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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: April 27, 2006 G. Montenegro 5 Microsoft Corporation 6 October 24, 2005 8 6LoWPAN: Overview, Assumptions, Problem Statement and Goals 9 draft-ietf-6lowpan-problem-01.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 April 27, 2006. 36 Copyright Notice 38 Copyright (C) The Internet Society (2005). 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 . . . . . . . . . . . . . . . . . . . . . . . . 5 57 4.3. Limited Packet Size . . . . . . . . . . . . . . . . . . . 6 58 4.4. Limited configuration and management . . . . . . . . . . . 6 59 4.5. Service discovery . . . . . . . . . . . . . . . . . . . . 6 60 4.6. Security . . . . . . . . . . . . . . . . . . . . . . . . . 7 61 5. Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 63 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 64 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 65 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 66 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 67 9.2. Informative References . . . . . . . . . . . . . . . . . . 10 68 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 69 Intellectual Property and Copyright Statements . . . . . . . . . . 12 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]. The 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 the requirements 80 of LoWPANs with regards to IP layer and above. It spells out the 81 underlying assumptions of IP for LoWPANs. Finally, it describes 82 problems associated with enabling IP communication between devices in 83 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 battery operated. 125 6. Relatively low cost, typically associated with sensors, switches, 126 etc. These drive some of the other characteristics such as low 127 processing, low memory, etc. Numerical values for "low" have not 128 been explicitly mentioned here as historically the costs tend to 129 change over time. 131 7. Large number of devices expected to be deployed during the life- 132 time of the technology. This number is expected to dwarf the 133 number of deployed personal computers, for example. 135 8. Location of the devices are typically not predefined, thus these 136 devices are deployed in an adhoc fashion. Furthermore, sometimes 137 the location of these devices may not be easily accessible. 139 9. Devices within LoWPANs have a higher possibility of being 140 unreliable due to variety of reasons: uncertain radio 141 connectivity, battery drain, device lockups, physical tampering, 142 etc. 144 The following sections take into account these characteristics in 145 describing the assumptions, problems statement and goals for LoWPANs. 147 3. Assumptions 149 Given the small packet size of LoWPANs, this document presumes 150 applications typically send small amounts of data. However, the 151 protocols themselves do not restrict bulk data transfers. 153 LoWPANs as described in this document are based on IEEE 802.15.4- 154 2003. It is possible that the specification may undergo changes in 155 the future and may change some of the requirements mentioned above. 157 Some of these assumptions are based on the limited capabilities of 158 devices within LoWPANs. As devices become more powerful, and consume 159 less power, some of the requirements mentioned above may be somewhat 160 relaxed. 162 Nevertheless, not all devices in a LoWPAN are expected to be 163 extremely limited. This is true of so-called "Reduced Function 164 Devices" (RFDs), but not necessarily of "Full Function Devices" 165 (FFDs). These will also be present albeit in much smaller numbers, 166 and will typically have more resources and be mains powered. 167 Accordingly, FFDs will aid RFDs by providing functions such as 168 network coordination, packet forwarding, interfacing with other types 169 of networks, etc. 171 IP technology is assumed to provide the following benefits: 173 1. The pervasive nature of IP networks allows use of existing 174 infrastructure. 175 2. IP based technologies already exist, are well known and proven to 176 be working. 177 3. An admittedly non-technical but important consideration is that 178 intellectual property conditions for IP networking technology are 179 either more favorable or at least better understood than 180 proprietary and newer solutions. 182 4. Problems 184 Based on the characteristics defined in the overview section, the 185 following sections elaborate on the main problems with IP for LoWPANs 186 Note that a common underlying goal is to reduce packet overhead, 187 bandwidth consumption, and processing requirements. 189 4.1. IP Connectivity 191 The requirement for IP connectivity within a LoWPAN is driven by the 192 following: 194 1. The many devices in a LoWPAN make network autoconfiguration and 195 statelessness highly desirable. And for this, IPv6 has ready 196 solutions. 197 2. The large number of devices poses the need for a large address 198 space, well met by IPv6. 199 3. Given the limited packet size of LoWPANs, the IPv6 address format 200 allows subsuming of IEEE 802.15.4 addresses if so desired. 202 However, given the limited packet size, headers for IPv6 and above 203 layers must be compressed whenever possible. 205 4.2. Topologies 207 LoWPANs must support various topologies including mesh and star. 209 Mesh topologies imply multi-hop routing. to a desired destination. 210 In this case, intermediate devices act as packet forwarders at the 211 link layer (akin to routers at the network layer). Typically these 212 are "full function devices" that have more capabilities in terms of 213 power, computation, etc. The requirements that apply on the chosen 214 routing protocol are: 216 1. Given the minimal packet size of LoWPANs, the routing protocol 217 must impose low (or no) overhead on data packets, hopefully 218 independently of the number of hops. 219 2. The routing protocols should have low routing overhead (less 220 chatty) balanced with topology changes and power conservation. 221 3. The computation and memory requirements in the routing protocol 222 should be minimal to satisfy low cost and low power 223 characteristics. Thus storage and maintaining of large routing 224 tables may be detrimental. 226 As with mesh topologies, star topologies include provisioning a 227 subset of devices with packet forwarding functionality. If, in 228 addition to IEEE 802.15.4, these devices use other kinds of network 229 interfaces such as ethernet, IEEE 802.11, etc., the goal is to 230 seamlessly integrate the networks built over those different 231 technologies. This, or course, is a primary motivation to use IP to 232 begin with. 234 4.3. Limited Packet Size 236 Applications within LoWPANs are expected to originate small packets. 237 Adding all layers for IP connectivity should still allow transmission 238 in one frame without incurring excessive fragmentation and 239 reassembly. Furthermore, protocols must be designed or chosen so 240 that the individual "control/protocol packets" fit within a single 241 802.15.4 frame. 243 4.4. Limited configuration and management 245 As alluded to above, devices within LoWPANs are expected to be 246 deployed in exceedingly large numbers. Additionally, they are 247 expected to have limited display and input capabilities. 248 Furthermore, the location of some of these devices may be hard to 249 access. As such, protocols designed for LoWPANs should have minimal 250 configuration, preferably work "out of the box", provide easy 251 bootstrapping, and should be able to self heal given the inherent 252 unreliable characteristic of these devices. The network management 253 should have less overhead yet be powerful to control dense deployment 254 of devices. 256 4.5. Service discovery 258 LoWPANs require simple service discovery network protocols to 259 discover, control and maintain services provided by devices. In some 260 cases, especially in dense deployments, abstraction of several nodes 261 to provide a service may be beneficial. In order to enable such 262 features, new protocols may have to be designed. 264 4.6. Security 266 Although IEEE 802.15.4 provides AES link layer security, a complete 267 end-to-end security is needed. 269 5. Goals 271 Goals mentioned here may point at relevant work that can be done 272 within the IETF (e.g., specification required to transmit IP, profile 273 of best practices for transmitting IP packets, and associated upper 274 level protocols, etc). It may also point at work to be done in other 275 standards bodies that exist or may exist in the future (e.g., 276 desirable changes or profiles relevant to IEEE 802.15.4, W3C, etc). 277 When the goals fall under the IETF's purview, they serve to point out 278 what those efforts should strive to accomplish. Regardless of 279 whether they are pursued within one (or more) new (or existing) 280 working groups. When the goals do not fall under the purview of the 281 IETF, documenting them here serves as input to those other 282 organizations [liaison]. 284 The following are the goals according to priority for LoWPANs: 286 1. As mentioned in the overview, the protocol data units may be as 287 small 81 bytes. This is obviously far below the minimum IPv6 288 packet size of 1280 octets, and in keeping with section 5 of the 289 IPv6 specification [RFC2460], a fragmentation and reassembly 290 adaptation layer must be provided at the layer below IP. 292 2. Given that in the worst case the maximum size available for 293 transmitting IP packets over IEEE 802.15.4 frame is 81 octets, 294 and that the IPv6 header is 40 octets long, (without optional 295 headers), this leaves only 41 octets for upper-layer protocols, 296 like UDP and TCP. UDP uses 8 octets in the header and TCP uses 297 20 octets. This leaves 33 octets for data over UDP and 21 octets 298 for data over TCP. Additionally, as pointed above, there is also 299 a need for a fragmentation and reassembly layer, which will use 300 even more octets leaving very few octets for data. Thus if one 301 were to use the protocols as is, it would lead to excessive 302 fragmentation and reassembly even when data packets are just 10s 303 of octets long. This points at the need for header compression 304 As there is much published and in-progress standardization work 305 on header compression, this goal needs to investigate using 306 existing header compression techniques and if necessary specify 307 new ones. 309 3. [I-D.ietf-ipv6-rfc2462bis] specify methods for creating IPv6 310 stateless address autoconfiguration. Stateless auto 311 configuration has an advantage over stateful by having less 312 configuration overhead on the hosts suitable for LoWPANs. The 313 goal should specify a method to generate an "interface 314 identifier" from the EUI-64 [EUI64] assigned to the IEEE 802.15.4 315 device. 317 4. A routing protocol to support a multi-hop mesh network is 318 necessary. There is much published work on adhoc multi hop 319 routing for devices. Some examples include [RFC3561], [RFC3626], 320 [RFC3684], all experimental. Also, these protocols are designed 321 to use IP based addresses that have large overheads. For 322 example, the AODV [RFC3561] routing protocol uses 48 octets for a 323 route request based on IPv6 addressing. Given the packet size 324 constraints, transmitting this packet without fragmentation and 325 reassembly may be difficult. Thus care should be taken when 326 using existing protocols or designing new protocols for routing 327 so that the routing packets fit within a single IEEE 802.15.4 328 frame. 330 5. One of the points of transmitting IPv6 packets, is to reuse 331 existing protocols as much as possible. Network management 332 functionality is critical for LoWPANs. [RFC3411] specifies 333 SNMPv3 protocol operations. SNMP functionality may be translated 334 "as is" to LoWPANs. However, further investigation is required. 335 SNMPv3 may not be the best protocol for this task. Or it may be 336 only after adapting it appropriately. 338 6. It may be the case that transmitting IP over IEEE 802.15.4 would 339 become more beneficial if implemented in a "certain" way. 340 Accordingly, implementation considerations are to be documented. 342 7. As header compression becomes more prevalent, overall performance 343 will depend even more on efficiency of application protocols. 344 Heavyweight protocols based on XML such as SOAP [SOAP], may not 345 be suitable for LoWPANs. As such, more compact encodings (and 346 perhaps protocols) may become necessary. The goal here is to 347 specify or suggest modifications to existing protocols so that it 348 is suitable for LoWPANs. Furthermore, application level 349 interoperability specifications may also become necessary in the 350 future and may thus be specified. 352 8. Security threats at different layers must be clearly understood 353 and documented. Bootstrapping of devices into a secure network 354 could also be considered given the location, limited display, 355 high density and ad hoc deployment of devices. 357 6. IANA Considerations 359 This document contains no IANA considerations. 361 7. Security Considerations 363 IEEE 802.15.4 provides AES link layer security. As 6LoWPAN imposes 364 unique set of challenges that are not prevelant in classical 365 networks, security threats across various layers should first be 366 understood before choosing any security protocol. Furthermore, these 367 devices may not have any front end to do configuration and 368 management. As such protocols must be chosen to have very little 369 configuration and management, but still not compramise on either 370 connectivity nor security. 372 8. Acknowledgements 374 Thanks to : 376 Geoff Mulligan 378 Soohong Daniel Park 380 Samita Chakrabarti 382 Brijesh Kumar 384 for their comments and help shaping this document. 386 9. References 388 9.1. Normative References 390 [EUI64] "GUIDELINES FOR 64-BIT GLOBAL IDENTIFIER (EUI-64) 391 REGISTRATION AUTHORITY", IEEE http://standards.ieee.org/ 392 regauth/oui/tutorials/EUI64.html. 394 [I-D.ietf-ipv6-2461bis] 395 Narten, T., "Neighbor Discovery for IP version 6 (IPv6)", 396 draft-ietf-ipv6-2461bis-05 (work in progress), 397 October 2005. 399 [I-D.ietf-ipv6-rfc2462bis] 400 Thomson, S., "IPv6 Stateless Address Autoconfiguration", 401 draft-ietf-ipv6-rfc2462bis-08 (work in progress), 402 May 2005. 404 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 405 Requirement Levels", BCP 14, RFC 2119, March 1997. 407 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 408 (IPv6) Specification", RFC 2460, December 1998. 410 [ieee802.15.4] 411 IEEE Computer Society, "IEEE Std. 802.15.4-2003", 412 October 2003. 414 9.2. Informative References 416 [RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An 417 Architecture for Describing Simple Network Management 418 Protocol (SNMP) Management Frameworks", STD 62, RFC 3411, 419 December 2002. 421 [RFC3561] Perkins, C., Belding-Royer, E., and S. Das, "Ad hoc On- 422 Demand Distance Vector (AODV) Routing", RFC 3561, 423 July 2003. 425 [RFC3626] Clausen, T. and P. Jacquet, "Optimized Link State Routing 426 Protocol (OLSR)", RFC 3626, October 2003. 428 [RFC3684] Ogier, R., Templin, F., and M. Lewis, "Topology 429 Dissemination Based on Reverse-Path Forwarding (TBRPF)", 430 RFC 3684, February 2004. 432 [RFC3756] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor 433 Discovery (ND) Trust Models and Threats", RFC 3756, 434 May 2004. 436 [SOAP] "SOAP", W3C http://www.w3c.org/2000/xp/Group/. 438 [liaison] "LIASONS", 439 IETF http://www.ietf.org/liaisonActivities.html. 441 Authors' Addresses 443 Nandakishore Kushalnagar 444 Intel Corp 446 Email: nandakishore.kushalnagar@intel.com 448 Gabriel Montenegro 449 Microsoft Corporation 451 Email: gabriel_montenegro_2000@yahoo.com 453 Intellectual Property Statement 455 The IETF takes no position regarding the validity or scope of any 456 Intellectual Property Rights or other rights that might be claimed to 457 pertain to the implementation or use of the technology described in 458 this document or the extent to which any license under such rights 459 might or might not be available; nor does it represent that it has 460 made any independent effort to identify any such rights. 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Please address the information to the IETF at 475 ietf-ipr@ietf.org. 477 Disclaimer of Validity 479 This document and the information contained herein are provided on an 480 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 481 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 482 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 483 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 484 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 485 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 487 Copyright Statement 489 Copyright (C) The Internet Society (2005). This document is subject 490 to the rights, licenses and restrictions contained in BCP 78, and 491 except as set forth therein, the authors retain all their rights. 493 Acknowledgment 495 Funding for the RFC Editor function is currently provided by the 496 Internet Society.