idnits 2.17.1 draft-ietf-roll-aodv-rpl-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (September 9, 2017) is 2413 days in the past. Is this intentional? 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 3561 ** Downref: Normative reference to an Informational RFC: RFC 5548 ** Downref: Normative reference to an Informational RFC: RFC 5673 ** Downref: Normative reference to an Informational RFC: RFC 5826 ** Downref: Normative reference to an Informational RFC: RFC 5867 ** Downref: Normative reference to an Experimental RFC: RFC 6997 ** Downref: Normative reference to an Experimental RFC: RFC 6998 Summary: 7 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 Huaiyin Institute of Technology 4 Intended status: Standards Track M. Zhang 5 Expires: March 13, 2018 AR. Sangi 6 Huawei Technologies 7 C. Perkins 8 Futurewei 9 S.V.R.Anand 10 Indian Institute of Science 11 September 9, 2017 13 Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs) 14 draft-ietf-roll-aodv-rpl-02 16 Abstract 18 Route discovery for symmetric and asymmetric Point-to-Point (P2P) 19 traffic flows is a desirable feature in Low power and Lossy Networks 20 (LLNs). For that purpose, this document specifies a reactive P2P 21 route discovery mechanism for hop-by-hop routing (storing mode) based 22 on Ad Hoc On-demand Distance Vector Routing (AODV) based RPL 23 protocol. Two separate Instances are used to construct directional 24 paths in case some of the links between source and target node are 25 asymmetric. 27 Status of This Memo 29 This Internet-Draft is submitted in full conformance with the 30 provisions of BCP 78 and BCP 79. 32 Internet-Drafts are working documents of the Internet Engineering 33 Task Force (IETF). Note that other groups may also distribute 34 working documents as Internet-Drafts. The list of current Internet- 35 Drafts is at https://datatracker.ietf.org/drafts/current/. 37 Internet-Drafts are draft documents valid for a maximum of six months 38 and may be updated, replaced, or obsoleted by other documents at any 39 time. It is inappropriate to use Internet-Drafts as reference 40 material or to cite them other than as "work in progress." 42 This Internet-Draft will expire on March 13, 2018. 44 Copyright Notice 46 Copyright (c) 2017 IETF Trust and the persons identified as the 47 document authors. All rights reserved. 49 This document is subject to BCP 78 and the IETF Trust's Legal 50 Provisions Relating to IETF Documents 51 (https://trustee.ietf.org/license-info) in effect on the date of 52 publication of this document. Please review these documents 53 carefully, as they describe your rights and restrictions with respect 54 to this document. Code Components extracted from this document must 55 include Simplified BSD License text as described in Section 4.e of 56 the Trust Legal Provisions and are provided without warranty as 57 described in the Simplified BSD License. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 62 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 3. Overview of AODV-RPL . . . . . . . . . . . . . . . . . . . . 5 64 4. AODV-RPL Mode of Operation (MoP) . . . . . . . . . . . . . . 5 65 5. RREQ Message . . . . . . . . . . . . . . . . . . . . . . . . 9 66 6. RREP Message . . . . . . . . . . . . . . . . . . . . . . . . 10 67 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 12 68 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 13 69 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 70 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 13 71 9.2. AODV-RPL Options: RREQ and RREP . . . . . . . . . . . . . 13 72 10. Security Considerations . . . . . . . . . . . . . . . . . . . 13 73 11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 13 74 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 75 12.1. Normative References . . . . . . . . . . . . . . . . . . 14 76 12.2. Informative References . . . . . . . . . . . . . . . . . 15 77 Appendix A. ETX/RSSI Values to select S bit . . . . . . . . . . 15 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 80 1. Introduction 82 RPL[RFC6550], the IPv6 distance vector routing protocol for Low-power 83 and Lossy Networks (LLNs), is designed to support multiple traffic 84 flows through a root-based Destination-Oriented Directed Acyclic 85 Graph (DODAG). For traffic flows between routers within the DODAG 86 (i.e., Point-to-Point (P2P) traffic), this means that data packets 87 either have to traverse the root in non-storing mode (source 88 routing), or traverse a common ancestor in storing mode (hop-by-hop 89 routing). Such P2P traffic is thereby likely to flow along sub- 90 optimal routes and may suffer severe traffic congestion near the DAG 91 root [RFC6997], [RFC6998]. 93 To discover optimal paths for P2P traffic flows in RPL, P2P-RPL 94 [RFC6997] specifies a temporary DODAG where the source acts as 95 temporary root. The source initiates "P2P Route Discovery mode (P2P- 96 RDO)" with an address vector for both non-storing mode (H=0) and 97 storing mode (H=1). Subsequently, each intermediate router adds its 98 IP address and multicasts the P2P-RDO message, until the message 99 reaches the target node (TargNode). TargNode sends the "Discovery 100 Reply" option. P2P-RPL is efficient for source routing, but much 101 less efficient for hop-by-hop routing due to the extra address vector 102 overhead. In fact, when the P2P-RDO message is being multicast from 103 the source hop-by-hop, receiving nodes are able to determine a next 104 hop towards the source in symmetric links. When TargNode 105 subsequently replies to the source along the established forward 106 route, receiving nodes can determine the next hop towards TargNode. 107 In other words, it is efficient to use only routing tables for P2P- 108 RDO message instead of "Address vector" for hop-by-hop routes (H=1) 109 in symmetric links. 111 RPL and P2P-RPL both specify the use of a single DODAG in networks of 112 symmetric links. But, application-specific routing requirements that 113 are defined in IETF ROLL Working Group [RFC5548], [RFC5673], 114 [RFC5826] and [RFC5867] may need routing metrics and constraints 115 enabling use of asymmetric bidirectional links. For this purpose, 116 [I-D.thubert-roll-asymlink] describes bidirectional asymmetric links 117 for RPL [RFC6550] with Paired DODAGs, for which the DAG root 118 (DODAGID) is common for two Instances. This can satisfy application- 119 specific routing requirements for bidirectional asymmetric links in 120 base RPL [RFC6550]. P2P-RPL for Paired DODAGs, on the other hand, 121 requires two DAG roots: one for the source and another for the target 122 node due to temporary DODAG formation. For networks composed of 123 bidirectional asymmetric links (see Section 4), AODV-RPL specifies 124 P2P route discovery, utilizing RPL with a new MoP. AODV-RPL makes 125 use of two multicast messages to discover possibly asymmetric routes. 126 AODV-RPL eliminates the need for address vector control overhead, 127 significantly reducing the control packet size which is important for 128 Constrained LLN networks. Both discovered routes meet the 129 application specific metrics and constraints that are defined in the 130 Objective Function for each Instance [RFC6552]. 132 The route discovery process in AODV-RPL is modeled on the analogous 133 process that has been specified in AODV [RFC6550]. The on-demand 134 nature of AODV route discovery is natural for the needs of peer-to- 135 peer routing as envisioned for RPL-based LLNs. Similar terminology 136 has been adopted for use with the discovery messages, namely RREQ for 137 Route Request, and RREP for Route Reply. AODV-RPL is, at heart, a 138 simpler protocol than AODV, since there are no analogous operations 139 for flagging Route Errors, blacklisting unidirectional links, 140 multihoming, or handling unnumbered interfaces. Some of the simpler 141 features of AODV, on the other hand, have been imported into AODV-RPL 142 -- for instance, prefix advertisement is allowed on RREP and RREQ 143 message where appropriate. 145 2. Terminology 147 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 148 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 149 "OPTIONAL" in this document are to be interpreted as described in 150 [RFC2119]. Additionally, this document uses the following terms: 152 AODV 153 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 155 AODV-Instance 156 Either the RREQ-Instance or RREP-Instance 158 Bi-directional Asymmetric Link 159 A link that can be used in both directions but with different link 160 characteristics (see [I-D.thubert-roll-asymlink]). 162 DODAG RREQ-Instance (or simply RREQ-Instance) 163 AODV Instance built using the RREQ option; used for control 164 transmission from OrigNode to TargNode, thus enabling data 165 transmission from TargNode to OrigNode. 167 DODAG RREP-Instance (or simply RREP-Instance) 168 AODV Instance built using the RREP option; used for control 169 transmission from TargNode to OrigNode thus enabling data 170 transmission from OrigNode to TargNode. 172 downstream 173 Routing along the direction from OrigNode to TargNode. 175 hop-by-hop routing 176 Routing when each node stores routing information about the next 177 hop. 179 OrigNode 180 The IPv6 router (Originating Node) initiating the AODV-RPL route 181 discovery to obtain a route to TargNode. 183 Paired DODAGs 184 Two DODAGs for a single application. 186 P2P 187 Point-to-Point -- in other words, not constrained to traverse a 188 common ancestor. 190 RREQ message 191 An AODV-RPL MoP DIO message containing the RREQ option. The 192 InstanceID in the DIO object of the RREQ option MUST be always an 193 odd number. 195 RREP message 196 An AODV-RPL MoP DIO message containing the RREP option. The 197 InstanceID in the DIO object of the RREP option MUST be always an 198 even number (usually, InstanceID of RREQ-Instance+1). 200 source routing 201 The mechanism by which the source supplies the complete route 202 towards the target node along with each data packet. [RFC6997]. 204 TargNode 205 The IPv6 router (Target Node) for which OrigNode requires a route 206 and initiates Route Discovery within the LLN network. 208 upstream 209 Routing along the direction from TargNode to OrigNode. 211 3. Overview of AODV-RPL 213 With AODV-RPL, routes from OrigNode to TargNode within the LLN 214 network established are "on-demand". In other words, the route 215 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 216 has data for delivery to the TargNode but existing routes do not 217 satisfy the application's requirements. The routes discovered by 218 AODV-RPL are point-to-point; in other words the routes are not 219 constrained to traverse a common ancestor. Unlike base RPL [RFC6550] 220 and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric communication 221 paths in networks with bidirectional asymmetric links. For this 222 purpose, AODV-RPL enables discovery of two routes: namely, one from 223 OrigNode to TargNode, and another from TargNode to OrigNode. When 224 possible, AODV-RPL also enables symmetric routing along Paired DODAGs 225 (see Section 4). 227 4. AODV-RPL Mode of Operation (MoP) 229 In AODV-RPL, route discovery is initiated by forming a temporary DAG 230 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 231 according to a new AODV-RPL Mode of Operation (MoP) during route 232 formation between the OrigNode and TargNode. The RREQ-Instance is 233 formed by route control messages from OrigNode to TargNode whereas 234 the RREP-Instance is formed by route control messages from TargNode 235 to OrigNode (as shown in Figure 2). Intermediate routers join the 236 Paired DODAGs based on the rank as calculated from the DIO message. 237 Henceforth in this document, the RREQ-Instance message means the 238 AODV-RPL DIO message from OrigNode to TargNode, containing the RREQ 239 option. Similarly, the RREP-Instance message means the AODV-RPL DIO 240 message from TargNode to OrigNode, containing the RREP option. 241 Subsequently, the RREQ-Instance is used for data transmission from 242 TargNode to OrigNode and RREP-Instance is used for Data transmission 243 from OrigNode to TargNode. 245 The AODV-RPL Mode of Operation defines a new bit, the Symmetric bit 246 ('S'), which is added to the base DIO message as illustrated in 247 Figure 1. OrigNode sets the the 'S' bit to 1 in the RREQ-Instance 248 message when initiating route discovery. 250 0 1 2 3 251 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 1 252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 253 | RPLInstanceID |Version Number | Rank | 254 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 255 |G|0| MOP | Prf | DTSN |S| Flags | Reserved | 256 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 257 | | 258 + + 259 | | 260 + DODAGID + 261 | | 262 + + 263 | | 264 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 265 | Option(s)... 267 Figure 1: DIO modification to support asymmetric route discovery 269 A device originating a AODV-RPL message supplies the following 270 information in the DIO header of the message: 272 'S' bit 274 Symmetric bit in the DIO base object 276 MOP 278 MOP operation in the DIO object MUST be set to "5(TBD1)" for AODV- 279 RPL DIO messages 281 RPLInstanceID 283 RPLInstanceID in the DIO object MUST be the InstanceID of AODV- 284 Instance(RREQ-Instance). The InstanceID for RREQ-Instance MUST be 285 always an odd number. 287 DODAGID 289 For RREQ-Instance : 291 DODAGID in the DIO object MUST be the IPv6 address of the device 292 that initiates the RREQ-Instance. 294 For RREP-Instance 296 DODAGID in the DIO object MUST be the IPv6 address of the device 297 that initiates the RREP-Instance. 299 Rank 301 Rank in the DIO object MUST be the the rank of the AODV-Instance 302 (RREQ-Instance). 304 Metric Container Options 306 AODV-Instance(RREQ-Instance) messages MAY carry one or more Metric 307 Container options to indicate the relevant routing metrics. 309 The 'S' bit is set to mean that the route is symmetric. If the RREQ- 310 Instance arrives over an interface that is known to be symmetric, and 311 the 'S' bit is set to 1, then it remains set at 1, as illustrated in 312 Figure 2. In Figure 2 and Figure 3, BR is the BorderRouter, S is the 313 OrigNode, R is an intermediate node, and D is the TargNode. 315 BR 316 / | \ 317 / | \ 318 / | \ 319 R R R 320 / \ | / \ 321 / \ | / \ 322 / \ | / \ 323 R -------- R --- R ----- R -------- R 324 / \ <--s=1--> / \ <--s=1--> / \ 325 <--s=1--> \ / \ / <--s=1--> 326 / \ / \ / \ 327 S ---------- R ------ R------ R ----- R ----------- D 328 / \ / \ / \ / \ 329 / \ / \ / \ / \ 330 / \ / \ / \ / \ 331 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 333 >---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> 334 <---- RREP-Instance (Control: D-->S; Data: S-->D) -------< 336 Figure 2: AODV-RPL with Symmetric Paired Instances 338 If the RREQ-Instance arrives over an interface that is not known to 339 be symmetric, or is known to be asymmetric, the 'S' bit is set to be 340 0. Moreover, if the 'S' bit arrives already set to be '0', it is set 341 to be '0' on retransmission (Figure 3). Based on the 'S' bit 342 received in RREQ-Instance, the TargNode decides whether or not the 343 route is symmetric before transmitting the RREP-Instance message 344 upstream towards the OrigNode. The metric used to determine symmetry 345 (i.e., set the "S" bit to be "1" (Symmetric) or "0" (asymmetric)) is 346 implementation specific. We used ETX/RSSI to verify the feasibility 347 of the protocol operations in this draft, as discussed in Appendix A. 349 BR 350 / | \ 351 / | \ 352 / | \ 353 R R R 354 / \ | / \ 355 / \ | / \ 356 / \ | / \ 357 R --------- R --- R ---- R --------- R 358 / \ --s=1--> / \ --s=0--> / \ 359 --s=1--> \ / \ / --s=0--> 360 / \ / \ / \ 361 S ---------- R ------ R------ R ----- R ----------- D 362 / \ / \ / \ / \ 363 / <--s=0-- / \ / \ / <--s=0-- 364 / \ / \ / \ / \ 365 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 366 <--s=0-- <--s=0-- <--s=0-- <--s=0-- <--s=0-- 368 >---- RREQ-Instance (Control: S-->D; Data: D-->S) -------> 369 <---- RREP-Instance (Control: D-->S; Data: S-->D) -------< 371 Figure 3: AODV-RPL with Asymmetric Paired Instances 373 5. RREQ Message 375 0 1 2 3 376 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 1 377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 378 | Type | Orig SeqNo | Dest SeqNo | 379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 380 | | 381 | TargNode IPv6 Address | 382 | | 383 | | 384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 386 Figure 4: DIO RREQ option format for AODV-RPL MoP 388 OrigNode supplies the following information in the RREQ option of the 389 RREQ-Instance message: 391 Type 393 The type of the RREQ option(see Section 9.2). 395 Orig SeqNo 396 Sequence Number of OrigNode. 398 Dest SeqNo 400 If nonzero, the last known Sequence Number for TargNode for which 401 a route is desired. 403 TargNode IPv6 Address 405 IPv6 address of the TargNode that receives RREQ-Instance message. 407 In order to establish the upstream route from TargNode to OrigNode, 408 OrigNode multicasts the RREQ-Instance message (see Figure 4) to its 409 one-hop neighbours. In order to enable intermediate nodes R_i to 410 associate a future RREP message to an incoming RREQ message, the 411 InstanceID of RREQ-Instance MUST assign an odd number. 413 Each intermediate node R_i computes the rank for RREQ-Instance and 414 creates a routing table entry for the upstream route towards the 415 source if the routing metrics/constraints are satisfied. For this 416 purpose R_i must use the asymmetric link metric measured in the 417 upstream direction, from R_i to its upstream neighbor that 418 multicasted the RREQ-Instance message. 420 When an intermediate node R_i receives a RREQ message in storing 421 mode, it MUST store the OrigNode's InstanceID (RREQ-Instance) along 422 with the other routing information needed to establish the route back 423 to the OrigNode. This will enable R_i to determine that a future 424 RREP message (containing a paired InstanceID for the TargNode) must 425 be transmitted back to the OrigNode's IP address. 427 If the paths to and from TargNode are not known, the intermediate 428 node multicasts the RREQ-Instance message with updated rank to its 429 next-hop neighbors until the message reaches TargNode (Figure 2). 430 Based on the 'S' bit in the received RREQ message, the TargNode will 431 decide whether to unicast or multicast the RREP message back to 432 OrigNode. 434 As described in Section 7, in certain circumstances R_i MAY unicast a 435 Gratuitous RREP towards OrigNode, thereby helping to minimize 436 multicast overhead during the Route Discovery process. 438 6. RREP Message 440 The TargNode supplies the following information in the RREP message: 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 | Type | Dest SeqNo | Prefix Sz |T|G| Rsvd | 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | | 448 | TargNode IPv6 Address (when present) | 449 | | 450 | | 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 Figure 5: DIO RREP option format for AODV-RPL MoP 455 Type 457 The type of the RREP option (see Section 9.2) 459 Dest SeqNo 461 The Sequence Number for the TargNode for which a route is 462 established. 464 Prefix Sz 466 The size of the prefix which the route to the TargNode is 467 available. This allows routing to other nodes on the same subnet 468 as the TargNode. 470 'T' bit 472 'T' is set to true to indicate that the TargNode IPv6 Address 473 field is present 475 'G' bit 477 (see Section 7) 479 TargNode IPv6 Address (when present) 481 IPv6 address of the TargNode that receives RREP-Instance message. 483 In order to reduce the need for the TargNode IPv6 Address to be 484 included with the RREP message, the InstanceID of the RREP-Instance 485 is paired, whenever possible, with the InstanceID from the RREQ 486 message, which is always an odd number. The pairing is accomplished 487 by adding one to the InstanceID from the RREQ message and using that, 488 whenever possible, as the InstanceID for the RREP message. If this 489 is not possible (for instance because the incremented InstanceID is 490 still a valid InstanceID for another route to the TargNode from an 491 earlier Route Discovery operation), then the 'T' bit is set and an 492 alternative even number is chosen for the InstanceID of RREP from 493 TargNode. 495 The OrigNode IP address for RREQ-Instance is available as the DODAGID 496 in the DIO base message (see Figure 1). When TargNode receives a 497 RREQ message with the 'S' bit set to 1 (as illustrated in Figure 2), 498 it unicasts the RREP message with the 'S' bit set to 1. In this 499 case, route control messages and application data between OrigNode 500 and TargNode for both RREQ-Instance and RREP-Instance are transmitted 501 along symmetric links. When the 'T' bit is set to "1" in the RREP- 502 Instance, then the TargNode IPv6 Address is transmitted in the RREP 503 option. Otherwise, the TargNode IPv6 Address is elided in the RREP 504 option. 506 When (as illustrated in Figure 3) the TargNode receives RREQ message 507 with the 'S' bit set to 0, it also multicasts the RREP message with 508 the 'S' bit set to 0. Intermediate nodes create a routing table 509 entry for the path towards the TargNode while processing the RREP 510 message to OrigNode. Once OrigNode receives the RREP message, it 511 starts transmitting the application data to TargNode along the path 512 as discovered through RREP messages. On the other hand, application 513 data from TargNode to OrigNode is transmitted through the path that 514 is discovered from RREQ message. 516 7. Gratuitous RREP 518 Under some circumstances, an Intermediate Node that receives a RREQ 519 message MAY transmit a "Gratuitous" RREP message back to OrigNode 520 instead of continuing to multicast the RREQ message towards TargNode. 521 For these circumstances, the 'G' bit of the RREP option is provided 522 to distinguish the Gratuitous RREP sent by the Intermediate node from 523 the RREP sent by TargNode. 525 When an Intermediate node R receives a RREQ message and has recent 526 information about the cost of an upstream route from TargNode to R, 527 then R MAY unicast the Gratuitous RREP (GRREP) message to OrigNode. 528 R determines whether its information is sufficiently recent by 529 comparing the value it has stored for the Sequence Number of TargNode 530 against the DestSeqno in the incoming RREQ message. R also must have 531 information about the metric information of the upstream route from 532 TargNode. The GRREP message MUST have PrefixSz == 0 and the 'G' bit 533 set to 1. R SHOULD also unicast the RREQ message to TargNode, to 534 make sure that TargNode will have a route to OrigNode. 536 8. Operation of Trickle Timer 538 The trickle timer operation to control RREQ-Instance/RREP-Instance 539 multicast is similar to that in P2P-RPL [RFC6997]. 541 9. IANA Considerations 543 9.1. New Mode of Operation: AODV-RPL 545 IANA is required to assign a new Mode of Operation, named "AODV-RPL" 546 for Point-to-Point(P2P) hop-by-hop routing under the RPL registry. 547 The value of TBD1 is assigned from the "Mode of Operation" space 548 [RFC6550]. 550 +-------------+---------------+---------------+ 551 | Value | Description | Reference | 552 +-------------+---------------+---------------+ 553 | TBD1 (5) | AODV-RPL | This document | 554 +-------------+---------------+---------------+ 556 Figure 6: Mode of Operation 558 9.2. AODV-RPL Options: RREQ and RREP 560 Two entries are required for new AODV-RPL options "RREQ-Instance" and 561 "RREQ-Instance", with values of TBD2 (0x0A) and TBD3 (0x0B) from the 562 "RPL Control Message Options" space [RFC6550]. 564 +-------------+---------------------+---------------+ 565 | Value | Meaning | Reference | 566 +-------------+---------------------+---------------+ 567 | TBD2 (0x0A) | RREQ Option | This document | 568 +-------------+---------------------+---------------+ 569 | TBD3 (0x0B) | RREP Option | This document | 570 +-------------+---------------------+---------------+ 572 Figure 7: AODV-RPL Options 574 10. Security Considerations 576 This document does not introduce additional security issues compared 577 to base RPL. For general RPL security considerations, see [RFC6550]. 579 11. Future Work 581 It may become feasible in the future to design a non-storing version 582 of AODV-RPL's route discovery protocol. Under the current assumption 583 of route asymmetry across bidirectional links, the specification is 584 expected to be straightforward. It should be possible to re-use the 585 same methods of incremental construction for source routes within 586 analogous fields within AODV-RPL's RREQ and RREP messages as is 587 currently done for DAO messages -- in other words the RPL messages 588 for DODAG construction. 590 There has been some discussion about how to determine the initial 591 state of a link after an AODV-RPL-based network has begun operation. 592 The current draft operates as if the links are symmetric until 593 additional metric information is collected. The means for making 594 link metric information is considered out of scope for AODV-RPL. In 595 the future, RREQ and RREP messages could be equipped with new fields 596 for use in verifying link metrics. In particular, it is possible to 597 identify unidirectional links; an RREQ received across a 598 unidirectional link has to be dropped, since the destination node 599 cannot make use of the received DODAG to route packets back to the 600 source node that originated the route discovery operation. This is 601 roughly the same as considering a unidirectional link to present an 602 infinite cost metric that automatically disqualifies it for use in 603 the reverse direction. 605 12. References 607 12.1. Normative References 609 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 610 Requirement Levels", BCP 14, RFC 2119, 611 DOI 10.17487/RFC2119, March 1997, 612 . 614 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 615 Demand Distance Vector (AODV) Routing", RFC 3561, 616 DOI 10.17487/RFC3561, July 2003, 617 . 619 [RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and 620 D. Barthel, Ed., "Routing Requirements for Urban Low-Power 621 and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May 622 2009, . 624 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 625 Phinney, "Industrial Routing Requirements in Low-Power and 626 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 627 2009, . 629 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation 630 Routing Requirements in Low-Power and Lossy Networks", 631 RFC 5826, DOI 10.17487/RFC5826, April 2010, 632 . 634 [RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen, 635 "Building Automation Routing Requirements in Low-Power and 636 Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June 637 2010, . 639 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 640 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 641 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 642 Low-Power and Lossy Networks", RFC 6550, 643 DOI 10.17487/RFC6550, March 2012, 644 . 646 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 647 Protocol for Low-Power and Lossy Networks (RPL)", 648 RFC 6552, DOI 10.17487/RFC6552, March 2012, 649 . 651 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 652 J. Martocci, "Reactive Discovery of Point-to-Point Routes 653 in Low-Power and Lossy Networks", RFC 6997, 654 DOI 10.17487/RFC6997, August 2013, 655 . 657 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 658 "A Mechanism to Measure the Routing Metrics along a Point- 659 to-Point Route in a Low-Power and Lossy Network", 660 RFC 6998, DOI 10.17487/RFC6998, August 2013, 661 . 663 12.2. Informative References 665 [I-D.thubert-roll-asymlink] 666 Thubert, P., "RPL adaptation for asymmetrical links", 667 draft-thubert-roll-asymlink-02 (work in progress), 668 December 2011. 670 Appendix A. ETX/RSSI Values to select S bit 672 We have tested the combination of "RSSI(downstream)" and "ETX 673 (upstream)" to decide whether the link is symmetric or asymmetric at 674 the intermediate nodes. The example of how the ETX and RSSI values 675 are used in conjuction is explained below: 677 Source---------->NodeA---------->NodeB------->Destination 679 Figure 8: Communication link from Source to Destination 681 +-------------------------+----------------------------------------+ 682 | RSSI at NodeA for NodeB | Expected ETX at NodeA for nodeB->nodeA | 683 +-------------------------+----------------------------------------+ 684 | > -15 | 150 | 685 | -25 to -15 | 192 | 686 | -35 to -25 | 226 | 687 | -45 to -35 | 662 | 688 | -55 to -45 | 993 | 689 +-------------------------+----------------------------------------+ 691 Table 1: Selection of 'S' bit based on Expected ETX value 693 We tested the operations in this specification by making the 694 following experiment, using the above parameters. In our experiment, 695 a communication link is considered as symmetric if the ETX value of 696 NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3 697 ratio. This ratio should be taken as a notional metric for deciding 698 link symmetric/asymmetric nature, and precise definition of the ratio 699 is beyond the scope of the draft. In general, NodeA can only know 700 the ETX value in the direction of NodeA -> NodeB but it has no direct 701 way of knowing the value of ETX from NodeB->NodeA. Using physical 702 testbed experiments and realistic wireless channel propagation 703 models, one can determine a relationship between RSSI and ETX 704 representable as an expression or a mapping table. Such a 705 relationship in turn can be used to estimate ETX value at nodeA for 706 link NodeB--->NodeA from the received RSSI from NodeB. Whenever 707 nodeA determines that the link towards the nodeB is bi-directional 708 asymmetric then the "S" bit is set to "S=0". Later on, the link from 709 NodeA to Destination is asymmetric with "S" bit remains to "0". 711 Authors' Addresses 713 Satish Anamalamudi 714 Huaiyin Institute of Technology 715 No.89 North Beijing Road, Qinghe District 716 Huaian 223001 717 China 719 Email: satishnaidu80@gmail.com 720 Mingui Zhang 721 Huawei Technologies 722 No. 156 Beiqing Rd. Haidian District 723 Beijing 100095 724 China 726 Email: zhangmingui@huawei.com 728 Abdur Rashid Sangi 729 Huawei Technologies 730 No.156 Beiqing Rd. Haidian District 731 Beijing 100095 732 P.R. China 734 Email: sangi_bahrian@yahoo.com 736 Charles E. Perkins 737 Futurewei 738 2330 Central Expressway 739 Santa Clara 95050 740 Unites States 742 Email: charliep@computer.org 744 S.V.R Anand 745 Indian Institute of Science 746 Bangalore 560012 747 India 749 Email: anand@ece.iisc.ernet.in