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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (10 December 2021) is 155 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Reliable and Available Wireless Working Group R.C. Sofia 3 Internet-Draft fortiss GmbH 4 Intended status: Informational M. Kovatsch 5 Expires: 13 June 2022 Huawei Technologies 6 P. Mendes 7 Airbus 8 10 December 2021 10 Requirements for Reliable Wireless Industrial Services 11 draft-ietf-raw-industrial-requirements-00 13 Abstract 15 This document provides an overview on communication requirements for 16 handling reliable wireless services within the context of industrial 17 environments. The goal of the draft is to bring awareness to 18 communication requirements of current and future wireless industrial 19 services; how can they co-exist with wired infrastructures; key 20 drivers for reliable wireless integration; relevant communication 21 requirements to take into consideration; current and future 22 challenges derived from the use of wireless. 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 13 June 2022. 41 Copyright Notice 43 Copyright (c) 2021 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 48 license-info) in effect on the date of publication of this document. 49 Please review these documents carefully, as they describe your rights 50 and restrictions with respect to this document. Code Components 51 extracted from this document must include Revised BSD License text as 52 described in Section 4.e of the Trust Legal Provisions and are 53 provided without warranty as described in the Revised BSD License. 55 Table of Contents 57 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 58 2. Conventions used in this document . . . . . . . . . . . . . . 3 59 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 4. Wireless Industrial Services Today . . . . . . . . . . . . . 4 61 4.1. Equipment and Process Control Services . . . . . . . . . 6 62 4.2. Quality Supervision Services . . . . . . . . . . . . . . 9 63 4.3. Factory Resource Management Services . . . . . . . . . . 10 64 4.4. Display Services . . . . . . . . . . . . . . . . . . . . 11 65 4.5. Human Safety Services . . . . . . . . . . . . . . . . . . 12 66 4.6. Mobile Robotics Services . . . . . . . . . . . . . . . . 12 67 4.7. Power Grid Control . . . . . . . . . . . . . . . . . . . 13 68 4.8. Wireless Avionics Intra-communication . . . . . . . . . . 14 69 5. Additional Reliable Wireless Industrial Services . . . . . . 15 70 5.1. AR/VR Services within Flexible Factories . . . . . . . . 15 71 5.1.1. Description . . . . . . . . . . . . . . . . . . . . . 15 72 5.1.2. Wireless Integration Recommendations . . . . . . . . 16 73 5.1.3. Requirements Considerations . . . . . . . . . . . . . 16 74 5.2. Decentralized Shop-floor Communication Services . . . . . 17 75 5.2.1. Description . . . . . . . . . . . . . . . . . . . . . 17 76 5.2.2. Wireless Integration Recommendations . . . . . . . . 18 77 5.2.3. Requirements Considerations . . . . . . . . . . . . . 18 78 5.3. Autonomous Airborne Services . . . . . . . . . . . . . . 19 79 5.3.1. Wireless Integration Recommendations . . . . . . . . 19 80 5.3.2. Requirements Considerations . . . . . . . . . . . . . 20 81 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 82 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 83 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 84 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 85 9.1. Normative References . . . . . . . . . . . . . . . . . . 21 86 9.2. Informative References . . . . . . . . . . . . . . . . . 21 87 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 89 1. Introduction 91 Within industrial environments, short-range wireless standards, such 92 as IEEE 802.11ax, are gaining prominence as there exists an 93 increasing need for flexibility in terms of infrastructure layout, of 94 processes support. Wireless, and specifically Wireless Fidelity (Wi- 95 Fi), is now reaching a maturity point where the available 96 transmission rates become highly competitive in comparison to wired 97 environments, thus increasing flexibility, providing a lower cost and 98 higher availability in scenarios requiring, for instance, mobility 99 support. There are, nonetheless, barriers to the integration of 100 wireless in industrial environments. Firstly, being wireless a 101 shared medium, it experiences challenges such as interference and 102 signal strength variability depending on its surroundings. These 103 features raise issues concerning critical services availability, 104 resilience, and security support. Secondly, wireless relies on 105 probabilistic Quality of Service (QoS) and therefore requires tuning 106 to be able to support time-sensitive traffic with bounded latency, 107 low jitter, zero congestion loss. However, the recent advancements 108 of OFDMA-based wireless in the context of IEEE 802.11 standards such 109 as 802.11ax and 802.11be bring in interesting features in the context 110 of supporting critical industrial applications, e.g., a higher degree 111 of flexibility in terms of resource management; frequency allocation 112 aspects that can provide better traffic isolation, or even mechanisms 113 that can assist a tighter time synchronization across wireless 114 environments, thus providing the means to better support traffic in 115 converged networks. Still, being able to address the communication 116 challenges that exist in industrial domains require a better 117 understanding of communication requirements that the existing and 118 future industrial applications may attain. Hence, the focus of this 119 draft is on discussing industrial application requirements, currently 120 and for the future and how to best support time-sensitive 121 applications and services within industrial converged networks. For 122 that purpose, the draft debates on wireless industrial services 123 collected from related normative and informational references on the 124 industrial domain; debates on key drivers for the integration of 125 wireless; debates on specific wireless mechanisms that may assist 126 such integration and challenges thereof; and elaborates on specific 127 requirements to observe both for current wireless services as well as 128 for a subset of future industrial wireless services. 130 2. Conventions used in this document 132 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 133 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 134 document are to be interpreted as described in RFC 2119 [RFC2119]. 135 In this document, these words will appear with that interpretation 136 only when in ALL CAPS. Lower case uses of these words are not to be 137 interpreted as carrying significance described in RFC 2119. 139 3. Definitions 140 * Latency (aka bounded latency), concerns the end-to-end 141 transmission delay between a transmitter and a receiver, when a 142 traffic flow is triggered by an application. By definition, 143 latency corresponds to the time interval between sending the first 144 packet of a flow from a source to a destination, until the instant 145 of reception of the last packet of that flow. 147 * Periodicity stands for whether or not the data transmission is 148 executed in a periodic fashion and whenever possible, the specific 149 periodicity per unit of time has been specified. 151 * "Transmit data size" corresponds to the data payload in bytes. 153 * Tolerance to packet loss is presented as "0" (zero congestion 154 loss); tolerant (the application has tolerance to packet loss). 155 Packet loss occurs when packets fail to reach a specific 156 destination on a network. Packet loss is usually measured as a 157 percentage of packets loss in regards to the overall packets sent. 158 In the context of deterministic networking and in particular, of 159 Time-sensitive Networking (TSN), a packet is lost when it is not 160 received within a specific deadline. 162 * "Time sync" refers to the need to ensure IEEE 1588 163 synchronization. 165 * "Node density" provides (wherever available) a glimpse into the 166 number of end-nodes per 20mx20m. 168 4. Wireless Industrial Services Today 170 This section describes industrial applications where IEEE 802.11 is 171 already being applied, derived from an analysis of related work. 173 Industrial wireless services focused on the strengthening of 174 industrial manufacturing environments have been intensively 175 documented via the IEEE Nendica group [NENDICA], the Internet 176 Industrial Consortium [IIC], the OPC FLC working group [OPCFLC]. The 177 IEEE Nendica 2020 report [NENDICA] comprises several end-to-end use- 178 cases and a technical analysis of the identified features and 179 functions supported via wireless/wired deterministic environments. 180 Based on surveys to industry, the report provides a first 181 characterization of wireless services in factories (Wi-Fi 5), 182 characterizing the scenarios in terms of aspects such as as payload 183 size in bytes, communication rate, arrival time tolerance, node 184 density. 186 The IEEE 802.11 RTA report [IEEERTA] provides additional input 187 concerning the support of wireless for time-sensitive and real-time 188 applications. For each category of application, the report provides 189 a description, basic information concerning topology and packet flow/ 190 traffic model, summarizing the problem statement (main challenges). 191 The industrial applications in this report are a subset and have also 192 considered sources such as IEEE Nendica, IEC/IEEE 60802 Use-cases, as 193 well as 3GPP TR 22.804. The report aggregates the different services 194 in 3 classes (A,B,C) and provides communication requirements for each 195 class categorized as: bounded latency (worst-case one-way latency 196 measured at the application layer); reliability (defined as the 197 percentage of packets expected to be received within the latency 198 bound); time synchronization needs (in the order of micro/ 199 milliseconds); throughput needs (high, moderate, low). The report 200 concludes with guidelines concerning implementation aspects, e.g., 201 traffic classification aspects and new capabilities to support real- 202 time applications. 204 The Avnu Alliance provides a white paper describing steps for the 205 integration of TSN over WiFi [AVNU2020], briefly describing the 206 integration of Wi-Fi in specific applications such as: closed loop 207 control, mobile robots, power grid control, professional Audio/Video, 208 gaming, AR/VR. The document also raises awareness to the possibility 209 of wireless replacing or being complementary to wired within 210 connected cabines, i.e., in regards to the wiring harness within 211 vehicles (cars, airplanes, trains), which are currently expensive and 212 which require a complex onboarding. Wireless can assist in lowering 213 the costs, if it can be adapted to the critical latency, safety 214 requirements and regulations. Such cases would require 100 215 micosecond level cycles, according to Avnu. The communication 216 requirements are summarised in terms of whether or not IEEE 1588 217 synchronisation is required; the typical packet size (data payload); 218 bounded latency; reliability. 220 Manufacturing wireless use-cases have also been debated in the 221 context of 5G ACIA [ACIA], NICT [NICT], and IETF Deterministic 222 Networking [RFC8578]. These sources provide an overview on user 223 stories, and debate on the challenges brought by the integration of 224 wireless. However, communication requirements are not presented in a 225 systematic way. Lastly, the IETF RAW working group has an active 226 draft which provides an initial overview on the challenges of 227 wireless industrial use-cases [IETFRAW-USECASES]. 229 Derived from the analysis of the aforementioned sources, this section 230 provides a description of categories of applications, and respective 231 communication requirements. The following categories of applications 232 are addressed: 234 * Equipment and process control. 236 * Quality supervision. 238 * Factory resource management. 240 * Display. 242 * Human safety. 244 * Industrial systems. 246 * Mobile robots. 248 * Drones/UAV control. 250 * Power grid control. 252 * Communication-based train networks. 254 * Mining industry. 256 * Connected cabin. 258 The selected communication requirements and which are presented for 259 each category of applications have been extracted from the different 260 available related work. The parameters are: bounded latency; 261 periodicity; transmit data size; tolerance to packet loss; time 262 synchronization needs; node density characterization. 264 4.1. Equipment and Process Control Services 266 This category of industrial wireless services refers to the data 267 exchange required to send, for instance, commands to mobile robots/ 268 vehicles, production equipment, and also to receive status 269 information. Reasons for wireless integration concern: flexibility 270 of deployment, reconfigurability, mobility, maintenance cost 271 reduction. 273 In this category, examples of applications and respective 274 communication requirements are: 276 * Control of machines and robots. 278 - Bounded latency: below 10 ms. 280 - Periodic. 282 - Transmit data size (bytes): 10-400 (small). 284 - Tolerance to packet loss: 0. 286 - Time synchronization: IEEE 1588. 288 - Node density: 1 to 20 (per 20mx20m area). 290 * AGVs with rails 292 - Bounded latency: 10 ms-100ms. 294 - Periodic, once per minute. 296 - Transmit data size (bytes): 10-400 (small). 298 - Tolerance to packet loss: 0. 300 - Time synchronization: IEEE 1588. 302 - Node density: 1 to 20 (per 20mx20m area). 304 * AGVs without rails 306 - Bounded latency:1 s. 308 - Periodic, once per minute. 310 - Transmit data size (bytes): 10-400 (small). 312 - Tolerance to packet loss: 0. 314 - Time synchronization: IEEE 1588. 316 - Node density: 1 to 20 (per 20mx20m area). 318 * Hard-real time isochronous control, motion control 320 - Bounded latency: 250us - 1ms. 322 - Periodic. 324 - Transmit data size (bytes): 10-400 (small). 326 - Tolerance to packet loss: 0. 328 - Time synchronization: IEEE 1588. 330 - Node density: 1 to 20 (per 20mx20m area). 332 * Printing, packaging 334 - Bounded latency: below 2 ms. 336 - Transmit data size (bytes): 10-400 (small). 338 - Tolerance to packet loss: 0. 340 - Time synchronization: IEEE 1588. 342 - Node density: over 50 to 100. 344 * PLC to PLC communication 346 - Bounded latency: 100 us-50 ms. 348 - Transmit data size (bytes): 100-700. 350 - Tolerance to packet loss: 0. 352 - Time synchronization: IEEE 1588. 354 * Interactive video 356 - Bounded latency: 50 -10 ms. 358 - Time synchronization: 10-1[micro]s. 360 * Mobile robotics 362 - Bounded latency: 50 -10 ms. 364 * AR/VR, remote HMI 366 - Bounded latency: 10 - 1 ms. 368 - Time synchronization: ~1 [micro]s. 370 - Time synchronization: 10-1[micro]s. 372 * Machine, production line controls 374 - Bounded latency: 10 - 1 ms. 376 4.2. Quality Supervision Services 378 Quality supervision comprises industrial services that collect and 379 assess information related to products and states of machines during 380 production. Reasons for wireless integration concern: flexibility of 381 deployment, maintenance cost reduction. 383 Examples of applications in this category, and their communication 384 requirements are: 386 * Inline inspection 388 - Bounded latency: bellow 10ms. 390 - Time synchronization: 10-1[micro]s. 392 - Periodic, once per second. 394 - Transmit data size (bytes): 64-1M. 396 - Tolerance to packet loss: 0. 398 - Node density: 1-10 (per 20mx20m). 400 * Machine operation recording 402 - Bounded latency: over 100 s. 404 - Time synchronization: 10-1[micro]s. 406 - Periodic, once per second. 408 - Transmit data size (bytes): 64-1M. 410 - Tolerance to packet loss: 0. 412 - Node density: 1-10 (per 20mx20m). 414 * Logging 416 - Bounded latency: over 100s. 418 - Time synchronization: 10-1[micro]s. 420 - Transmit data size (bytes): 64-1M. 422 - Tolerance to packet loss: 0. 424 - Node density: 1-10 (per 20mx20m). 426 4.3. Factory Resource Management Services 428 Refers to capturing information about whether production is 429 proceeding under proper environmental conditions, and whether staff 430 and devices contributing to productivity enhancement are being 431 managed appropriately. Reasons for wireless integration concern: 432 flexibility of deployment, reconfigurability, maintenance cost 433 reduction. 435 Services debated in this context are: 437 * Machine monitoring 439 - Bounded latency: 100ms-10s. 441 - Periodic. 443 - Time synchronization: 10-1[micro]s. 445 - Transmit data size (bytes): 10-10M. 447 - Tolerance to packet loss: 0. 449 - Node density: 1-30. 451 * Preventive maintenance 453 - Bounded latency: over 100ms. 455 - Periodic, once per event. 457 * Positioning, motion analysis 459 - Bounded latency: 50ms-10s. 461 - Periodic, once per second. 463 * Inventory control 465 - Bounded latency: 50ms-10s. 467 - Periodic, once per second. 469 * Facility control environment 471 - Bounded latency: 1s-50s. 473 - Periodic, once per minute. 475 * Checking status of material, small equipment 477 - Bounded latency: 100ms-1s. 479 - Sporadic, 1 to 10 times per 30 minutes. 481 4.4. Display Services 483 This category of services targets workers, allowing them to receive 484 requested support information. It also targets managers in regards 485 to monitoring of production status and processes. Reasons for 486 wireless integration are: scalability, flexibility of deployment, 487 mobility support. Examples of services are: 489 * Work commands, e.g., wearable displays 491 - Bounded latency: 1-10s. 493 - Sporadic, once per 10s-1m. 495 - Transmit data size (bytes): 10-6K. 497 - Tolerance to packet loss: yes. 499 - Node density: 1-30 501 * Display information 503 - Bounded latency: 10s. 505 - Sporadic, once per hour. 507 - Transmit data size (bytes): 10-6K. 509 - Tolerance to packet loss: yes. 511 - Node density: 1-30. 513 * Supporting maintenance (video, audio) 515 - Bounded latency: 500ms. 517 - Sporadic, once per 100ms. 519 - Transmit data size (bytes): 10-6K. 521 - Tolerance to packet loss: yes. 523 - Node density: 1-30. 525 4.5. Human Safety Services 527 Refers to industrial wireless services that concern collecting data 528 to infer about potential dangers to workers in industrial 529 environments. The need for wireless integration concerns: support 530 for pervasive deployment; mobility. 532 Examples of services are: 534 * Detection of dangerous situations/operations 536 - Bounded latency: 1s. 538 - Periodic, 10 per second (10 fps). 540 - Transmit data size (bytes): 2-100K. 542 - Tolerance to packet loss: yes. 544 - Node density: 1-50. 546 * Vital sign monitoring, dangerous behaviour detection 548 - Bounded latency: 1s-50s. 550 - Periodic, once per minute. 552 - Transmit data size (bytes): 2-100K. 554 - Tolerance to packet loss: 0. 556 - Node density: 1-30. 558 4.6. Mobile Robotics Services 560 Refers to services that support the communication between robots, 561 e.g., task sharing; guidance control including data processing, AV, 562 alerts. Reasons to consider wireless integration are: the need to 563 support mobility and reconfigurability. 565 * Video operated remote control 567 - Bounded latency: 10-100ms. 569 - Transmit data size (bytes): 15-150K. 571 - Tolerance to packet loss: yes. 573 - Node density: 2-100. 575 * Assembly of robots or milling machines 577 - Bounded latency: 4-8ms. 579 - Transmit data size (bytes): 40-250. 581 - Tolerance to packet loss: yes. 583 - Node density: 2-100. 585 * Operation of mobile cranes 587 - Bounded latency: 12ms. 589 - Periodic, once per 2-5ms. 591 - Transmit data size (bytes): 40-250. 593 - Tolerance to packet loss: yes. 595 - Node density: 2-100. 597 * Drone/UAV air monitoring 599 - Bounded latency: 100ms. 601 - Tolerance to packet loss: yes. 603 4.7. Power Grid Control 605 Power grid control concerns services that support communication links 606 for predictive maintenance and to isolate faults on high voltage 607 lines, transformers, reactors, etc. Reasons to integrate wireless 608 concern: wire replacement maintenance cost reduction. 610 * Bounded latency: 1-10ms. 612 * Transmit data size (bytes): 20-50. 614 * Time synchronization: IEEE 1588. 616 * Tolerance to packet loss: yes. 618 * Node density: 2-100. 620 4.8. Wireless Avionics Intra-communication 622 Wireless integration is also relevant to industrial environments in 623 the context of replacing cabling. Within the context of avionics 624 [AVIONICS], _Wireless Avionics Intra-communication (WAIC)_ systems 625 [WAIC] are expected to significantly benefit from determinist 626 communications, given their higher criticality. For instance, flight 627 control systems, integrating a large number of endpoints (sensors and 628 actuators), require high reliability and bounded latency to assist in 629 estimating and controlling the state of the aircraft. Real-time data 630 needs to be delivered with strict deadlines for most control systems. 632 The WAIC standardization process is still ongoing, without a clear 633 indication about the frequencies that would be reserved for such 634 systems, although the frequency band 4.2 GHz to 4.4 GHz is the one 635 that currently seems most popular. Nevertheless, independently of 636 the allocated frequency bands, the determinisc guarantees required by 637 WAIC services may be achieved by means of the integration of 638 functionality developed in current wireless standards. 640 However, the following requirements are expected to be supported by 641 wireless technology in order to ensure the deterministic operation of 642 WAIC systems: 644 * Must provide deterministic behaviour in short radio ranges (< 645 100m). 647 * Must use low transmit power levels for low rate (10mW) and high 648 rate (50mW) applications. 650 * Must ensure good system reconfigurability. 652 * Must support dissimilar redundancy. 654 In terms of potential KPIs, specific communication requirements can 655 be identified: 657 * Latency: 20-40ms [PARK2020]. 659 * Packet payload: small (e.g., 50 bytes) and variable bit rate 660 [PARK2020]. 662 * Support between 125 to 4150 nodes [AVIONICS]. 664 * Maximum distance between transmitter and receiver: 15m [AVIONICS]. 666 * Aggregate average data rate of network (kbit/s): 394 to 18385 667 [AVIONICS]. 669 * Latency: below 5s for High data rate Inside (HI) applications 670 [AVIONICS]. 672 * Jitter: below 50ms for HI applications [AVIONICS]. 674 As an example of current standards that may support the deterministic 675 requirements of WAIC system, we can point to IEEE 802.11ax, which is 676 being devised to operate between 1 and 7GHz (in addition to 2.4 GHz 677 and 5GHz). The WAIC requirement for high reliability and bounded 678 latency may be supported by 802.11ax capability of dividing the 679 spectrum in frequency resource units (RUs), which are assigned to 680 stations for reception and transmission by a central coordinating 681 entity, the wireless Access Point. Reliability can be achieved by 682 assigning more than one RU to the same station, for instance (an 683 aspect that is not covered by IEEE 802.11ax but already under 684 discussion for IEEE 802.11be). Through the central scheduling of the 685 RUs contention overhead can be avoided, which increases efficiency in 686 scenarios of dense deployments as is the case of WAIC applications. 687 In this context, OFDMA and the concept of spatial reuse is relevant, 688 to assist large-scale simultaneous transmission, while at the same 689 time preventing collision and interference, and guaranteeing high 690 throughput [ROBOTS1]. 692 5. Additional Reliable Wireless Industrial Services 694 This section provides examples of additional wireless industrial 695 services. We have specifically selected three different examples of 696 such use-cases: i) remote AR/VR for maintenance and control; ii) 697 decentralized shop-floor communication and iii) wireless cabin intra- 698 communications. Based on these examples, wireless integration 699 recommendations are debated and a list of specific requirements is 700 provided. 702 5.1. AR/VR Services within Flexible Factories 704 5.1.1. Description 706 While Video is today integrated both into industrial automation 707 systems, and also used with the shop-floor to assist the worker, the 708 integration of AR/VR in the shop-floor in industrial environments is 709 still in the beginning. It is, however, being applied within the 710 electric industry as a way to improve productivity and safety of 711 workers, also overlaying real-time metadata over equipment under 712 maintenance or operation. 714 In this context, it is important to ensure that the AR/AV traffic 715 does not interfere with the critical traffic of the production 716 system, i.e., performance characteristics like latency and jitter for 717 the critical traffic shall be independent from disturbances. 718 Moreover, it is also important to provide the AR/VR application with 719 low latency, also in the verge of mobility. 721 5.1.2. Wireless Integration Recommendations 723 The support of AR/AV in the context of remote maintenance 724 environments is bound to increase within industrial environments, 725 given the relevancy in terms of remote maintenance and equipment 726 operations. It is also relevant to consider its use within the 727 context of worker safety and it can be foreseen that AV-based remote 728 maintenance will, in the future, be supported via mobile devices 729 carried by workers on the go. Wireless is therefore a key 730 communication asset for this type of applications. In terms of 731 traffic in a converged network, AR/AV is a bandwidth intensive real- 732 time service. It therefore requires specific handling (other than 733 Best Effort, BE). Moreover, the AR/AV traffic flows must not create 734 disturbance when transmitted via wireless. Hence, traffic isolation 735 is an important aspect to ensure for this type of traffic profile. 737 A third aspect to address in the future concerns the fact that there 738 will most likely be the need to support multiple AR/AV streams from 739 different end-users within a single Wireless Local Area Network 740 (WLAN), thus increasing the need for traffic isolation. A fourth 741 aspect concerns the fact that VR systems, if not adequately support, 742 result in VR sickness. Specific network and non-network requirements 743 have already been identified by IEEE 802, MPEG, 3GPP. Such 744 requirements contemplate, for instance, support of higher frame 745 rates, reducing the motion-to-photon latency, higher data 746 transmission rates, low jitter, etc. 748 5.1.3. Requirements Considerations 750 In such applications, to ensure minimum interference, a few aspects 751 need to be ensured: 753 * The AR/AV traffic needs to be isolated in order to prevent 754 interference, i.e., it SHOULD have a specific CoS assigned 755 (downlink and uplink). 757 * Between wireless devices (stations) and AP, there is the need to 758 ensure that the AR/AV traffic is handled in a way that does not 759 hinder critical traffic. 761 * Low mobility SHOULD be supported. 763 * Multiple user support SHOULD be provided. 765 * VR sickness MUST be prevented [IEEERTA]. 767 * A tight integration of the AR/VR systems with production systems 768 SHOULD be address in way compatible with the deterministic wired 769 infrastructure. For instance, Audio Video Bridging (AVB) in the 770 wired TSN infrastructure. Specifically, AVB is usually blocked by 771 the time-aware shaper, and impacted by: TAS, CBS, FIFO and FPNS 772 (fixed priority non-preemptive scheduling). 774 * A software-based mechanism on the AP SHOULD support an adequate 775 mapping of CoS to the wireless QoS (e.g., EDCA UPs). 777 * MAC layer contention MUST be mitigated for all wireless stations 778 within the area (within the range of the same AP or not). 780 Specific communication requirements: 782 * Latency: 3-10ms [IEEERTA]. 784 * Bandwidth, 0.1-2Gbps [IEEERTA]. 786 * Data payload, over 4Kbytes [IEEERTA]. 788 5.2. Decentralized Shop-floor Communication Services 790 5.2.1. Description 792 The increasing automation of industrial environments implies an 793 increase in the number of integrated nodes, including mobile nodes. 794 Wireless is, for instance, a key driver for scenarios involving 795 mobile vehicles [NICT]. NICT also describes already production 796 environments, in particular environments with elevated temperatures, 797 where wireless communication is used to support safety of workers and 798 to remotely monitor production status. Such environments comprise 799 different applications (e.g., safety of workers, mobile robots, 800 factory resource management) and debate on the interconnection of 801 different wireless technologies and devices, from PLCs, to autonomous 802 mobile robots, e.g., UAVs, AGVs. Wireless/wired integration 803 mechanisms have also been debated in the cost of self-organizing 804 production lines [DIETRICH2018]. Therefore, the notion of flexible 805 and heterogeneous shop-floor communication is already present in 806 industrial environments, based on hybrid wired/wireless systems and 807 the integration of multi-AP environments. 809 5.2.2. Wireless Integration Recommendations 811 Prior related work debates on centralized communication architectures 812 (infrastructure mode), and for this case, the issue of connectivity 813 is usually circumvented via multiple AP coordination mechanisms. 814 Within the context of multi-AP coordination and assuming TDMA-based 815 communication, a well-organized schedule can prevent collisions 816 [FERN2019]. Hence, for this specific type of scenario, the main 817 issue concerns handling handovers in a timely and precise way, 818 capable of providing deterministic guarantees. However, with an 819 increase on the number of nodes on a shop-floor, connectivity issues 820 become more complex. 822 Therefore, it is relevant to explore also the possibility of a 823 "decentralized" approach to shop-floor communication, considering 824 both mobile and static nodes. In this case, and from a topology 825 perspective, wireless industrial services are expected to be provided 826 over both ad-hoc and infrastructure mode. Within the ad-hoc 827 communication areas, there is control-based traffic integrated with 828 sensing (critical, non-critical), with real-time traffic, as well as 829 time-triggered traffic. Each node is responsible for managing its 830 access to the medium, thus requiring a cooperative protocol approach. 832 5.2.3. Requirements Considerations 834 In such environment, connectivity becomes more complex requiring 835 additional support: 837 * A wider variety of traffic profiles MUST be supported, thus 838 increasing the management complexity. 840 * Devices communicating via ad-hoc mode MUST integrate a 841 collaborative communication approach, e.g., relaying, cluster- 842 based scheduling approach. 844 * Low mobility MUST be supported (e.g., up to 2 m/s within a BSS). 846 * Multi-AP coordination MUST still be integrated. 848 * Frequent handover MUST be supported, ideally with a make-before- 849 break approach. 851 * Neighbor detection and coverage problem detection MUST be 852 implemented in ad-hoc nodes. 854 Specific communication requirements: * Latency: 20-40ms [ROBOTS1]. * 855 Packet payload: small (e.g., 50 bytes) and variable bit rate 856 [ROBOTS1]. 858 5.3. Autonomous Airborne Services 860 ### Description 862 Over the last decade several services emerged that rely on the 863 autonomous (total or partial) operation of airborne systems. 864 Examples of such systems are: logistic drones; swarm of drones (e.g. 865 for surveillance); urban Air Mobility [UAM18]; single Pilot operation 866 of commercial aircrafts [BBN8436]. 868 Such autonomous airborne systems rely on advances in communications, 869 navigation, and air traffic management to mitigate the significant 870 workload of autonomous operations, namely by means of air-ground 871 collaborative decision making. Such decision making processes rely 872 on expanding the role of ground operators, including tactical (re- 873 routing) and emergency flight phases, as well as higher levels of 874 decision support including systems monitoring in real-time. 876 Such air-ground collaborative decision making process can only be 877 possible with the support of a reliable wireless network able to 878 assist in the required data exchange (of different types of traffic) 879 within significant constraints in terms of delay and error avoidance. 881 5.3.1. Wireless Integration Recommendations 883 Independently of the type of application (logistics, surveillance, 884 urban air mobility, single pilot operation), an autonomous airborne 885 system can be models as a multi-agent system, in which agents need to 886 use a wireless network to communicate reliably between them and in 887 possible with a control entity. The nature and position of such 888 agentes differ from application to application. For instance, all 889 agents may be collocated in the same or different flying vehicles. 891 A high-performance and reliable wireless network has an important 892 role in meeting the challenges of autonomous airborne systems, such 893 as coordination and collaboration strategies, control mechanisms, and 894 mission planning algorithms. Hence, wireless technologies plan a 895 central role in the creation of the needed networking system, 896 including air-to-air communications (single or multi-hop) but air-to- 897 ground communications. 899 Air-to-air communications allow all airborne agents to establish 900 efficient communication, allowing the reception of error prune data 901 exchanged within the required time frames. For instance, in a swarm 902 drones can either communicate with each other directly, or indirectly 903 by constructing multi-hop communication paths with other drones. 905 In what concerns air-to-ground communications, airborne agents 906 communicate with a control center, such as a ground station, to 907 obtain real-time updated information (e.g. mission related). Air-to- 908 ground communication is usually direct communication. 910 The air-to-air and air-to-ground communications are combined through 911 a communication architecture, which can be of different types. In 912 small autonomous systems (single drones used for logistics), a 913 central control station is deployed with enough powerf to communicate 914 with the drone. In autonomous systems with a large number of agents, 915 a decentralized approach should be used. 917 5.3.2. Requirements Considerations 919 When analysing the major properties of wireless communication 920 architectures, the first priority should go to requirements of high 921 coverage and maintaining connectivity. The former plays an important 922 role in gathering the information needed for the operation of the 923 autonomous system, while maintaining connectivity ensures the real- 924 time communication within the system. 926 However, autonomous systems may operate in unknown environments, with 927 the unpredicted appearance of threats and obstacles in time and 928 space. Hence such systems should rely on wireless technology that 929 has a high level of reliability and availability. For instance, 930 wireless technology that is able to keep two neighbour agents 931 connected, even when their direct link drops below the required 932 minimum signal-to-noise ratio (SNR) or receive signal strength 933 indicators (RSSI) range. On a system level, wireless network 934 technologies, such as routing, should be able to react cognitively to 935 changes of the environment to adapt the communication system in order 936 to ensure the needed coverage and connectivity levels. 938 In this sense it is required the investigation of routing protocols 939 able to ensure the desirable level or reliability and availability of 940 complete system. This means that the wireless routing function 941 should fulfill a set of requirements, including: * Suitable for 942 dynamic topologies. * Scalable with the number of networked agents. * 943 Ensure low values of packet delays (KPI depends upon the specific 944 application). * Ensure high values of packet delivery (KPI depends 945 upon the specific application). * Ensure fast recovery in the 946 presence of interrupted communications. * Ensure low cost in terms of 947 the utilization of network resources (e.g. network queues, 948 transmission opportunities). * Ensure high robustness to link 949 failure. 951 6. Security Considerations 953 This document describes industrial application communication 954 requirements for the integration of reliable Wi-Fi technologies. The 955 different applications have security considerations which have been 956 described in the respective sources [IEEERTA], [NICT], [IIC], 957 [AVNU2020], [ACIA]. 959 7. IANA Considerations 961 This document has no IANA actions. 963 8. Acknowledgments 965 The research leading to these results received funding from joint 966 fortiss GmbH and Huawei project TSNWiFi (https://www.fortiss.org/en/r 967 esearch/projects/detail/tsnwifi(https://www.fortiss.org/en/research/ 968 projects/detail/tsnwifi)) 970 9. References 972 9.1. Normative References 974 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 975 Requirement Levels", BCP 14, RFC 2119, 976 DOI 10.17487/RFC2119, March 1997, 977 . 979 9.2. Informative References 981 [ACIA] 5G ACIA, ., "5G for Connected Industries and Automation", 982 November 2019. 984 [AVIONICS] Fischione, P.Park, P.Di Marco, J.Nah, and C., "Wireless 985 Avionics Intra-Communications, A Survey of Benefits, 986 Challenges, and Solutions, pp. 1–24", 2020. 988 [AVNU2020] Bush, S., "Avnu Alliance White Paper Wireless TSN- 989 Definitions, Use Cases & Standards Roadmap", 2020. 991 [BBN8436] Pew, Deutsch, Stephen, and Richard W., "Single pilot 992 commercial aircraft operation. BBN Report.", 2005. 994 [DIETRICH2018] 995 , & Fohler, G, Dietrich, S., May, G., von Hoyningen-Huene, 996 J., Mueller, A., "Frame conversion schemes for cascaded 997 wired/wireless communication networks of factory 998 automation, Mobile Networks and Applications, 23(4), 999 817-827", 2018. 1001 [FERN2019] Fernández Ganzabal, Z., "Analysis of the Impact of 1002 Wireless Mobile Devices in Critical Industrial 1003 Applications", May 2019. 1005 [IEEERTA] Meng, K., "IEEE 802.11 Real Time Applications TIG Report", 1006 2018. 1008 [IETFRAW-USECASES] 1009 Bernardos, G.P.P.T.F.T.a.C., "RAW use cases,” IETF draft - 1010 RAW working group", 2020, 1011 . 1014 [IIC] Linehan, M., "Time Sensitive Networks for Flexible 1015 Manufacturing Testbed Characterization and Mapping of 1016 Converged Traffic Types", 2020. 1018 [NENDICA] Zein, Ed, N., "IEEE 802 Nendica Report, Flexible Factory 1019 IoT-Use Cases and Communication Requirements for Wired and 1020 Wireless Bridged Networks", 2020. 1022 [NICT] NICT, "Wireless use cases and communication requirements 1023 in factories ( abridged edition ), Flex. Factories Proj", 1024 February 2018. 1026 [OPCFLC] "OPC Foundation Field Level Communications (FLC) 1027 Initiative", September 2020, 1028 . 1030 [PARK2020] Park, Pangun, et al, ., "Wireless Avionics Intra- 1031 Communications, A Survey of Benefits, Challenges, and 1032 Solutions. IEEE Internet of Things Journal", 2020. 1034 [RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases", 1035 RFC 8578, DOI 10.17487/RFC8578, May 2019, 1036 . 1038 [ROBOTS1] Hoebeke, J.Haxhibeqiri, E.A.Jarchlo, I.Moerman, and J., 1039 "Flexible Wi-Fi Communication among Mobile Robots in 1040 Indoor Industrial Environments, Mob. Inf. Syst.", 2018. 1042 [UAM18] Shamiyeh, Michael, Raoul Rothfeld, and Mirko Hornung, ., 1043 "A performance benchmark of recent personal air vehicle 1044 concepts for urban air mobility. Proceedings of the 31st 1045 Congress of the International Council of the Aeronautical 1046 Sciences, Belo Horizonte, Brazil", 2018. 1048 [WAIC] International Telecommunication Union, "Technical 1049 characteristics and operational objectives for wireless 1050 avionics intra-communications, Policy, vol. 2197, p. 58,". 1052 Authors' Addresses 1054 Rute C. Sofia 1055 fortiss GmbH 1056 Guerickestr. 25 1057 80805 Munich 1058 Germany 1060 Email: sofia@fortiss.org 1062 Matthias Kovatsch 1063 Huawei Technologies 1064 Riesstr. 25 C, 3.0G 1065 80992 Munich 1066 Germany 1068 Email: ietf@kovatsch.net 1070 Paulo Milheiro Mendes 1071 Airbus 1072 Willy-Messerschmitt Strasse 1 1073 81663 Munich 1074 Germany 1076 Email: paulo.mendes@airbus.com