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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) ** Downref: Normative reference to an Experimental RFC: RFC 6998 ** Downref: Normative reference to an Informational RFC: RFC 7416 Summary: 2 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: August 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 February 2, 2021 14 AODV based RPL Extensions for Supporting Asymmetric P2P Links in 15 Low-Power and Lossy Networks 16 draft-ietf-roll-aodv-rpl-09 18 Abstract 20 Route discovery for symmetric and asymmetric Point-to-Point (P2P) 21 traffic flows is a desirable feature in Low power and Lossy Networks 22 (LLNs). For that purpose, this document specifies a reactive P2P 23 route discovery mechanism for both hop-by-hop routing and source 24 routing: Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 25 protocol (AODV-RPL). Paired Instances are used to construct 26 directional paths, in case some of the links between source and 27 target node are asymmetric. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on August 6, 2021. 46 Copyright Notice 48 Copyright (c) 2021 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 65 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 6 66 4. AODV-RPL DIO Options . . . . . . . . . . . . . . . . . . . . 6 67 4.1. AODV-RPL RREQ Option . . . . . . . . . . . . . . . . . . 6 68 4.2. AODV-RPL RREP Option . . . . . . . . . . . . . . . . . . 8 69 4.3. AODV-RPL Target Option . . . . . . . . . . . . . . . . . 10 70 5. Symmetric and Asymmetric Routes . . . . . . . . . . . . . . . 11 71 6. AODV-RPL Operation . . . . . . . . . . . . . . . . . . . . . 13 72 6.1. Route Request Generation . . . . . . . . . . . . . . . . 13 73 6.2. Receiving and Forwarding RREQ messages . . . . . . . . . 14 74 6.2.1. General Processing . . . . . . . . . . . . . . . . . 14 75 6.2.2. Additional Processing for Multiple Targets . . . . . 15 76 6.3. Generating Route Reply (RREP) at TargNode . . . . . . . . 16 77 6.3.1. RREP-DIO for Symmetric route . . . . . . . . . . . . 16 78 6.3.2. RREP-DIO for Asymmetric Route . . . . . . . . . . . . 16 79 6.3.3. RPLInstanceID Pairing . . . . . . . . . . . . . . . . 17 80 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 81 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 19 82 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 83 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 84 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 19 85 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 20 86 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 87 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 88 11.1. Normative References . . . . . . . . . . . . . . . . . . 21 89 11.2. Informative References . . . . . . . . . . . . . . . . . 22 90 Appendix A. Example: Using ETX/RSSI Values to determine value of 91 S bit . . . . . . . . . . . . . . . . . . . . . . . 23 92 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 24 93 B.1. Changes from version 08 to version 09 . . . . . . . . . . 24 94 B.2. Changes from version 07 to version 08 . . . . . . . . . . 25 95 B.3. Changes from version 06 to version 07 . . . . . . . . . . 26 96 B.4. Changes from version 05 to version 06 . . . . . . . . . . 26 97 B.5. Changes from version 04 to version 05 . . . . . . . . . . 26 98 B.6. Changes from version 03 to version 04 . . . . . . . . . . 26 99 B.7. Changes from version 02 to version 03 . . . . . . . . . . 27 100 Appendix C. Contributors . . . . . . . . . . . . . . . . . . . . 27 101 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 103 1. Introduction 105 RPL [RFC6550] (Routing Protocol for Low-Power and Lossy Networks) 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 DAG 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 DAO message of RPL. AODV-RPL 133 specifies a new MOP running in a separate instance dedicated to 134 discover P2P routes, which may differ from the P2MP routes 135 discoverable by native RPL. AODV-RPL can be operated whether or not 136 native RPL is running otherwise. 138 2. Terminology 140 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 141 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 142 "OPTIONAL" in this document are to be interpreted as described in BCP 143 14 [RFC2119] [RFC8174] when, and only when, they appear in all 144 capitals, as shown here. 146 AODV 147 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 149 AODV-RPL Instance 150 Either the RREQ-Instance or RREP-Instance 152 Asymmetric Route 153 The route from the OrigNode to the TargNode can traverse different 154 nodes than the route from the TargNode to the OrigNode. An 155 asymmetric route may result from the asymmetry of links, such that 156 only one direction of the series of links satisfies the Objective 157 Function during route discovery. 159 Bi-directional Asymmetric Link 160 A link that can be used in both directions but with different link 161 characteristics. 163 DIO 164 DODAG Information Object 166 DODAG RREQ-Instance (or simply RREQ-Instance) 167 RPL Instance built using the DIO with RREQ option; used for 168 control message transmission from OrigNode to TargNode, thus 169 enabling data transmission from TargNode to OrigNode. 171 DODAG RREP-Instance (or simply RREP-Instance) 172 RPL Instance built using the DIO with RREP option; used for 173 control message transmission from TargNode to OrigNode thus 174 enabling data transmission from OrigNode to TargNode. 176 Downward Direction 177 The direction from the OrigNode to the TargNode. 179 Downward Route 180 A route in the downward direction. 182 hop-by-hop routing 183 Routing when each node stores routing information about the next 184 hop. 186 on-demand routing 187 Routing in which a route is established only when needed. 189 OrigNode 190 The IPv6 router (Originating Node) initiating the AODV-RPL route 191 discovery to obtain a route to TargNode. 193 Paired DODAGs 194 Two DODAGs for a single route discovery process between OrigNode 195 and TargNode. 197 P2P 198 Point-to-Point -- in other words, not constrained a priori to 199 traverse a common ancestor. 201 reactive routing 202 Same as "on-demand" routing. 204 RREQ-DIO message 205 An AODV-RPL MOP DIO message containing the RREQ option. The 206 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 207 The RREQ-DIO message has a secure variant as noted in [RFC6550]. 209 RREP-DIO message 210 An AODV-RPL MOP DIO message containing the RREP option. The 211 RPLInstanceID in RREP-DIO is typically paired to the one in the 212 associated RREQ-DIO message. The RREP-DIO message has a secure 213 variant as noted in [RFC6550]. 215 Source routing 216 A mechanism by which the source supplies the complete route 217 towards the target node along with each data packet [RFC6550]. 219 Symmetric route 220 The upstream and downstream routes traverse the same routers. 222 TargNode 223 The IPv6 router (Target Node) for which OrigNode requires a route 224 and initiates Route Discovery within the LLN network. 226 Upward Direction 227 The direction from the TargNode to the OrigNode. 229 Upward Route 230 A route in the upward direction. 232 ART option 233 AODV-RPL Target option: a target option defined in this document. 235 3. Overview of AODV-RPL 237 With AODV-RPL, routes from OrigNode to TargNode within the LLN 238 network are established "on-demand". In other words, the route 239 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 240 has data for delivery to the TargNode but existing routes do not 241 satisfy the application's requirements. AODV-RPL is thus functional 242 without requiring the use of RPL or any other routing protocol. 244 The routes discovered by AODV-RPL are not constrained to traverse a 245 common ancestor. AODV-RPL can enable asymmetric communication paths 246 in networks with bidirectional asymmetric links. For this purpose, 247 AODV-RPL enables discovery of two routes: namely, one from OrigNode 248 to TargNode, and another from TargNode to OrigNode. When possible, 249 AODV-RPL also enables symmetric route discovery along Paired DODAGs 250 (see Section 5). 252 In AODV-RPL, routes are discovered by first forming a temporary DAG 253 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 254 according to the AODV-RPL Mode of Operation (MOP) during route 255 formation between the OrigNode and TargNode. The RREQ-Instance is 256 formed by route control messages from OrigNode to TargNode whereas 257 the RREP-Instance is formed by route control messages from TargNode 258 to OrigNode. Intermediate routers join the Paired DODAGs based on 259 the Rank as calculated from the DIO message. Henceforth in this 260 document, the RREQ-DIO message means the AODV-RPL mode DIO message 261 from OrigNode to TargNode, containing the RREQ option (see 262 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 263 mode DIO message from TargNode to OrigNode, containing the RREP 264 option (see Section 4.2). The route discovered in the RREQ-Instance 265 is used for transmitting data from TargNode to OrigNode, and the 266 route discovered in RREP-Instance is used for transmitting data from 267 OrigNode to TargNode. 269 4. AODV-RPL DIO Options 271 4.1. AODV-RPL RREQ Option 273 OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO 274 message. A RREQ-DIO message MUST carry exactly one RREQ option, 275 otherwise it SHOULD be dropped. 277 0 1 2 3 278 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 1 279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 280 | Option Type | Option Length |S|H|X| Compr | L | MaxRank | 281 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 282 | Orig SeqNo | | 283 +-+-+-+-+-+-+-+-+ | 284 | | 285 | | 286 | Address Vector (Optional, Variable Length) | 287 | | 288 | | 289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 291 Figure 1: Format for AODV-RPL RREQ Option 293 OrigNode supplies the following information in the RREQ option: 295 Option Type 296 TBD2 298 Option Length 299 The length of the option in octets, excluding the Type and Length 300 fields. Variable due to the presence of the address vector and 301 the number of octets elided according to the Compr value. 303 S 304 Symmetric bit indicating a symmetric route from the OrigNode to 305 the router transmitting this RREQ-DIO. 307 H 308 Set to one for a hop-by-hop route. Set to zero for a source 309 route. This flag controls both the downstream route and upstream 310 route. 312 X 313 Reserved. 315 Compr 316 4-bit unsigned integer. Number of prefix octets that are elided 317 from the Address Vector. The octets elided are shared with the 318 IPv6 address in the DODAGID. This field is only used in source 319 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 320 set to zero and ignored upon reception. 322 L 323 2-bit unsigned integer determining the duration that a node is 324 able to belong to the temporary DAG in RREQ-Instance, including 325 the OrigNode and the TargNode. Once the time is reached, a node 326 MUST leave the DAG and stop sending or receiving any more DIOs for 327 the temporary DODAG. 329 * 0x00: No time limit imposed. 330 * 0x01: 16 seconds 331 * 0x02: 64 seconds 332 * 0x03: 256 seconds 334 L is independent from the route lifetime, which is defined in the 335 DODAG configuration option. 337 MaxRank 338 This field indicates the upper limit on the integer portion of the 339 Rank (calculated using the DAGRank() macro defined in [RFC6550]). 340 A value of 0 in this field indicates the limit is infinity. 342 Orig SeqNo 343 Sequence Number of OrigNode. See Section 6.1. 345 Address Vector 346 A vector of IPv6 addresses representing the route that the RREQ- 347 DIO has passed. It is only present when the H bit is set to 0. 348 The prefix of each address is elided according to the Compr field. 350 TargNode can join the RREQ instance at a Rank whose integer portion 351 is equal to the MaxRank. Other nodes MUST NOT join a RREQ instance 352 if its own Rank would be equal to or higher than MaxRank. A router 353 MUST discard a received RREQ if the integer part of the advertised 354 Rank equals or exceeds the MaxRank limit. 356 4.2. AODV-RPL RREP Option 358 TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO 359 message. A RREP-DIO message MUST carry exactly one RREP option, 360 otherwise the message SHOULD be dropped. TargNode supplies the 361 following information in the RREP option: 363 0 1 2 3 364 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 1 365 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 366 | Option Type | Option Length |G|H|X| Compr | L | MaxRank | 367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 368 | Shift |Rsv| | 369 +-+-+-+-+-+-+-+-+ | 370 | | 371 | | 372 | Address Vector (Optional, Variable Length) | 373 . . 374 . . 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 377 Figure 2: Format for AODV-RPL RREP option 379 Option Type 380 TBD3 382 Option Length 383 The length of the option in octets, excluding the Type and Length 384 fields. Variable due to the presence of the address vector and 385 the number of octets elided according to the Compr value. 387 G 388 Gratuitous route (see Section 7). 390 H 391 Requests either source routing (H=0) or hop-by-hop (H=1) for the 392 downstream route. It MUST be set to be the same as the H bit in 393 RREQ option. 395 X 396 Reserved. 398 Compr 399 4-bit unsigned integer. Same definition as in RREQ option. 401 L 402 2-bit unsigned integer defined as in RREQ option. 404 MaxRank 405 Similarly to MaxRank in the RREQ message, this field indicates the 406 upper limit on the integer portion of the Rank. A value of 0 in 407 this field indicates the limit is infinity. 409 Shift 410 6-bit unsigned integer. This field is used to recover the 411 original RPLInstanceID (see Section 6.3.3); 0 indicates that the 412 original RPLInstanceID is used. 414 Rsv 415 MUST be initialized to zero and ignored upon reception. 417 Address Vector 418 Only present when the H bit is set to 0. For an asymmetric route, 419 the Address Vector represents the IPv6 addresses of the route that 420 the RREP-DIO has passed. For a symmetric route, it is the Address 421 Vector when the RREQ-DIO arrives at the TargNode, unchanged during 422 the transmission to the OrigNode. 424 4.3. AODV-RPL Target Option 426 The AODV-RPL Target (ART) Option is based on the Target Option in 427 core RPL [RFC6550]. The Flags field is replaced by the Destination 428 Sequence Number of the TargNode and the Prefix Length field is 429 reduced to 7 bits so that the value is limited to be no greater than 430 127. 432 A RREQ-DIO message MUST carry at least one ART Option. A RREP-DIO 433 message MUST carry exactly one ART Option. Otherwise, the message 434 MUST be dropped. 436 OrigNode can include multiple TargNode addresses via multiple AODV- 437 RPL Target Options in the RREQ-DIO, for routes that share the same 438 requirement on metrics. This reduces the cost to building only one 439 DODAG. 441 0 1 2 3 442 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 1 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 444 | Option Type | Option Length | Dest SeqNo |r|Prefix Length| 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 | | 447 + | 448 | Target Prefix / Address (Variable Length) | 449 . . 450 . . 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 Figure 3: ART Option format for AODV-RPL MOP 455 Option Type 456 TBD4 458 Option Length 459 Length of the option in octets excluding the Type and Length 460 fields 462 Dest SeqNo 464 In RREQ-DIO, if nonzero, it is the last known Sequence Number for 465 TargNode for which a route is desired. In RREP-DIO, it is the 466 destination sequence number associated to the route. 468 r 469 A one-bit reserved field. This field MUST be initialized to zero 470 by the sender and MUST be ignored by the receiver. 472 Prefix Length 473 7-bit unsigned integer. Number of valid leading bits in the IPv6 474 Prefix. If Prefix Length is 0, then the value in the Target 475 Prefix / Address field represents an IPv6 address, not a prefix. 477 Target Prefix / Address 478 (variable-length field) An IPv6 destination address or prefix. 479 The Prefix Length field contains the number of valid leading bits 480 in the prefix. The length of the field is the least number of 481 octets that can contain all of the bits of the Prefix, in other 482 words Floor((7+(Prefix Length))/8) octets. The remaining bits in 483 the Target Prefix / Address field after the prefix length (if any) 484 MUST be set to zero on transmission and MUST be ignored on 485 receipt. 487 5. Symmetric and Asymmetric Routes 489 Links are considered symmetric until additional information is 490 collected. In Figure 4 and Figure 5, BR is the Border Router, O is 491 the OrigNode, R is an intermediate router, and T is the TargNode. If 492 the RREQ-DIO arrives over an interface that is known to be symmetric, 493 and the S bit is set to 1, then it remains as 1, as illustrated in 494 Figure 4. If an intermediate router sends out RREQ-DIO with the S 495 bit set to 1, then all the one-hop links on the route from the 496 OrigNode O to this router meet the requirements of route discovery, 497 and the route can be used symmetrically. 499 BR 500 /----+----\ 501 / | \ 502 / | \ 503 R R R 504 _/ \ | / \ 505 / \ | / \ 506 / \ | / \ 507 R -------- R --- R ----- R -------- R 508 / \ <--S=1--> / \ <--S=1--> / \ 509 <--S=1--> \ / \ / <--S=1--> 510 / \ / \ / \ 511 O ---------- R ------ R------ R ----- R ----------- T 512 / \ / \ / \ / \ 513 / \ / \ / \ / \ 514 / \ / \ / \ / \ 515 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 517 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 518 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 520 Figure 4: AODV-RPL with Symmetric Paired Instances 522 Upon receiving a RREQ-DIO with the S bit set to 1, a node determines 523 whether this one-hop link can be used symmetrically, i.e., both the 524 two directions meet the requirements of data transmission. If the 525 RREQ-DIO arrives over an interface that is not known to be symmetric, 526 or is known to be asymmetric, the S bit is set to 0. If the S bit 527 arrives already set to be '0', it is set to be '0' on retransmission 528 (Figure 5). For an asymmetric route, there is at least one hop which 529 doesn't satisfy the Objective Function. Based on the S bit received 530 in RREQ-DIO, TargNode T determines whether or not the route is 531 symmetric before transmitting the RREP-DIO message upstream towards 532 the OrigNode O. 534 The criteria used to determine whether or not each link is symmetric 535 is beyond the scope of the document. For instance, intermediate 536 routers can use local information (e.g., bit rate, bandwidth, number 537 of cells used in 6tisch), a priori knowledge (e.g. link quality 538 according to previous communication) or use averaging techniques as 539 appropriate to the application. Other link metric information can be 540 acquired before AODV-RPL operation, by executing evaluation 541 procedures; for instance test traffic can be generated between nodes 542 of the deployed network. During AODV-RPL operation, OAM techniques 543 for evaluating link state (see([RFC7548], [RFC7276], [co-ioam]) MAY 544 be used (at regular intervals appropriate for the LLN). The 545 evaluation procedures are out of scope for AODV-RPL. 547 Appendix A describes an example method using the upstream Expected 548 Number of Transmissions" (ETX) and downstream Received Signal 549 Strength Indicator (RSSI) to estimate whether the link is symmetric 550 in terms of link quality is given in using an averaging technique. 552 BR 553 /----+----\ 554 / | \ 555 / | \ 556 R R R 557 / \ | / \ 558 / \ | / \ 559 / \ | / \ 560 R --------- R --- R ---- R --------- R 561 / \ --S=1--> / \ --S=0--> / \ 562 --S=1--> \ / \ / --S=0--> 563 / \ / \ / \ 564 O ---------- R ------ R------ R ----- R ----------- T 565 / \ / \ / \ / \ 566 / <--S=0-- / \ / \ / <--S=0-- 567 / \ / \ / \ / \ 568 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 569 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 571 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 572 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 574 Figure 5: AODV-RPL with Asymmetric Paired Instances 576 6. AODV-RPL Operation 578 6.1. Route Request Generation 580 The route discovery process is initiated when an application at the 581 OrigNode has data to be transmitted to the TargNode, but does not 582 have a route that satisfies the Objective Function for the target of 583 the data transmission. In this case, the OrigNode builds a local 584 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 585 message containing exactly one RREQ option (see Section 4.1) via 586 link-local multicast. The DIO MUST contain at least one ART Option 587 (see Section 4.3). The S bit in RREQ-DIO sent out by the OrigNode is 588 set to 1. 590 Each node maintains a sequence number; the operation is specified in 591 section 7.2 of [RFC6550]. When the OrigNode initiates a route 592 discovery process, it MUST increase its own sequence number to avoid 593 conflicts with previously established routes. The sequence number is 594 carried in the Orig SeqNo field of the RREQ option. 596 The address in the ART Option can be a unicast IPv6 address or a 597 prefix. The OrigNode can initiate the route discovery process for 598 multiple targets simultaneously by including multiple ART Options, 599 and within a RREQ-DIO the requirements for the routes to different 600 TargNodes MUST be the same. 602 OrigNode can maintain different RPLInstances to discover routes with 603 different requirements to the same targets. Using the RPLInstanceID 604 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 605 different RPLInstances can be distinguished. 607 The transmission of RREQ-DIO obeys the Trickle timer [RFC6206]. If 608 the duration specified by the L bit has elapsed, the OrigNode MUST 609 leave the DODAG and stop sending RREQ-DIOs in the related 610 RPLInstance. 612 6.2. Receiving and Forwarding RREQ messages 614 6.2.1. General Processing 616 Upon receiving a RREQ-DIO, a router goes through the steps below. If 617 the router does not belong to the RREQ-Instance, then the maximum 618 useful rank (MaxUseRank) is MaxRank. Otherwise, MaxUseRank is set to 619 be the Rank value that was stored when the router processed the best 620 previous RREQ for the DODAG with the given RREQ-Instance. 622 Step 1: 624 If the S bit in the received RREQ-DIO is set to 1, the router MUST 625 determine whether each direction of the link (by which the RREQ- 626 DIO is received) satisfies the Objective Function. In case that 627 the downward (i.e. towards the TargNode) direction of the link 628 does not satisfy the Objective Function, the link can't be used 629 symmetrically, thus the S bit of the RREQ-DIO to be sent out MUST 630 be set as 0. If the S bit in the received RREQ-DIO is set to 0, 631 the router MUST determine into the upward direction (towards the 632 OrigNode) of the link. 634 If the upward direction of the link can satisfy the Objective 635 Function, and the router's Rank would not exceed the MaxUseRank 636 limit, the router joins the DODAG of the RREQ-Instance. The 637 router that transmitted the received RREQ-DIO is selected as the 638 preferred parent. Otherwise, if the Objective Function is not 639 satisfied or the MaxUseRank limit is exceeded, the router MUST 640 discard the received RREQ-DIO and MUST NOT join the DODAG. 642 Step 2: 644 Then the router checks if one of its addresses is included in one 645 of the ART Options. If so, this router is one of the TargNodes. 646 Otherwise, it is an intermediate router. 648 Step 3: 650 If the H bit is set to 1, then the router (TargNode or 651 intermediate) MUST build an upward route entry towards OrigNode 652 which includes at least the following items: Source Address, 653 RPLInstanceID, Destination Address, Next Hop, Lifetime, and 654 Sequence Number. The Destination Address and the RPLInstanceID 655 respectively can be learned from the DODAGID and the RPLInstanceID 656 of the RREQ-DIO, and the Source Address is the address used by the 657 local router to send data to the OrigNode. The Next Hop is the 658 preferred parent. The lifetime is set according to DODAG 659 configuration (i.e., not the L bit) and can be extended when the 660 route is actually used. The sequence number represents the 661 freshness of the route entry, and it is copied from the Orig SeqNo 662 field of the RREQ option. A route entry with the same source and 663 destination address, same RPLInstanceID, but stale sequence 664 number, MUST be deleted. 666 Step 4: 668 If the router is an intermediate router, then it transmits a RREQ- 669 DIO via link-local multicast; if the H bit is set to 0, the 670 intermediate router MUST include the address of the interface 671 receiving the RREQ-DIO into the address vector. Otherwise, if the 672 router (i.e., TargNode) was not already associated with the RREQ- 673 Instance, it prepares a RREP-DIO (Section 6.3). If, on the other 674 hand TargNode was already associated with the RREQ-Instance, it 675 takes no further action and does not send an RREP-DIO. 677 6.2.2. Additional Processing for Multiple Targets 679 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 680 Instance, one of the TargNodes can be an intermediate router to the 681 others, therefore it MUST continue sending RREQ-DIO to reach other 682 targets. In this case, before rebroadcasting the RREQ-DIO, a 683 TargNode MUST delete the Target Option encapsulating its own address, 684 so that downstream routers with higher Rank values do not try to 685 create a route to this TargNode. 687 An intermediate router could receive several RREQ-DIOs from routers 688 with lower Rank values in the same RREQ-Instance but have different 689 lists of Target Options. When rebroadcasting the RREQ-DIO, the 690 intersection of these lists MUST be included. For example, suppose 691 two RREQ-DIOs are received with the same RPLInstance and OrigNode. 693 Suppose further that the first RREQ has (T1, T2) as the targets, and 694 the second one has (T2, T4) as targets. Then only T2 needs to be 695 included in the generated RREQ-DIO. If the intersection is empty, it 696 means that all the targets have been reached, and the router MUST NOT 697 send out any RREQ-DIO. For the purposes of determining the 698 intersection with previous incoming RREQ-DIOs, the intermediate 699 router maintains a record of the targets that have been requested 700 associated with the RREQ-Instance. Any RREQ-DIO message with 701 different ART Options coming from a router with higher Rank is 702 ignored. 704 6.3. Generating Route Reply (RREP) at TargNode 706 6.3.1. RREP-DIO for Symmetric route 708 If a RREQ-DIO arrives at TargNode with the S bit set to 1, there is a 709 symmetric route along which both directions satisfy the Objective 710 Function. Other RREQ-DIOs might later provide asymmetric upward 711 routes (i.e. S=0). Selection between a qualified symmetric route 712 and an asymmetric route that might have better performance is 713 implementation-specific and out of scope. If the implementation 714 selects the symmetric route, and the L bit is not 0, the TargNode MAY 715 delay transmitting the RREP-DIO for duration RREP_WAIT_TIME to await 716 a symmetric route with a lower Rank. The value of RREP_WAIT_TIME is 717 set by default to 1/4 of the time duration determined by the L bit. 719 For a symmetric route, the RREP-DIO message is unicast to the next 720 hop according to the accumulated address vector (H=0) or the route 721 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 722 built. The RPLInstanceID in the RREP-Instance is paired as defined 723 in Section 6.3.3. In case the H bit is set to 0, the address vector 724 received in the RREQ-DIO MUST be included in the RREP-DIO. TargNode 725 increments its current sequence number and uses the incremented 726 result in the Dest SeqNo in the ART option of the RREQ-DIO. The 727 address of the OrigNode MUST be encapsulated in the ART Option and 728 included in this RREP-DIO message. 730 6.3.2. RREP-DIO for Asymmetric Route 732 When a RREQ-DIO arrives at a TargNode with the S bit set to 0, the 733 TargNode MUST build a DODAG in the RREP-Instance rooted at itself in 734 order to discover the downstream route from the OrigNode to the 735 TargNode. The RREP-DIO message MUST be re-transmitted via link-local 736 multicast until the OrigNode is reached or MaxRank is exceeded. The 737 TargNode MAY delay transmitting the RREP-DIO for duration 738 RREP_WAIT_TIME to await a route with a lower Rank. The value of 739 RREP_WAIT_TIME is set by default to 1/4 of the time duration 740 determined by the L bit. 742 The settings of the fields in RREP option and ART option are the same 743 as for the symmetric route, except for the S bit. 745 6.3.3. RPLInstanceID Pairing 747 Since the RPLInstanceID is assigned locally (i.e., there is no 748 coordination between routers in the assignment of RPLInstanceID), the 749 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 750 identify a discovered route. It is possible that multiple route 751 discoveries with dissimilar Objective Functions are initiated 752 simultaneously. Thus between the same pair of OrigNode and TargNode, 753 there can be multiple AODV-RPL route discovery instances. To avoid 754 any mismatch, the RREQ-Instance and the RREP-Instance in the same 755 route discovery MUST be paired using the RPLInstanceID. 757 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 758 to be used for the RREP-Instance is already occupied by another RPL 759 Instance from an earlier route discovery operation which is still 760 active. In other words, it might happen that two distinct OrigNodes 761 need routes to the same TargNode, and they happen to use the same 762 RPLInstanceID for RREQ-Instance. In this case, the occupied 763 RPLInstanceID MUST NOT be used again. Then the second RPLInstanceID 764 MUST be shifted into another integer so that the two RREP-instances 765 can be distinguished. In RREP option, the Shift field indicates the 766 shift to be applied to original RPLInstanceID. When the new 767 RPLInstanceID after shifting exceeds 63, it rolls over starting at 0. 768 For example, the original RPLInstanceID is 60, and shifted by 6, the 769 new RPLInstanceID will be 2. Related operations can be found in 770 Section 6.4. 772 6.4. Receiving and Forwarding Route Reply 774 Upon receiving a RREP-DIO, a router which does not belong to the 775 RREQ-Instance goes through the following steps: 777 Step 1: 779 If the S bit is set to 1, the router MUST proceed to step 2. 781 If the S bit of the RREP-DIO is set to 0, the router MUST 782 determine whether the downward direction of the link (towards the 783 TargNode) over which the RREP-DIO is received satisfies the 784 Objective Function, and the router's Rank would not exceed the 785 MaxRank limit. If so, the router joins the DODAG of the RREP- 786 Instance. The router that transmitted the received RREP-DIO is 787 selected as the preferred parent. Afterwards, other RREP-DIO 788 messages can be received. 790 If the Objective Function is not satisfied, the router MUST NOT 791 join the DODAG; the router MUST discard the RREQ-DIO, and does not 792 execute the remaining steps in this section. 794 Step 2: 796 The router next checks if one of its addresses is included in the 797 ART Option. If so, this router is the OrigNode of the route 798 discovery. Otherwise, it is an intermediate router. 800 Step 3: 802 If the H bit is set to 1, then the router (OrigNode or 803 intermediate) MUST build a downward route entry towards TargNode 804 which includes at least the following items: OrigNode Address, 805 RPLInstanceID, TargNode Address as destination, Next Hop, Lifetime 806 and Sequence Number. For a symmetric route, the Next Hop in the 807 route entry is the router from which the RREP-DIO is received. 808 For an asymmetric route, the Next Hop is the preferred parent in 809 the DODAG of RREQ-Instance. The RPLInstanceID in the route entry 810 MUST be the original RPLInstanceID (after subtracting the Shift 811 field value). The source address is learned from the ART Option, 812 and the destination address is learned from the DODAGID. The 813 lifetime is set according to DODAG configuration (i.e., not the L 814 bit) and can be extended when the route is actually used. The 815 sequence number represents the freshness of the route entry, and 816 is copied from the Dest SeqNo field of the ART option of the RREP- 817 DIO. A route entry with same source and destination address, same 818 RPLInstanceID, but stale sequence number, MUST be deleted. 820 Step 4: 822 If the receiver is the OrigNode, it can start transmitting the 823 application data to TargNode along the path as provided in RREP- 824 Instance, and processing for the RREP-DIO is complete. Otherwise, 825 in case of an asymmetric route, the intermediate router MUST 826 include the address of the interface receiving the RREP-DIO into 827 the address vector, and then transmit the RREP-DIO via link-local 828 multicast. In case of a symmetric route, the RREP-DIO message is 829 unicast to the Next Hop according to the address vector in the 830 RREP-DIO (H=0) or the local route entry (H=1). The RPLInstanceID 831 in the transmitted RREP-DIO is the same as the value in the 832 received RREP-DIO. The local knowledge for the TargNode's 833 sequence number SHOULD be updated. 835 Upon receiving a RREP-DIO, a router which already belongs to the 836 RREQ-Instance SHOULD drop the RREP-DIO. 838 7. Gratuitous RREP 840 In some cases, an Intermediate router that receives a RREQ-DIO 841 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 842 instead of continuing to multicast the RREQ-DIO towards TargNode. 843 The intermediate router effectively builds the RREP-Instance on 844 behalf of the actual TargNode. The G bit of the RREP option is 845 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 846 Intermediate node from the RREP-DIO sent by TargNode (G=0). 848 The gratuitous RREP-DIO can be sent out when an intermediate router 849 receives a RREQ-DIO for a TargNode, and the router has a more recent 850 (larger destination sequence number) pair of downward and upward 851 routes to the TargNode which also satisfy the Objective Function. 853 In case of source routing, the intermediate router MUST unicast the 854 received RREQ-DIO to TargNode including the address vector between 855 the OrigNode and the router. Thus the TargNode can have a complete 856 upward route address vector from itself to the OrigNode. Then the 857 router MUST send out the gratuitous RREP-DIO including the address 858 vector from the router itself to the TargNode. 860 In case of hop-by-hop routing, the intermediate router MUST unicast 861 the received RREQ-DIO to the Next Hop on the route. The Next Hop 862 router along the route MUST build new route entries with the related 863 RPLInstanceID and DODAGID in the downward direction. The above 864 process will happen recursively until the RREQ-DIO arrives at the 865 TargNode. Then the TargNode MUST unicast recursively the RREP-DIO 866 hop-by-hop to the intermediate router, and the routers along the 867 route SHOULD build new route entries in the upward direction. Upon 868 receiving the unicast RREP-DIO, the intermediate router sends the 869 gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 871 8. Operation of Trickle Timer 873 The trickle timer operation to control RREQ-Instance/RREP-Instance 874 multicast uses [RFC6206] to control RREQ-DIO and RREP-DIO 875 transmissions. The Trickle control of these DIO transmissions follow 876 the procedures described in the Section 8.3 of [RFC6550] entitled 877 "DIO Transmission". 879 9. IANA Considerations 881 9.1. New Mode of Operation: AODV-RPL 883 IANA is asked to assign a new Mode of Operation, named "AODV-RPL" for 884 Point-to-Point(P2P) hop-by-hop routing from the "Mode of Operation" 885 Registry. The parenthesized number 5 is only a suggestion. 887 +-------------+---------------+---------------+ 888 | Value | Description | Reference | 889 +-------------+---------------+---------------+ 890 | TBD1 (5) | AODV-RPL | This document | 891 +-------------+---------------+---------------+ 893 Figure 6: Mode of Operation 895 9.2. AODV-RPL Options: RREQ, RREP, and Target 897 IANA is asked to assign three new AODV-RPL options "RREQ", "RREP" and 898 "ART", as described in Figure 7 from the "RPL Control Message 899 Options" Registry. The parenthesized numbers are only suggestions. 901 +-------------+------------------------+---------------+ 902 | Value | Meaning | Reference | 903 +-------------+------------------------+---------------+ 904 | TBD2 (0x0B) | RREQ Option | This document | 905 +-------------+------------------------+---------------+ 906 | TBD3 (0x0C) | RREP Option | This document | 907 +-------------+------------------------+---------------+ 908 | TBD4 (0x0D) | ART Option | This document | 909 +-------------+------------------------+---------------+ 911 Figure 7: AODV-RPL Options 913 10. Security Considerations 915 In general, the security considerations for the operation of AODV-RPL 916 are similar to those for the operation of RPL (as described in 917 Section 19 of the RPL specification [RFC6550]). Sections 6.1 and 10 918 of [RFC6550] describe RPL's security framework, which provides data 919 confidentiality, authentication, replay protection, and delay 920 protection services. Additional analysis for the security threats to 921 RPL can be found in [RFC7416]. 923 A router can join a temporary DAG created for a secure AODV-RPL route 924 discovery only if it can support the Security Configuration in use, 925 which also specifies the key in use. It does not matter whether the 926 key is preinstalled or dynamically acquired. The router must have 927 the key in use before it can join the DAG being created for a secure 928 P2P-RPL route discovery. 930 If a rogue router knows the key for the Security Configuration in 931 use, it can join the secure AODV-RPL route discovery and cause 932 various types of damage. Such a rogue router could advertise false 933 information in its DIOs in order to include itself in the discovered 934 route(s). It could generate bogus RREQ-DIO, and RREP-DIO messages 935 carrying bad routes or maliciously modify genuine RREP-DIO messages 936 it receives. A rogue router acting as the OrigNode could launch 937 denial-of-service attacks against the LLN deployment by initiating 938 fake AODV-RPL route discoveries. In this type of scenario, RPL's 939 preinstalled mode of operation, where the key to use for a P2P-RPL 940 route discovery is preinstalled, SHOULD be used. If a future IETF 941 document specifies the authenticated mode of operation as described 942 in [RFC6550], then future AODV-RPL implementations SHOULD use the 943 authenticated mode of operation. 945 When a RREQ-DIO message uses the source routing option by setting the 946 H bit to 0, a rogue router may populate the Address Vector field with 947 a set of addresses that may result in the RREP-DIO traveling in a 948 routing loop. The TargNode MUST NOT generate a RREP if one of its 949 addresses is present in the Address Vector. An Intermediate Router 950 MUST NOT forward a RREP if one of its addresses is present in the 951 Address Vector. 953 11. References 955 11.1. Normative References 957 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 958 Requirement Levels", BCP 14, RFC 2119, 959 DOI 10.17487/RFC2119, March 1997, 960 . 962 [RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko, 963 "The Trickle Algorithm", RFC 6206, DOI 10.17487/RFC6206, 964 March 2011, . 966 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 967 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 968 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 969 Low-Power and Lossy Networks", RFC 6550, 970 DOI 10.17487/RFC6550, March 2012, 971 . 973 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N., 974 and D. Barthel, "Routing Metrics Used for Path Calculation 975 in Low-Power and Lossy Networks", RFC 6551, 976 DOI 10.17487/RFC6551, March 2012, 977 . 979 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 980 "A Mechanism to Measure the Routing Metrics along a Point- 981 to-Point Route in a Low-Power and Lossy Network", 982 RFC 6998, DOI 10.17487/RFC6998, August 2013, 983 . 985 [RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A., 986 and M. Richardson, Ed., "A Security Threat Analysis for 987 the Routing Protocol for Low-Power and Lossy Networks 988 (RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015, 989 . 991 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 992 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 993 May 2017, . 995 11.2. Informative References 997 [co-ioam] Ballamajalu, Rashmi., S.V.R., Anand., and Malati Hegde, 998 "Co-iOAM: In-situ Telemetry Metadata Transport for 999 Resource Constrained Networks within IETF Standards 1000 Framework", 2018 10th International Conference on 1001 Communication Systems & Networks (COMSNETS) pp.573-576, 1002 Jan 2018. 1004 [contiki] Contiki contributors, "The Contiki Open Source OS for the 1005 Internet of Things (Contiki Version 2.7)", Nov 2013, 1006 . 1008 [Contiki-ng] 1009 Contiki-NG contributors, "Contiki-NG: The OS for Next 1010 Generation IoT Devices (Contiki-NG Version 4.6)", Dec 1011 2020, . 1013 [cooja] Contiki/Cooja contributors, "Cooja Simulator for Wireless 1014 Sensor Networks (Contiki/Cooja Version 2.7)", Nov 2013, 1015 . 1018 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 1019 Demand Distance Vector (AODV) Routing", RFC 3561, 1020 DOI 10.17487/RFC3561, July 2003, 1021 . 1023 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 1024 J. Martocci, "Reactive Discovery of Point-to-Point Routes 1025 in Low-Power and Lossy Networks", RFC 6997, 1026 DOI 10.17487/RFC6997, August 2013, 1027 . 1029 [RFC7276] Mizrahi, T., Sprecher, N., Bellagamba, E., and Y. 1030 Weingarten, "An Overview of Operations, Administration, 1031 and Maintenance (OAM) Tools", RFC 7276, 1032 DOI 10.17487/RFC7276, June 2014, 1033 . 1035 [RFC7548] Ersue, M., Ed., Romascanu, D., Schoenwaelder, J., and A. 1036 Sehgal, "Management of Networks with Constrained Devices: 1037 Use Cases", RFC 7548, DOI 10.17487/RFC7548, May 2015, 1038 . 1040 Appendix A. Example: Using ETX/RSSI Values to determine value of S bit 1042 The combination of Received Signal Strength Indication(downstream) 1043 (RSSI) and Expected Number of Transmissions(upstream)" (ETX) has been 1044 tested to determine whether a link is symmetric or asymmetric at 1045 intermediate nodes. We present two methods to obtain an ETX value 1046 from RSSI measurement. 1048 Method 1: In the first method, we constructed a table measuring RSSI 1049 vs ETX using the Cooja simulation [cooja] setup in the Contiki OS 1050 environment[contiki]. We used Contiki-2.7 running 6LoWPAN/RPL 1051 protocol stack for the simulations. For approximating the number 1052 of packet drops based on the RSSI values, we implemented simple 1053 logic that drops transmitted packets with certain pre-defined 1054 ratios before handing over the packets to the receiver. The 1055 packet drop ratio is implemented as a table lookup of RSSI ranges 1056 mapping to different packet drop ratios with lower RSSI ranges 1057 resulting in higher values. While this table has been defined for 1058 the purpose of capturing the overall link behavior, it is highly 1059 recommended to conduct physical radio measurement experiments, in 1060 general. By keeping the receiving node at different distances, we 1061 let the packets experience different packet drops as per the 1062 described method. The ETX value computation is done by another 1063 module which is part of RPL Objective Function implementation. 1064 Since ETX value is reflective of the extent of pakcet drops, it 1065 allowed us to prepare a useful ETX vs RSSI table. ETX versus RSSI 1066 values obtained in this way may be used as explained below: 1068 Source---------->NodeA---------->NodeB------->Destination 1070 Figure 8: Communication link from Source to Destination 1072 +-------------------------+----------------------------------------+ 1073 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 1074 +-------------------------+----------------------------------------+ 1075 | > -60 | 150 | 1076 | -70 to -60 | 192 | 1077 | -80 to -70 | 226 | 1078 | -90 to -80 | 662 | 1079 | -100 to -90 | 3840 | 1080 +-------------------------+----------------------------------------+ 1082 Table 1: Selection of S bit based on Expected ETX value 1084 Method 2: One could also make use of the function 1085 guess_etx_from_rssi() defined in the 6LoWPAN/RPL protocol stack of 1086 Contiki-ng OS [Contiki-ng] to obtain RSSI-ETX mapping. This 1087 function outputs ETX value ranging between 128 and 3840 for -60 <= 1088 rssi <= -89. The function description is beyond the scope of this 1089 document. 1091 We tested the operations in this specification by making the 1092 following experiment, using the above parameters. In our experiment, 1093 a communication link is considered as symmetric if the ETX value of 1094 NodeA->NodeB and NodeB->NodeA (see Figure 8) are within, say, a 1:3 1095 ratio. This ratio should be understood as determining the link's 1096 symmetric/asymmetric nature. NodeA can typically know the ETX value 1097 in the direction of NodeA -> NodeB but it has no direct way of 1098 knowing the value of ETX from NodeB->NodeA. Using physical testbed 1099 experiments and realistic wireless channel propagation models, one 1100 can determine a relationship between RSSI and ETX representable as an 1101 expression or a mapping table. Such a relationship in turn can be 1102 used to estimate ETX value at nodeA for link NodeB--->NodeA from the 1103 received RSSI from NodeB. Whenever nodeA determines that the link 1104 towards the nodeB is bi-directional asymmetric then the S bit is set 1105 to 0. Afterwards, the link from NodeA to Destination remains 1106 designated as asymmetric and the S bit remains set to 0. 1108 Appendix B. Changelog 1110 Note to the RFC Editor: please remove this section before 1111 publication. 1113 B.1. Changes from version 08 to version 09 1115 o Removed section "Link State Determination" and put some of the 1116 relevant material into Section 5. 1118 o Cited security section of [RFC6550] as part of the RREP-DIO 1119 message description in Section 2. 1121 o SHOULD has been changed to MUST in Section 4.2. 1123 o Expanded the terms ETX and RSSI in Section 5. 1125 o Section 6.4 has been expanded to provide a more precise 1126 explanation of the handling of route reply. 1128 o Added [RFC7416] in the Security Considerations (Section 10) for 1129 RPL security threats. Cited [RFC6550] for authenticated mode of 1130 operation. 1132 o Appendix A has been mostly re-written to describe methods to 1133 determine whether or not the 'S' bit should be set to 1. 1135 o For consistency, adjusted several mandates from SHOULD to MUST and 1136 from SHOULD NOT to MUST NOT. 1138 o Numerous editorial improvements and clarifications. 1140 B.2. Changes from version 07 to version 08 1142 o Instead of describing the need for routes to "fulfill the 1143 requirements", specify that routes need to "satisfy the Objective 1144 Function". 1146 o Removed all normative dependencies on [RFC6997] 1148 o Rewrote Section 10 to avoid duplication of language in cited 1149 specifications. 1151 o Added a new section "Link State Determination" with text and 1152 citations to more fully describe how implementations determine 1153 whether links are symmetric. 1155 o Modified text comparing AODV-RPL to other protocols to emphasize 1156 the need for AODV-RPL instead of the problems with the other 1157 protocols. 1159 o Clarified that AODV-RPL uses some of the base RPL specification 1160 but does not require an instance of RPL to run. 1162 o Improved capitalization, quotation, and spelling variations. 1164 o Specified behavior upon reception of a RREQ-DIO or RREP-DIO 1165 message for an already existing DODAGID (e.g, Section 6.4). 1167 o Fixed numerous language issues in IANA Considerations Section 9. 1169 o For consistency, adjusted several mandates from SHOULD to MUST and 1170 from SHOULD NOT to MUST NOT. 1172 o Numerous editorial improvements and clarifications. 1174 B.3. Changes from version 06 to version 07 1176 o Added definitions for all fields of the ART option (see 1177 Section 4.3). Modified definition of Prefix Length to prohibit 1178 Prefix Length values greater than 127. 1180 o Modified the language from [RFC6550] Target Option definition so 1181 that the trailing zero bits of the Prefix Length are no longer 1182 described as "reserved". 1184 o Reclassified [RFC3561] and [RFC6998] as Informative. 1186 o Added citation for [RFC8174] to Terminology section. 1188 B.4. Changes from version 05 to version 06 1190 o Added Security Considerations based on the security mechanisms 1191 defined in [RFC6550]. 1193 o Clarified the nature of improvements due to P2P route discovery 1194 versus bidirectional asymmetric route discovery. 1196 o Editorial improvements and corrections. 1198 B.5. Changes from version 04 to version 05 1200 o Add description for sequence number operations. 1202 o Extend the residence duration L in section 4.1. 1204 o Change AODV-RPL Target option to ART option. 1206 B.6. Changes from version 03 to version 04 1208 o Updated RREP option format. Remove the T bit in RREP option. 1210 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1211 [RFC6550]. 1213 o Explanation of Shift field in RREP. 1215 o Multiple target options handling during transmission. 1217 B.7. Changes from version 02 to version 03 1219 o Include the support for source routing. 1221 o Import some features from [RFC6997], e.g., choice between hop-by- 1222 hop and source routing, the L bit which determines the duration of 1223 residence in the DAG, MaxRank, etc. 1225 o Define new target option for AODV-RPL, including the Destination 1226 Sequence Number in it. Move the TargNode address in RREQ option 1227 and the OrigNode address in RREP option into ADOV-RPL Target 1228 Option. 1230 o Support route discovery for multiple targets in one RREQ-DIO. 1232 o New RPLInstanceID pairing mechanism. 1234 Appendix C. Contributors 1236 Abdur Rashid Sangi 1237 Huaiyin Institute of Technology 1238 No.89 North Beijing Road, Qinghe District 1239 Huaian 223001 1240 P.R. China 1241 Email: sangi_bahrian@yahoo.com 1243 Authors' Addresses 1245 Satish Anamalamudi 1246 SRM University-AP 1247 Amaravati Campus 1248 Amaravati, Andhra Pradesh 522 502 1249 India 1251 Email: satishnaidu80@gmail.com 1253 Mingui Zhang 1254 Huawei Technologies 1255 No. 156 Beiqing Rd. Haidian District 1256 Beijing 100095 1257 China 1259 Email: zhangmingui@huawei.com 1260 Charles E. Perkins 1261 Lupin Lodge 1262 Saratoga 95070 1263 United States 1265 Email: charliep@computer.org 1267 S.V.R Anand 1268 Indian Institute of Science 1269 Bangalore 560012 1270 India 1272 Email: anandsvr@iisc.ac.in 1274 Bing Liu 1275 Huawei Technologies 1276 No. 156 Beiqing Rd. Haidian District 1277 Beijing 100095 1278 China 1280 Email: remy.liubing@huawei.com