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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 DetNet H. Wang 2 Internet Draft P. Wang 3 Interned status: Standards Track H. Yang 4 Expires: May 19, 2017 Chongqing University of 5 Posts and Telecommunications 6 November 15, 2016 8 Joint Real-Time Scheduling Methods for Deterministic Industrial 9 Field/Backhaul Networks 10 draft-wang-detnet-joint-scheduling-00 12 Abstract 14 In industrial field/backhaul networks, the joint real-time 15 scheduling method is important to keep end-to-end data streams 16 meeting the deadline. This document proposes four joint scheduling 17 methods, the four methods consider time slotting the industrial 18 backhaul network, regarding industrial backhaul network as a black 19 box system, ignoring delay of industrial backhaul and establishing 20 latency model of an industrial backhaul network. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF), its areas, and its working groups. Note that 29 other groups may also distribute working documents as Internet- 30 Drafts. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or obsoleted by other documents 34 at any time. It is inappropriate to use Internet-Drafts as reference 35 material or to cite them other than as "work in progress." 37 The list of current Internet-Drafts can be accessed at 38 http://www.ietf.org/ietf/1id-abstracts.txt 40 The list of Internet-Draft Shadow Directories can be accessed at 41 http://www.ietf.org/shadow.html 43 This Internet-Draft will expire on May 19, 2017. 45 Copyright Notice 47 Copyright (c) 2016 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with 55 respect to this document. Code Components extracted from this 56 document must include Simplified BSD License text as described in 57 Section 4.e of the Trust Legal Provisions and are provided without 58 warranty as described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction ................................................. 2 63 2. Deterministic industrial field-backhaul network requirement .. 4 64 3. Deterministic Industrial field-backhaul network Joint Scheduling 65 Key Technology .................................................. 5 66 3.1. End-to-end Network Data Stream .......................... 5 67 3.2. Network Communication Resource .......................... 5 68 3.3. Network Time Slot Scheduling ............................ 6 69 4. Joint real-Time scheduling methods for deterministic industrial 70 field-backhaul network .......................................... 6 71 4.1. Time-Slotted Industrial Backhaul Networks ............... 6 72 4.2. Consider Industrial Backhaul Network as a Black Box .... 10 73 4.3. Ignore the Delay of Industrial Backhaul Network ........ 11 74 4.4. Build Delay Model of Industrial Backhaul Network ....... 11 75 5. Security Considerations ..................................... 11 76 6. IANA Considerations ......................................... 11 77 7. References .................................................. 11 78 7.1. Normative References ................................... 11 79 7.2. Informative References ................................. 11 80 Authors' Addresses ............................................. 13 82 1. Introduction 84 Industrial field network is a network that can be deployed in 85 industrial process and monitor industrial field equipment and 86 systems to achieve the target of control and management. It can 87 improve production efficiency, reduce human intervention to 88 industrial production process and decrease the cost of production. 89 It has significant importance for industrial modernization. 91 Industrial field bus and industrial ethernet are two kinds of common 92 solutions to industrial automation with the development of 93 industrial field network, however they are both wired network. If 94 they can combine the technology of wireless sensor network, a new 95 network, industrial wireless network, can free from being bonded to 96 wires and cables, and is more easy and flexible to deployment. 97 Industrial wireless network is a communication network which is 98 oriented toward building automation, and process automation, and 99 industrial automation. There are three major international standards 100 (ISA100[ISA100.11a], WirelessHART[WirelessHART],WIA-PA[WIA-PA]) in 101 the area of industrial wireless network currently. 103 Industrial backhaul network is a transition network, which combines 104 industrial field network with higher level network to achieve the 105 goal of interconnection. It mainly solves the problem of access of 106 industrial field network data to higher level network. Industrial 107 field network is generally limited to a specific region, such as a 108 plant. By this network, transaction data of industrial field network 109 can be transferred to internet or other industrial field networks. 110 Industrial backhaul network is a medium-sized network, which can 111 cover from a few kilometers to tens of kilometers. The major 112 technology of industrial wireless backhaul network consists of Wi-Fi, 113 WiMAX and LET. 115 In order to adapt the presentation and development of industry 4.0, 116 which is aimed to elevate the level of manufacturing, industrial 117 field network should not be confined to a plant network only. 118 Therefore, it is necessary to introduce the technology of industrial 119 backhaul network to break the restrictions of interconnection 120 between different networks, and to form a mixed network of 121 industrial field network and backhaul network. Figure 1 indicates a 122 typical network architecture of the mixed network. It is a type of 123 deterministic network, and had been illustrated about use cases and 124 architecture in the drafts proposed by DetNet Workgroup of IETF of 125 draft-bas-usecase-detnet-02 and draft-finn-detnet-architecture-04. 127 +-----------------------------------+ 128 | | 129 | | 130 | Backhaul network | 131 | | 132 | | 133 +-----------------------------------+ 134 / \ 135 / \ 136 +-------------------------------+ +-------------------------------+ 137 | | | | 138 | | | | 139 | Field network | | Field network | 140 | | | | 141 | | | | 142 +-------------------------------+ +-------------------------------+ 144 Figure 1. Typical industrial field-backhaul network 146 In this mixed network architecture of industrial field network and 147 backhaul network, field network is made up of ISA100, which is 148 industrial wireless sensor network protocol. In the former network, 149 a node deployed in a plant can communicate with a node deployed in 150 another plant through a backhaul network. 152 2. Deterministic industrial field-backhaul network requirement 154 The draft of draft-finn-detnet-problem-statement put forward by 155 DetNet Workgroup of IETF had described the requirement of 156 deterministic network and deterministic scheduling partially. 157 Because industrial field network directly faces the monitoring of 158 industrial process, it is a difference between industrial field 159 network data and general network data. Industrial field network has 160 high demands about the deterministic delay bounds. It will affect 161 the productivity, and even generate industrial accidents, when there 162 are high packet loss and latency in a field network. For instance, 163 real-time monitoring of level measurement and control are required 164 to avoid overfilling of oil tanks that may lead to serious economic 165 loss and environmental threats. 167 So, it is needed that a deterministic joint scheduling method can 168 guarantee the determination of network data in such a new network 169 architecture. 171 3. Deterministic Industrial field-backhaul network Joint Scheduling Key 172 Technology 174 3.1. End-to-end Network Data Stream 176 In an industrial field network, end-to-end network data stream 177 indicates a complete transmission path that a source device node 178 transfers to a destination device node (common node or gateway). 179 While in an industrial field-backhaul network, it indicates a 180 complete transmission path that a field network source device node 181 transfers through an industrial backhaul to another field network 182 destination device node. 184 Industrial field-backhaul network data stream have following 185 features: 187 o Period. Every data stream in network generates period data. 189 o Deterministic. Every data stream in network has a deadline, 190 network scheduling should ensure every data stream arrive at 191 destination node before its deadline. 193 o Sequential. A path of an end-to-end network data stream are made 194 up of every two sequential node transmission link. In the process 195 of scheduling, it must be scheduled by the order of sequence of 196 links in the path. 198 3.2. Network Communication Resource 200 In the deterministic industrial field networks with backhaul network 201 architecture, schedulable network communication resources are time 202 slot, channel and link. If the backhaul network is SDN architecture, 203 then the SDN controller could schedule the bandwidth and cache of 204 switch. Therefore, bandwidth and cache resources can be included in 205 schedulable network communication resources. 207 o Time slot. Time slot is the basic unit in the TDMA based network 208 communications. The length of time slots is settled and is the 209 same in the entire network. Only one packet or ACK can be 210 transmitted in one time slot. 212 o Channel. In order to increase network throughput, industrial 213 field network standards provide a number of channels of different 214 frequencies. If the links do not interfere with each other, then 215 we can use different channels to transmit simultaneously. 217 o Link. Link refers to a direct communication link between one node 218 and another and no intermediate switching nodes. The network data 219 stream is composed of a lot of links. The devices in the 220 industrial field network devices are half-duplex, so the links in 221 the industrial field network are unidirectional. 223 3.3. Network Time Slot Scheduling 225 In TDMA-based industrial field network, time is divided into time 226 slots of the same length. One transmission can be conducted in each 227 time slot and the links using different channels to transmit if they 228 do not interfere each other. 230 In the time slot scheduling process, it will cause link collision 231 when a node arranged to transmit and receive simultaneously, and it 232 will cause channel collision when the same channel is used within a 233 certain range. AS shown in figure 2, the network time slot 234 scheduling process should avoid such collisions. 236 +---+ +---+ +---+ +---+ +---+ +---+ +---+ 237 | A |-->| B |-->| C | | A |-->| B | | C |-->| D | 238 +---+ +---+ +---+ +---+ +---+ +---+ +---+ 240 +---------+------------+ +---------+------------+ 241 |Time slot| Time slot 0| |Time slot| Time slot 0| 242 +---------+------------+ +---------+------------+ 243 |Channel 0| A->B | |Channel 0| A->B | 244 +---------+------------+ | | C->D | 245 |Channel 1| B->C | +---------+------------+ 246 +---------+------------+ 247 Figure 2. Link Collision & Channel Collision 249 4. Joint real-Time scheduling methods for deterministic industrial 250 field-backhaul network 252 Joint real-time scheduling methods for deterministic industrial 253 field/backhaul networks, which cross networks, are intend to solve 254 the deterministic problem of industrial field /backhaul networks. 255 Since the current network infrastructure imports backhaul network, 256 the deterministic scheduling algorithm need to collaborate with 257 backhaul network to conduct joint scheduling to ensure data 258 certainty. The proposal put forward the following solutions. 260 4.1. Time-Slotted Industrial Backhaul Networks 262 In order to ensure determinism, industrial field networks utilize 263 TDMA to make the network time-slotted. If the industrial backhaul 264 network can also be time-slotted, then the deterministic scheduling 265 algorithm can jointly schedule with minor alterations. Industrial 266 backhaul network can be built with a variety of network standards 267 such as Wi-Fi, WiMAX, LTE and so on. But in consideration of the 268 high cost and poor feasibility of time-slotted WiMAX and LTE, we 269 assume that the IEEE802.11 can be time-slotted. Wi-Fi network has 270 various networking modes, such as peer to peer networking mode, 271 point to multi-point networking mode and the relay network mode. 272 Here we consider the hierarchical network constructed in point to 273 multi-point networking mode, as shown in Figure 3. 275 +----------------------------------------+ 276 | | 277 | +--------+ | 278 | +-------| Head AP|-------+ | 279 | | +--------+ | | 280 | | | | 281 | +--------+ +--------+ | 282 +---+---| AP1 | | AP2 |---+---+ 283 | | +--------+ +--------+ | | 284 | +----------------------------------------+ | 285 | | 286 +------------------------------+ +-------------------------------+ 287 |ISA100 field wireless network | | ISA100 field wireless network | 288 +------------------------------+ +-------------------------------+ 290 Figure 3. Industrial Backhaul Network consisting of WIFI 292 Although IEEE802.11 also supports 13 channels, but the AP was not 293 free to switch channels, which means that the AP cannot use a 294 channel in the current time slot and use another channel the next 295 time slot. However, we assume that the network architecture, the 296 following points AP under head AP, which are AP1 and AP2 in FIG 1, 297 can transmit packets simultaneously as long as their transmission 298 task do not contain the same AP, i.e. head AP. For example, when a 299 data stream of field network is transmitting packets to AP1 in a 300 time slot, AP2 is able to receive packets from head AP, or send 301 packets to field network in the same time slot. Therefore, the 302 backhaul network constructed with wireless APs can be considered as 303 a single-channel linear network, which is shown in Figure 4. 305 +---------+ +--------+ +--------+ +--------+ +---------+ 306 | Gateway |--> | AP |--> | AP |--> | AP |--> | Gateway | 307 +---------+ +--------+ +--------+ +--------+ +---------+ 309 Figure 4. A single-channel linear network 311 Therefore, the data stream in industrial field/ backhaul network can 312 be deemed to be equivalent to the data stream in field network, only 313 that every piece of data streams need to go through the linear 314 network consisting of wireless APs. So the scheduling process is 315 proposed as follows: 317 1. Abstract end to end data stream in the entire network, and 318 initialize a different priority for each stream. 320 2. Establish the delay model of network data stream. If collisions 321 happened between different priority data stream, the low-priority 322 data stream will be delayed by high-priority data stream, so a 323 model can be built under the worst circumstances that the low- 324 priority data streams impacted by higher priority data streams. 326 3. Estimate the network schedulability. A data stream is schedulable 327 if the minimum time for the data stream to complete transmission, 328 plus the worst delay time caused by higher priority data streams, 329 is less than or equal to deadline, In the current priority 330 allocation scheme, if each data stream is schedulable, the 331 network can be considered as schedulable. If the data stream 332 cannot be scheduled, then change the priority allocation scheme 333 and estimate again until a corresponding scheme is found. 335 4. Allocate time slot and channel for every data stream. Traverse 336 data streams according to their priority, and each data stream 337 should allocate the next link that is about to be released in 338 each time slot to the greatest extent. According to the rule that 339 low-priority data streams should give way to high-priority data 340 streams, the spare channels can be utilized if there is no 341 collision. However, if collisions happened between data streams 342 of different priority, then the lower-priority data stream should 343 be placed in the next time slot until there are no unallocated 344 higher priority data streams. Follow these rules until the whole 345 network scheduling is completed. 347 The scheduling process is shown in Figure 5: 349 +----------+ 350 | Begin | 351 +----------+ 352 | 353 | 354 +---------------------------+ 355 | Initial the priority of | 356 | each data stream | 357 +---------------------------+ 358 |<--------------------------------------+ 359 | | 360 +--------------------+ +------------------------------+ 361 / Traverse every data \ no | If the data stream cannot be | 362 / stream and estimate the\--------->| scheduled, then change the | 363 \ schedulablity according/ | priority allocation scheme | 364 \ to delay model / | and estimate again | 365 +--------------------+ +------------------------------+ 366 | 367 |yes 368 +-----------------------------------+ 369 | Traverse data streams according to| 370 | their priority, each data stream | 371 | should allocate the next link that| 372 | is about to be released in each | 373 | time slot to the greatest extent | 374 +-----------------------------------+ 375 | 376 | 377 +-----------------------------------+ 378 | The spare channels can be utilized| 379 | if there is no collision. If | 380 | collisions happened, then the | 381 | lower-priority data stream should | 382 | be placed in the next time slot | 383 +-----------------------------------+ 384 | 385 | 386 +-------+ 387 | End | 388 +-------+ 389 Figure 5. Scheduling of times-slotted industrial backhaul network 391 4.2. Consider Industrial Backhaul Network as a Black Box 393 In order to solve the deterministic problem of industrial backhaul 394 network, industrial backhaul can be deemed as white box to conduct 395 fine controls through inner mechanism. While it can also be regarded 396 as a black box so that we can only consider its delay impacts and 397 ignore its internal details. 399 When the packet goes through the industrial backhaul network, we can 400 give it a timestamp at the application layer and read it after the 401 transmission completed. Then delay caused by the backhaul network 402 can be figured out and a fitting curve of delay can be worked out by 403 collecting large amount of data. It has been verified experimentally 404 that the delay is concentrated in a numerical range despite its 405 randomness. Therefore, we can get the approximate delay of packets 406 caused by the industrial backhaul network. 408 After that, a few of scheduling paths of different priority can be 409 implemented in the industrial field network. A main scheduling path 410 can be configured according to the average delay of the backhaul 411 network. And some redundant paths should be pre-configured in case 412 the delay of the main path is too high. 414 The scheduling process of industrial field/backhaul network can be 415 divided into three periods, as shown in Figure 6: 417 +--------------------+ +-----------------+ +------------------------+ 418 | Scheduling of | | Delay of | | Scheduling of | 419 |source field subnet |->| backhaul network|->|destination field subnet| 420 | (deterministic) | |(indeterministic)| |( deterministic dynamic)| 421 +--------------------+ +-----------------+ +------------------------+ 422 Period 1 Period 2 Period 3 424 Figure 6. Three periods of scheduling 426 In source field subnet we can apply the deterministic scheduling 427 algorithm of field network to conduct deterministic polymerization 428 and get the time spent by each data stream to go through the source 429 subnet. Then the data stream goes through the backhaul network, 430 which is a black box and it will cause indeterministic delay which 431 is in a numerical range. When the data stream comes out the backhaul 432 network, the timestamp should be parsed. If the deadline is missed, 433 it indicates that the packet has gone through poor network and need 434 to be retransmitted. If there is time left, scheduling path can be 435 dynamically selected at downward gateway to get the schedulability 436 of the end to end data stream. 438 4.3. Ignore the Delay of Industrial Backhaul Network 440 Since the field network is slow-speed (256 KB/s), while industrial 441 backhaul network is a high-speed, if the industrial backhaul 442 networks adopt IEEE802.11, gigabit wireless routers supporting 443 IEEE802.11 ac can make the delay of industrial backhaul network 444 quite small. As a result, the joint deterministic scheduling of the 445 entire network only needs to cover the field network that is located 446 at the ends of the backhaul network. 448 4.4. Build Delay Model of Industrial Backhaul Network 450 If industrial backhaul network is built with IEEE802.11, the network 451 access delay test model under IEEE802.11 DCF mode can be established 452 by using Markov chain or queuing theory. At the same time, the model 453 under IEEE802.11 PCF mode can be established based on queuing theory. 455 Therefore, the field network only need to build the delay model of 456 backhaul network that follows one delay model, then the total 457 transmission scheduling delay will follow certain regularity. The 458 total transmission delay will meet delay requirements with specified 459 probability by scheduling, in other words, the unsuccessfulness of 460 scheduling is acceptable, but the scheduling success rate should be 461 in a range of 90% ~ 95%. 463 5. Security Considerations 465 This memo includes no request to IANA. 467 6. IANA Considerations 469 This memo includes no request to IANA. 471 7. References 473 7.1. Normative References 475 7.2. Informative References 477 [ISA100.11a] 478 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 479 also IEC 62734", 2011, < 480 http://www.isa100wci.org/enUS/Documents/PDF/3405-ISA100- 481 WirelessSystems-Future-brochWEB-ETSI.aspx>. 483 [WirelessHART] 484 www.hartcomm.org, "Industrial Communication Networks - 485 Wireless Communication Network and Communication Profiles 486 - WirelessHART - IEC 62591", 2010. 488 [WIA-PA] 489 CN-GB. GB/T 26790.1-2011. Industrial wireless networks WIA 490 specification.Part 1: WIA System architecture and 491 communication specification for process automation (WIA- 492 PA)[S]. China: CN-GB, 2011. 494 [I-D.finn-detnet-problem-statement] 495 Finn, N. and P. Thubert, "Deterministic Networking Problem 496 Statement", draft-finn-detnet-problem-statement-04 (work in 497 progress), October 2015. 499 [I-D.finn-detnet-architecture] 500 Finn, N., Thubert, P., and M. Teener, "Deterministic 501 Networking Architecture", draft-finn-detnetarchitecture-03 502 (work in progress), March 2016. 504 [I-D.bas-usecase-detnet] 505 Kaneko, Y., Toshiba and Das, S, "Building Automation Use 506 Cases and Requirements for Deterministic Networking", draft- 507 bas-usecase-detnet-00 (work in progress), April 2016. 509 Authors' Addresses 511 Heng Wang 512 Chongqing University of Posts and Telecommunications 513 2 Chongwen Road 514 Chongqing, 400065 515 China 517 Phone: (86)-23-6248-7845 518 Email: wangheng@cqupt.edu.cn 520 Ping Wang 521 Chongqing University of Posts and Telecommunications 522 2 Chongwen Road 523 Chongqing, 400065 524 China 526 Phone: (86)-23-6246-1061 527 Email: wangping@cqupt.edu.cn 529 Hang Yang 530 Chongqing University of Posts and Telecommunications 531 2 Chongwen Road 532 Chongqing, 400065 533 China 535 Phone: (86)-23-6246-1061 536 Email: 18716322620@163.com