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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ROLL S. Anamalamudi 3 Internet-Draft SRM University-AP 4 Intended status: Standards Track M. Zhang 5 Expires: October 6, 2021 Huawei Technologies 6 C. Perkins 7 Lupin Lodge 8 S.V.R.Anand 9 Indian Institute of Science 10 B. Liu 11 Huawei Technologies 12 April 4, 2021 14 Supporting Asymmetric Links in Low Power Networks: AODV-RPL 15 draft-ietf-roll-aodv-rpl-10 17 Abstract 19 Route discovery for symmetric and asymmetric Point-to-Point (P2P) 20 traffic flows is a desirable feature in Low power and Lossy Networks 21 (LLNs). For that purpose, this document specifies a reactive P2P 22 route discovery mechanism for both hop-by-hop routing and source 23 routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 24 protocol (AODV-RPL). Paired Instances are used to construct 25 directional paths, in case some of the links between source and 26 target node are asymmetric. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on October 6, 2021. 45 Copyright Notice 47 Copyright (c) 2021 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 64 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 65 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 66 4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 6 67 4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 8 68 4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10 69 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 70 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 71 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 72 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 73 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 74 6.2.2. Additional Processing for Multiple Targets . . . . . 15 75 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 76 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 77 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16 78 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 17 79 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 80 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 19 81 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 82 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 83 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 20 84 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 20 85 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 86 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 87 11.1. Normative References . . . . . . . . . . . . . . . . . . 21 88 11.2. Informative References . . . . . . . . . . . . . . . . . 22 89 Appendix A. Example: Using ETX/RSSI Values to determine value of 90 S bit . . . . . . . . . . . . . . . . . . . . . . . 23 91 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 24 92 B.1. Changes from version 09 to version 10 . . . . . . . . . . 24 93 B.2. Changes from version 08 to version 09 . . . . . . . . . . 25 94 B.3. Changes from version 07 to version 08 . . . . . . . . . . 25 95 B.4. Changes from version 06 to version 07 . . . . . . . . . . 26 96 B.5. Changes from version 05 to version 06 . . . . . . . . . . 26 97 B.6. Changes from version 04 to version 05 . . . . . . . . . . 26 98 B.7. Changes from version 03 to version 04 . . . . . . . . . . 27 99 B.8. Changes from version 02 to version 03 . . . . . . . . . . 27 100 Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 27 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 103 1. Introduction 105 RPL (Routing Protocol for Low-Power and Lossy Networks) [RFC6550] is 106 an IPv6 distance vector routing protocol designed to support multiple 107 traffic flows through a root-based Destination-Oriented Directed 108 Acyclic Graph (DODAG). Typically, a router does not have routing 109 information for most other routers. Consequently, for traffic 110 between routers within the DODAG (i.e., Point-to-Point (P2P) traffic) 111 data packets either have to traverse the root in non-storing mode, or 112 traverse a common ancestor in storing mode. Such P2P traffic is 113 thereby likely to traverse longer routes and may suffer severe 114 congestion near the root (for more information see [RFC6997], 115 [RFC6998]). 117 The route discovery process in AODV-RPL is modeled on the analogous 118 procedure specified in AODV [RFC3561]. The on-demand nature of AODV 119 route discovery is natural for the needs of peer-to-peer routing in 120 RPL-based LLNs. AODV terminology has been adapted for use with AODV- 121 RPL messages, namely RREQ for Route Request, and RREP for Route 122 Reply. AODV-RPL currently omits some features compared to AODV -- in 123 particular, flagging Route Errors, blacklisting unidirectional links, 124 multihoming, and handling unnumbered interfaces. 126 AODV-RPL reuses and provides a natural extension to the core RPL 127 functionality to support routes with birectional asymmetric links. 128 It retains RPL's DODAG formation, RPL Instance and the associated 129 Objective Function (defined in [RFC6551]), trickle timers, and 130 support for storing and non-storing modes. AODV adds basic messages 131 RREQ and RREP as part of RPL DIO (DODAG Information Object) control 132 messages, and does not utilize the Destination Advertisement Object 133 (DAO) message of RPL. AODV-RPL specifies a new MOP (Mode of 134 Operation) running in a separate instance dedicated to discover P2P 135 routes, which may differ from the point-to-multipoint routes 136 discoverable by native RPL. AODV-RPL can be operated whether or not 137 native RPL is running otherwise. 139 2. Terminology 141 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 142 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 143 "OPTIONAL" in this document are to be interpreted as described in BCP 144 14 [RFC2119] [RFC8174] when, and only when, they appear in all 145 capitals, as shown here. 147 AODV 148 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 150 AODV-RPL Instance 151 Either the RREQ-Instance or RREP-Instance 153 Asymmetric Route 154 The route from the OrigNode to the TargNode can traverse different 155 nodes than the route from the TargNode to the OrigNode. An 156 asymmetric route may result from the asymmetry of links, such that 157 only one direction of the series of links satisfies the Objective 158 Function during route discovery. 160 Bi-directional Asymmetric Link 161 A link that can be used in both directions but with different link 162 characteristics. 164 DIO 165 DODAG Information Object 167 DODAG RREQ-Instance (or simply RREQ-Instance) 168 RPL Instance built using the DIO with RREQ option; used for 169 control message transmission from OrigNode to TargNode, thus 170 enabling data transmission from TargNode to OrigNode. 172 DODAG RREP-Instance (or simply RREP-Instance) 173 RPL Instance built using the DIO with RREP option; used for 174 control message transmission from TargNode to OrigNode thus 175 enabling data transmission from OrigNode to TargNode. 177 Downward Direction 178 The direction from the OrigNode to the TargNode. 180 Downward Route 181 A route in the downward direction. 183 hop-by-hop routing 184 Routing when each node stores routing information about the next 185 hop. 187 on-demand routing 188 Routing in which a route is established only when needed. 190 OrigNode 191 The IPv6 router (Originating Node) initiating the AODV-RPL route 192 discovery to obtain a route to TargNode. 194 Paired DODAGs 195 Two DODAGs for a single route discovery process between OrigNode 196 and TargNode. 198 P2P 199 Point-to-Point -- in other words, not constrained a priori to 200 traverse a common ancestor. 202 reactive routing 203 Same as "on-demand" routing. 205 RREQ-DIO message 206 An AODV-RPL MOP DIO message containing the RREQ option. The 207 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 208 The RREQ-DIO message has a secure variant as noted in [RFC6550]. 210 RREP-DIO message 211 An AODV-RPL MOP DIO message containing the RREP option. The 212 RPLInstanceID in RREP-DIO is typically paired to the one in the 213 associated RREQ-DIO message. The RREP-DIO message has a secure 214 variant as noted in [RFC6550]. 216 Source routing 217 A mechanism by which the source supplies the complete route 218 towards the target node along with each data packet [RFC6550]. 220 Symmetric route 221 The upstream and downstream routes traverse the same routers. 223 TargNode 224 The IPv6 router (Target Node) for which OrigNode requires a route 225 and initiates Route Discovery within the LLN network. 227 Upward Direction 228 The direction from the TargNode to the OrigNode. 230 Upward Route 231 A route in the upward direction. 233 ART option 234 AODV-RPL Target option: a target option defined in this document. 236 3. Overview of AODV-RPL 238 With AODV-RPL, routes from OrigNode to TargNode within the LLN 239 network are established "on-demand". In other words, the route 240 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 241 has data for delivery to the TargNode but existing routes do not 242 satisfy the application's requirements. AODV-RPL is thus functional 243 without requiring the use of RPL or any other routing protocol. 245 The routes discovered by AODV-RPL are not constrained to traverse a 246 common ancestor. AODV-RPL can enable asymmetric communication paths 247 in networks with bidirectional asymmetric links. For this purpose, 248 AODV-RPL enables discovery of two routes: namely, one from OrigNode 249 to TargNode, and another from TargNode to OrigNode. When possible, 250 AODV-RPL also enables symmetric route discovery along Paired DODAGs 251 (see Section 5). 253 In AODV-RPL, routes are discovered by first forming a temporary DAG 254 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 255 according to the AODV-RPL Mode of Operation (MOP) during route 256 formation between the OrigNode and TargNode. The RREQ-Instance is 257 formed by route control messages from OrigNode to TargNode whereas 258 the RREP-Instance is formed by route control messages from TargNode 259 to OrigNode. Intermediate routers join the Paired DODAGs based on 260 the Rank as calculated from the DIO message. Henceforth in this 261 document, the RREQ-DIO message means the AODV-RPL mode DIO message 262 from OrigNode to TargNode, containing the RREQ option (see 263 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 264 mode DIO message from TargNode to OrigNode, containing the RREP 265 option (see Section 4.2). The route discovered in the RREQ-Instance 266 is used for transmitting data from TargNode to OrigNode, and the 267 route discovered in RREP-Instance is used for transmitting data from 268 OrigNode to TargNode. 270 4. AODV-RPL DIO Options 272 4.1. AODV-RPL RREQ Option 274 OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO 275 message. A RREQ-DIO message MUST carry exactly one RREQ option, 276 otherwise it MUST be dropped. 278 0 1 2 3 279 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 281 | Option Type | Option Length |S|H|X| Compr | L | MaxRank | 282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 283 | Orig SeqNo | | 284 +-+-+-+-+-+-+-+-+ | 285 | | 286 | | 287 | Address Vector (Optional, Variable Length) | 288 | | 289 | | 290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 292 Figure 1: Format for AODV-RPL RREQ Option 294 OrigNode supplies the following information in the RREQ option: 296 Option Type 297 TBD2 299 Option Length 300 The length of the option in octets, excluding the Type and Length 301 fields. Variable due to the presence of the address vector and 302 the number of octets elided according to the Compr value. 304 S 305 Symmetric bit indicating a symmetric route from the OrigNode to 306 the router transmitting this RREQ-DIO. 308 H 309 Set to one for a hop-by-hop route. Set to zero for a source 310 route. This flag controls both the downstream route and upstream 311 route. 313 X 314 Reserved. 316 Compr 317 4-bit unsigned integer. Number of prefix octets that are elided 318 from the Address Vector. The octets elided are shared with the 319 IPv6 address in the DODAGID. This field is only used in source 320 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 321 set to zero and ignored upon reception. 323 L 324 2-bit unsigned integer determining the duration that a node is 325 able to belong to the temporary DAG in RREQ-Instance, including 326 the OrigNode and the TargNode. Once the time is reached, a node 327 MUST leave the DAG and stop sending or receiving any more DIOs for 328 the temporary DODAG. 330 * 0x00: No time limit imposed. 331 * 0x01: 16 seconds 332 * 0x02: 64 seconds 333 * 0x03: 256 seconds 335 L is independent from the route lifetime, which is defined in the 336 DODAG configuration option. 338 MaxRank 339 This field indicates the upper limit on the integer portion of the 340 Rank (calculated using the DAGRank() macro defined in [RFC6550]). 341 A value of 0 in this field indicates the limit is infinity. 343 Orig SeqNo 344 Sequence Number of OrigNode. See Section 6.1. 346 Address Vector 347 A vector of IPv6 addresses representing the route that the RREQ- 348 DIO has passed. It is only present when the H bit is set to 0. 349 The prefix of each address is elided according to the Compr field. 351 TargNode can join the RREQ instance at a Rank whose integer portion 352 is equal to the MaxRank. Other nodes MUST NOT join a RREQ instance 353 if its own Rank would be equal to or higher than MaxRank. A router 354 MUST discard a received RREQ if the integer part of the advertised 355 Rank equals or exceeds the MaxRank limit. 357 4.2. AODV-RPL RREP Option 359 TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO 360 message. A RREP-DIO message MUST carry exactly one RREP option, 361 otherwise the message MUST be dropped. TargNode supplies the 362 following information in the RREP option: 364 0 1 2 3 365 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 367 | Option Type | Option Length |G|H|X| Compr | L | MaxRank | 368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 369 | Shift |Rsv| | 370 +-+-+-+-+-+-+-+-+ | 371 | | 372 | | 373 | Address Vector (Optional, Variable Length) | 374 . . 375 . . 376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 378 Figure 2: Format for AODV-RPL RREP option 380 Option Type 381 TBD3 383 Option Length 384 The length of the option in octets, excluding the Type and Length 385 fields. Variable due to the presence of the address vector and 386 the number of octets elided according to the Compr value. 388 G 389 Gratuitous route (see Section 7). 391 H 392 Requests either source routing (H=0) or hop-by-hop (H=1) for the 393 downstream route. It MUST be set to be the same as the H bit in 394 RREQ option. 396 X 397 Reserved. 399 Compr 400 4-bit unsigned integer. Same definition as in RREQ option. 402 L 403 2-bit unsigned integer defined as in RREQ option. 405 MaxRank 406 Similarly to MaxRank in the RREQ message, this field indicates the 407 upper limit on the integer portion of the Rank. A value of 0 in 408 this field indicates the limit is infinity. 410 Shift 411 6-bit unsigned integer. This field is used to recover the 412 original RPLInstanceID (see Section 6.3.3); 0 indicates that the 413 original RPLInstanceID is used. 415 Rsv 416 MUST be initialized to zero and ignored upon reception. 418 Address Vector 419 Only present when the H bit is set to 0. For an asymmetric route, 420 the Address Vector represents the IPv6 addresses of the route that 421 the RREP-DIO has passed. For a symmetric route, it is the Address 422 Vector when the RREQ-DIO arrives at the TargNode, unchanged during 423 the transmission to the OrigNode. 425 4.3. AODV-RPL Target Option 427 The AODV-RPL Target (ART) Option is based on the Target Option in 428 core RPL [RFC6550]. The Flags field is replaced by the Destination 429 Sequence Number of the TargNode and the Prefix Length field is 430 reduced to 7 bits so that the value is limited to be no greater than 431 127. 433 A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO 434 message MUST carry exactly one ART Option. Otherwise, the message 435 MUST be dropped. 437 OrigNode can include multiple TargNode addresses via multiple AODV- 438 RPL Target Options in the RREQ-DIO, for routes that share the same 439 requirement on metrics. This reduces the cost to building only one 440 DODAG. 442 0 1 2 3 443 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 444 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 | Option Type | Option Length | Dest SeqNo |X|Prefix Length| 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | | 448 + | 449 | Target Prefix / Address (Variable Length) | 450 . . 451 . . 452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 454 Figure 3: ART Option format for AODV-RPL MOP 456 Option Type 457 TBD4 459 Option Length 460 Length of the option in octets excluding the Type and Length 461 fields. 463 Dest SeqNo 465 In RREQ-DIO, if nonzero, it is the last known Sequence Number for 466 TargNode for which a route is desired. In RREP-DIO, it is the 467 destination sequence number associated to the route. 469 r 470 A one-bit reserved field. This field MUST be initialized to zero 471 by the sender and MUST be ignored by the receiver. 473 Prefix Length 474 7-bit unsigned integer. Number of valid leading bits in the IPv6 475 Prefix. If Prefix Length is 0, then the value in the Target 476 Prefix / Address field represents an IPv6 address, not a prefix. 478 Target Prefix / Address 479 (variable-length field) An IPv6 destination address or prefix. 480 The Prefix Length field contains the number of valid leading bits 481 in the prefix. The length of the field is the least number of 482 octets that can contain all of the bits of the Prefix, in other 483 words Floor((7+(Prefix Length))/8) octets. The remaining bits in 484 the Target Prefix / Address field after the prefix length (if any) 485 MUST be set to zero on transmission and MUST be ignored on 486 receipt. 488 5. Symmetric and Asymmetric Routes 490 Links are considered symmetric until additional information is 491 collected. In Figure 4 and Figure 5, BR is the Border Router, O is 492 the OrigNode, R is an intermediate router, and T is the TargNode. If 493 the RREQ-DIO arrives over an interface that is known to be symmetric, 494 and the S bit is set to 1, then it remains as 1, as illustrated in 495 Figure 4. If an intermediate router sends out RREQ-DIO with the S 496 bit set to 1, then all the one-hop links on the route from the 497 OrigNode O to this router meet the requirements of route discovery, 498 and the route can be used symmetrically. 500 BR 501 /----+----\ 502 / | \ 503 / | \ 504 R R R 505 _/ \ | / \ 506 / \ | / \ 507 / \ | / \ 508 R -------- R --- R ----- R -------- R 509 / \ <--S=1--> / \ <--S=1--> / \ 510 <--S=1--> \ / \ / <--S=1--> 511 / \ / \ / \ 512 O ---------- R ------ R------ R ----- R ----------- T 513 / \ / \ / \ / \ 514 / \ / \ / \ / \ 515 / \ / \ / \ / \ 516 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 518 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 519 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 521 Figure 4: AODV-RPL with Symmetric Paired Instances 523 Upon receiving a RREQ-DIO with the S bit set to 1, a node determines 524 whether this one-hop link can be used symmetrically, i.e., both the 525 two directions meet the requirements of data transmission. If the 526 RREQ-DIO arrives over an interface that is not known to be symmetric, 527 or is known to be asymmetric, the S bit is set to 0. If the S bit 528 arrives already set to be '0', it is set to be '0' on retransmission 529 (Figure 5). For an asymmetric route, there is at least one hop which 530 doesn't satisfy the Objective Function. Based on the S bit received 531 in RREQ-DIO, TargNode T determines whether or not the route is 532 symmetric before transmitting the RREP-DIO message upstream towards 533 the OrigNode O. 535 The criteria used to determine whether or not each link is symmetric 536 is beyond the scope of the document. For instance, intermediate 537 routers can use local information (e.g., bit rate, bandwidth, number 538 of cells used in 6tisch), a priori knowledge (e.g. link quality 539 according to previous communication) or use averaging techniques as 540 appropriate to the application. Other link metric information can be 541 acquired before AODV-RPL operation, by executing evaluation 542 procedures; for instance test traffic can be generated between nodes 543 of the deployed network. During AODV-RPL operation, OAM techniques 544 for evaluating link state (see([RFC7548], [RFC7276], [co-ioam]) MAY 545 be used (at regular intervals appropriate for the LLN). The 546 evaluation procedures are out of scope for AODV-RPL. 548 Appendix A describes an example method using the upstream Expected 549 Number of Transmissions" (ETX) and downstream Received Signal 550 Strength Indicator (RSSI) to estimate whether the link is symmetric 551 in terms of link quality is given in using an averaging technique. 553 BR 554 /----+----\ 555 / | \ 556 / | \ 557 R R R 558 / \ | / \ 559 / \ | / \ 560 / \ | / \ 561 R --------- R --- R ---- R --------- R 562 / \ --S=1--> / \ --S=0--> / \ 563 --S=1--> \ / \ / --S=0--> 564 / \ / \ / \ 565 O ---------- R ------ R------ R ----- R ----------- T 566 / \ / \ / \ / \ 567 / <--S=0-- / \ / \ / <--S=0-- 568 / \ / \ / \ / \ 569 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 570 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 572 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 573 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 575 Figure 5: AODV-RPL with Asymmetric Paired Instances 577 6. AODV-RPL Operation 579 6.1. Route Request Generation 581 The route discovery process is initiated when an application at the 582 OrigNode has data to be transmitted to the TargNode, but does not 583 have a route that satisfies the Objective Function for the target of 584 the data transmission. In this case, the OrigNode builds a local 585 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 586 message containing exactly one RREQ option (see Section 4.1) via 587 link-local multicast. The DIO MUST contain at least one ART Option 588 (see Section 4.3). The S bit in RREQ-DIO sent out by the OrigNode is 589 set to 1. 591 Each node maintains a sequence number; the operation is specified in 592 section 7.2 of [RFC6550]. When the OrigNode initiates a route 593 discovery process, it MUST increase its own sequence number to avoid 594 conflicts with previously established routes. The sequence number is 595 carried in the Orig SeqNo field of the RREQ option. 597 The address in the ART Option can be a unicast IPv6 address or a 598 prefix. The OrigNode can initiate the route discovery process for 599 multiple targets simultaneously by including multiple ART Options, 600 and within a RREQ-DIO the requirements for the routes to different 601 TargNodes MUST be the same. 603 OrigNode can maintain different RPLInstances to discover routes with 604 different requirements to the same targets. Using the RPLInstanceID 605 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 606 different RPLInstances can be distinguished. 608 The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If 609 the duration specified by the L bit has elapsed, the OrigNode MUST 610 leave the DODAG and stop sending RREQ-DIOs in the related 611 RPLInstance. 613 6.2. Receiving and Forwarding RREQ messages 615 6.2.1. General Processing 617 Upon receiving a RREQ-DIO, a router goes through the steps below. If 618 the router does not belong to the RREQ-Instance, then the maximum 619 useful rank (MaxUseRank) is MaxRank. Otherwise, MaxUseRank is set to 620 be the Rank value that was stored when the router processed the best 621 previous RREQ for the DODAG with the given RREQ-Instance. 623 Step 1: 625 If the S bit in the received RREQ-DIO is set to 1, the router MUST 626 determine whether each direction of the link (by which the RREQ- 627 DIO is received) satisfies the Objective Function. In case that 628 the downward (i.e. towards the TargNode) direction of the link 629 does not satisfy the Objective Function, the link can't be used 630 symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST 631 be set as 0. If the S bit in the received RREQ-DIO is set to 0, 632 the router MUST determine into the upward direction (towards the 633 OrigNode) of the link. 635 If the upward direction of the link can satisfy the Objective 636 Function, and the router's Rank would not exceed the MaxUseRank 637 limit, the router joins the DODAG of the RREQ-Instance. The 638 router that transmitted the received RREQ-DIO is selected as the 639 preferred parent. Otherwise, if the Objective Function is not 640 satisfied or the MaxUseRank limit is exceeded, the router MUST 641 discard the received RREQ-DIO and MUST NOT join the DODAG. 643 Step 2: 645 Then the router checks if one of its addresses is included in one 646 of the ART Options. If so, this router is one of the TargNodes. 647 Otherwise, it is an intermediate router. 649 Step 3: 651 If the H bit is set to 1, then the router (TargNode or 652 intermediate) MUST build an upward route entry towards OrigNode 653 which includes at least the following items: Source Address, 654 RPLInstanceID, Destination Address, Next Hop, Lifetime, and 655 Sequence Number. The Destination Address and the RPLInstanceID 656 respectively can be learned from the DODAGID and the RPLInstanceID 657 of the RREQ-DIO, and the Source Address is the address used by the 658 local router to send data to the OrigNode. The Next Hop is the 659 preferred parent. The lifetime is set according to DODAG 660 configuration (i.e., not the L bit) and can be extended when the 661 route is actually used. The sequence number represents the 662 freshness of the route entry, and it is copied from the Orig SeqNo 663 field of the RREQ option. A route entry with the same source and 664 destination address, same RPLInstanceID, but stale sequence 665 number, MUST be deleted. 667 Step 4: 669 If the router is an intermediate router, then it transmits a RREQ- 670 DIO via link-local multicast; if the H bit is set to 0, the 671 intermediate router MUST include the address of the interface 672 receiving the RREQ-DIO into the address vector. Otherwise, if the 673 router (i.e., TargNode) was not already associated with the RREQ- 674 Instance, it prepares a RREP-DIO (Section 6.3). If, on the other 675 hand TargNode was already associated with the RREQ-Instance, it 676 takes no further action and does not send an RREP-DIO. 678 6.2.2. Additional Processing for Multiple Targets 680 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 681 Instance, one of the TargNodes can be an intermediate router to the 682 others, therefore it MUST continue sending RREQ-DIO to reach other 683 targets. In this case, before rebroadcasting the RREQ-DIO, a 684 TargNode MUST delete the Target Option encapsulating its own address, 685 so that downstream routers with higher Rank values do not try to 686 create a route to this TargNode. 688 An intermediate router could receive several RREQ-DIOs from routers 689 with lower Rank values in the same RREQ-Instance but have different 690 lists of Target Options. When rebroadcasting the RREQ-DIO, the 691 intersection of these lists MUST be included. For example, suppose 692 two RREQ-DIOs are received with the same RPLInstance and OrigNode. 694 Suppose further that the first RREQ has (T1, T2) as the targets, and 695 the second one has (T2, T4) as targets. Then only T2 needs to be 696 included in the generated RREQ-DIO. If the intersection is empty, it 697 means that all the targets have been reached, and the router MUST NOT 698 send out any RREQ-DIO. For the purposes of determining the 699 intersection with previous incoming RREQ-DIOs, the intermediate 700 router maintains a record of the targets that have been requested 701 associated with the RREQ-Instance. Any RREQ-DIO message with 702 different ART Options coming from a router with higher Rank is 703 ignored. 705 6.3. Generating Route Reply (RREP) at TargNode 707 6.3.1. RREP-DIO for Symmetric route 709 If a RREQ-DIO arrives at TargNode with the S bit set to 1, there is a 710 symmetric route along which both directions satisfy the Objective 711 Function. Other RREQ-DIOs might later provide asymmetric upward 712 routes (i.e. S=0). Selection between a qualified symmetric route 713 and an asymmetric route that might have better performance is 714 implementation-specific and out of scope. If the implementation 715 selects the symmetric route, and the L bit is not 0, the TargNode MAY 716 delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await 717 a symmetric route with a lower Rank. The value of RREP_WAIT_TIME is 718 set by default to 1/4 of the time duration determined by the L bit. 720 For a symmetric route, the RREP-DIO message is unicast to the next 721 hop according to the accumulated address vector (H=0) or the route 722 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 723 built. The RPLInstanceID in the RREP-Instance is paired as defined 724 in Section 6.3.3. In case the H bit is set to 0, the address vector 725 received in the RREQ-DIO MUST be included in the RREP-DIO. TargNode 726 increments its current sequence number and uses the incremented 727 result in the Dest SeqNo in the ART option of the RREQ-DIO. The 728 address of the OrigNode MUST be encapsulated in the ART Option and 729 included in this RREP-DIO message. 731 6.3.2. RREP-DIO for Asymmetric Route 733 When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the 734 TargNode MUST build a DODAG in the RREP-Instance rooted at itself in 735 order to discover the downstream route from the OrigNode to the 736 TargNode. The RREP-DIO message MUST be re-transmitted via link-local 737 multicast until the OrigNode is reached or MaxRank is exceeded. The 738 TargNode MAY delay transmitting the RREP-DIO for duration 739 RREP_WAIT_TIME to await a route with a lower Rank. The value of 740 RREP_WAIT_TIME is set by default to 1/4 of the time duration 741 determined by the L bit. 743 The settings of the fields in RREP option and ART option are the same 744 as for the symmetric route, except for the S bit. 746 6.3.3. RPLInstanceID Pairing 748 Since the RPLInstanceID is assigned locally (i.e., there is no 749 coordination between routers in the assignment of RPLInstanceID), the 750 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 751 identify a discovered route. It is possible that multiple route 752 discoveries with dissimilar Objective Functions are initiated 753 simultaneously. Thus between the same pair of OrigNode and TargNode, 754 there can be multiple AODV-RPL route discovery instances. To avoid 755 any mismatch, the RREQ-Instance and the RREP-Instance in the same 756 route discovery MUST be paired using the RPLInstanceID. 758 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 759 to be used for the RREP-Instance is already occupied by another RPL 760 Instance from an earlier route discovery operation which is still 761 active. In other words, it might happen that two distinct OrigNodes 762 need routes to the same TargNode, and they happen to use the same 763 RPLInstanceID for RREQ-Instance. In this case, the occupied 764 RPLInstanceID MUST NOT be used again. Then the second RPLInstanceID 765 MUST be shifted into another integer so that the two RREP-instances 766 can be distinguished. In RREP option, the Shift field indicates the 767 shift to be applied to original RPLInstanceID. When the new 768 RPLInstanceID after shifting exceeds 63, it rolls over starting at 0. 769 For example, the original RPLInstanceID is 60, and shifted by 6, the 770 new RPLInstanceID will be 2. Related operations can be found in 771 Section 6.4. 773 6.4. Receiving and Forwarding Route Reply 775 Upon receiving a RREP-DIO, a router which does not belong to the 776 RREQ-Instance goes through the following steps: 778 Step 1: 780 If the S bit is set to 1, the router MUST proceed to step 2. 782 If the S bit of the RREP-DIO is set to 0, the router MUST 783 determine whether the downward direction of the link (towards the 784 TargNode) over which the RREP-DIO is received satisfies the 785 Objective Function, and the router's Rank would not exceed the 786 MaxRank limit. If so, the router joins the DODAG of the RREP- 787 Instance. The router that transmitted the received RREP-DIO is 788 selected as the preferred parent. Afterwards, other RREP-DIO 789 messages can be received. 791 If the Objective Function is not satisfied, the router MUST NOT 792 join the DODAG; the router MUST discard the RREQ-DIO, and does not 793 execute the remaining steps in this section. 795 Step 2: 797 The router next checks if one of its addresses is included in the 798 ART Option. If so, this router is the OrigNode of the route 799 discovery. Otherwise, it is an intermediate router. 801 Step 3: 803 If the H bit is set to 1, then the router (OrigNode or 804 intermediate) MUST build a downward route entry towards TargNode 805 which includes at least the following items: OrigNode Address, 806 RPLInstanceID, TargNode Address as destination, Next Hop, Lifetime 807 and Sequence Number. For a symmetric route, the Next Hop in the 808 route entry is the router from which the RREP-DIO is received. 809 For an asymmetric route, the Next Hop is the preferred parent in 810 the DODAG of RREQ-Instance. The RPLInstanceID in the route entry 811 MUST be the original RPLInstanceID (after subtracting the Shift 812 field value). The source address is learned from the ART Option, 813 and the destination address is learned from the DODAGID. The 814 lifetime is set according to DODAG configuration (i.e., not the L 815 bit) and can be extended when the route is actually used. The 816 sequence number represents the freshness of the route entry, and 817 is copied from the Dest SeqNo field of the ART option of the RREP- 818 DIO. A route entry with same source and destination address, same 819 RPLInstanceID, but stale sequence number, MUST be deleted. 821 Step 4: 823 If the receiver is the OrigNode, it can start transmitting the 824 application data to TargNode along the path as provided in RREP- 825 Instance, and processing for the RREP-DIO is complete. Otherwise, 826 in case of an asymmetric route, the intermediate router MUST 827 include the address of the interface receiving the RREP-DIO into 828 the address vector, and then transmit the RREP-DIO via link-local 829 multicast. In case of a symmetric route, the RREP-DIO message is 830 unicast to the Next Hop according to the address vector in the 831 RREP-DIO (H=0) or the local route entry (H=1). The RPLInstanceID 832 in the transmitted RREP-DIO is the same as the value in the 833 received RREP-DIO. The local knowledge for the TargNode's 834 sequence number SHOULD be updated. 836 Upon receiving a RREP-DIO, a router which already belongs to the 837 RREQ-Instance SHOULD drop the RREP-DIO. 839 7. Gratuitous RREP 841 In some cases, an Intermediate router that receives a RREQ-DIO 842 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 843 instead of continuing to multicast the RREQ-DIO towards TargNode. 844 The intermediate router effectively builds the RREP-Instance on 845 behalf of the actual TargNode. The G bit of the RREP option is 846 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 847 Intermediate node from the RREP-DIO sent by TargNode (G=0). 849 The gratuitous RREP-DIO can be sent out when an intermediate router 850 receives a RREQ-DIO for a TargNode, and the router has a more recent 851 (larger destination sequence number) pair of downward and upward 852 routes to the TargNode which also satisfy the Objective Function. 854 In case of source routing, the intermediate router MUST unicast the 855 received RREQ-DIO to TargNode including the address vector between 856 the OrigNode and the router. Thus the TargNode can have a complete 857 upward route address vector from itself to the OrigNode. Then the 858 router MUST send out the gratuitous RREP-DIO including the address 859 vector from the router itself to the TargNode. 861 In case of hop-by-hop routing, the intermediate router MUST unicast 862 the received RREQ-DIO to the Next Hop on the route. The Next Hop 863 router along the route MUST build new route entries with the related 864 RPLInstanceID and DODAGID in the downward direction. The above 865 process will happen recursively until the RREQ-DIO arrives at the 866 TargNode. Then the TargNode MUST unicast recursively the RREP-DIO 867 hop-by-hop to the intermediate router, and the routers along the 868 route SHOULD build new route entries in the upward direction. Upon 869 receiving the unicast RREP-DIO, the intermediate router sends the 870 gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 872 8. Operation of Trickle Timer 874 The trickle timer operation to control RREQ-Instance/RREP-Instance 875 multicast uses [RFC6206] to control RREQ-DIO and RREP-DIO 876 transmissions. The Trickle control of these DIO transmissions follow 877 the procedures described in the Section 8.3 of [RFC6550] entitled 878 "DIO Transmission". 880 9. IANA Considerations 882 Note to RFC editor: 884 The sentences "The parenthesized number 5 is only a suggestion." and 885 "The parenthesized numbers are only suggestions." are to be removed 886 prior publication. 888 9.1. New Mode of Operation: AODV-RPL 890 IANA is asked to assign a new Mode of Operation, named "AODV-RPL" for 891 Point-to-Point(P2P) hop-by-hop routing from the "Mode of Operation" 892 Registry. The parenthesized number 5 is only a suggestion. 894 +-------------+---------------+---------------+ 895 | Value | Description | Reference | 896 +-------------+---------------+---------------+ 897 | TBD1 (5) | AODV-RPL | This document | 898 +-------------+---------------+---------------+ 900 Figure 6: Mode of Operation 902 9.2. AODV-RPL Options: RREQ, RREP, and Target 904 IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and 905 "ART", as described in Figure 7 from the "RPL Control Message 906 Options" Registry. The parenthesized numbers are only suggestions. 908 +-------------+------------------------+---------------+ 909 | Value | Meaning | Reference | 910 +-------------+------------------------+---------------+ 911 | TBD2 (0x0B) | RREQ Option | This document | 912 +-------------+------------------------+---------------+ 913 | TBD3 (0x0C) | RREP Option | This document | 914 +-------------+------------------------+---------------+ 915 | TBD4 (0x0D) | ART Option | This document | 916 +-------------+------------------------+---------------+ 918 Figure 7: AODV-RPL Options 920 10. Security Considerations 922 In general, the security considerations for the operation of AODV-RPL 923 are similar to those for the operation of RPL (as described in 924 Section 19 of the RPL specification [RFC6550]). Sections 6.1 and 10 925 of [RFC6550] describe RPL's security framework, which provides data 926 confidentiality, authentication, replay protection, and delay 927 protection services. Additional analysis for the security threats to 928 RPL can be found in [RFC7416]. 930 A router can join a temporary DAG created for a secure AODV-RPL route 931 discovery only if it can support the Security Configuration in use, 932 which also specifies the key in use. It does not matter whether the 933 key is preinstalled or dynamically acquired. The router must have 934 the key in use before it can join the DAG being created for a secure 935 P2P-RPL route discovery. 937 If a rogue router knows the key for the Security Configuration in 938 use, it can join the secure AODV-RPL route discovery and cause 939 various types of damage. Such a rogue router could advertise false 940 information in its DIOs in order to include itself in the discovered 941 route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages 942 carrying bad routes or maliciously modify genuine RREP-DIO messages 943 it receives. A rogue router acting as the OrigNode could launch 944 denial-of-service attacks against the LLN deployment by initiating 945 fake AODV-RPL route discoveries. In this type of scenario, RPL's 946 preinstalled mode of operation, where the key to use for a P2P-RPL 947 route discovery is preinstalled, SHOULD be used. 949 When a RREQ-DIO message uses the source routing option by setting the 950 H bit to 0, a rogue router may populate the Address Vector field with 951 a set of addresses that may result in the RREP-DIO traveling in a 952 routing loop. The TargNode MUST NOT generate a RREP if one of its 953 addresses is present in the Address Vector. An Intermediate Router 954 MUST NOT forward a RREP if one of its addresses is present in the 955 Address Vector. 957 11. References 959 11.1. Normative References 961 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 962 Requirement Levels", BCP 14, RFC 2119, 963 DOI 10.17487/RFC2119, March 1997, 964 . 966 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 967 "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, 968 March 2011, . 970 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 971 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 972 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 973 Low-Power and Lossy Networks", RFC 6550, 974 DOI 10.17487/RFC6550, March 2012, 975 . 977 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 978 and D. Barthel, "Routing Metrics Used for Path Calculation 979 in Low-Power and Lossy Networks", RFC 6551, 980 DOI 10.17487/RFC6551, March 2012, 981 . 983 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 984 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 985 May 2017, . 987 11.2. Informative References 989 [co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati Hegde, 990 "Co-iOAM: In-situ Telemetry Metadata Transport for 991 Resource Constrained Networks within IETF Standards 992 Framework", 2018 10th International Conference on 993 Communication Systems & Networks (COMSNETS) pp.573-576, 994 Jan 2018. 996 [contiki] Contiki contributors, "The Contiki Open Source OS for the 997 Internet of Things (Contiki Version 2.7)", Nov 2013, 998 . 1000 [Contiki-ng] 1001 Contiki-NG contributors, "Contiki-NG: The OS for Next 1002 Generation IoT Devices (Contiki-NG Version 4.6)", Dec 1003 2020, . 1005 [cooja] Contiki/Cooja contributors, "Cooja Simulator for Wireless 1006 Sensor Networks (Contiki/Cooja Version 2.7)", Nov 2013, 1007 . 1010 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 1011 Demand Distance Vector (AODV) Routing", RFC 3561, 1012 DOI 10.17487/RFC3561, July 2003, 1013 . 1015 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1016 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1017 in Low-Power and Lossy Networks", RFC 6997, 1018 DOI 10.17487/RFC6997, August 2013, 1019 . 1021 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 1022 "A Mechanism to Measure the Routing Metrics along a Point- 1023 to-Point Route in a Low-Power and Lossy Network", 1024 RFC 6998, DOI 10.17487/RFC6998, August 2013, 1025 . 1027 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 1028 Weingarten, "An Overview of Operations, Administration, 1029 and Maintenance (OAM) Tools", RFC 7276, 1030 DOI 10.17487/RFC7276, June 2014, 1031 . 1033 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 1034 and M. Richardson, Ed., "A Security Threat Analysis for 1035 the Routing Protocol for Low-Power and Lossy Networks 1036 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 1037 . 1039 [RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A. 1040 Sehgal, "Management of Networks with Constrained Devices: 1041 Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015, 1042 . 1044 Appendix A. Example: Using ETX/RSSI Values to determine value of S bit 1046 The combination of Received Signal Strength Indication(downstream) 1047 (RSSI) and Expected Number of Transmissions(upstream)" (ETX) has been 1048 tested to determine whether a link is symmetric or asymmetric at 1049 intermediate nodes. We present two methods to obtain an ETX value 1050 from RSSI measurement. 1052 Method 1: In the first method, we constructed a table measuring RSSI 1053 vs ETX using the Cooja simulation [cooja] setup in the Contiki OS 1054 environment[contiki]. We used Contiki-2.7 running 6LoWPAN/RPL 1055 protocol stack for the simulations. For approximating the number 1056 of packet drops based on the RSSI values, we implemented simple 1057 logic that drops transmitted packets with certain pre-defined 1058 ratios before handing over the packets to the receiver. The 1059 packet drop ratio is implemented as a table lookup of RSSI ranges 1060 mapping to different packet drop ratios with lower RSSI ranges 1061 resulting in higher values. While this table has been defined for 1062 the purpose of capturing the overall link behavior, it is highly 1063 recommended to conduct physical radio measurement experiments, in 1064 general. By keeping the receiving node at different distances, we 1065 let the packets experience different packet drops as per the 1066 described method. The ETX value computation is done by another 1067 module which is part of RPL Objective Function implementation. 1068 Since ETX value is reflective of the extent of pakcet drops, it 1069 allowed us to prepare a useful ETX vs RSSI table. ETX versus RSSI 1070 values obtained in this way may be used as explained below: 1072 Source---------->NodeA---------->NodeB------->Destination 1074 Figure 8: Communication link from Source to Destination 1076 +-------------------------+----------------------------------------+ 1077 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 1078 +-------------------------+----------------------------------------+ 1079 | > -60 | 150 | 1080 | -70 to -60 | 192 | 1081 | -80 to -70 | 226 | 1082 | -90 to -80 | 662 | 1083 | -100 to -90 | 3840 | 1084 +-------------------------+----------------------------------------+ 1086 Table 1: Selection of S bit based on Expected ETX value 1088 Method 2: One could also make use of the function 1089 guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of 1090 Contiki-ng OS [Contiki-ng] to obtain RSSI-ETX mapping. This 1091 function outputs ETX value ranging between 128 and 3840 for -60 <= 1092 rssi <= -89. The function description is beyond the scope of this 1093 document. 1095 We tested the operations in this specification by making the 1096 following experiment, using the above parameters. In our experiment, 1097 a communication link is considered as symmetric if the ETX value of 1098 NodeA->NodeB and NodeB->NodeA (see Figure 8) are within, say, a 1:3 1099 ratio. This ratio should be understood as determining the link's 1100 symmetric/asymmetric nature. NodeA can typically know the ETX value 1101 in the direction of NodeA -> NodeB but it has no direct way of 1102 knowing the value of ETX from NodeB->NodeA. Using physical testbed 1103 experiments and realistic wireless channel propagation models, one 1104 can determine a relationship between RSSI and ETX representable as an 1105 expression or a mapping table. Such a relationship in turn can be 1106 used to estimate ETX value at nodeA for link NodeB--->NodeA from the 1107 received RSSI from NodeB. Whenever nodeA determines that the link 1108 towards the nodeB is bi-directional asymmetric then the S bit is set 1109 to 0. Afterwards, the link from NodeA to Destination remains 1110 designated as asymmetric and the S bit remains set to 0. 1112 Appendix B. Changelog 1114 Note to the RFC Editor: please remove this section before 1115 publication. 1117 B.1. Changes from version 09 to version 10 1119 o Changed the title for brevity and to remove acronyms. 1121 o Added "Note to the RFC Editor" in Section 9. 1123 o Expanded DAO and P2MP in Section 1. 1125 o Reclassified [RFC6998] and [RFC7416] as Informational. 1127 o SHOULD changed to MUST in Section 4.1 and Section 4.2. 1129 o Several editorial improvements and clarifications. 1131 B.2. Changes from version 08 to version 09 1133 o Removed section "Link State Determination" and put some of the 1134 relevant material into Section 5. 1136 o Cited security section of [RFC6550] as part of the RREP-DIO 1137 message description in Section 2. 1139 o SHOULD has been changed to MUST in Section 4.2. 1141 o Expanded the terms ETX and RSSI in Section 5. 1143 o Section 6.4 has been expanded to provide a more precise 1144 explanation of the handling of route reply. 1146 o Added [RFC7416] in the Security Considerations (Section 10) for 1147 RPL security threats. Cited [RFC6550] for authenticated mode of 1148 operation. 1150 o Appendix A has been mostly re-written to describe methods to 1151 determine whether or not the 'S' bit should be set to 1. 1153 o For consistency, adjusted several mandates from SHOULD to MUST and 1154 from SHOULD NOT to MUST NOT. 1156 o Numerous editorial improvements and clarifications. 1158 B.3. Changes from version 07 to version 08 1160 o Instead of describing the need for routes to "fulfill the 1161 requirements", specify that routes need to "satisfy the Objective 1162 Function". 1164 o Removed all normative dependencies on [RFC6997] 1166 o Rewrote Section 10 to avoid duplication of language in cited 1167 specifications. 1169 o Added a new section "Link State Determination" with text and 1170 citations to more fully describe how implementations determine 1171 whether links are symmetric. 1173 o Modified text comparing AODV-RPL to other protocols to emphasize 1174 the need for AODV-RPL instead of the problems with the other 1175 protocols. 1177 o Clarified that AODV-RPL uses some of the base RPL specification 1178 but does not require an instance of RPL to run. 1180 o Improved capitalization, quotation, and spelling variations. 1182 o Specified behavior upon reception of a RREQ-DIO or RREP-DIO 1183 message for an already existing DODAGID (e.g, Section 6.4). 1185 o Fixed numerous language issues in IANA Considerations Section 9. 1187 o For consistency, adjusted several mandates from SHOULD to MUST and 1188 from SHOULD NOT to MUST NOT. 1190 o Numerous editorial improvements and clarifications. 1192 B.4. Changes from version 06 to version 07 1194 o Added definitions for all fields of the ART option (see 1195 Section 4.3). Modified definition of Prefix Length to prohibit 1196 Prefix Length values greater than 127. 1198 o Modified the language from [RFC6550] Target Option definition so 1199 that the trailing zero bits of the Prefix Length are no longer 1200 described as "reserved". 1202 o Reclassified [RFC3561] and [RFC6998] as Informative. 1204 o Added citation for [RFC8174] to Terminology section. 1206 B.5. Changes from version 05 to version 06 1208 o Added Security Considerations based on the security mechanisms 1209 defined in [RFC6550]. 1211 o Clarified the nature of improvements due to P2P route discovery 1212 versus bidirectional asymmetric route discovery. 1214 o Editorial improvements and corrections. 1216 B.6. Changes from version 04 to version 05 1218 o Add description for sequence number operations. 1220 o Extend the residence duration L in section 4.1. 1222 o Change AODV-RPL Target option to ART option. 1224 B.7. Changes from version 03 to version 04 1226 o Updated RREP option format. Remove the T bit in RREP option. 1228 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1229 [RFC6550]. 1231 o Explanation of Shift field in RREP. 1233 o Multiple target options handling during transmission. 1235 B.8. Changes from version 02 to version 03 1237 o Include the support for source routing. 1239 o Import some features from [RFC6997], e.g., choice between hop-by- 1240 hop and source routing, the L bit which determines the duration of 1241 residence in the DAG, MaxRank, etc. 1243 o Define new target option for AODV-RPL, including the Destination 1244 Sequence Number in it. Move the TargNode address in RREQ option 1245 and the OrigNode address in RREP option into ADOV-RPL Target 1246 Option. 1248 o Support route discovery for multiple targets in one RREQ-DIO. 1250 o New RPLInstanceID pairing mechanism. 1252 Appendix C. Contributors 1254 Abdur Rashid Sangi 1255 Huaiyin Institute of Technology 1256 No.89 North Beijing Road, Qinghe District 1257 Huaian 223001 1258 P.R. China 1259 Email: sangi_bahrian@yahoo.com 1261 Authors' Addresses 1263 Satish Anamalamudi 1264 SRM University-AP 1265 Amaravati Campus 1266 Amaravati, Andhra Pradesh 522 502 1267 India 1269 Email: satishnaidu80@gmail.com 1270 Mingui Zhang 1271 Huawei Technologies 1272 No. 156 Beiqing Rd. Haidian District 1273 Beijing 100095 1274 China 1276 Email: zhangmingui@huawei.com 1278 Charles E. Perkins 1279 Lupin Lodge 1280 Los Gatos 95033 1281 United States 1283 Email: charliep@computer.org 1285 S.V.R Anand 1286 Indian Institute of Science 1287 Bangalore 560012 1288 India 1290 Email: anandsvr@iisc.ac.in 1292 Bing Liu 1293 Huawei Technologies 1294 No. 156 Beiqing Rd. Haidian District 1295 Beijing 100095 1296 China 1298 Email: remy.liubing@huawei.com