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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-09) exists of draft-pthubert-raw-architecture-05 == Outdated reference: A later version (-12) exists of draft-ietf-roll-nsa-extension-10 == Outdated reference: A later version (-13) exists of draft-ietf-bier-te-arch-09 == Outdated reference: A later version (-07) exists of draft-ietf-detnet-ip-over-tsn-05 Summary: 1 error (**), 0 flaws (~~), 6 warnings (==), 1 comment (--). 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: 23 August 2021 Intel 6 X. Vilajosana 7 Universitat Oberta de Catalunya 8 C. Schmitt 9 Research Institute CODE, UniBwM 10 J. Farkas 11 Ericsson 12 19 February 2021 14 Reliable and Available Wireless Technologies 15 draft-ietf-raw-technologies-01 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 23 August 2021. 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 . . . . . . . . 11 70 4.4. 802.11ad and 802.11ay (mmWave operation) . . . . . . . . 12 71 4.4.1. General Characteristics . . . . . . . . . . . . . . . 13 72 4.4.2. Applicability to deterministic flows . . . . . . . . 13 73 5. IEEE 802.15.4 . . . . . . . . . . . . . . . . . . . . . . . . 13 74 5.1. Provenance and Documents . . . . . . . . . . . . . . . . 13 75 5.2. TimeSlotted Channel Hopping . . . . . . . . . . . . . . . 15 76 5.2.1. General Characteristics . . . . . . . . . . . . . . . 15 77 5.2.2. Applicability to Deterministic Flows . . . . . . . . 17 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 . . . . . . . . . . . . . . . . . . . . . . . . . 45 89 7. L-band Digital Aeronautical Communications System . . . . . . 46 90 7.1. Provenance and Documents . . . . . . . . . . . . . . . . 47 91 7.2. General Characteristics . . . . . . . . . . . . . . . . . 48 92 7.3. Deployment and Spectrum . . . . . . . . . . . . . . . . . 49 93 7.4. Applicability to Deterministic Flows . . . . . . . . . . 49 94 7.4.1. System Architecture . . . . . . . . . . . . . . . . . 50 95 7.4.2. Overview of The Radio Protocol Stack . . . . . . . . 50 96 7.4.3. Radio (PHY) . . . . . . . . . . . . . . . . . . . . . 51 97 7.4.4. Scheduling, Frame Structure and QoS (MAC) . . . . . . 52 98 7.5. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 54 99 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 55 100 9. Security Considerations . . . . . . . . . . . . . . . . . . . 55 101 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 55 102 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 55 103 12. Normative References . . . . . . . . . . . . . . . . . . . . 55 104 13. Informative References . . . . . . . . . . . . . . . . . . . 56 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 64 107 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 FEC: Forward error correction, sending redundant coded data to help 161 the receiver recover transmission errors without the delays 162 incurred with ARQ. 164 HARQ: Hybrid ARQ, a combination of FEC and ARQ. 166 PCE: Path Computation Element. 168 PAREO (functions): the wireless extension of DetNet PREOF. PAREO 169 functions include scheduled ARQ at selected hops, and expect the 170 use of new operations like overhearing where available. 172 Reliable: That consistently performs as expected, the expectation 173 for a network being to always deliver a packet in due time. 175 Track: A DODAG oriented to a destination, and that enables Packet 176 ARQ, Replication, Elimination, and Ordering Functions. 178 3. On Scheduling 180 The operations of a Deterministic Network often rely on precisely 181 applying a tight schedule, in order to avoid collision loss and 182 guarantee the worst-case time of delivery. To achieve this, there 183 must be a shared sense of time throughout the network. The sense of 184 time is usually provided by the lower layer and is not in scope for 185 RAW. 187 3.1. Benefits of Scheduling on Wires 189 A network is reliable when the statistical effects that affect the 190 packet transmission are eliminated. This involves maintaining at all 191 time the amount of critical packets within the physical capabilities 192 of the hardware and that of the radio medium. This is achieved by 193 controlling the use of time-shared resources such as CPUs and 194 buffers, by shaping the flows and by scheduling the time of 195 transmission of the packets that compose the flow at every hop. 197 Equipment failure, such as an access point rebooting, a broken radio 198 adapter, or a permanent obstacle to the transmission, is a secondary 199 source of packet loss. When a breakage occurs, multiple packets are 200 lost in a row before the flows are rerouted or the system may 201 recover. This is not acceptable for critical applications such as 202 related to safety. A typical process control loop will tolerate an 203 occasional packet loss, but a loss of several packets in a row will 204 cause an emergency stop (e.g., after 4 packets lost, within a period 205 of 1 second). 207 Network Availability is obtained by making the transmission resilient 208 against hardware failures and radio transmission losses due to 209 uncontrolled events such as co-channel interferers, multipath fading 210 or moving obstacles. The best results are typically achieved by 211 pseudo randomly cumulating all forms of diversity, in the spatial 212 domain with replication and elimination, in the time domain with ARQ 213 and diverse scheduled transmissions, and in the frequency domain with 214 frequency hopping or channel hopping between frames. 216 3.2. Benefits of Scheduling on Wireless 218 In addition to the benefits listed in Section 3.1, scheduling 219 transmissions provides specific value to the wireless medium. 221 On the one hand, scheduling avoids collisions between scheduled 222 transmissions and can ensure both time and frequency diversity 223 between retries in order to defeat co-channel interference from un- 224 controlled transmitters as well as multipath fading. Transmissions 225 can be scheduled on multiple channels in parallel, which enables to 226 use the full available spectrum while avoiding the hidden terminal 227 problem, e.g., when the next packet in a same flow interferes on a 228 same channel with the previous one that progressed a few hops 229 farther. 231 On the other hand, scheduling optimizes the bandwidth usage: compared 232 to classical Collision Avoidance techniques, there is no blank time 233 related to inter-frame space (IFS) and exponential back-off in 234 scheduled operations. A minimal Clear Channel Assessment may be 235 needed to comply with the local regulations such as ETSI 300-328, but 236 that will not detect a collision when the senders are synchronized. 237 And because scheduling allows a time-sharing operation, there is no 238 limit to the ratio of isolated critical traffic. 240 Finally, scheduling plays a critical role to save energy. In IOT, 241 energy is the foremost concern, and synchronizing sender and listener 242 enables to always maintain them in deep sleep when there is no 243 scheduled transmission. This avoids idle listening and long 244 preambles and enables long sleep periods between traffic and 245 resynchronization, allowing battery-operated nodes to operate in a 246 mesh topology for multiple years. 248 4. IEEE 802.11 250 4.1. Provenance and Documents 252 With an active portfolio of nearly 1,300 standards and projects under 253 development, IEEE is a leading developer of industry standards in a 254 broad range of technologies that drive the functionality, 255 capabilities, and interoperability of products and services, 256 transforming how people live, work, and communicate. 258 The IEEE 802 LAN/MAN Standards Committee (SC) develops and maintains 259 networking standards and recommended practices for local, 260 metropolitan, and other area networks, using an open and accredited 261 process, and advocates them on a global basis. The most widely used 262 standards are for Ethernet, Bridging and Virtual Bridged LANs 263 Wireless LAN, Wireless PAN, Wireless MAN, Wireless Coexistence, Media 264 Independent Handover Services, and Wireless RAN. An individual 265 Working Group provides the focus for each area. Standards produced 266 by the IEEE 802 SC are freely available from the IEEE GET Program 267 after they have been published in PDF for six months. 269 The IEEE 802.11 LAN standards define the underlying MAC and PHY 270 layers for the Wi-Fi technology. Wi-Fi/802.11 is one of the most 271 successful wireless technologies, supporting many application 272 domains. While previous 802.11 generations, such as 802.11n and 273 802.11ac, have focused mainly on improving peak throughput, more 274 recent generations are also considering other performance vectors, 275 such as efficiency enhancements for dense environments in 802.11ax, 276 and latency and support for Time-Sensitive Networking (TSN) 277 capabilities in 802.11be. 279 IEEE 802.11 already supports some 802.1 TSN standards and it is 280 undergoing efforts to support for other 802.1 TSN capabilities 281 required to address the use cases that require time synchronization 282 and timeliness (bounded latency) guarantees with high reliability and 283 availability. The IEEE 802.11 working group has been working in 284 collaboration with the IEEE 802.1 group for several years extending 285 802.1 features over 802.11. As with any wireless media, 802.11 286 imposes new constraints and restrictions to TSN-grade QoS, and 287 tradeoffs between latency and reliability guarantees must be 288 considered as well as managed deployment requirements. An overview 289 of 802.1 TSN capabilities and their extensions to 802.11 are 290 discussed in [Cavalcanti_2019]. 292 Wi-Fi Alliance (WFA) is the worldwide network of companies that 293 drives global Wi-Fi adoption and evolution through thought 294 leadership, spectrum advocacy, and industry-wide collaboration. The 295 WFA work helps ensure that Wi-Fi devices and networks provide users 296 the interoperability, security, and reliability they have come to 297 expect. 299 The following [IEEE Std. 802.11] specifications/certifications are 300 relevant in the context of reliable and available wireless services 301 and support for time-sensitive networking capabilities: 303 Time Synchronization: IEEE802.11-2016 with IEEE802.1AS; WFA TimeSync 304 Certification. 306 Congestion Control: IEEE802.11-2016 Admission Control; WFA Admission 307 Control. 309 Security: WFA Wi-Fi Protected Access, WPA2 and WPA3. 311 Interoperating with IEEE802.1Q bridges: [IEEE Std. 802.11ak]. 313 Stream Reservation Protocol (part of [IEEE Std. 802.1Qat]): AIEEE802 314 .11-2016 316 Scheduled channel access: IEEE802.11ad Enhancements for very high 317 throughput in the 60 GHz band [IEEE Std. 802.11ad]. 319 802.11 Real-Time Applications: Topic Interest Group (TIG) ReportDoc 320 [IEEE_doc_11-18-2009-06]. 322 In addition, major amendments being developed by the IEEE802.11 323 Working Group include capabilities that can be used as the basis for 324 providing more reliable and predictable wireless connectivity and 325 support time-sensitive applications: 327 IEEE 802.11ax D4.0: Enhancements for High Efficiency (HE). [IEEE 328 Std. 802.11ax] 330 IEEE 802.11be Extreme High Throughput (EHT). [IEEE 802.11be WIP] 332 IEE 802.11ay Enhanced throughput for operation in license-exempt 333 bands above 45 GHz. [IEEE Std. 802.11ay] 335 The main 802.11ax and 802.11be capabilities and their relevance to 336 RAW are discussed in the remainder of this document. 338 4.2. 802.11ax High Efficiency (HE) 340 4.2.1. General Characteristics 342 The next generation Wi-Fi (Wi-Fi 6) is based on the IEEE802.11ax 343 amendment [IEEE Std. 802.11ax], which includes new capabilities to 344 increase efficiency, control and reduce latency. Some of the new 345 features include higher order 1024-QAM modulation, support for uplink 346 multi-user MIMO, OFDMA, trigger-based access and Target Wake time 347 (TWT) for enhanced power savings. The OFDMA mode and trigger-based 348 access enable scheduled operation, which is a key capability required 349 to support deterministic latency and reliability for time-sensitive 350 flows. 802.11ax can operate in up to 160 MHz channels and it includes 351 support for operation in the new 6 GHz band, which is expected to be 352 open to unlicensed use by the FCC and other regulatory agencies 353 worldwide. 355 4.2.1.1. Multi-User OFDMA and Trigger-based Scheduled Access 357 802.11ax introduced a new orthogonal frequency-division multiple 358 access (OFDMA) mode in which multiple users can be scheduled across 359 the frequency domain. In this mode, the Access Point (AP) can 360 initiate multi-user (MU) Uplink (UL) transmissions in the same PHY 361 Protocol Data Unit (PPDU) by sending a trigger frame. This 362 centralized scheduling capability gives the AP much more control of 363 the channel, and it can remove contention between devices for uplink 364 transmissions, therefore reducing the randomness caused by CSMA-based 365 access between stations. The AP can also transmit simultaneously to 366 multiple users in the downlink direction by using a Downlink (DL) MU 367 OFDMA PPDU. In order to initiate a contention free Transmission 368 Opportunity (TXOP) using the OFDMA mode, the AP still follows the 369 typical listen before talk procedure to acquire the medium, which 370 ensures interoperability and compliance with unlicensed band access 371 rules. However, 802.11ax also includes a multi-user Enhanced 372 Distributed Channel Access (MU-EDCA) capability, which allows the AP 373 to get higher channel access priority. 375 4.2.1.2. Improved PHY Robustness 377 The 802.11ax PHY can operate with 0.8, 1.6 or 3.2 microsecond guard 378 interval (GI). The larger GI options provide better protection 379 against multipath, which is expected to be a challenge in industrial 380 environments. The possibility to operate with smaller resource units 381 (e.g. 2 MHz) enabled by OFDMA also helps reduce noise power and 382 improve SNR, leading to better packet error rate (PER) performance. 384 802.11ax supports beamforming as in 802.11ac, but introduces UL MU 385 MIMO, which helps improve reliability. The UL MU MIMO capability is 386 also enabled by the trigger based access operation in 802.11ax. 388 4.2.1.3. Support for 6GHz band 390 The 802.11ax specification [IEEE Std. 802.11ax] includes support for 391 operation in the new 6 GHz band. Given the amount of new spectrum 392 available as well as the fact that no legacy 802.11 device (prior 393 802.11ax) will be able to operate in this new band, 802.11ax 394 operation in this new band can be even more efficient. 396 4.2.2. Applicability to deterministic flows 398 TSN capabilities, as defined by the IEEE 802.1 TSN standards, provide 399 the underlying mechanism for supporting deterministic flows in a 400 Local Area Network (LAN). The 802.11 working group has already 401 incorporated support for several TSN capabilities, so that time- 402 sensitive flow can experience precise time synchronization and 403 timeliness when operating over 802.11 links. TSN capabilities 404 supported over 802.11 (which also extends to 802.11ax), include: 406 1. 802.1AS based Time Synchronization (other time synchronization 407 techniques may also be used) 409 2. Interoperating with IEEE802.1Q bridges 411 3. Time-sensitive Traffic Stream identification 413 The exiting 802.11 TSN capabilities listed above, and the 802.11ax 414 OFDMA and scheduled access provide a new set of tools to better 415 server time-sensitive flows. However, it is important to understand 416 the tradeoffs and constraints associated with such capabilities, as 417 well as redundancy and diversity mechanisms that can be used to 418 provide more predictable and reliable performance. 420 4.2.2.1. 802.11 Managed network operation and admission control 422 Time-sensitive applications and TSN standards are expected to operate 423 under a managed network (e.g. industrial/enterprise network). Thus, 424 the Wi-Fi operation must also be carefully managed and integrated 425 with the overall TSN management framework, as defined in the 426 [IEEE8021Qcc] specification. 428 Some of the random-access latency and interference from legacy/ 429 unmanaged devices can be minimized under a centralized management 430 mode as defined in [IEEE8021Qcc], in which admission control 431 procedures are enforced. 433 Existing traffic stream identification, configuration and admission 434 control procedures defined in [IEEE Std. 802.11] QoS mechanism can be 435 re-used. However, given the high degree of determinism required by 436 many time-sensitive applications, additional capabilities to manage 437 interference and legacy devices within tight time-constraints need to 438 be explored. 440 4.2.2.2. Scheduling for bounded latency and diversity 442 As discussed earlier, the [IEEE Std. 802.11ax] OFDMA mode introduces 443 the possibility of assigning different RUs (frequency resources) to 444 users within a PPDU. Several RU sizes are defined in the 445 specification (26, 52, 106, 242, 484, 996 subcarriers). In addition, 446 the AP can also decide on MCS and grouping of users within a given 447 OFMDA PPDU. Such flexibility can be leveraged to support time- 448 sensitive applications with bounded latency, especially in a managed 449 network where stations can be configured to operate under the control 450 of the AP. 452 As shown in [Cavalcanti_2019], it is possible to achieve latencies in 453 the order of 1msec with high reliability in an interference free 454 environment. Obviously, there are latency, reliability and capacity 455 tradeoffs to be considered. For instance, smaller Resource Units 456 (RU)s result in longer transmission durations, which may impact the 457 minimal latency that can be achieved, but the contention latency and 458 randomness elimination due to multi-user transmission is a major 459 benefit of the OFDMA mode. 461 The flexibility to dynamically assign RUs to each transmission also 462 enables the AP to provide frequency diversity, which can help 463 increase reliability. 465 4.3. 802.11be Extreme High Throughput (EHT) 467 4.3.1. General Characteristics 469 The [IEEE 802.11be WIP]is the next major 802.11 amendment (after 470 [IEEE Std. 802.11ax]) for operation in the 2.4, 5 and 6 GHz bands. 471 802.11be is expected to include new PHY and MAC features and it is 472 targeting extremely high throughput (at least 30 Gbps), as well as 473 enhancements to worst case latency and jitter. It is also expected 474 to improve the integration with 802.1 TSN to support time-sensitive 475 applications over Ethernet and Wireless LANs. 477 The 802.11be Task Group started its operation in May 2019, therefore, 478 detailed information about specific features is not yet available. 479 Only high level candidate features have been discussed so far, 480 including: 482 1. 320MHz bandwidth and more efficient utilization of non-contiguous 483 spectrum. 485 2. Multi-band/multi-channel aggregation and operation. 487 3. 16 spatial streams and related MIMO enhancements. 489 4. Multi-Access Point (AP) Coordination. 491 5. Enhanced link adaptation and retransmission protocol, e.g. 492 Hybrid Automatic Repeat Request (HARQ). 494 6. Any required adaptations to regulatory rules for the 6 GHz 495 spectrum. 497 4.3.2. Applicability to deterministic flows 499 The 802.11 Real-Time Applications (RTA) Topic Interest Group (TIG) 500 provided detailed information on use cases, issues and potential 501 solution directions to improve support for time-sensitive 502 applications in 802.11. The RTA TIG report [IEEE_doc_11-18-2009-06] 503 was used as input to the 802.11be project scope. 505 Improvements for worst-case latency, jitter and reliability were the 506 main topics identified in the RTA report, which were motivated by 507 applications in gaming, industrial automation, robotics, etc. The 508 RTA report also highlighted the need to support additional TSN 509 capabilities, such as time-aware (802.1Qbv) shaping and packet 510 replication and elimination as defined in 802.1CB. 512 802.11be is expected to build on and enhance 802.11ax capabilities to 513 improve worst case latency and jitter. Some of the enhancement areas 514 are discussed next. 516 4.3.2.1. Enhanced scheduled operation for bounded latency 518 In addition to the throughput enhancements, 802.11be will leverage 519 the trigger-based scheduled operation enabled by 802.11ax to provide 520 efficient and more predictable medium access. 802.11be is expected to 521 include enhancements to reduce overhead and enable more efficient 522 operation in managed network deployments [IEEE_doc_11-19-0373-00]. 524 4.3.2.2. Multi-AP coordination 526 Multi-AP coordination is one of the main new candidate features in 527 802.11be. It can provide benefits in throughput and capacity and has 528 the potential to address some of the issues that impact worst case 529 latency and reliability. Multi-AP coordination is expected to 530 address the contention due to overlapping Basic Service Sets (OBSS), 531 which is one of the main sources of random latency variations. 532 802.11be can define methods to enable better coordination between 533 APs, for instance, in a managed network scenario, in order to reduce 534 latency due to unmanaged contention. 536 Several multi-AP coordination approaches have been discussed with 537 different levels of complexities and benefits, but specific 538 coordination methods have not yet been defined. 540 4.3.2.3. Multi-band operation 542 802.11be will introduce new features to improve operation over 543 multiple bands and channels. By leveraging multiple bands/channels, 544 802.11be can isolate time-sensitive traffic from network congestion, 545 one of the main causes of large latency variations. In a managed 546 802.11be network, it should be possible to steer traffic to certain 547 bands/channels to isolate time-sensitive traffic from other traffic 548 and help achieve bounded latency. 550 4.4. 802.11ad and 802.11ay (mmWave operation) 551 4.4.1. General Characteristics 553 The IEEE 802.11ad amendment defines PHY and MAC capabilities to 554 enable multi-Gbps throughput in the 60 GHz millimeter wave (mmWave) 555 band. The standard addresses the adverse mmWave signal propagation 556 characteristics and provides directional communication capabilities 557 that take advantage of beamforming to cope with increased 558 attenuation. An overview of the 802.11ad standard can be found in 559 [Nitsche_2015] . 561 The IEEE 802.11ay is currently developing enhancements to the 562 802.11ad standard to enable the next generation mmWave operation 563 targeting 100 Gbps throughput. Some of the main enhancements in 564 802.11ay include MIMO, channel bonding, improved channel access and 565 beamforming training. An overview of the 802.11ay capabilities can 566 be found in [Ghasempour_2017] 568 4.4.2. Applicability to deterministic flows 570 The high data rates achievable with 802.11ad and 802.11ay can 571 significantly reduce latency down to microsecond levels. Limited 572 interference from legacy and other unlicensed devices in 60 GHz is 573 also a benefit. However, directionality and short range typical in 574 mmWave operation impose new challenges such as the overhead required 575 for beam training and blockage issues, which impact both latency and 576 reliability. Therefore, it is important to understand the use case 577 and deployment conditions in order to properly apply and configure 578 802.11ad/ay networks for time sensitive applications. 580 The 802.11ad standard include a scheduled access mode in which 581 stations can be allocated contention-free service periods by a 582 central controller. This scheduling capability is also available in 583 802.11ay, and it is one of the mechanisms that can be used to provide 584 bounded latency to time-sensitive data flows. An analysis of the 585 theoretical latency bounds that can be achieved with 802.11ad service 586 periods is provided in [Cavalcanti_2019]. 588 5. IEEE 802.15.4 590 5.1. Provenance and Documents 592 The IEEE802.15.4 Task Group has been driving the development of low- 593 power low-cost radio technology. The IEEE802.15.4 physical layer has 594 been designed to support demanding low-power scenarios targeting the 595 use of unlicensed bands, both the 2.4 GHz and sub GHz Industrial, 596 Scientific and Medical (ISM) bands. This has imposed requirements in 597 terms of frame size, data rate and bandwidth to achieve reduced 598 collision probability, reduced packet error rate, and acceptable 599 range with limited transmission power. The PHY layer supports frames 600 of up to 127 bytes. The Medium Access Control (MAC) sublayer 601 overhead is in the order of 10-20 bytes, leaving about 100 bytes to 602 the upper layers. IEEE802.15.4 uses spread spectrum modulation such 603 as the Direct Sequence Spread Spectrum (DSSS). 605 The Timeslotted Channel Hopping (TSCH) mode was added to the 2015 606 revision of the IEEE802.15.4 standard [IEEE Std. 802.15.4]. TSCH is 607 targeted at the embedded and industrial world, where reliability, 608 energy consumption and cost drive the application space. 610 At the IETF, the 6TiSCH Working Group (WG) [TiSCH] deals with best 611 effort operation of IPv6 [RFC8200] over TSCH. 6TiSCH has enabled 612 distributed scheduling to exploit the deterministic access 613 capabilities provided by TSCH. The group designed the essential 614 mechanisms to enable the management plane operation while ensuring 615 IPv6 is supported. Yet the charter did not focus to providing a 616 solution to establish end to end Tracks while meeting quality of 617 service requirements. 6TiSCH, through the RFC8480 [RFC8480] defines 618 the 6P protocol which provides a pairwise negotiation mechanism to 619 the control plane operation. The protocol supports agreement on a 620 schedule between neighbors, enabling distributed scheduling. 6P goes 621 hand-in-hand with a Scheduling Function (SF), the policy that decides 622 how to maintain cells and trigger 6P transactions. The Minimal 623 Scheduling Function (MSF) [I-D.ietf-6tisch-msf] is the default SF 624 defined by the 6TiSCH WG; other standardized SFs can be defined in 625 the future. MSF extends the minimal schedule configuration, and is 626 used to add child-parent links according to the traffic load. 628 Time sensitive networking on low power constrained wireless networks 629 have been partially addressed by ISA100.11a [ISA100.11a] and 630 WirelessHART [WirelessHART]. Both technologies involve a central 631 controller that computes redundant paths for industrial process 632 control traffic over a TSCH mesh. Moreover, ISA100.11a introduces 633 IPv6 capabilities with a Link-Local Address for the join process and 634 a global unicast addres for later exchanges, but the IPv6 traffic 635 typically ends at a local application gateway and the full power of 636 IPv6 for end-to-end communication is not enabled. Compared to that 637 state of the art, work at the IETF and in particular at RAW could 638 provide additional techniques such as optimized P2P routing, PAREO 639 functions, and end-to-end secured IPv6/CoAP connectivity. 641 The 6TiSCH architecture [I-D.ietf-6tisch-architecture] identifies 642 different models to schedule resources along so-called Tracks (see 643 Section 5.2.2.2) exploiting the TSCH schedule structure however the 644 focus at 6TiSCH is on best effort traffic and the group was never 645 chartered to produce standard work related to Tracks. 647 Useful References include: 649 1. IEEE Std 802.15.4: "IEEE Std. 802.15.4, Part. 15.4: Wireless 650 Medium Access Control (MAC) and Physical Layer (PHY) 651 Specifications for Low-Rate Wireless Personal Area Networks" 652 [IEEE Std. 802.15.4]. The latest version at the time of this 653 writing is dated year 2015. 655 2. Morell, A. , Vilajosana, X. , Vicario, J. L. and Watteyne, T. 656 (2013), Label switching over IEEE802.15.4e networks. Trans. 657 Emerging Tel. Tech., 24: 458-475. doi:10.1002/ett.2650" 658 [morell13]. 660 3. De Armas, J., Tuset, P., Chang, T., Adelantado, F., Watteyne, T., 661 Vilajosana, X. (2016, September). Determinism through path 662 diversity: Why packet replication makes sense. In 2016 663 International Conference on Intelligent Networking and 664 Collaborative Systems (INCoS) (pp. 150-154). IEEE. [dearmas16]. 666 4. X. Vilajosana, T. Watteyne, M. Vucinic, T. Chang and K. S. 667 J. Pister, "6TiSCH: Industrial Performance for IPv6 Internet-of- 668 Things Networks," in Proceedings of the IEEE, vol. 107, no. 6, 669 pp. 1153-1165, June 2019. [vilajosana19]. 671 5.2. TimeSlotted Channel Hopping 673 5.2.1. General Characteristics 675 As a core technique in IEEE802.15.4, TSCH splits time in multiple 676 time slots that repeat over time. A set of timeslots constructs a 677 Slotframe (see Section 5.2.2.1.4). For each timeslot, a set of 678 available frequencies can be used, resulting in a matrix-like 679 schedule (see Figure 1). 681 timeslot offset 682 | 0 1 2 3 4 | 0 1 2 3 4 | Nodes 683 +------------------------+------------------------+ +-----+ 684 | | | | | | | | | | | | C | 685 CH-1 | EB | | |C->B| | EB | | |C->B| | | | 686 | | | | | | | | | | | +-----+ 687 +-------------------------------------------------+ | 688 | | | | | | | | | | | | 689 CH-2 | | |B->C| |B->A| | |B->C| |B->A| +-----+ 690 | | | | | | | | | | | | B | 691 +-------------------------------------------------+ | | 692 ... +-----+ 693 | 694 +-------------------------------------------------+ | 695 | | | | | | | | | | | +-----+ 696 CH-15| |A->B| | | | |A->B| | | | | A | 697 | | | | | | | | | | | | | 698 +-------------------------------------------------+ +-----+ 699 ch. 700 offset 702 Figure 1: Slotframe example with scheduled cells between nodes A, 703 B and C 705 This schedule represents the possible communications of a node with 706 its neighbors, and is managed by a Scheduling Function such as the 707 Minimal Scheduling Function (MSF) [I-D.ietf-6tisch-msf]. Each cell 708 in the schedule is identified by its slotoffset and channeloffset 709 coordinates. A cell's timeslot offset indicates its position in 710 time, relative to the beginning of the slotframe. A cell's channel 711 offset is an index which maps to a frequency at each iteration of the 712 slotframe. Each packet exchanged between neighbors happens within 713 one cell. The size of a cell is a timeslot duration, between 10 to 714 15 milliseconds. An Absolute Slot Number (ASN) indicates the number 715 of slots elapsed since the network started. It increments at every 716 slot. This is a 5 byte counter that can support networks running for 717 more than 300 years without wrapping (assuming a 10 ms timeslot). 718 Channel hopping provides increased reliability to multi-path fading 719 and external interference. It is handled by TSCH through a channel 720 hopping sequence referred as macHopSeq in the IEEE802.15.4 721 specification. 723 The Time-Frequency Division Multiple Access provided by TSCH enables 724 the orchestration of traffic flows, spreading them in time and 725 frequency, and hence enabling an efficient management of the 726 bandwidth utilization. Such efficient bandwidth utilization can be 727 combined to OFDM modulations also supported by the IEEE802.15.4 728 standard [IEEE Std. 802.15.4] since the 2015 version. 730 In the RAW context, low power reliable networks should address non- 731 critical control scenarios such as Class 2 and monitoring scenarios 732 such as Class 4 defined by the RFC5673 [RFC5673]. As a low power 733 technology targeting industrial scenarios radio transducers provide 734 low data rates (typically between 50kbps to 250kbps) and robust 735 modulations to trade-off performance to reliability. TSCH networks 736 are organized in mesh topologies and connected to a backbone. 737 Latency in the mesh network is mainly influenced by propagation 738 aspects such as interference. ARQ methods and redundancy techniques 739 such as replication and elimination should be studied to provide the 740 needed performance to address deterministic scenarios. 742 5.2.2. Applicability to Deterministic Flows 744 Nodes in a TSCH network are tightly synchronized. This enables to 745 build the slotted structure and ensure efficient utilization of 746 resources thanks to proper scheduling policies. Scheduling is a key 747 to orchestrate the resources that different nodes in a Track or a 748 path are using. Slotframes can be split in resource blocks reserving 749 the needed capacity to certain flows. Periodic and bursty traffic 750 can be handled independently in the schedule, using active and 751 reactive policies and taking advantage of overprovisionned cells to 752 measu reth excursion. Along a Track, resource blocks can be chained 753 so nodes in previous hops transmit their data before the next packet 754 comes. This provides a tight control to latency along a Track. 755 Collision loss is avoided for best effort traffic by 756 overprovisionning resources, giving time to the management plane of 757 the network to dedicate more resources if needed. 759 5.2.2.1. Centralized Path Computation 761 In a controlled environment, a 6TiSCH device usually does not place a 762 request for bandwidth between itself and another device in the 763 network. Rather, an Operation Control System (OCS) invoked through 764 an Human/Machine Interface (HMI) iprovides the Traffic Specification, 765 in particular in terms of latency and reliability, and the end nodes, 766 to a Path Computation element (PCE). With this, the PCE computes a 767 Track between the end nodes and provisions every hop in the Track 768 with per-flow state that describes the per-hop operation for a given 769 packet, the corresponding timeSlots, and the flow identification to 770 recognize which packet is placed in which Track, sort out duplicates, 771 etc. In Figure 2, an example of Operational Control System and HMI 772 is depicted. 774 For a static configuration that serves a certain purpose for a long 775 period of time, it is expected that a node will be provisioned in one 776 shot with a full schedule, which incorporates the aggregation of its 777 behavior for multiple Tracks. The 6TiSCH Architecture expects that 778 the programing of the schedule is done over CoAP as discussed in 779 "6TiSCH Resource Management and Interaction using CoAP" 780 [I-D.ietf-6tisch-coap]. 782 But an Hybrid mode may be required as well whereby a single Track is 783 added, modified, or removed, for instance if it appears that a Track 784 does not perform as expected for, say, Packet Delivery Ratio (PDR). 785 For that case, the expectation is that a protocol that flows along a 786 Track (to be), in a fashion similar to classical Traffic Engineering 787 (TE) [CCAMP], may be used to update the state in the devices. 6TiSCH 788 provides means for a device to negotiate a timeSlot with a neighbor, 789 but in general that flow was not designed and no protocol was 790 selected and it is expected that DetNet will determine the 791 appropriate end-to-end protocols to be used in that case. 793 Stream Management Entity 795 Operational Control System and HMI 797 -+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 799 PCE PCE PCE PCE 801 -+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 803 --- 6TiSCH------6TiSCH------6TiSCH------6TiSCH-- 804 6TiSCH / Device Device Device Device \ 805 Device- - 6TiSCH 806 \ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device 807 ----Device------Device------Device------Device-- 809 Figure 2 811 5.2.2.1.1. Packet Marking and Handling 813 Section "Packet Marking and Handling" of 814 [I-D.ietf-6tisch-architecture] describes the packet tagging and 815 marking that is expected in 6TiSCH networks. 817 5.2.2.1.1.1. Tagging Packets for Flow Identification 819 For packets that are routed by a PCE along a Track, the tuple formed 820 by the IPv6 source address and a local RPLInstanceID is tagged in the 821 packets to identify uniquely the Track and associated transmit bundle 822 of timeSlots. 824 It results that the tagging that is used for a DetNet flow outside 825 the 6TiSCH LLN MUST be swapped into 6TiSCH formats and back as the 826 packet enters and then leaves the 6TiSCH network. 828 Note: The method and format used for encoding the RPLInstanceID at 829 6lo is generalized to all 6TiSCH topological Instances, which 830 includes Tracks. 832 5.2.2.1.1.2. Replication, Retries and Elimination 834 PRE establishes several paths in a network to provide redundancy and 835 parallel transmissions to bound the end-to-end delay. Considering 836 the scenario shown in Figure 3, many different paths are possible for 837 S to reach R. A simple way to benefit from this topology could be to 838 use the two independent paths via nodes A, C, E and via B, D, F. But 839 more complex paths are possible as well. 841 (A) (C) (E) 843 source (S) (R) (destination) 845 (B) (D) (F) 847 Figure 3: A Typical Ladder Shape with Two Parallel Paths Toward 848 the Destination 850 By employing a Packet Replication function, each node forwards a copy 851 of each data packet over two different branches. For instance, in 852 Figure 4, the source node S transmits the data packet to nodes A and 853 B, in two different timeslots within the same TSCH slotframe. 855 ===> (A) => (C) => (E) === 856 // \\// \\// \\ 857 source (S) //\\ //\\ (R) (destination) 858 \\ // \\ // \\ // 859 ===> (B) => (D) => (F) === 861 Figure 4: Packet Replication: S transmits twice the same data 862 packet, to its DP (A) and to its AP (B). 864 By employing Packet Elimination function once a node receives the 865 first copy of a data packet, it discards the subsequent copies. 866 Because the first copy that reaches a node is the one that matters, 867 it is the only copy that will be forwarded upward. 869 Considering that the wireless medium is broadcast by nature, any 870 neighbor of a transmitter may overhear a transmission. By employing 871 the Promiscuous Overhearing function, nodes will have multiple 872 opportunities to receive a given data packet. For instance, in 873 Figure 4, when the source node S transmits the data packet to node A, 874 node B may overhear this transmission. 876 6TiSCH expects elimination and replication of packets along a complex 877 Track, but has no position about how the sequence numbers would be 878 tagged in the packet. 880 As it goes, 6TiSCH expects that timeSlots corresponding to copies of 881 a same packet along a Track are correlated by configuration, and does 882 not need to process the sequence numbers. 884 The semantics of the configuration MUST enable correlated timeSlots 885 to be grouped for transmit (and respectively receive) with 886 a'OR'relations, and then a'AND'relation MUST be configurable between 887 groups. The semantics is that if the transmit (and respectively 888 receive) operation succeeded in one timeSlot in a'OR'group, then all 889 the other timeSLots in the group are ignored. Now, if there are at 890 least two groups, the'AND'relation between the groups indicates that 891 one operation must succeed in each of the groups. 893 On the transmit side, timeSlots provisioned for retries along a same 894 branch of a Track are placed a same'OR'group. The'OR'relation 895 indicates that if a transmission is acknowledged, then further 896 transmissions SHOULD NOT be attempted for timeSlots in that group. 897 There are as many'OR'groups as there are branches of the Track 898 departing from this node. Different'OR'groups are programmed for the 899 purpose of replication, each group corresponding to one branch of the 900 Track. The'AND'relation between the groups indicates that 901 transmission over any of branches MUST be attempted regardless of 902 whether a transmission succeeded in another branch. It is also 903 possible to place cells to different next-hop routers in a 904 same'OR'group. This allows to route along multi-path Tracks, trying 905 one next-hop and then another only if sending to the first fails. 907 On the receive side, all timeSlots are programmed in a same'OR'group. 908 Retries of a same copy as well as converging branches for elimination 909 are converged, meaning that the first successful reception is enough 910 and that all the other timeSlots can be ignored. 912 5.2.2.1.1.3. Differentiated Services Per-Hop-Behavior 914 Additionally, an IP packet that is sent along a Track uses the 915 Differentiated Services Per-Hop-Behavior Group called Deterministic 916 Forwarding, as described in 917 [I-D.svshah-tsvwg-deterministic-forwarding]. 919 5.2.2.1.2. Topology and capabilities 921 6TiSCH nodes are usually IoT devices, characterized by very limited 922 amount of memory, just enough buffers to store one or a few IPv6 923 packets, and limited bandwidth between peers. It results that a node 924 will maintain only a small number of peering information, and will 925 not be able to store many packets waiting to be forwarded. Peers can 926 be identified through MAC or IPv6 addresses. 928 Neighbors can be discovered over the radio using mechanism such as 929 Enhanced Beacons, but, though the neighbor information is available 930 in the 6TiSCH interface data model, 6TiSCH does not describe a 931 protocol to pro-actively push the neighborhood information to a PCE. 932 This protocol should be described and should operate over CoAP. The 933 protocol should be able to carry multiple metrics, in particular the 934 same metrics as used for RPL operations [RFC6551]. 936 The energy that the device consumes in sleep, transmit and receive 937 modes can be evaluated and reported. So can the amount of energy 938 that is stored in the device and the power that it can be scavenged 939 from the environment. The PCE SHOULD be able to compute Tracks that 940 will implement policies on how the energy is consumed, for instance 941 balance between nodes, ensure that the spent energy does not exceeded 942 the scavenged energy over a period of time, etc... 944 5.2.2.1.3. Schedule Management by a PCE 946 6TiSCH supports a mixed model of centralized routes and distributed 947 routes. Centralized routes can for example be computed by a entity 948 such as a PCE [PCE]. Distributed routes are computed by RPL 949 [RFC6550]. 951 Both methods may inject routes in the Routing Tables of the 6TiSCH 952 routers. In either case, each route is associated with a 6TiSCH 953 topology that can be a RPL Instance topology or a Track. The 6TiSCH 954 topology is indexed by a Instance ID, in a format that reuses the 955 RPLInstanceID as defined in RPL. 957 Both RPL and PCE rely on shared sources such as policies to define 958 Global and Local RPLInstanceIDs that can be used by either method. 959 It is possible for centralized and distributed routing to share a 960 same topology. Generally they will operate in different slotFrames, 961 and centralized routes will be used for scheduled traffic and will 962 have precedence over distributed routes in case of conflict between 963 the slotFrames. 965 5.2.2.1.4. SlotFrames and Priorities 967 A slotFrame is the base object that a PCE needs to manipulate to 968 program a schedule into an LLN node. Elaboration on that concept can 969 be fond in section "SlotFrames and Priorities" of 970 [I-D.ietf-6tisch-architecture] 972 IEEE802.15.4 TSCH avoids contention on the medium by formatting time 973 and frequencies in cells of transmission of equal duration. In order 974 to describe that formatting of time and frequencies, the 6TiSCH 975 architecture defines a global concept that is called a Channel 976 Distribution and Usage (CDU) matrix; a CDU matrix is a matrix of 977 cells with an height equal to the number of available channels 978 (indexed by ChannelOffsets) and a width (in timeSlots) that is the 979 period of the network scheduling operation (indexed by slotOffsets) 980 for that CDU matrix. The size of a cell is a timeSlot duration, and 981 values of 10 to 15 milliseconds are typical in 802.15.4 TSCH to 982 accommodate for the transmission of a frame and an acknowledgement, 983 including the security validation on the receive side which may take 984 up to a few milliseconds on some device architecture. 986 The frequency used by a cell in the matrix rotates in a pseudo-random 987 fashion, from an initial position at an epoch time, as the matrix 988 iterates over and over. 990 A CDU matrix is computed by the PCE, but unallocated timeSlots may be 991 used opportunistically by the nodes for classical best effort IP 992 traffic. The PCE has precedence in the allocation in case of a 993 conflict. 995 In a given network, there might be multiple CDU matrices that operate 996 with different width, so they have different durations and represent 997 different periodic operations. It is recommended that all CDU 998 matrices in a 6TiSCH domain operate with the same cell duration and 999 are aligned, so as to reduce the chances of interferences from 1000 slotted-aloha operations. The PCE MUST compute the CDU matrices and 1001 shared that knowledge with all the nodes. The matrices are used in 1002 particular to define slotFrames. 1004 A slotFrame is a MAC-level abstraction that is common to all nodes 1005 and contains a series of timeSlots of equal length and precedence. 1006 It is characterized by a slotFrame_ID, and a slotFrame_size. A 1007 slotFrame aligns to a CDU matrix for its parameters, such as number 1008 and duration of timeSlots. 1010 Multiple slotFrames can coexist in a node schedule, i.e., a node can 1011 have multiple activities scheduled in different slotFrames, based on 1012 the precedence of the 6TiSCH topologies. The slotFrames may be 1013 aligned to different CDU matrices and thus have different width. 1014 There is typically one slotFrame for scheduled traffic that has the 1015 highest precedence and one or more slotFrame(s) for RPL traffic. The 1016 timeSlots in the slotFrame are indexed by the SlotOffset; the first 1017 cell is at SlotOffset 0. 1019 The 6TiSCH architecture introduces the concept of chunks 1020 ([I-D.ietf-6tisch-architecture]) to operate such spectrum 1021 distribution for a whole group of cells at a time. The CDU matrix is 1022 formatted into a set of chunks, each of them identified uniquely by a 1023 chunk-ID, see Figure 5. The PCE MUST compute the partitioning of CDU 1024 matrices into chunks and shared that knowledge with all the nodes in 1025 a 6TiSCH network. 1027 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1028 chan.Off. 0 |chnkA|chnkP|chnk7|chnkO|chnk2|chnkK|chnk1| ... |chnkZ| 1029 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1030 chan.Off. 1 |chnkB|chnkQ|chnkA|chnkP|chnk3|chnkL|chnk2| ... |chnk1| 1031 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1032 ... 1033 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1034 chan.Off. 15 |chnkO|chnk6|chnkN|chnk1|chnkJ|chnkZ|chnkI| ... |chnkG| 1035 +-----+-----+-----+-----+-----+-----+-----+ +-----+ 1036 0 1 2 3 4 5 6 M 1038 Figure 5: CDU matrix Partitioning in Chunks 1040 The appropriation of a chunk can be requested explicitly by the PCE 1041 to any node. After a successful appropriation, the PCE owns the 1042 cells in that chunk, and may use them as hard cells to set up Tracks. 1043 Then again, 6TiSCH did not propose a method for chunk definition and 1044 a protocol for appropriation. This is to be done at RAW. 1046 5.2.2.2. 6TiSCH Tracks 1048 A Track at 6TiSCH is the application to wireless of the concept of a 1049 path in the Detnet architecture [I-D.ietf-detnet-architecture]. A 1050 Track can follow a simple sequence of relay nodes or can be 1051 structured as a more complex Destination Oriented Directed Acyclic 1052 Graph (DODAG) to a unicast destination. Along a Track, 6TiSCH nodes 1053 reserve the resources to enable the efficient transmission of packets 1054 while aiming to optimize certain properties such as reliability and 1055 ensure small jitter or bounded latency. The Track structure enables 1056 Layer-2 forwarding schemes, reducing the overhead of taking routing 1057 decisions at the Layer-3. 1059 Serial Tracks can be understood as the concatenation of cells or 1060 bundles along a routing path from a source towards a destination. 1061 The serial Track concept is analogous to the circuit concept where 1062 resources are chained through the multi-hop topology. For example, A 1063 bundle of Tx Cells in a particular node is paired to a bundle of Rx 1064 Cells in the next hop node following a routing path. 1066 Whereas scheduling ensures reliable delivery in bounded time along 1067 any Track, high availability requires the application of PAREO 1068 functions along a more complex DODAG Track structure. A DODAG has 1069 forking and joining nodes where the concepts such as Replication and 1070 Elimination can be exploited. Spatial redundancy increases the 1071 oveall energy consumption in the network but improves significantly 1072 the availability of the network as well as the packet delivery ratio. 1073 A Track may also branch off and rejoin, for the purpose of the so- 1074 called Packet Replication and Elimination (PRE), over non congruent 1075 branches. PRE may be used to complement layer-2 Automatic Repeat 1076 reQuest (ARQ) and receiver-end Ordering to form the PAREO functions. 1077 PAREO functions enable to meet industrial expectations in PDR within 1078 bounded delivery time over a Track that includes wireless links, even 1079 when the Track extends beyond the 6TiSCH network. 1081 +-----+ 1082 | IoT | 1083 | G/W | 1084 +-----+ 1085 ^ <---- Elimination 1086 | | 1087 Track branch | | 1088 +-------+ +--------+ Subnet Backbone 1089 | | 1090 +--|--+ +--|--+ 1091 | | | Backbone | | | Backbone 1092 o | | | router | | | router 1093 +--/--+ +--|--+ 1094 o / o o---o----/ o 1095 o o---o--/ o o o o o 1096 o \ / o o LLN o 1097 o v <---- Replication 1098 o 1100 Figure 6: End-to-End deterministic Track 1102 In the example above (see Figure 6), a Track is laid out from a field 1103 device in a 6TiSCH network to an IoT gateway that is located on a 1104 IEEE802.1 TSN backbone. 1106 The Replication function in the field device sends a copy of each 1107 packet over two different branches, and a PCE schedules each hop of 1108 both branches so that the two copies arrive in due time at the 1109 gateway. In case of a loss on one branch, hopefully the other copy 1110 of the packet still makes it in due time. If two copies make it to 1111 the IoT gateway, the Elimination function in the gateway ignores the 1112 extra packet and presents only one copy to upper layers. 1114 At each 6TiSCH hop along the Track, the PCE may schedule more than 1115 one timeSlot for a packet, so as to support Layer-2 retries (ARQ). 1116 It is also possible that the field device only uses the second branch 1117 if sending over the first branch fails. 1119 In current deployments, a TSCH Track does not necessarily support PRE 1120 but is systematically multi-path. This means that a Track is 1121 scheduled so as to ensure that each hop has at least two forwarding 1122 solutions, and the forwarding decision is to try the preferred one 1123 and use the other in case of Layer-2 transmission failure as detected 1124 by ARQ. 1126 Methods to implement complex Tracks are described in 1127 [I-D.papadopoulos-paw-pre-reqs] and complemented by extensions to the 1128 RPL routing protocol in [I-D.ietf-roll-nsa-extension] for best effort 1129 traffic, but a centralized routing technique such as promoted in 1130 DetNet is still missing. 1132 5.2.2.2.1. Track Scheduling Protocol 1134 Section "Schedule Management Mechanisms" of the 6TiSCH architecture 1135 describes 4 paradigms to manage the TSCH schedule of the LLN nodes: 1136 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring 1137 and scheduling management, and Hop-by-hop scheduling. The Track 1138 operation for DetNet corresponds to a remote monitoring and 1139 scheduling management by a PCE. 1141 Early work at 6TiSCH on a data model and a protocol to program the 1142 schedule in the 6TiSCH device was never concluded as the group 1143 focussed on best effort traffic. This work would be revived by RAW: 1145 The 6top interface document [RFC8480] (to be reopened at RAW) was 1146 intended to specify the generic data model that can be used to 1147 monitor and manage resources of the 6top sublayer. Abstract 1148 methods were suggested for use by a management entity in the 1149 device. The data model also enables remote control operations on 1150 the 6top sublayer. 1152 [I-D.ietf-6tisch-coap] (to be reopened at RAW) was intended to 1153 define a mapping of the 6top set of commands, which is described 1154 in RFC 8480, to CoAP resources. This allows an entity to interact 1155 with the 6top layer of a node that is multiple hops away in a 1156 RESTful fashion. 1158 [I-D.ietf-6tisch-coap] also defined a basic set CoAP resources and 1159 associated RESTful access methods (GET/PUT/POST/DELETE). The 1160 payload (body) of the CoAP messages is encoded using the CBOR 1161 format. The PCE commands are expected to be issued directly as 1162 CoAP requests or to be mapped back and forth into CoAP by a 1163 gateway function at the edge of the 6TiSCH network. For instance, 1164 it is possible that a mapping entity on the backbone transforms a 1165 non-CoAP protocol such as PCEP into the RESTful interfaces that 1166 the 6TiSCH devices support. 1168 5.2.2.2.2. Track Forwarding 1170 By forwarding, this specification means the per-packet operation that 1171 allows to deliver a packet to a next hop or an upper layer in this 1172 node. Forwarding is based on pre-existing state that was installed 1173 as a result of the routing computation of a Track by a PCE. The 1174 6TiSCH architecture supports three different forwarding model, G-MPLS 1175 Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and IPv6 1176 Forwarding (6F) which is the classical IP operation 1177 [I-D.ietf-6tisch-architecture]. The DetNet case relates to the Track 1178 Forwarding operation under the control of a PCE. 1180 A Track is a unidirectional path between a source and a destination. 1181 In a Track cell, the normal operation of IEEE802.15.4 Automatic 1182 Repeat-reQuest (ARQ) usually happens, though the acknowledgment may 1183 be omitted in some cases, for instance if there is no scheduled cell 1184 for a retry. 1186 Track Forwarding is the simplest and fastest. A bundle of cells set 1187 to receive (RX-cells) is uniquely paired to a bundle of cells that 1188 are set to transmit (TX-cells), representing a layer-2 forwarding 1189 state that can be used regardless of the network layer protocol. 1190 This model can effectively be seen as a Generalized Multi-protocol 1191 Label Switching (G-MPLS) operation in that the information used to 1192 switch a frame is not an explicit label, but rather related to other 1193 properties of the way the packet was received, a particular cell in 1194 the case of 6TiSCH. As a result, as long as the TSCH MAC (and 1195 Layer-2 security) accepts a frame, that frame can be switched 1196 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN 1197 fragment, or a frame from an alternate protocol such as WirelessHART 1198 or ISA100.11a. 1200 A data frame that is forwarded along a Track normally has a 1201 destination MAC address that is set to broadcast - or a multicast 1202 address depending on MAC support. This way, the MAC layer in the 1203 intermediate nodes accepts the incoming frame and 6top switches it 1204 without incurring a change in the MAC header. In the case of 1205 IEEE802.15.4, this means effectively broadcast, so that along the 1206 Track the short address for the destination of the frame is set to 1207 0xFFFF. 1209 A Track is thus formed end-to-end as a succession of paired bundles, 1210 a receive bundle from the previous hop and a transmit bundle to the 1211 next hop along the Track, and a cell in such a bundle belongs to at 1212 most one Track. For a given iteration of the device schedule, the 1213 effective channel of the cell is obtained by adding a pseudo-random 1214 number to the channelOffset of the cell, which results in a rotation 1215 of the frequency that used for transmission. The bundles may be 1216 computed so as to accommodate both variable rates and 1217 retransmissions, so they might not be fully used at a given iteration 1218 of the schedule. The 6TiSCH architecture provides additional means 1219 to avoid waste of cells as well as overflows in the transmit bundle, 1220 as follows: 1222 In one hand, a TX-cell that is not needed for the current iteration 1223 may be reused opportunistically on a per-hop basis for routed 1224 packets. When all of the frame that were received for a given Track 1225 are effectively transmitted, any available TX-cell for that Track can 1226 be reused for upper layer traffic for which the next-hop router 1227 matches the next hop along the Track. In that case, the cell that is 1228 being used is effectively a TX-cell from the Track, but the short 1229 address for the destination is that of the next-hop router. It 1230 results that a frame that is received in a RX-cell of a Track with a 1231 destination MAC address set to this node as opposed to broadcast must 1232 be extracted from the Track and delivered to the upper layer (a frame 1233 with an unrecognized MAC address is dropped at the lower MAC layer 1234 and thus is not received at the 6top sublayer). 1236 On the other hand, it might happen that there are not enough TX-cells 1237 in the transmit bundle to accommodate the Track traffic, for instance 1238 if more retransmissions are needed than provisioned. In that case, 1239 the frame can be placed for transmission in the bundle that is used 1240 for layer-3 traffic towards the next hop along the Track as long as 1241 it can be routed by the upper layer, that is, typically, if the frame 1242 transports an IPv6 packet. The MAC address should be set to the 1243 next-hop MAC address to avoid confusion. It results that a frame 1244 that is received over a layer-3 bundle may be in fact associated to a 1245 Track. In a classical IP link such as an Ethernet, off-Track traffic 1246 is typically in excess over reservation to be routed along the non- 1247 reserved path based on its QoS setting. But with 6TiSCH, since the 1248 use of the layer-3 bundle may be due to transmission failures, it 1249 makes sense for the receiver to recognize a frame that should be re- 1250 Tracked, and to place it back on the appropriate bundle if possible. 1251 A frame should be re-Tracked if the Per-Hop-Behavior group indicated 1252 in the Differentiated Services Field in the IPv6 header is set to 1253 Deterministic Forwarding, as discussed in Section 5.2.2.1.1. A frame 1254 is re-Tracked by scheduling it for transmission over the transmit 1255 bundle associated to the Track, with the destination MAC address set 1256 to broadcast. 1258 There are 2 modes for a Track, transport mode and tunnel mode. 1260 5.2.2.2.2.1. Transport Mode 1262 In transport mode, the Protocol Data Unit (PDU) is associated with 1263 flow-dependant meta-data that refers uniquely to the Track, so the 1264 6top sublayer can place the frame in the appropriate cell without 1265 ambiguity. In the case of IPv6 traffic, this flow identification is 1266 transported in the Flow Label of the IPv6 header. Associated with 1267 the source IPv6 address, the Flow Label forms a globally unique 1268 identifier for that particular Track that is validated at egress 1269 before restoring the destination MAC address (DMAC) and punting to 1270 the upper layer. 1272 | ^ 1273 +--------------+ | | 1274 | IPv6 | | | 1275 +--------------+ | | 1276 | 6LoWPAN HC | | | 1277 +--------------+ ingress egress 1278 | 6top | sets +----+ +----+ restores 1279 +--------------+ dmac to | | | | dmac to 1280 | TSCH MAC | brdcst | | | | self 1281 +--------------+ | | | | | | 1282 | LLN PHY | +-------+ +--...-----+ +-------+ 1283 +--------------+ 1285 Figure 7: Track Forwarding, Transport Mode 1287 5.2.2.2.2.2. Tunnel Mode 1289 In tunnel mode, the frames originate from an arbitrary protocol over 1290 a compatible MAC that may or may not be synchronized with the 6TiSCH 1291 network. An example of this would be a router with a dual radio that 1292 is capable of receiving and sending WirelessHART or ISA100.11a frames 1293 with the second radio, by presenting itself as an Access Point or a 1294 Backbone Router, respectively. 1296 In that mode, some entity (e.g. PCE) can coordinate with a 1297 WirelessHART Network Manager or an ISA100.11a System Manager to 1298 specify the flows that are to be transported transparently over the 1299 Track. 1301 +--------------+ 1302 | IPv6 | 1303 +--------------+ 1304 | 6LoWPAN HC | 1305 +--------------+ set restore 1306 | 6top | +dmac+ +dmac+ 1307 +--------------+ to|brdcst to|nexthop 1308 | TSCH MAC | | | | | 1309 +--------------+ | | | | 1310 | LLN PHY | +-------+ +--...-----+ +-------+ 1311 +--------------+ | ingress egress | 1312 | | 1313 +--------------+ | | 1314 | LLN PHY | | | 1315 +--------------+ | | 1316 | TSCH MAC | | | 1317 +--------------+ | dmac = | dmac = 1318 |ISA100/WiHART | | nexthop v nexthop 1319 +--------------+ 1321 Figure 8: Track Forwarding, Tunnel Mode 1323 In that case, the flow information that identifies the Track at the 1324 ingress 6TiSCH router is derived from the RX-cell. The dmac is set 1325 to this node but the flow information indicates that the frame must 1326 be tunneled over a particular Track so the frame is not passed to the 1327 upper layer. Instead, the dmac is forced to broadcast and the frame 1328 is passed to the 6top sublayer for switching. 1330 At the egress 6TiSCH router, the reverse operation occurs. Based on 1331 metadata associated to the Track, the frame is passed to the 1332 appropriate link layer with the destination MAC restored. 1334 5.2.2.2.2.3. Tunnel Metadata 1336 Metadata coming with the Track configuration is expected to provide 1337 the destination MAC address of the egress endpoint as well as the 1338 tunnel mode and specific data depending on the mode, for instance a 1339 service access point for frame delivery at egress. If the tunnel 1340 egress point does not have a MAC address that matches the 1341 configuration, the Track installation fails. 1343 In transport mode, if the final layer-3 destination is the tunnel 1344 termination, then it is possible that the IPv6 address of the 1345 destination is compressed at the 6LoWPAN sublayer based on the MAC 1346 address. It is thus mandatory at the ingress point to validate that 1347 the MAC address that was used at the 6LoWPAN sublayer for compression 1348 matches that of the tunnel egress point. For that reason, the node 1349 that injects a packet on a Track checks that the destination is 1350 effectively that of the tunnel egress point before it overwrites it 1351 to broadcast. The 6top sublayer at the tunnel egress point reverts 1352 that operation to the MAC address obtained from the tunnel metadata. 1354 5.2.2.2.2.4. OAM 1356 An Overview of Operations, Administration, and Maintenance (OAM) 1357 Tools [RFC7276] provides an overwiew of the existing tooling for OAM 1358 [RFC6291]. Tracks are complex paths and new tooling is necessary to 1359 manage them, with respect to load control, timing, and the Packet 1360 Replication and Elimination Functions (PREF). 1362 An example of such tooling can be found in the context of BIER 1363 [RFC8279] and more specifically BIER Traffic Engineering 1364 [I-D.ietf-bier-te-arch] (BIER-TE): 1365 [I-D.thubert-bier-replication-elimination] leverages BIER-TE to 1366 control the process of PREF, and to provide traceability of these 1367 operations, in the deterministic dataplane, along a complex Track. 1368 For the 6TiSCH type of constrained environment, 1369 [I-D.thubert-6lo-bier-dispatch] enables an efficient encoding of the 1370 BIER bitmap within the 6LoRH framework. 1372 6. 5G 1374 6.1. Provenance and Documents 1376 The 3rd Generation Partnership Project (3GPP) incorporates many 1377 companies whose business is related to cellular network operation as 1378 well as network equipment and device manufacturing. All generations 1379 of 3GPP technologies provide scheduled wireless segments, primarily 1380 in licensed spectrum which is beneficial for reliability and 1381 availability. 1383 In 2016, the 3GPP started to design New Radio (NR) technology 1384 belonging to the fifth generation (5G) of cellular networks. NR has 1385 been designed from the beginning to not only address enhanced Mobile 1386 Broadband (eMBB) services for consumer devices such as smart phones 1387 or tablets but is also tailored for future Internet of Things (IoT) 1388 communication and connected cyber-physical systems. In addition to 1389 eMBB, requirement categories have been defined on Massive Machine- 1390 Type Communication (M-MTC) for a large number of connected devices/ 1391 sensors, and Ultra-Reliable Low-Latency Communication (URLLC) for 1392 connected control systems and critical communication as illustrated 1393 in Figure 9. It is the URLLC capabilities that make 5G a great 1394 candidate for reliable low-latency communication. With these three 1395 corner stones, NR is a complete solution supporting the connectivity 1396 needs of consumers, enterprises, and public sector for both wide area 1397 and local area, e.g. indoor deployments. A general overview of NR 1398 can be found in [TS38300]. 1400 enhanced 1401 Mobile Broadband 1402 ^ 1403 / \ 1404 / \ 1405 / \ 1406 / \ 1407 / 5G \ 1408 / \ 1409 / \ 1410 / \ 1411 +-----------------+ 1412 Massive Ultra-Reliable 1413 Machine-Type Low-Latency 1414 Communication Communication 1416 Figure 9: 5G Application Areas 1418 As a result of releasing the first NR specification in 2018 (Release 1419 15), it has been proven by many companies that NR is a URLLC-capable 1420 technology and can deliver data packets at 10^-5 packet error rate 1421 within 1ms latency budget [TR37910]. Those evaluations were 1422 consolidated and forwarded to ITU to be included in the [IMT2020] 1423 work. 1425 In order to understand communication requirements for automation in 1426 vertical domains, 3GPP studied different use cases [TR22804] and 1427 released technical specification with reliability, availability and 1428 latency demands for a variety of applications [TS22104]. 1430 As an evolution of NR, multiple studies have been conducted in scope 1431 of 3GPP Release 16 including the following two, focusing on radio 1432 aspects: 1434 1. Study on physical layer enhancements for NR ultra-reliable and 1435 low latency communication (URLLC) [TR38824]. 1437 2. Study on NR industrial Internet of Things (I-IoT) [TR38825]. 1439 In addition, several enhancements have been done on system 1440 architecture level which are reflected in System architecture for the 1441 5G System (5GS) [TS23501]. 1443 6.2. General Characteristics 1445 The 5G Radio Access Network (5G RAN) with its NR interface includes 1446 several features to achieve Quality of Service (QoS), such as a 1447 guaranteeably low latency or tolerable packet error rates for 1448 selected data flows. Determinism is achieved by centralized 1449 admission control and scheduling of the wireless frequency resources, 1450 which are typically licensed frequency bands assigned to a network 1451 operator. 1453 NR enables short transmission slots in a radio subframe, which 1454 benefits low-latency applications. NR also introduces mini-slots, 1455 where prioritized transmissions can be started without waiting for 1456 slot boundaries, further reducing latency. As part of giving 1457 priority and faster radio access to URLLC traffic, NR introduces 1458 preemption where URLLC data transmission can preempt ongoing non- 1459 URLLC transmissions. Additionally, NR applies very fast processing, 1460 enabling retransmissions even within short latency bounds. 1462 NR defines extra-robust transmission modes for increased reliability 1463 both for data and control radio channels. Reliability is further 1464 improved by various techniques, such as multi-antenna transmission, 1465 the use of multiple frequency carriers in parallel and packet 1466 duplication over independent radio links. NR also provides full 1467 mobility support, which is an important reliability aspect not only 1468 for devices that are moving, but also for devices located in a 1469 changing environment. 1471 Network slicing is seen as one of the key features for 5G, allowing 1472 vertical industries to take advantage of 5G networks and services. 1473 Network slicing is about transforming a Public Land Mobile Network 1474 (PLMN) from a single network to a network where logical partitions 1475 are created, with appropriate network isolation, resources, optimized 1476 topology and specific configuration to serve various service 1477 requirements. An operator can configure and manage the mobile 1478 network to support various types of services enabled by 5G, for 1479 example eMBB and URLLC, depending on the different customers' needs. 1481 Exposure of capabilities of 5G Systems to the network or applications 1482 outside the 3GPP domain have been added to Release 16 [TS23501]. Via 1483 exposure interfaces, applications can access 5G capabilities, e.g., 1484 communication service monitoring and network maintenance. 1486 For several generations of mobile networks, 3GPP has considered how 1487 the communication system should work on a global scale with billions 1488 of users, taking into account resilience aspects, privacy regulation, 1489 protection of data, encryption, access and core network security, as 1490 well as interconnect. Security requirements evolve as demands on 1491 trustworthiness increase. For example, this has led to the 1492 introduction of enhanced privacy protection features in 5G. 5G also 1493 employs strong security algorithms, encryption of traffic, protection 1494 of signaling and protection of interfaces. 1496 One particular strength of mobile networks is the authentication, 1497 based on well-proven algorithms and tightly coupled with a global 1498 identity management infrastructure. Since 3G, there is also mutual 1499 authentication, allowing the network to authenticate the device and 1500 the device to authenticate the network. Another strength is secure 1501 solutions for storage and distribution of keys fulfilling regulatory 1502 requirements and allowing international roaming. When connecting to 1503 5G, the user meets the entire communication system, where security is 1504 the result of standardization, product security, deployment, 1505 operations and management as well as incident handling capabilities. 1506 The mobile networks approach the entirety in a rather coordinated 1507 fashion which is beneficial for security. 1509 6.3. Deployment and Spectrum 1511 The 5G system allows deployment in a vast spectrum range, addressing 1512 use-cases in both wide-area as well as local networks. Furthermore, 1513 5G can be configured for public and non-public access. 1515 When it comes to spectrum, NR allows combining the merits of many 1516 frequency bands, such as the high bandwidths in millimeter Waves 1517 (mmW) for extreme capacity locally, as well as the broad coverage 1518 when using mid- and low frequency bands to address wide-area 1519 scenarios. URLLC is achievable in all these bands. Spectrum can be 1520 either licensed, which means that the license holder is the only 1521 authorized user of that spectrum range, or unlicensed, which means 1522 that anyone who wants to use the spectrum can do so. 1524 A prerequisite for critical communication is performance 1525 predictability, which can be achieved by the full control of the 1526 access to the spectrum, which 5G provides. Licensed spectrum 1527 guarantees control over spectrum usage by the system, making it a 1528 preferable option for critical communication. However, unlicensed 1529 spectrum can provide an additional resource for scaling non-critical 1530 communications. While NR is initially developed for usage of 1531 licensed spectrum, the functionality to access also unlicensed 1532 spectrum was introduced in 3GPP Release 16. 1534 Licensed spectrum dedicated to mobile communications has been 1535 allocated to mobile service providers, i.e. issued as longer-term 1536 licenses by national administrations around the world. These 1537 licenses have often been associated with coverage requirements and 1538 issued across whole countries, or in large regions. Besides this, 1539 configured as a non-public network (NPN) deployment, 5G can provide 1540 network services also to a non-operator defined organization and its 1541 premises such as a factory deployment. By this isolation, quality of 1542 service requirements, as well as security requirements can be 1543 achieved. An integration with a public network, if required, is also 1544 possible. The non-public (local) network can thus be interconnected 1545 with a public network, allowing devices to roam between the networks. 1547 In an alternative model, some countries are now in the process of 1548 allocating parts of the 5G spectrum for local use to industries. 1549 These non-service providers then have a choice of applying for a 1550 local license themselves and operating their own network or 1551 cooperating with a public network operator or service provider. 1553 6.4. Applicability to Deterministic Flows 1555 6.4.1. System Architecture 1557 The 5G system [TS23501] consists of the User Equipment (UE) at the 1558 terminal side, and the Radio Access Network (RAN) with the gNB as 1559 radio base station node, as well as the Core Network (CN). The core 1560 network is based on a service-based architecture with the central 1561 functions: Access and Mobility Management Function (AMF), Session 1562 Management Function (SMF) and User Plane Function (UPF) as 1563 illustrated in Figure 10. 1565 The gNB's main responsibility is the radio resource management, 1566 including admission control and scheduling, mobility control and 1567 radio measurement handling. The AMF handles the UE's connection 1568 status and security, while the SMF controls the UE's data sessions. 1569 The UPF handles the user plane traffic. 1571 The SMF can instantiate various Packet Data Unit (PDU) sessions for 1572 the UE, each associated with a set of QoS flows, i.e., with different 1573 QoS profiles. Segregation of those sessions is also possible, e.g., 1574 resource isolation in the RAN and in the CN can be defined (slicing). 1576 +----+ +---+ +---+ +---+ +---+ +---+ 1577 |NSSF| |NEF| |NRF| |PCF| |UDM| |AF | 1578 +--+-+ +-+-+ +-+-+ +-+-+ +-+-+ +-+-+ 1579 | | | | | | 1580 Nnssf| Nnef| Nnrf| Npcf| Nudm| Naf| 1581 | | | | | | 1582 ---+------+-+-----+-+------------+--+-----+-+--- 1583 | | | | 1584 Nausf| Nausf| Nsmf| | 1585 | | | | 1586 +--+-+ +-+-+ +-+-+ +-+-+ 1587 |AUSF| |AMF| |SMF| |SCP| 1588 +----+ +++-+ +-+-+ +---+ 1589 / | | 1590 / | | 1591 / | | 1592 N1 N2 N4 1593 / | | 1594 / | | 1595 / | | 1596 +--+-+ +--+--+ +--+---+ +----+ 1597 | UE +---+(R)AN+--N3--+ UPF +--N6--+ DN | 1598 +----+ +-----+ ++----++ +----+ 1599 | | 1600 +-N9-+ 1602 Figure 10: 5G System Architecture 1604 To allow UE mobility across cells/gNBs, handover mechanisms are 1605 supported in NR. For an established connection, i.e., connected mode 1606 mobility, a gNB can configure a UE to report measurements of received 1607 signal strength and quality of its own and neighbouring cells, 1608 periodically or event-based. Based on these measurement reports, the 1609 gNB decides to handover a UE to another target cell/gNB. Before 1610 triggering the handover, it is hand-shaked with the target gNB based 1611 on network signalling. A handover command is then sent to the UE and 1612 the UE switches its connection to the target cell/gNB. The Packet 1613 Data Convergence Protocol (PDCP) of the UE can be configured to avoid 1614 data loss in this procedure, i.e., handle retransmissions if needed. 1615 Data forwarding is possible between source and target gNB as well. 1616 To improve the mobility performance further, i.e., to avoid 1617 connection failures, e.g., due to too-late handovers, the mechanism 1618 of conditional handover is introduced in Release 16 specifications. 1620 Therein a conditional handover command, defining a triggering point, 1621 can be sent to the UE before UE enters a handover situation. A 1622 further improvement introduced in Release 16 is the Dual Active 1623 Protocol Stack (DAPS), where the UE maintains the connection to the 1624 source cell while connecting to the target cell. This way, potential 1625 interruptions in packet delivery can be avoided entirely. 1627 6.4.2. Overview of The Radio Protocol Stack 1629 The protocol architecture for NR consists of the L1 Physical layer 1630 (PHY) and as part of the L2, the sublayers of Medium Access Control 1631 (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol 1632 (PDCP), as well as the Service Data Adaption Protocol (SDAP). 1634 The PHY layer handles signal processing related actions, such as 1635 encoding/decoding of data and control bits, modulation, antenna 1636 precoding and mapping. 1638 The MAC sub-layer handles multiplexing and priority handling of 1639 logical channels (associated with QoS flows) to transport blocks for 1640 PHY transmission, as well as scheduling information reporting and 1641 error correction through Hybrid Automated Repeat Request (HARQ). 1643 The RLC sublayer handles sequence numbering of higher layer packets, 1644 retransmissions through Automated Repeat Request (ARQ), if 1645 configured, as well as segmentation and reassembly and duplicate 1646 detection. 1648 The PDCP sublayer consists of functionalities for ciphering/ 1649 deciphering, integrity protection/verification, re-ordering and in- 1650 order delivery, duplication and duplicate handling for higher layer 1651 packets, and acts as the anchor protocol to support handovers. 1653 The SDAP sublayer provides services to map QoS flows, as established 1654 by the 5G core network, to data radio bearers (associated with 1655 logical channels), as used in the 5G RAN. 1657 Additionally, in RAN, the Radio Resource Control (RRC) protocol, 1658 handles the access control and configuration signalling for the 1659 aforementioned protocol layers. RRC messages are considered L3 and 1660 thus transmitted also via those radio protocol layers. 1662 To provide low latency and high reliability for one transmission 1663 link, i.e., to transport data (or control signaling) of one radio 1664 bearer via one carrier, several features have been introduced on the 1665 user plane protocols for PHY and L2, as explained in the following. 1667 6.4.3. Radio (PHY) 1669 NR is designed with native support of antenna arrays utilizing 1670 benefits from beamforming, transmissions over multiple MIMO layers 1671 and advanced receiver algorithms allowing effective interference 1672 cancellation. Those antenna techniques are the basis for high signal 1673 quality and effectiveness of spectral usage. Spatial diversity with 1674 up to 4 MIMO layers in UL and up to 8 MIMO layers in DL is supported. 1675 Together with spatial-domain multiplexing, antenna arrays can focus 1676 power in desired direction to form beams. NR supports beam 1677 management mechanisms to find the best suitable beam for UE initially 1678 and when it is moving. In addition, gNBs can coordinate their 1679 respective DL and UL transmissions over the backhaul network keeping 1680 interference reasonably low, and even make transmissions or 1681 receptions from multiple points (multi-TRP). Multi-TRP can be used 1682 for repetition of data packet in time, in frequency or over multiple 1683 MIMO layers which can improve reliability even further. 1685 Any downlink transmission to a UE starts from resource allocation 1686 signaling over the Physical Downlink Control Channel (PDCCH). If it 1687 is successfully received, the UE will know about the scheduled 1688 transmission and may receive data over the Physical Downlink Shared 1689 Channel (PDSCH). If retransmission is required according to the HARQ 1690 scheme, a signaling of negative acknowledgement (NACK) on the 1691 Physical Uplink Control Channel (PUCCH) is involved and PDCCH 1692 together with PDSCH transmissions (possibly with additional 1693 redundancy bits) are transmitted and soft-combined with previously 1694 received bits. Otherwise, if no valid control signaling for 1695 scheduling data is received, nothing is transmitted on PUCCH 1696 (discontinuous transmission - DTX),and the base station upon 1697 detecting DTX will retransmit the initial data. 1699 An uplink transmission normally starts from a Scheduling Request (SR) 1700 - a signaling message from the UE to the base station sent via PUCCH. 1701 Once the scheduler is informed about buffer data in UE, e.g., by SR, 1702 the UE transmits a data packet on the Physical Uplink Shared Channel 1703 (PUSCH). Pre-scheduling not relying on SR is also possible (see 1704 following section). 1706 Since transmission of data packets require usage of control and data 1707 channels, there are several methods to maintain the needed 1708 reliability. NR uses Low Density Parity Check (LDPC) codes for data 1709 channels, Polar codes for PDCCH, as well as orthogonal sequences and 1710 Polar codes for PUCCH. For ultra-reliability of data channels, very 1711 robust (low spectral efficiency) Modulation and Coding Scheme (MCS) 1712 tables are introduced containing very low (down to 1/20) LDPC code 1713 rates using BPSK or QPSK. Also, PDCCH and PUCCH channels support 1714 multiple code rates including very low ones for the channel 1715 robustness. 1717 A connected UE reports downlink (DL) quality to gNB by sending 1718 Channel State Information (CSI) reports via PUCCH while uplink (UL) 1719 quality is measured directly at gNB. For both uplink and downlink, 1720 gNB selects the desired MCS number and signals it to the UE by 1721 Downlink Control Information (DCI) via PDCCH channel. For URLLC 1722 services, the UE can assist the gNB by advising that MCS targeting 1723 10^-5 Block Error Rate (BLER) are used. Robust link adaptation 1724 algorithms can maintain the needed level of reliability considering a 1725 given latency bound. 1727 Low latency on the physical layer is provided by short transmission 1728 duration which is possible by using high Subcarrier Spacing (SCS) and 1729 the allocation of only one or a few Orthogonal Frequency Division 1730 Multiplexing (OFDM) symbols. For example, the shortest latency for 1731 the worst case in DL can be 0.23ms and in UL can be 0.24ms according 1732 to (section 5.7.1 in [TR37910]). Moreover, if the initial 1733 transmission has failed, HARQ feedback can quickly be provided and an 1734 HARQ retransmission is scheduled. 1736 Dynamic multiplexing of data associated with different services is 1737 highly desirable for efficient use of system resources and to 1738 maximize system capacity. Assignment of resources for eMBB is 1739 usually done with regular (longer) transmission slots, which can lead 1740 to blocking of low latency services. To overcome the blocking, eMBB 1741 resources can be pre-empted and re-assigned to URLLC services. In 1742 this way, spectrally efficient assignments for eMBB can be ensured 1743 while providing flexibility required to ensure a bounded latency for 1744 URLLC services. In downlink, the gNB can notify the eMBB UE about 1745 pre-emption after it has happened, while in uplink there are two pre- 1746 emption mechanisms: special signaling to cancel eMBB transmission and 1747 URLLC dynamic power boost to suppress eMBB transmission. 1749 6.4.4. Scheduling and QoS (MAC) 1751 One integral part of the 5G system is the Quality of Service (QoS) 1752 framework [TS23501]. QoS flows are setup by the 5G system for 1753 certain IP or Ethernet packet flows, so that packets of each flow 1754 receive the same forwarding treatment, i.e., in scheduling and 1755 admission control. QoS flows can for example be associated with 1756 different priority level, packet delay budgets and tolerable packet 1757 error rates. Since radio resources are centrally scheduled in NR, 1758 the admission control function can ensure that only those QoS flows 1759 are admitted for which QoS targets can be reached. 1761 NR transmissions in both UL and DL are scheduled by the gNB 1762 [TS38300]. This ensures radio resource efficiency, fairness in 1763 resource usage of the users and enables differentiated treatment of 1764 the data flows of the users according to the QoS targets of the 1765 flows. Those QoS flows are handled as data radio bearers or logical 1766 channels in NR RAN scheduling. 1768 The gNB can dynamically assign DL and UL radio resources to users, 1769 indicating the resources as DL assignments or UL grants via control 1770 channel to the UE. Radio resources are defined as blocks of OFDM 1771 symbols in spectral domain and time domain. Different lengths are 1772 supported in time domain, i.e., (multiple) slot or mini-slot lengths. 1773 Resources of multiple frequency carriers can be aggregated and 1774 jointly scheduled to the UE. 1776 Scheduling decisions are based, e.g., on channel quality measured on 1777 reference signals and reported by the UE (cf. periodical CSI reports 1778 for DL channel quality). The transmission reliability can be chosen 1779 in the scheduling algorithm, i.e., by link adaptation where an 1780 appropriate transmission format (e.g., robustness of modulation and 1781 coding scheme, controlled UL power) is selected for the radio channel 1782 condition of the UE. Retransmissions, based on HARQ feedback, are 1783 also controlled by the scheduler. If needed to avoid HARQ round-trip 1784 time delays, repeated transmissions can be also scheduled beforehand, 1785 to the cost of reduced spectral efficiency. 1787 In dynamic DL scheduling, transmission can be initiated immediately 1788 when DL data becomes available in the gNB. However, for dynamic UL 1789 scheduling, when data becomes available but no UL resources are 1790 available yet, the UE indicates the need for UL resources to the gNB 1791 via a (single bit) scheduling request message in the UL control 1792 channel. When thereupon UL resources are scheduled to the UE, the UE 1793 can transmit its data and may include a buffer status report, 1794 indicating the exact amount of data per logical channel still left to 1795 be sent. More UL resources may be scheduled accordingly. To avoid 1796 the latency introduced in the scheduling request loop, UL radio 1797 resources can also be pre-scheduled. 1799 In particular for periodical traffic patterns, the pre-scheduling can 1800 rely on the scheduling features DL Semi-Persistent Scheduling (SPS) 1801 and UL Configured Grant (CG). With these features, periodically 1802 recurring resources can be assigned in DL and UL. Multiple parallels 1803 of those configurations are supported, in order to serve multiple 1804 parallel traffic flows of the same UE. 1806 To support QoS enforcement in the case of mixed traffic with 1807 different QoS requirements, several features have recently been 1808 introduced. This way, e.g., different periodical critical QoS flows 1809 can be served together with best effort transmissions, by the same 1810 UE. Among others, these features (partly Release 16) are: 1) UL 1811 logical channel transmission restrictions allowing to map logical 1812 channels of certain QoS only to intended UL resources of a certain 1813 frequency carrier, slot-length, or CG configuration, and 2) intra-UE 1814 pre-emption, allowing critical UL transmissions to pre-empt non- 1815 critical transmissions. 1817 When multiple frequency carriers are aggregated, duplicate parallel 1818 transmissions can be employed (beside repeated transmissions on one 1819 carrier). This is possible in the Carrier Aggregation (CA) 1820 architecture where those carriers originate from the same gNB, or in 1821 the Dual Connectivity (DC) architecture where the carriers originate 1822 from different gNBs, i.e., the UE is connected to two gNBs in this 1823 case. In both cases, transmission reliability is improved by this 1824 means of providing frequency diversity. 1826 In addition to licensed spectrum, a 5G system can also utilize 1827 unlicensed spectrum to offload non-critical traffic. This version of 1828 NR is called NR-U, part of 3GPP Release 16. The central scheduling 1829 approach applies also for unlicensed radio resources, but in addition 1830 also the mandatory channel access mechanisms for unlicensed spectrum, 1831 e.g., Listen Before Talk (LBT) are supported in NR-U. This way, by 1832 using NR, operators have and can control access to both licensed and 1833 unlicensed frequency resources. 1835 6.4.5. Time-Sensitive Networking (TSN) Integration 1837 The main objective of Time-Sensitive Networking (TSN) is to provide 1838 guaranteed data delivery within a guaranteed time window, i.e., 1839 bounded low latency. IEEE 802.1 TSN [IEEE802.1TSN] is a set of open 1840 standards that provide features to enable deterministic communication 1841 on standard IEEE 802.3 Ethernet [IEEE802.3]. TSN standards can be 1842 seen as a toolbox for traffic shaping, resource management, time 1843 synchronization, and reliability. 1845 A TSN stream is a data flow between one end station (Talker) to 1846 another end station (Listener). In the centralized configuration 1847 model, TSN bridges are configured by the Central Network Controller 1848 (CNC) [IEEE802.1Qcc] to provide deterministic connectivity for the 1849 TSN stream through the network. Time-based traffic shaping provided 1850 by Scheduled Traffic [IEEE802.1Qbv] may be used to achieve bounded 1851 low latency. The TSN tool for time synchronization is the 1852 generalized Precision Time Protocol (gPTP) [IEEE802.1AS]), which 1853 provides reliable time synchronization that can be used by end 1854 stations and by other TSN tools, e.g., Scheduled Traffic 1855 [IEEE802.1Qbv]. High availability, as a result of ultra-reliability, 1856 is provided for data flows by the Frame Replication and Elimination 1857 for Reliability (FRER) [IEEE802.1CB] mechanism. 1859 3GPP Release 16 includes integration of 5G with TSN, i.e., specifies 1860 functions for the 5G System (5GS) to deliver TSN streams such that 1861 the meet their QoS requirements. A key aspect of the integration is 1862 the 5GS appears from the rest of the network as a set of TSN bridges, 1863 in particular, one virtual bridge per User Plane Function (UPF) on 1864 the user plane. The 5GS includes TSN Translator (TT) functionality 1865 for the adaptation of the 5GS to the TSN bridged network and for 1866 hiding the 5GS internal procedures. The 5GS provides the following 1867 components: 1869 1. interface to TSN controller, as per [IEEE802.1Qcc] for the fully 1870 centralized configuration model 1872 2. time synchronization via reception and transmission of gPTP PDUs 1873 [IEEE802.1AS] 1875 3. low latency, hence, can be integrated with Scheduled Traffic 1876 [IEEE802.1Qbv] 1878 4. reliability, hence, can be integrated with FRER [IEEE802.1CB] 1879 Figure 10 shows an illustration of 5G-TSN integration where an 1880 industrial controller (Ind Ctrlr) is connected to industrial Input/ 1881 Output devices (I/O dev) via 5G. The 5GS can directly transport 1882 Ethernet frames since Release 15, thus, end-to-end Ethernet 1883 connectivity is provided. The 5GS implements the required interfaces 1884 towards the TSN controller functions such as the CNC, thus adapts to 1885 the settings of the TSN network. A 5G user plane virtual bridge 1886 interconnects TSN bridges or connect end stations, e.g., I/O devices 1887 to the network. Note that the introduction of 5G brings flexibility 1888 in various aspects, e.g., more flexible network topology because a 1889 wireless hop can replace several wireline hops thus significantly 1890 reduce the number of hops end-to-end. [ETR5GTSN] dives more into the 1891 integration of 5G with TSN. 1893 +------------------------------+ 1894 | 5G System | 1895 | +---+| 1896 | +-+ +-+ +-+ +-+ +-+ |TSN|| 1897 | | | | | | | | | | | |AF |......+ 1898 | +++ +++ +++ +++ +++ +-+-+| . 1899 | | | | | | | | . 1900 | -+---+---++--+-+-+--+-+- | . 1901 | | | | | | +--+--+ 1902 | +++ +++ +++ +++ | | TSN | 1903 | | | | | | | | | | |Ctrlr+.......+ 1904 | +++ +++ +++ +++ | +--+--+ . 1905 | | . . 1906 | | . . 1907 | +..........................+ | . . 1908 | . Virtual Bridge . | . . 1909 +---+ | . +--+--+ +---+ +---+--+ . | +--+---+ . 1910 |I/O+----------------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+ . 1911 |dev| | . |TT| | | | | |TT| . | |bridge| | . 1912 +---+ | . +--+--+ +---+ +---+--+ . | +------+ | . 1913 | +..........................+ | . +-+-+-+ 1914 | | . | Ind | 1915 | +..........................+ | . |Ctrlr| 1916 | . Virtual Bridge . | . +-+---+ 1917 +---+ +------+ | . +--+--+ +---+ +---+--+ . | +--+---+ | 1918 |I/O+--+ TSN +------+DS|UE+---+RAN+-+UPF|NW+------+ TSN +----+ 1919 |dev| |bridge| | . |TT| | | | | |TT| . | |bridge| 1920 +---+ +------+ | . +--+--+ +---+ +---+--+ . | +------+ 1921 | +..........................+ | 1922 +------------------------------+ 1924 <----------------- end-to-end Ethernet -------------------> 1926 Figure 11: 5G - TSN Integration 1928 NR supports accurate reference time synchronization in 1us accuracy 1929 level. Since NR is a scheduled system, an NR UE and a gNB are 1930 tightly synchronized to their OFDM symbol structures. A 5G internal 1931 reference time can be provided to the UE via broadcast or unicast 1932 signaling, associating a known OFDM symbol to this reference clock. 1933 The 5G internal reference time can be shared within the 5G network, 1934 i.e., radio and core network components. For the interworking with 1935 gPTP for multiple time domains, the 5GS acts as a virtual gPTP time- 1936 aware system and supports the forwarding of gPTP time synchronization 1937 information between end stations and bridges through the 5G user 1938 plane TTs. These account for the residence time of the 5GS in the 1939 time synchronization procedure. One special option is when the 5GS 1940 internal reference time in not only used within the 5GS, but also to 1941 the rest of the devices in the deployment, including connected TSN 1942 bridges and end stations. 1944 Redundancy architectures were specified in order to provide 1945 reliability against any kind of failure on the radio link or nodes in 1946 the RAN and the core network, Redundant user plane paths can be 1947 provided based on the dual connectivity architecture, where the UE 1948 sets up two PDU sessions towards the same data network, and the 5G 1949 system makes the paths of the two PDU sessions independent as 1950 illustrated in Figure 13. There are two PDU sessions involved in the 1951 solution: the first spans from the UE via gNB1 to UPF1, acting as the 1952 first PDU session anchor, while the second spans from the UE via gNB2 1953 to UPF2, acting as second the PDU session anchor. The independent 1954 paths may continue beyond the 3GPP network. Redundancy Handling 1955 Functions (RHFs) are deployed outside of the 5GS, i.e., in Host A 1956 (the device) and in Host B (the network). RHF can implement 1957 replication and elimination functions as per [IEEE802.1CB] or the 1958 Packet Replication, Elimination, and Ordering Functions (PREOF) of 1959 IETF Deterministic Networking (DetNet) [RFC8655]. 1961 +........+ 1962 . Device . +------+ +------+ +------+ 1963 . . + gNB1 +--N3--+ UPF1 |--N6--+ | 1964 . ./+------+ +------+ | | 1965 . +----+ / | | 1966 . | |/. | | 1967 . | UE + . | DN | 1968 . | |\. | | 1969 . +----+ \ | | 1970 . .\+------+ +------+ | | 1971 +........+ + gNB2 +--N3--+ UPF2 |--N6--+ | 1972 +------+ +------+ +------+ 1974 Figure 12: Reliability with Single UE 1976 An alternative solution is that multiple UEs per device are used for 1977 user plane redundancy as illustrated in Figure 13. Each UE sets up a 1978 PDU session. The 5GS ensures that those PDU sessions of the 1979 different UEs are handled independently internal to the 5GS. There 1980 is no single point of failure in this solution, which also includes 1981 RHF outside of the 5G system, e.g., as per FRER or as PREOF 1982 specifications. 1984 +.........+ 1985 . Device . 1986 . . 1987 . +----+ . +------+ +------+ +------+ 1988 . | UE +-----+ gNB1 +--N3--+ UPF1 |--N6--+ | 1989 . +----+ . +------+ +------+ | | 1990 . . | DN | 1991 . +----+ . +------+ +------+ | | 1992 . | UE +-----+ gNB2 +--N3--+ UPF2 |--N6--+ | 1993 . +----+ . +------+ +------+ +------+ 1994 . . 1995 +.........+ 1997 Figure 13: Reliability with Dual UE 1999 Note that the abstraction provided by the RHF and the location of the 2000 RHF being outside of the 5G system make 5G equally supporting 2001 integration for reliability both with FRER of TSN and PREOF of DetNet 2002 as they both rely on the same concept. 2004 Note also that TSN is the primary subnetwork technology for DetNet. 2005 Thus, the DetNet over TSN work, e.g., [I-D.ietf-detnet-ip-over-tsn], 2006 can be leveraged via the TSN support built in 5G. 2008 6.5. Summary 2010 5G technology enables deterministic communication. Based on the 2011 centralized admission control and the scheduling of the wireless 2012 resources, licensed or unlicensed, quality of service such as latency 2013 and reliability can be guaranteed. 5G contains several features to 2014 achieve ultra-reliable and low latency performance, e.g., support for 2015 different OFDM numerologies and slot-durations, as well as fast 2016 processing capabilities and redundancy techniques that lead to 2017 achievable latency numbers of below 1ms with reliability guarantees 2018 up to 99.999%. 2020 5G also includes features to support Industrial IoT use cases, e.g., 2021 via the integration of 5G with TSN. This includes 5G capabilities 2022 for each TSN component, latency, resource management, time 2023 synchronization, and reliability. Furthermore, 5G support for TSN 2024 can be leveraged when 5G is used as subnet technology for DetNet, in 2025 combination with or instead of TSN, which is the primary subnet for 2026 DetNet. In addition, the support for integration with TSN 2027 reliability was added to 5G by making DetNet reliability also 2028 applicable, thus making 5G DetNet ready. Moreover, providing IP 2029 service is native to 5G. 2031 Overall, 5G provides scheduled wireless segments with high 2032 reliability and availability. In addition, 5G includes capabilities 2033 for integration to IP networks. 2035 7. L-band Digital Aeronautical Communications System 2037 One of the main pillars of the modern Air Traffic Management (ATM) 2038 system is the existence of a communication infrastructure that 2039 enables efficient aircraft guidance and safe separation in all phases 2040 of flight. Although current systems are technically mature, they are 2041 suffering from the VHF band's increasing saturation in high-density 2042 areas and the limitations posed by analogue radio. Therefore, 2043 aviation globally and the European Union (EU) in particular, strives 2044 for a sustainable modernization of the aeronautical communication 2045 infrastructure. 2047 In the long-term, ATM communication shall transition from analogue 2048 VHF voice and VDL2 communication to more spectrum efficient digital 2049 data communication. The European ATM Master Plan foresees this 2050 transition to be realized for terrestrial communications by the 2051 development and implementation of the L-band Digital Aeronautical 2052 Communications System (LDACS). LDACS shall enable IPv6 based air- 2053 ground communication related to the safety and regularity of the 2054 flight. The particular challenge is that no new frequencies can be 2055 made available for terrestrial aeronautical communication. It was 2056 thus necessary to develop procedures to enable the operation of LDACS 2057 in parallel with other services in the same frequency band. 2059 7.1. Provenance and Documents 2061 The development of LDACS has already made substantial progress in the 2062 Single European Sky ATM Research (SESAR) framework, and is currently 2063 being continued in the follow-up program, SESAR2020 [RIH18]. A key 2064 objective of the SESAR activities is to develop, implement and 2065 validate a modern aeronautical data link able to evolve with aviation 2066 needs over long-term. To this end, an LDACS specification has been 2067 produced [GRA19] and is continuously updated; transmitter 2068 demonstrators were developed to test the spectrum compatibility of 2069 LDACS with legacy systems operating in the L-band [SAJ14]; and the 2070 overall system performance was analyzed by computer simulations, 2071 indicating that LDACS can fulfill the identified requirements 2072 [GRA11]. 2074 LDACS standardization within the framework of the International Civil 2075 Aviation Organization (ICAO) started in December 2016. The ICAO 2076 standardization group has produced an initial Standards and 2077 Recommended Practices (SARPs) document [ICAO18]. The SARPs document 2078 defines the general characteristics of LDACS. The ICAO 2079 standardization group plans to produce an ICAO technical manual - the 2080 ICAO equivalent to a technical standard - within the next years. 2081 Generally, the group is open to input from all sources and develops 2082 LDACS in the open. 2084 Up to now the LDACS standardization has been focused on the 2085 development of the physical layer and the data link layer, only 2086 recently have higher layers come into the focus of the LDACS 2087 development activities. There is currently no "IPv6 over LDACS" 2088 specification; however, SESAR2020 has started the testing of 2089 IPv6-based LDACS testbeds. The IPv6 architecture for the 2090 aeronautical telecommunication network is called the Future 2091 Communications Infrastructure (FCI). FCI shall support quality of 2092 service, diversity, and mobility under the umbrella of the "multi- 2093 link concept". This work is conducted by ICAO working group WG-I. 2095 In addition to standardization activities several industrial LDACS 2096 prototypes have been built. One set of LDACS prototypes has been 2097 evaluated in flight trials confirming the theoretical results 2098 predicting the system performance [GRA18][SCH19]. 2100 7.2. General Characteristics 2102 LDACS will become one of several wireless access networks connecting 2103 aircraft to the Aeronautical Telecommunications Network (ATN). The 2104 LDACS access network contains several ground stations, each of them 2105 providing one LDACS radio cell. The LDACS air interface is a 2106 cellular data link with a star-topology connecting aircraft to 2107 ground-stations with a full duplex radio link. Each ground-station 2108 is the centralized instance controlling all air-ground communications 2109 within its radio cell. 2111 The user data rate of LDACS is 315 kbit/s to 1428 kbit/s on the 2112 forward link, and 294 kbit/s to 1390 kbit/s on the reverse link, 2113 depending on coding and modulation. Due to strong interference from 2114 legacy systems in the L-band, the most robust coding and modulation 2115 SHOULD be expected for initial deployment i.e. 315/294 kbit/s on the 2116 forward/reverse link, respectively. 2118 In addition to the communications capability, LDACS also offers a 2119 navigation capability. Ranging data, similar to DME (Distance 2120 Measuring Equipment), is extracted from the LDACS communication links 2121 between aircraft and LDACS ground stations. This results in LDACS 2122 providing an APNT (Alternative Position, Navigation and Timing) 2123 capability to supplement the existing on-board GNSS (Global 2124 Navigation Satellite System) without the need for additional 2125 bandwidth. Operationally, there will be no difference for pilots 2126 whether the navigation data are provided by LDACS or DME. This 2127 capability was flight tested and proven during the MICONAV flight 2128 trials in 2019 [BAT19]. 2130 In previous works and during the MICONAV flight campaign in 2019, it 2131 was also shown, that LDACS can be used for surveillance capability. 2132 Filip et al. [FIL19] shown passive radar capabilities of LDACS and 2133 Automatic Dependence Surveillance - Contract (ADS-C) was demonstrated 2134 via LDACS during the flight campaign 2019 [SCH19]. 2136 Since LDACS has been mainly designed for air traffic management 2137 communication it supports mutual entity authentication, integrity and 2138 confidentiality capabilities of user data messages and some control 2139 channel protection capabilities [MAE18], [MAE191], [MAE192], [MAE20]. 2141 Overall this makes LDACS the world's first truly integrated CNS 2142 system and is the worldwide most mature, secure, terrestrial long- 2143 range CNS technology for civil aviation. 2145 7.3. Deployment and Spectrum 2147 LDACS has its origin in merging parts of the B-VHF [BRA06], B-AMC 2148 [SCH08], TIA-902 (P34) [HAI09], and WiMAX IEEE 802.16e technologies 2149 [EHA11]. In 2007 the spectrum for LDACS was allocated at the World 2150 Radio Conference (WRC). 2152 It was decided to allocate the spectrum next to Distance Measuring 2153 Equipment (DME), resulting in an in-lay approach between the DME 2154 channels for LDAC [SCH14]. 2156 LDACS is currently being standardized by ICAO and several roll-out 2157 strategies are discussed: 2159 The LDACS data link provides enhanced capabilities to existing 2160 Aeronautical communications infrastructure enabling them to better 2161 support user needs and new applications. The deployment scalability 2162 of LDACS allows its implementation to start in areas where most 2163 needed to Improve immediately the performance of already fielded 2164 infrastructure. Later the deployment is extended based on 2165 operational demand. An attractive scenario for upgrading the 2166 existing VHF communication systems by adding an additional LDACS data 2167 link is described below. 2169 When considering the current VDL Mode 2 infrastructure and user base, 2170 a very attractive win-win situation comes about, when the 2171 technological advantages of LDACS are combined with the existing VDL 2172 mode 2 infrastructure. LDACS provides at least 50 time more capacity 2173 than VDL Mode 2 and is a natural enhancement to the existing VDL Mode 2174 2 business model. The advantage of this approach is that the VDL 2175 Mode 2 infrastructure can be fully reused. Beyond that, it opens the 2176 way for further enhancements which can increase business efficiency 2177 and minimize investment risk. [ICAO19] 2179 7.4. Applicability to Deterministic Flows 2181 As LDACS is a ground-based digital communications system for flight 2182 guidance and communications related to safety and regularity of 2183 flight, time-bounded deterministic arrival times for safety critical 2184 messages are a key feature for its successful deployment and roll- 2185 out. 2187 7.4.1. System Architecture 2189 Up to 512 Aircraft Station (AS) communicate to an LDACS Ground 2190 Station (GS) in the Reverse Link (RL). GS communicate to AS in the 2191 Forward Link (FL). Via an Access-Router (AC-R) GSs connect the LDACS 2192 sub-network to the global Aeronautical Telecommunications Network 2193 (ATN) to which the corresponding Air Traffic Services (ATS) and 2194 Aeronautical Operational Control (AOC) end systems are attached. 2196 7.4.2. Overview of The Radio Protocol Stack 2198 The protocol stack of LDACS is implemented in the AS and GS: It 2199 consists of the Physical Layer (PHY) with five major functional 2200 blocks above it. Four are placed in the Data Link Layer (DLL) of the 2201 AS and GS: (1) Medium Access Layer (MAC), (2) Voice Interface (VI), 2202 (3) Data Link Service (DLS), and (4) LDACS Management Entity (LME). 2203 The last entity resides within the Sub-Network Layer: Sub-Network 2204 Protocol (SNP). The LDACS network is externally connected to voice 2205 units, radio control units, and the ATN Network Layer. 2207 Figure 14 shows the protocol stack of LDACS as implemented in the AS 2208 and GS. 2210 IPv6 Network Layer 2211 | 2212 | 2213 +------------------+ +----+ 2214 | SNP |--| | Sub-Network 2215 | | | | Layer 2216 +------------------+ | | 2217 | | LME| 2218 +------------------+ | | 2219 | DLS | | | Logical Link 2220 | | | | Control Layer 2221 +------------------+ +----+ 2222 | | 2223 DCH DCCH/CCCH 2224 | RACH/BCCH 2225 | | 2226 +--------------------------+ 2227 | MAC | Medium Access 2228 | | Layer 2229 +--------------------------+ 2230 | 2231 +--------------------------+ 2232 | PHY | Physical Layer 2233 +--------------------------+ 2234 | 2235 | 2236 ((*)) 2237 FL/RL radio channels 2238 separated by 2239 Frequency Division Duplex 2241 Figure 14: LDACS protocol stack in AS and GS 2243 7.4.3. Radio (PHY) 2245 The physical layer provides the means to transfer data over the radio 2246 channel. The LDACS ground-station supports bi-directional links to 2247 multiple aircraft under its control. The forward link direction (FL; 2248 ground-to-air) and the reverse link direction (RL; air-to-ground) are 2249 separated by frequency division duplex. Forward link and reverse 2250 link use a 500 kHz channel each. The ground-station transmits a 2251 continuous stream of OFDM symbols on the forward link. In the 2252 reverse link different aircraft are separated in time and frequency 2253 using a combination of Orthogonal Frequency-Division Multiple-Access 2254 (OFDMA) and Time-Division Multiple-Access (TDMA). Aircraft thus 2255 transmit discontinuously on the reverse link with radio bursts sent 2256 in precisely defined transmission opportunities allocated by the 2257 ground-station. The most important service on the PHY layer of LDACS 2258 is the PHY time framing service, which indicates that the PHY layer 2259 is ready to transmit in a given slot and to indicate PHY layer 2260 framing and timing to the MAC time framing service. LDACS does not 2261 support beam-forming or Multiple Input Multiple Output (MIMO). 2263 7.4.4. Scheduling, Frame Structure and QoS (MAC) 2265 The data-link layer provides the necessary protocols to facilitate 2266 concurrent and reliable data transfer for multiple users. The LDACS 2267 data link layer is organized in two sub-layers: The medium access 2268 sub-layer and the logical link control sub-layer. The medium access 2269 sub-layer manages the organization of transmission opportunities in 2270 slots of time and frequency. The logical link control sub-layer 2271 provides acknowledged point-to-point logical channels between the 2272 aircraft and the ground-station using an automatic repeat request 2273 protocol. LDACS supports also unacknowledged point-to-point channels 2274 and ground-to-air broadcast. Before going more into depth about the 2275 LDACS medium access, the frame structure of LDACS is introduced: 2277 The LDACS framing structure for FL and RL is based on Super-Frames 2278 (SF) of 240 ms duration. Each SF corresponds to 2000 OFDM symbols. 2279 The FL and RL SF boundaries are aligned in time (from the view of the 2280 GS). 2282 In the FL, an SF contains a Broadcast Frame of duration 6.72 ms (56 2283 OFDM symbols) for the Broadcast Control Channel (BCCH), and four 2284 Multi-Frames (MF), each of duration 58.32 ms (486 OFDM symbols). 2286 In the RL, each SF starts with a Random Access (RA) slot of length 2287 6.72 ms with two opportunities for sending RL random access frames 2288 for the Random Access Channel (RACH), followed by four MFs. These 2289 MFs have the same fixed duration of 58.32 ms as in the FL, but a 2290 different internal structure 2292 Figure 15 and Figure 16 illustrate the LDACS frame structure. 2294 ^ 2295 | +------+------------+------------+------------+------------+ 2296 | FL | BCCH | MF | MF | MF | MF | 2297 F +------+------------+------------+------------+------------+ 2298 r <---------------- Super-Frame (SF) - 240ms ----------------> 2299 e 2300 q +------+------------+------------+------------+------------+ 2301 u RL | RACH | MF | MF | MF | MF | 2302 e +------+------------+------------+------------+------------+ 2303 n <---------------- Super-Frame (SF) - 240ms ----------------> 2304 c 2305 y 2306 | 2307 ----------------------------- Time ------------------------------> 2308 | 2310 Figure 15: SF structure for LDACS 2312 ^ 2313 | +-------------+------+-------------+ 2314 | FL | DCH | CCCH | DCH | 2315 F +-------------+------+-------------+ 2316 r <---- Multi-Frame (MF) - 58.32ms --> 2317 e 2318 q +------+---------------------------+ 2319 u RL | DCCH | DCH | 2320 e +------+---------------------------+ 2321 n <---- Multi-Frame (MF) - 58.32ms --> 2322 c 2323 y 2324 | 2325 -------------------- Time ------------------> 2326 | 2328 Figure 16: MF structure for LDACS 2330 This fixed frame structure allows for a reliable and dependable 2331 transmission of data. Next, the LDACS medium access layer is 2332 introduced: 2334 LDACS medium access is always under the control of the ground-station 2335 of a radio cell. Any medium access for the transmission of user data 2336 has to be requested with a resource request message stating the 2337 requested amount of resources and class of service. The ground- 2338 station performs resource scheduling on the basis of these requests 2339 and grants resources with resource allocation messages. Resource 2340 request and allocation messages are exchanged over dedicated 2341 contention-free control channels. 2343 LDACS has two mechanisms to request resources from the scheduler in 2344 the ground-station. Resources can either be requested "on demand" 2345 with a given class of service. On the forward link, this is done 2346 locally in the ground-station, on the reverse link a dedicated 2347 contention-free control channel is used (Dedicated Control Channel 2348 (DCCH); roughly 83 bit every 60 ms). A resource allocation is always 2349 announced in the control channel of the forward link (Common Control 2350 Channel (CCCH); variable sized). Due to the spacing of the reverse 2351 link control channels of every 60 ms, a medium access delay in the 2352 same order of magnitude is to be expected. 2354 Resources can also be requested "permanently". The permanent 2355 resource request mechanism supports requesting recurring resources in 2356 given time intervals. A permanent resource request has to be 2357 canceled by the user (or by the ground-station, which is always in 2358 control). User data transmissions over LDACS are therefore always 2359 scheduled by the ground-station, while control data uses statically 2360 (i.e. at net entry) allocated recurring resources (DCCH and CCCH). 2361 The current specification documents specify no scheduling algorithm. 2362 However performance evaluations so far have used strict priority 2363 scheduling and round robin for equal priorities for simplicity. In 2364 the current prototype implementations LDACS classes of service are 2365 thus realized as priorities of medium access and not as flows. Note 2366 that this can starve out low priority flows. However, this is not 2367 seen as a big problem since safety related message always go first in 2368 any case. Scheduling of reverse link resources is done in physical 2369 Protocol Data Units (PDU) of 112 bit (or larger if more aggressive 2370 coding and modulation is used). Scheduling on the forward link is 2371 done Byte-wise since the forward link is transmitted continuously by 2372 the ground-station. 2374 In order to support diversity, LDACS supports handovers to other 2375 ground-stations on different channels. Handovers may be initiated by 2376 the aircraft (break-before-make) or by the ground-station (make- 2377 before-break). Beyond this, FCI diversity shall be implemented by 2378 the multi-link concept. 2380 7.5. Summary 2382 LDACS has been designed with applications related to the safety and 2383 regularity of the flight in mind. It has therefore been designed as 2384 a deterministic wireless data link (as far as possible). 2386 It is a secure, scalable and spectrum efficient data link with 2387 embedded navigation capability and thus, is the first truly 2388 integrated CNS system recognized by ICAO. During flight tests the 2389 LDACS capabilities have been successfully demonstrated. A viable 2390 roll-out scenario has been developed which allows gradual 2391 introduction of LDACS with immediate use and revenues. Finally, ICAO 2392 is developing LDACS standards to pave the way for a successful roll- 2393 out in the near future. 2395 8. IANA Considerations 2397 This specification does not require IANA action. 2399 9. Security Considerations 2401 Most RAW technologies integrate some authentication or encryption 2402 mechanisms that were defined outside the IETF. 2404 10. Contributors 2406 Georgios Z. Papadopoulos: Contributed to the TSCH section. 2408 Nils Mäurer: Contributed to the LDACS section. 2410 Thomas Gräupl: Contributed to the LDACS section. 2412 Janos Farkas, Torsten Dudda, Alexey Shapin, and Sara Sandberg: Contr 2413 ibuted to the 5G section. 2415 11. Acknowledgments 2417 Many thanks to the participants of the RAW WG where a lot of the work 2418 discussed here happened. 2420 12. Normative References 2422 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 2423 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 2424 DOI 10.17487/RFC8480, November 2018, 2425 . 2427 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2428 (IPv6) Specification", STD 86, RFC 8200, 2429 DOI 10.17487/RFC8200, July 2017, 2430 . 2432 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 2433 Phinney, "Industrial Routing Requirements in Low-Power and 2434 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 2435 2009, . 2437 [I-D.ietf-detnet-architecture] 2438 Finn, N., Thubert, P., Varga, B., and J. Farkas, 2439 "Deterministic Networking Architecture", Work in Progress, 2440 Internet-Draft, draft-ietf-detnet-architecture-13, 6 May 2441 2019, . 2444 [I-D.ietf-6tisch-architecture] 2445 Thubert, P., "An Architecture for IPv6 over the TSCH mode 2446 of IEEE 802.15.4", Work in Progress, Internet-Draft, 2447 draft-ietf-6tisch-architecture-30, 26 November 2020, 2448 . 2451 13. Informative References 2453 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 2454 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 2455 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 2456 Low-Power and Lossy Networks", RFC 6550, 2457 DOI 10.17487/RFC6550, March 2012, 2458 . 2460 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 2461 and D. Barthel, "Routing Metrics Used for Path Calculation 2462 in Low-Power and Lossy Networks", RFC 6551, 2463 DOI 10.17487/RFC6551, March 2012, 2464 . 2466 [RFC6291] Andersson, L., van Helvoort, H., Bonica, R., Romascanu, 2467 D., and S. Mansfield, "Guidelines for the Use of the "OAM" 2468 Acronym in the IETF", BCP 161, RFC 6291, 2469 DOI 10.17487/RFC6291, June 2011, 2470 . 2472 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 2473 Weingarten, "An Overview of Operations, Administration, 2474 and Maintenance (OAM) Tools", RFC 7276, 2475 DOI 10.17487/RFC7276, June 2014, 2476 . 2478 [RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A., 2479 Przygienda, T., and S. Aldrin, "Multicast Using Bit Index 2480 Explicit Replication (BIER)", RFC 8279, 2481 DOI 10.17487/RFC8279, November 2017, 2482 . 2484 [I-D.ietf-6tisch-msf] 2485 Chang, T., Vucinic, M., Vilajosana, X., Duquennoy, S., and 2486 D. Dujovne, "6TiSCH Minimal Scheduling Function (MSF)", 2487 Work in Progress, Internet-Draft, draft-ietf-6tisch-msf- 2488 18, 12 September 2020, 2489 . 2491 [I-D.pthubert-raw-architecture] 2492 Thubert, P., Papadopoulos, G., and R. Buddenberg, 2493 "Reliable and Available Wireless Architecture/Framework", 2494 Work in Progress, Internet-Draft, draft-pthubert-raw- 2495 architecture-05, 15 November 2020, 2496 . 2499 [I-D.ietf-roll-nsa-extension] 2500 Koutsiamanis, R., Papadopoulos, G., Montavont, N., and P. 2501 Thubert, "Common Ancestor Objective Function and Parent 2502 Set DAG Metric Container Extension", Work in Progress, 2503 Internet-Draft, draft-ietf-roll-nsa-extension-10, 29 2504 October 2020, . 2507 [I-D.papadopoulos-paw-pre-reqs] 2508 Papadopoulos, G., Koutsiamanis, R., Montavont, N., and P. 2509 Thubert, "Exploiting Packet Replication and Elimination in 2510 Complex Tracks in LLNs", Work in Progress, Internet-Draft, 2511 draft-papadopoulos-paw-pre-reqs-01, 25 March 2019, 2512 . 2515 [I-D.thubert-bier-replication-elimination] 2516 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 2517 TE extensions for Packet Replication and Elimination 2518 Function (PREF) and OAM", Work in Progress, Internet- 2519 Draft, draft-thubert-bier-replication-elimination-03, 3 2520 March 2018, . 2523 [I-D.thubert-6lo-bier-dispatch] 2524 Thubert, P., Brodard, Z., Jiang, H., and G. Texier, "A 2525 6loRH for BitStrings", Work in Progress, Internet-Draft, 2526 draft-thubert-6lo-bier-dispatch-06, 28 January 2019, 2527 . 2530 [I-D.ietf-bier-te-arch] 2531 Eckert, T., Cauchie, G., and M. Menth, "Tree Engineering 2532 for Bit Index Explicit Replication (BIER-TE)", Work in 2533 Progress, Internet-Draft, draft-ietf-bier-te-arch-09, 30 2534 October 2020, 2535 . 2537 [I-D.ietf-6tisch-coap] 2538 Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and 2539 Interaction using CoAP", Work in Progress, Internet-Draft, 2540 draft-ietf-6tisch-coap-03, 9 March 2015, 2541 . 2543 [I-D.svshah-tsvwg-deterministic-forwarding] 2544 Shah, S. and P. Thubert, "Deterministic Forwarding PHB", 2545 Work in Progress, Internet-Draft, draft-svshah-tsvwg- 2546 deterministic-forwarding-04, 30 August 2015, 2547 . 2550 [IEEE Std. 802.15.4] 2551 IEEE standard for Information Technology, "IEEE Std. 2552 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 2553 and Physical Layer (PHY) Specifications for Low-Rate 2554 Wireless Personal Area Networks". 2556 [IEEE Std. 802.11] 2557 "IEEE Standard 802.11 - IEEE Standard for Information 2558 Technology - Telecommunications and information exchange 2559 between systems Local and metropolitan area networks - 2560 Specific requirements - Part 11: Wireless LAN Medium 2561 Access Control (MAC) and Physical Layer (PHY) 2562 Specifications.". 2564 [IEEE Std. 802.11ak] 2565 "802.11ak: Enhancements for Transit Links Within Bridged 2566 Networks", 2017. 2568 [IEEE Std. 802.11ax] 2569 "802.11ax D4.0: Enhancements for High Efficiency WLAN". 2571 [IEEE Std. 802.11ay] 2572 "802.11ay: Enhanced throughput for operation in license- 2573 exempt bands above 45 GHz". 2575 [IEEE Std. 802.11ad] 2576 "802.11ad: Enhancements for very high throughput in the 60 2577 GHz band". 2579 [IEEE 802.11be WIP] 2580 "802.11be: Extreme High Throughput". 2582 [IEEE Std. 802.1Qat] 2583 "802.1Qat: Stream Reservation Protocol". 2585 [IEEE8021Qcc] 2586 "802.1Qcc: IEEE Standard for Local and Metropolitan Area 2587 Networks--Bridges and Bridged Networks -- Amendment 31: 2588 Stream Reservation Protocol (SRP) Enhancements and 2589 Performance Improvements". 2591 [Cavalcanti_2019] 2592 Dave Cavalcanti et al., "Extending Time Distribution and 2593 Timeliness Capabilities over the Air to Enable Future 2594 Wireless Industrial Automation Systems, the Proceedings of 2595 IEEE", June 2019. 2597 [Nitsche_2015] 2598 Thomas Nitsche et al., "IEEE 802.11ad: directional 60 GHz 2599 communication for multi-Gigabit-per-second Wi-Fi", 2600 December 2014. 2602 [Ghasempour_2017] 2603 Yasaman Ghasempour et al., "802.11ay: Next-Generation 60 2604 GHz Communications for 100 Gb/s Wi-Fi", December 2017. 2606 [IEEE_doc_11-18-2009-06] 2607 "802.11 Real-Time Applications (RTA) Topic Interest Group 2608 (TIG) Report", November 2018. 2610 [IEEE_doc_11-19-0373-00] 2611 Kevin Stanton et Al., "Time-Sensitive Applications Support 2612 in EHT", March 2019. 2614 [morell13] Antoni Morell et al., "Label switching over IEEE802.15.4e 2615 networks", April 2013. 2617 [dearmas16] 2618 Jesica de Armas et al., "Determinism through path 2619 diversity: Why packet replication makes sense", September 2620 2016. 2622 [vilajosana19] 2623 Xavier Vilajosana et al., "6TiSCH: Industrial Performance 2624 for IPv6 Internet-of-Things Networks", June 2019. 2626 [ISA100.11a] 2627 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 2628 also IEC 62734", 2011, . 2632 [WirelessHART] 2633 www.hartcomm.org, "Industrial Communication Networks - 2634 Wireless Communication Network and Communication Profiles 2635 - WirelessHART - IEC 62591", 2010. 2637 [PCE] IETF, "Path Computation Element", 2638 . 2640 [CCAMP] IETF, "Common Control and Measurement Plane", 2641 . 2643 [TiSCH] IETF, "IPv6 over the TSCH mode over 802.15.4", 2644 . 2646 [RIH18] Rihacek, C., Haindl, B., Fantappie, P., Pierattelli, S., 2647 Gräupl, T., Schnell, M., and N. Fistas, "L-band Digital 2648 Aeronautical Communications System (LDACS) Activities in 2649 SESAR2020", Proceedings of the Integrated Communications 2650 Navigation and Surveillance Conference (ICNS) Herndon, VA, 2651 USA, April 2018. 2653 [GRA19] Gräupl, T., Rihacek, C., and B. Haindl, "LDACS A/G 2654 Specification", SESAR2020 PJ14-02-01 D3.3.010, February 2655 2019. 2657 [SAJ14] Sajatovic, M., Günzel, H., and S. Müller, "WA04 D22 Test 2658 Report for Assessing LDACS1 Transmitter Impact upon DME/ 2659 TACAN Receivers", April 2014. 2661 [GRA11] Gräupl, T. and M. Ehammer, "L-DACS1 Data Link Layer 2662 Evolution of ATN/IPS", Proceedings of the 30th IEEE/AIAA 2663 Digital Avionics Systems Conference (DASC) Seattle, WA, 2664 USA, October 2011. 2666 [ICAO18] International Civil Aviation Organization (ICAO), "L-Band 2667 Digital Aeronautical Communication System (LDACS)", 2668 International Standards and Recommended Practices Annex 10 2669 - Aeronautical Telecommunications, Vol. III - 2670 Communication Systems, July 2018. 2672 [GRA18] al., T. G. E., "L-band Digital Aeronautical Communications 2673 System (LDACS) flight trials in the national German 2674 project MICONAV", Proceedings of the Integrated 2675 Communications, Navigation, Surveillance Conference 2676 (ICNS) Herndon, VA, USA, April 2018. 2678 [SCH19] Schnell, M., "DLR tests digital communications 2679 technologies combined with additional navigation functions 2680 for the first time", 3 March 2019, 2681 . 2684 [TR37910] "3GPP TR 37.910, Study on self evaluation towards IMT-2020 2685 submission", 2686 . 2689 [TR38824] "3GPP TR 38.824, Study on physical layer enhancements for 2690 NR ultra-reliable and low latency case (URLLC)", 2691 . 2694 [TR38825] "3GPP TR 38.825, Study on NR industrial Internet of Things 2695 (IoT)", 2696 . 2699 [TS22104] "3GPP TS 22.104, Service requirements for cyber-physical 2700 control applications in vertical domains", 2701 . 2704 [TR22804] "3GPP TR 22.804, Study on Communication for Automation in 2705 Vertical domains (CAV)", 2706 . 2709 [TS23501] "3GPP TS 23.501, System architecture for the 5G System 2710 (5GS)", 2711 . 2714 [TS38300] "3GPP TS 38.300, NR Overall description", 2715 . 2718 [IMT2020] "ITU towards IMT for 2020 and beyond", 2719 . 2722 [RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas, 2723 "Deterministic Networking Architecture", RFC 8655, 2724 DOI 10.17487/RFC8655, October 2019, 2725 . 2727 [I-D.ietf-detnet-ip-over-tsn] 2728 Varga, B., Farkas, J., Malis, A., and S. Bryant, "DetNet 2729 Data Plane: IP over IEEE 802.1 Time Sensitive Networking 2730 (TSN)", Work in Progress, Internet-Draft, draft-ietf- 2731 detnet-ip-over-tsn-05, 13 December 2020, 2732 . 2735 [IEEE802.1TSN] 2736 IEEE 802.1, "Time-Sensitive Networking (TSN) Task Group", 2737 . 2739 [IEEE802.1AS] 2740 IEEE, "IEEE Standard for Local and metropolitan area 2741 networks -- Timing and Synchronization for Time-Sensitive 2742 Applications", IEEE 802.1AS-2020, 2743 . 2746 [IEEE802.1CB] 2747 IEEE, "IEEE Standard for Local and metropolitan area 2748 networks -- Frame Replication and Elimination for 2749 Reliability", DOI 10.1109/IEEESTD.2017.8091139, IEEE 2750 802.1CB-2017, 2751 . 2753 [IEEE802.1Qbv] 2754 IEEE, "IEEE Standard for Local and metropolitan area 2755 networks -- Bridges and Bridged Networks -- Amendment 25: 2756 Enhancements for Scheduled Traffic", IEEE 802.1Qbv-2015, 2757 . 2759 [IEEE802.1Qcc] 2760 IEEE, "IEEE Standard for Local and metropolitan area 2761 networks -- Bridges and Bridged Networks -- Amendment 31: 2763 Stream Reservation Protocol (SRP) Enhancements and 2764 Performance Improvements", IEEE 802.1Qcc-2018, 2765 . 2767 [IEEE802.3] 2768 IEEE, "IEEE Standard for Ethernet", IEEE 802.3-2018, 2769 . 2771 [ETR5GTSN] Farkas, J., Varga, B., Miklos, G., and J. Sachs, "5G-TSN 2772 integration meets networking requirements for industrial 2773 automation", Ericsson Technology Review, Volume 9, No 7, 2774 August 2019, . 2778 [MAE18] Maeurer, N. and A. Bilzhause, "A Cybersecurity 2779 Architecture for the L-band Digital Aeronautical 2780 Communications System (LDACS)", IEEE 37th Digital Avionics 2781 Systems Conference (DASC), pp. 1-10, London, UK , 2017. 2783 [MAE191] Maeurer, N. and C. Schmitt, "Towards Successful 2784 Realization of the LDACS Cybersecurity Architecture: An 2785 Updated Datalink Security Threat- and Risk Analysis", IEEE 2786 Integrated Communications, Navigation and Surveillance 2787 Conference (ICNS), pp. 1-13, Herndon, VA, USA , 2019. 2789 [ICAO19] International Civil Aviation Organization (ICAO), "TLDACS 2790 White Paper–A Roll-out Scenario", Working Paper 2791 COMMUNICATIONS PANEL-DATA COMMUNICATIONS INFRASTRUCTURE 2792 WORKING GROUP, Montreal, Canada , October 2019. 2794 [MAE192] Maeurer, N., Graeupl, T., and C. Schmitt, "Evaluation of 2795 the LDACS Cybersecurity Implementation", IEEE 38th Digital 2796 Avionics Systems Conference (DACS), pp. 1-10, San Diego, 2797 CA, USA , September 2019. 2799 [MAE20] Maeurer, N., Graeupl, T., and C. Schmitt, "Comparing 2800 Different Diffie-Hellman Key Exchange Flavors for LDACS", 2801 IEEE 39th Digital Avionics Systems Conference (DACS), pp. 2802 1-10, San Diego, CA, USA , October 2019. 2804 [FIL19] Filip-Dhaubhadel, A. and D. Shutin, "LDACS- Based Non- 2805 Cooperative Surveillance Multistatic Radar Design and 2806 Detection Coverage Assessment", IEEE 38th Digital Avionics 2807 Systems Conference (DACS), pp. 1-10, San Diego, CA, USA , 2808 September 2019. 2810 [BAT19] Battista, G., Osechas, O., Narayanan, S., Crespillo, O.G., 2811 Gerbeth, D., Maeurer, N., Mielke, D., and T. Graeupl, 2812 "Real-Time Demonstration of Integrated Communication and 2813 Navigation Services Using LDACS", IEEE Integrated 2814 Communications, Navigation and Surveillance Conference 2815 (ICNS), pp. 1-12, Herndon, VA, USA , 2019. 2817 [BRA06] Brandes, S., Schnell, M., Rokitansky, C.H., Ehammer, M., 2818 Graeupl, T., Steendam, H., Guenach, M., Rihacek, C., and 2819 B. Haindl, "B-VHF -Selected Simulation Results and Final 2820 Assessment", IEEE 25th Digital Avionics Systems Conference 2821 (DACS), pp. 1-12, New York, NY, USA , September 2019. 2823 [SCH08] Schnell, M., Brandes, S., Gligorevic, S., Rokitansky, 2824 C.H., Ehammer, M., Graeupl, T., Rihacek, C., and M. 2825 Sajatovic, "B-AMC - Broadband Aeronautical Multi-carrier 2826 Communications", IEEE 8th Integrated Communications, 2827 Navigation and Surveillance Conference (ICNS), pp. 1-13, 2828 New York, NY, USA , April 2008. 2830 [HAI09] Haindl, B., Rihacek, C., Sajatovic, M., Phillips, B., 2831 Budinger, J., Schnell, M., Kamiano, D., and W. Wilson, 2832 "Improvement of L-DACS1 Design by Combining B-AMC with P34 2833 and WiMAX Technologies", IEEE 9th Integrated 2834 Communications, Navigation and Surveillance Conference 2835 (ICNS), pp. 1-8, New York, NY, USA , May 2009. 2837 [EHA11] Ehammer, M. and T. Graeupl, "AeroMACS - An Airport 2838 Communications System", IEEE 30th Digital Avionics Systems 2839 Conference (DACS), pp. 1-16, New York, NY, USA , September 2840 2011. 2842 [SCH14] Schnell, M., Epple, U., Shutin, D., and N. 2843 Schneckenburger, "LDACS: Future Aeronautical 2844 Communications for Air- Traffic Management", IEEE 2845 Communications Magazine, 52(5), 104-110 , 2017. 2847 Authors' Addresses 2849 Pascal Thubert (editor) 2850 Cisco Systems, Inc 2851 Building D 2852 45 Allee des Ormes - BP1200 2853 06254 MOUGINS - Sophia Antipolis 2854 France 2856 Phone: +33 497 23 26 34 2857 Email: pthubert@cisco.com 2858 Dave Cavalcanti 2859 Intel Corporation 2860 2111 NE 25th Ave 2861 Hillsboro, OR, 97124 2862 United States of America 2864 Phone: 503 712 5566 2865 Email: dave.cavalcanti@intel.com 2867 Xavier Vilajosana 2868 Universitat Oberta de Catalunya 2869 156 Rambla Poblenou 2870 08018 Barcelona Catalonia 2871 Spain 2873 Email: xvilajosana@uoc.edu 2875 Corinna Schmitt 2876 Research Institute CODE, UniBwM 2877 Werner-Heisenberg-Weg 39 2878 85577 Neubiberg 2879 Germany 2881 Email: corinna.schmitt@unibw.de 2883 Janos Farkas 2884 Ericsson 2885 Budapest 2886 Magyar tudosok korutja 11 2887 1117 2888 Hungary 2890 Email: janos.farkas@ericsson.com