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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 roll P. Thubert, Ed. 3 Internet-Draft Cisco 4 Intended status: Standards Track C. Bormann 5 Expires: April 28, 2017 Uni Bremen TZI 6 L. Toutain 7 IMT-TELECOM Bretagne 8 R. Cragie 9 ARM 10 October 25, 2016 12 6LoWPAN Routing Header 13 draft-ietf-roll-routing-dispatch-03 15 Abstract 17 This specification introduces a new 6LoWPAN dispatch type for use in 18 6LoWPAN Route-Over topologies, that initially covers the needs of RPL 19 (RFC6550) data packets compression. Using this dispatch type, this 20 specification defines a method to compress RPL Option (RFC6553) 21 information and Routing Header type 3 (RFC6554), an efficient IP-in- 22 IP technique and is extensible for more applications. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on April 28, 2017. 41 Copyright Notice 43 Copyright (c) 2016 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 3. Using the Page Dispatch . . . . . . . . . . . . . . . . . . . 6 61 3.1. New Routing Header Dispatch (6LoRH) . . . . . . . . . . . 6 62 3.2. Placement Of 6LoRH headers . . . . . . . . . . . . . . . 7 63 3.2.1. Relative To Non-6LoRH Headers . . . . . . . . . . . . 7 64 3.2.2. Relative To Other 6LoRH Headers . . . . . . . . . . . 7 65 4. 6LoWPAN Routing Header General Format . . . . . . . . . . . . 8 66 4.1. Elective Format . . . . . . . . . . . . . . . . . . . . . 9 67 4.2. Critical Format . . . . . . . . . . . . . . . . . . . . . 9 68 4.3. Compressing Addresses . . . . . . . . . . . . . . . . . . 10 69 4.3.1. Coalescence . . . . . . . . . . . . . . . . . . . . . 10 70 4.3.2. DODAG Root Address Determination . . . . . . . . . . 11 71 5. The SRH 6LoRH Header . . . . . . . . . . . . . . . . . . . . 12 72 5.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 12 73 5.2. SRH-6LoRH General Operation . . . . . . . . . . . . . . . 13 74 5.2.1. Uncompressed SRH Operation . . . . . . . . . . . . . 13 75 5.2.2. 6LoRH-Compressed SRH Operation . . . . . . . . . . . 14 76 5.2.3. Inner LOWPAN_IPHC Compression . . . . . . . . . . . . 14 77 5.3. The Design Point of Popping Entries . . . . . . . . . . . 15 78 5.4. Compression Reference for SRH-6LoRH header entries . . . 16 79 5.5. Popping Headers . . . . . . . . . . . . . . . . . . . . . 17 80 5.6. Forwarding . . . . . . . . . . . . . . . . . . . . . . . 17 81 6. The RPL Packet Information 6LoRH . . . . . . . . . . . . . . 18 82 6.1. Compressing the RPLInstanceID . . . . . . . . . . . . . . 19 83 6.2. Compressing the SenderRank . . . . . . . . . . . . . . . 20 84 6.3. The Overall RPI-6LoRH encoding . . . . . . . . . . . . . 20 85 7. The IP-in-IP 6LoRH Header . . . . . . . . . . . . . . . . . . 23 86 8. Management Considerations . . . . . . . . . . . . . . . . . . 24 87 9. Security Considerations . . . . . . . . . . . . . . . . . . . 25 88 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 89 10.1. Reserving Space in 6LoWPAN Dispatch Page 1 . . . . . . . 26 90 10.2. New Critical 6LoWPAN Routing Header Type Registry . . . 26 91 10.3. New Elective 6LoWPAN Routing Header Type Registry . . . 26 92 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27 93 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27 94 12.1. Normative References . . . . . . . . . . . . . . . . . . 27 95 12.2. Informative References . . . . . . . . . . . . . . . . . 28 96 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 29 97 A.1. Examples Compressing The RPI . . . . . . . . . . . . . . 29 98 A.2. Example Of Downward Packet In Non-Storing Mode . . . . . 31 99 A.3. Example of SRH-6LoRH life-cycle . . . . . . . . . . . . . 33 100 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 102 1. Introduction 104 The design of Low Power and Lossy Networks (LLNs) is generally 105 focused on saving energy, a very constrained resource in most cases. 106 The other constraints, such as the memory capacity and the duty 107 cycling of the LLN devices, derive from that primary concern. Energy 108 is often available from primary batteries that are expected to last 109 for years, or is scavenged from the environment in very limited 110 quantities. Any protocol that is intended for use in LLNs must be 111 designed with the primary concern of saving energy as a strict 112 requirement. 114 Controlling the amount of data transmission is one possible venue to 115 save energy. In a number of LLN standards, the frame size is limited 116 to much smaller values than the IPv6 maximum transmission unit (MTU) 117 of 1280 bytes. In particular, an LLN that relies on the classical 118 Physical Layer (PHY) of IEEE 802.15.4 [IEEE802154] is limited to 127 119 bytes per frame. The need to compress IPv6 packets over IEEE 120 802.15.4 led to the "6LoWPAN Header Compression" [RFC6282] work 121 (6LoWPAN_HC). 123 Innovative Route-over techniques have been and are still being 124 developed for routing inside a LLN. In a general fashion, such 125 techniques require additional information in the packet to provide 126 loop prevention and to indicate information such as flow 127 identification, source routing information, etc. 129 For reasons such as security and the capability to send ICMPv6 errors 130 (see "Internet Control Message Protocol (ICMPv6)" [RFC4443]) back to 131 the source, an original packet must not be tampered with, and any 132 information that must be inserted in or removed from an IPv6 packet 133 must be placed in an extra IP-in-IP encapsulation . 135 This is the case when the additional routing information is inserted 136 by a router on the path of a packet, for instance the root of a mesh, 137 as opposed to the source node, with the non-storing mode of the "IPv6 138 Routing Protocol for Low-Power and Lossy Networks" [RFC6550] (RPL). 140 This is also the case when some routing information must be removed 141 from a packet that flows outside the LLN. 143 "When to use RFC 6553, RFC 6554 and IPv6-in-IPv6" 144 [I-D.ietf-roll-useofrplinfo] details different cases where IPv6 145 headers defined in the "RPL Option for Carrying RPL Information in 146 Data-Plane Datagrams" [RFC6553] and the "Routing Header for Source 147 Routes with RPL" [RFC6554], and IPv6-in-IPv6 encapsulation, are 148 inserted or removed from packets in a LLN environments operating RPL. 150 When using RFC 6282 [RFC6282] the outer IP header of an IP-in-IP 151 encapsulation may be compressed down to 2 octets in stateless 152 compression and down to 3 octets in stateful compression when context 153 information must be added. 155 0 1 156 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 157 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 158 | 0 | 1 | 1 | TF |NH | HLIM |CID|SAC| SAM | M |DAC| DAM | 159 +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ 161 Figure 1: LOWPAN_IPHC base Encoding (RFC6282). 163 The Stateless Compression of an IPv6 addresses can only happen if the 164 IPv6 address can de deduced from the MAC addresses, meaning that the 165 IP end point is also the MAC-layer endpoint. This is generally not 166 the case in a RPL network which is generally a multi-hop route-over 167 (i.e., operated at Layer-3) network. A better compression, which 168 does not involve variable compressions depending on the hop in the 169 mesh, can be achieved based on the fact that the outer encapsulation 170 is usually between the source (or destination) of the inner packet 171 and the root. Also, the inner IP header can only be compressed by 172 RFC 6282 [RFC6282] if all the fields preceding it are also 173 compressed. This specification makes the inner IP header the first 174 header to be compressed by RFC 6282 [RFC6282], and keeps the inner 175 packet encoded the same way whether it is encapsulated or not, thus 176 preserving existing implementations. 178 As an example, RPL [RFC6550] is designed to optimize the routing 179 operations in constrained LLNs. As part of this optimization, RPL 180 requires the addition of RPL Packet Information (RPI) in every 181 packet, as defined in Section 11.2 of RFC 6550 [RFC6550]. 183 The "RPL Option for Carrying RPL Information in Data-Plane Datagrams" 184 [RFC6553] specification indicates how the RPI can be placed in a RPL 185 Option (RPL-OPT) that is placed in an IPv6 Hop-by-Hop header. 187 This representation demands a total of 8 bytes, while in most cases 188 the actual RPI payload requires only 19 bits. Since the Hop-by-Hop 189 header must not flow outside of the RPL domain, it must be inserted 190 in packets entering the domain and be removed from packets that leave 191 the domain. In both cases, this operation implies an IP-in-IP 192 encapsulation. 194 Additionally, in the case of the Non-Storing Mode of Operation (MOP), 195 RPL requires a Source Routing Header (SRH) in all packets that are 196 routed down a RPL graph. for that purpose, the "IPv6 Routing Header 197 for Source Routes with RPL" [RFC6554] specification defines the type 198 3 Routing Header for IPv6 (RH3). 200 ------+--------- ^ 201 | Internet | 202 | | Native IPv6 203 +-----+ | 204 | | Border Router (RPL Root) ^ | ^ 205 | | | | | 206 +-----+ | | | IPv6 in 207 | | | | IPv6 208 o o o o | | | plus 209 o o o o o o o o o | | | RPL SRH 210 o o o o o o o o o o | | | 211 o o o o o o o o o | | | 212 o o o o o o o o v v v 213 o o o o 214 LLN 216 Figure 2: IP-in-IP Encapsulation within the LLN. 218 With Non-Storing RPL, even if the source is a node in the same LLN, 219 the packet must first reach up the graph to the root so that the root 220 can insert the SRH to go down the graph. In any fashion, whether the 221 packet was originated in a node in the LLN or outside the LLN, and 222 regardless of whether the packet stays within the LLN or not, as long 223 as the source of the packet is not the root itself, the source- 224 routing operation also implies an IP-in-IP encapsulation at the root 225 in order to insert the SRH. 227 "The 6TiSCH Architecture" [I-D.ietf-6tisch-architecture] specifies 228 the operation of IPv6 over the "TimeSlotted Channel Hopping" 229 [RFC7554] (TSCH) mode of operation of IEEE 802.15.4. The 230 architecture requires the use of both RPL and the 6lo adaptation 231 layer over IEEE 802.15.4. Because it inherits the constraints on 232 frame size from the MAC layer, 6TiSCH cannot afford to allocate 8 233 bytes per packet on the RPI. Hence the requirement for 6LoWPAN 234 header compression of the RPI. 236 An extensible compression technique is required that simplifies IP- 237 in-IP encapsulation when it is needed, and optimally compresses 238 existing routing artifacts found in RPL LLNs. 240 This specification extends the 6lo adaptation layer framework (RFC 241 4944 [RFC4944] and RFC 6282 [RFC6282]) so as to carry routing 242 information for route-over networks based on RPL. The specification 243 includes the formats necessary for RPL and is extensible for 244 additional formats. 246 2. Terminology 248 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 249 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 250 "OPTIONAL" in this document are to be interpreted as described in RFC 251 2119 [RFC2119]. 253 The Terminology used in this document is consistent with and 254 incorporates that described in Terminology in Low power And Lossy 255 Networks [RFC7102] and RPL [RFC6550]. 257 The terms Route-over and Mesh-under are defined in RFC 6775 258 [RFC6775]. 260 Other terms in use in LLNs are found in "Terminology for Constrained- 261 Node Networks" [RFC7228]. 263 The term "byte" is used in its now customary sense as a synonym for 264 "octet". 266 3. Using the Page Dispatch 268 The 6LoWPAN Paging Dispatch [I-D.ietf-6lo-paging-dispatch] 269 specification extends the 6lo adaptation layer framework (RFC 4944 270 [RFC4944] and RFC 6282 [RFC6282]) by introducing a concept of 271 "context" in the 6LoWPAN parser, a context being identified by a Page 272 number. The specification defines 16 Pages. 274 This draft operates within Page 1, which is indicated by a Dispatch 275 Value of binary 11110001. 277 3.1. New Routing Header Dispatch (6LoRH) 279 This specification introduces a new 6LoWPAN Routing Header (6LoRH) to 280 carry IPv6 routing information. The 6LoRH may contain source routing 281 information such as a compressed form of SRH, as well as other sorts 282 of routing information such as the RPI and IP-in-IP encapsulation. 284 The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value 285 (TLV) field, which is extensible for future use. 287 It is expected that a router that does not recognize the 6LoRH 288 general format detailed in Section 4 will drop the packet when a 289 6LoRH is present. 291 This specification uses the bit pattern 10xxxxxx in Page 1 for the 292 new 6LoRH Dispatch. Section 4 describes how RPL artifacts in data 293 packets can be compressed as 6LoRH headers. 295 3.2. Placement Of 6LoRH headers 297 3.2.1. Relative To Non-6LoRH Headers 299 In a zone of a packet where Page 1 is active (that is, once the Page 300 1 Paging Dispatch is parsed, and until another Paging Dispatch is 301 parsed as described in the 6LoWPAN Paging Dispatch specification 302 [I-D.ietf-6lo-paging-dispatch]), the parsing of the packet MUST 303 follow this specification if the 6LoRH Bit Pattern (see Section 3.1) 304 is found. 306 With this specification, the 6LoRH Dispatch is only defined in Page 307 context is active. 309 Because a 6LoRH header requires a Page 1 context, it MUST always be 310 placed after any Fragmentation Header and/or Mesh Header as defined 311 in RFC 4944 [RFC4944]. 313 A 6LoRH header MUST always be placed before the LOWPAN_IPHC as 314 defined in RFC 6282 [RFC6282]. It is designed in such a fashion that 315 placing or removing a header that is encoded with 6LoRH does not 316 modify the part of the packet that is encoded with LOWPAN_IPHC, 317 whether there is an IP-in-IP encapsulation or not. For instance, the 318 final destination of the packet is always the one in the LOWPAN_IPHC 319 whether there is a Routing Header or not. 321 3.2.2. Relative To Other 6LoRH Headers 323 The "Internet Protocol, Version 6 (IPv6) Specification" [RFC2460] 324 defines chains of headers that are introduced by an IPv6 header and 325 terminated by either another IPv6 header (IP-in-IP) or an Upper Layer 326 Protocol (ULP) header. When an outer header is stripped from the 327 packet, the whole chain goes with it. When one or more header(s) are 328 inserted by an intermediate router, that router normally chains the 329 headers and encapsulates the result in IP-in-IP. 331 With this specification, the chains of headers MUST be compressed in 332 the same order as they appear in the uncompressed form of the packet. 333 This means that if there is more than one nested IP-in-IP 334 encapsulations, the first IP-in-IP encapsulation, with all its chain 335 of headers, is encoded first in the compressed form. 337 In the compressed form of a packet that has a Source Route or a Hop- 338 by-Hop (HbH) Options Header [RFC2460] after the inner IPv6 header 339 (e.g. if there is no IP-in-IP encapsulation), these headers are 340 placed in the 6LoRH form before the 6LOWPAN_IPHC that represents the 341 IPv6 header (see Section 3.2.1). If this packet gets encapsulated 342 and some other SRH or HbH Options Headers are added as part of the 343 encapsulation, placing the 6LoRH headers next to one another may 344 present an ambiguity on which header belong to which chain in the 345 uncompressed form. 347 In order to disambiguate the headers that follow the inner IPv6 348 header in the uncompressed form from the headers that follow the 349 outer IP-in-IP header, it is REQUIRED that the compressed IP-in-IP 350 header is placed last in the encoded chain. This means that the 351 6LoRH headers that are found after the last compressed IP-in-IP 352 header are to be inserted after the IPv6 header that is encoded with 353 the 6LOWPAN_IPHC when decompressing the packet. 355 With regards to the relative placement of the SRH and the RPI in the 356 compressed form, it is a design point for this specification that the 357 SRH entries are consumed as the packet progresses down the LLN (see 358 Section 5.3). In order to make this operation simpler in the 359 compressed form, it is REQUIRED that in the compressed form, the 360 addresses along the source route path are encoded in the order of the 361 path, and that the compressed SRH are placed before the compressed 362 RPI. 364 4. 6LoWPAN Routing Header General Format 366 The 6LoRH uses the Dispatch Value Bit Pattern of 10xxxxxx in Page 1. 368 The Dispatch Value Bit Pattern is split in two forms of 6LoRH: 370 Elective (6LoRHE) that may skipped if not understood 372 Critical (6LoRHC) that may not be ignored 374 For each form, a Type field is used to encode the type of 6LoRH. 376 Note that there is a different registry for the Type field of each 377 form of 6LoRH. 379 This means that a value for the Type that is defined for one form of 380 6LoRH may be redefined in the future for the other form. 382 4.1. Elective Format 384 The 6LoRHE uses the Dispatch Value Bit Pattern of 101xxxxx. A 6LoRHE 385 may be ignored and skipped in parsing. If it is ignored, the 6LoRHE 386 is forwarded with no change inside the LLN. 388 0 1 389 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 391 |1|0|1| Length | Type | | 392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 393 <-- Length --> 395 Figure 3: Elective 6LoWPAN Routing Header. 397 Length: Length of the 6LoRHE expressed in bytes, excluding the first 398 2 bytes. This enables a node to skip a 6LoRHE header that it 399 does not support and/or cannot parse, for instance if the Type 400 is not recognized. 402 Type: Type of the 6LoRHE 404 4.2. Critical Format 406 The 6LoRHC uses the Dispatch Value Bit Pattern of 100xxxxx. 408 A node which does not support the 6LoRHC Type MUST silently discard 409 the packet. 411 Note: the situation where a node receives a message with a Critical 412 6LoWPAN Routing Header that it does not understand should not occur 413 and is an administrative error, see Section 8. 415 0 1 416 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 418 |1|0|0| TSE | Type | | 419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 420 <-- Length implied by Type/TSE --> 422 Figure 4: Critical 6LoWPAN Routing Header. 424 TSE: Type Specific Extension. The meaning depends on the Type, 425 which must be known in all of the nodes. The interpretation of 426 the TSE depends on the Type field that follows. For instance, 427 it may be used to transport control bits, the number of 428 elements in an array, or the length of the remainder of the 429 6LoRHC expressed in a unit other than bytes. 431 Type: Type of the 6LoRHC 433 4.3. Compressing Addresses 435 The general technique used in this draft to compress an address is 436 first to determine a reference that has a long prefix match with this 437 address, and then elide that matching piece. In order to reconstruct 438 the compressed address, the receiving node will perform the process 439 of coalescence described in Section 4.3.1. 441 One possible reference is the root of the RPL DODAG that is being 442 traversed. It is used by 6LoRH as the reference to compress an outer 443 IP header, in case of an IP-in-IP encapsulation. If the root is the 444 source of the packet, this technique allows to fully elide the source 445 address in the compressed form of the IP header. If the root is not 446 the encapsulator, then the encapsulator address may still be 447 compressed using the root as reference. How the address of the root 448 is determined is discussed in Section 4.3.2. 450 Once the address of the source of the packet is determined, it 451 becomes the reference for the compression of the addresses that are 452 located in compressed SRH headers that are present inside the IP-in- 453 IP encapsulation in the uncompressed form. 455 4.3.1. Coalescence 457 An IPv6 compressed address is coalesced with a reference address by 458 overriding the N rightmost bytes of the reference address with the 459 compressed address, where N is the length of the compressed address, 460 as indicated by the Type of the SRH-6LoRH header in Figure 7. 462 The reference address MAY be a compressed address as well, in which 463 case it MUST be compressed in a form that is of an equal or greater 464 length than the address that is being coalesced. 466 A compressed address is expanded by coalescing it with a reference 467 address. In the particular case of a Type 4 SRH-6LoRH, the address 468 is expressed in full and the coalescence is a complete override as 469 illustrated in Figure 5. 471 RRRRRRRRRRRRRRRRRRRR reference address, may be compressed or not 473 CCCCCCC compressed address, shorter or same as reference 475 RRRRRRRRRRRRRCCCCCCC Coalesced address, same compression as reference 477 Figure 5: Coalescing addresses. 479 4.3.2. DODAG Root Address Determination 481 Stateful Address compression requires that some state is installed in 482 the devices to store the compression information that is elided from 483 the packet. That state is stored in an abstract context table and 484 some form of index is found in the packet to obtain the compression 485 information from the context table. 487 With RFC 6282 [RFC6282], the state is provided to the stack by the 488 "6LoWPAN Neighbor Discovery Protocol (NDP)" [RFC6775]. NDP exchanges 489 the context through 6LoWPAN Context Option in Router Advertisement 490 (RA) messages. In the compressed form of the packet, the context can 491 be signaled in a Context Identifier Extension. 493 With this specification, the compression information is provided to 494 the stack by RPL, and RPL exchanges it through the DODAGID field in 495 the DAG Information Object (DIO) messages, as described in more 496 detail below. In the compressed form of the packet, the context can 497 be signaled in by the RPLInstanceID in the RPI. 499 With RPL [RFC6550], the address of the DODAG root is known from the 500 DODAGID field of the DIO messages. For a Global Instance, the 501 RPLInstanceID that is present in the RPI is enough information to 502 identify the DODAG that this node participates to and its associated 503 root. But for a Local Instance, the address of the root MUST be 504 explicit, either in some device configuration or signaled in the 505 packet, as the source or the destination address, respectively. 507 When implicit, the address of the DODAG root MUST be determined as 508 follows: 510 If the whole network is a single DODAG then the root can be well- 511 known and does not need to be signaled in the packets. But since RPL 512 does not expose that property, it can only be known by a 513 configuration applied to all nodes. 515 Else, the router that encapsulates the packet and compresses it with 516 this specification MUST also place an RPI in the packet as prescribed 517 by RPL to enable the identification of the DODAG. The RPI must be 518 present even in the case when the router also places an SRH header in 519 the packet. 521 It is expected that the RPL implementation maintains an abstract 522 context table, indexed by Global RPLInstanceID, that provides the 523 address of the root of the DODAG that this nodes participates to for 524 that particular RPL Instance. 526 5. The SRH 6LoRH Header 528 5.1. Encoding 530 A Source Routing Header 6LoRH (SRH-6LoRH) header provides a 531 compressed form for the SRH, as defined in RFC 6554 [RFC6554] for use 532 by RPL routers. 534 One or more SRH-6LoRH header(s) MAY be placed in a 6LoWPAN packet. 536 If a non-RPL router receives a packet with a SRH-6LoRH header, there 537 was a routing or a configuration error (see Section 8). 539 The desired reaction for the non-RPL router is to drop the packet as 540 opposed to skip the header and forward the packet. 542 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 543 Critical. Routers that understand the 6LoRH general format detailed 544 in Section 4 cannot ignore a 6LoRH header of this type, and will drop 545 the packet if it is unknown to them. 547 0 1 548 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 550 |1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN | 551 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+ 553 Where N = Size + 1 555 Figure 6: The SRH-6LoRH. 557 The 6LoRH Type of a SRH-6LoRH header indicates the compression level 558 used for that header. 560 The fields following the 6LoRH Type are compressed addresses 561 indicating the consecutive hops, and are ordered from the first to 562 the last hop. 564 All the addresses in a given SRH-6LoRH header MUST be compressed in 565 an identical fashion, so the Length of the compressed form is the 566 same for all. 568 In order to get different degrees of compression, multiple 569 consecutive SRH-6LoRH headers MUST be used. 571 Type 0 means that the address is compressed down to one byte, whereas 572 Type 4 means that the address is provided in full in the SRH-6LoRH 573 with no compression. The complete list of Types of SRH-6LoRH and the 574 corresponding compression level are provided in Figure 7: 576 +-----------+----------------------+ 577 | 6LoRH | Length of compressed | 578 | Type | IPv6 address (bytes) | 579 +-----------+----------------------+ 580 | 0 | 1 | 581 | 1 | 2 | 582 | 2 | 4 | 583 | 3 | 8 | 584 | 4 | 16 | 585 +-----------+----------------------+ 587 Figure 7: The SRH-6LoRH Types. 589 In the case of a SRH-6LoRH header, the TSE field is used as a Size, 590 which encodes the number of hops minus 1; so a Size of 0 means one 591 hop, and the maximum that can be encoded is 32 hops. (If more than 592 32 hops need to be expressed, a sequence of SRH-6LoRH elements can be 593 employed.) It results that the Length in bytes of a SRH-6LoRH header 594 is: 596 2 + Length_of_compressed_IPv6_address * (Size + 1) 598 5.2. SRH-6LoRH General Operation 600 5.2.1. Uncompressed SRH Operation 602 In the non-compressed form, when the root generates or forwards a 603 packet in non-Storing Mode, it needs to include a Source Routing 604 Header [RFC6554] to signal a strict source-route path to a final 605 destination down the DODAG. 607 All the hops along the path, but the first one, are encoded in order 608 in the SRH. The last entry in the SRH is the final destination and 609 the destination in the IPv6 header is the first hop along the source- 610 route path. The intermediate hops perform a swap and the Segment- 611 Left field indicates the active entry in the Routing Header 612 [RFC2460]. 614 The current destination of the packet, which is the termination of 615 the current segment, is indicated at all times by the destination 616 address of the IPv6 header. 618 5.2.2. 6LoRH-Compressed SRH Operation 620 The handling of the SRH-6LoRH is different: there is no swap, and a 621 forwarding router that corresponds to the first entry in the first 622 SRH-6LoRH upon reception of a packet effectively consumes that entry 623 when forwarding. This means that the size of a compressed source- 624 routed packet decreases as the packet progresses along its path and 625 that the routing information is lost along the way. This also means 626 that an SRH encoded with 6LoRH is not recoverable and cannot be 627 protected. 629 When compressed with this specification, all the remaining hops MUST 630 be encoded in order in one or more consecutive SRH-6LoRH headers. 631 Whether or not there is a SRH-6LoRH header present, the address of 632 the final destination is indicated in the LOWPAN_IPHC at all times 633 along the path. Examples of this are provided in Appendix A. 635 The current destination (termination of the current segment) for a 636 compressed source-routed packet is indicated in the first entry of 637 the first SRH-6LoRH. In strict source-routing, that entry MUST match 638 an address of the router that receives the packet. 640 The last entry in the last SRH-6LoRH is the last router on the way to 641 the final destination in the LLN. This router can be the final 642 destination if it is found desirable to carry a whole IP-in-IP 643 encapsulation all the way. Else, it is the RPL parent of the final 644 destination, or a router acting at 6LR [RFC6775] for the destination 645 host, and advertising the host as an external route to RPL. 647 If the SRH-6LoRH header is contained in an IP-in-IP encapsulation, 648 the last router removes the whole chain of headers. Otherwise, it 649 removes the SRH-6LoRH header only. 651 5.2.3. Inner LOWPAN_IPHC Compression 653 6LoWPAN ND [RFC6282] is designed to support more than one IPv6 654 address per node and per Interface Identifier (IID), an IID being 655 typically derived from a MAC address to optimize the LOWPAN_IPHC 656 compression. 658 Link local addresses are compressed with stateless address 659 compression (S/DAC=0). The other addresses are derived from 660 different prefixes and they can be compressed with stateful address 661 compression based on a context (S/DAC=1). 663 But stateless compression is only defined for the specific link-local 664 prefix as opposed to the prefix in an encapsulating header. And with 665 stateful compression, the compression reference is found in a 666 context, as opposed to an encapsulating header. 668 It results that in the case of an IP-in-IP encapsulation, it is 669 possible to compress an inner source (respectively destination) IP 670 address in a LOWPAN_IPHC based on the encapsulating IP header only if 671 stateful (context-based) compression is used. The compression will 672 operate only if the IID in the source (respectively the destination) 673 IP address in the outer and inner headers match, which usually means 674 that they refer to the same node . This is encoded as S/DAC = 1 and 675 S/AM=11. It must be noted that the outer destination address that is 676 used to compress the inner destination address is the last entry in 677 the last SRH-6LoRH header. 679 5.3. The Design Point of Popping Entries 681 In order to save energy and to optimize the chances of transmission 682 success on lossy media, it is a design point for this specification 683 that the entries in the SRH that have been used are removed from the 684 packet. This creates a discrepancy from the art of IPv6 where 685 Routing Header are mutable but recoverable. 687 With this specification, the packet can be expanded at any hop into a 688 valid IPv6 packet, including a SRH, and compressed back. But the 689 packet as decompressed along the way will not carry all the consumed 690 addresses that packet would have if it had been forwarded in the 691 uncompressed form. 693 It is noted that: 695 The value of keeping the whole RH in an IPv6 header is for the 696 receiver to reverse it to use the symmetrical path on the way 697 back. 699 It is generally not a good idea to reverse a routing header. The 700 RH may have been used to stay away from the shortest path for some 701 reason that is only valid on the way in (segment routing). 703 There is no use of reversing a RH in the present RPL 704 specifications. 706 P2P RPL reverses a path that was learned reactively, as a part of 707 the protocol operation, which is probably a cleaner way than a 708 reversed echo on the data path. 710 Reversing a header is discouraged by RFC 2460 [RFC2460] for RH0 711 unless it is authenticated, which requires an Authentication 712 Header (AH). There is no definition of an AH operation for SRH, 713 and there is no indication that the need exists in LLNs. 715 It is noted that AH does not protect the RH on the way. AH is a 716 validation at the receiver with the sole value of enabling the 717 receiver to reversing it. 719 A RPL domain is usually protected by L2 security and that secures 720 both RPL itself and the RH in the packets, at every hop. This is 721 a better security than that provided by AH. 723 In summary, the benefit of saving energy and lowering the chances of 724 loss by sending smaller frames over the LLN are seen as overwhelming 725 compared to the value of possibly reversing the header. 727 5.4. Compression Reference for SRH-6LoRH header entries 729 In order to optimize the compression of IP addresses present in the 730 SRH headers, this specification requires that the 6LoWPAN layer 731 identifies an address that is used as reference for the compression. 733 With this specification, the Compression Reference for the first 734 address found in an SRH header is the source of the IPv6 packet, and 735 then the reference for each subsequent entry is the address of its 736 predecessor once it is uncompressed. 738 With RPL [RFC6550], an SRH header may only be present in Non-Storing 739 mode, and it may only be placed in the packet by the root of the 740 DODAG, which must be the source of the resulting IPv6 packet 741 [RFC2460]. In this case, the address used as Compression Reference 742 is the address of the root. 744 The Compression Reference MUST be determined as follows: 746 The reference address may be obtained by configuration. The 747 configuration may indicate either the address in full, or the 748 identifier of a 6LoWPAN Context that carries the address [RFC6775], 749 for instance one of the 16 Context Identifiers used in LOWPAN_IPHC 750 [RFC6282]. 752 Else, and if there is no IP-in-IP encapsulation, the source address 753 in the IPv6 header that is compressed with LOWPAN_IPHC is the 754 reference for the compression. 756 Else, and if the IP-in-IP compression specified in this document is 757 used and the Encapsulator Address is provided, then the Encapsulator 758 Address is the reference. 760 Else, meaning that the IP-in-IP compression specified in this 761 document is used and the encapsulator is implicitly the root, the 762 address of the root is the reference. 764 5.5. Popping Headers 766 Upon reception, the router checks whether the address in the first 767 entry of the first SRH-6LoRH one of its own addresses. In that case, 768 router MUST consume that entry before forwarding, which is an action 769 of popping from a stack, where the stack is effectively the sequence 770 of entries in consecutive SRH-6LoRH headers. 772 Popping an entry of an SRH-6LoRH header is a recursive action 773 performed as follows: 775 If the Size of the SRH-6LoRH header is 1 or more, indicating that 776 there are at least 2 entries in the header, the router removes the 777 first entry and decrements the Size (by 1). 779 Else (meaning that this is the last entry in the SRH-6LoRH header), 780 and if there is no next SRH-6LoRH header after this then the SRH- 781 6LoRH is removed. 783 Else, if there is a next SRH-6LoRH of a Type with a larger or equal 784 value, meaning a same or lesser compression yielding same or larger 785 compressed forms, then the SRH-6LoRH is removed. 787 Else, the first entry of the next SRH-6LoRH is popped from the next 788 SRH-6LoRH and coalesced with the first entry of this SRH-6LoRH. 790 At the end of the process, if there is no more SRH-6LoRH in the 791 packet, then the processing node is the last router along the source 792 route path. 794 An example of this operation is provided in Appendix A.3. 796 5.6. Forwarding 798 When receiving a packet with a SRH-6LoRH, a router determines the 799 IPv6 address of the current segment endpoint. 801 If strict source routing is enforced and this router is not the 802 segment endpoint for the packet then this router MUST drop the 803 packet. 805 If this router is the current segment endpoint, then the router pops 806 its address as described in Section 5.5 and continues processing the 807 packet. 809 If there is still a SRH-6LoRH, then the router determines the new 810 segment endpoint and routes the packet towards that endpoint. 812 Otherwise the router uses the destination in the inner IP header to 813 forward or accept the packet. 815 The segment endpoint of a packet MUST be determined as follows: 817 The router first determines the Compression Reference as discussed in 818 Section 4.3.1. 820 The router then coalesces the Compression Reference with the first 821 entry of the first SRH-6LoRH header as discussed in Section 5.4. If 822 the type of the SRH-6LoRH header is type 4 then the coalescence is a 823 full override. 825 Since the Compression Reference is an uncompressed address, the 826 coalesced IPv6 address is also expressed in the full 128bits. 828 6. The RPL Packet Information 6LoRH 830 RPL [RFC6550], Section 11.2, specifies the RPL Packet Information 831 (RPI) as a set of fields that are placed by RPL routers in IP packets 832 to identify the RPL Instance, detect anomalies and trigger corrective 833 actions. 835 In particular, the SenderRank, which is the scalar metric computed by 836 a specialized Objective Function such as described in RFC 6552 837 [RFC6552], indicates the Rank of the sender and is modified at each 838 hop. The SenderRank field is used to validate that the packet 839 progresses in the expected direction, either upwards or downwards, 840 along the DODAG. 842 RPL defines the "RPL Option for Carrying RPL Information in Data- 843 Plane Datagrams" [RFC6553] to transport the RPI, which is carried in 844 an IPv6 Hop-by-Hop Options Header [RFC2460], typically consuming 845 eight bytes per packet. 847 With RFC 6553 [RFC6553], the RPL option is encoded as six octets, 848 which must be placed in a Hop-by-Hop header that consumes two 849 additional octets for a total of eight octets. To limit the header's 850 range to just the RPL domain, the Hop-by-Hop header must be added to 851 (or removed from) packets that cross the border of the RPL domain. 853 The 8-byte overhead is detrimental to LLN operation, in particular 854 with regards to bandwidth and battery constraints. These bytes may 855 cause a containing frame to grow above maximum frame size, leading to 856 Layer 2 or 6LoWPAN [RFC4944] fragmentation, which in turn leads to 857 even more energy expenditure and issues discussed in "LLN Fragment 858 Forwarding and Recovery" [I-D.thubert-6lo-forwarding-fragments]. 860 An additional overhead comes from the need, in certain cases, to add 861 an IP-in-IP encapsulation to carry the Hop-by-Hop header. This is 862 needed when the router that inserts the Hop-by-Hop header is not the 863 source of the packet, so that an error can be returned to the router. 864 This is also the case when a packet originated by a RPL node must be 865 stripped from the Hop-by-Hop header to be routed outside the RPL 866 domain. 868 For that reason, this specification defines an IP-in-IP-6LoRH header 869 in Section 7, but it must be noted that removal of a 6LoRH header 870 does not require manipulation of the packet in the LOWPAN_IPHC, and 871 thus, if the source address in the LOWPAN_IPHC is the node that 872 inserted the IP-in-IP-6LoRH header then this situation alone does not 873 mandate an IP-in-IP-6LoRH header. 875 Note: it was found that some implementations omit the RPI for packets 876 going down the RPL graph in Non-Storing Mode, even though RPL 877 indicates that the RPI should be placed in the packet. With this 878 specification, the RPI is important to indicate the RPLInstanceID so 879 the RPI should not be omitted. 881 As a result, a RPL packet may bear only an RPI-6LoRH header and no 882 IP-in-IP-6LoRH header. In that case, the source and destination of 883 the packet are specified by the LOWPAN_IPHC. 885 As with RFC 6553 [RFC6553], the fields in the RPI include an 'O', an 886 'R', and an 'F' bit, an 8-bit RPLInstanceID (with some internal 887 structure), and a 16-bit SenderRank. 889 The remainder of this section defines the RPI-6LoRH header, which is 890 a Critical 6LoWPAN Routing Header that is designed to transport the 891 RPI in 6LoWPAN LLNs. 893 6.1. Compressing the RPLInstanceID 895 RPL Instances are discussed in Section 5 of the RPL specification 896 [RFC6550]. A number of simple use cases do not require more than one 897 RPL Instance, and in such cases, the RPL Instance is expected to be 898 the Global Instance 0. A global RPLInstanceID is encoded in a 899 RPLInstanceID field as follows: 901 0 1 2 3 4 5 6 7 902 +-+-+-+-+-+-+-+-+ 903 |0| ID | Global RPLInstanceID in 0..127 904 +-+-+-+-+-+-+-+-+ 906 Figure 8: RPLInstanceID Field Format for Global Instances. 908 For the particular case of the Global Instance 0, the RPLInstanceID 909 field is all zeros. This specification allows to elide a 910 RPLInstanceID field that is all zeros, and defines a I flag that, 911 when set, signals that the field is elided. 913 6.2. Compressing the SenderRank 915 The SenderRank is the result of the DAGRank operation on the rank of 916 the sender; here the DAGRank operation is defined in Section 3.5.1 of 917 the RPL specification [RFC6550] as: 919 DAGRank(rank) = floor(rank/MinHopRankIncrease) 921 If MinHopRankIncrease is set to a multiple of 256, the least 922 significant 8 bits of the SenderRank will be all zeroes; by eliding 923 those, the SenderRank can be compressed into a single byte. This 924 idea is used in RFC 6550 [RFC6550] by defining 925 DEFAULT_MIN_HOP_RANK_INCREASE as 256 and in RFC 6552 [RFC6552] that 926 defaults MinHopRankIncrease to DEFAULT_MIN_HOP_RANK_INCREASE. 928 This specification allows to encode the SenderRank as either one or 929 two bytes, and defines a K flag that, when set, signals that a single 930 byte is used. 932 6.3. The Overall RPI-6LoRH encoding 934 The RPI-6LoRH header provides a compressed form for the RPL RPI. 935 Routers that need to forward a packet with a RPI-6LoRH header are 936 expected to be RPL routers that support this specification. 938 If a non-RPL router receives a packet with a RPI-6LoRH header, there 939 was a routing or a configuration error (see Section 8). 941 The desired reaction for the non-RPL router is to drop the packet as 942 opposed to skip the header and forward the packet, which could end up 943 forming loops by reinjecting the packet in the wrong RPL Instance. 945 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 946 Critical. Routers that understand the 6LoRH general format detailed 947 in Section 4 cannot ignore a 6LoRH header of this type, and will drop 948 the packet if it is unknown to them. 950 Since the RPI-6LoRH header is a critical header, the TSE field does 951 not need to be a length expressed in bytes. In that case the field 952 is fully reused for control bits that encode the O, R and F flags 953 from the RPI, as well as the I and K flags that indicate the 954 compression format. 956 The Type for the RPI-6LoRH is 5. 958 The RPI-6LoRH header is immediately followed by the RPLInstanceID 959 field, unless that field is fully elided, and then the SenderRank, 960 which is either compressed into one byte or fully in-lined as two 961 bytes. The I and K flags in the RPI-6LoRH header indicate whether 962 the RPLInstanceID is elided and/or the SenderRank is compressed. 963 Depending on these bits, the Length of the RPI-6LoRH may vary as 964 described hereafter. 966 0 1 2 967 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 968 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 969 |1|0|0|O|R|F|I|K| 6LoRH Type=5 | Compressed fields | 970 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+ 972 Figure 9: The Generic RPI-6LoRH Format. 974 O, R, and F bits: The O, R, and F bits are defined in section 11.2 975 of RFC 6550 [RFC6550]. 977 I flag: If it is set, the RPLInstanceID is elided and the 978 RPLInstanceID is the Global RPLInstanceID 0. If it is not set, 979 the octet immediately following the type field contains the 980 RPLInstanceID as specified in section 5.1 of RFC 6550 981 [RFC6550],. 983 K flag: If it is set, the SenderRank is compressed into one octet, 984 with the least significant octet elided. If it is not set, the 985 SenderRank, is fully inlined as two octets. 987 In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, and 988 the MinHopRankIncrease is a multiple of 256 so the least significant 989 byte is all zeros and can be elided: 991 0 1 2 992 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 994 |1|0|0|O|R|F|1|1| 6LoRH Type=5 | SenderRank | 995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 996 I=1, K=1 998 Figure 10: The most compressed RPI-6LoRH. 1000 In Figure 11, the RPLInstanceID is the Global RPLInstanceID 0, but 1001 both bytes of the SenderRank are significant so it can not be 1002 compressed: 1004 0 1 2 3 1005 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 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1007 |1|0|0|O|R|F|1|0| 6LoRH Type=5 | SenderRank | 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 I=1, K=0 1011 Figure 11: Eliding the RPLInstanceID. 1013 In Figure 12, the RPLInstanceID is not the Global RPLInstanceID 0, 1014 and the MinHopRankIncrease is a multiple of 256: 1016 0 1 2 3 1017 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 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1019 |1|0|0|O|R|F|0|1| 6LoRH Type=5 | RPLInstanceID | SenderRank | 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1021 I=0, K=1 1023 Figure 12: Compressing SenderRank. 1025 In Figure 13, the RPLInstanceID is not the Global RPLInstanceID 0, 1026 and both bytes of the SenderRank are significant: 1028 0 1 2 3 1029 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 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1031 |1|0|0|O|R|F|0|0| 6LoRH Type=5 | RPLInstanceID | Sender-... 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1033 ...-Rank | 1034 +-+-+-+-+-+-+-+-+ 1035 I=0, K=0 1037 Figure 13: Least compressed form of RPI-6LoRH. 1039 7. The IP-in-IP 6LoRH Header 1041 The IP-in-IP 6LoRH (IP-in-IP-6LoRH) header is an Elective 6LoWPAN 1042 Routing Header that provides a compressed form for the encapsulating 1043 IPv6 Header in the case of an IP-in-IP encapsulation. 1045 An IP-in-IP encapsulation is used to insert a field such as a Routing 1046 Header or an RPI at a router that is not the source of the packet. 1047 In order to send an error back regarding the inserted field, the 1048 address of the router that performs the insertion must be provided. 1050 The encapsulation can also enable the last router prior to 1051 Destination to remove a field such as the RPI, but this can be done 1052 in the compressed form by removing the RPI-6LoRH, so an IP-in-IP- 1053 6LoRH encapsulation is not required for that sole purpose. 1055 The Dispatch Value Bit Pattern for the SRH-6LoRH header indicates 1056 Elective. This field is not critical for routing since it does not 1057 indicate the destination of the packet, which is either encoded in a 1058 SRH-6LoRH header or in the inner IP header. A 6LoRH header of this 1059 type can be skipped if not understood (per Section 4), and the 6LoRH 1060 header indicates the Length in bytes. 1062 0 1 2 1063 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 1064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 1065 |1|0|1| Length | 6LoRH Type 6 | Hop Limit | Encaps. Address | 1066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+ 1068 Figure 14: The IP-in-IP-6LoRH. 1070 The Length of an IP-in-IP-6LoRH header is expressed in bytes and MUST 1071 be at least 1, to indicate a Hop Limit (HL), that is decremented at 1072 each hop. When the HL reaches 0, the packet is dropped per RFC 2460 1073 [RFC2460]. 1075 If the Length of an IP-in-IP-6LoRH header is exactly 1, then the 1076 Encapsulator Address is elided, which means that the Encapsulator is 1077 a well-known router, for instance the root in a RPL graph. 1079 The most efficient compression of an IP-in-IP encapsulation that can 1080 be achieved with this specification is obtained when an endpoint of 1081 the packet is the root of the RPL DODAG associated to the RPL 1082 Instance that is used to forward the packet, and the root address is 1083 known implicitly as opposed to signaled explicitly in the data 1084 packets. 1086 If the Length of an IP-in-IP-6LoRH header is greater than 1, then an 1087 Encapsulator Address is placed in a compressed form after the Hop 1088 Limit field. The value of the Length indicates which compression is 1089 performed on the Encapsulator Address. For instance, a Length of 3 1090 indicates that the Encapsulator Address is compressed to 2 bytes. 1091 The reference for the compression is the address of the root of the 1092 DODAG. The way the address of the root is determined is discussed in 1093 Section 4.3.2. 1095 With RPL, the destination address in the IP-in-IP header is 1096 implicitly the root in the RPL graph for packets going upwards, and, 1097 in storing mode, it is the destination address in the LOWPAN_IPHC for 1098 packets going downwards. In non-storing mode, there is no implicit 1099 value for packets going downwards. 1101 If the implicit value is correct, the destination IP address of the 1102 IP-in-IP encapsulation can be elided. Else, the destination IP 1103 address of the IP-in-IP header is transported in a SRH-6LoRH header 1104 as the first entry of the first of these headers. 1106 If the final destination of the packet is a leaf that does not 1107 support this specification, then the chain of 6LoRH headers must be 1108 stripped by the RPL/6LR router to which the leaf is attached. In 1109 that example, the destination IP address of the IP-in-IP header 1110 cannot be elided. 1112 In the special case where a 6LoRH header is used to route 6LoWPAN 1113 fragments, the destination address is not accessible in the 1114 LOWPAN_IPHC on all fragments and can be elided only for the first 1115 fragment and for packets going upwards. 1117 8. Management Considerations 1119 Though it is possible to decompress a packet at any hop, this 1120 specification is optimized to enable that a packet is forwarded in 1121 its compressed form all the way, and it makes sense to deploy 1122 homogeneous networks, where all nodes, or no node at all, use the 1123 compression technique detailed therein. 1125 This specification aims at a simple implementation running in 1126 constrained nodes, so it does indeed expect an homogeneous network 1127 and as a consequence it does not provide a method to determine the 1128 level of support by the next hops at forwarding time. 1130 Should an extension to this specification provide such a method, 1131 forwarding nodes could compress or uncompress the RPL artifacts 1132 appropriately and enable a backward compatibility between nodes that 1133 support this specification and nodes that do not. 1135 It results that this specification does not attempt to enable such 1136 backwards compatibility. It does not require extraneous code to 1137 exchange and handle error messages to correct automatically mismatch 1138 situations, either. 1140 When a packet is expected to carry a 6LoRH header but it does not, 1141 the node that discovers the issue is expected to send an ICMPv6 error 1142 message to the root, at an adapted rate limitation and with a Type 4 1143 indicating a "Parameter Problem", and a Code 0 indicating an 1144 "erroneous header field encountered", embedding the relevant portion 1145 of the received packet and pointing at the offset therein where the 1146 6LoRH header was expected. 1148 When a packet is received with a 6LoRH header that is not recognized, 1149 the node that discovers the issue is expected to send an ICMPv6 error 1150 message, to the root, at an adapted rate limitation and with a Type 4 1151 indicating a "Parameter Problem", and a Code 1 indicating an 1152 "unrecognized Next Header type", embedding the relevant portion of 1153 the received packet and pointing at the offset therein where the 1154 6LoRH header was expected. 1156 In both cases, the node SHOULD NOT place a 6LoRH header defined in 1157 this specification in the resulting message, and should either omit 1158 the RPI or place it uncompressed after the IPv6 header. 1160 In both cases also, an alternate management method may be preferred 1161 in order to notify the network administrator that there is a 1162 configuration error. 1164 Keeping the network homogeneous is either a deployment issue, by 1165 deploying only devices with a same capability, or a management issue, 1166 by configuring all devices to either use, or not use, a certain level 1167 of this compression technique and its future additions. 1169 In particular, the situation where a node receives a message with a 1170 Critical 6LoWPAN Routing Header that it does not understand is an 1171 administrative error whereby the wrong device is placed in a network, 1172 or the device is mis-configured. 1174 When a mismatch situation is detected, it is expected that the device 1175 raises some management alert, indicating the issue, e.g. that it has 1176 to drop a packet with a Critical 6LoRH. 1178 9. Security Considerations 1180 The security considerations of RFC 4944 [RFC4944], RFC 6282 1181 [RFC6282], and RFC 6553 [RFC6553] apply. 1183 Using a compressed format as opposed to the full in-line format is 1184 logically equivalent and is believed to not create an opening for a 1185 new threat when compared to RFC 6550 [RFC6550], RFC 6553 [RFC6553] 1186 and RFC 6554 [RFC6554], noting that, even though intermediate hops 1187 are removed from the SRH header as they are consumed, a node may 1188 still identify that the rest of the source routed path includes a 1189 loop or not (see Security section of RFC 6554). It must be noted 1190 that if the attacker is not part of the loop, then there is always a 1191 node at the beginning of the loop that can detect it and remove it. 1193 10. IANA Considerations 1195 This specification reserves Dispatch Value Bit Patterns within the 1196 6LoWPAN Dispatch Page 1 as follows: 1198 101xxxxx: for Elective 6LoWPAN Routing Headers 1200 100xxxxx: for Critical 6LoWPAN Routing Headers. 1202 Additionally this document creates two IANA registries, one for the 1203 Critical 6LoWPAN Routing Header Type and one for the Elective 6LoWPAN 1204 Routing Header Type, each with 32 possible values from 0 to 31, as 1205 described below. 1207 Future assignments in these registries are to be coordinated via IANA 1208 under the policy of "RFC Required" (per RFC 5226 [RFC5226]) to enable 1209 any type of RFC to obtain a value in the registry. 1211 10.2. New Critical 6LoWPAN Routing Header Type Registry 1213 This document creates an IANA registry for the Critical 6LoWPAN 1214 Routing Header Type, and assigns the following values: 1216 0..4: SRH-6LoRH [RFCthis] 1218 5: RPI-6LoRH [RFCthis] 1220 10.3. New Elective 6LoWPAN Routing Header Type Registry 1222 This document creates an IANA registry for the Elective 6LoWPAN 1223 Routing Header Type, and assigns the following value: 1225 6: IP-in-IP-6LoRH [RFCthis] 1227 11. Acknowledgments 1229 The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei 1230 Chang, Martin Turon, James Woodyatt, Samita Chakrabarti, Jonathan 1231 Hui, Gabriel Montenegro and Ralph Droms for constructive reviews to 1232 the design in the 6lo Working Group. The overall discussion involved 1233 participants to the 6MAN, 6TiSCH and ROLL WGs, thank you all. 1234 Special thanks to the chairs of the ROLL WG, Michael Richardson and 1235 Ines Robles, Brian Haberman, Internet Area A-D, and Alvaro Retana and 1236 Adrian Farrel, Routing Area A-Ds, for driving this complex effort 1237 across Working Groups and Areas. 1239 12. References 1241 12.1. Normative References 1243 [I-D.ietf-6lo-paging-dispatch] 1244 Thubert, P. and R. Cragie, "6LoWPAN Paging Dispatch", 1245 draft-ietf-6lo-paging-dispatch-05 (work in progress), 1246 October 2016. 1248 [IEEE802154] 1249 IEEE standard for Information Technology, "IEEE std. 1250 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) 1251 and Physical Layer (PHY) Specifications for Low-Rate 1252 Wireless Personal Area Networks", 2015. 1254 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1255 Requirement Levels", BCP 14, RFC 2119, 1256 DOI 10.17487/RFC2119, March 1997, 1257 . 1259 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1260 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, 1261 December 1998, . 1263 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 1264 Control Message Protocol (ICMPv6) for the Internet 1265 Protocol Version 6 (IPv6) Specification", RFC 4443, 1266 DOI 10.17487/RFC4443, March 2006, 1267 . 1269 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 1270 "Transmission of IPv6 Packets over IEEE 802.15.4 1271 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 1272 . 1274 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1275 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1276 DOI 10.17487/RFC5226, May 2008, 1277 . 1279 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6 1280 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282, 1281 DOI 10.17487/RFC6282, September 2011, 1282 . 1284 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J., 1285 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur, 1286 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for 1287 Low-Power and Lossy Networks", RFC 6550, 1288 DOI 10.17487/RFC6550, March 2012, 1289 . 1291 [RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing 1292 Protocol for Low-Power and Lossy Networks (RPL)", 1293 RFC 6552, DOI 10.17487/RFC6552, March 2012, 1294 . 1296 [RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low- 1297 Power and Lossy Networks (RPL) Option for Carrying RPL 1298 Information in Data-Plane Datagrams", RFC 6553, 1299 DOI 10.17487/RFC6553, March 2012, 1300 . 1302 [RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6 1303 Routing Header for Source Routes with the Routing Protocol 1304 for Low-Power and Lossy Networks (RPL)", RFC 6554, 1305 DOI 10.17487/RFC6554, March 2012, 1306 . 1308 12.2. Informative References 1310 [I-D.ietf-6tisch-architecture] 1311 Thubert, P., "An Architecture for IPv6 over the TSCH mode 1312 of IEEE 802.15.4", draft-ietf-6tisch-architecture-10 (work 1313 in progress), June 2016. 1315 [I-D.ietf-roll-useofrplinfo] 1316 Robles, I., Richardson, M., and P. Thubert, "When to use 1317 RFC 6553, 6554 and IPv6-in-IPv6", draft-ietf-roll- 1318 useofrplinfo-09 (work in progress), October 2016. 1320 [I-D.thubert-6lo-forwarding-fragments] 1321 Thubert, P. and J. Hui, "LLN Fragment Forwarding and 1322 Recovery", draft-thubert-6lo-forwarding-fragments-02 (work 1323 in progress), November 2014. 1325 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. 1326 Bormann, "Neighbor Discovery Optimization for IPv6 over 1327 Low-Power Wireless Personal Area Networks (6LoWPANs)", 1328 RFC 6775, DOI 10.17487/RFC6775, November 2012, 1329 . 1331 [RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and 1332 Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January 1333 2014, . 1335 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 1336 Constrained-Node Networks", RFC 7228, 1337 DOI 10.17487/RFC7228, May 2014, 1338 . 1340 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using 1341 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the 1342 Internet of Things (IoT): Problem Statement", RFC 7554, 1343 DOI 10.17487/RFC7554, May 2015, 1344 . 1346 Appendix A. Examples 1348 A.1. Examples Compressing The RPI 1350 The example in Figure 15 illustrates the 6LoRH compression of a 1351 classical packet in Storing Mode in all directions, as well as in 1352 non-Storing mode for a packet going up the DODAG following the 1353 default route to the root. In this particular example, a 1354 fragmentation process takes place per RFC 4944 [RFC4944], and the 1355 fragment headers must be placed in Page 0 before switching to Page 1: 1357 +- ... -+- ... -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+... 1358 |Frag type|Frag hdr |11110001| RPI- |IP-in-IP| LOWPAN_IPHC | ... 1359 |RFC 4944 |RFC 4944 | Page 1 | 6LoRH | 6LoRH | | 1360 +- ... -+- ... -+-+ ... -+- ... +-+-+ ... -+-+-+-+-+-+-+-+-+-+... 1361 <- RFC 6282 -> 1362 No RPL artifact 1364 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1365 |Frag type|Frag hdr | 1366 |RFC 4944 |RFC 4944 | Payload (cont) 1367 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1369 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1370 |Frag type|Frag hdr | 1371 |RFC 4944 |RFC 4944 | Payload (cont) 1372 +- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+... 1374 Figure 15: Example Compressed Packet with RPI. 1376 In Storing Mode, if the packet stays within the RPL domain, then it 1377 is possible to save the IP-in-IP encapsulation, in which case only 1378 the RPI is compressed with a 6LoRH, as illustrated in Figure 16 in 1379 the case of a non-fragmented ICMP packet: 1381 +- ... -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+... 1382 |11110001| RPI-6LoRH | NH = 0 | NH = 58 | ICMP message ... 1383 |Page 1 | type 5 | 6LOWPAN_IPHC | (ICMP) | (no compression) 1384 +- ... -+-+- ... -+-+-+-+ ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+... 1385 <- RFC 6282 -> 1386 No RPL artifact 1388 Figure 16: Example ICMP Packet with RPI in Storing Mode. 1390 The format in Figure 16 is logically equivalent to the non-compressed 1391 format illustrated in Figure 17: 1393 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... 1394 | IPv6 Header | Hop-by-Hop | RPI in | ICMP message ... 1395 | NH = 58 | Header | RPL Option | 1396 +-+-+-+- ... -+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+... 1398 Figure 17: Uncompressed ICMP Packet with RPI. 1400 For a UDP packet, the transport header can be compressed with 6LoWPAN 1401 HC [RFC6282] as illustrated in Figure 18: 1403 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+... 1404 |11110001| RPI- | NH=1 |11110CPP| Compressed | UDP 1405 |Page 1 | 6LoRH | LOWPAN_IPHC | UDP | UDP header | Payload 1406 +-+ ... -+-+-...-+-+- ... -+-+-+-+ ... -+-+-+ ... -+-+-+-+-+... 1407 <- RFC 6282 -> 1408 No RPL artifact 1410 Figure 18: Uncompressed ICMP Packet with RPI. 1412 If the packet is received from the Internet in Storing Mode, then the 1413 root is supposed to encapsulate the packet to insert the RPI. The 1414 resulting format would be as represented in Figure 19: 1416 +-+ ... -+-+-...-+-+-- ... -+-+-+-+- ... -+-+ ... -+-+-+ ... -+-+-+... 1417 |11110001| RPI- | IP-in-IP | NH=1 |11110CPP| Compressed | UDP 1418 |Page 1 | 6LoRH | 6LoRH | LOWPAN_IPHC | UDP | UDP header | Payld 1419 +-+ ... -+-+-...-+-+-- ... -+-+-+-+- ... -+-+ ... -+-+-+ ... -+-+-+... 1420 <- RFC 6282 -> 1421 No RPL artifact 1423 Figure 19: RPI inserted by the root in Storing Mode. 1425 A.2. Example Of Downward Packet In Non-Storing Mode 1427 The example illustrated in Figure 20 is a classical packet in non- 1428 Storing mode for a packet going down the DODAG following a source 1429 routed path from the root. Say that we have 4 forwarding hops to 1430 reach a destination. In the non-compressed form, when the root 1431 generates the packet, the last 3 hops are encoded in a Routing Header 1432 type 3 (SRH) and the first hop is the destination of the packet. The 1433 intermediate hops perform a swap and the hop count indicates the 1434 current active hop as defiend in RFC 2460 [RFC2460] and RFC 6554 1435 [RFC6554]. 1437 When compressed with this specification, the 4 hops are encoded in 1438 SRH-6LoRH when the root generates the packet, and the final 1439 destination is left in the LOWPAN_IPHC. There is no swap, and the 1440 forwarding node that corresponds to the first entry effectively 1441 consumes it when forwarding, which means that the size of the encoded 1442 packet decreases and that the hop information is lost. 1444 If the last hop in a SRH-6LoRH is not the final destination then it 1445 removes the SRH-6LoRH before forwarding. 1447 In the particular example illustrated in Figure 20, all addresses in 1448 the DODAG are assigned from a same /112 prefix and the last 2 octets 1449 encoding an identifier such as a IEEE 802.15.4 short address. In 1450 that case, all addresses can be compressed to 2 octets, using the 1451 root address as reference. There will be one SRH_6LoRH header, with, 1452 in this example, 3 compressed addresses: 1454 +-+ ... -+-+ ... +-+- ... -+-+- ... +-+-+-+ ... +-+-+ ... -+ ... +-... 1455 |11110001|SRH-6LoRH| RPI- | IP-in-IP | NH=1 |11110CPP| UDP | UDP 1456 |Page 1 |Type1 S=2| 6LoRH | 6LoRH |LOWPAN_IPHC| UDP | hdr |Payld 1457 +-+ ... -+-+ ... +-+- ... -+-+-- ... -+-+-+ ... +-+-+ ... -+ ... +-... 1458 <-8bytes-> <- RFC 6282 -> 1459 No RPL artifact 1461 Figure 20: Example Compressed Packet with SRH. 1463 One may note that the RPI is provided. This is because the address 1464 of the root that is the source of the IP-in-IP header is elided and 1465 inferred from the RPLInstanceID in the RPI. Once found from a local 1466 context, that address is used as Compression Reference to expand 1467 addresses in the SRH-6LoRH. 1469 With the RPL specifications available at the time of writing this 1470 draft, the root is the only node that may incorporate a SRH in an IP 1471 packet. When the root forwards a packet that it did not generate, it 1472 has to encapsulate the packet with IP-in-IP. 1474 But if the root generates the packet towards a node in its DODAG, 1475 then it should avoid the extra IP-in-IP as illustrated in Figure 21: 1477 +- ... -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+... 1478 |11110001| SRH-6LoRH | NH=1 | 11110CPP | Compressed | UDP 1479 |Page 1 | Type1 S=3 | LOWPAN_IPHC| LOWPAN-NHC| UDP header | Payload 1480 +- ... -+-+-+ ... +-+-+-+ ... -+-+-+-+-+-+-+-++-+- ... -+-+-+-+-+... 1481 <- RFC 6282 -> 1483 Figure 21: compressed SRH 4*2bytes entries sourced by root. 1485 Note: the RPI is not represented though RPL [RFC6550] generally 1486 expects it. In this particular case, since the Compression Reference 1487 for the SRH-6LoRH is the source address in the LOWPAN_IPHC, and the 1488 routing is strict along the source route path, the RPI does not 1489 appear to be absolutely necessary. 1491 In Figure 21, all the nodes along the source route path share a same 1492 /112 prefix. This is typical of IPv6 addresses derived from an 1493 IEEE802.15.4 short address, as long as all the nodes share a same 1494 PAN-ID. In that case, a type-1 SRH-6LoRH header can be used for 1495 encoding. The IPv6 address of the root is taken as reference, and 1496 only the last 2 octets of the address of the intermediate hops is 1497 encoded. The Size of 3 indicates 4 hops, resulting in a SRH-6LoRH of 1498 10 bytes. 1500 A.3. Example of SRH-6LoRH life-cycle 1502 This section illustrates the operation specified in Section 5.6 of 1503 forwarding a packet with a compressed SRH along an A->B->C->D source 1504 route path. The operation of popping addresses is exemplified at 1505 each hop. 1507 Packet as received by node A 1508 ---------------------------- 1509 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA AAAA 1510 Type 1 SRH-6LoRH Size = 0 BBBB 1511 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1512 DDDD DDDD 1514 Step 1 popping BBBB the first entry of the next SRH-6LoRH 1515 Step 2 next is if larger value (2 vs. 1) the SRH-6LoRH is removed 1517 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA AAAA 1518 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1519 DDDD DDDD 1521 Step 3: recursion ended, coalescing BBBB with the first entry 1522 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1524 Step 4: routing based on next segment endpoint to B 1526 Figure 22: Processing at Node A. 1528 Packet as received by node B 1529 ---------------------------- 1530 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1531 Type 2 SRH-6LoRH Size = 1 CCCC CCCC 1532 DDDD DDDD 1534 Step 1 popping CCCC CCCC, the first entry of the next SRH-6LoRH 1535 Step 2 removing the first entry and decrementing the Size (by 1) 1537 Type 3 SRH-6LoRH Size = 0 AAAA AAAA AAAA BBBB 1538 Type 2 SRH-6LoRH Size = 0 DDDD DDDD 1540 Step 3: recursion ended, coalescing CCCC CCCC with the first entry 1541 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1543 Step 4: routing based on next segment endpoint to C 1545 Figure 23: Processing at Node B. 1547 Packet as received by node C 1548 ---------------------------- 1550 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1551 Type 2 SRH-6LoRH Size = 0 DDDD DDDD 1553 Step 1 popping DDDD DDDD, the first entry of the next SRH-6LoRH 1554 Step 2 the SRH-6LoRH is removed 1556 Type 3 SRH-6LoRH Size = 0 AAAA AAAA CCCC CCCC 1558 Step 3: recursion ended, coalescing DDDD DDDDD with the first entry 1559 Type 3 SRH-6LoRH Size = 0 AAAA AAAA DDDD DDDD 1561 Step 4: routing based on next segment endpoint to D 1563 Figure 24: Processing at Node C. 1565 Packet as received by node D 1566 ---------------------------- 1567 Type 3 SRH-6LoRH Size = 0 AAAA AAAA DDDD DDDD 1569 Step 1 the SRH-6LoRH is removed. 1570 Step 2 no more header, routing based on inner IP header. 1572 Figure 25: Processing at Node D. 1574 Authors' Addresses 1576 Pascal Thubert (editor) 1577 Cisco Systems 1578 Building D - Regus 1579 45 Allee des Ormes 1580 BP1200 1581 MOUGINS - Sophia Antipolis 06254 1582 FRANCE 1584 Phone: +33 4 97 23 26 34 1585 Email: pthubert@cisco.com 1587 Carsten Bormann 1588 Universitaet Bremen TZI 1589 Postfach 330440 1590 Bremen D-28359 1591 Germany 1593 Phone: +49-421-218-63921 1594 Email: cabo@tzi.org 1596 Laurent Toutain 1597 Institut MINES TELECOM; TELECOM Bretagne 1598 2 rue de la Chataigneraie 1599 CS 17607 1600 Cesson-Sevigne Cedex 35576 1601 France 1603 Email: Laurent.Toutain@telecom-bretagne.eu 1604 Robert Cragie 1605 ARM Ltd. 1606 110 Fulbourn Road 1607 Cambridge CB1 9NJ 1608 UK 1610 Email: robert.cragie@gridmerge.com