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Thubert 5 Expires: January 17, 2019 Cisco 6 July 16, 2018 8 Deterministic Networking Problem Statement 9 draft-ietf-detnet-problem-statement-06 11 Abstract 13 This paper documents the needs in various industries to establish 14 multi-hop paths for characterized flows with deterministic 15 properties. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at https://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on January 17, 2019. 34 Copyright Notice 36 Copyright (c) 2018 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (https://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. On Deterministic Networking . . . . . . . . . . . . . . . . . 3 53 3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 6 54 3.1. Supported topologies . . . . . . . . . . . . . . . . . . 6 55 3.2. Flow Characterization . . . . . . . . . . . . . . . . . . 6 56 3.3. Centralized Path Computation and Installation . . . . . . 6 57 3.4. Distributed Path Setup . . . . . . . . . . . . . . . . . 7 58 3.5. Duplicated data format . . . . . . . . . . . . . . . . . 8 59 4. Security Considerations . . . . . . . . . . . . . . . . . . . 8 60 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 61 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 62 7. Informative References . . . . . . . . . . . . . . . . . . . 9 63 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 65 1. Introduction 67 The Deterministic Networking Use Cases [I-D.ietf-detnet-use-cases] 68 document illustrates that beyond the classical case of industrial 69 automation and control systems (IACS), there are in fact multiple 70 industries with strong and yet relatively similar needs for 71 deterministic network services with latency guarantees and ultra-low 72 packet loss. 74 The generalization of the needs for more deterministic networks have 75 led to the IEEE 802.1 AVB Task Group becoming the Time-Sensitive 76 Networking (TSN) [IEEE802.1TSNTG] Task Group (TG), with a much- 77 expanded constituency from the industrial and vehicular markets. 79 Along with this expansion, the networks in consideration are becoming 80 larger and structured, requiring deterministic forwarding beyond the 81 LAN boundaries. For instance, IACS segregates the network along the 82 broad lines of the Purdue Enterprise Reference Architecture (PERA) 83 [ISA95], typically using deterministic local area networks for level 84 2 control systems, whereas public infrastructures such as Electricity 85 Automation require deterministic properties over the Wide Area. The 86 realization is now coming that the convergence of IT and Operational 87 Technology (OT) networks requires Layer-3, as well as Layer-2, 88 capabilities. 90 While the initial user base has focused almost entirely on Ethernet 91 physical media and Ethernet-based bridging protocol (from several 92 Standards Development Organizations), the need for Layer-3 expressed 93 above, must not be confined to Ethernet and Ethernet-like media, and 94 while such media must be encompassed by any useful DetNet 95 architecture, cooperation between IETF and other SDOs must not be 96 limited to IEEE or IEEE 802. Furthermore, while the work completed 97 and ongoing in other SDOs, and in IEEE 802 in particular, provide an 98 obvious starting point for a DetNet architecture, we must not assume 99 that these other SDOs' work confines the space in which the DetNet 100 architecture progresses. 102 The properties of deterministic networks will have specific 103 requirements for the use of routed networks to support these 104 applications and a new model must be proposed to integrate 105 determinism in IT technology. The proposed model should enable a 106 fully scheduled operation orchestrated by a central controller, and 107 may support a more distributed operation with probably lesser 108 capabilities. In any fashion, the model should not compromise the 109 ability of a network to keep carrying the sorts of traffic that is 110 already carried today in conjunction with new, more deterministic 111 flows. 113 Once the abstract model is agreed upon, the IETF will need to specify 114 the signaling elements to be used to establish a path and the tagging 115 elements to be used identify the flows that are to be forwarded along 116 that path. The IETF will also need to specify the necessary 117 protocols, or protocol additions, based on relevant IETF 118 technologies, to implement the selected model. 120 As a result of this work, it will be possible to establish a multi- 121 hop path over the IP or MPLS network, for a particular flow with 122 given timing and precise throughput requirements, and carry this 123 particular flow along the multi-hop path with such characteristics as 124 low latency and ultra-low jitter, reordering and/or replication and 125 elimination of packets over non-congruent paths for a higher delivery 126 ratio, and/or zero congestion loss, regardless of the amount of other 127 flows in the network. 129 Depending on the network capabilities and on the current state, 130 requests to establish a path by an end-node or a network management 131 entity may be granted or rejected, an existing path may be moved or 132 removed, and DetNet flows exceeding their contract may face packet 133 declassification and drop. 135 2. On Deterministic Networking 137 The Internet is not the only digital network that has grown 138 dramatically over the last 30-40 years. Video and audio 139 entertainment, and control systems for machinery, manufacturing 140 processes, and vehicles are also ubiquitous, and are now based almost 141 entirely on digital technologies. Over the past 10 years, engineers 142 in these fields have come to realize that significant advantages in 143 both cost and in the ability to accelerate growth can be obtained by 144 basing all of these disparate digital technologies on packet 145 networks. 147 The goals of Deterministic Networking (DetNet) are to enable the 148 migration of applications with critical timing and reliability issues 149 that currently use special-purpose fieldbus technologies (HDMI, 150 CANbus, ProfiBus, etc... even RS-232!) to packet technologies in 151 general, and the Internet Protocol in particular, and to support both 152 these new applications, and existing packet network applications, 153 over the same physical network. 155 Considerable experience ([ODVA]/[EIP],[AVnu], 156 [Profinet],[HART],[IEC62439], [ISA100.11a] and [WirelessHART], 157 etc...) has shown that these applications need a some or all of a 158 suite of features that includes: 160 1. Time synchronization of all host and network nodes (routers and/ 161 or bridges), accurate to something between 10 nanoseconds and 10 162 microseconds, depending on the application. 164 2. Support for Deterministic packet flows that: 166 * Can be unicast or multicast; 168 * Need absolute guarantees of minimum and maximum latency end- 169 to-end across the network; sometimes a tight jitter is 170 required as well; 172 * Need a packet loss ratio beyond the classical range for a 173 particular medium, in the range of 10^-9 to 10^-12, or better, 174 on Ethernet, and in the order of 10^-5 in Wireless Sensor Mesh 175 Networks; 177 * Can, in total, absorb more than half of the network's 178 available bandwidth (that is, massive over-provisioning is 179 ruled out as a solution); 181 * Cannot suffer throttling, congestion feedback, or any other 182 network-imposed transmission delay, although the flows can be 183 meaningfully characterized either by a fixed, repeating 184 transmission schedule, or by a maximum bandwidth and packet 185 size; 187 3. Multiple methods to schedule, shape, limit, and otherwise control 188 the transmission of critical packets at each hop through the 189 network data plane; 191 4. Robust defenses against misbehaving hosts, routers, or bridges, 192 both in the data and control planes, with guarantees that a 193 critical flow within its guaranteed resources cannot be affected 194 by other flows whatever the pressures on the network; 196 5. One or more methods to reserve resources in bridges and routers 197 to carry these flows. 199 Time synchronization techniques need not be addressed by an IETF 200 Working Group; there are a number of standards available for this 201 purpose, including IEEE 1588, IEEE 802.1AS, and more. 203 The multicast, latency, loss ratio, and non-throttling needs are made 204 necessary by the algorithms employed by the applications. They are 205 not simply the transliteration of fieldbus needs to a packet-based 206 fieldbus simulation, but reflect fundamental mathematics of the 207 control of a physical system. 209 With classical forwarding latency- and loss-sensitive packets across 210 a network, interactions among different critical flows introduce 211 fundamental uncertainties in delivery schedules. The details of the 212 queuing, shaping, and scheduling algorithms employed by each bridge 213 or router to control the output sequence on a given port affect the 214 detailed makeup of the output stream, e.g. how finely a given flow's 215 packets are mixed among those of other flows. 217 This, in turn, has a strong effect on the buffer requirements, and 218 hence the latency guarantees deliverable, by the next bridge or 219 router along the path. For this reason, the IEEE 802.1 Time- 220 Sensitive Networking Task Group has defined a new set of queuing, 221 shaping, and scheduling algorithms that enable each bridge or router 222 to compute the exact number of buffers to be allocated for each flow 223 or class of flows. 225 Robustness is a common need for networking protocols, but plays a 226 more important part in real-time control networks, where expensive 227 equipment, and even lives, can be lost due to misbehaving equipment. 229 Reserving resources before packet transmission is the one fundamental 230 shift in the behavior of network applications that is impossible to 231 avoid. In the first place, a network cannot deliver finite latency 232 and practically zero packet loss to an arbitrarily high offered load. 233 Secondly, achieving practically zero packet loss for un-throttled 234 (though bandwidth limited) flows means that bridges and routers have 235 to dedicate buffer resources to specific flows or to classes of 236 flows. The requirements of each reservation have to be translated 237 into the parameters that control each host's, bridge's, and router's 238 queuing, shaping, and scheduling functions and delivered to the 239 hosts, bridges, and routers. 241 3. Problem Statement 243 3.1. Supported topologies 245 In some use cases, the end point which run the application is 246 involved in the deterministic networking operation, for instance by 247 controlling certain aspects of its throughput such as rate or precise 248 time of emission. In that case, the deterministic path is end-to-end 249 from application host to application host. 251 On the other end, the deterministic portion of a path may be a tunnel 252 between and ingress and an egress router. In any case, routers and 253 switches in between should not need to be aware whether the path is 254 end-to-end of a tunnel. 256 While it is clear that DetNet does not aim at setting up 257 deterministic paths over the global Internet, there is still a lack 258 of clarity on the limits of a domain where a deterministic path can 259 be set up. These limits may depend in the technology that is used to 260 set the path up, whether it is centralized or distributed. 262 3.2. Flow Characterization 264 Deterministic forwarding can only apply on flows with well-defined 265 characteristics such as periodicity and burstiness. Before a path 266 can be established to serve them, the expression of those 267 characteristics, and how the network can serve them, for instance in 268 shaping and forwarding operations, must be specified. 270 3.3. Centralized Path Computation and Installation 272 A centralized routing model, such as provided with a Path Computation 273 Element (PCE) (see [RFC4655]), enables global and per-flow 274 optimizations. The model is attractive but a number of issues are 275 left to be solved. In particular: 277 o whether and how the path computation can be installed by 1) an end 278 device or 2) a Network Management entity, 280 o and how the path is set up, either by installing state at each hop 281 with a direct interaction between the forwarding device and the 282 PCE, or along a path by injecting a source-routed request at one 283 end of the path following classical Traffic Engineering (TE) 284 models. 286 To enable a centralized model, DetNet should produce a description of 287 the high level interaction and data models to: 289 o report the topology and device capabilities to the central 290 controller; 292 o establish a direct interface between the centralized PCE to each 293 device under its control in order to enable a vertical signaling 295 o request a path setup for a new flow with particular 296 characteristics over the service interface and control it through 297 its life cycle; 299 o support for life cycle management for a path 300 (instantiate/modify/update/delete) 302 o support for adaptability to cope with various events such as loss 303 of a link, etc... 305 o expose the status of the path to the end devices (UNI interface) 307 o provide additional reliability through redundancy, in particular 308 with packet replication and elimination; 310 o indicate the flows and packet sequences in-band with the flows; 312 3.4. Distributed Path Setup 314 Whether a distributed alternative without a PCE can be valuable could 315 be studied as well. Such an alternative could for instance inherit 316 from the Resource ReSerVation Protocol [RFC3209] (RSVP-TE) flows. 317 But the focus of the work should be to deliver the centralized 318 approach first. 320 To enable a RSVP-TE like functionality, the following steps would 321 take place: 323 1. Neighbors and their capabilities are discovered and exposed to 324 compute a path that fits the DetNet constraints, typically of 325 latency, time precision and resource availability. 327 2. A constrained path is calculated with an improved version of 328 Constrained Shortest Path First (CSPF) that is aware of DetNet. 330 3. The path may be installed using a control protocol such as RSVP- 331 TE, associated with flow identification, per-hop behavior such as 332 Packet Replication and Elimination, and blocked resources. In 333 that case, traffic flows can be transported through an MPLS-TE 334 tunnel, using the reserved resources for this flow at each hop. 336 3.5. Duplicated data format 338 In some cases the duplication and elimination of packets over non- 339 congruent paths is required to achieve a sufficiently high delivery 340 ratio to meet application needs. In these cases, a small number of 341 packet formats and supporting protocols are required (preferably, 342 just one) to serialize the packets of a DetNet stream at one point in 343 the network, replicate them at one or more points in the network, and 344 discard duplicates at one or more other points in the network, 345 including perhaps the destination host. Using an existing solution 346 would be preferable to inventing a new one. 348 4. Security Considerations 350 Security in the context of Deterministic Networking has an added 351 dimension; the time of delivery of a packet can be just as important 352 as the contents of the packet, itself. A man-in-the-middle attack, 353 for example, can impose, and then systematically adjust, additional 354 delays into a link, and thus disrupt or subvert a real-time 355 application without having to crack any encryption methods employed. 356 See [RFC7384] for an exploration of this issue in a related context. 358 Typical control networks today rely on complete physical isolation to 359 prevent rogue access to network resources. DetNet enables the 360 virtualization of those networks over a converged IT/OT 361 infrastructure. Doing so, DetNet introduces an additional risk that 362 flows interact and interfere with one another as they share physical 363 resources such as Ethernet trunks and radio spectrum. The 364 requirement is that there is no possible data leak from and into a 365 deterministic flow, and in a more general fashion there is no 366 possible influence whatsoever from the outside on a deterministic 367 flow. The expectation is that physical resources are effectively 368 associated with a given flow at a given point of time. In that 369 model, Time Sharing of physical resources becomes transparent to the 370 individual flows which have no clue whether the resources are used by 371 other flows at other times. 373 The overall security of a deterministic system must cover: 375 o the protection of the signaling protocol 377 o the authentication and authorization of the controlling nodes 378 including plug-and-play participating end systems. 380 o the identification and shaping of the flows 381 o the isolation of flows from leakage and other influences from any 382 activity sharing physical resources. 384 5. IANA Considerations 386 This document does not require an action from IANA. 388 6. Acknowledgments 390 The authors wish to thank Lou Berger, Stewart Bryant, Janos Farkas, 391 Andrew Malis, Jouni Korhonen, Erik Nordmark, George Swallow, Rudy 392 Klecka, Anca Zamfir, David Black, Thomas Watteyne, Shitanshu Shah, 393 Kiran Makhijani, Craig Gunther, Rodney Cummings, Wilfried Steiner, 394 Marcel Kiessling, Karl Weber, Ethan Grossman, Patrick Wetterwald, 395 Subha Dhesikan, Rudy Klecka and Pat Thaler for their various 396 contributions to this work. 398 7. Informative References 400 [AVnu] http://www.avnu.org/, "The AVnu Alliance tests and 401 certifies devices for interoperability, providing a simple 402 and reliable networking solution for AV network 403 implementation based on the IEEE Audio Video Bridging 404 (AVB) and Time-Sensitive Networking (TSN) standards.". 406 [EIP] http://www.odva.org/, "EtherNet/IP provides users with the 407 network tools to deploy standard Ethernet technology (IEEE 408 802.3 combined with the TCP/IP Suite) for industrial 409 automation applications while enabling Internet and 410 enterprise connectivity data anytime, anywhere.", 411 . 415 [HART] www.hartcomm.org, "Highway Addressable Remote Transducer, 416 a group of specifications for industrial process and 417 control devices administered by the HART Foundation". 419 [I-D.ietf-detnet-use-cases] 420 Grossman, E., "Deterministic Networking Use Cases", draft- 421 ietf-detnet-use-cases-17 (work in progress), June 2018. 423 [IEC62439] 424 IEC, "Industrial communication networks - High 425 availability automation networks - Part 3: Parallel 426 Redundancy Protocol (PRP) and High-availability Seamless 427 Redundancy (HSR) - IEC62439-3", 2012, 428 . 430 [IEEE802.1TSNTG] 431 IEEE Standards Association, "IEEE 802.1 Time-Sensitive 432 Networks Task Group", 2013, 433 . 435 [ISA100.11a] 436 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 437 also IEC 62734", 2011, < http://www.isa100wci.org/en- 438 US/Documents/PDF/3405-ISA100-WirelessSystems-Future-broch- 439 WEB-ETSI.aspx>. 441 [ISA95] ANSI/ISA, "Enterprise-Control System Integration Part 1: 442 Models and Terminology", 2000, 443 . 445 [ODVA] http://www.odva.org/, "The organization that supports 446 network technologies built on the Common Industrial 447 Protocol (CIP) including EtherNet/IP.". 449 [Profinet] 450 http://us.profinet.com/technology/profinet/, "PROFINET is 451 a standard for industrial networking in automation.", 452 . 454 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 455 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 456 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 457 . 459 [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation 460 Element (PCE)-Based Architecture", RFC 4655, 461 DOI 10.17487/RFC4655, August 2006, 462 . 464 [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in 465 Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, 466 October 2014, . 468 [WirelessHART] 469 www.hartcomm.org, "Industrial Communication Networks - 470 Wireless Communication Network and Communication Profiles 471 - WirelessHART - IEC 62591", 2010. 473 Authors' Addresses 474 Norman Finn 475 Huawei Technologies Co. Ltd 476 3755 Avocado Blvd. 477 PMB 436 478 La Mesa, California 91941 479 US 481 Phone: +1 925 980 6430 482 Email: norman.finn@mail01.huawei.com 484 Pascal Thubert 485 Cisco Systems 486 Village d'Entreprises Green Side 487 400, Avenue de Roumanille 488 Batiment T3 489 Biot - Sophia Antipolis 06410 490 FRANCE 492 Phone: +33 497 232 634 493 Email: pthubert@cisco.com