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Thubert 5 Expires: December 8, 2018 Cisco 6 June 6, 2018 8 Deterministic Networking Problem Statement 9 draft-ietf-detnet-problem-statement-04 11 Abstract 13 This paper documents the needs in various industries to establish 14 multi-hop paths for characterized flows with deterministic properties 15 . 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 December 8, 2018. 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 . . . . . . . . . . . . . . . . . . . . . . . 11 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 network, for a particular flow with given timing 122 and precise throughput requirements, and carry this particular flow 123 along the multi-hop path with such characteristics as low latency and 124 ultra-low jitter, duplication and elimination of packets over non- 125 congruent paths for a higher delivery ratio, and/or zero congestion 126 loss, regardless of the amount of other flows in the network. 128 Depending on the network capabilities and on the current state, 129 requests to establish a path by an end-node or a network management 130 entity may be granted or rejected, an existing path may be moved or 131 removed, and DetNet flows exceeding their contract may face packet 132 declassification and drop. 134 2. On Deterministic Networking 136 The Internet is not the only digital network that has grown 137 dramatically over the last 30-40 years. Video and audio 138 entertainment, and control systems for machinery, manufacturing 139 processes, and vehicles are also ubiquitous, and are now based almost 140 entirely on digital technologies. Over the past 10 years, engineers 141 in these fields have come to realize that significant advantages in 142 both cost and in the ability to accelerate growth can be obtained by 143 basing all of these disparate digital technologies on packet 144 networks. 146 The goals of Deterministic Networking are to enable the migration of 147 applications with critical timing and reliability issues that 148 currently use special-purpose fieldbus technologies (HDMI, CANbus, 149 ProfiBus, etc... even RS-232!) to packet technologies in general, and 150 the Internet Protocol in particular, and to support both these new 151 applications, and existing packet network applications, over the same 152 physical network. 154 Considerable experience ([ODVA]/[EIP],[AVnu], 155 [Profinet],[HART],[IEC62439], [ISA100.11a] and [WirelessHART], 156 etc...) has shown that these applications need a some or all of a 157 suite of features that includes: 159 1. Time synchronization of all host and network nodes (routers and/ 160 or bridges), accurate to something between 10 nanoseconds and 10 161 microseconds, depending on the application. 163 2. Support for Deterministic packet flows that: 165 * Can be unicast or multicast; 167 * Need absolute guarantees of minimum and maximum latency end- 168 to-end across the network; sometimes a tight jitter is 169 required as well; 171 * Need a packet loss ratio beyond the classical range for a 172 particular medium, in the range of 10^-9 to 10^-12, or better, 173 on Ethernet, and in the order of 10^-5 in Wireless Sensor Mesh 174 Networks; 176 * Can, in total, absorb more than half of the network's 177 available bandwidth (that is, massive over-provisioning is 178 ruled out as a solution); 180 * Cannot suffer throttling, congestion feedback, or any other 181 network-imposed transmission delay, although the flows can be 182 meaningfully characterized either by a fixed, repeating 183 transmission schedule, or by a maximum bandwidth and packet 184 size; 186 3. Multiple methods to schedule, shape, limit, and otherwise control 187 the transmission of critical packets at each hop through the 188 network data plane; 190 4. Robust defenses against misbehaving hosts, routers, or bridges, 191 both in the data and control planes, with guarantees that a 192 critical flow within its guaranteed resources cannot be affected 193 by other flows whatever the pressures on the network; 195 5. One or more methods to reserve resources in bridges and routers 196 to carry these flows. 198 Time synchronization techniques need not be addressed by an IETF 199 Working Group; there are a number of standards available for this 200 purpose, including IEEE 1588, IEEE 802.1AS, and more. 202 The multicast, latency, loss ratio, and non-throttling needs are made 203 necessary by the algorithms employed by the applications. They are 204 not simply the transliteration of fieldbus needs to a packet-based 205 fieldbus simulation, but reflect fundamental mathematics of the 206 control of a physical system. 208 With classical forwarding latency- and loss-sensitive packets across 209 a network, interactions among different critical flows introduce 210 fundamental uncertainties in delivery schedules. The details of the 211 queuing, shaping, and scheduling algorithms employed by each bridge 212 or router to control the output sequence on a given port affect the 213 detailed makeup of the output stream, e.g. how finely a given flow's 214 packets are mixed among those of other flows. 216 This, in turn, has a strong effect on the buffer requirements, and 217 hence the latency guarantees deliverable, by the next bridge or 218 router along the path. For this reason, the IEEE 802.1 Time- 219 Sensitive Networking Task Group has defined a new set of queuing, 220 shaping, and scheduling algorithms that enable each bridge or router 221 to compute the exact number of buffers to be allocated for each flow 222 or class of flows. 224 Robustness is a common need for networking protocols, but plays a 225 more important part in real-time control networks, where expensive 226 equipment, and even lives, can be lost due to misbehaving equipment. 228 Reserving resources before packet transmission is the one fundamental 229 shift in the behavior of network applications that is impossible to 230 avoid. In the first place, a network cannot deliver finite latency 231 and practically zero packet loss to an arbitrarily high offered load. 232 Secondly, achieving practically zero packet loss for un-throttled 233 (though bandwidth limited) flows means that bridges and routers have 234 to dedicate buffer resources to specific flows or to classes of 235 flows. The requirements of each reservation have to be translated 236 into the parameters that control each host's, bridge's, and router's 237 queuing, shaping, and scheduling functions and delivered to the 238 hosts, bridges, and routers. 240 3. Problem Statement 242 3.1. Supported topologies 244 In some use cases, the end point which run the application is 245 involved in the deterministic networking operation, for instance by 246 controlling certain aspects of its throughput such as rate or precise 247 time of emission. In that case, the deterministic path is end-to-end 248 from application host to application host. 250 On the other end, the deterministic portion of a path may be a tunnel 251 between and ingress and an egress router. In any case, routers and 252 switches in between should not need to be aware whether the path is 253 end-to-end of a tunnel. 255 While it is clear that DetNet does not aim at setting up 256 deterministic paths over the global Internet, there is still a lack 257 of clarity on the limits of a domain where a deterministic path can 258 be set up. These limits may depend in the technology that is used to 259 set the path up, whether it is centralized or distributed. 261 3.2. Flow Characterization 263 Deterministic forwarding can only apply on flows with well-defined 264 characteristics such as periodicity and burstiness. Before a path 265 can be established to serve them, the expression of those 266 characteristics, and how the network can serve them, for instance in 267 shaping and forwarding operations, must be specified. 269 3.3. Centralized Path Computation and Installation 271 A centralized routing model, such as provided with a PCE, enables 272 global and per-flow optimizations. The model is attractive but a 273 number of issues are left to be solved. In particular: 275 o whether and how the path computation can be installed by 1) an end 276 device or 2) a Network Management entity, 278 o and how the path is set up, either by installing state at each hop 279 with a direct interaction between the forwarding device and the 280 PCE, or along a path by injecting a source-routed request at one 281 end of the path following classical Traffic Engineering (TE) 282 models. 284 To enable a centralized model, DetNet should produce the complete SDN 285 architecture with describes at a high level the interaction and data 286 models to: 288 o report the topology and device capabilities to the central 289 controller; 291 o establish a direct interface between the centralized PCE to each 292 device under its control in order to enable a vertical signaling 294 o request a path setup for a new flow with particular 295 characteristics over the service interface and control it through 296 its life cycle; 298 o support for life cycle management for a path 299 (instantiate/modify/update/delete) 301 o support for adaptability to cope with various events such as loss 302 of a link, etc... 304 o expose the status of the path to the end devices (UNI interface) 306 o provide additional reliability through redundancy, in particular 307 with packet replication and elimination; 309 o indicate the flows and packet sequences in-band with the flows; 311 3.4. Distributed Path Setup 313 Whether a distributed alternative without a PCE can be valuable could 314 be studied as well. Such an alternative could for instance inherit 315 from the Resource ReSerVation Protocol [RFC3209] (RSVP-TE) flows. 316 But the focus of the work should be to deliver the centralized 317 approach first. 319 To enable a RSVP-TE like functionality, the following steps would 320 take place: 322 1. Neighbors and their capabilities are discovered and exposed to 323 compute a path that fits the DetNet constraints, typically of 324 latency, time precision and resource availability. 326 2. A constrained path is calculated with an improved version of CSPF 327 that is aware of DetNet. 329 3. The path may be installed using a control protocol such as RSVP- 330 TE, associated with flow identification, per-hop behavior such as 331 Packet Replication and Elimination, blocked resources, and flow 332 timing information. Alternatively, the routing and flow 333 information may be placed in-band in the packet, e.g., using 334 Segment Routing, in which case the packet is routed along a 335 prescribed source route path following forwarding indications 336 that are present in the packet. 338 4. Traffic flows are transported through the MPLS-TE tunnel, using 339 the reserved resources for this flow at each hop. 341 3.5. Duplicated data format 343 In some cases the duplication and elimination of packets over non- 344 congruent paths is required to achieve a sufficiently high delivery 345 ratio to meet application needs. In these cases, a small number of 346 packet formats and supporting protocols are required (preferably, 347 just one) to serialize the packets of a DetNet stream at one point in 348 the network, replicate them at one or more points in the network, and 349 discard duplicates at one or more other points in the network, 350 including perhaps the destination host. Using an existing solution 351 would be preferable to inventing a new one. 353 4. Security Considerations 355 Security in the context of Deterministic Networking has an added 356 dimension; the time of delivery of a packet can be just as important 357 as the contents of the packet, itself. A man-in-the-middle attack, 358 for example, can impose, and then systematically adjust, additional 359 delays into a link, and thus disrupt or subvert a real-time 360 application without having to crack any encryption methods employed. 361 See [RFC7384] for an exploration of this issue in a related context. 363 Typical control networks today rely on complete physical isolation to 364 prevent rogue access to network resources. DetNet enables the 365 virtualization of those networks over a converged IT/OT 366 infrastructure. Doing so, DetNet introduces an additional risk that 367 flows interact and interfere with one another as they share physical 368 resources such as Ethernet trunks and radio spectrum. The 369 requirement is that there is no possible data leak from and into a 370 deterministic flow, and in a more general fashion there is no 371 possible influence whatsoever from the outside on a deterministic 372 flow. The expectation is that physical resources are effectively 373 associated with a given flow at a given point of time. In that 374 model, Time Sharing of physical resources becomes transparent to the 375 individual flows which have no clue whether the resources are used by 376 other flows at other times. 378 The overall security of a deterministic system must cover: 380 o the protection of the signaling protocol 382 o the authentication and authorization of the controlling nodes 383 o the identification and shaping of the flows 385 o the isolation of flows from leakage and other influences from any 386 activity sharing physical resources. 388 5. IANA Considerations 390 This document does not require an action from IANA. 392 6. Acknowledgments 394 The authors wish to thank Lou Berger, Stewart Bryant, Janos Farkas, 395 Andrew Malis, Jouni Korhonen, Erik Nordmark, George Swallow, Rudy 396 Klecka, Anca Zamfir, David Black, Thomas Watteyne, Shitanshu Shah, 397 Kiran Makhijani, Craig Gunther, Rodney Cummings, Wilfried Steiner, 398 Marcel Kiessling, Karl Weber, Ethan Grossman, Patrick Wetterwald, 399 Subha Dhesikan, Rudy Klecka and Pat Thaler for their various 400 contributions to this work. 402 7. Informative References 404 [AVnu] http://www.avnu.org/, "The AVnu Alliance tests and 405 certifies devices for interoperability, providing a simple 406 and reliable networking solution for AV network 407 implementation based on the IEEE Audio Video Bridging 408 (AVB) and Time-Sensitive Networking (TSN) standards.". 410 [EIP] http://www.odva.org/, "EtherNet/IP provides users with the 411 network tools to deploy standard Ethernet technology (IEEE 412 802.3 combined with the TCP/IP Suite) for industrial 413 automation applications while enabling Internet and 414 enterprise connectivity data anytime, anywhere.", 415 . 419 [HART] www.hartcomm.org, "Highway Addressable Remote Transducer, 420 a group of specifications for industrial process and 421 control devices administered by the HART Foundation". 423 [I-D.ietf-detnet-use-cases] 424 Grossman, E., "Deterministic Networking Use Cases", draft- 425 ietf-detnet-use-cases-16 (work in progress), May 2018. 427 [IEC62439] 428 IEC, "Industrial communication networks - High 429 availability automation networks - Part 3: Parallel 430 Redundancy Protocol (PRP) and High-availability Seamless 431 Redundancy (HSR) - IEC62439-3", 2012, 432 . 434 [IEEE802.1TSNTG] 435 IEEE Standards Association, "IEEE 802.1 Time-Sensitive 436 Networks Task Group", 2013, 437 . 439 [ISA100.11a] 440 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 441 also IEC 62734", 2011, < http://www.isa100wci.org/en- 442 US/Documents/PDF/3405-ISA100-WirelessSystems-Future-broch- 443 WEB-ETSI.aspx>. 445 [ISA95] ANSI/ISA, "Enterprise-Control System Integration Part 1: 446 Models and Terminology", 2000, 447 . 449 [ODVA] http://www.odva.org/, "The organization that supports 450 network technologies built on the Common Industrial 451 Protocol (CIP) including EtherNet/IP.". 453 [Profinet] 454 http://us.profinet.com/technology/profinet/, "PROFINET is 455 a standard for industrial networking in automation.", 456 . 458 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 459 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 460 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 461 . 463 [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in 464 Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, 465 October 2014, . 467 [WirelessHART] 468 www.hartcomm.org, "Industrial Communication Networks - 469 Wireless Communication Network and Communication Profiles 470 - WirelessHART - IEC 62591", 2010. 472 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