idnits 2.17.1 draft-wang-detnet-joint-scheduling-03.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (May 14, 2018) is 2168 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: 'I-D.finn-detnet-architecture' is defined on line 491, but no explicit reference was found in the text Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 DetNet H. Wang 2 Internet Draft P. Wang 3 Intended status: Standards Track H. Yang 4 Expires: November 15, 2018 Chongqing University of 5 Posts and Telecommunications 6 May 14, 2018 8 Joint Real-Time Scheduling Methods for Deterministic Industrial 9 Field/Backhaul Networks 10 draft-wang-detnet-joint-scheduling-03 12 Abstract 14 In industrial field/backhaul networks, joint real-time scheduling 15 method is important to make end-to-end flows meet their deadline. 16 This document proposes four joint scheduling methods, and they 17 involve four scenarios: time-slotted industrial backhaul network, 18 regarding industrial backhaul network as a black box system, 19 ignoring delay of industrial backhaul and establishing latency model 20 of 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 November 15, 2018. 45 Copyright Notice 47 Copyright (c) 2018 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 .................................................. 12 78 7.1. Normative References ................................... 12 79 7.2. Informative References ................................. 12 80 Authors' Addresses ............................................. 13 82 1. Introduction 84 Industrial field networks are often deployed to process control 85 industry to monitor industrial field equipment. Industrial field 86 network can improve production efficiency, reduce human intervention 87 and decrease cost, which are significant for industrial 88 modernization. 90 Industrial field bus and industrial Ethernet are two kinds of common 91 networks deployed in industrial automation, while they are wired 92 networks. With the development of industrial wireless technology, 93 Wireless Sensor Networks (WSN), a typical industrial wireless 94 network, has been applied to industrial network. WSN can free 95 traditional field devices from the limits of abundant cables, and it 96 is flexible to deploy in industrial environment. WSN can be applied 97 to building automation, process automation, and industrial 98 automation. Currently, There are three major industrial wireless 99 networks international standards: ISA100.11a[IEC62734], 100 WirelessHART[IEC62591], WIA-PA[IEC62601]. 102 Industrial backhaul network is used as transition network, which 103 combines industrial field network with high-level network to achieve 104 the goal of interconnection. It mainly solves the problem that makes 105 the sensor or control data from industrial field network transmit to 106 high-level network. Generally, industrial field network is deployed 107 to a specific region. Through industrial backhaul network, data of 108 industrial field network can be transferred to internet or other 109 industrial field networks. Industrial backhaul network is a medium- 110 sized network, which can cover from a few kilometers to tens of 111 kilometers. The major technology of industrial wireless backhaul 112 network consists of Wi-Fi, WiMAX and LTE. 114 To apply well in the burgeoning industry 4.0, which aims to elevate 115 the level of manufacturing, industrial field network should not be 116 confined to a plant network only. Therefore, it is necessary to 117 introduce the technology of industrial backhaul network to break the 118 restrictions of interconnection between different networks, and 119 construct a hybrid industrial network. Figure 1 indicates a typical 120 network architecture of the hybrid industrial network. It is a type 121 of architecture of industrial deterministic network that was 122 illustrated with use cases in the drafts proposed by DetNet 123 Workgroup of IETF of [I-D.bas-usecase-detnet] and [I-D.finn-detnet- 124 architecture]. 126 +-----------------------------------+ 127 | | 128 | | 129 | Backhaul network | 130 | | 131 | | 132 +-----------------------------------+ 133 / \ 134 / \ 135 +-------------------------------+ +-------------------------------+ 136 | | | | 137 | | | | 138 | Field network | | Field network | 139 | | | | 140 | | | | 141 +-------------------------------+ +-------------------------------+ 143 Figure 1. Typical industrial field/backhaul network 145 In the hybrid network architecture, field network may be an 146 ISA100.11a. In Figure 1, a node deployed in a plant can communicate 147 with a node in another plant through backhaul network. 149 2. Deterministic Industrial Field/Backhaul Network Requirement 151 The draft of [I-D.finn-detnet-problem-statement], proposed by DetNet 152 Workgroup of IETF, has described the requirements of deterministic 153 network and deterministic scheduling partially. Due to industrial 154 field network directly monitor the industrial process, a difference 155 between industrial field network and general network exists. 156 Industrial field network has high demands on the deterministic delay 157 bounds. In a field network, the delay of data flows will affect 158 productivity, and even cause industrial accidents when happening 159 high packet loss ratio and transmission latency. For example, real- 160 time measure and control of liquid level is required to avoid 161 overfilling of oil tanks, because overflow may lead to serious 162 economic loss and environmental threats. Therefore, it requires a 163 deterministic joint scheduling method to guarantee the deterministic 164 transmission of data stream in the new network architecture. 166 3. Deterministic Industrial Field/Backhaul Network Joint Scheduling Key 167 Technology 169 3.1. End-to-end Network Data Stream 171 In industrial field/backhaul network, end-to-end data stream 172 indicates a complete transmission path that a source node of field 173 network transfers to destination node located in another field 174 network through an industrial backhaul network. 176 Industrial field/backhaul network data stream has following features: 178 o Period. Every data stream generates data with periodicity. 180 o Deterministic. Every data stream has a deadline, and scheduling 181 methods should ensure each data stream arrives at destination 182 node before its deadline. 184 o Sequential. A path of an end-to-end data stream contains some 185 transmission links. In the process of scheduling, it must be 186 scheduled in the order of sequence of links on the path. 188 o Priority. End-to-end data stream has a priority. When data 189 streams with different priorities occur collisions, the data 190 streams with lower priority should be delayed by higher priority 191 data streams. 193 3.2. Network Communication Resource 195 In deterministic industrial field/backhaul network architecture, 196 network communication resources include time slot, channel and link. 197 If backhaul network adopts Software Defined Network (SDN) 198 architecture, then the SDN controller can schedule the bandwidth and 199 cache of switch. Therefore, bandwidth and cache resources can be 200 included in schedulable communication resources. 202 o Time slot. Time slot is the basic transmission unit in the 203 network communications based on Time Division Multiple Access 204 (TDMA). In the entire network, the length of time slots is fixed 205 and stays the same. Only one sending packet and its corresponding 206 ACK can be accommodated in one time slot. 208 o Channel. In order to increase network throughput, industrial 209 field network provides a number of channels with different 210 frequencies. 212 o Link. Link refers to a direct packet transmission between two 213 nodes that located in a communication radius of each other. A 214 data stream comprises many links. 216 3.3. Network Time Slot Scheduling 218 In TDMA-based industrial field network, time is divided into time 219 slots with the same length. In the time-slot scheduling process, it 220 will cause link collisions when a node transmits and receives 221 simultaneously, and it will cause channel collisions when the same 222 channel is used within a certain range. As shown in Figure 2, the 223 time-slot scheduling process should avoid such collisions. 225 +---+ +---+ +---+ +---+ +---+ +---+ +---+ 226 | A |-->| B |-->| C | | A |-->| B | | C |-->| D | 227 +---+ +---+ +---+ +---+ +---+ +---+ +---+ 229 +---------+------------+ +---------+------------+ 230 |Time slot| Time slot 0| |Time slot| Time slot 0| 231 +---------+------------+ +---------+------------+ 232 |Channel 0| A->B | |Channel 0| A->B | 233 +---------+------------+ | | C->D | 234 |Channel 1| B->C | +---------+------------+ 235 +---------+------------+ 236 Figure 2. Link Collision & Channel Collision 238 4. Joint Real-Time Scheduling Methods for Deterministic Industrial 239 Field-Backhaul Network 241 Joint real-time scheduling methods of industrial field/backhaul 242 networks intend to solve the deterministic problem of industrial 243 field/backhaul networks. Due to the investigative architecture 244 includes backhaul network, the deterministic scheduling algorithm 245 needs to collaborate with backhaul network to conduct joint 246 scheduling to ensure data deterministic transmission. The proposed 247 joint scheduling methods are described as follows. 249 4.1. Time-Slotted Industrial Backhaul Networks 251 In order to ensure determinism, industrial field networks adopts 252 TDMA to make the network time-slotted. If the industrial backhaul 253 network can also be time-slotted, then the deterministic scheduling 254 algorithm can jointly schedule with small modification. Industrial 255 backhaul network contains various of network standards such as WIFI, 256 WiMAX, and LTE. WiMAX and LTE are high cost and poor feasibility, 257 thus we assume the IEEE 802.11 as backhaul network. Wi-Fi network 258 has various operating modes, such as peer-to-peer mode, point to 259 multi-point networking mode and the relay network mode. Here we 260 consider the hierarchical network architecture in a way of point to 261 multi-point networking mode, as shown in Figure 3. 263 +----------------------------------------+ 264 | | 265 | +--------+ | 266 | +-------| Head AP|-------+ | 267 | | +--------+ | | 268 | | | | 269 | +--------+ +--------+ | 270 +---+---| AP1 | | AP2 |---+---+ 271 | | +--------+ +--------+ | | 272 | +----------------------------------------+ | 273 | | 274 +---------------------------------++----------------------------------+ 275 |ISA100.11a field wireless network||ISA100.11a field wireless network | 276 +---------------------------------++----------------------------------+ 278 Figure 3. Industrial Backhaul Network consisting of WIFI 280 Although IEEE 802.11 supports multiple channels, but AP is not able 281 to perform channel hopping between transmission timeslots, which 282 means that the AP cannot use a channel in the current time slot and 283 use another channel the next time slot. We assume that AP1 and AP2 284 in Figure 3 can transmit packets simultaneously as long as their 285 transmission tasks do not contain the same AP, i.e. head AP. For 286 example, when a data stream of field network is transmitting packets 287 to AP1 in a time slot, AP2 is able to receive packets from head AP, 288 or send packets to field network in the same time slot. Therefore, 289 the backhaul network framework with wireless APs can be considered 290 as a single-channel linear network, which is shown in Figure 4. 292 +---------+ +--------+ +--------+ +--------+ +---------+ 293 | Gateway |--> | AP |--> | AP |--> | AP |--> | Gateway | 294 +---------+ +--------+ +--------+ +--------+ +---------+ 296 Figure 4. A single-channel linear network 298 Therefore, the data stream in industrial field/backhaul network can 299 be seen as equivalent to the data stream in field network, except 300 that each data stream needs to flow through the WIFI. The scheduling 301 process is illustrated as follows: 303 1. Abstract end-to-end data stream in the entire network, and 304 allocate a priority for each stream. 306 2. Establish the delay model of network data stream. If collisions 307 happened between different priority data stream, the low priority 308 data stream will be delayed by high priority, so a model can be 309 built under the worst circumstances that the low-priority data 310 streams impacted by all higher priority data streams. 312 3. Estimate the network schedulability. A data stream is schedulable 313 when the minimum time for the data stream to complete its once 314 transmission task plus the worst delay time caused by higher 315 priority data streams is less than or equal to its deadline, In 316 the current priority allocation scheme, if each data stream is 317 schedulable, the network can be considered as schedulable. If the 318 data stream cannot be scheduled, then try to change the priority 319 allocation scheme and estimate again until a corresponding scheme 320 is found or return no schedulable results. 322 4. Allocate time slot and channel for each data stream. Traverse 323 data streams according to their priorities, and each data stream 324 should allocate link that is about to be released in a time slot. 325 According to the rule that low priority data streams should give 326 way to high priority data streams, the channels can be utilized 327 if it is not unoccupied. However, if collisions happened between 328 data streams of different priority, then the lower priority data 329 stream should be placed in the next time slot until there are no 330 unallocated higher priority data streams. Repeat these steps 331 until the whole network scheduling is completed. 333 The scheduling process is described in Figure 5: 335 +----------+ 336 | Begin | 337 +----------+ 338 | 339 | 340 +---------------------------+ 341 | Initial the priority of | 342 | each data stream | 343 +---------------------------+ 344 |<--------------------------------------+ 345 | | 346 +--------------------+ +------------------------------+ 347 / Traverse every data \ no | If the data stream cannot be | 348 / stream and estimate the\--------->| scheduled, then change the | 349 \ schedulablity according/ | priority allocation scheme | 350 \ to delay model / | and estimate again | 351 +--------------------+ +------------------------------+ 352 | 353 |yes 354 +-----------------------------------+ 355 | Traverse data streams according to| 356 | their priority, each data stream | 357 | should allocate the next link that| 358 | is about to be released in each | 359 | time slot to the greatest extent | 360 +-----------------------------------+ 361 | 362 | 363 +-----------------------------------+ 364 | The spare channels can be utilized| 365 | if there is no collision. If | 366 | collisions happened, then the | 367 | lower priority data stream should | 368 | be placed in the next time slot | 369 +-----------------------------------+ 370 | 371 | 372 +-------+ 373 | End | 374 +-------+ 375 Figure 5. Scheduling of times-slotted industrial backhaul network 377 Further, if the backhaul network can support TDMA mechanism like the 378 industrial field network completely, the deterministic scheduling 379 methods in field network can be applied in industrial field/backhaul 380 networks. 382 For backhaul network using wired technology, time-sensitive network 383 based on Ethernet is preferred for industrial scenarios. Time- 384 sensitive network can provide dedicated slots for scheduled traffic, 385 so above scheduling method can be used in this kind of backhaul 386 network to guarantee the deterministic performance for data flows 387 across field and backhaul networks. 389 4.2. Consider Industrial Backhaul Network as a Black Box 391 In order to solve the deterministic problem of industrial network, 392 backhaul network can be regarded as a black box so that we can only 393 consider its delay impacts and ignore its internal details. 395 When the packet passes through the industrial backhaul network, we 396 can give it a timestamp at the application layer and read it after 397 the transmission is ready to leave the backhaul network. Delay 398 caused in backhaul network can be calculated, and a fitting curve of 399 delay can be obtained by collecting large amount of data. It has 400 been verified experimentally that the delay is concentrated in a 401 numerical range despite its randomness. Therefore, we can estimate 402 the approximate delay time caused by industrial backhaul network. 404 A main scheduling path can be configured according to the average 405 delay of the backhaul network. Some redundant paths should be pre- 406 configured in case the delay of the main path is too high. The 407 scheduling process of industrial field/backhaul network can be 408 divided into three sections, as shown in Figure 6: 410 +--------------------+ +-----------------+ +------------------------+ 411 | Scheduling of | | Delay of | | Scheduling of | 412 |source field subnet |->| backhaul network|->|destination field subnet| 413 | (deterministic) | |(indeterministic)| |( deterministic dynamic)| 414 +--------------------+ +-----------------+ +------------------------+ 415 Period 1 Period 2 Period 3 417 Figure 6. Three periods of scheduling 419 In source field subnet we can apply the deterministic scheduling 420 algorithm of field network to get the time spent by each data stream 421 before entering the source subnet. Then the data stream enters the 422 backhaul network, which will cause indeterministic delay in a 423 numerical range. When the data stream leaves the backhaul network, 424 the timestamp should be parsed. If the deadline is missed, it 425 indicates that the packet has gone through poor network and needs to 426 be retransmitted. If there is free time after leaving the backhaul 427 network, scheduling path can be dynamically selected at downward 428 gateway to get the schedulability of the end-to-end data stream. 430 4.3. Ignore the Delay of Industrial Backhaul Network 432 Since the field network is slow-speed (250 KB/s), while industrial 433 backhaul network is high-speed, if the industrial backhaul networks 434 adopt IEEE 802.11 protocol, gigabit wireless routers supporting IEEE 435 802.11 ac can make the delay of industrial backhaul network quite 436 low. As a result, the joint deterministic scheduling of the entire 437 network only needs to consider the field networks. 439 4.4. Build Delay Model of Industrial Backhaul Network 441 If industrial backhaul network is constructed with IEEE 802.11, the 442 network access delay test model in IEEE 802.11 Distributed 443 Coordination Function (DCF) mode can be established by using Markov 444 chain or queue theory. While the model in IEEE 802.11 Point 445 Coordination Function (PCF) mode can be established based on queue 446 theory. 448 Therefore, the field network needs to build a delay model, while 449 backhaul network follows another delay model, then the total 450 transmission scheduling delay will have certain regularity. The 451 total transmission delay will meet delay requirements with specified 452 probability by scheduling, in other words, the unsuccessful 453 scheduling is acceptable. 455 5. Security Considerations 457 6. IANA Considerations 459 This memo includes no request to IANA. 461 7. References 463 7.1. Normative References 465 7.2. Informative References 467 [IEC62734] 468 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 469 also IEC 62734", 2011, . 473 [IEC62591] 474 IEC, "Industrial Communication Networks - 475 Wireless Communication Network and Communication Profiles 476 - WirelessHART - IEC 62591", 2010, 477 480 [IEC62601] 481 IEC, "Industrial networks - Wireless communication network 482 and communication profiles - WIA-PA - IEC 62601", 2015, < 483 https://webstore.iec.ch/preview/info_iec62601%7Bed2.0%7Db 484 .pdf> 486 [I-D.finn-detnet-problem-statement] 487 Finn, N. and P. Thubert, "Deterministic Networking Problem 488 Statement", draft-finn-detnet-problem-statement-05 (work in 489 progress), March 2016. 491 [I-D.finn-detnet-architecture] 492 Finn, N., Thubert, P., and M. Teener, "Deterministic 493 Networking Architecture", draft-finn-detnet-architecture-08 494 (work in progress), August 2016. 496 [I-D.bas-usecase-detnet] 497 Kaneko, Y., Toshiba and Das, S, "Building Automation Use 498 Cases and Requirements for Deterministic Networking", draft- 499 bas-usecase-detnet-00 (work in progress), October 2015. 501 Authors' Addresses 503 Heng Wang 504 Chongqing University of Posts and Telecommunications 505 2 Chongwen Road 506 Chongqing, 400065 507 China 509 Phone: (86)-23-6248-7845 510 Email: wangheng@cqupt.edu.cn 512 Ping Wang 513 Chongqing University of Posts and Telecommunications 514 2 Chongwen Road 515 Chongqing, 400065 516 China 518 Phone: (86)-23-6246-1061 519 Email: wangping@cqupt.edu.cn 521 Hang Yang 522 Chongqing University of Posts and Telecommunications 523 2 Chongwen Road 524 Chongqing, 400065 525 China 527 Phone: (86)-23-6246-1061 528 Email: 18716322620@163.com