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Thubert 5 Expires: March 20, 2018 Cisco 6 September 16, 2017 8 Deterministic Networking Problem Statement 9 draft-ietf-detnet-problem-statement-02 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 March 20, 2018. 34 Copyright Notice 36 Copyright (c) 2017 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 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 that use special-purpose fieldbus technologies (HDMI, 148 CANbus, ProfiBus, etc... even RS-232!) to packet technologies in 149 general, and the Internet Protocol in particular, and to support both 150 these new applications, and existing packet network applications, 151 over the same physical network. 153 Considerable experience ([ODVA]/[EIP],[AVnu], 154 [Profinet],[HART],[IEC62439], [ISA100.11a] and [WirelessHART], 155 etc...) has shown that these applications need a some or all of a 156 suite of features that includes: 158 1. Time synchronization of all host and network nodes (routers and/ 159 or bridges), accurate to something between 10 nanoseconds and 10 160 microseconds, depending on the application. 162 2. Support for critical packet flows that: 164 * Can be unicast or multicast; 166 * Need absolute guarantees of minimum and maximum latency end- 167 to-end across the network; sometimes a tight jitter is 168 required as well; 170 * Need a packet loss ratio beyond the classical range for a 171 particular medium, in the range of 1.0e-9 to 1.0e-12, or 172 better, on Ethernet, and in the order of 1.0e-5 in Wireless 173 Sensor mesh Networks; 175 * Can, in total, absorb more than half of the network's 176 available bandwidth (that is, massive over-provisioning is 177 ruled out as a solution); 179 * Cannot suffer throttling, congestion feedback, or any other 180 network-imposed transmission delay, although the flows can be 181 meaningfully characterized either by a fixed, repeating 182 transmission schedule, or by a maximum bandwidth and packet 183 size; 185 3. Multiple methods to schedule, shape, limit, and otherwise control 186 the transmission of critical packets at each hop through the 187 network data plane; 189 4. Robust defenses against misbehaving hosts, routers, or bridges, 190 both in the data and control planes, with guarantees that a 191 critical flow within its guaranteed resources cannot be affected 192 by other flows whatever the pressures on the network; 194 5. One or more methods to reserve resources in bridges and routers 195 to carry these flows. 197 Time synchronization techniques need not be addressed by an IETF 198 Working Group; there are a number of standards available for this 199 purpose, including IEEE 1588, IEEE 802.1AS, and more. 201 The multicast, latency, loss ratio, and non-throttling needs are made 202 necessary by the algorithms employed by the applications. They are 203 not simply the transliteration of fieldbus needs to a packet-based 204 fieldbus simulation, but reflect fundamental mathematics of the 205 control of a physical system. 207 With classical forwarding latency- and loss-sensitive packets across 208 a network, interactions among different critical flows introduce 209 fundamental uncertainties in delivery schedules. The details of the 210 queuing, shaping, and scheduling algorithms employed by each bridge 211 or router to control the output sequence on a given port affect the 212 detailed makeup of the output stream, e.g. how finely a given flow's 213 packets are mixed among those of other flows. 215 This, in turn, has a strong effect on the buffer requirements, and 216 hence the latency guarantees deliverable, by the next bridge or 217 router along the path. For this reason, the IEEE 802.1 Time- 218 Sensitive Networking Task Group has defined a new set of queuing, 219 shaping, and scheduling algorithms that enable each bridge or router 220 to compute the exact number of buffers to be allocated for each flow 221 or class of flows. 223 Robustness is a common need for networking protocols, but plays a 224 more important part in real-time control networks, where expensive 225 equipment, and even lives, can be lost due to misbehaving equipment. 227 Reserving resources before packet transmission is the one fundamental 228 shift in the behavior of network applications that is impossible to 229 avoid. In the first place, a network cannot deliver finite latency 230 and practically zero packet loss to an arbitrarily high offered load. 231 Secondly, achieving practically zero packet loss for un-throttled 232 (though bandwidth limited) flows means that bridges and routers have 233 to dedicate buffer resources to specific flows or to classes of 234 flows. The requirements of each reservation have to be translated 235 into the parameters that control each host's, bridge's, and router's 236 queuing, shaping, and scheduling functions and delivered to the 237 hosts, bridges, and routers. 239 3. Problem Statement 241 3.1. Supported topologies 243 In some use cases, the end point which run the application is 244 involved in the deterministic networking operation, for instance by 245 controlling certain aspects of its throughput such as rate or precise 246 time of emission. In that case, the deterministic path is end-to-end 247 from application host to application host. 249 On the other end, the deterministic portion of a path may be a tunnel 250 between and ingress and an egress router. In any case, routers and 251 switches in between should not need to be aware whether the path is 252 end-to-end of a tunnel. 254 While it is clear that DetNet does not aim at setting up 255 deterministic paths over the global Internet, there is still a lack 256 of clarity on the limits of a domain where a deterministic path can 257 be set up. These limits may depend in the technology that is used to 258 seu th epath up, whether it is centralized or distributed. 260 3.2. Flow Characterization 262 Deterministic forwarding can only apply on flows with well-defined 263 characteristics such as periodicity and burstiness. Before a path 264 can be established to serve them, the expression of those 265 characteristics, and how the network can serve them, for instance in 266 shaping and forwarding operations, must be specified. 268 3.3. Centralized Path Computation and Installation 270 A centralized routing model, such as provided with a PCE, enables 271 global and per-flow optimizations. The model is attractive but a 272 number of issues are left to be solved. In particular: 274 o whether and how the path computation can be installed by 1) an end 275 device or 2) a Network Management entity, 277 o and how the path is set up, either by installing state at each hop 278 with a direct interaction between the forwarding device and the 279 PCE, or along a path by injecting a source-routed request at one 280 end of the path following classical Traffic Engineering (TE) 281 models. 283 To enable a centralized model, DetNet should produce the complete SDN 284 architecture with describes at a high level the interaction and data 285 models to: 287 o report the topology and device capabilities to the central 288 controller; 290 o establish a direct interface between the centralized PCE to each 291 device under its control in order to enable a vertical signaling 293 o request a path setup for a new flow with particular 294 characteristics over the service interface and control it through 295 its life cycle; 297 o support for life cycle management for a path 298 (instantiate/modify/update/delete) 300 o support for adaptability to cope with various events such as loss 301 of a link, etc... 303 o expose the status of the path to the end devices (UNI interface) 305 o provide additional reliability through redundancy, in particular 306 with packet replication and elimination; 308 o indicate the flows and packet sequences in-band with the flows; 310 3.4. Distributed Path Setup 312 Whether a distributed alternative without a PCE can be valuable could 313 be studied as well. Such an alternative could for instance inherit 314 from the Resource ReSerVation Protocol [RFC3209] (RSVP-TE) flows. 315 But the focus of the work should be to deliver the centralized 316 approach first. 318 To enable a RSVP-TE like functionality, the following steps would 319 take place: 321 1. Neighbors and their capabilities are discovered and exposed to 322 compute a path that fits the DetNet constraints, typically of 323 latency, time precision and resource availability. 325 2. A constrained path is calculated with an improved version of CSPF 326 that is aware of DetNet. 328 3. The path is installed using RSVP-TE, associated with flow 329 identification, per-hop behavior such as replication and 330 elimination, blocked resources, and flow timing information. 332 4. Traffic flows are transported through the MPLS-TE tunnel, using 333 the reserved resources for this flow at each hop. 335 3.5. Duplicated data format 337 In some cases the duplication and elimination of packets over non- 338 congruent paths is required to achieve a sufficiently high delivery 339 ratio to meet application needs. In these cases, a small number of 340 packet formats and supporting protocols are required (preferably, 341 just one) to serialize the packets of a DetNet stream at one point in 342 the network, replicate them at one or more points in the network, and 343 discard duplicates at one or more other points in the network, 344 including perhaps the destination host. Using an existing solution 345 would be preferable to inventing a new one. 347 4. Security Considerations 349 Security in the context of Deterministic Networking has an added 350 dimension; the time of delivery of a packet can be just as important 351 as the contents of the packet, itself. A man-in-the-middle attack, 352 for example, can impose, and then systematically adjust, additional 353 delays into a link, and thus disrupt or subvert a real-time 354 application without having to crack any encryption methods employed. 355 See [RFC7384] for an exploration of this issue in a related context. 357 Typical control networks today rely on complete physical isolation to 358 prevent rogue access to network resources. DetNet enables the 359 virtualization of those networks over a converged IT/OT 360 infrastructure. Doing so, DetNet introduces an additional risk that 361 flows interact and interfere with one another as they share physical 362 resources such as Ethernet trunks and radio spectrum. The 363 requirement is that there is no possible data leak from and into a 364 deterministic flow, and in a more general fashion there is no 365 possible influence whatsoever from the outside on a deterministic 366 flow. The expectation is that physical resources are effectively 367 associated with a given flow at a given point of time. In that 368 model, Time Sharing of physical resources becomes transparent to the 369 individual flows which have no clue whether the resources are used by 370 other flows at other times. 372 Security must cover: 374 o the protection of the signaling protocol 376 o the authentication and authorization of the controlling nodes 378 o the identification and shaping of the flows 380 o the isolation of flows from leakage and other influences from any 381 activity sharing physical resources. 383 5. IANA Considerations 385 This document does not require an action from IANA. 387 6. Acknowledgments 389 The authors wish to thank Lou Berger, Jouni Korhonen, Erik Nordmark, 390 George Swallow, Rudy Klecka, Anca Zamfir, David Black, Thomas 391 Watteyne, Shitanshu Shah, Craig Gunther, Rodney Cummings, Wilfried 392 Steiner, Marcel Kiessling, Karl Weber, Ethan Grossman, Patrick 393 Wetterwald, Subha Dhesikan, Rudy Klecka and Pat Thaler for their 394 various contribution to this work. 396 7. Informative References 398 [AVnu] http://www.avnu.org/, "The AVnu Alliance tests and 399 certifies devices for interoperability, providing a simple 400 and reliable networking solution for AV network 401 implementation based on the IEEE Audio Video Bridging 402 (AVB) and Time-Sensitive Networking (TSN) standards.". 404 [EIP] http://www.odva.org/, "EtherNet/IP provides users with the 405 network tools to deploy standard Ethernet technology (IEEE 406 802.3 combined with the TCP/IP Suite) for industrial 407 automation applications while enabling Internet and 408 enterprise connectivity data anytime, anywhere.", 409 . 413 [HART] www.hartcomm.org, "Highway Addressable Remote Transducer, 414 a group of specifications for industrial process and 415 control devices administered by the HART Foundation". 417 [I-D.ietf-detnet-use-cases] 418 Grossman, E., Gunther, C., Thubert, P., Wetterwald, P., 419 Raymond, J., Korhonen, J., Kaneko, Y., Das, S., Zha, Y., 420 Varga, B., Farkas, J., Goetz, F., Schmitt, J., Vilajosana, 421 X., Mahmoodi, T., Spirou, S., and P. Vizarreta, 422 "Deterministic Networking Use Cases", draft-ietf-detnet- 423 use-cases-12 (work in progress), April 2017. 425 [IEC62439] 426 IEC, "Industrial communication networks - High 427 availability automation networks - Part 3: Parallel 428 Redundancy Protocol (PRP) and High-availability Seamless 429 Redundancy (HSR) - IEC62439-3", 2012, 430 . 432 [IEEE802.1TSNTG] 433 IEEE Standards Association, "IEEE 802.1 Time-Sensitive 434 Networks Task Group", 2013, 435 . 437 [ISA100.11a] 438 ISA/IEC, "ISA100.11a, Wireless Systems for Automation, 439 also IEC 62734", 2011, < http://www.isa100wci.org/en- 440 US/Documents/PDF/3405-ISA100-WirelessSystems-Future-broch- 441 WEB-ETSI.aspx>. 443 [ISA95] ANSI/ISA, "Enterprise-Control System Integration Part 1: 444 Models and Terminology", 2000, 445 . 447 [ODVA] http://www.odva.org/, "The organization that supports 448 network technologies built on the Common Industrial 449 Protocol (CIP) including EtherNet/IP.". 451 [Profinet] 452 http://us.profinet.com/technology/profinet/, "PROFINET is 453 a standard for industrial networking in automation.", 454 . 456 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., 457 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP 458 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, 459 . 461 [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in 462 Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, 463 October 2014, . 465 [WirelessHART] 466 www.hartcomm.org, "Industrial Communication Networks - 467 Wireless Communication Network and Communication Profiles 468 - WirelessHART - IEC 62591", 2010. 470 Authors' Addresses 472 Norman Finn 473 Huawei 474 3101 Rio Way 475 Spring Valley, California 91977 476 US 478 Phone: +1 925 980 6430 479 Email: norman.finn@mail01.huawei.com 480 Pascal Thubert 481 Cisco Systems 482 Village d'Entreprises Green Side 483 400, Avenue de Roumanille 484 Batiment T3 485 Biot - Sophia Antipolis 06410 486 FRANCE 488 Phone: +33 4 97 23 26 34 489 Email: pthubert@cisco.com