idnits 2.17.1 draft-ietf-lwig-terminology-04.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (April 23, 2013) is 4021 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-01) exists of draft-arkko-lwig-cellular-00 == Outdated reference: A later version (-02) exists of draft-brandt-6man-lowpanz-00 == Outdated reference: A later version (-11) exists of draft-clausen-lln-rpl-experiences-06 == Outdated reference: A later version (-13) exists of draft-ietf-roll-terminology-12 == Outdated reference: A later version (-03) exists of draft-mariager-6lowpan-v6over-dect-ule-02 -- Obsolete informational reference (is this intentional?): RFC 793 (Obsoleted by RFC 9293) Summary: 0 errors (**), 0 flaws (~~), 6 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LWIG Working Group C. Bormann 3 Internet-Draft Universitaet Bremen TZI 4 Intended status: Informational M. Ersue 5 Expires: October 25, 2013 Nokia Siemens Networks 6 A. Keranen 7 Ericsson 8 April 23, 2013 10 Terminology for Constrained Node Networks 11 draft-ietf-lwig-terminology-04 13 Abstract 15 The Internet Protocol Suite is increasingly used on small devices 16 with severe constraints, creating constrained node networks. This 17 document provides a number of basic terms that have turned out to be 18 useful in the standardization work for constrained environments. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on October 25, 2013. 37 Copyright Notice 39 Copyright (c) 2013 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2.1. Constrained Nodes . . . . . . . . . . . . . . . . . . . . 3 57 2.2. Constrained Networks . . . . . . . . . . . . . . . . . . 4 58 2.2.1. Challenged Networks . . . . . . . . . . . . . . . . . 5 59 2.3. Constrained Node Networks . . . . . . . . . . . . . . . . 5 60 2.3.1. LLN ("low-power lossy network") . . . . . . . . . . . 5 61 2.3.2. LoWPAN, 6LoWPAN . . . . . . . . . . . . . . . . . . . 6 62 3. Classes of Constrained Devices . . . . . . . . . . . . . . . 7 63 4. Power Terminology . . . . . . . . . . . . . . . . . . . . . . 9 64 4.1. Scaling Properties . . . . . . . . . . . . . . . . . . . 9 65 4.2. Classes of Energy Limitation . . . . . . . . . . . . . . 9 66 4.3. Strategies of Using Power for Communication . . . . . . . 10 67 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 69 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 70 8. Informative References . . . . . . . . . . . . . . . . . . . 12 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 73 1. Introduction 75 Small devices with limited CPU, memory, and power resources, so 76 called constrained devices (also known as sensor, smart object, or 77 smart device) can constitute a network, becoming "constrained nodes" 78 in that network. Such a network may itself exhibit constraints, e.g. 79 with unreliable or lossy channels, limited and unpredictable 80 bandwidth, and a highly dynamic topology. 82 Constrained devices might be in charge of gathering information in 83 diverse settings including natural ecosystems, buildings, and 84 factories and sending the information to one or more server stations. 85 Constrained devices may work under severe resource constraints such 86 as limited battery and computing power, little memory and 87 insufficient wireless bandwidth, and communication capabilities. 88 Other entities on the network, e.g., a base station or controlling 89 server, might have more computational and communication resources and 90 could support the interaction between the constrained devices and 91 applications in more traditional networks. 93 Today diverse sizes of constrained devices with different resources 94 and capabilities are becoming connected. Mobile personal gadgets, 95 building-automation devices, cellular phones, Machine-to-machine 96 (M2M) devices, etc. benefit from interacting with other "things" 97 nearby or somewhere in the Internet. With this, the Internet of 98 Things (IoT) becomes a reality, built up out of uniquely identifiable 99 and addressable objects (things). And over the next decade, this 100 could grow to large numbers [fifty-billion] of Internet-connected 101 constrained devices, greatly increasing the Internet's size and 102 scope. 104 The present document provides a number of basic terms that have 105 turned out to be useful in the standardization work for constrained 106 environments. The intention is not to exhaustively cover the field, 107 but to make sure a few core terms are used consistently between 108 different groups cooperating in this space. 110 2. Terminology 112 The main focus of this field of work appears to be _scaling_: 114 o Scaling up Internet technologies to a large number [fifty-billion] 115 of inexpensive nodes, while 117 o scaling down the characteristics of each of these nodes and of the 118 networks being built out of them, to make this scaling up 119 economically and physically viable. 121 The need for scaling down the characteristics of nodes leads to 122 _constrained nodes_. 124 2.1. Constrained Nodes 126 The term "constrained node" is best defined by contrasting the 127 characteristics of a constrained node with certain widely held 128 expectations on more familiar Internet nodes: 130 Constrained Node: A node where some of the characteristics that are 131 otherwise pretty much taken for granted for Internet nodes in 2013 132 are not attainable, often due to cost constraints and/or physical 133 constraints on characteristics such as size, weight, and available 134 power and energy. 136 While this is less than satisfying as a rigorous definition, it is 137 grounded in the state of the art and clearly sets apart constrained 138 nodes from server systems, desktop or laptop computers, powerful 139 mobile devices such as smartphones etc. There may be many design 140 considerations that lead to these constraints, including cost, size, 141 weight, and other scaling factors. 143 (An alternative name, when the properties as a network node are not 144 in focus, is "constrained device".) 145 There are multiple facets to the constraints on nodes, often applying 146 in combination, e.g.: 148 o constraints on the maximum code complexity (ROM/Flash); 150 o constraints on the size of state and buffers (RAM); 152 o constraints on the available power. 154 Section 3 defines a small number of interesting classes ("class-N" 155 for N=0,1,2) of constrained nodes focusing on relevant combinations 156 of the first two constraints. With respect to available power, 157 [RFC6606] distinguishes "power-affluent" nodes (mains-powered or 158 regularly recharged) from "power-constrained nodes" that draw their 159 power from primary batteries or by using energy harvesting; more 160 detailed power terminology is given in Section 4. 162 The use of constrained nodes in networks often also leads to 163 constraints on the networks themselves. However, there may also be 164 constraints on networks that are largely independent from those of 165 the nodes. We therefore distinguish _constrained networks_ and 166 _constrained node networks_. 168 2.2. Constrained Networks 170 We define "constrained network" in a similar way: 172 Constrained Network: A network where some of the characteristics 173 pretty much taken for granted for Internet link layers in 2013 are 174 not attainable. 176 Again, there may be several reasons for this: 178 o cost constraints on the network, 180 o constraints of the nodes (for constrained node networks), 182 o physical constraints (e.g., power constraints, media constraints 183 such as underwater operation, limited spectrum for very high 184 density, electromagnetic compatibility), 186 o regulatory constraints, such as very limited spectrum availability 187 (including limits on effective radiated power and duty cycle), or 188 explosion safety. 190 Constraints may include: 192 o low achievable bit rate (including limits on duty cycle), 193 o high packet loss, packet loss (delivery rate) variability, 195 o severe penalties for using larger packets (e.g., high packet loss 196 due to link layer fragmentation), 198 o lack of (or severe constraints on) advanced services such as IP 199 multicast. 201 2.2.1. Challenged Networks 203 A constrained network is not necessarily a _challenged_ network 204 [FALL]: 206 Challenged Network: A network that has serious trouble maintaining 207 what an application would today expect of the end-to-end IP model, 208 e.g., by: 210 o not being able to offer end-to-end IP connectivity at all; 212 o exhibiting serious interruptions in end-to-end IP connectivity; 214 o exhibiting delay well beyond the Maximum Segment Lifetime (MSL) 215 defined by TCP [RFC0793]. 217 All challenged networks are constrained networks in some sense, but 218 not all constrained networks are challenged networks. There is no 219 well-defined boundary between the two, though. Delay-Tolerant 220 Networking (DTN) has been designed to cope with challenged networks 221 [RFC4838]. 223 2.3. Constrained Node Networks 225 Constrained Node Network: A network whose characteristics are 226 influenced by being composed of a significant portion of 227 constrained nodes. 229 A constrained node network always is a constrained network because of 230 the network constraints stemming from the node constraints, but may 231 also have other constraints that already make it a constrained 232 network. 234 2.3.1. LLN ("low-power lossy network") 236 A related term that has been used recently is "low-power lossy 237 network" (LLN). In its terminology document, the ROLL working group 238 is saying [I-D.ietf-roll-terminology]: 240 LLN: Low power and Lossy networks (LLNs) are typically composed of 241 many embedded devices with limited power, memory, and processing 242 resources interconnected by a variety of links, such as IEEE 243 802.15.4 or Low Power WiFi. There is a wide scope of application 244 areas for LLNs, including industrial monitoring, building 245 automation (HVAC, lighting, access control, fire), connected home, 246 healthcare, environmental monitoring, urban sensor networks, 247 energy management, assets tracking and refrigeration.. [sic] 249 In common usage, LLN often stands for "the network characteristics 250 that RPL has been designed for". Beyond what is said in the ROLL 251 terminology document, LLNs do appear to have significant loss at the 252 physical layer, with significant variability of the delivery rate, 253 and some short-term unreliability, coupled with some medium term 254 stability that makes it worthwhile to construct medium-term stable 255 directed acyclic graphs for routing and do measurements on the edges 256 such as ETX [RFC6551]. Actual "low power" does not seem to be 257 required for an LLN [I-D.hui-vasseur-roll-rpl-deployment], and the 258 positions on scaling of LLNs appear to vary widely 259 [I-D.clausen-lln-rpl-experiences]. 261 The ROLL terminology document states that LLNs typically are composed 262 of constrained nodes; this is also supported by the design of 263 operation modes such as RPL's "non-storing mode". So, in the 264 terminology of the present document, an LLN seems to be a constrained 265 node network with certain network characteristics, which include 266 constraints on the network as well. 268 2.3.2. LoWPAN, 6LoWPAN 270 One interesting class of a constrained network often used as a 271 constrained node network is the "LoWPAN" [RFC4919], a term inspired 272 from the name of the IEEE 802.15.4 working group (low-rate wireless 273 personal area networks (LR-WPANs)). The expansion of that acronym, 274 "Low-Power Wireless Personal Area Network" contains a hard to justify 275 "Personal" that is due to IEEE politics more than due to an 276 orientation of LoWPANs around a single person. Actually, LoWPANs 277 have been suggested for urban monitoring, control of large buildings, 278 and industrial control applications, so the "Personal" can only be 279 considered a vestige. Maybe the term is best read as "Low-Power 280 Wireless Area Networks" (LoWPANs) [WEI]. Originally focused on IEEE 281 802.15.4, "LoWPAN" (or when used for IPv6, "6LoWPAN") is now also 282 being used for networks built from similarly constrained link layer 283 technologies [I-D.ietf-6lowpan-btle] 284 [I-D.mariager-6lowpan-v6over-dect-ule] [I-D.brandt-6man-lowpanz]. 286 3. Classes of Constrained Devices 288 Despite the overwhelming variety of Internet-connected devices that 289 can be envisioned, it may be worthwhile to have some succinct 290 terminology for different classes of constrained devices. In this 291 document, the class designations in Table 1 may be used as rough 292 indications of device capabilities: 294 +-------------+-----------------------+-------------------------+ 295 | Name | data size (e.g., RAM) | code size (e.g., Flash) | 296 +-------------+-----------------------+-------------------------+ 297 | Class 0, C0 | << 10 KiB | << 100 KiB | 298 | | | | 299 | Class 1, C1 | ~ 10 KiB | ~ 100 KiB | 300 | | | | 301 | Class 2, C2 | ~ 50 KiB | ~ 250 KiB | 302 +-------------+-----------------------+-------------------------+ 304 Table 1: Classes of Constrained Devices (KiB = 1024 bytes) 306 As of the writing of this document, these characteristics correspond 307 to distinguishable clusters of commercially available chips and 308 design cores for constrained devices. While it is expected that the 309 boundaries of these classes will move over time, Moore's law tends to 310 be less effective in the embedded space than in personal computing 311 devices: Gains made available by increases in transistor count and 312 density are more likely to be invested in reductions of cost and 313 power requirements than into continual increases in computing power. 315 Class 0 devices are very constrained sensor-like motes. Most likely 316 they will not be able to communicate directly with the Internet in a 317 secure manner. Class 0 devices will participate in Internet 318 communications with the help of larger devices acting as proxies, 319 gateways or servers. Class 0 devices generally cannot be secured or 320 managed comprehensively in the traditional sense. They will most 321 likely be preconfigured (and will be reconfigured rarely, if at all), 322 with a very small data set. For management purposes, they could 323 answer keepalive signals and send on/off or basic health indications. 325 Class 1 devices cannot easily talk to other Internet nodes employing 326 a full protocol stack such as using HTTP, TLS and related security 327 protocols and XML-based data representations. However, they have 328 enough power to use a protocol stack specifically designed for 329 constrained nodes (e.g., CoAP over UDP) and participate in meaningful 330 conversations without the help of a gateway node. In particular, 331 they can provide support for the security functions required on a 332 large network. Therefore, they can be integrated as fully developed 333 peers into an IP network, but they need to be parsimonious with state 334 memory, code space, and often power expenditure for protocol and 335 application usage. 337 Class 2 can already support mostly the same protocol stacks as used 338 on notebooks or servers. However, even these devices can benefit 339 from lightweight and energy-efficient protocols and from consuming 340 less bandwidth. Furthermore, using fewer resources for networking 341 leaves more resources available to applications. Thus, using the 342 protocol stacks defined for very constrained devices also on Class 2 343 devices might reduce development costs and increase the 344 interoperability. 346 Constrained devices with capabilities significantly beyond Class 2 347 devices exist. They are less demanding from a standards development 348 point of view as they can largely use existing protocols unchanged. 349 The present document therefore does not make any attempt to define 350 classes beyond Class 2. These devices can still be constrained by a 351 limited energy supply. 353 With respect to examining the capabilities of constrained nodes, 354 particularly for Class 1 devices, it is important to understand what 355 type of applications they are able to run and which protocol 356 mechanisms would be most suitable. Because of memory and other 357 limitations, each specific Class 1 device might be able to support 358 only a few selected functions needed for its intended operation. In 359 other words, the set of functions that can actually be supported is 360 not static per device type: devices with similar constraints might 361 choose to support different functions. Even though Class 2 devices 362 have some more functionality available and may be able to provide a 363 more complete set of functions, they still need to be assessed for 364 the type of applications they will be running and the protocol 365 functions they would need. To be able to derive any requirements, 366 the use cases and the involvement of the devices in the application 367 and the operational scenario need to be analyzed. Use cases may 368 combine constrained devices of multiple classes as well as more 369 traditional Internet nodes. 371 4. Power Terminology 373 Devices not only differ in their computing capabilities, but also in 374 available electrical power and/or energy. While it is harder to find 375 recognizable clusters in this space, it is still useful to introduce 376 some common terminology. 378 4.1. Scaling Properties 380 The power and/or energy available to a device may vastly differ, from 381 kilowatts to microwatts, from essentially unlimited to hundreds of 382 microjoules. 384 Instead of defining classes or clusters, we propose simply stating, 385 in SI units, an approximate value for one or both of the quantities 386 listed in Table 2: 388 +--------+---------------------------------------------+------------+ 389 | Name | Definition | SI Unit | 390 +--------+---------------------------------------------+------------+ 391 | Ps | Sustainable average power available for the | W (Watt) | 392 | | device over the time it is functioning | | 393 | | | | 394 | Et | Total electrical energy available before | J (Joule) | 395 | | the energy source is exhausted | | 396 +--------+---------------------------------------------+------------+ 398 Table 2: Quantities Relevant to Power and Energy 400 The value of Et may need to be interpreted in conjunction with an 401 indication over which period of time the value is given; see the next 402 subsection. 404 4.2. Classes of Energy Limitation 406 As discussed above, some devices are limited in available energy as 407 opposed to (or in addition to) being limited in available power. 408 Where no relevant limitations exist with respect to energy, the 409 device is classified as E3. The energy limitation may be in total 410 energy available in the usable lifetime of the device (e.g. a device 411 with a non-replaceable primary battery, which is discarded when this 412 battery is exhausted), classified as E2. Where the relevant 413 limitation is for a specific period, this is classified as E1, e.g. 414 a limited amount of energy available for the night with a solar- 415 powered device, or for the period between recharges with a device 416 that is manually connected to a charger, or by a periodic (primary) 417 battery replacement interval. Finally, there may be a limited amount 418 of energy available for a specific event, e.g. for a button press in 419 an energy harvesting light switch; this is classified as E0. Note 420 that many E1 devices in a sense also are E2, as the rechargeable 421 battery has a limited number of useful recharging cycles. 423 In summary, we distinguish (Table 3): 425 +------+------------------------------+-----------------------------+ 426 | Name | Type of energy limitation | Example Power Source | 427 +------+------------------------------+-----------------------------+ 428 | E0 | Event energy-limited | Event-based harvesting | 429 | | | | 430 | E1 | Period energy-limited | Battery that is | 431 | | | periodically recharged or | 432 | | | replaced | 433 | | | | 434 | E2 | Lifetime energy-limited | Non-replaceable primary | 435 | | | battery | 436 | | | | 437 | E3 | No direct quantitative | Mains powered | 438 | | limitations to available | | 439 | | energy | | 440 +------+------------------------------+-----------------------------+ 442 Table 3: Classes of Energy Limitation 444 4.3. Strategies of Using Power for Communication 446 Especially when wireless transmission is used, the radio often 447 consumes a big portion of the total energy consumed by the device. 448 Design parameters such as the available spectrum, the desired range, 449 and the bitrate aimed for, influence the power consumed during 450 transmission and reception; the duration of transmission and 451 reception (including potential reception) influence the total energy 452 consumption. 454 Based on the type of the energy source (e.g., battery or mains power) 455 and how often device needs to communicate, it may use different kinds 456 of strategies for power usage and network attachment. 458 The general strategies for power usage can be described as follows: 460 Always-on: This strategy is most applicable if there is no reason 461 for extreme measures for power saving. The device can stay on in 462 the usual manner all the time. It may be useful to employ power- 463 friendly hardware or limit the number of wireless transmissions, 464 CPU speeds, and other aspects for general power saving and cooling 465 needs, but the device can be connected to the network all the 466 time. 468 Always-off: Under this strategy, the device sleeps such long periods 469 at a time that once it wakes up, it makes sense for it to not 470 pretend that it has been connected to the network during sleep: 471 The device re-attaches to the network as it is woken up. The main 472 optimization goal is to minimize the effort during such re- 473 attachment process and any resulting application communications. 475 If the device sleeps for long periods of time, and needs to 476 communicate infrequently, the relative increase in energy 477 expenditure during reattachment may be acceptable. 479 Low-power: This strategy is most applicable to devices that need to 480 operate on a very small amount of power, but still need to be able 481 to communicate on a relatively frequent basis. This implies that 482 extremely low power solutions needs to be used for the hardware, 483 chosen link layer mechanisms, and so on. Typically, given the 484 small amount of time between transmissions, despite their sleep 485 state these devices retain some form of network attachment to the 486 network. Techniques used for minimizing power usage for the 487 network communications include minimizing any work from re- 488 establishing communications after waking up, tuning the frequency 489 of communications, and other parameters appropriately. 491 In summary, we distinguish (Table 4): 493 +------+------------+----------------------------------------------+ 494 | Name | Strategy | Ability to communicate | 495 +------+------------+----------------------------------------------+ 496 | S0 | Always-off | Re-attach when required | 497 | | | | 498 | S1 | Low-power | Appears connected, perhaps with high latency | 499 | | | | 500 | S2 | Always-on | Always connected | 501 +------+------------+----------------------------------------------+ 503 Table 4: Strategies of Using Power for Communication 505 5. Security Considerations 507 This draft introduces common terminology that does not raise any new 508 security issue. 510 6. IANA Considerations 512 This document has no actions for IANA. 514 7. Acknowledgements 516 Dominique Barthel and Peter van der Stok provided useful comments; 517 Charles Palmer provided a full editorial review. 519 Peter van der Stok insisted that we should have power terminology, 520 hence Section 4. The text for Section 4.3 is mostly lifted from 521 [I-D.arkko-lwig-cellular] and has been adapted for this document. 523 8. Informative References 525 [FALL] Fall, K., "A Delay-Tolerant Network Architecture for 526 Challenged Internets", SIGCOMM 2003, 2003. 528 [I-D.arkko-lwig-cellular] 529 Arkko, J., Eriksson, A., and A. Keraenen, "Building Power- 530 Efficient CoAP Devices for Cellular Networks", draft- 531 arkko-lwig-cellular-00 (work in progress), February 2013. 533 [I-D.brandt-6man-lowpanz] 534 Brandt, A. and J. Buron, "Transmission of IPv6 packets 535 over ITU-T G.9959 Networks", draft-brandt-6man-lowpanz-00 536 (work in progress), February 2013. 538 [I-D.clausen-lln-rpl-experiences] 539 Clausen, T., Verdiere, A., Yi, J., Herberg, U., and Y. 540 Igarashi, "Observations of RPL: IPv6 Routing Protocol for 541 Low power and Lossy Networks", draft-clausen-lln-rpl- 542 experiences-06 (work in progress), February 2013. 544 [I-D.hui-vasseur-roll-rpl-deployment] 545 Vasseur, J., Hui, J., Dasgupta, S., and G. Yoon, "RPL 546 deployment experience in large scale networks", draft-hui- 547 vasseur-roll-rpl-deployment-01 (work in progress), July 548 2012. 550 [I-D.ietf-6lowpan-btle] 551 Nieminen, J., Savolainen, T., Isomaki, M., Patil, B., 552 Shelby, Z., and C. Gomez, "Transmission of IPv6 Packets 553 over BLUETOOTH Low Energy", draft-ietf-6lowpan-btle-12 554 (work in progress), February 2013. 556 [I-D.ietf-roll-terminology] 557 Vasseur, J., "Terminology in Low power And Lossy 558 Networks", draft-ietf-roll-terminology-12 (work in 559 progress), March 2013. 561 [I-D.mariager-6lowpan-v6over-dect-ule] 562 Mariager, P. and J. Petersen, "Transmission of IPv6 563 Packets over DECT Ultra Low Energy", draft-mariager- 564 6lowpan-v6over-dect-ule-02 (work in progress), May 2012. 566 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 567 793, September 1981. 569 [RFC4838] Cerf, V., Burleigh, S., Hooke, A., Torgerson, L., Durst, 570 R., Scott, K., Fall, K., and H. Weiss, "Delay-Tolerant 571 Networking Architecture", RFC 4838, April 2007. 573 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 574 over Low-Power Wireless Personal Area Networks (6LoWPANs): 575 Overview, Assumptions, Problem Statement, and Goals", RFC 576 4919, August 2007. 578 [RFC6551] Vasseur, JP., Kim, M., Pister, K., Dejean, N., and D. 579 Barthel, "Routing Metrics Used for Path Calculation in 580 Low-Power and Lossy Networks", RFC 6551, March 2012. 582 [RFC6606] Kim, E., Kaspar, D., Gomez, C., and C. Bormann, "Problem 583 Statement and Requirements for IPv6 over Low-Power 584 Wireless Personal Area Network (6LoWPAN) Routing", RFC 585 6606, May 2012. 587 [WEI] Shelby, Z. and C. Bormann, "6LoWPAN: the Wireless Embedded 588 Internet", ISBN 9780470747995, 2009. 590 [fifty-billion] 591 Ericsson, "More Than 50 Billion Connected Devices", 592 Ericsson White Paper 284 23-3149 Uen, February 2011, 593 . 596 Authors' Addresses 598 Carsten Bormann 599 Universitaet Bremen TZI 600 Postfach 330440 601 D-28359 Bremen 602 Germany 604 Phone: +49-421-218-63921 605 Email: cabo@tzi.org 607 Mehmet Ersue 608 Nokia Siemens Networks 609 St.-Martinstrasse 76 610 81541 Munich 611 Germany 613 Phone: +49 172 8432301 614 Email: mehmet.ersue@nsn.com 616 Ari Keranen 617 Ericsson 618 Hirsalantie 11 619 02420 Jorvas 620 Finland 622 Email: ari.keranen@ericsson.com