idnits 2.17.00 (12 Aug 2021) /tmp/idnits23127/draft-pthubert-raw-problem-statement-04.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 (23 October 2019) is 934 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'Function' is mentioned on line 242, but not defined == Outdated reference: draft-ietf-6tisch-architecture has been published as RFC 9030 == Outdated reference: draft-ietf-detnet-architecture has been published as RFC 8655 == Outdated reference: A later version (-04) exists of draft-bernardos-raw-use-cases-00 == Outdated reference: draft-ietf-detnet-data-plane-framework has been published as RFC 8938 == Outdated reference: A later version (-03) exists of draft-mirsky-detnet-ip-oam-00 Summary: 0 errors (**), 0 flaws (~~), 7 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RAW P. Thubert, Ed. 3 Internet-Draft Cisco Systems 4 Intended status: Informational G.Z. Papadopoulos 5 Expires: 25 April 2020 IMT Atlantique 6 23 October 2019 8 Reliable and Available Wireless Problem Statement 9 draft-pthubert-raw-problem-statement-04 11 Abstract 13 Due to uncontrolled interferences, including the self-induced 14 multipath fading, deterministic networking can only be approached on 15 wireless links. The radio conditions may change -way- faster than a 16 centralized routing can adapt and reprogram, in particular when the 17 controller is distant and connectivity is slow and limited. RAW 18 separates the routing time scale at which a complex path is 19 recomputed from the forwarding time scale at which the forwarding 20 decision is taken for an individual packet. RAW operates at the 21 forwarded time scale. The RAW problem is to decide, within the 22 redundant solutions that are proposed by the routing, which will be 23 used for each individual packet to provide a DetNet service while 24 minimizing the waste of resources. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at https://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on 25 April 2020. 43 Copyright Notice 45 Copyright (c) 2019 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 50 license-info) in effect on the date of publication of this document. 51 Please review these documents carefully, as they describe your rights 52 and restrictions with respect to this document. Code Components 53 extracted from this document must include Simplified BSD License text 54 as described in Section 4.e of the Trust Legal Provisions and are 55 provided without warranty as described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 61 3. Use Cases and Requirements Served . . . . . . . . . . . . . . 5 62 4. Routing Time Scale vs. Forwarding Time Scale . . . . . . . . 5 63 5. Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . 7 64 6. Related Work at The IETF . . . . . . . . . . . . . . . . . . 7 65 7. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 8 66 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 67 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 68 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 10.1. Normative References . . . . . . . . . . . . . . . . . . 9 70 10.2. Informative References . . . . . . . . . . . . . . . . . 10 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 73 1. Introduction 75 Bringing determinism in a packet network means eliminating the 76 statistical effects of multiplexing that result in probabilistic 77 jitter and loss. This can be approached with a tight control of the 78 physical resources to maintain the amount of traffic within a 79 budgetted volume of data per unit of time that fits the physical 80 capabilities of the underlying technology, and the use of time-shared 81 resources (bandwidth and buffers) per circuit, and/or by shaping and/ 82 or scheduling the packets at every hop. 84 Wireless networks operate on a shared medium where uncontrolled 85 interference, including the self-induced multipath fading, adds 86 another dimension to the statistical effects that affect the 87 delivery. Scheduling transmissions can alleviate those effects by 88 leveraging diversity in the spatial, time, code, and frequency 89 domains, and provide a Reliable and Available service while 90 preserving energy and optimizing the use of the shared spectrum. 92 Deterministic Networking is an attempt to mostly eliminate packet 93 loss for a committed bandwidth with a guaranteed worst-case end-to- 94 end latency, even when co-existing with best-effort traffic in a 95 shared network. This innovation is enabled by recent developments in 96 technologies including IEEE 802.1 TSN (for Ethernet LANs) and IETF 97 DetNet (for wired IP networks). It is getting traction in various 98 industries including manufacturing, online gaming, professional A/V, 99 cellular radio and others, making possible many cost and performance 100 optimizations. 102 The DetNet architecture [DetNet-ARCH] is composed of three planes: a 103 (User)Application Plane, a Controller Plane, and a Network Plane. 104 Reliable and Available Wireless (RAW) extends DetNet to focus on 105 issues that are mostly a concern on wireless links, and inherits the 106 architecture and the planes. A RAW Network Plane is thus a Network 107 Plane inherited by RAW from DetNet. 109 RAW networking aims at providing highly available and reliable end- 110 to-end performances in a network with scheduled wireless segments. 111 Uncontrolled interference and transmission obstacles may impede the 112 transmission, and techniques such as beamforming with Multi-User MIMO 113 can only alleviate some of those issues, so the term "deterministic" 114 is usually not associated with short range radios, in particular in 115 the ISM band. This uncertainty places limits to the amount of 116 traffic that can be transmitted on a link while conforming to a RAW 117 Service Level Agreement (SLA) that may vary rapidly. 119 The wireless and wired media are fundamentally different at the 120 physical level, and while the generic Problem Statement for DetNet 121 applies to the wired as well as the wireless medium, the methods to 122 achieve RAW will differ from those used to support time-sensitive 123 networking over wires, as a RAW solution will need to address less 124 consistent transmissions, energy conservation and shared spectrum 125 efficiency. 127 The development of RAW technologies has been lagging behind 128 deterministic efforts for wired systems both at the IEEE and the 129 IETF. But recent efforts at the IEEE and 3GPP indicate that wireless 130 is finally catching up at the lower layer and that it is now possible 131 for the IETF to extend DetNet for wireless segments that are capable 132 of scheduled wireless transmissions. 134 The intent for RAW is to provide DetNet elements that are specialized 135 for short range radios. From this inheritance, RAW stays agnostic to 136 the radio layer underneath though the capability to schedule 137 transmissions is assumed. How the PHY is programmed to do so, and 138 whether the radio is single-hop or meshed, are unknown at the IP 139 layer and not part of the RAW abstraction. 141 Still, in order to focus on real-worlds issues and assert the 142 feasibility of the proposed capabilities, RAW will focus on selected 143 technologies that can be scheduled at the lower layers: IEEE Std. 145 802.15.4 timeslotted channel hopping (TSCH), 3GPP 5G ultra-reliable 146 low latency communications (URLLC), IEEE 802.11ax/be where 802.11be 147 is extreme high throughput (EHT), and L-band Digital Aeronautical 148 Communications System (LDACS). See [RAW-TECHNOS] for more. 150 The establishment of a path is not in-scope for RAW. It may be the 151 product of a centralized Controller Plane as described for DetNet. 152 As opposed to wired networks, the action of installing a path over a 153 set of wireless links may be very slow relative to the speed at which 154 the radio conditions vary, and it makes sense in the wireless case to 155 provide redundant forwarding solutions along a complex path and to 156 leave it to the Network Plane to select which of those forwarding 157 solutions are to be used for a given packet based on the current 158 conditions. 160 RAW distinguishes the longer time scale at which routes are computed 161 from the the shorter forwarding time scale where per-packet decisions 162 are made. RAW operates at the forwarding time scale on one DetNet 163 flow over one path that is preestablished and installed by means 164 outside of the scope of RAW. The scope of the RAW WG comprises 165 Network plane protocol elements such as OAM and in-band control to 166 improve the RAW operation at the Service and at the forwarding sub- 167 layers, e.g., controlling whether to use packet replication, Hybrid 168 ARQ and coding, with a constraint to limit the use of redundancy when 169 it is really needed, e.g., when a spike of loss is observed. This is 170 discussed in more details in Section 4 and the next sections. 172 2. Terminology 174 RAW reuses terminology defined for DetNet in [DetNet-ARCH], e.g., 175 PREOF for Packet Replication, Elimination and Ordering Functions. 177 RAW also reuses terminology defined for 6TiSCH in [6TiSCH-ARCH] such 178 as Track. 6TiSCH defined the term Track for that complex path with 179 associated PAREO operations. 181 RAW defines the following terms: 183 PAREO: Packet (hybrid) ARQ, Replication, Elimination and Ordering. 184 PAREO is a superset Of DetNet's PREOF that includes radio-specific 185 techniques such as short range broadcast, MUMIMO, constructive 186 interference and overhearing, which can be leveraged separately or 187 combined to increase the reliability. 189 Flapping: In the context of RAW, a link flaps when the wireles 190 connectivity is interrupted for short transient times, typically 191 of a subsecond duration. 193 This document reuses terms that are well-defined in the context of 194 automation to networking and packet delivery, in particular for 195 reliability and availability. In the context of the RAW work, they 196 are defined as follows: 198 Reliability: Reliability is a measure of the probability that an 199 item will perform its intended function for a specified interval 200 under stated conditions. For RAW, the service that is expected is 201 delivery within a bounded latency and a failure is when the packet 202 is either lost or delivered too late. RAW expresses reliability 203 in terms of Mean Time Between Failure (MTBF) and Maximum 204 Consecutive Failures (MCF). 206 Availability: Availability is a measure of the relative amount of 207 time where a path operates in stated condition, in other words 208 (uptime)/(uptime+downtime). Because a serial wireless path may 209 not be good enough to provide the required availability, and even 210 2 parallel paths may not be over a longer period of time, the RAW 211 availability implies a path that is a lot more complex than what 212 DetNet typically envisages (a Track). 214 3. Use Cases and Requirements Served 216 [RFC8578] presents a number of wireless use cases including Wireless 217 for Industrial Applications. [RAW-USE-CASES] adds a number of use 218 cases that demonstrate the need for RAW capabilities in Pro-Audio, 219 gaming and robotics. 221 4. Routing Time Scale vs. Forwarding Time Scale 223 With DetNet, the end-to-end routing can be centralized and can reside 224 outside the network. In wireless, and in particular in a wireless 225 mesh, the path to the controller that performs the route computation 226 and maintenance expensive in terms of critical resources such as air 227 time and energy. 229 Reaching to the routing computation can also be slow in regards to 230 the speed of events that affect the forwarding operation at the radio 231 layer. Due to the cost and latency to perform a route computation, 232 the controller plane is not expected to be sensitive/reactive to 233 transient changes. The abstraction of a link at the routing level is 234 expected to use statistical operational metrics that aggregate the 235 behavior of a link over long periods of time, and represent its 236 availability as shades of gray as opposed to either up or down. 238 +----------------+ 239 | Controller | 240 | (PCE) | 241 | [Routing ] | 242 | [Function] | 243 +----------------+ 244 ^ 245 | 246 Slow 247 | 248 _-._-._-._-._-._-. | ._-._-._-._-._-._-._-._-._-._-._-._- 249 _-._-._-._-._-._-._-. | _-._-._-._-._-._-._-._-._-._-._-._- 250 | 251 Expensive 252 .... | ....... 253 .... . | . ..... 254 .... v ... 255 .. A-------B-------C---D .. 256 ... / \ / / \ .. 257 . I ----M-------N--zzz-- E .. 258 .. \ \ / / . 259 .. P--zzz--Q----------R .. 260 .. .. 261 ....... ... 262 ............... 263 zzz = flapping now 265 Figure 1: Time Scales 267 In the case of wireless, the changes that affect the forwarding 268 decision can happen frequently and often for short durations, e.g., a 269 mobile object moves between a transmitter and a receiver, and will 270 cancel the line of sight transmission for a few seconds, or a radar 271 measures the depth of a pool and interferes on a particular channel 272 for a split second. 274 There is thus a desire to separate the long term computation of the 275 route and the short term forwarding decision. In such a model, the 276 routing operation computes a complex Track that enables multiple Non- 277 Equal Cost Multi-Path (N-ECMP) forwarding solutions, and leaves it to 278 the forwarding plane to make the per-packet decision of which of 279 these possibilities should be used. 281 In the case of wires, the concept is known in traffic engineering 282 where an alternate path can be used upon the detection of a failure 283 in the main path, e.g., using OAM in MPLS-TP or BFD over a collection 284 of SD-WAN tunnels. RAW formalizes a forwarding time scale that is an 285 order(s) of magnitude shorter than the controler plane routing time 286 scale, and separates the protocols and metrics that are used at both 287 scales. Routing can operate on long term statistics such as delivery 288 ratio over minutes to hours, but as a first approximation can ignore 289 flapping. On the other hand, the RAW forwarding decision is made at 290 packet speed, and uses information that must be pertinent at the 291 present time for the current transmission. 293 5. Prerequisites 295 A prerequisite to the RAW work is that an end-to-end routing function 296 computes a complex sub-topology along which forwarding can happen 297 between a source and one or more destinations. For 6TiSCH, this is a 298 Track. The concept of Track is specified in the 6TiSCH Architecture 299 [6TiSCH-ARCH]. Tracks provide a high degree of redundancy and 300 diversity and enable DetNet PREOF, end-to-end network coding, and 301 possibly radio-specific abstracted techniques such as ARQ, 302 overhearing, frequency diversity, time slotting, and possibly others. 304 How the routing operation computes the Track is out of scope for RAW. 305 The scope of the RAW operation is one Track, and the goal of the RAW 306 operation is to optimize the use of the Track at the forwarding 307 timescale to maintain the expected service while optimizing the usage 308 of constrained resources such as energy and spectrum. 310 Another prerequisite is that an IP link can be established over the 311 radio with some guarantees in terms of service reliability, e.g., it 312 can be relied upon to transmit a packet within a bounded latency and 313 provides a guaranteed BER/PDR outside rare but existing transient 314 outage windows that can last from split seconds to minutes. The 315 radio layer can be programmed with abstract parameters, and can 316 return an abstract view of the state of the Link to help forwarding 317 decision (think DLEP from MANET). In the layered approach, how the 318 radio manages its PHY layer is out of control and out of scope. 319 Whether it is single hop or meshed is also unknown and out of scope. 321 6. Related Work at The IETF 323 RAW intersects with protocols or practices in development at the IETF 324 as follows: 326 * The Dynamic Link Exchange Protocol (DLEP) [RFC8175] from [MANET] 327 can be leveraged at each hop to derive generic radio metrics 328 (e.g., based on LQI, RSSI, queueing delays and ETX) on individual 329 hops. 331 * Operations, Administration and Maintenance (OAM) work at [DetNet] 332 such as [DetNet-IP-OAM] for the case of the IP Data Plane observes 333 the state of DetNet paths, typically MPLS and IPv6 pseudowires 335 [DetNet-DP-FW], in the direction of the traffic. RAW needs 336 feedback that flows on the reverse path and gathers instantaneous 337 values from the radio receivers at each hop to inform back the 338 source and replicating relays so they can make optimized 339 forwarding decisions. The work named ICAN may be related as well. 341 * [BFD] detect faults in the path between an ingress and an egress 342 forwarding engines, but is unaware of the complexity of a path 343 with replication, and expects bidirectionality. BFD considers 344 delivery as success whereas with RAW the bounded latency can be as 345 important as the delivery itself. 347 * [SPRING] and [BIER] define in-band signaling that influences the 348 routing when decided at the head-end on the path. There's already 349 one RAW-related draft at BIER [BIER-PREF] more may follow. RAW 350 will need new in-band signaling when the decision is distributed, 351 e.g., required chances of reliable delivery to destination within 352 latency. This signaling enables relays to tune retries and 353 replication to meet the required SLA. 355 * [CCAMP] defines protocol-independent metrics and parameters 356 (measurement attributes) for describing links and paths that are 357 required for routing and signaling in technology-specific 358 networks. RAW would be a source of requirements for CCAMP to 359 define metrics that are significant to the focus radios. 361 7. Problem Statement 363 Within a large routed topology, the routing operation builds a 364 particular complex Track with one source and one or more 365 destinations; within the Track, packets may follow different paths 366 and may be subject to RAW forwarding operations that include 367 replication, elimination, retries, overhearing and reordering. 369 The RAW forwarding decisions include the selection of points of 370 replication and elimination, how many retries can take place, and a 371 limit of validity for the packet beyond which the packet should be 372 destroyed rather than forwarded uselessly further down the Track. 374 The decision to apply the RAW techniques must be done quickly, and 375 depends on a very recent and precise knowledge of the forwarding 376 conditions within the complex Track. There is a need for an 377 observation method to provide the RAW forwarding plane with the 378 specific knowledge of the state of the Track for the type of flow of 379 interest (e.g., for a QoS level of interest). To observe the whole 380 Track in quasi real time, RAW will consider existing tools such as 381 L2-triggers, DLEP, BFD and in-band and out-of-band OAM. 383 One possible way of making the RAW forwarding decisions is to make 384 them all at the ingress and express them in-band in the packet, which 385 requires new loose or strict Hop-by-hop signaling. To control the 386 RAW forwarding operation along a Track for the individual packets, 387 RAW may leverage and extend known techniques such as DetNet tagging, 388 Segment Routing (SRv6) or BIER-TE such as done with [BIER-PREF]. 390 An alternate way is to enable each forwarding node to make the RAW 391 forwarding decisions for a packet on its own, based on its knowledge 392 of the expectation (timeliness and reliability) for that packet and a 393 recent observation of the rest of the way across the possible paths 394 within the Track. Information about the service should be placed in 395 the packet and matched with the forwarding node's capabilities and 396 policies. 398 In either case, a per-flow state is installed in all intermediate 399 nodes to recognize the flow and determine the forwarding policy to be 400 applied. 402 8. Security Considerations 404 This document is a problem statement and does not propose a solution 405 that could yield security issues. 407 9. IANA Considerations 409 This document has no IANA actions. 411 10. References 413 10.1. Normative References 415 [6TiSCH-ARCH] 416 Thubert, P., "An Architecture for IPv6 over the TSCH mode 417 of IEEE 802.15.4", Work in Progress, Internet-Draft, 418 draft-ietf-6tisch-architecture-27, 18 October 2019, 419 . 422 [DetNet-ARCH] 423 Finn, N., Thubert, P., Varga, B., and J. Farkas, 424 "Deterministic Networking Architecture", Work in Progress, 425 Internet-Draft, draft-ietf-detnet-architecture-13, 6 May 426 2019, . 429 [RAW-TECHNOS] 430 Thubert, P., Cavalcanti, D., Vilajosana, X., and C. 432 Schmitt, "Reliable and Available Wireless Technologies", 433 Work in Progress, Internet-Draft, draft-thubert-raw- 434 technologies-03, 1 July 2019, 435 . 438 [RAW-USE-CASES] 439 Papadopoulos, G., Thubert, P., Theoleyre, F., and C. 440 Bernardos, "RAW use cases", Work in Progress, Internet- 441 Draft, draft-bernardos-raw-use-cases-00, 5 July 2019, 442 . 445 [RFC8175] Ratliff, S., Jury, S., Satterwhite, D., Taylor, R., and B. 446 Berry, "Dynamic Link Exchange Protocol (DLEP)", RFC 8175, 447 DOI 10.17487/RFC8175, June 2017, 448 . 450 [RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases", 451 RFC 8578, DOI 10.17487/RFC8578, May 2019, 452 . 454 10.2. Informative References 456 [BFD] IETF, "Bidirectional Forwarding Detection", October 2019, 457 . 459 [BIER] IETF, "Bit Indexed Explicit Replication", October 2019, 460 . 462 [BIER-PREF] 463 Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER- 464 TE extensions for Packet Replication and Elimination 465 Function (PREF) and OAM", Work in Progress, Internet- 466 Draft, draft-thubert-bier-replication-elimination-03, 3 467 March 2018, . 470 [CCAMP] IETF, "Common Control and Measurement Plane", October 471 2019, 472 . 474 [DetNet] IETF, "Deterministic Networking", October 2019, 475 . 477 [DetNet-DP-FW] 478 Varga, B., Farkas, J., Berger, L., Fedyk, D., Malis, A., 479 Bryant, S., and J. Korhonen, "DetNet Data Plane 480 Framework", Work in Progress, Internet-Draft, draft-ietf- 481 detnet-data-plane-framework-02, 13 September 2019, 482 . 485 [DetNet-IP-OAM] 486 Mirsky, G. and M. Chen, "Operations, Administration and 487 Maintenance (OAM) for Deterministic Networks (DetNet) with 488 IP Data Plane", Work in Progress, Internet-Draft, draft- 489 mirsky-detnet-ip-oam-00, 8 July 2019, 490 . 493 [MANET] IETF, "Mobile Ad hoc Networking", October 2019, 494 . 496 [SPRING] IETF, "Source Packet Routing in Networking", October 2019, 497 . 499 Authors' Addresses 501 Pascal Thubert (editor) 502 Cisco Systems, Inc 503 Building D, 45 Allee des Ormes - BP1200 504 06254 MOUGINS - Sophia Antipolis 505 France 507 Phone: +33 497 23 26 34 508 Email: pthubert@cisco.com 510 Georgios Z. Papadopoulos 511 IMT Atlantique 512 Office B00 - 114A, 2 Rue de la Chataigneraie 513 35510 Cesson-Sevigne - Rennes 514 France 516 Phone: +33 299 12 70 04 517 Email: georgios.papadopoulos@imt-atlantique.fr