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'ieee802.15.4' Summary: 4 errors (**), 0 flaws (~~), 6 warnings (==), 9 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group N. Kushalnagar 3 Internet-Draft Intel Corp 4 Expires: January 19, 2007 G. Montenegro 5 Microsoft Corporation 6 July 18, 2006 8 6LoWPAN: Overview, Assumptions, Problem Statement and Goals 9 draft-ietf-6lowpan-problem-04.txt 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on January 19, 2007. 36 Copyright Notice 38 Copyright (C) The Internet Society (2006). 40 Abstract 42 This document describes the assumptions, problem statement and goals 43 for transmitting IP over IEEE 802.15.4 networks. The set of goals 44 enumerated in this document form an initial set only. Additional 45 goals may be found necessary over time and may be added to this 46 document. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 1.1. Requirements notation . . . . . . . . . . . . . . . . . . 3 52 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 3. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 4 54 4. Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 55 4.1. IP Connectivity . . . . . . . . . . . . . . . . . . . . . 5 56 4.2. Topologies . . . . . . . . . . . . . . . . . . . . . . . . 6 57 4.3. Limited Packet Size . . . . . . . . . . . . . . . . . . . 6 58 4.4. Limited configuration and management . . . . . . . . . . . 7 59 4.5. Service discovery . . . . . . . . . . . . . . . . . . . . 7 60 4.6. Security . . . . . . . . . . . . . . . . . . . . . . . . . 7 61 5. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 64 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 65 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 66 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 67 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 69 Intellectual Property and Copyright Statements . . . . . . . . . . 14 71 1. Introduction 73 Low-power wireless personal area networks (LoWPANs) comprise devices 74 that conform to the IEEE 802.15.4-2003 standard by the IEEE 75 [ieee802.15.4]. IEEE 802.15.4 devices are characterized by short 76 range, low bit rate, low power and low cost. 78 This document gives an overview of LoWPANs and describes how they 79 benefit from IP and IPv6 networking. It describes LoWPAN 80 requirements with regards to the IP layer and above, and spells out 81 the underlying assumptions of IP for LoWPANs. Finally, it describes 82 problems associated with enabling IP communication between devices in 83 a LoWPAN, and defines goals to address these in a prioritized manner. 84 Admittedly, not all items on this list are necessarily appropriate 85 tasks for the IETF. Nevertheless, they are documented here to give a 86 general overview of the larger problem. This is useful both to 87 structure work within the IETF as well as to understand better how to 88 coordinate with external organizations. 90 1.1. Requirements notation 92 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 93 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 94 document are to be interpreted as described in [RFC2119]. 96 2. Overview 98 A LoWPAN is a simple low cost communication network that allows 99 wireless connectivity in applications with limited power and relaxed 100 throughput requirements. A LoWPAN typically includes devices that 101 work together to connect the physical environment to real-world 102 applications, e.g., wireless sensors. LoWPANs conform to the IEEE 103 802.15.4-2003 standard. [ieee802.15.4]. 105 Some of the characteristics of LoWPANs are: 107 1. Small packet size. Given that the maximum physical layer packet 108 is 127 bytes, the resulting maximum frame size at the media 109 access control layer is 102 octets. Link-layer security imposes 110 further overhead, which in the maximum case (21 octets of 111 overhead in the AES-CCM-128 case, versus 9 and 13 for AES-CCM-32 112 and AES-CCM-64, respectively) leaves 81 octets for data packets. 114 2. Support for both 16-bit short or IEEE 64-bit extended media 115 access control addresses. 117 3. Low bandwidth. Data rates of 250 kbps, 40 kbps and 20 kbps for 118 each of the currently defined physical layers (2.4 GHz, 915 MHz 119 and 868 MHz, respectively). 121 4. Topologies include star and mesh operation. 123 5. Low power. Typically, some or all devices are battery operated. 125 6. Low cost. These devices are typically associated with sensors, 126 switches, etc. This drives some of the other characteristics 127 such as low processing, low memory, etc. Numerical values for 128 "low" elided on purpose since costs tend to change over time. 130 7. Large number of devices expected to be deployed during the life- 131 time of the technology. This number is expected to dwarf the 132 number of deployed personal computers, for example. 134 8. Location of the devices is typically not predefined, as they 135 tend to be deployed in an ad hoc fashion. Furthermore, 136 sometimes the location of these devices may not be easily 137 accessible. Additionally, these devices may move to new 138 locations. 140 9. Devices within LoWPANs tend to be unreliable due to variety of 141 reasons: uncertain radio connectivity, battery drain, device 142 lockups, physical tampering, etc. 144 10. Devices within LoWPANs tend to be unavailable because they often 145 are in sleep mode or in a power-down mode to conserve power. 147 The following sections take into account these characteristics in 148 describing the assumptions, problems statement and goals for LoWPANs, 149 and, in particular, for 6LoWPANs (IPv6-based LoWPAN networks). 151 3. Assumptions 153 Given the small packet size of LoWPANs, this document presumes 154 applications typically send small amounts of data. However, the 155 protocols themselves do not restrict bulk data transfers. 157 LoWPANs as described in this document are based on IEEE 802.15.4- 158 2003. It is possible that the specification may undergo changes in 159 the future and may change some of the requirements mentioned above. 161 Some of these assumptions are based on the limited capabilities of 162 devices within LoWPANs. As devices become more powerful, and consume 163 less power, some of the requirements mentioned above may be somewhat 164 relaxed. 166 While some LoWPAN devices are expected to be extremely limited (the 167 so-called "Reduced Function Devices" or RFDs), more capable "Full 168 Function Devices" (FFDs) will also be present, albeit in much smaller 169 numbers. FFDs will typically have more resources and may be mains 170 powered. Accordingly, FFDs will aid RFDs by providing functions such 171 as network coordination, packet forwarding, interfacing with other 172 types of networks, etc. 174 The application of IP technology is assumed to provide the following 175 benefits: 177 1. The pervasive nature of IP networks allows use of existing 178 infrastructure. 179 2. IP-based technologies already exist, are well known and proven to 180 be working. 181 3. An admittedly non-technical but important consideration is that 182 intellectual property conditions for IP networking technology are 183 either more favorable or at least better understood than 184 proprietary and newer solutions. 185 4. Tools for diagnostics, management and commissioning of IP 186 networks already exist. 187 5. IP-based devices can be connected readily to other IP-based 188 networks, without the need for intermediate entities like 189 translation gateways or proxies. 191 4. Problems 193 Based on the characteristics defined in the overview section, the 194 following sections elaborate on the main problems with IP for 195 LoWPANs. 197 4.1. IP Connectivity 199 The requirement for IP connectivity within a LoWPAN is driven by the 200 following: 202 1. The many devices in a LoWPAN make network auto configuration and 203 statelessness highly desirable. And for this, IPv6 has ready 204 solutions. 205 2. The large number of devices poses the need for a large address 206 space, well met by IPv6. 207 3. Given the limited packet size of LoWPANs, the IPv6 address format 208 allows subsuming of IEEE 802.15.4 addresses if so desired. 210 4. Simple interconnectivity to other IP networks including the 211 Internet. 213 However, given the limited packet size, headers for IPv6 and layers 214 above must be compressed whenever possible. 216 4.2. Topologies 218 LoWPANs must support various topologies including mesh and star. 220 Mesh topologies imply multi-hop routing, to a desired destination. 221 In this case, intermediate devices act as packet forwarders at the 222 link layer (akin to routers at the network layer). Typically these 223 are "full function devices" that have more capabilities in terms of 224 power, computation, etc. The requirements on the routing protocol 225 are: 227 1. Given the minimal packet size of LoWPANs, the routing protocol 228 must impose low (or no) overhead on data packets, hopefully 229 independently of the number of hops. 230 2. The routing protocols should have low routing overhead (low 231 chattiness) balanced with topology changes and power 232 conservation. 233 3. The computation and memory requirements in the routing protocol 234 should be minimal to satisfy the low cost and low power 235 objectives. Thus, storage and maintenance of large routing 236 tables is detrimental. 237 4. Support for network topologies in which either FFDs or RFDs may 238 be battery or mains-powered. This implies the appropriate 239 considerations for routing in the presence of sleeping nodes. 241 As with mesh topologies, star topologies include provisioning a 242 subset of devices with packet forwarding functionality. If, in 243 addition to IEEE 802.15.4, these devices use other kinds of network 244 interfaces such as ethernet or IEEE 802.11, the goal is to seamlessly 245 integrate the networks built over those different technologies. 246 This, of course, is a primary motivation to use IP to begin with. 248 4.3. Limited Packet Size 250 Applications within LoWPANs are expected to originate small packets. 251 Adding all layers for IP connectivity should still allow transmission 252 in one frame without incurring excessive fragmentation and 253 reassembly. Furthermore, protocols must be designed or chosen so 254 that the individual "control/protocol packets" fit within a single 255 802.15.4 frame. 257 4.4. Limited configuration and management 259 As alluded to above, devices within LoWPANs are expected to be 260 deployed in exceedingly large numbers. Additionally, they are 261 expected to have limited display and input capabilities. 262 Furthermore, the location of some of these devices may be hard to 263 reach. Accordingly, protocols used in LoWPANs should have minimal 264 configuration, preferably work "out of the box", be easy to 265 bootstrap, and enable the network to self heal given the inherent 266 unreliable characteristic of these devices. Network management 267 should have little overhead yet be powerful enough to control dense 268 deployment of devices. 270 4.5. Service discovery 272 LoWPANs require simple service discovery network protocols to 273 discover, control and maintain services provided by devices. In some 274 cases, especially in dense deployments, abstraction of several nodes 275 to provide a service may be beneficial. In order to enable such 276 features, new protocols may have to be designed. 278 4.6. Security 280 IEEE 802.15.4 mandates link-layer security based on AES, but it omits 281 any details about topics like bootstrapping, key management and 282 security at higher layers. Of course, a complete security solution 283 for LoWPAN devices must consider application needs very carefully. 284 Please refer to the security consideration section below for a more 285 detailed discussion and in-depth security requirements. 287 5. Goals 289 The goals mentioned below are general and not limited to IETF 290 activities. As such, they may not only refer to work that can be 291 done within the IETF (e.g., specification required to transmit IP, 292 profile of best practices for transmitting IP packets, and associated 293 upper level protocols, etc). They also point at work more relevant 294 to other standards bodies (e.g., desirable changes to or profiles 295 relevant to IEEE 802.15.4, W3C, etc). When the goals fall under the 296 IETF's purview, they serve to point out what those efforts should 297 strive to accomplish, regardless of whether they are pursued within 298 one (or more) new (or existing) working groups. When the goals do 299 not fall under the purview of the IETF, documenting them here serves 300 as input to other organizations [liaison]. 302 Note that a common underlying goal is to reduce packet overhead, 303 bandwidth consumption, processing requirements and power consumption. 305 The following are the goals according to priority for LoWPANs: 307 1. Fragmentation and Reassembly layer: As mentioned in the overview, 308 the protocol data units may be as small 81 bytes. This is 309 obviously far below the minimum IPv6 packet size of 1280 octets, 310 and in keeping with section 5 of the IPv6 specification 311 [RFC2460], a fragmentation and reassembly adaptation layer must 312 be provided at the layer below IP. 314 2. Header Compression: Given that in the worst case the maximum size 315 available for transmitting IP packets over IEEE 802.15.4 frame is 316 81 octets, and that the IPv6 header is 40 octets long, (without 317 optional headers), this leaves only 41 octets for upper-layer 318 protocols, like UDP and TCP. UDP uses 8 octets in the header and 319 TCP uses 20 octets. This leaves 33 octets for data over UDP and 320 21 octets for data over TCP. Additionally, as pointed above, 321 there is also a need for a fragmentation and reassembly layer, 322 which will use even more octets leaving very few octets for data. 323 Thus if one were to use the protocols as is, it would lead to 324 excessive fragmentation and reassembly even when data packets are 325 just 10s of octets long. This points to the need for header 326 compression. As there is much published and in-progress 327 standardization work on header compression, the 6LoWPAN community 328 needs to investigate using existing header compression 329 techniques, and, if necessary, specify new ones. 331 3. Address Autoconfiguration: [I-D.ietf-ipv6-rfc2462bis] specifies 332 methods for creating IPv6 stateless address auto configuration. 333 Stateless auto configuration (as compared to stateful) is 334 attractive for 6LoWPANs, because it reduces the configuration 335 overhead on the hosts. There is a need for a method to generate 336 an "interface identifier" from the EUI-64 [EUI64] assigned to the 337 IEEE 802.15.4 device. 339 4. Mesh Routing Protocol: A routing protocol to support a multi-hop 340 mesh network is necessary. There is much published work on adhoc 341 multi hop routing for devices. Some examples include [RFC3561], 342 [RFC3626], [RFC3684], all experimental. Also, these protocols 343 are designed to use IP-based addresses that have large overheads. 344 For example, the AODV [RFC3561] routing protocol uses 48 octets 345 for a route request based on IPv6 addressing. Given the packet- 346 size constraints, transmitting this packet without fragmentation 347 and reassembly may be difficult. Thus, care should be taken when 348 using existing routing protocols (or designing new ones) so that 349 the routing packets fit within a single IEEE 802.15.4 frame. 351 5. Network Management: One of the points of transmitting IPv6 352 packets, is to reuse existing protocols as much as possible. 353 Network management functionality is critical for LoWPANs. 354 [RFC3411] specifies SNMPv3 protocol operations. SNMP 355 functionality may be translated "as is" to LoWPANs. However, 356 further investigation is required to determine if it is suitable, 357 or if an appropriate adaption is in order. This adaptation could 358 include limiting the data types and simplifying the Basic 359 Encoding Rules so as to reduce the size and complexity of the 360 ASN.1 parser, thereby reducing the memory and processing needs to 361 better fit into the limited memory and power of LoWPAN devices. 363 6. Implementation Considerations: It may be the case that 364 transmitting IP over IEEE 802.15.4 would become more beneficial 365 if implemented in a "certain" way. Accordingly, implementation 366 considerations are to be documented. 368 7. Application and higher layer Considerations: As header 369 compression becomes more prevalent, overall performance will 370 depend even more on efficiency of application protocols. 371 Heavyweight protocols based on XML such as SOAP [SOAP], may not 372 be suitable for LoWPANs. As such, more compact encodings (and 373 perhaps protocols) may become necessary. The goal here is to 374 specify or suggest modifications to existing protocols so that 375 they are suitable for LoWPANs. Furthermore, application level 376 interoperability specifications may also become necessary in the 377 future and may thus be specified. 379 8. Security Considerations: Security threats at different layers 380 must be clearly understood and documented. Bootstrapping of 381 devices into a secure network could also be considered given the 382 location, limited display, high density and ad hoc deployment of 383 devices. 385 6. IANA Considerations 387 This document contains no IANA considerations. 389 7. Security Considerations 391 IPv6 over LoWPAN (6LoWPAN) applications often require confidentiality 392 and integrity protection. This can be provided at the application, 393 transport, network, and/or at the link layer (i.e., within the 394 6LoWPAN set of specifications). In all these cases, prevailing 395 constraints will influence the choice of a particular protocol. Some 396 of the more relevant constraints are small code size, low power 397 operation, low complexity, and small bandwidth requirements. 399 Given these constraints, first, a threat model for 6LoWPAN devices 400 needs to be developed in order to weigh any risks against the cost of 401 their mitigations while making meaningful assumptions and 402 simplifications. Some examples for threats that should be considered 403 are man-in-the-middle attacks and denial of service attacks. 405 A separate set of security considerations apply to bootstrapping a 406 6LoWPAN device into the network (e.g., for initial key 407 establishment). This generally involves application level exchanges 408 or out-of-band techniques for the initial key establishment, and may 409 rely on application- specific trust models; thus, it is considered 410 extraneous to 6LoWPAN and is not addressed in these specifications. 411 In order to be able to select (or design) this next set of protocols, 412 there needs to be a common model of the keying material created by 413 the initial key establishment. 415 Beyond initial key establishment, protocols for subsequent key 416 management as well as to secure the data traffic do fall under the 417 purview of 6LoWPAN. Here, the different alternatives (TLS, IKE/ 418 IPsec, etc.) must be evaluated in light of the 6LoWPAN constraints. 420 One argument for using link layer security is that most IEEE 802.15.4 421 devices already have support for AES link-layer security. AES is a 422 block cipher operating on blocks of fixed length, i.e., 128 bits. To 423 encrypt longer messages, several modes of operation may be used. The 424 earliest modes described, such as ECB, CBC, OFB and CFB provide only 425 confidentiality, and this does not ensure message integrity. Other 426 modes have been designed which ensure both confidentiality and 427 message integrity, such as CCM* mode. 6LoWPAN networks can operate in 428 any of the previous modes, but it is desirable to utilize the most 429 secure modes available for link-layer security (e.g., CCM*), and 430 build upon it. 432 For network layer security, two models are applicable: end-to-end 433 security, e.g. using IPsec transport mode, or security that is 434 limited to the wireless portion of the network, e.g. using a security 435 gateway and IPsec tunnel mode. The disadvantage of the latter is the 436 larger header size, which is significant at the 6LoWPAN frame MTUs. 437 To simplify 6LoWPAN implementations, it is beneficial to identify the 438 relevant security model, and to identify a preferred set of cipher 439 suites that are appropriate given the constraints. 441 8. Acknowledgements 443 Thanks to Geoff Mulligan, Soohong Daniel Park, Samita Chakrabarti and 444 Brijesh Kumar for their comments and help in shaping this document. 446 9. References 448 9.1. Normative References 450 [EUI64] "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64) 451 REGISTRATION AUTHORITY", IEEE http://standards.ieee.org/ 452 regauth/oui/tutorials/EUI64.html. 454 [I-D.ietf-ipv6-2461bis] 455 Narten, T., "Neighbor Discovery for IP version 6 (IPv6)", 456 draft-ietf-ipv6-2461bis-07 (work in progress), May 2006. 458 [I-D.ietf-ipv6-rfc2462bis] 459 Thomson, S., "IPv6 Stateless Address Autoconfiguration", 460 draft-ietf-ipv6-rfc2462bis-08 (work in progress), 461 May 2005. 463 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 464 Requirement Levels", BCP 14, RFC 2119, March 1997. 466 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 467 (IPv6) Specification", RFC 2460, December 1998. 469 [ieee802.15.4] 470 IEEE Computer Society, "IEEE Std. 802.15.4-2003", 471 October 2003. 473 9.2. Informative References 475 [RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An 476 Architecture for Describing Simple Network Management 477 Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, 478 December 2002. 480 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 481 Demand Distance Vector (AODV) Routing", RFC 3561, 482 July 2003. 484 [RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing 485 Protocol (OLSR)", RFC 3626, October 2003. 487 [RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology 488 Dissemination Based on Reverse-Path Forwarding (TBRPF)", 489 RFC 3684, February 2004. 491 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 492 Discovery (ND) Trust Models and Threats", RFC 3756, 493 May 2004. 495 [SOAP] "SOAP", W3C http://www.w3c.org/2000/xp/Group/. 497 [liaison] "LIASONS", 498 IETF http://www.ietf.org/liaisonActivities.html. 500 Authors' Addresses 502 Nandakishore Kushalnagar 503 Intel Corp 505 Email: nandakishore.kushalnagar@intel.com 507 Gabriel Montenegro 508 Microsoft Corporation 510 Email: gabriel_montenegro_2000@yahoo.com 512 Intellectual Property Statement 514 The IETF takes no position regarding the validity or scope of any 515 Intellectual Property Rights or other rights that might be claimed to 516 pertain to the implementation or use of the technology described in 517 this document or the extent to which any license under such rights 518 might or might not be available; nor does it represent that it has 519 made any independent effort to identify any such rights. Information 520 on the procedures with respect to rights in RFC documents can be 521 found in BCP 78 and BCP 79. 523 Copies of IPR disclosures made to the IETF Secretariat and any 524 assurances of licenses to be made available, or the result of an 525 attempt made to obtain a general license or permission for the use of 526 such proprietary rights by implementers or users of this 527 specification can be obtained from the IETF on-line IPR repository at 528 http://www.ietf.org/ipr. 530 The IETF invites any interested party to bring to its attention any 531 copyrights, patents or patent applications, or other proprietary 532 rights that may cover technology that may be required to implement 533 this standard. Please address the information to the IETF at 534 ietf-ipr@ietf.org. 536 Disclaimer of Validity 538 This document and the information contained herein are provided on an 539 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 540 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 541 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 542 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 543 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 544 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 546 Copyright Statement 548 Copyright (C) The Internet Society (2006). This document is subject 549 to the rights, licenses and restrictions contained in BCP 78, and 550 except as set forth therein, the authors retain all their rights. 552 Acknowledgment 554 Funding for the RFC Editor function is currently provided by the 555 Internet Society.