 1557 frequency bands, such as the high bandwidths in millimeter Waves 1558 (mmW) for extreme capacity locally, as well as the broad coverage 1559 when using mid- and low frequency bands to address wide-area 1560 scenarios. URLLC is achievable in all these bands. Spectrum can be 1561 either licensed, which means that the license holder is the only 1562 authorized user of that spectrum range, or unlicensed, which means 1563 that anyone who wants to use the spectrum can do so. 1565 A prerequisite for critical communication is performance 1566 predictability, which can be achieved by the full control of the 1567 access to the spectrum, which 5G provides. Licensed spectrum 1568 guarantees control over spectrum usage by the system, making it a 1569 preferable option for critical communication. However, unlicensed 1570 spectrum can provide an additional resource for scaling non-critical 1571 communications. While NR is initially developed for usage of 1572 licensed spectrum, the functionality to access also unlicensed 1573 spectrum was introduced in 3GPP Release 16. 1575 Licensed spectrum dedicated to mobile communications has been 1576 allocated to mobile service providers, i.e. issued as longer-term 1577 licenses by national administrations around the world. These 1578 licenses have often been associated with coverage requirements and 1579 issued across whole countries, or in large regions. Besides this, 1580 configured as a non-public network (NPN) deployment, 5G can provide 1581 network services also to a non-operator defined organization and its 1582 premises such as a factory deployment. By this isolation, quality of 1583 service requirements, as well as security requirements can be 1584 achieved. An integration with a public network, if required, is also 1585 possible. The non-public (local) network can thus be interconnected 1586 with a public network, allowing devices to roam between the networks. 1588 In an alternative model, some countries are now in the process of 1589 allocating parts of the 5G spectrum for local use to industries. 1590 These non-service providers then have a choice of applying for a 1591 local license themselves and operating their own network or 1592 cooperating with a public network operator or service provider. 1594 6.4. Applicability to Deterministic Flows 1596 6.4.1. System Architecture 1598 The 5G system [TS23501] consists of the User Equipment (UE) at the 1599 terminal side, and the Radio Access Network (RAN) with the gNB as 1600 radio base station node, as well as the Core Network (CN). The core 1601 network is based on a service-based architecture with the central 1602 functions: Access and Mobility Management Function (AMF), Session 1603 Management Function (SMF) and User Plane Function (UPF) as 1604 illustrated in Figure 10. 1606 The gNB's main responsibility is the radio resource management, 1607 including admission control and scheduling, mobility control and 1608 radio measurement handling. The AMF handles the UE's connection 1609 status and security, while the SMF controls the UE's data sessions. 1610 The UPF handles the user plane traffic. 1612 The SMF can instantiate various Packet Data Unit (PDU) sessions for 1613 the UE, each associated with a set of QoS flows, i.e., with different 1614 QoS profiles. Segregation of those sessions is also possible, e.g., 1615 resource isolation in the RAN and in the CN can be defined (slicing). 1617 +----+ +---+ +---+ +---+ +---+ +---+ 1618 |NSSF| |NEF| |NRF| |PCF| |UDM| |AF | 1619 +--+-+ +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ 1620 | | | | | | 1621 Nnssf| Nnef| Nnrf| Npcf| Nudm| Naf| 1622 | | | | | | 1623 ---+------+-+-----+-+------------+--+-----+-+--- 1624 | | | | 1625 Nausf| Nausf| Nsmf| | 1626 | | | | 1627 +--+-+ +-+-+ +-+-+ +-+-+ 1628 |AUSF| |AMF| |SMF| |SCP| 1629 +----+ +++-+ +-+-+ +---+ 1630 / | | 1631 / | | 1632 / | | 1633 N1 N2 N4 1634 / | | 1635 / | | 1636 / | | 1637 +--+-+ +--+--+ +--+---+ +----+ 1638 | UE +---+(R)AN+--N3--+ UPF +--N6--+ DN | 1639 +----+ +-----+ ++----++ +----+ 1640 | | 1641 +-N9-+ 1643 Figure 10: 5G System Architecture 1645 To allow UE mobility across cells/gNBs, handover mechanisms are 1646 supported in NR. For an established connection, i.e., connected mode 1647 mobility, a gNB can configure a UE to report measurements of received 1648 signal strength and quality of its own and neighbouring cells, 1649 periodically or event-based. Based on these measurement reports, the 1650 gNB decides to handover a UE to another target cell/gNB. Before 1651 triggering the handover, it is hand-shaked with the target gNB based 1652 on network signalling. A handover command is then sent to the UE and 1653 the UE switches its connection to the target cell/gNB. The Packet 1654 Data Convergence Protocol (PDCP) of the UE can be configured to avoid 1655 data loss in this procedure, i.e., handle retransmissions if needed. 1656 Data forwarding is possible between source and target gNB as well. 1657 To improve the mobility performance further, i.e., to avoid 1658 connection failures, e.g., due to too-late handovers, the mechanism 1659 of conditional handover is introduced in Release 16 specifications. 1660 Therein a conditional handover command, defining a triggering point, 1661 can be sent to the UE before UE enters a handover situation. A 1662 further improvement introduced in Release 16 is the Dual Active 1663 Protocol Stack (DAPS), where the UE maintains the connection to the 1664 source cell while connecting to the target cell. This way, potential 1665 interruptions in packet delivery can be avoided entirely. 1667 6.4.2. Overview of The Radio Protocol Stack 1669 The protocol architecture for NR consists of the L1 Physical layer 1670 (PHY) and as part of the L2, the sublayers of Medium Access Control 1671 (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol 1672 (PDCP), as well as the Service Data Adaption Protocol (SDAP). 1674 The PHY layer handles signal processing related actions, such as 1675 encoding/decoding of data and control bits, modulation, antenna 1676 precoding and mapping. 1678 The MAC sub-layer handles multiplexing and priority handling of 1679 logical channels (associated with QoS flows) to transport blocks for 1680 PHY transmission, as well as scheduling information reporting and 1681 error correction through Hybrid Automated Repeat Request (HARQ). 1683 The RLC sublayer handles sequence numbering of higher layer packets, 1684 retransmissions through Automated Repeat Request (ARQ), if 1685 configured, as well as segmentation and reassembly and duplicate 1686 detection. 1688 The PDCP sublayer consists of functionalities for ciphering/ 1689 deciphering, integrity protection/verification, re-ordering and in- 1690 order delivery, duplication and duplicate handling for higher layer 1691 packets, and acts as the anchor protocol to support handovers. 1693 The SDAP sublayer provides services to map QoS flows, as established 1694 by the 5G core network, to data radio bearers (associated with 1695 logical channels), as used in the 5G RAN. 1697 Additionally, in RAN, the Radio Resource Control (RRC) protocol, 1698 handles the access control and configuration signalling for the 1699 aforementioned protocol layers. RRC messages are considered L3 and 1700 thus transmitted also via those radio protocol layers. 1702 To provide low latency and high reliability for one transmission 1703 link, i.e., to transport data (or control signaling) of one radio 1704 bearer via one carrier, several features have been introduced on the 1705 user plane protocols for PHY and L2, as explained in the following. 1707 6.4.3. Radio (PHY) 1709 NR is designed with native support of antenna arrays utilizing 1710 benefits from beamforming, transmissions over multiple MIMO layers 1711 and advanced receiver algorithms allowing effective interference 1712 cancellation. Those antenna techniques are the basis for high signal 1713 quality and effectiveness of spectral usage. Spatial diversity with 1714 up to 4 MIMO layers in UL and up to 8 MIMO layers in DL is supported. 1715 Together with spatial-domain multiplexing, antenna arrays can focus 1716 power in desired direction to form beams. NR supports beam 1717 management mechanisms to find the best suitable beam for UE initially 1718 and when it is moving. In addition, gNBs can coordinate their 1719 respective DL and UL transmissions over the backhaul network keeping 1720 interference reasonably low, and even make transmissions or 1721 receptions from multiple points (multi-TRP). Multi-TRP can be used 1722 for repetition of data packet in time, in frequency or over multiple 1723 MIMO layers which can improve reliability even further. 1725 Any downlink transmission to a UE starts from resource allocation 1726 signaling over the Physical Downlink Control Channel (PDCCH). If it 1727 is successfully received, the UE will know about the scheduled 1728 transmission and may receive data over the Physical Downlink Shared 1729 Channel (PDSCH). If retransmission is required according to the HARQ 1730 scheme, a signaling of negative acknowledgement (NACK) on the 1731 Physical Uplink Control Channel (PUCCH) is involved and PDCCH 1732 together with PDSCH transmissions (possibly with additional 1733 redundancy bits) are transmitted and soft-combined with previously 1734 received bits. Otherwise, if no valid control signaling for 1735 scheduling data is received, nothing is transmitted on PUCCH 1736 (discontinuous transmission - DTX),and the base station upon 1737 detecting DTX will retransmit the initial data. 1739 An uplink transmission normally starts from a Scheduling Request (SR) 1740 - a signaling message from the UE to the base station sent via PUCCH. 1741 Once the scheduler is informed about buffer data in UE, e.g., by SR, 1742 the UE transmits a data packet on the Physical Uplink Shared Channel 1743 (PUSCH). Pre-scheduling not relying on SR is also possible (see 1744 following section). 1746 Since transmission of data packets require usage of control and data 1747 channels, there are several methods to maintain the needed 1748 reliability. NR uses Low Density Parity Check (LDPC) codes for data 1749 channels, Polar codes for PDCCH, as well as orthogonal sequences and 1750 Polar codes for PUCCH. For ultra-reliability of data channels, very 1751 robust (low spectral efficiency) Modulation and Coding Scheme (MCS) 1752 tables are introduced containing very low (down to 1/20) LDPC code 1753 rates using BPSK or QPSK. Also, PDCCH and PUCCH channels support 1754 multiple code rates including very low ones for the channel 1755 robustness. 1757 A connected UE reports downlink (DL) quality to gNB by sending 1758 Channel State Information (CSI) reports via PUCCH while uplink (UL) 1759 quality is measured directly at gNB. For both uplink and downlink, 1760 gNB selects the desired MCS number and signals it to the UE by 1761 Downlink Control Information (DCI) via PDCCH channel. For URLLC 1762 services, the UE can assist the gNB by advising that MCS targeting 1763 10^-5 Block Error Rate (BLER) are used. Robust link adaptation 1764 algorithms can maintain the needed level of reliability considering a 1765 given latency bound. 1767 Low latency on the physical layer is provided by short transmission 1768 duration which is possible by using high Subcarrier Spacing (SCS) and 1769 the allocation of only one or a few Orthogonal Frequency Division 1770 Multiplexing (OFDM) symbols. For example, the shortest latency for 1771 the worst case in DL can be 0.23ms and in UL can be 0.24ms according 1772 to (section 5.7.1 in [TR37910]). Moreover, if the initial 1773 transmission has failed, HARQ feedback can quickly be provided and an 1774 HARQ retransmission is scheduled. 1776 Dynamic multiplexing of data associated with different services is 1777 highly desirable for efficient use of system resources and to 1778 maximize system capacity. Assignment of resources for eMBB is 1779 usually done with regular (longer) transmission slots, which can lead 1780 to blocking of low latency services. To overcome the blocking, eMBB 1781 resources can be pre-empted and re-assigned to URLLC services. In 1782 this way, spectrally efficient assignments for eMBB can be ensured 1783 while providing flexibility required to ensure a bounded latency for 1784 URLLC services. In downlink, the gNB can notify the eMBB UE about 1785 pre-emption after it has happened, while in uplink there are two pre- 1786 emption mechanisms: special signaling to cancel eMBB transmission and 1787 URLLC dynamic power boost to suppress eMBB transmission. 1789 6.4.4. Scheduling and QoS (MAC) 1791 One integral part of the 5G system is the Quality of Service (QoS) 1792 framework [TS23501]. QoS flows are setup by the 5G system for 1793 certain IP or Ethernet packet flows, so that packets of each flow 1794 receive the same forwarding treatment, i.e., in scheduling and 1795 admission control. QoS flows can for example be associated with 1796 different priority level, packet delay budgets and tolerable packet 1797 error rates. Since radio resources are centrally scheduled in NR, 1798 the admission control function can ensure that only those QoS flows 1799 are admitted for which QoS targets can be reached. 1801 NR transmissions in both UL and DL are scheduled by the gNB 1802 [TS38300]. This ensures radio resource efficiency, fairness in 1803 resource usage of the users and enables differentiated treatment of 1804 the data flows of the users according to the QoS targets of the 1805 flows. Those QoS flows are handled as data radio bearers or logical 1806 channels in NR RAN scheduling. 1808 The gNB can dynamically assign DL and UL radio resources to users, 1809 indicating the resources as DL assignments or UL grants via control 1810 channel to the UE. Radio resources are defined as blocks of OFDM 1811 symbols in spectral domain and time domain. Different lengths are 1812 supported in time domain, i.e., (multiple) slot or mini-slot lengths. 1813 Resources of multiple frequency carriers can be aggregated and 1814 jointly scheduled to the UE. 1816 Scheduling decisions are based, e.g., on channel quality measured on 1817 reference signals and reported by the UE (cf. periodical CSI reports 1818 for DL channel quality). The transmission reliability can be chosen 1819 in the scheduling algorithm, i.e., by link adaptation where an 1820 appropriate transmission format (e.g., robustness of modulation and 1821 coding scheme, controlled UL power) is selected for the radio channel 1822 condition of the UE. Retransmissions, based on HARQ feedback, are 1823 also controlled by the scheduler. If needed to avoid HARQ round-trip 1824 time delays, repeated transmissions can be also scheduled beforehand, 1825 to the cost of reduced spectral efficiency. 1827 In dynamic DL scheduling, transmission can be initiated immediately 1828 when DL data becomes available in the gNB. However, for dynamic UL 1829 scheduling, when data becomes available but no UL resources are 1830 available yet, the UE indicates the need for UL resources to the gNB 1831 via a (single bit) scheduling request message in the UL control 1832 channel. When thereupon UL resources are scheduled to the UE, the UE 1833 can transmit its data and may include a buffer status report, 1834 indicating the exact amount of data per logical channel still left to 1835 be sent. More UL resources may be scheduled accordingly. To avoid 1836 the latency introduced in the scheduling request loop, UL radio 1837 resources can also be pre-scheduled. 1839 In particular for periodical traffic patterns, the pre-scheduling can 1840 rely on the scheduling features DL Semi-Persistent Scheduling (SPS) 1841 and UL Configured Grant (CG). With these features, periodically 1842 recurring resources can be assigned in DL and UL. Multiple parallels 1843 of those configurations are supported, in order to serve multiple 1844 parallel traffic flows of the same UE. 1846 To support QoS enforcement in the case of mixed traffic with 1847 different QoS requirements, several features have recently been 1848 introduced. This way, e.g., different periodical critical QoS flows 1849 can be served together with best effort transmissions, by the same 1850 UE. Among others, these features (partly Release 16) are: 1) UL 1851 logical channel transmission restrictions allowing to map logical 1852 channels of certain QoS only to intended UL resources of a certain 1853 frequency carrier, slot-length, or CG configuration, and 2) intra-UE 1854 pre-emption, allowing critical UL transmissions to pre-empt non- 1855 critical transmissions. 1857 When multiple frequency carriers are aggregated, duplicate parallel 1858 transmissions can be employed (beside repeated transmissions on one 1859 carrier). This is possible in the Carrier Aggregation (CA) 1860 architecture where those carriers originate from the same gNB, or in 1861 the Dual Connectivity (DC) architecture where the carriers originate 1862 from different gNBs, i.e., the UE is connected to two gNBs in this 1863 case. In both cases, transmission reliability is improved by this 1864 means of providing frequency diversity. 1866 In addition to licensed spectrum, a 5G system can also utilize 1867 unlicensed spectrum to offload non-critical traffic. This version of 1868 NR is called NR-U, part of 3GPP Release 16. The central scheduling 1869 approach applies also for unlicensed radio resources, but in addition 1870 also the mandatory channel access mechanisms for unlicensed spectrum, 1871 e.g., Listen Before Talk (LBT) are supported in NR-U. This way, by 1872 using NR, operators have and can control access to both licensed and 1873 unlicensed frequency resources. 1875 6.4.5. Time-Sensitive Networking (TSN) Integration 1877 The main objective of Time-Sensitive Networking (TSN) is to provide 1878 guaranteed data delivery within a guaranteed time window, i.e., 1879 bounded low latency. IEEE 802.1 TSN [IEEE802.1TSN] is a set of open 1880 standards that provide features to enable deterministic communication 1881 on standard IEEE 802.3 Ethernet [IEEE802.3]. TSN standards can be 1882 seen as a toolbox for traffic shaping, resource management, time 1883 synchronization, and reliability. 1885 A TSN stream is a data flow between one end station (Talker) to 1886 another end station (Listener). In the centralized configuration 1887 model, TSN bridges are configured by the Central Network Controller 1888 (CNC) [IEEE802.1Qcc] to provide deterministic connectivity for the 1889 TSN stream through the network. Time-based traffic shaping provided 1890 by Scheduled Traffic [IEEE802.1Qbv] may be used to achieve bounded 1891 low latency. The TSN tool for time synchronization is the 1892 generalized Precision Time Protocol (gPTP) [IEEE802.1AS]), which 1893 provides reliable time synchronization that can be used by end 1894 stations and by other TSN tools, e.g., Scheduled Traffic 1895 [IEEE802.1Qbv]. High availability, as a result of ultra-reliability, 1896 is provided for data flows by the Frame Replication and Elimination 1897 for Reliability (FRER) [IEEE802.1CB] mechanism. 1899 3GPP Release 16 includes integration of 5G with TSN, i.e., specifies 1900 functions for the 5G System (5GS) to deliver TSN streams such that 1901 the meet their QoS requirements. A key aspect of the integration is 1902 the 5GS appears from the rest of the network as a set of TSN bridges, 1903 in particular, one virtual bridge per User Plane Function (UPF) on 1904 the user plane. The 5GS includes TSN Translator (TT) functionality 1905 for the adaptation of the 5GS to the TSN bridged network and for 1906 hiding the 5GS internal procedures. The 5GS provides the following 1907 components: 1909 1. interface to TSN controller, as per [IEEE802.1Qcc] for the fully 1910 centralized configuration model 1912 2. time synchronization via reception and transmission of gPTP PDUs 1913 [IEEE802.1AS] 1915 3. low latency, hence, can be integrated with Scheduled Traffic 1916 [IEEE802.1Qbv] 1918 4. reliability, hence, can be integrated with FRER [IEEE802.1CB] 1920 Figure 10 shows an illustration of 5G-TSN integration where an 1921 industrial controller (Ind Ctrlr) is connected to industrial Input/ 1922 Output devices (I/O dev) via 5G. The 5GS can directly transport 1923 Ethernet frames since Release 15, thus, end-to-end Ethernet 1924 connectivity is provided. The 5GS implements the required interfaces 1925 towards the TSN controller functions such as the CNC, thus adapts to 1926 the settings of the TSN network. A 5G user plane virtual bridge 1927 interconnects TSN bridges or connect end stations, e.g., I/O devices 1928 to the network. Note that the introduction of 5G brings flexibility 1929 in various aspects, e.g., more flexible network topology because a 1930 wireless hop can replace several wireline hops thus significantly 1931 reduce the number of hops end-to-end. [ETR5GTSN] dives more into the 1932 integration of 5G with TSN. 1934 +------------------------------+ 1935 | 5G System | 1936 | +---+| 1937 | +-+ +-+ +-+ +-+ +-+ |TSN|| 1938 | | | | | | | | | | | |AF |......+ 1939 | +++ +++ +++ +++ +++ +-+-+| . 1940 | | | | | | | | . 1941 | -+---+---++--+-+-+--+-+- | . 1942 | | | | | | +--+--+ 1943 | +++ +++ +++ +++ | | TSN | 1944 | | | | | | | | | | |Ctrlr+.......+ 1945 | +++ +++ +++ +++ | +--+--+ . 1946 | | . . 1947 | | . . 1948 | +..........................+ | . . 1949 | . Virtual Bridge . | . . 1950 +---+ | . +--+--+ +---+ +---+--+ . | +--+---+ . 1951 |I/O+----------------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+ . 1952 |dev| | . |TT| | | | | |TT| . | |bridge| | . 1953 +---+ | . +--+--+ +---+ +---+--+ . | +------+ | . 1954 | +..........................+ | . +-+-+-+ 1955 | | . | Ind | 1956 | +..........................+ | . |Ctrlr| 1957 | . Virtual Bridge . | . +-+---+ 1958 +---+ +------+ | . +--+--+ +---+ +---+--+ . | +--+---+ | 1959 |I/O+--+ TSN +------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+ 1960 |dev| |bridge| | . |TT| | | | | |TT| . | |bridge| 1961 +---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+ 1962 | +..........................+ | 1963 +------------------------------+ 1965 <----------------- end-to-end Ethernet -------------------> 1967 Figure 11: 5G - TSN Integration 1969 NR supports accurate reference time synchronization in 1us accuracy 1970 level. Since NR is a scheduled system, an NR UE and a gNB are 1971 tightly synchronized to their OFDM symbol structures. A 5G internal 1972 reference time can be provided to the UE via broadcast or unicast 1973 signaling, associating a known OFDM symbol to this reference clock. 1974 The 5G internal reference time can be shared within the 5G network, 1975 i.e., radio and core network components. For the interworking with 1976 gPTP for multiple time domains, the 5GS acts as a virtual gPTP time- 1977 aware system and supports the forwarding of gPTP time synchronization 1978 information between end stations and bridges through the 5G user 1979 plane TTs. These account for the residence time of the 5GS in the 1980 time synchronization procedure. One special option is when the 5GS 1981 internal reference time in not only used within the 5GS, but also to 1982 the rest of the devices in the deployment, including connected TSN 1983 bridges and end stations. 1985 Redundancy architectures were specified in order to provide 1986 reliability against any kind of failure on the radio link or nodes in 1987 the RAN and the core network, Redundant user plane paths can be 1988 provided based on the dual connectivity architecture, where the UE 1989 sets up two PDU sessions towards the same data network, and the 5G 1990 system makes the paths of the two PDU sessions independent as 1991 illustrated in Figure 13. There are two PDU sessions involved in the 1992 solution: the first spans from the UE via gNB1 to UPF1, acting as the 1993 first PDU session anchor, while the second spans from the UE via gNB2 1994 to UPF2, acting as second the PDU session anchor. The independent 1995 paths may continue beyond the 3GPP network. Redundancy Handling 1996 Functions (RHFs) are deployed outside of the 5GS, i.e., in Host A 1997 (the device) and in Host B (the network). RHF can implement 1998 replication and elimination functions as per [IEEE802.1CB] or the 1999 Packet Replication, Elimination, and Ordering Functions (PREOF) of 2000 IETF Deterministic Networking (DetNet) [RFC8655]. 2002 +........+ 2003 . Device . +------+ +------+ +------+ 2004 . . + gNB1 +--N3--+ UPF1 |--N6--+ | 2005 . ./+------+ +------+ | | 2006 . +----+ / | | 2007 . | |/. | | 2008 . | UE + . | DN | 2009 . | |\. | | 2010 . +----+ \ | | 2011 . .\+------+ +------+ | | 2012 +........+ + gNB2 +--N3--+ UPF2 |--N6--+ | 2013 +------+ +------+ +------+ 2015 Figure 12: Reliability with Single UE 2017 An alternative solution is that multiple UEs per device are used for 2018 user plane redundancy as illustrated in Figure 13. Each UE sets up a 2019 PDU session. The 5GS ensures that those PDU sessions of the 2020 different UEs are handled independently internal to the 5GS. There 2021 is no single point of failure in this solution, which also includes 2022 RHF outside of the 5G system, e.g., as per FRER or as PREOF 2023 specifications. 2025 +.........+ 2026 . Device . 2027 . . 2028 . +----+ . +------+ +------+ +------+ 2029 . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ | 2030 . +----+ . +------+ +------+ | | 2031 . . | DN | 2032 . +----+ . +------+ +------+ | | 2033 . | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ | 2034 . +----+ . +------+ +------+ +------+ 2035 . . 2036 +.........+ 2038 Figure 13: Reliability with Dual UE 2040 Note that the abstraction provided by the RHF and the location of the 2041 RHF being outside of the 5G system make 5G equally supporting 2042 integration for reliability both with FRER of TSN and PREOF of DetNet 2043 as they both rely on the same concept. 2045 Note also that TSN is the primary subnetwork technology for DetNet. 2046 Thus, the DetNet over TSN work, e.g., [I-D.ietf-detnet-ip-over-tsn], 2047 can be leveraged via the TSN support built in 5G. 2049 6.5. Summary 2051 5G technology enables deterministic communication. Based on the 2052 centralized admission control and the scheduling of the wireless 2053 resources, licensed or unlicensed, quality of service such as latency 2054 and reliability can be guaranteed. 5G contains several features to 2055 achieve ultra-reliable and low latency performance, e.g., support for 2056 different OFDM numerologies and slot-durations, as well as fast 2057 processing capabilities and redundancy techniques that lead to 2058 achievable latency numbers of below 1ms with reliability guarantees 2059 up to 99.999%. 2061 5G also includes features to support Industrial IoT use cases, e.g., 2062 via the integration of 5G with TSN. This includes 5G capabilities 2063 for each TSN component, latency, resource management, time 2064 synchronization, and reliability. Furthermore, 5G support for TSN 2065 can be leveraged when 5G is used as subnet technology for DetNet, in 2066 combination with or instead of TSN, which is the primary subnet for 2067 DetNet. In addition, the support for integration with TSN 2068 reliability was added to 5G by making DetNet reliability also 2069 applicable, thus making 5G DetNet ready. Moreover, providing IP 2070 service is native to 5G. 2072 Overall, 5G provides scheduled wireless segments with high 2073 reliability and availability. In addition, 5G includes capabilities 2074 for integration to IP networks. 2076 7. L-band Digital Aeronautical Communications System 2078 One of the main pillars of the modern Air Traffic Management (ATM) 2079 system is the existence of a communication infrastructure that 2080 enables efficient aircraft guidance and safe separation in all phases 2081 of flight. Although current systems are technically mature, they are 2082 suffering from the VHF band's increasing saturation in high-density 2083 areas and the limitations posed by analogue radio. Therefore, 2084 aviation globally and the European Union (EU) in particular, strives 2085 for a sustainable modernization of the aeronautical communication 2086 infrastructure. 2088 In the long-term, ATM communication shall transition from analogue 2089 VHF voice and VDL2 communication to more spectrum efficient digital 2090 data communication. The European ATM Master Plan foresees this 2091 transition to be realized for terrestrial communications by the 2092 development and implementation of the L-band Digital Aeronautical 2093 Communications System (LDACS). LDACS shall enable IPv6 based air- 2094 ground communication related to the safety and regularity of the 2095 flight. The particular challenge is that no new frequencies can be 2096 made available for terrestrial aeronautical communication. It was 2097 thus necessary to develop procedures to enable the operation of LDACS 2098 in parallel with other services in the same frequency band. 2100 7.1. Provenance and Documents 2102 The development of LDACS has already made substantial progress in the 2103 Single European Sky ATM Research (SESAR) framework, and is currently 2104 being continued in the follow-up program, SESAR2020 [RIH18]. A key 2105 objective of the SESAR activities is to develop, implement and 2106 validate a modern aeronautical data link able to evolve with aviation 2107 needs over long-term. To this end, an LDACS specification has been 2108 produced [GRA19] and is continuously updated; transmitter 2109 demonstrators were developed to test the spectrum compatibility of 2110 LDACS with legacy systems operating in the L-band [SAJ14]; and the 2111 overall system performance was analyzed by computer simulations, 2112 indicating that LDACS can fulfill the identified requirements 2113 [GRA11]. 2115 LDACS standardization within the framework of the International Civil 2116 Aviation Organization (ICAO) started in December 2016. The ICAO 2117 standardization group has produced an initial Standards and 2118 Recommended Practices (SARPs) document [ICAO18]. The SARPs document 2119 defines the general characteristics of LDACS. The ICAO 2120 standardization group plans to produce an ICAO technical manual - the 2121 ICAO equivalent to a technical standard - within the next years. 2122 Generally, the group is open to input from all sources and develops 2123 LDACS in the open. 2125 Up to now the LDACS standardization has been focused on the 2126 development of the physical layer and the data link layer, only 2127 recently have higher layers come into the focus of the LDACS 2128 development activities. There is currently no "IPv6 over LDACS" 2129 specification; however, SESAR2020 has started the testing of 2130 IPv6-based LDACS testbeds. The IPv6 architecture for the 2131 aeronautical telecommunication network is called the Future 2132 Communications Infrastructure (FCI). FCI shall support quality of 2133 service, diversity, and mobility under the umbrella of the "multi- 2134 link concept". This work is conducted by ICAO working group WG-I. 2136 In addition to standardization activities several industrial LDACS 2137 prototypes have been built. One set of LDACS prototypes has been 2138 evaluated in flight trials confirming the theoretical results 2139 predicting the system performance [GRA18][SCH19]. 2141 7.2. General Characteristics 2143 LDACS will become one of several wireless access networks connecting 2144 aircraft to the Aeronautical Telecommunications Network (ATN). The 2145 LDACS access network contains several ground stations, each of them 2146 providing one LDACS radio cell. The LDACS air interface is a 2147 cellular data link with a star-topology connecting aircraft to 2148 ground-stations with a full duplex radio link. Each ground-station 2149 is the centralized instance controlling all air-ground communications 2150 within its radio cell. 2152 The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the 2153 forward link, and 294 kbit/s to 1390 kbit/s on the reverse link, 2154 depending on coding and modulation. Due to strong interference from 2155 legacy systems in the L-band, the most robust coding and modulation 2156 SHOULD be expected for initial deployment i.e. 315/294 kbit/s on the 2157 forward/reverse link, respectively. 2159 In addition to the communications capability, LDACS also offers a 2160 navigation capability. Ranging data, similar to DME (Distance 2161 Measuring Equipment), is extracted from the LDACS communication links 2162 between aircraft and LDACS ground stations. This results in LDACS 2163 providing an APNT (Alternative Position, Navigation and Timing) 2164 capability to supplement the existing on-board GNSS (Global 2165 Navigation Satellite System) without the need for additional 2166 bandwidth. Operationally, there will be no difference for pilots 2167 whether the navigation data are provided by LDACS or DME. This 2168 capability was flight tested and proven during the MICONAV flight 2169 trials in 2019 [BAT19]. 2171 In previous works and during the MICONAV flight campaign in 2019, it 2172 was also shown, that LDACS can be used for surveillance capability. 2173 Filip et al. [FIL19] shown passive radar capabilities of LDACS and 2174 Automatic Dependence Surveillance - Contract (ADS-C) was demonstrated 2175 via LDACS during the flight campaign 2019 [SCH19]. 2177 Since LDACS has been mainly designed for air traffic management 2178 communication it supports mutual entity authentication, integrity and 2179 confidentiality capabilities of user data messages and some control 2180 channel protection capabilities [MAE18], [MAE191], [MAE192], [MAE20]. 2182 Overall this makes LDACS the world's first truly integrated CNS 2183 system and is the worldwide most mature, secure, terrestrial long- 2184 range CNS technology for civil aviation. 2186 7.3. Deployment and Spectrum 2188 LDACS has its origin in merging parts of the B-VHF [BRA06], B-AMC 2189 [SCH08], TIA-902 (P34) [HAI09], and WiMAX IEEE 802.16e technologies 2190 [EHA11]. In 2007 the spectrum for LDACS was allocated at the World 2191 Radio Conference (WRC). 2193 It was decided to allocate the spectrum next to Distance Measuring 2194 Equipment (DME), resulting in an in-lay approach between the DME 2195 channels for LDAC [SCH14]. 2197 LDACS is currently being standardized by ICAO and several roll-out 2198 strategies are discussed: 2200 The LDACS data link provides enhanced capabilities to existing 2201 Aeronautical communications infrastructure enabling them to better 2202 support user needs and new applications. The deployment scalability 2203 of LDACS allows its implementation to start in areas where most 2204 needed to Improve immediately the performance of already fielded 2205 infrastructure. Later the deployment is extended based on 2206 operational demand. An attractive scenario for upgrading the 2207 existing VHF communication systems by adding an additional LDACS data 2208 link is described below. 2210 When considering the current VDL Mode 2 infrastructure and user base, 2211 a very attractive win-win situation comes about, when the 2212 technological advantages of LDACS are combined with the existing VDL 2213 mode 2 infrastructure. LDACS provides at least 50 time more capacity 2214 than VDL Mode 2 and is a natural enhancement to the existing VDL Mode 2215 2 business model. The advantage of this approach is that the VDL 2216 Mode 2 infrastructure can be fully reused. Beyond that, it opens the 2217 way for further enhancements which can increase business efficiency 2218 and minimize investment risk. [ICAO19] 2220 7.4. Applicability to Deterministic Flows 2222 As LDACS is a ground-based digital communications system for flight 2223 guidance and communications related to safety and regularity of 2224 flight, time-bounded deterministic arrival times for safety critical 2225 messages are a key feature for its successful deployment and roll- 2226 out. 2228 7.4.1. System Architecture 2230 Up to 512 Aircraft Station (AS) communicate to an LDACS Ground 2231 Station (GS) in the Reverse Link (RL). GS communicate to AS in the 2232 Forward Link (FL). Via an Access-Router (AC-R) GSs connect the LDACS 2233 sub-network to the global Aeronautical Telecommunications Network 2234 (ATN) to which the corresponding Air Traffic Services (ATS) and 2235 Aeronautical Operational Control (AOC) end systems are attached. 2237 7.4.2. Overview of The Radio Protocol Stack 2239 The protocol stack of LDACS is implemented in the AS and GS: It 2240 consists of the Physical Layer (PHY) with five major functional 2241 blocks above it. Four are placed in the Data Link Layer (DLL) of the 2242 AS and GS: (1) Medium Access Layer (MAC), (2) Voice Interface (VI), 2243 (3) Data Link Service (DLS), and (4) LDACS Management Entity (LME). 2244 The last entity resides within the Sub-Network Layer: Sub-Network 2245 Protocol (SNP). The LDACS network is externally connected to voice 2246 units, radio control units, and the ATN Network Layer. 2248 Figure 14 shows the protocol stack of LDACS as implemented in the AS 2249 and GS. 2251 IPv6 Network Layer 2252 | 2253 | 2254 +------------------+ +----+ 2255 | SNP |--| | Sub-Network 2256 | | | | Layer 2257 +------------------+ | | 2258 | | LME| 2259 +------------------+ | | 2260 | DLS | | | Logical Link 2261 | | | | Control Layer 2262 +------------------+ +----+ 2263 | | 2264 DCH DCCH/CCCH 2265 | RACH/BCCH 2266 | | 2267 +--------------------------+ 2268 | MAC | Medium Access 2269 | | Layer 2270 +--------------------------+ 2271 | 2272 +--------------------------+ 2273 | PHY | Physical Layer 2274 +--------------------------+ 2275 | 2276 | 2277 ((*)) 2278 FL/RL radio channels 2279 separated by 2280 Frequency Division Duplex 2282 Figure 14: LDACS protocol stack in AS and GS 2284 7.4.3. Radio (PHY) 2286 The physical layer provides the means to transfer data over the radio 2287 channel. The LDACS ground-station supports bi-directional links to 2288 multiple aircraft under its control. The forward link direction (FL; 2289 ground-to-air) and the reverse link direction (RL; air-to-ground) are 2290 separated by frequency division duplex. Forward link and reverse 2291 link use a 500 kHz channel each. The ground-station transmits a 2292 continuous stream of OFDM symbols on the forward link. In the 2293 reverse link different aircraft are separated in time and frequency 2294 using a combination of Orthogonal Frequency-Division Multiple-Access 2295 (OFDMA) and Time-Division Multiple-Access (TDMA). Aircraft thus 2296 transmit discontinuously on the reverse link with radio bursts sent 2297 in precisely defined transmission opportunities allocated by the 2298 ground-station. The most important service on the PHY layer of LDACS 2299 is the PHY time framing service, which indicates that the PHY layer 2300 is ready to transmit in a given slot and to indicate PHY layer 2301 framing and timing to the MAC time framing service. LDACS does not 2302 support beam-forming or Multiple Input Multiple Output (MIMO). 2304 7.4.4. Scheduling, Frame Structure and QoS (MAC) 2306 The data-link layer provides the necessary protocols to facilitate 2307 concurrent and reliable data transfer for multiple users. The LDACS 2308 data link layer is organized in two sub-layers: The medium access 2309 sub-layer and the logical link control sub-layer. The medium access 2310 sub-layer manages the organization of transmission opportunities in 2311 slots of time and frequency. The logical link control sub-layer 2312 provides acknowledged point-to-point logical channels between the 2313 aircraft and the ground-station using an automatic repeat request 2314 protocol. LDACS supports also unacknowledged point-to-point channels 2315 and ground-to-air broadcast. Before going more into depth about the 2316 LDACS medium access, the frame structure of LDACS is introduced: 2318 The LDACS framing structure for FL and RL is based on Super-Frames 2319 (SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbols. 2320 The FL and RL SF boundaries are aligned in time (from the view of the 2321 GS). 2323 In the FL, an SF contains a Broadcast Frame of duration 6.72 ms (56 2324 OFDM symbols) for the Broadcast Control Channel (BCCH), and four 2325 Multi-Frames (MF), each of duration 58.32 ms (486 OFDM symbols). 2327 In the RL, each SF starts with a Random Access (RA) slot of length 2328 6.72 ms with two opportunities for sending RL random access frames 2329 for the Random Access Channel (RACH), followed by four MFs. These 2330 MFs have the same fixed duration of 58.32 ms as in the FL, but a 2331 different internal structure 2333 Figure 15 and Figure 16 illustrate the LDACS frame structure. 2335 ^ 2336 | +------+------------+------------+------------+------------+ 2337 | FL | BCCH | MF | MF | MF | MF | 2338 F +------+------------+------------+------------+------------+ 2339 r <---------------- Super-Frame (SF) - 240ms ----------------> 2340 e 2341 q +------+------------+------------+------------+------------+ 2342 u RL | RACH | MF | MF | MF | MF | 2343 e +------+------------+------------+------------+------------+ 2344 n <---------------- Super-Frame (SF) - 240ms ----------------> 2345 c 2346 y 2347 | 2348 ----------------------------- Time ------------------------------> 2349 | 2351 Figure 15: SF structure for LDACS 2353 ^ 2354 | +-------------+------+-------------+ 2355 | FL | DCH | CCCH | DCH | 2356 F +-------------+------+-------------+ 2357 r <---- Multi-Frame (MF) - 58.32ms --> 2358 e 2359 q +------+---------------------------+ 2360 u RL | DCCH | DCH | 2361 e +------+---------------------------+ 2362 n <---- Multi-Frame (MF) - 58.32ms --> 2363 c 2364 y 2365 | 2366 -------------------- Time ------------------> 2367 | 2369 Figure 16: MF structure for LDACS 2371 This fixed frame structure allows for a reliable and dependable 2372 transmission of data. Next, the LDACS medium access layer is 2373 introduced: 2375 LDACS medium access is always under the control of the ground-station 2376 of a radio cell. Any medium access for the transmission of user data 2377 has to be requested with a resource request message stating the 2378 requested amount of resources and class of service. The ground- 2379 station performs resource scheduling on the basis of these requests 2380 and grants resources with resource allocation messages. Resource 2381 request and allocation messages are exchanged over dedicated 2382 contention-free control channels. 2384 LDACS has two mechanisms to request resources from the scheduler in 2385 the ground-station. Resources can either be requested "on demand" 2386 with a given class of service. On the forward link, this is done 2387 locally in the ground-station, on the reverse link a dedicated 2388 contention-free control channel is used (Dedicated Control Channel 2389 (DCCH); roughly 83 bit every 60 ms). A resource allocation is always 2390 announced in the control channel of the forward link (Common Control 2391 Channel (CCCH); variable sized). Due to the spacing of the reverse 2392 link control channels of every 60 ms, a medium access delay in the 2393 same order of magnitude is to be expected. 2395 Resources can also be requested "permanently". The permanent 2396 resource request mechanism supports requesting recurring resources in 2397 given time intervals. A permanent resource request has to be 2398 canceled by the user (or by the ground-station, which is always in 2399 control). User data transmissions over LDACS are therefore always 2400 scheduled by the ground-station, while control data uses statically 2401 (i.e. at net entry) allocated recurring resources (DCCH and CCCH). 2402 The current specification documents specify no scheduling algorithm. 2403 However performance evaluations so far have used strict priority 2404 scheduling and round robin for equal priorities for simplicity. In 2405 the current prototype implementations LDACS classes of service are 2406 thus realized as priorities of medium access and not as flows. Note 2407 that this can starve out low priority flows. However, this is not 2408 seen as a big problem since safety related message always go first in 2409 any case. Scheduling of reverse link resources is done in physical 2410 Protocol Data Units (PDU) of 112 bit (or larger if more aggressive 2411 coding and modulation is used). Scheduling on the forward link is 2412 done Byte-wise since the forward link is transmitted continuously by 2413 the ground-station. 2415 In order to support diversity, LDACS supports handovers to other 2416 ground-stations on different channels. Handovers may be initiated by 2417 the aircraft (break-before-make) or by the ground-station (make- 2418 before-break). Beyond this, FCI diversity shall be implemented by 2419 the multi-link concept. 2421 7.5. Summary 2423 LDACS has been designed with applications related to the safety and 2424 regularity of the flight in mind. It has therefore been designed as 2425 a deterministic wireless data link (as far as possible). 2427 It is a secure, scalable and spectrum efficient data link with 2428 embedded navigation capability and thus, is the first truly 2429 integrated CNS system recognized by ICAO. During flight tests the 2430 LDACS capabilities have been successfully demonstrated. A viable 2431 roll-out scenario has been developed which allows gradual 2432 introduction of LDACS with immediate use and revenues. Finally, ICAO 2433 is developing LDACS standards to pave the way for a successful roll- 2434 out in the near future. 2436 8. IANA Considerations 2438 This specification does not require IANA action. 2440 9. Security Considerations 2442 Most RAW technologies integrate some authentication or encryption 2443 mechanisms that were defined outside the IETF. 2445 10. Contributors 2447 This document aggregates articles from authors specialized in each 2448 technologies. Beyond the main authors listed in the front page, the 2449 following contributors proposed additional text and refinement that 2450 improved the documertn greatly! 2452 Georgios Z. Papadopoulos: Contributed to the TSCH section. 2454 Nils Mäurer: Contributed to the LDACS section. 2456 Thomas Gräupl: Contributed to the LDACS section. 2458 Janos Farkas, Torsten Dudda, Alexey Shapin, and Sara Sandberg: Contr 2459 ibuted to the 5G section. 2461 Rocco Di Taranto: Contributed to the Wi-Fi section 2463 11. Acknowledgments 2465 Many thanks to the participants of the RAW WG where a lot of the work 2466 discussed here happened. 2468 12. Normative References 2470 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 2471 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 2472 DOI 10.17487/RFC8480, November 2018, 2473 . 2475 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2476 (IPv6) Specification", STD 86, RFC 8200, 2477 DOI 10.17487/RFC8200, July 2017, 2478 . 2480 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 2481 Phinney, "Industrial Routing Requirements in Low-Power and 2482 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 2483 2009, . 2485 [RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem 2486 Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019, 2487 . 2489 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 2490 "Deterministic Networking Architecture", RFC 8655, 2491 DOI 10.17487/RFC8655, October 2019, 2492 . 2494 [RFC9030] Thubert, P., Ed., "An Architecture for IPv6 over the Time- 2495 Slotted Channel Hopping Mode of IEEE 802.15.4 (6TiSCH)", 2496 RFC 9030, DOI 10.17487/RFC9030, May 2021, 2497 . 2499 [RFC9033] Chang, T., Ed., Vučinić, M., Vilajosana, X., Duquennoy, 2500 S., and D. Dujovne, "6TiSCH Minimal Scheduling Function 2501 (MSF)", RFC 9033, DOI 10.17487/RFC9033, May 2021, 2502 . 2504 13. Informative References 2506 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 2507 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 2508 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 2509 Low-Power and Lossy Networks", RFC 6550, 2510 DOI 10.17487/RFC6550, March 2012, 2511 . 2513 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 2514 and D. Barthel, "Routing Metrics Used for Path Calculation 2515 in Low-Power and Lossy Networks", RFC 6551, 2516 DOI 10.17487/RFC6551, March 2012, 2517 . 2519 [RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu, 2520 D., and S. Mansfield, "Guidelines for the Use of the "OAM" 2521 Acronym in the IETF", BCP 161, RFC 6291, 2522 DOI 10.17487/RFC6291, June 2011, 2523 . 2525 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 2526 Weingarten, "An Overview of Operations, Administration, 2527 and Maintenance (OAM) Tools", RFC 7276, 2528 DOI 10.17487/RFC7276, June 2014, 2529 . 2531 [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., 2532 Przygienda, T., and S. Aldrin, "Multicast Using Bit Index 2533 Explicit Replication (BIER)", RFC 8279, 2534 DOI 10.17487/RFC8279, November 2017, 2535 . 2537 [I-D.pthubert-raw-architecture] 2538 Thubert, P., Papadopoulos, G. Z., and L. Berger, "Reliable 2539 and Available Wireless Architecture/Framework", Work in 2540 Progress, Internet-Draft, draft-pthubert-raw-architecture- 2541 09, 7 July 2021, . 2544 [I-D.ietf-roll-nsa-extension] 2545 Koutsiamanis, R., Papadopoulos, G., Montavont, N., and P. 2546 Thubert, "Common Ancestor Objective Function and Parent 2547 Set DAG Metric Container Extension", Work in Progress, 2548 Internet-Draft, draft-ietf-roll-nsa-extension-10, 29 2549 October 2020, . 2552 [I-D.papadopoulos-paw-pre-reqs] 2553 Papadopoulos, G., Koutsiamanis, R., Montavont, N., and P. 2554 Thubert, "Exploiting Packet Replication and Elimination in 2555 Complex Tracks in LLNs", Work in Progress, Internet-Draft, 2556 draft-papadopoulos-paw-pre-reqs-01, 25 March 2019, 2557 . 2560 [I-D.thubert-bier-replication-elimination] 2561 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 2562 TE extensions for Packet Replication and Elimination 2563 Function (PREF) and OAM", Work in Progress, Internet- 2564 Draft, draft-thubert-bier-replication-elimination-03, 3 2565 March 2018, . 2568 [I-D.thubert-6lo-bier-dispatch] 2569 Thubert, P., Brodard, Z., Jiang, H., and G. Texier, "A 2570 6loRH for BitStrings", Work in Progress, Internet-Draft, 2571 draft-thubert-6lo-bier-dispatch-06, 28 January 2019, 2572 . 2575 [I-D.ietf-bier-te-arch] 2576 Eckert, T., Cauchie, G., and M. Menth, "Tree Engineering 2577 for Bit Index Explicit Replication (BIER-TE)", Work in 2578 Progress, Internet-Draft, draft-ietf-bier-te-arch-10, 9 2579 July 2021, . 2582 [I-D.ietf-6tisch-coap] 2583 Sudhaakar, R. S. and P. Zand, "6TiSCH Resource Management 2584 and Interaction using CoAP", Work in Progress, Internet- 2585 Draft, draft-ietf-6tisch-coap-03, 9 March 2015, 2586 . 2589 [I-D.svshah-tsvwg-deterministic-forwarding] 2590 Shah, S. and P. Thubert, "Deterministic Forwarding PHB", 2591 Work in Progress, Internet-Draft, draft-svshah-tsvwg- 2592 deterministic-forwarding-04, 30 August 2015, 2593 . 2596 [IEEE Std. 802.15.4] 2597 IEEE standard for Information Technology, "IEEE Std. 2598 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 2599 and Physical Layer (PHY) Specifications for Low-Rate 2600 Wireless Personal Area Networks". 2602 [IEEE Std. 802.11] 2603 "IEEE Standard 802.11 - IEEE Standard for Information 2604 Technology - Telecommunications and information exchange 2605 between systems Local and metropolitan area networks - 2606 Specific requirements - Part 11: Wireless LAN Medium 2607 Access Control (MAC) and Physical Layer (PHY) 2608 Specifications.". 2610 [IEEE Std. 802.11ak] 2611 "802.11ak: Enhancements for Transit Links Within Bridged 2612 Networks", 2017. 2614 [IEEE Std. 802.11ax] 2615 "802.11ax D4.0: Enhancements for High Efficiency WLAN". 2617 [IEEE Std. 802.11ay] 2618 "802.11ay: Enhanced throughput for operation in license- 2619 exempt bands above 45 GHz". 2621 [IEEE Std. 802.11ad] 2622 "802.11ad: Enhancements for very high throughput in the 60 2623 GHz band". 2625 [IEEE 802.11be WIP] 2626 "802.11be: Extreme High Throughput". 2628 [IEEE Std. 802.1Qat] 2629 "802.1Qat: Stream Reservation Protocol". 2631 [IEEE8021Qcc] 2632 "802.1Qcc: IEEE Standard for Local and Metropolitan Area 2633 Networks--Bridges and Bridged Networks -- Amendment 31: 2634 Stream Reservation Protocol (SRP) Enhancements and 2635 Performance Improvements". 2637 [Cavalcanti_2019] 2638 Dave Cavalcanti et al., "Extending Time Distribution and 2639 Timeliness Capabilities over the Air to Enable Future 2640 Wireless Industrial Automation Systems, the Proceedings of 2641 IEEE", June 2019. 2643 [Nitsche_2015] 2644 Thomas Nitsche et al., "IEEE 802.11ad: directional 60 GHz 2645 communication for multi-Gigabit-per-second Wi-Fi", 2646 December 2014. 2648 [Ghasempour_2017] 2649 Yasaman Ghasempour et al., "802.11ay: Next-Generation 60 2650 GHz Communications for 100 Gb/s Wi-Fi", December 2017. 2652 [IEEE_doc_11-18-2009-06] 2653 "802.11 Real-Time Applications (RTA) Topic Interest Group 2654 (TIG) Report", November 2018. 2656 [IEEE_doc_11-19-0373-00] 2657 Kevin Stanton et Al., "Time-Sensitive Applications Support 2658 in EHT", March 2019. 2660 [morell13] Antoni Morell et al., "Label switching over IEEE802.15.4e 2661 networks", April 2013. 2663 [dearmas16] 2664 Jesica de Armas et al., "Determinism through path 2665 diversity: Why packet replication makes sense", September 2666 2016. 2668 [vilajosana19] 2669 Xavier Vilajosana et al., "6TiSCH: Industrial Performance 2670 for IPv6 Internet-of-Things Networks", June 2019. 2672 [ISA100.11a] 2673 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 2674 also IEC 62734", 2011, . 2678 [WirelessHART] 2679 www.hartcomm.org, "Industrial Communication Networks - 2680 Wireless Communication Network and Communication Profiles 2681 - WirelessHART - IEC 62591", 2010. 2683 [PCE] IETF, "Path Computation Element", 2684 . 2686 [CCAMP] IETF, "Common Control and Measurement Plane", 2687 . 2689 [TiSCH] IETF, "IPv6 over the TSCH mode over 802.15.4", 2690 . 2692 [RIH18] Rihacek, C., Haindl, B., Fantappie, P., Pierattelli, S., 2693 Gräupl, T., Schnell, M., and N. Fistas, "L-band Digital 2694 Aeronautical Communications System (LDACS) Activities in 2695 SESAR2020", Proceedings of the Integrated Communications 2696 Navigation and Surveillance Conference (ICNS) Herndon, VA, 2697 USA, April 2018. 2699 [GRA19] Gräupl, T., Rihacek, C., and B. Haindl, "LDACS A/G 2700 Specification", SESAR2020 PJ14-02-01 D3.3.010, February 2701 2019. 2703 [SAJ14] Sajatovic, M., Günzel, H., and S. Müller, "WA04 D22 Test 2704 Report for Assessing LDACS1 Transmitter Impact upon DME/ 2705 TACAN Receivers", April 2014. 2707 [GRA11] Gräupl, T. and M. Ehammer, "L-DACS1 Data Link Layer 2708 Evolution of ATN/IPS", Proceedings of the 30th IEEE/AIAA 2709 Digital Avionics Systems Conference (DASC) Seattle, WA, 2710 USA, October 2011. 2712 [ICAO18] International Civil Aviation Organization (ICAO), "L-Band 2713 Digital Aeronautical Communication System (LDACS)", 2714 International Standards and Recommended Practices Annex 10 2715 - Aeronautical Telecommunications, Vol. III - 2716 Communication Systems, July 2018. 2718 [GRA18] al., T. G. E., "L-band Digital Aeronautical Communications 2719 System (LDACS) flight trials in the national German 2720 project MICONAV", Proceedings of the Integrated 2721 Communications, Navigation, Surveillance Conference 2722 (ICNS) Herndon, VA, USA, April 2018. 2724 [SCH19] Schnell, M., "DLR tests digital communications 2725 technologies combined with additional navigation functions 2726 for the first time", 3 March 2019, 2727 . 2730 [TR37910] "3GPP TR 37.910, Study on self evaluation towards IMT-2020 2731 submission", 2732 . 2735 [TR38824] "3GPP TR 38.824, Study on physical layer enhancements for 2736 NR ultra-reliable and low latency case (URLLC)", 2737 . 2740 [TR38825] "3GPP TR 38.825, Study on NR industrial Internet of Things 2741 (IoT)", 2742 . 2745 [TS22104] "3GPP TS 22.104, Service requirements for cyber-physical 2746 control applications in vertical domains", 2747 . 2750 [TR22804] "3GPP TR 22.804, Study on Communication for Automation in 2751 Vertical domains (CAV)", 2752 . 2755 [TS23501] "3GPP TS 23.501, System architecture for the 5G System 2756 (5GS)", 2757 . 2760 [TS38300] "3GPP TS 38.300, NR Overall description", 2761 . 2764 [IMT2020] "ITU towards IMT for 2020 and beyond", 2765 . 2768 [I-D.ietf-detnet-ip-over-tsn] 2769 Varga, B., Farkas, J., Malis, A. G., and S. Bryant, 2770 "Deterministic Networking (DetNet) Data Plane: IP over 2771 IEEE 802.1 Time-Sensitive Networking (TSN)", Work in 2772 Progress, Internet-Draft, draft-ietf-detnet-ip-over-tsn- 2773 07, 19 February 2021, 2774 . 2777 [IEEE802.1TSN] 2778 IEEE 802.1, "Time-Sensitive Networking (TSN) Task Group", 2779 . 2781 [IEEE802.1AS] 2782 IEEE, "IEEE Standard for Local and metropolitan area 2783 networks -- Timing and Synchronization for Time-Sensitive 2784 Applications", IEEE 802.1AS-2020, 2785 . 2788 [IEEE802.1CB] 2789 IEEE, "IEEE Standard for Local and metropolitan area 2790 networks -- Frame Replication and Elimination for 2791 Reliability", DOI 10.1109/IEEESTD.2017.8091139, IEEE 2792 802.1CB-2017, 2793 . 2795 [IEEE802.1Qbv] 2796 IEEE, "IEEE Standard for Local and metropolitan area 2797 networks -- Bridges and Bridged Networks -- Amendment 25: 2798 Enhancements for Scheduled Traffic", IEEE 802.1Qbv-2015, 2799 . 2801 [IEEE802.1Qcc] 2802 IEEE, "IEEE Standard for Local and metropolitan area 2803 networks -- Bridges and Bridged Networks -- Amendment 31: 2804 Stream Reservation Protocol (SRP) Enhancements and 2805 Performance Improvements", IEEE 802.1Qcc-2018, 2806 . 2808 [IEEE802.3] 2809 IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018, 2810 . 2812 [ETR5GTSN] Farkas, J., Varga, B., Miklos, G., and J. Sachs, "5G-TSN 2813 integration meets networking requirements for industrial 2814 automation", Ericsson Technology Review, Volume 9, No 7, 2815 August 2019, . 2819 [MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity 2820 Architecture for the L-band Digital Aeronautical 2821 Communications System (LDACS)", IEEE 37th Digital Avionics 2822 Systems Conference (DASC), pp. 1-10, London, UK , 2017. 2824 [MAE191] Maeurer, N. and C. Schmitt, "Towards Successful 2825 Realization of the LDACS Cybersecurity Architecture: An 2826 Updated Datalink Security Threat- and Risk Analysis", IEEE 2827 Integrated Communications, Navigation and Surveillance 2828 Conference (ICNS), pp. 1-13, Herndon, VA, USA , 2019. 2830 [ICAO19] International Civil Aviation Organization (ICAO), "TLDACS 2831 White Paper–A Roll-out Scenario", Working Paper 2832 COMMUNICATIONS PANEL-DATA COMMUNICATIONS INFRASTRUCTURE 2833 WORKING GROUP, Montreal, Canada , October 2019. 2835 [MAE192] Maeurer, N., Graeupl, T., and C. Schmitt, "Evaluation of 2836 the LDACS Cybersecurity Implementation", IEEE 38th Digital 2837 Avionics Systems Conference (DACS), pp. 1-10, San Diego, 2838 CA, USA , September 2019. 2840 [MAE20] Maeurer, N., Graeupl, T., and C. Schmitt, "Comparing 2841 Different Diffie-Hellman Key Exchange Flavors for LDACS", 2842 IEEE 39th Digital Avionics Systems Conference (DACS), pp. 2843 1-10, San Diego, CA, USA , October 2019. 2845 [FIL19] Filip-Dhaubhadel, A. and D. Shutin, "LDACS- Based Non- 2846 Cooperative Surveillance Multistatic Radar Design and 2847 Detection Coverage Assessment", IEEE 38th Digital Avionics 2848 Systems Conference (DACS), pp. 1-10, San Diego, CA, USA , 2849 September 2019. 2851 [BAT19] Battista, G., Osechas, O., Narayanan, S., Crespillo, O.G., 2852 Gerbeth, D., Maeurer, N., Mielke, D., and T. Graeupl, 2853 "Real-Time Demonstration of Integrated Communication and 2854 Navigation Services Using LDACS", IEEE Integrated 2855 Communications, Navigation and Surveillance Conference 2856 (ICNS), pp. 1-12, Herndon, VA, USA , 2019. 2858 [BRA06] Brandes, S., Schnell, M., Rokitansky, C.H., Ehammer, M., 2859 Graeupl, T., Steendam, H., Guenach, M., Rihacek, C., and 2860 B. Haindl, "B-VHF -Selected Simulation Results and Final 2861 Assessment", IEEE 25th Digital Avionics Systems Conference 2862 (DACS), pp. 1-12, New York, NY, USA , September 2019. 2864 [SCH08] Schnell, M., Brandes, S., Gligorevic, S., Rokitansky, 2865 C.H., Ehammer, M., Graeupl, T., Rihacek, C., and M. 2866 Sajatovic, "B-AMC - Broadband Aeronautical Multi-carrier 2867 Communications", IEEE 8th Integrated Communications, 2868 Navigation and Surveillance Conference (ICNS), pp. 1-13, 2869 New York, NY, USA , April 2008. 2871 [HAI09] Haindl, B., Rihacek, C., Sajatovic, M., Phillips, B., 2872 Budinger, J., Schnell, M., Kamiano, D., and W. Wilson, 2873 "Improvement of L-DACS1 Design by Combining B-AMC with P34 2874 and WiMAX Technologies", IEEE 9th Integrated 2875 Communications, Navigation and Surveillance Conference 2876 (ICNS), pp. 1-8, New York, NY, USA , May 2009. 2878 [EHA11] Ehammer, M. and T. Graeupl, "AeroMACS - An Airport 2879 Communications System", IEEE 30th Digital Avionics Systems 2880 Conference (DACS), pp. 1-16, New York, NY, USA , September 2881 2011. 2883 [SCH14] Schnell, M., Epple, U., Shutin, D., and N. 2884 Schneckenburger, "LDACS: Future Aeronautical 2885 Communications for Air- Traffic Management", IEEE 2886 Communications Magazine, 52(5), 104-110 , 2017. 2888 [CAL1287] Cavalcanti, D., Venkatesan, G., Cariou, L., and C. 2889 Vordeiro, "TSN support in 802.11 and potential extensions 2890 for TGbe", 2019, 2891 . 2893 [SUR2021] Sudhakaran, S., Montgomery, K., Kashef, M., Cavalcanti, 2894 D., and R. Candell, "Wireless Time Sensitive Networking 2895 for Industrial Collaborative Robotic Workcells", 17th IEEE 2896 International Conference on Factory Communication Systems 2897 (WFCS) , 2021, 2898 . 2900 Authors' Addresses 2902 Pascal Thubert (editor) 2903 Cisco Systems, Inc 2904 Building D 2905 45 Allee des Ormes - BP1200 2906 06254 MOUGINS - Sophia Antipolis 2907 France 2909 Phone: +33 497 23 26 34 2910 Email: pthubert@cisco.com 2912 Dave Cavalcanti 2913 Intel Corporation 2914 2111 NE 25th Ave 2915 Hillsboro, OR, 97124 2916 United States of America 2918 Phone: 503 712 5566 2919 Email: dave.cavalcanti@intel.com 2921 Xavier Vilajosana 2922 Universitat Oberta de Catalunya 2923 156 Rambla Poblenou 2924 08018 Barcelona Catalonia 2925 Spain 2927 Email: xvilajosana@uoc.edu 2929 Corinna Schmitt 2930 Research Institute CODE, UniBwM 2931 Werner-Heisenberg-Weg 39 2932 85577 Neubiberg 2933 Germany 2935 Email: corinna.schmitt@unibw.de 2937 Janos Farkas 2938 Ericsson 2939 Budapest 2940 Magyar tudosok korutja 11 2941 1117 2942 Hungary 2943 Email: janos.farkas@ericsson.com