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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC4861' is mentioned on line 294, but not defined == Missing Reference: 'RFC3610' is mentioned on line 429, but not defined == Unused Reference: 'RFC4994' is defined on line 483, but no explicit reference was found in the text == Outdated reference: A later version (-21) exists of draft-ietf-6lowpan-nd-17 Summary: 0 errors (**), 0 flaws (~~), 5 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 6LoWPAN Working Group J. Nieminen, Ed. 2 Internet-Draft B. Patil 3 Intended status: Standards Track T. Savolainen 4 Expires: April 12, 2012 M. Isomaki 5 Nokia 6 Z. Shelby 7 Sensinode 8 C. Gomez 9 Universitat Politecnica de 10 Catalunya/i2CAT 11 October 10, 2011 13 Transmission of IPv6 Packets over Bluetooth Low Energy 14 draft-ietf-6lowpan-btle-03 16 Abstract 18 Bluetooth Low Energy is a low power air interface technology defined 19 by the Bluetooth Special Interest Group (BT SIG). The standard 20 Bluetooth radio has been widely implemented and available in mobile 21 phones, notebook computers, audio headsets and many other devices. 22 The low power version of Bluetooth is a new specification and enables 23 the use of this air interface with devices such as sensors, smart 24 meters, appliances, etc. The low power variant of Bluetooth is 25 commonly specified in revision 4.0 of the Bluetooth specifications 26 and commonly refered to as Bluetooth 4.0. This document describes 27 how IPv6 is transported over Bluetooth Low Energy using 6LoWPAN 28 techniques. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 12, 2012. 47 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 65 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 66 2. Bluetooth Low Energy . . . . . . . . . . . . . . . . . . . . . 4 67 2.1. Bluetooth Low Energy stack . . . . . . . . . . . . . . . . 4 68 2.2. Link layer roles and topology . . . . . . . . . . . . . . 5 69 2.3. BT-LE device addressing . . . . . . . . . . . . . . . . . 5 70 2.4. BT-LE packets sizes and MTU . . . . . . . . . . . . . . . 5 71 3. Specification of IPv6 over Bluetooth Low Energy . . . . . . . 6 72 3.1. Protocol stack . . . . . . . . . . . . . . . . . . . . . . 6 73 3.2. Link model . . . . . . . . . . . . . . . . . . . . . . . . 7 74 3.2.1. IPv6 Address configuration . . . . . . . . . . . . . . 7 75 3.2.2. Header compression . . . . . . . . . . . . . . . . . . 8 76 3.2.3. Unicast and Multicast address mapping . . . . . . . . 9 77 3.3. Internet connectivity scenarios . . . . . . . . . . . . . 9 78 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 79 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 80 6. Additional contributors . . . . . . . . . . . . . . . . . . . 10 81 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 82 8. Normative References . . . . . . . . . . . . . . . . . . . . . 10 83 Appendix A. Bluetooth Low Energy fragmentation and L2CAP Modes . 11 84 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 86 1. Introduction 88 Bluetooth Low Energy (BT-LE) is a radio technology targeted for 89 devices that operate with coin cell batteries or minimalistic power 90 sources, which means that low power consumption is essential. BT-LE 91 is an especially attractive technology for the Internet of Things 92 applications, such as health monitors, environmental sensing, 93 proximity applications and many others. 95 Considering the potential for the exponential growth in the number of 96 sensors and Internet connected devices and things, IPv6 is an ideal 97 protocol due to the large address space it provides. In addition, 98 IPv6 provides tools for autoconfiguration, which is particularly 99 suitable for sensor network applications and nodes which have very 100 limited processing power or a full-fledged operating system. 102 [RFC4944] specifies the transmission of IPv6 over IEEE 802.15.4. The 103 Bluetooth Low Energy link in many respects has similar 104 characteristics to that of IEEE 802.15.4. Many of the mechanisms 105 defined in [RFC4944] can be applied to the transmission of IPv6 on 106 Bluetooth Low Energy links. This document specifies the details of 107 IPv6 transmission over Bluetooth Low Energy links. 109 1.1. Requirements Language 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in RFC 2119 [RFC2119]. 115 1.2. Terminology 117 Bluetooth Low Energy 119 Bluetooth Low Energy is a low power air interface technology 120 specified by the Bluetooth Special Interest Group (SIG). BT-LE is 121 specified in Revision 4.0 of the Bluetooth specifications (BT 122 4.0). 124 Gateway 126 Network element connecting the BT-LE sensors to the Internet. Can 127 be e.g a home gateway or a mobile device. 129 6LR and 6LBR 131 These terms correspond to those defined in [I-D.ietf-6lowpan-nd] 133 2. Bluetooth Low Energy 135 BT-LE is designed for transferring small amounts of data infrequently 136 at modest data rates at a very low cost per bit. 138 BT-LE is an integral part of the BT 4.0 specification [BTCorev4.0]. 139 Devices such as mobile phones, notebooks, tablets and other handheld 140 computing devices which include BT 4.0 chipsets also have the low- 141 energy functionality of Bluetooth. BT-LE is also included in many 142 different types of accessories that collaborate with mobile devices 143 such as phones, tablets and notebook computers. An example of a use 144 case for a BT-LE accessory is a heart rate monitor that sends data 145 via the mobile phone to a server on the Internet. 147 2.1. Bluetooth Low Energy stack 149 The lower layer of the BT-LE stack consists of the Physical (PHY) and 150 the Link Layer (LL). The Physical Layer transmits and receives the 151 actual packets. The Link Layer is responsible for providing medium 152 access, connection establishment, error control and flow control. 153 The upper layer consists of the Logical Link Control and Adaptation 154 Protocol (L2CAP), Generic Attribute protocol (GATT) and Generic 155 Access Profile (GAP) as shown in Figure 1. GATT and BT-LE profiles 156 together enable the creation of applications in a standardized way 157 without using IP. L2CAP provides multiplexing capability by 158 multiplexing the data channels from the above layers. L2CAP also 159 provides fragmentation and reassembly for large data packets. 161 +----------------------------------------+------------------+ 162 | Applications | 163 +----------------------------------------+------------------+ 164 | Generic Attribute Profile | Generic Access | 165 +----------------------------------------+ Profile | 166 | Attribute Protocol |Security Manager | | 167 +--------------------+-------------------+------------------+ 168 | Logical Link Control and Adaptation | 169 +--------------------+-------------------+------------------+ 170 | Host Controller Interface | 171 +--------------------+-------------------+------------------+ 172 | Link Layer | Direct Test Mode | 173 +--------------------+-------------------+------------------+ 174 | Physical Layer | 175 +--------------------+-------------------+------------------+ 177 Figure 1: BT-LE Protocol Stack 179 2.2. Link layer roles and topology 181 BT-LE defines two Link Layer roles: the Master Role and the Slave 182 Role. A device in the Master Role, which is called master, can 183 manage multiple simultaneous connections with a number of devices in 184 the Slave Role, called slaves. A slave can only be connected to a 185 single master. Hence, a BT-LE network (i.e. a BT-LE piconet) follows 186 a star topology. 188 [BTLE-Slave]-----\ /-----[BTLE-Slave] 189 \ / 190 [BTLE-Slave]-----/[BTLE-Master]/-----[BTLE-Slave] 191 / \ 192 [BTLE-Slave]-----/ \-----[BTLE-Slave] 194 Figure 2: BT-LE Star Topology 196 A master is assumed to be less constrained than a slave. Hence, 197 master and slave can correspond with 6LoWPAN Border Router (6LBR) and 198 host, respectively. 200 In BT-LE, communication only takes place between a master and a 201 slave. Hence, in a BT-LE network using IP, a radio hop is equivalent 202 to an IP link and vice versa. 204 2.3. BT-LE device addressing 206 Every BT-LE device is identified by a unique 48 bit Bluetooth Device 207 Address (BD_ADDR). An BT-LE-only device such as a sensor may use a 208 public (obtained from IEEE Registration Authority) or a random device 209 address (generated internally). The public address is created 210 according to the IEEE 802-2001 standard and using a valid 211 Organizationally Unique Identifier (OUI) obtained from the IEEE 212 Registration Authority. This specification mandates that the 213 Bluetooth Device Address MUST be a public address. 215 2.4. BT-LE packets sizes and MTU 217 Maximum size of the payload in a BT-LE data channel PDU is 27 bytes. 218 Depending on the L2CAP mode in use, the amount of data available for 219 transporting IP bytes in a single BT-LE data channel PDU ranges 220 between 19 and 27 octets. For power efficient communication between 221 two BT-LE devices, data and its header should fit in a single BT-LE 222 data channel PDU. MTU larger than the above mentioned values can be 223 supported by the L2CAP specification. The Basic L2CAP Mode allows a 224 maximum payload size (i.e. IP datagram size) of 65535 bytes per 225 L2CAP PDU. The rest of L2CAP modes allow a maximum payload size that 226 ranges between 65527 and 65533 bytes per L2CAP PDU. 228 3. Specification of IPv6 over Bluetooth Low Energy 230 BT-LE technology sets strict requirements for low power consumption 231 and thus limits the allowed protocol overhead. 6LoWPAN standard 232 [RFC4944], [I-D.ietf-6lowpan-nd] and [I-D.ietf-6lowpan-hc] provides 233 useful generic functionality like header compression, link-local IPv6 234 addresses, Neighbor Discovery and stateless IP-address 235 autoconfiguration for reducing the overhead in 802.15.4 networks. 236 This functionality can be partly applied to BT-LE. 238 A significant difference between IEEE 802.15.4 and BT-LE is that the 239 former supports the mesh topology (and requires a routing protocol), 240 whereas BT-LE does not currently support the formation of multihop 241 networks. In consequence, the mesh header defined in [RFC4944] for 242 mesh under routing MUST NOT be used in BT-LE networks. On the other 243 hand, a BT-LE device MUST NOT play the role of a 6LoWPAN Router 244 (6LR). 246 The maximum payload size of a BT-LE data channel PDU is 27 bytes, 247 from which L2CAP headers may consume additional bytes. The smallest 248 However, IP data packets may be much larger and IPv6 requires support 249 for an MTU of 1280 bytes. Segmentation and Reassembly (SAR) 250 functionality is an inherent function of the BT-LE L2CAP layer. 251 Larger L2CAP packets can be transferred with the assistance of the 252 SAR functionality. Appendix A describes also another fragmentation 253 method called Fragmentation and Recombination (FAR) as well as five 254 L2CAP Modes. This specification requires that SAR functionality MUST 255 be provided in the L2CAP layer up to the IPv6 minimum MTU of 1280 256 bytes. The corresponding L2CAP Mode MUST be Streaming Mode. It is 257 RECOMMENDED that also FAR with Basic L2CAP Mode is supported. Since 258 SAR and FAR in BT-LE are functions of the L2CAP layer, fragmentation 259 functionality as defined in [RFC4944] MUST NOT be used in BT-LE 260 networks. 262 3.1. Protocol stack 264 In order to enable transmission of IPv6 packets over BT-LE, a new 265 fixed L2CAP channel ID MUST be reserved for IPv6 traffic by the BT- 266 SIG. A request for allocation of a new fixed channel ID for IPv6 267 traffic by the BT-SIG should be submitted through the liaison process 268 or formal communique from the 6lowpan chairs and respective area 269 directors. This specification defines the use of channel ID 0x0007 270 for this purpose. Figure 3 illustrates IPv6 over BT-LE stack. 272 +-------------------+ 273 | UDP/TCP | 274 +-------------------+ 275 | IPv6 | 276 +-------------------+ 277 | 6LoWPAN adapted | 278 | to BT-LE | 279 +-------------------+ 280 | BT-LE L2CAP | 281 +-------------------+ 282 | BT-LE Link Layer | 283 +-------------------+ 284 | BT-LE Physical | 285 +-------------------+ 287 Figure 3: IPv6 over BT-LE Stack 289 3.2. Link model 291 The concept of IP link (layer 3) and the physical link (combination 292 of PHY and MAC) needs to be clear and the relationship has to be well 293 understood in order to specify the addressing scheme for transmitting 294 IPv6 packets over the BT-LE link. [RFC4861] defines a link as "a 295 communication facility or medium over which nodes can communicate at 296 the link layer, i.e., the layer immediately below IP." 298 In the case of BT-LE, L2CAP is an adaptation layer that supports the 299 transmission of IPv6 packets. L2CAP also provides multiplexing 300 capability in addition to SAR functionality. 302 The BT-LE link between two communicating nodes can be considered to 303 be a point-to-point or point-to-multipoint link. When one of the 304 communicating nodes is in the role of a master, then the link can be 305 viewed as a point-to-multipoint link. 307 When a host connects to another BT-LE device the link is up and IP 308 address configuration and transmission can occur. 310 3.2.1. IPv6 Address configuration 312 The Interface Identifier (IID) for a BT-LE interface MUST be formed 313 from the 48-bit public device Bluetooth address as per the "IPv6 over 314 Ethernet" specification [RFC2464]. An IPv6 prefix used for stateless 315 autoconfiguration [RFC4862] of a BT-LE interface MUST have a length 316 of 64 bits. Thus, this prefix is EUI-64 compliant. 318 The IPv6 link-local address [RFC4291] for a BT-LE interface is formed 319 by appending the IID, as defined above, to the prefix FE80::/64, as 320 depicted in Figure 4. 322 10 bits 54 bits 64 bits 323 +----------+-----------------+----------------------+ 324 |1111111010| zeros | Interface Identifier | 325 +----------+-----------------+----------------------+ 327 Figure 4: IPv6 link-local address in BT-LE 329 3.2.2. Header compression 331 This document assumes [I-D.ietf-6lowpan-hc], which specifies the 332 compression format for IPv6 datagrams on top of IEEE 802.15.4, as the 333 basis for IPv6 header compression on top of BT-LE. It is required 334 that all headers MUST be compressed according to HC base encoding. 335 The following text describes the principles of IPv6 address 336 compression on top of BT-LE. 338 In a link-local communication, both the IPv6 source and destination 339 addresses MUST be elided. In this type of communication, a node that 340 receives a data channel PDU containing an IPv6 packet (or a part of 341 it) can infer that the IPv6 destination address of the packet is its 342 own IPv6 address. On the other hand, a node SHALL learn the IID of 343 the other endpoint of each L2CAP connection it participates in. By 344 exploiting this information, a node that receives a data channel PDU 345 containing an IPv6 packet (or a part of it) can infer the 346 corresponding IPv6 source address. A device MAY learn the IID of the 347 other endpoint of an L2CAP connection e.g. from the RS/RA/NS/NA 348 Neighbor Discovery (ND) message exchange [I-D.ietf-6lowpan-nd]. A 349 device MAY also derive the IID of the other endpoint of a L2CAP 350 connection from the Link Layer connection establishment messages. 351 The device MUST maintain a Neighbor Cache, in which the entries 352 include both the IID of the neighbor and the Device Address that 353 identifies the neighbor. 355 When a BT-LE slave transmits an IPv6 packet to a remote destination 356 using global IPv6 addresses, the slave MUST elide the IPv6 source 357 address. The 6LBR/master can infer the elided IPv6 source address 358 since 1) the master/6LBR has previously assigned the prefix to the 359 slaves; and 2) the master/6LBR maintains a Neighbor Cache that 360 relates the Device Address and the IID of the corresponding slave. 361 If a context is defined for the IPv6 destination address, the slave 362 MUST also elide the prefix of the destination IPv6 address. In that 363 case, the 6LBR/master can infer the elided destination prefix by 364 using the context. 366 When a master/6LBR receives an IPv6 packet sent by a remote node 367 outside the BT-LE network, and the destination of the packet is a 368 slave, the master/6LBR MUST elide the IPv6 destination address of the 369 packet before forwarding it to the slave. The slave can infer that 370 the IPv6 destination address of the packet is its own IPv6 address. 371 If a context is defined for the prefix of the IPv6 source address, 372 the master/6LBR MUST elide that prefix as well. 374 3.2.3. Unicast and Multicast address mapping 376 The BT-LE link layer does not support multicast. Hence traffic is 377 always unicast between two BT-LE devices. Even in the case where a 378 master is attached to multiple slave BT-LE devices, the master device 379 cannot do a multicast to all the connected slave devices. If the 380 master device needs to send a multicast packet to all its slave 381 devices, it has to replicate the packet and unicast it on each link. 382 However, this may not be energy-efficient and particular care must be 383 taken if the master is battery-powered. In the opposite direction, a 384 slave can only transmit data to a single destination (i.e. the 385 master). Hence, if a slave transmits an IPv6 multicast packet, the 386 slave can unicast the corresponding BT-LE packet to the master. It 387 is required that the master MUST provide a table for mapping 388 different types of multicast addresses (all-nodes, all-routers and 389 solicited-node multicast addresses) to the corresponding IIDs and 390 Device Addresses. 392 3.3. Internet connectivity scenarios 394 In a typical scenario, BT-LE network is connected to the Internet. 396 h ____________ 397 \ / \ 398 h ---- 6LBR --- | Internet | 399 / \____________/ 400 h 401 h: host 402 <-- BT-LE --> 6LBR: 6LoWPAN Border Router 404 Figure 5: BT-LE network connected to the Internet 406 In some scenarios, the BT-LE network may transiently or permanently 407 be an isolated network. 409 h h h: host 410 \ / 6LBR: 6LoWPAN Border Router 411 h --- 6LBR -- h 412 / \ 413 h h 415 Figure 6: Isolated BT-LE network 417 4. IANA Considerations 419 While there are no actions for IANA, we do expect BT SIG to allocate 420 an L2CAP channel ID. 422 5. Security Considerations 424 The transmission of IPv6 over BT-LE links has similar requirements 425 and concerns for security as for IEEE 802.15.4. IPv6 over BT-LE 426 SHOULD be protected by using BT-LE Link Layer security. 428 BT-LE Link Layer supports encryption and authentication by using the 429 Counter with CBC-MAC (CCM) mechanism [RFC3610] and a 128-bit AES 430 block cipher. Upper layer security mechanisms may exploit this 431 functionality when it is available. (Note: CCM does not consume 432 bytes from the maximum per-packet L2CAP data size, since the link 433 layer data unit has a specific field for them when they are used.) 435 Key management in BT-LE is provided by the Security Manager Protocol 436 (SMP). 438 6. Additional contributors 440 Kanji Kerai, Jari Mutikainen, David Canfeng-Chen and Minjun Xi from 441 Nokia have contributed significantly to this document. 443 7. Acknowledgements 445 Samita Chakrabarti and Erik Nordmark have provided valuable feedback 446 for this draft. 448 8. Normative References 450 [BTCorev4.0] 451 "Bluetooth Core Specification v4.0, http:// 452 www.bluetooth.com/English/Technology/Building/Pages/ 453 Specification.aspx". 455 [I-D.ietf-6lowpan-hc] 456 Hui, J. and P. Thubert, "Compression Format for IPv6 457 Datagrams in Low Power and Lossy Networks (6LoWPAN)", 458 draft-ietf-6lowpan-hc-15 (work in progress), 459 February 2011. 461 [I-D.ietf-6lowpan-nd] 462 Shelby, Z., Chakrabarti, S., and E. Nordmark, "Neighbor 463 Discovery Optimization for Low Power and Lossy Networks 464 (6LoWPAN)", draft-ietf-6lowpan-nd-17 (work in progress), 465 June 2011. 467 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 468 Requirement Levels", BCP 14, RFC 2119, March 1997. 470 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 471 Networks", RFC 2464, December 1998. 473 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 474 Architecture", RFC 4291, February 2006. 476 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 477 Address Autoconfiguration", RFC 4862, September 2007. 479 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 480 "Transmission of IPv6 Packets over IEEE 802.15.4 481 Networks", RFC 4944, September 2007. 483 [RFC4994] Zeng, S., Volz, B., Kinnear, K., and J. Brzozowski, 484 "DHCPv6 Relay Agent Echo Request Option", RFC 4994, 485 September 2007. 487 Appendix A. Bluetooth Low Energy fragmentation and L2CAP Modes 489 This section provides an overview of fragmentation methods and L2CAP 490 modes in Bluetooth Low Energy. There are two possible fragmentation 491 mechanisms to take into account (both of them are L2CAP mechanisms): 492 Segmentation and Reassembly (SAR) and Fragmentation and Recombination 493 (FAR). When the upper layer PDU is large, SAR allows to break it 494 into segments. Each segment will be contained as the payload of a 495 new L2CAP data unit, including the basic L2CAP header (4 bytes) plus 496 the SAR header (4 bytes for the first segment and 2 bytes for the 497 rest of segments) for each new data unit. In FAR an L2CAP entity can 498 take the (large) upper layer PDU, prepend the L2CAP header (4 bytes 499 in the Basic L2CAP mode) and break the resulting L2CAP PDU into 500 fragments which can then be directly encapsulated into Data channel 501 PDUs. There are bits in the Data channel PDUs which identify whether 502 the payload is a complete L2CAP PDU or the first of a set of 503 fragments, or one of the rest of the fragments. 505 There are five L2CAP modes defined in the BT 4.0 spec. These modes 506 are: Retransmission Mode (a Go-Back-N mechanism is used), Enhanced 507 Retransmission Mode (includes selective NAK among others), Flow 508 Control Mode (PDUs are numbered, but there are no retransmissions), 509 Streaming Mode (PDUs are numbered, but there are no ACKs of any 510 kind). The Basic L2CAP Mode does not support SAR. The other modes 511 do. 513 Authors' Addresses 515 Johanna Nieminen (editor) 516 Nokia 517 Itaemerenkatu 11-13 518 FI-00180 Helsinki 519 Finland 521 Email: johanna.1.nieminen@nokia.com 523 Basavaraj Patil 524 Nokia 525 6021 Connection drive 526 Irving, TX 75039 527 USA 529 Email: basavaraj.patil@nokia.com 531 Teemu Savolainen 532 Nokia 533 Hermiankatu 12 D 534 FI-33720 Tampere 535 Finland 537 Email: teemu.savolainen@nokia.com 538 Markus Isomaki 539 Nokia 540 Keilalahdentie 2-4 541 FI-02150 Espoo 542 Finland 544 Email: markus.isomaki@nokia.com 546 Zach Shelby 547 Sensinode 548 Hallituskatu 13-17D 549 FI-90100 Oulu 550 Finland 552 Email: zach.shelby@sensinode.com 554 Carles Gomez 555 Universitat Politecnica de Catalunya/i2CAT 556 C/Esteve Terradas, 7 557 Castelldefels 08860 558 Spain 560 Email: carlesgo@entel.upc.edu