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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'IEEE802154-2015' is mentioned on line 396, but not defined == Outdated reference: draft-ietf-6tisch-architecture has been published as RFC 9030 == Outdated reference: draft-ietf-detnet-architecture has been published as RFC 8655 == Outdated reference: A later version (-10) exists of draft-ietf-roll-nsa-extension-01 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RAW G. Papadopoulos, Ed. 3 Internet-Draft R. Koutsiamanis 4 Intended status: Standards Track N. Montavont 5 Expires: December 22, 2019 IMT Atlantique 6 P. Thubert 7 Cisco 8 June 20, 2019 10 Exploiting Packet Replication and Elimination in Complex Tracks in LLNs 11 draft-papadopoulos-raw-pareo-reqs-00 13 Abstract 15 The Packet Replication and Elimination (PRE) mechanism duplicates 16 data packets into several paths in the network to increase 17 reliability and provide low jitter. PRE may be used to complement 18 layer-2 Automatic Repeat reQuest (ARQ) and receiver-end Ordering to 19 form the PAREO functions. Over a wireless medium, this technique can 20 take advantage of communication Overhearing, when parallel 21 transmissions over two adjacent paths are scheduled. This document 22 presents the concept and details the required changes to the current 23 specifications that will be necessary to enable the PAREO functions. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on December 22, 2019. 42 Copyright Notice 44 Copyright (c) 2019 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 61 3. Tracks . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 62 3.1. Tracks Overview . . . . . . . . . . . . . . . . . . . . . 3 63 3.2. Complex Tracks . . . . . . . . . . . . . . . . . . . . . 3 64 4. Packet Replication and Elimination principles . . . . . . . . 3 65 4.1. Packet Replication . . . . . . . . . . . . . . . . . . . 4 66 4.2. Packet Elimination . . . . . . . . . . . . . . . . . . . 5 67 4.3. Promiscuous Overhearing . . . . . . . . . . . . . . . . . 5 68 5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 69 5.1. Requirements Related to Alternative Parent Selection . . 6 70 5.2. Requirements Related to Propagated Information . . . . . 6 71 5.3. Requirements Related to Promiscuous Overhearing . . . . . 7 72 5.4. Requirements Related to Packet Elimination . . . . . . . 8 73 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 74 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 75 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 8.1. Informative references . . . . . . . . . . . . . . . . . 8 77 8.2. Other Informative References . . . . . . . . . . . . . . 9 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 80 1. Introduction 82 This draft describes industrial use cases which require deterministic 83 flows over wireless multi-hop paths. 85 The RAW use cases explicitly do not propose any specific solution or 86 design for the RAW architecture or protocols. These are the subjects 87 of other RAW drafts. The RAW use cases are not considered to be 88 concrete requirements by the RAW Working Group. 90 The industrial use cases covered in this draft are professional 91 audio, wireless for industrial applications and amusement parks. 93 2. Terminology 95 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 96 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 97 document are to be interpreted as described in [RFC2119]. 99 3. Tracks 101 3.1. Tracks Overview 103 The 6TiSCH architecture introduces the concept of Tracks in 6TiSCH 104 Architecture [I-D.ietf-6tisch-architecture]. A simple track is 105 composed of a sequence of cells (a combination of a transmitter, a 106 receiver and a given channel offset) to ensure the transmission of a 107 single packet from a source node to a destination node across a 108 multihop path. 110 3.2. Complex Tracks 112 A Complex Track is designed as a directed acyclic graph from a source 113 node towards a destination node to support multi-path forwarding, as 114 introduced in 6TiSCH Architecture [I-D.ietf-6tisch-architecture]. By 115 employing DetNet [I-D.ietf-detnet-architecture] Packet Replication 116 and Elimination (PRE) functions, several paths may be computed, and 117 these paths may be more or less independent. For example, a complex 118 Track may branch off and rejoin over non-congruent paths (branches). 120 Some more details for Deterministic Network PRE techniques are 121 presented in the following Section. 123 4. Packet Replication and Elimination principles 125 In a nutshell, PRE establishes several paths in a network to provide 126 redundancy and parallel transmissions to bound the end-to-end delay 127 to traverse the network. Optionally, promiscuous listening between 128 paths is possible, such that the nodes on one path may overhear 129 transmissions along the other path. Considering the scenario shown 130 in Figure 1, many different paths are possible for S to reach R. A 131 simple way to benefit from this topology could be to use the two 132 independent paths via nodes A, C, E and via B, D, F. But more 133 complex paths are possible by interleaving transmissions from the 134 lower level of the path to the upper level. 136 PRE may also take advantage of the shared properties of the wireless 137 medium to compensate for the potential loss that is incurred with 138 radio transmissions. For instance, when the source sends to A, B may 139 listen also and get a second chance to receive the frame without an 140 additional transmission. Note that B would not have to listen if it 141 already received that particular frame at an earlier timeslot in a 142 dedicated transmission towards B. 144 (A) (C) (E) 146 source (S) (R) (root) 148 (B) (D) (F) 150 Figure 1: A Typical Ladder Shape with Two Parallel Paths Toward the 151 Destination 153 The PRE model can be implemented in both centralized and distributed 154 scheduling approaches. In the centralized approach, a Path 155 Computation Element (PCE) scheduler calculates the routes and 156 schedules the communication among the nodes along a circuit such as a 157 Label switched path. In the distributed approach, each node selects 158 its route to the destination, typically using a source routing 159 header. In both cases, at each node in the paths, a default parent 160 and alternative parent(s) should be selected to set up complex 161 tracks. 163 In the following Subsections, all the required operations defined by 164 PRE, namely, Alternative Path Selection, Packet Replication, Packet 165 Elimination and Promiscuous Overhearing, are described. 167 4.1. Packet Replication 169 The objective of PRE is to provide deterministic networking 170 properties: high reliability and bounded latency. To achieve this 171 goal, determinism in every hop of the forwarding paths MUST be 172 guaranteed. By employing a Packet Replication procedure, each node 173 forwards a copy of each data packet to multiple parents: its Default 174 Parent (DP) and multiple Alternative Parents (APs). To do so, each 175 node (i.e., source and intermediate node) transmits the data packet 176 multiple times in unicast to each parent. For instance, in Figure 2, 177 the source node S is transmitting the packet to both parents, nodes A 178 and B, in two different timeslots within the same TSCH slotframe. An 179 example TSCH schedule is shown in Figure 3. Thus, the packet 180 eventually obtains parallel paths to the destination. 182 ===> (A) => (C) => (E) === 183 // \\// \\// \\ 184 source (S) //\\ //\\ (R) (root) 185 \\ // \\ // \\ // 186 ===> (B) => (D) => (F) === 188 Figure 2: Packet Replication: S transmits twice the same data packet, 189 to its DP (A) and to its AP (B). 191 Timeslot 192 +---------++------+------+------+------+------+------+------+ 193 | Channel || 0 | 1 | 2 | 3 | 4 | 5 | 6 | 194 +---------++======+======+======+======+======+======+======+ 195 | 0 || S->A | S->B | B->C | B->D | C->F | E->R | F->R | 196 +---------++------+------+------+------+------+------+------+ 197 | 1 || | A->C | A->D | C->E | D->E | D->F | | 198 +---------++------+------+------+------+------+------+------+ 200 Figure 3: Packet Replication: Sample TSCH schedule 202 4.2. Packet Elimination 204 The replication operation increases the traffic load in the network, 205 due to packet duplications. Thus, a Packet Elimination operation 206 SHOULD be applied at each RPL DODAG level to reduce the unnecessary 207 traffic. To this aim, once a node receives the first copy of a data 208 packet, it discards the subsequent copies. Because the first copy 209 that reaches a node is the one that matters, it is the only copy that 210 will be forwarded upward. Then, once a node performs the Packet 211 Elimination operation, it will proceed with the Packet Replication 212 operation to forward the packet toward the RPL DODAG Root. 214 4.3. Promiscuous Overhearing 216 Considering that the wireless medium is broadcast by nature, any 217 neighbor of a transmitter may overhear a transmission. By employing 218 the Promiscuous Overhearing operation, a DP and some AP(s) eventually 219 have more chances to receive the data packets. In Figure 4, when 220 node A is transmitting to its DP (node C), the AP (node D) and its 221 sibling (node B) may decode this data packet as well. As a result, 222 by employing corellated paths, a node may have multiple opportunities 223 to receive a given data packet. This feature not only enhances the 224 end-to-end reliability but also it reduces the end-to-end delay and 225 increases energy efficiency. 227 ===> (A) ====> (C) ====> (E) ==== 228 // ^ | \\ \\ 229 source (S) | | \\ (R) (root) 230 \\ | v \\ // 231 ===> (B) ====> (D) ====> (F) ==== 233 Figure 4: Unicast to DP with Overhearing: by employing Promiscuous 234 Overhearing, DP, AP and the sibling nodes have more opportunities to 235 receive the same data packet. 237 5. Requirements 239 5.1. Requirements Related to Alternative Parent Selection 241 To perform the Packet Replication procedure, it is necessary to 242 define the Alternative Parent(s) and, consequently, the path to the 243 destination node, for each node in the wireless network. An AP can 244 be selected in many different ways, and is dependent on the 245 implementation. 247 The requirements are: 249 Req1.1: The routing protocol SHOULD be extended to allow for each 250 node to select AP(s) in addition to the DP. This enables 251 packet replication to multiple parents. 253 Req1.2: Considering that the Packet Replication procedure 254 significantly increases the traffic in a network, when 255 proposing solutions for Alternative Parent Selection, they 256 should be efficient enough to mitigate the potential 257 uncontrolled packet duplications. 259 Req1.3: The topology SHOULD be defined when proposing solutions for 260 Alternative Parent Selection. For instance, the ladder 261 topology should be defined explicitly e.g., number of parallel 262 paths, density. 264 5.2. Requirements Related to Propagated Information 266 For Alternative Parent(s) selection, nodes MAY need additional 267 information about the network topology. This draft does not 268 prescribe the information required for AP selcetion or how it is to 269 be propagated to the nodes that need to select AP(s). TODO: To be 270 discussed. 272 The requirement is: 274 Req2.1: Nodes MUST have a way of receiving the required information 275 for efficient Alternative Parent Selection. 277 As an example, it is possible to use and extend the RPL [RFC6550] 278 DODAG Information Object (DIO) Control Message to allow nodes to 279 propagate information about themselves to potential children. For 280 instance, "RPL DAG Metric Container (MC) Node State and Attribute 281 (NSA) object type extension" [I-D.ietf-roll-nsa-extension] focuses on 282 extending the DAG Metric Container [RFC6551] by defining a new type- 283 length-value (TLV), entitled Parent Set (PS) which can be carried in 284 the Node State and Attribute (NSA) object. 286 5.3. Requirements Related to Promiscuous Overhearing 288 As stated previously, to further increase the network reliability and 289 to achieve deterministic packet deliveries at the destination node, 290 Promiscuous Overhearing can be considered. 292 As it is described in BCP 210 [RFC8180], in TSCH mode, the data 293 frames are transmitted in unicast mode and are acknowledged by the 294 receiving neighbor. To perform the promiscuous overhearing 295 procedure, there SHOULD be an option for the transmitted frames, 296 i.e., in unicast, to be overheard by the potential neighborhood node. 298 Destination address filtering is performed at the Medium Access 299 Control (MAC) layer. For example, according to IEEE std. 802.15.4 300 [IEEE802154-2015], a node receiving a packet with a destination 301 address different than its own and different to 0xFF discards the 302 packet. A change is needed to be able to receive packets whose 303 destination address is neither multicast nor the overhearing node's 304 MAC address. 306 The requirements are: 308 Req3.1: The MAC implementation MUST be able to disable MAC address 309 filtering to accept the overheard frame. 311 Req3.2: The 6top Protocol [RFC8480] specification MUST be extended 312 to indicate disabling MAC filtering in a receiving cell. This 313 can be achieved by reserving a bit in the 6P CellOptions Bitmap 314 (Section 6.2.6 [RFC8480]) for this purpose. 316 Req3.3: The overhearing node can be configured with the timeslot set 317 to shared reception, thus, there will be no acknowledgement 318 from it. However, there is the security issue that needs to be 319 considered. Since the overhearing case implies that it is not 320 possible to have per-pair keying, there MUST be a key that the 321 overhearing node will be aware of. Hence, the Minimal Security 322 Framework for 6TiSCH [I-D.ietf-6tisch-architecture] 323 specification should consider such a scenario. 325 5.4. Requirements Related to Packet Elimination 327 By employing Packet Replication, the wireless network is expected to 328 also perform Packet Elimination to restrict the number of the 329 duplicated packets, i.e., the unnecessary traffic. As per the 6TiSCH 330 Architecture [I-D.ietf-6tisch-architecture], 6TiSCH has no position 331 about how the sequence numbers would be tagged in the packet. 333 The requirement is: 335 Req4.1: To perform Packet Elimination the packet copies MUST contain 336 a sequence number which allows identifying the copies. 338 6. Security Considerations 340 TODO. 342 7. IANA Considerations 344 This document has no IANA considerations. 346 8. References 348 8.1. Informative references 350 [I-D.ietf-6tisch-architecture] 351 Thubert, P., "An Architecture for IPv6 over the TSCH mode 352 of IEEE 802.15.4", draft-ietf-6tisch-architecture-20 (work 353 in progress), March 2019. 355 [I-D.ietf-detnet-architecture] 356 Finn, N., Thubert, P., Varga, B., and J. Farkas, 357 "Deterministic Networking Architecture", draft-ietf- 358 detnet-architecture-13 (work in progress), May 2019. 360 [I-D.ietf-roll-nsa-extension] 361 Koutsiamanis, R., Papadopoulos, G., Montavont, N., and P. 362 Thubert, "RPL DAG Metric Container Node State and 363 Attribute object type extension", draft-ietf-roll-nsa- 364 extension-01 (work in progress), March 2019. 366 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 367 Requirement Levels", BCP 14, RFC 2119, 368 DOI 10.17487/RFC2119, March 1997, 369 . 371 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 372 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 373 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 374 Low-Power and Lossy Networks", RFC 6550, 375 DOI 10.17487/RFC6550, March 2012, 376 . 378 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 379 and D. Barthel, "Routing Metrics Used for Path Calculation 380 in Low-Power and Lossy Networks", RFC 6551, 381 DOI 10.17487/RFC6551, March 2012, 382 . 384 [RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal 385 IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH) 386 Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180, 387 May 2017, . 389 [RFC8480] Wang, Q., Ed., Vilajosana, X., and T. Watteyne, "6TiSCH 390 Operation Sublayer (6top) Protocol (6P)", RFC 8480, 391 DOI 10.17487/RFC8480, November 2018, 392 . 394 8.2. Other Informative References 396 [IEEE802154-2015] 397 IEEE standard for Information Technology, "IEEE standard 398 for Information Technology, "IEEE Std 802.15.4-2015 399 Standard for Low-Rate Wireless Personal Area Networks 400 (WPANs)", December 2015". 402 Authors' Addresses 404 Georgios Papadopoulos (editor) 405 IMT Atlantique 406 Office B00 - 102A 407 2 Rue de la Chataigneraie 408 Cesson-Sevigne - Rennes 35510 409 FRANCE 411 Phone: +33 299 12 70 04 412 Email: georgios.papadopoulos@imt-atlantique.fr 413 Remous-Aris Koutsiamanis 414 IMT Atlantique 415 Office B00 - 126A 416 2 Rue de la Chataigneraie 417 Cesson-Sevigne - Rennes 35510 418 FRANCE 420 Phone: +33 299 12 70 49 421 Email: aris@ariskou.com 423 Nicolas Montavont 424 IMT Atlantique 425 Office B00 - 106A 426 2 Rue de la Chataigneraie 427 Cesson-Sevigne - Rennes 35510 428 FRANCE 430 Phone: +33 299 12 70 23 431 Email: nicolas.montavont@imt-atlantique.fr 433 Pascal Thubert 434 Cisco Systems, Inc 435 Building D 436 45 Allee des Ormes - BP1200 437 MOUGINS - Sophia Antipolis 06254 438 FRANCE 440 Phone: +33 497 23 26 34 441 Email: pthubert@cisco.com