idnits 2.17.1 draft-ietf-roll-aodv-rpl-05.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 (October 18, 2018) is 2015 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 6998 Summary: 6 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: April 21, 2019 Huawei Technologies 6 C. Perkins 7 Futurewei 8 S.V.R.Anand 9 Indian Institute of Science 10 B. Liu 11 Huawei Technologies 12 October 18, 2018 14 Asymmetric AODV-P2P-RPL in Low-Power and Lossy Networks (LLNs) 15 draft-ietf-roll-aodv-rpl-05 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. Paired Instances are used to construct directional paths, 25 in case some of the links between source and target node are 26 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 April 21, 2019. 45 Copyright Notice 47 Copyright (c) 2018 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 . . . . . . . . . . . . . . . . . . . . 7 66 4.1. AODV-RPL DIO RREQ Option . . . . . . . . . . . . . . . . 7 67 4.2. AODV-RPL DIO RREP Option . . . . . . . . . . . . . . . . 9 68 4.3. AODV-RPL DIO 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 . . . . . . . . . . . . . . . . 16 79 6.4. Receiving and Forwarding Route Reply . . . . . . . . . . 17 80 7. Gratuitous RREP . . . . . . . . . . . . . . . . . . . . . . . 18 81 8. Operation of Trickle Timer . . . . . . . . . . . . . . . . . 19 82 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 83 9.1. New Mode of Operation: AODV-RPL . . . . . . . . . . . . . 19 84 9.2. AODV-RPL Options: RREQ, RREP, and Target . . . . . . . . 19 85 10. Security Considerations . . . . . . . . . . . . . . . . . . . 20 86 11. Future Work . . . . . . . . . . . . . . . . . . . . . . . . . 20 87 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20 88 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 89 13.1. Normative References . . . . . . . . . . . . . . . . . . 21 90 13.2. Informative References . . . . . . . . . . . . . . . . . 22 91 Appendix A. Example: ETX/RSSI Values to select S bit . . . . . . 22 92 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 23 93 B.1. Changes to version 02 . . . . . . . . . . . . . . . . . . 23 94 B.2. Changes to version 03 . . . . . . . . . . . . . . . . . . 23 95 B.3. Changes to version 04 . . . . . . . . . . . . . . . . . . 24 96 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 98 1. Introduction 100 RPL[RFC6550] is a IPv6 distance vector routing protocol for Low-power 101 and Lossy Networks (LLNs), and is designed to support multiple 102 traffic flows through a root-based Destination-Oriented Directed 103 Acyclic Graph (DODAG). Typically, a router does not have routing 104 information for most other routers. Consequently, for traffic 105 between routers within the DODAG (i.e., Point-to-Point (P2P) traffic) 106 data packets either have to traverse the root in non-storing mode, or 107 traverse a common ancestor in storing mode. Such P2P traffic is 108 thereby likely to traverse longer routes and may suffer severe 109 congestion near the DAG root [RFC6997], [RFC6998]. 111 To discover better paths for P2P traffic flows in RPL, P2P-RPL 112 [RFC6997] specifies a temporary DODAG where the source acts as a 113 temporary root. The source initiates DIOs encapsulating the P2P 114 Route Discovery option (P2P-RDO) with an address vector for both hop- 115 by-hop mode (H=1) and source routing mode (H=0). Subsequently, each 116 intermediate router adds its IP address and multicasts the P2P mode 117 DIOs, until the message reaches the target node (TargNode), which 118 then sends the "Discovery Reply" object. P2P-RPL is efficient for 119 source routing, but much less efficient for hop-by-hop routing due to 120 the extra address vector overhead. However, for symmetric links, 121 when the P2P mode DIO message is being multicast from the source hop- 122 by-hop, receiving nodes can infer a next hop towards the source. 123 When TargNode subsequently replies to the source along the 124 established forward route, receiving nodes determine the next hop 125 towards TargNode. For hop-by-hop routes (H=1) over symmetric links, 126 this would allow efficient use of routing tables for P2P-RDO messages 127 instead of the "Address Vector". 129 RPL and P2P-RPL both specify the use of a single DODAG in networks of 130 symmetric links, where the two directions of a link MUST both satisfy 131 the constraints of the objective function. This disallows the use of 132 asymmetric links which are qualified in one direction. But, 133 application-specific routing requirements as defined in IETF ROLL 134 Working Group [RFC5548], [RFC5673], [RFC5826] and [RFC5867] may be 135 satisfied by routing paths using bidirectional asymmetric links. For 136 this purpose, [I-D.thubert-roll-asymlink] described bidirectional 137 asymmetric links for RPL [RFC6550] with Paired DODAGs, for which the 138 DAG root (DODAGID) is common for two Instances. This can satisfy 139 application-specific routing requirements for bidirectional 140 asymmetric links in core RPL [RFC6550]. Using P2P-RPL twice with 141 Paired DODAGs, on the other hand, requires two roots: one for the 142 source and another for the target node due to temporary DODAG 143 formation. For networks composed of bidirectional asymmetric links 144 (see Section 5), AODV-RPL specifies P2P route discovery, utilizing 145 RPL with a new MoP. AODV-RPL makes use of two multicast messages to 146 discover possibly asymmetric routes, which can achieve higher route 147 diversity. AODV-RPL eliminates the need for address vector overhead 148 in hop-by-hop mode. This significantly reduces the control packet 149 size, which is important for Constrained LLN networks. Both 150 discovered routes (upward and downward) meet the application specific 151 metrics and constraints that are defined in the Objective Function 152 for each Instance [RFC6552]. 154 The route discovery process in AODV-RPL is modeled on the analogous 155 procedure specified in AODV [RFC3561]. The on-demand nature of AODV 156 route discovery is natural for the needs of peer-to-peer routing in 157 RPL-based LLNs. AODV terminology has been adapted for use with AODV- 158 RPL messages, namely RREQ for Route Request, and RREP for Route 159 Reply. AODV-RPL currently omits some features compared to AODV -- in 160 particular, flagging Route Errors, blacklisting unidirectional links, 161 multihoming, and handling unnumbered interfaces. 163 2. Terminology 165 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 166 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 167 "OPTIONAL" in this document are to be interpreted as described in 168 [RFC2119]. This document uses the following terms: 170 AODV 171 Ad Hoc On-demand Distance Vector Routing[RFC3561]. 173 AODV-RPL Instance 174 Either the RREQ-Instance or RREP-Instance 176 Asymmetric Route 177 The route from the OrigNode to the TargNode can traverse different 178 nodes than the route from the TargNode to the OrigNode. An 179 asymmetric route may result from the asymmetry of links, such that 180 only one direction of the series of links fulfills the constraints 181 in route discovery. 183 Bi-directional Asymmetric Link 184 A link that can be used in both directions but with different link 185 characteristics. 187 DIO 188 DODAG Information Object 190 DODAG RREQ-Instance (or simply RREQ-Instance) 191 RPL Instance built using the DIO with RREQ option; used for 192 control message transmission from OrigNode to TargNode, thus 193 enabling data transmission from TargNode to OrigNode. 195 DODAG RREP-Instance (or simply RREP-Instance) 196 RPL Instance built using the DIO with RREP option; used for 197 control message transmission from TargNode to OrigNode thus 198 enabling data transmission from OrigNode to TargNode. 200 Downward Direction 201 The direction from the OrigNode to the TargNode. 203 Downward Route 204 A route in the downward direction. 206 hop-by-hop routing 207 Routing when each node stores routing information about the next 208 hop. 210 on-demand routing 211 Routing in which a route is established only when needed. 213 OrigNode 214 The IPv6 router (Originating Node) initiating the AODV-RPL route 215 discovery to obtain a route to TargNode. 217 Paired DODAGs 218 Two DODAGs for a single route discovery process between OrigNode 219 and TargNode. 221 P2P 222 Point-to-Point -- in other words, not constrained a priori to 223 traverse a common ancestor. 225 reactive routing 226 Same as "on-demand" routing. 228 RREQ-DIO message 229 An AODV-RPL MoP DIO message containing the RREQ option. The 230 RPLInstanceID in RREQ-DIO is assigned locally by the OrigNode. 232 RREP-DIO message 233 An AODV-RPL MoP DIO message containing the RREP option. The 234 RPLInstanceID in RREP-DIO is typically paired to the one in the 235 associated RREQ-DIO message. 237 Source routing 238 A mechanism by which the source supplies the complete route 239 towards the target node along with each data packet [RFC6550]. 241 Symmetric route 242 The upstream and downstream routes traverse the same routers. 244 TargNode 245 The IPv6 router (Target Node) for which OrigNode requires a route 246 and initiates Route Discovery within the LLN network. 248 Upward Direction 249 The direction from the TargNode to the OrigNode. 251 Upward Route 252 A route in the upward direction. 254 ART option 255 AODV-RPL Target option: a target option defined in this document. 257 3. Overview of AODV-RPL 259 With AODV-RPL, routes from OrigNode to TargNode within the LLN 260 network established are "on-demand". In other words, the route 261 discovery mechanism in AODV-RPL is invoked reactively when OrigNode 262 has data for delivery to the TargNode but existing routes do not 263 satisfy the application's requirements. The routes discovered by 264 AODV-RPL are not constrained to traverse a common ancestor. Unlike 265 RPL [RFC6550] and P2P-RPL [RFC6997], AODV-RPL can enable asymmetric 266 communication paths in networks with bidirectional asymmetric links. 267 For this purpose, AODV-RPL enables discovery of two routes: namely, 268 one from OrigNode to TargNode, and another from TargNode to OrigNode. 269 When possible, AODV-RPL also enables symmetric route discovery along 270 Paired DODAGs (see Section 5). 272 In AODV-RPL, routes are discovered by first forming a temporary DAG 273 rooted at the OrigNode. Paired DODAGs (Instances) are constructed 274 according to the AODV-RPL Mode of Operation (MoP) during route 275 formation between the OrigNode and TargNode. The RREQ-Instance is 276 formed by route control messages from OrigNode to TargNode whereas 277 the RREP-Instance is formed by route control messages from TargNode 278 to OrigNode. Intermediate routers join the Paired DODAGs based on 279 the rank as calculated from the DIO message. Henceforth in this 280 document, the RREQ-DIO message means the AODV-RPL mode DIO message 281 from OrigNode to TargNode, containing the RREQ option (see 282 Section 4.1). Similarly, the RREP-DIO message means the AODV-RPL 283 mode DIO message from TargNode to OrigNode, containing the RREP 284 option (see Section 4.2). The route discovered in the RREQ-Instance 285 is used for transmitting data from TargNode to OrigNode, and the 286 route discovered in RREP-Instance is used for transmitting data from 287 OrigNode to TargNode. 289 4. AODV-RPL DIO Options 291 4.1. AODV-RPL DIO RREQ Option 293 OrigNode sets its IPv6 address in the DODAGID field of the RREQ-DIO 294 message. A RREQ-DIO message MUST carry exactly one RREQ option. 296 0 1 2 3 297 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 1 298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 299 | Type | Option Length |S|H|X| Compr | L | MaxRank | 300 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 301 | Orig SeqNo | | 302 +-+-+-+-+-+-+-+-+ | 303 | | 304 | | 305 | Address Vector (Optional, Variable Length) | 306 | | 307 | | 308 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 310 Figure 1: DIO RREQ option format for AODV-RPL MoP 312 OrigNode supplies the following information in the RREQ option: 314 Type 315 The type assigned to the RREQ option (see Section 9.2). 317 Option Length 318 The length of the option in octets, excluding the Type and Length 319 fields. Variable due to the presence of the address vector and 320 the number of octets elided according to the Compr value. 322 S 323 Symmetric bit indicating a symmetric route from the OrigNode to 324 the router transmitting this RREQ-DIO. 326 H 327 Set to one for a hop-by-hop route. Set to zero for a source 328 route. This flag controls both the downstream route and upstream 329 route. 331 X 332 Reserved. 334 Compr 335 4-bit unsigned integer. Number of prefix octets that are elided 336 from the Address Vector. The octets elided are shared with the 337 IPv6 address in the DODAGID. This field is only used in source 338 routing mode (H=0). In hop-by-hop mode (H=1), this field MUST be 339 set to zero and ignored upon reception. 341 L 343 2-bit unsigned integer determining the duration that a node is 344 able to belong to the temporary DAG in RREQ-Instance, including 345 the OrigNode and the TargNode. Once the time is reached, a node 346 MUST leave the DAG and stop sending or receiving any more DIOs for 347 the temporary DODAG. The definition for the "L" bit is similar to 348 that found in [RFC6997], except that the values are adjusted to 349 enable arbitrarily long route lifetime. 351 * 0x00: No time limit imposed. 352 * 0x01: 16 seconds 353 * 0x02: 64 seconds 354 * 0x03: 256 seconds 356 L is independent from the route lifetime, which is defined in the 357 DODAG configuration option. The route entries in hop-by-hop 358 routing and states of source routing can still be maintained even 359 after the DAG expires. 361 MaxRank 362 This field indicates the upper limit on the integer portion of the 363 rank (calculated using the DAGRank() macro defined in [RFC6550]). 364 A value of 0 in this field indicates the limit is infinity. 366 Orig SeqNo 367 Sequence Number of OrigNode, defined similarly as in AODV 368 [RFC3561]. 370 Address Vector 371 A vector of IPv6 addresses representing the route that the RREQ- 372 DIO has passed. It is only present when the 'H' bit is set to 0. 373 The prefix of each address is elided according to the Compr field. 375 A node MUST NOT join a RREQ instance if its own rank would equal to 376 or higher than MaxRank. Targnode can join the RREQ instance at a 377 rank whose integer portion is equal to the MaxRank. A router MUST 378 discard a received RREQ if the integer part of the advertised rank 379 equals or exceeds the MaxRank limit. This definition of MaxRank is 380 the same as that found in [RFC6997]. 382 4.2. AODV-RPL DIO RREP Option 384 TargNode sets its IPv6 address in the DODAGID field of the RREP-DIO 385 message. A RREP-DIO message MUST carry exactly one RREP option. 386 TargNode supplies the following information in the RREP option: 388 0 1 2 3 389 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 1 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 391 | Type | Option Length |G|H|X| Compr | L | MaxRank | 392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 393 | Shift |Rsv| | 394 +-+-+-+-+-+-+-+-+ | 395 | | 396 | | 397 | Address Vector (Optional, Variable Length) | 398 . . 399 . . 400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 Figure 2: DIO RREP option format for AODV-RPL MoP 404 Type 405 The type assigned to the RREP option (see Section 9.2) 407 Option Length 408 The length of the option in octets, excluding the Type and Length 409 fields. Variable due to the presence of the address vector and 410 the number of octets elided according to the Compr value. 412 G 413 Gratuitous route (see Section 7). 415 H 416 Requests either source routing (H=0) or hop-by-hop (H=1) for the 417 downstream route. It MUST be set to be the same as the 'H' bit in 418 RREQ option. 420 X 421 Reserved. 423 Compr 424 4-bit unsigned integer. Same definition as in RREQ option. 426 L 427 2-bit unsigned integer defined as in RREQ option. 429 MaxRank 430 Similarly to MaxRank in the RREQ message, this field indicates the 431 upper limit on the integer portion of the rank. A value of 0 in 432 this field indicates the limit is infinity. 434 Shift 435 6-bit unsigned integer. This field is used to recover the 436 original InstanceID (see Section 6.3.3); 0 indicates that the 437 original InstanceID is used. 439 Rsv 440 MUST be initialized to zero and ignored upon reception. 442 Address Vector 443 Only present when the 'H' bit is set to 0. For an asymmetric 444 route, the Address Vector represents the IPv6 addresses of the 445 route that the RREP-DIO has passed. For a symmetric route, it is 446 the Address Vector when the RREQ-DIO arrives at the TargNode, 447 unchanged during the transmission to the OrigNode. 449 4.3. AODV-RPL DIO Target Option 451 The AODV-RPL Target (ART) Option is defined based on the Target 452 Option in core RPL [RFC6550]: the Destination Sequence Number of the 453 TargNode is added. 455 A RREQ-DIO message MUST carry at least one ART Options. A RREP-DIO 456 message MUST carry exactly one ART Option. 458 OrigNode can include multiple TargNode addresses via multiple AODV- 459 RPL Target Options in the RREQ-DIO, for routes that share the same 460 constraints. This reduces the cost to building only one DODAG. 461 Furthermore, a single Target Option can be used for different 462 TargNode addresses if they share the same prefix; in that case the 463 use of the destination sequence number is not defined in this 464 document. 466 0 1 2 3 467 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 1 468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 469 | Type | Option Length | Dest SeqNo | Prefix Length | 470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 471 | | 472 + | 473 | Target Prefix (Variable Length) | 474 . . 475 . . 476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 478 Figure 3: Target option format for AODV-RPL MoP 480 Type 481 The type assigned to the ART Option 483 Dest SeqNo 485 In RREQ-DIO, if nonzero, it is the last known Sequence Number for 486 TargNode for which a route is desired. In RREP-DIO, it is the 487 destination sequence number associated to the route. 489 5. Symmetric and Asymmetric Routes 491 In Figure 4 and Figure 5, BR is the Border Router, O is the OrigNode, 492 R is an intermediate router, and T is the TargNode. If the RREQ-DIO 493 arrives over an interface that is known to be symmetric, and the 'S' 494 bit is set to 1, then it remains as 1, as illustrated in Figure 4. 495 If an intermediate router sends out RREQ-DIO with the 'S' bit set to 496 1, then all the one-hop links on the route from the OrigNode O to 497 this router meet the requirements of route discovery, and the route 498 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 524 determines whether this one-hop link can be used symmetrically, i.e., 525 both the two directions meet the requirements of data transmission. 526 If the RREQ-DIO arrives over an interface that is not known to be 527 symmetric, or is known to be asymmetric, the 'S' bit is set to 0. If 528 the 'S' bit arrives already set to be '0', it is set to be '0' on 529 retransmission (Figure 5). Therefore, for asymmetric route, there is 530 at least one hop which doesn't fulfill the constraints in the two 531 directions. Based on the 'S' bit received in RREQ-DIO, the TargNode 532 T determines whether or not the route is symmetric before 533 transmitting the RREP-DIO message upstream towards the OrigNode O. 535 The criteria used to determine whether or not each link is symmetric 536 is beyond the scope of the document, and may be implementation- 537 specific. For instance, intermediate routers MAY use local 538 information (e.g., bit rate, bandwidth, number of cells used in 539 6tisch), a priori knowledge (e.g. link quality according to previous 540 communication) or use averaging techniques as appropriate to the 541 application. 543 Appendix A describes an example method using the ETX and RSSI to 544 estimate whether the link is symmetric in terms of link quality is 545 given in using an averaging technique. 547 BR 548 /----+----\ 549 / | \ 550 / | \ 551 R R R 552 / \ | / \ 553 / \ | / \ 554 / \ | / \ 555 R --------- R --- R ---- R --------- R 556 / \ --S=1--> / \ --S=0--> / \ 557 --S=1--> \ / \ / --S=0--> 558 / \ / \ / \ 559 O ---------- R ------ R------ R ----- R ----------- T 560 / \ / \ / \ / \ 561 / <--S=0-- / \ / \ / <--S=0-- 562 / \ / \ / \ / \ 563 R ----- R ----------- R ----- R ----- R ----- R ---- R----- R 564 <--S=0-- <--S=0-- <--S=0-- <--S=0-- <--S=0-- 566 >---- RREQ-Instance (Control: O-->T; Data: T-->O) -------> 567 <---- RREP-Instance (Control: T-->O; Data: O-->T) -------< 569 Figure 5: AODV-RPL with Asymmetric Paired Instances 571 6. AODV-RPL Operation 573 6.1. Route Request Generation 575 The route discovery process is initiated when an application at the 576 OrigNode has data to be transmitted to the TargNode, but does not 577 have a route for the target that fulfills the requirements of the 578 data transmission. In this case, the OrigNode builds a local 579 RPLInstance and a DODAG rooted at itself. Then it transmits a DIO 580 message containing exactly one RREQ option (see Section 4.1) via 581 link-local multicast. The DIO MUST contain at least one ART Option 582 (see Section 4.3). The 'S' bit in RREQ-DIO sent out by the OrigNode 583 is set to 1. 585 Each node maintains a sequence number, which rolls over like a 586 lollipop counter [Perlman83], detailed operation can refer to the 587 section 7.2 of [RFC6550]. When the OrigNode initiates a route 588 discovery process, it MUST increse its own sequence number to avoid 589 conflicts with previous established routes. The increased number is 590 carried in the OrigSeqNo field of the RREQ option. 592 The address in the ART Option can be a unicast IPv6 address or a 593 prefix. The OrigNode can initiate the route discovery process for 594 multiple targets simultaneously by including multiple ART Options, 595 and within a RREQ-DIO the requirements for the routes to different 596 TargNodes MUST be the same. 598 OrigNode can maintain different RPLInstances to discover routes with 599 different requirements to the same targets. Using the InstanceID 600 pairing mechanism (see Section 6.3.3), route replies (RREP-DIOs) for 601 different RPLInstances can be distinguished. 603 The transmission of RREQ-DIO obeys the Trickle timer. If the 604 duration specified by the "L" bit has elapsed, the OrigNode MUST 605 leave the DODAG and stop sending RREQ-DIOs in the related 606 RPLInstance. 608 6.2. Receiving and Forwarding RREQ messages 610 6.2.1. General Processing 612 Upon receiving a RREQ-DIO, a router which does not belong to the 613 RREQ-instance goes through the following steps: 615 Step 1: 617 If the 'S' bit in the received RREQ-DIO is set to 1, the router 618 MUST check the two directions of the link by which the RREQ-DIO is 619 received. In case that the downward (i.e. towards the TargNode) 620 direction of the link can't fulfill the requirements, the link 621 can't be used symmetrically, thus the 'S' bit of the RREQ-DIO to 622 be sent out MUST be set as 0. If the 'S' bit in the received 623 RREQ-DIO is set to 0, the router only checks into the upward 624 direction (towards the OrigNode) of the link. 626 If the upward direction of the link can fulfill the requirements 627 indicated in the constraint option, and the router's rank would 628 not exceed the MaxRank limit, the router joins the DODAG of the 629 RREQ-Instance. The router that transmitted the received RREQ-DIO 630 is selected as the preferred parent. Later, other RREQ-DIO 631 messages might be received. How to maintain the parent set, 632 select the preferred parent, and update the router's rank obeys 633 the core RPL and the OFs defined in ROLL WG. In case that the 634 constraint or the MaxRank limit is not fulfilled, the router MUST 635 discard the received RREQ-DIO and MUST NOT join the DODAG. 637 Step 2: 639 Then the router checks if one of its addresses is included in one 640 of the ART Options. If so, this router is one of the TargNodes. 641 Otherwise, it is an intermediate router. 643 Step 3: 645 If the 'H' bit is set to 1, then the router (TargNode or 646 intermediate) MUST build the upward route entry accordingly. The 647 route entry MUST include at least the following items: Source 648 Address, InstanceID, Destination Address, Next Hop, Lifetime, and 649 Sequence Number. The Destination Address and the InstanceID can 650 be respectively learned from the DODAGID and the RPLInstanceID of 651 the RREQ-DIO, and the Source Address is copied from the ART 652 Option. The next hop is the preferred parent. And the lifetime 653 is set according to DODAG configuration and can be extended when 654 the route is actually used. The sequence number represents the 655 freshness of the route entry, and it is copied from the Orig SeqNo 656 field of the RREQ option. A route entry with same source and 657 destination address, same InstanceID, but stale sequence number, 658 SHOULD be deleted. 660 If the 'H' bit is set to 0, an intermediate router MUST include 661 the address of the interface receiving the RREQ-DIO into the 662 address vector. 664 Step 4: 666 An intermediate router transmits a RREQ-DIO via link-local 667 multicast. TargNode prepares a RREP-DIO. 669 6.2.2. Additional Processing for Multiple Targets 671 If the OrigNode tries to reach multiple TargNodes in a single RREQ- 672 instance, one of the TargNodes can be an intermediate router to the 673 others, therefore it SHOULD continue sending RREQ-DIO to reach other 674 targets. In this case, before rebroadcasting the RREQ-DIO, a 675 TargNode MUST delete the Target Option encapsulating its own address, 676 so that downstream routers with higher ranks do not try to create a 677 route to this TargetNode. 679 An intermediate router could receive several RREQ-DIOs from routers 680 with lower ranks in the same RREQ-instance but have different lists 681 of Target Options. When rebroadcasting the RREQ-DIO, the 682 intersection of these lists SHOULD be included. For example, suppose 683 two RREQ-DIOs are received with the same RPLInstance and OrigNode. 684 Suppose further that the first RREQ has (T1, T2) as the targets, and 685 the second one has (T2, T4) as targets. Then only T2 needs to be 686 included in the generated RREQ-DIO. If the intersection is empty, it 687 means that all the targets have been reached, and the router SHOULD 688 NOT send out any RREQ-DIO. Any RREQ-DIO message with different ART 689 Options coming from a router with higher rank is ignored. 691 6.3. Generating Route Reply (RREP) at TargNode 693 6.3.1. RREP-DIO for Symmetric route 695 If a RREQ-DIO arrives at TargNode with the 'S' bit set to 1, there is 696 a symmetric route along which both directions can fulfill the 697 requirements. Other RREQ-DIOs might later provide asymmetric upward 698 routes (i.e. S=0). Selection between a qualified symmetric route 699 and an asymmetric route that might have better performance is 700 implementation-specific and out of scope. If the implementation uses 701 the symmetric route, the TargNode MAY delay transmitting the RREP-DIO 702 for duration RREP_WAIT_TIME to await a better symmetric route. 704 For a symmetric route, the RREP-DIO message is unicast to the next 705 hop according to the accumulated address vector (H=0) or the route 706 entry (H=1). Thus the DODAG in RREP-Instance does not need to be 707 built. The RPLInstanceID in the RREP-Instance is paired as defined 708 in Section 6.3.3. In case the 'H' bit is set to 0, the address 709 vector received in the RREQ-DIO MUST be included in the RREP-DIO. 710 The sequence number of the TargNode is updated to the maximum of its 711 current sequence number and the Dest SeqNo in the ART option of the 712 RREQ-DIO, using a mechanism similar to that used in [RFC3561]. This 713 updated sequence number is then copied to the Dest SeqNo field of the 714 ART option. The address of the OrigNode MUST be encapsulated in the 715 ART Option and included in this RREP-DIO message. 717 6.3.2. RREP-DIO for Asymmetric Route 719 When a RREQ-DIO arrives at a TargNode with the 'S' bit set to 0, the 720 TargNode MUST build a DODAG in the RREP-Instance rooted at itself in 721 order to discover the downstream route from the OrigNode to the 722 TargNode. The RREP-DIO message MUST be re-transmitted via link-local 723 multicast until the OrigNode is reached or MaxRank is exceeded. 725 The settings of the fields in RREP option and ART option are the same 726 as for the symmetric route, except for the 'S' bit. 728 6.3.3. RPLInstanceID Pairing 730 Since the RPLInstanceID is assigned locally (i.e., there is no 731 coordination between routers in the assignment of RPLInstanceID), the 732 tuple (OrigNode, TargNode, RPLInstanceID) is needed to uniquely 733 identify a discovered route. The upper layer applications may have 734 different requirements and they can initiate the route discoveries 735 simultaneously. Thus between the same pair of OrigNode and TargNode, 736 there can be multiple AODV-RPL instances. To avoid any mismatch, the 737 RREQ-Instance and the RREP-Instance in the same route discovery MUST 738 be paired somehow, e.g. using the RPLInstanceID. 740 When preparing the RREP-DIO, a TargNode could find the RPLInstanceID 741 to be used for the RREP-Instance is already occupied by another RPL 742 Instance from an earlier route discovery operation which is still 743 active. In other words, it might happen that two distinct OrigNodes 744 need routes to the same TargNode, and they happen to use the same 745 RPLInstanceID for RREQ-Instance. In this case, the occupied 746 RPLInstanceID MUST NOT be used again. Then the second RPLInstanceID 747 MUST be shifted into another integer so that the two RREP-instances 748 can be distinguished. In RREP option, the Shift field indicates the 749 shift to be applied to original RPLInstanceID. When the new 750 InstanceID after shifting exceeds 63, it rolls over starting at 0. 751 For example, the original InstanceID is 60, and shifted by 6, the new 752 InstanceID will be 2. Related operations can be found in 753 Section 6.4. 755 6.4. Receiving and Forwarding Route Reply 757 Upon receiving a RREP-DIO, a router which does not belong to the 758 RREQ-instance goes through the following steps: 760 Step 1: 762 If the 'S' bit is set to 1, the router proceeds to step 2. 764 If the 'S' bit of the RREP-DIO is set to 0, the router MUST check 765 the downward direction of the link (towards the TargNode) over 766 which the RREP-DIO is received. If the downward direction of the 767 link can fulfill the requirements indicated in the constraint 768 option, and the router's rank would not exceed the MaxRank limit, 769 the router joins the DODAG of the RREP-Instance. The router that 770 transmitted the received RREP-DIO is selected as the preferred 771 parent. Afterwards, other RREP-DIO messages can be received. How 772 to maintain the parent set, select the preferred parent, and 773 update the router's rank obeys the core RPL and the OFs defined in 774 ROLL WG. 776 If the constraints are not fulfilled, the router MUST NOT join the 777 DODAG; the router MUST discard the RREQ-DIO, and does not execute 778 the remaining steps in this section. 780 Step 2: 782 The router next checks if one of its addresses is included in the 783 ART Option. If so, this router is the OrigNode of the route 784 discovery. Otherwise, it is an intermediate router. 786 Step 3: 788 If the 'H' bit is set to 1, then the router (OrigNode or 789 intermediate) MUST build a downward route entry. The route entry 790 SHOULD include at least the following items: OrigNode Address, 791 InstanceID, TargNode Address as destination, Next Hop, Lifetime 792 and Sequence Number. For a symmetric route, the next hop in the 793 route entry is the router from which the RREP-DIO is received. 794 For an asymmetric route, the next hop is the preferred parent in 795 the DODAG of RREQ-Instance. The InstanceID in the route entry 796 MUST be the original RPLInstanceID (after subtracting the Shift 797 field value). The source address is learned from the ART Option, 798 and the destination address is learned from the DODAGID. The 799 lifetime is set according to DODAG configuration and can be 800 extended when the route is actually used. The sequence number 801 represents the freshness of the route entry, and is copied from 802 the Dest SeqNo field of the ART option of the RREP-DIO. A route 803 entry with same source and destination address, same InstanceID, 804 but stale sequence number, SHOULD be deleted. 806 If the 'H' bit is set to 0, for an asymmetric route, an 807 intermediate router MUST include the address of the interface 808 receiving the RREP-DIO into the address vector; for a symmetric 809 route, there is nothing to do in this step. 811 Step 4: 813 If the receiver is the OrigNode, it can start transmitting the 814 application data to TargNode along the path as provided in RREP- 815 Instance, and processing for the RREP-DIO is complete. Otherwise, 816 in case of an asymmetric route, the intermediate router transmits 817 the RREP-DIO via link-local multicast. In case of a symmetric 818 route, the RREP-DIO message is unicast to the next hop according 819 to the address vector in the RREP-DIO (H=0) or the local route 820 entry (H=1). The RPLInstanceID in the transmitted RREP-DIO is the 821 same as the value in the received RREP-DIO. The local knowledge 822 for the TargNode's sequence number SHOULD be updated. 824 7. Gratuitous RREP 826 In some cases, an Intermediate router that receives a RREQ-DIO 827 message MAY transmit a "Gratuitous" RREP-DIO message back to OrigNode 828 instead of continuing to multicast the RREQ-DIO towards TargNode. 829 The intermediate router effectively builds the RREP-Instance on 830 behalf of the actual TargNode. The 'G' bit of the RREP option is 831 provided to distinguish the Gratuitous RREP-DIO (G=1) sent by the 832 Intermediate node from the RREP-DIO sent by TargNode (G=0). 834 The gratuitous RREP-DIO can be sent out when an intermediate router R 835 receives a RREQ-DIO for a TargNode T, and R happens to have a more 836 recent (larger destination sequence number) pair of downward and 837 upward routes to T which also fulfill the requirements. 839 In case of source routing, the intermediate router R MUST unicast the 840 received RREQ-DIO to TargNode T including the address vector between 841 the OrigNode O and the router R. Thus T can have a complete upward 842 route address vector from itself to O. Then R MUST send out the 843 gratuitous RREP-DIO including the address vector from R to T. 845 In case of hop-by-hop routing, R MUST unicast the received RREQ-DIO 846 hop-by-hop to T. The routers along the route SHOULD build new route 847 entries with the related RPLInstanceID and DODAGID in the downward 848 direction. Then T MUST unicast the RREP-DIO hop-by-hop to R, and the 849 routers along the route SHOULD build new route entries in the upward 850 direction. Upon receiving the unicast RREP-DIO, R sends the 851 gratuitous RREP-DIO to the OrigNode as defined in Section 6.3. 853 8. Operation of Trickle Timer 855 The trickle timer operation to control RREQ-Instance/RREP-Instance 856 multicast is similar to that in P2P-RPL [RFC6997]. 858 9. IANA Considerations 860 9.1. New Mode of Operation: AODV-RPL 862 IANA is required to assign a new Mode of Operation, named "AODV-RPL" 863 for Point-to-Point(P2P) hop-by-hop routing under the RPL registry. 864 The value of TBD1 is assigned from the "Mode of Operation" space 865 [RFC6550]. 867 +-------------+---------------+---------------+ 868 | Value | Description | Reference | 869 +-------------+---------------+---------------+ 870 | TBD1 (5) | AODV-RPL | This document | 871 +-------------+---------------+---------------+ 873 Figure 6: Mode of Operation 875 9.2. AODV-RPL Options: RREQ, RREP, and Target 877 Three entries are required for new AODV-RPL options "RREQ", "RREP" 878 and "ART" with values of TBD2 (0x0A), TBD3 (0x0B) and TBD4 (0x0C) 879 from the "RPL Control Message Options" space [RFC6550]. 881 +-------------+------------------------+---------------+ 882 | Value | Meaning | Reference | 883 +-------------+------------------------+---------------+ 884 | TBD2 (0x0A) | RREQ Option | This document | 885 +-------------+------------------------+---------------+ 886 | TBD3 (0x0B) | RREP Option | This document | 887 +-------------+------------------------+---------------+ 888 | TBD3 (0x0C) | ART Option | This document | 889 +-------------+------------------------+---------------+ 891 Figure 7: AODV-RPL Options 893 10. Security Considerations 895 This document does not introduce additional security issues compared 896 to base RPL. For general RPL security considerations, see [RFC6550]. 898 11. Future Work 900 There has been some discussion about how to determine the initial 901 state of a link after an AODV-RPL-based network has begun operation. 902 The current draft operates as if the links are symmetric until 903 additional metric information is collected. The means for making 904 link metric information is considered out of scope for AODV-RPL. In 905 the future, RREQ and RREP messages could be equipped with new fields 906 for use in verifying link metrics. In particular, it is possible to 907 identify unidirectional links; an RREQ received across a 908 unidirectional link has to be dropped, since the destination node 909 cannot make use of the received DODAG to route packets back to the 910 source node that originated the route discovery operation. This is 911 roughly the same as considering a unidirectional link to present an 912 infinite cost metric that automatically disqualifies it for use in 913 the reverse direction. 915 12. Contributors 917 Abdur Rashid Sangi 918 Huaiyin Institute of Technology 919 No.89 North Beijing Road, Qinghe District 920 Huaian 223001 921 P.R. China 922 Email: sangi_bahrian@yahoo.com 924 13. References 925 13.1. Normative References 927 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 928 Requirement Levels", BCP 14, RFC 2119, 929 DOI 10.17487/RFC2119, March 1997, 930 . 932 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 933 Demand Distance Vector (AODV) Routing", RFC 3561, 934 DOI 10.17487/RFC3561, July 2003, 935 . 937 [RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and 938 D. Barthel, Ed., "Routing Requirements for Urban Low-Power 939 and Lossy Networks", RFC 5548, DOI 10.17487/RFC5548, May 940 2009, . 942 [RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T. 943 Phinney, "Industrial Routing Requirements in Low-Power and 944 Lossy Networks", RFC 5673, DOI 10.17487/RFC5673, October 945 2009, . 947 [RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation 948 Routing Requirements in Low-Power and Lossy Networks", 949 RFC 5826, DOI 10.17487/RFC5826, April 2010, 950 . 952 [RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen, 953 "Building Automation Routing Requirements in Low-Power and 954 Lossy Networks", RFC 5867, DOI 10.17487/RFC5867, June 955 2010, . 957 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 958 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 959 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 960 Low-Power and Lossy Networks", RFC 6550, 961 DOI 10.17487/RFC6550, March 2012, 962 . 964 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 965 Protocol for Low-Power and Lossy Networks (RPL)", 966 RFC 6552, DOI 10.17487/RFC6552, March 2012, 967 . 969 [RFC6998] Goyal, M., Ed., Baccelli, E., Brandt, A., and J. Martocci, 970 "A Mechanism to Measure the Routing Metrics along a Point- 971 to-Point Route in a Low-Power and Lossy Network", 972 RFC 6998, DOI 10.17487/RFC6998, August 2013, 973 . 975 13.2. Informative References 977 [I-D.thubert-roll-asymlink] 978 Thubert, P., "RPL adaptation for asymmetrical links", 979 draft-thubert-roll-asymlink-02 (work in progress), 980 December 2011. 982 [Perlman83] 983 Perlman, R., "Fault-Tolerant Broadcast of Routing 984 Information", December 1983. 986 [RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and 987 J. Martocci, "Reactive Discovery of Point-to-Point Routes 988 in Low-Power and Lossy Networks", RFC 6997, 989 DOI 10.17487/RFC6997, August 2013, 990 . 992 Appendix A. Example: ETX/RSSI Values to select S bit 994 We have tested the combination of "RSSI(downstream)" and "ETX 995 (upstream)" to determine whether the link is symmetric or asymmetric 996 at the intermediate nodes. The example of how the ETX and RSSI 997 values are used in conjuction is explained below: 999 Source---------->NodeA---------->NodeB------->Destination 1001 Figure 8: Communication link from Source to Destination 1003 +-------------------------+----------------------------------------+ 1004 | RSSI at NodeA for NodeB | Expected ETX at NodeA for NodeB->NodeA | 1005 +-------------------------+----------------------------------------+ 1006 | > -60 | 150 | 1007 | -70 to -60 | 192 | 1008 | -80 to -70 | 226 | 1009 | -90 to -80 | 662 | 1010 | -100 to -90 | 993 | 1011 +-------------------------+----------------------------------------+ 1013 Table 1: Selection of 'S' bit based on Expected ETX value 1015 We tested the operations in this specification by making the 1016 following experiment, using the above parameters. In our experiment, 1017 a communication link is considered as symmetric if the ETX value of 1018 NodeA->NodeB and NodeB->NodeA (See Figure.8) are, say, within 1:3 1019 ratio. This ratio should be taken as a notional metric for deciding 1020 link symmetric/asymmetric nature, and precise definition of the ratio 1021 is beyond the scope of the draft. In general, NodeA can only know 1022 the ETX value in the direction of NodeA -> NodeB but it has no direct 1023 way of knowing the value of ETX from NodeB->NodeA. Using physical 1024 testbed experiments and realistic wireless channel propagation 1025 models, one can determine a relationship between RSSI and ETX 1026 representable as an expression or a mapping table. Such a 1027 relationship in turn can be used to estimate ETX value at nodeA for 1028 link NodeB--->NodeA from the received RSSI from NodeB. Whenever 1029 nodeA determines that the link towards the nodeB is bi-directional 1030 asymmetric then the "S" bit is set to "S=0". Later on, the link from 1031 NodeA to Destination is asymmetric with "S" bit remains to "0". 1033 Appendix B. Changelog 1035 B.1. Changes to version 02 1037 o Include the support for source routing. 1039 o Import some features from [RFC6997], e.g., choice between hop-by- 1040 hop and source routing, the "L" bit which determines the duration 1041 of residence in the DAG, MaxRank, etc. 1043 o Define new target option for AODV-RPL, including the Destination 1044 Sequence Number in it. Move the TargNode address in RREQ option 1045 and the OrigNode address in RREP option into ADOV-RPL Target 1046 Option. 1048 o Support route discovery for multiple targets in one RREQ-DIO. 1050 o New InstanceID pairing mechanism. 1052 B.2. Changes to version 03 1054 o Updated RREP option format. Remove the 'T' bit in RREP option. 1056 o Using the same RPLInstanceID for RREQ and RREP, no need to update 1057 [RFC6550]. 1059 o Explanation of Shift field in RREP. 1061 o Multiple target options handling during transmission. 1063 B.3. Changes to version 04 1065 o Add description for sequence number operations. 1067 o Extend the residence duration L in the section 4.1. 1069 o Change AODV-RPL Target option to ART option. 1071 Authors' Addresses 1073 Satish Anamalamudi 1074 SRM University-AP 1075 Amaravati Campus 1076 Amaravati, Andhra Pradesh 522 502 1077 India 1079 Email: satishnaidu80@gmail.com 1081 Mingui Zhang 1082 Huawei Technologies 1083 No. 156 Beiqing Rd. Haidian District 1084 Beijing 100095 1085 China 1087 Email: zhangmingui@huawei.com 1089 Charles E. Perkins 1090 Futurewei 1091 2330 Central Expressway 1092 Santa Clara 95050 1093 Unites States 1095 Email: charliep@computer.org 1097 S.V.R Anand 1098 Indian Institute of Science 1099 Bangalore 560012 1100 India 1102 Email: anand@ece.iisc.ernet.in 1103 Bing Liu 1104 Huawei Technologies 1105 No. 156 Beiqing Rd. Haidian District 1106 Beijing 100095 1107 China 1109 Email: remy.liubing@huawei.com