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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-04) exists of draft-zuniga-lpwan-sigfox-system-description-00 Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 lpwan S. Farrell, Ed. 3 Internet-Draft Trinity College Dublin 4 Intended status: Informational October 29, 2016 5 Expires: May 2, 2017 7 LPWAN Overview 8 draft-farrell-lpwan-overview-01 10 Abstract 12 Low Power Wide Area Networks (LPWAN) are wireless technologies with 13 characteristics such as large coverage areas, low bandwidth, possibly 14 very small packet and application layer data sizes and long battery 15 life operation. This memo is an informational overview of the set of 16 LPWAN technologies being considered in the IETF and of the gaps that 17 exist between the needs of those technologies and the goal of running 18 IP in LPWANs. 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 May 2, 2017. 37 Copyright Notice 39 Copyright (c) 2016 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 3. Common Concerns . . . . . . . . . . . . . . . . . . . . . . . 3 57 4. LPWAN Technologies . . . . . . . . . . . . . . . . . . . . . 3 58 4.1. LoRaWAN . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 4.1.1. Provenance and Documents . . . . . . . . . . . . . . 4 60 4.1.2. Characteristics . . . . . . . . . . . . . . . . . . . 4 61 4.2. Narrowband IoT (NB-IoT) . . . . . . . . . . . . . . . . . 12 62 4.2.1. Provenance and Documents . . . . . . . . . . . . . . 12 63 4.2.2. Characteristics . . . . . . . . . . . . . . . . . . . 12 64 4.3. SIGFOX . . . . . . . . . . . . . . . . . . . . . . . . . 16 65 4.3.1. Provenance and Documents . . . . . . . . . . . . . . 17 66 4.3.2. Characteristics . . . . . . . . . . . . . . . . . . . 17 67 4.4. WI-SUN . . . . . . . . . . . . . . . . . . . . . . . . . 21 68 5. Gap Analysis . . . . . . . . . . . . . . . . . . . . . . . . 21 69 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 70 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 71 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 21 72 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 73 10. Informative References . . . . . . . . . . . . . . . . . . . 24 74 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 26 76 1. Introduction 78 [[Editor comments/queries are in double square brackets like this.]] 80 This document provides background material and an overview of the 81 technologies being considered in the IETF's Low Power Wide-Area 82 Networking (LPWAN) working group. We also provide a gap analysis 83 between the needs of these technologies and currently available IETF 84 specifications. 86 This document is largely the work of the people listed in Section 8. 87 Discussion of this document should take place on the lpwan@ietf.org 88 list. 90 [[Editor's note: the eventual fate of this draft is a topic for the 91 WG to consider - it might end up as a useful RFC, or it might be best 92 maintained as a draft only until its utility has dissapated. FWIW, 93 the editor doesn't mind what outcome the WG choose.]] 95 2. Terminology 97 [[Not sure if 2119 terms will be needed. Leave it here for now.]] 98 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 99 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 100 document are to be interpreted as described in RFC 2119 [RFC2119]. 102 [[Extract common terms here. Maybe define and relate technology 103 specific terms, e.g. lora g/w similar to sigfox bs etc. There is 104 text for this in the current "gaps" draft.]] 106 3. Common Concerns 108 [[Editors note: We may want a section like this that describes some 109 cross-cutting issues, e.g. duty-cycles, some of the ISM band 110 restrictions. This isn't intended to be a problem statement nor a 111 set of requirements but just to describe some issues that affect more 112 than one of the LPWAN technologies. Such a section might be better 113 before or after Section 4, will see when text's added there. There 114 is some text for this in the current "gaps" draft.]] 116 Most technologies in this space aim for similar goals of supporting 117 large numbers of low-cost, low-throughput devices at very low-cost 118 and with very-low power consumption, so that even battery-powered 119 devices can be deployed for years. And as the name implies, coverage 120 of large areas is also a common goal. There are some differences 121 however, e.g., the Narrowband IoT specifications Section 4.2 also aim 122 for increased indoor coverage. However, by and large, the different 123 technologies aim for deployment in very similar circumstances. 125 4. LPWAN Technologies 127 This section provides an overview of the set of LPWAN technologies 128 that are being considered in the LPWAN working group. The text for 129 each was mainly contributed by proponents of each technology. 131 Note that this text is not intended to be normative in any sesne, but 132 simply to help the reader in finding the relevant layer 2 133 specifications and in understanding how those integrate with IETF- 134 defined technologies. Similarly, there is no attempt here to set out 135 the pros and cons of the relevant technologies. [[Editor: I assume 136 that's the right target here. Please comment if you disagree.]] 138 [[Editor's note: the goal here is 2-3 pages per technology. If 139 there's much more needed then we could add appendices I guess 140 depending on what text the WG find useful to include.]] 142 4.1. LoRaWAN 144 [[Text here is from [I-D.farrell-lpwan-lora-overview] And yes, this 145 section is too long right now. Will shorten.]] 147 4.1.1. Provenance and Documents 149 LoRaWAN is a wireless technology for long-range low-power low-data- 150 rate applications developed by the LoRa Alliance, a membership 151 consortium. This draft is based on 152 version 1.0.2 [LoRaSpec] of the LoRa specification. (Note that 153 version 1.0.2 is expected to be published in a few weeks. We will 154 update this draft when that has happened. For now, version 1.0 is 155 available at [LoRaSpec1.0]) 157 4.1.2. Characteristics 159 In LoRaWAN networks, end-device transmissions may be received at 160 multiple gateways, so during nominal operation a network server may 161 see multiple instances of the same uplink message from an end-device. 163 The LoRaWAN network infrastructure manages the data rate and RF 164 output power for each end-device individually by means of an adaptive 165 data rate (ADR) scheme. End-devices may transmit on any channel 166 allowed by local regulation at any time, using any of the currently 167 available data rates. 169 LoRaWAN networks are typically organized in a star-of-stars topology 170 in which gateways relay messages between end-devices and a central 171 "network server" in the backend. Gateways are connected to the 172 network server via IP links while end-devices use single-hop LoRaWAN 173 communication that can be received at one or more gateways. All 174 communication is generally bi-directional, although uplink 175 communication from end-devices to the network server are favoured in 176 terms of overall bandwidth availability. 178 This section introduces some LoRaWAN terms. Figure 1 shows the 179 entities involved in a LoRaWAN network. 181 +----------+ 182 |End-device| * * * 183 +----------+ * +---------+ 184 * | Gateway +---+ 185 +----------+ * +---------+ | +---------+ 186 |End-device| * * * +---+ Network +--- Application 187 +----------+ * | | Server | 188 * +---------+ | +---------+ 189 +----------+ * | Gateway +---+ 190 |End-device| * * * * +---------+ 191 +----------+ 192 Key: * LoRaWAN Radio 193 +---+ IP connectivity 195 Figure 1: LoRaWAN architecture 197 o End-device: a LoRa client device, sometimes called a mote. 198 Communicates with gateways. 200 o Gateway: a radio on the infrastructure-side, sometimes called a 201 concentrator or base-station. Communicates with end-devices and, 202 via IP, with a network server. 204 o Network Server: The Network Server (NS) terminates the LoRaWAN MAC 205 layer for the end-devices connected to the network. It is the 206 center of the star topology. 208 o Uplink message: refers to communications from end-device to 209 network server or appliction via one or more gateways. 211 o Downlink message: refers to communications from network server or 212 application via one gateway to a single end-device or a group of 213 end-devices (considering multicasting). 215 o Application: refers to application layer code both on the end- 216 device and running "behind" the network server. For LoRaWAN, 217 there will generally only be one application running on most end- 218 devices. Interfaces between the network server and application 219 are not further described here. 221 o Classes A, B and C define different device capabilities and modes 222 of operation for end-devices. End-devices can transmit uplink 223 messages at any time in any mode of operation (so long as e.g., 224 ISM band restrictions are honoured). An end-device in Class A can 225 only receive downlink messages at predetermined timeslots after 226 each uplink message transmission. Class B allows the end-device 227 to receive downlink messages at periodically scheduled timeslots. 228 Class C allows receipt of downlink messages at anytime. Class 229 selection is based on the end-devices' application use case and 230 its power supply. (While Classes B and C are not further 231 described here, readers may have seen those terms elsewhere so we 232 include them for clarity.) 234 LoRaWAN radios make use of ISM bands, for example, 433MHz and 868MHz 235 within the European Union and 915MHz in the Americas. 237 The end-device changes channel in a pseudo-random fashion for every 238 transmission to help make the system more robust to interference and/ 239 or to conform to local regulations. 241 As with other LPWAN radio technologies, LoRaWAN end-devices respect 242 the frequency, power and maximum transmit duty cycle requirements for 243 the sub-band imposed by local regulators. In most cases, this means 244 an end-device is only transmitting for 1% of the time, as specified 245 by ISM band regulations. And in some cases the LoRaWAN specification 246 calls for end-devices to transmit less often than is called for by 247 the ISM band regulations in order to avoid congestion. 249 Figure 2 below shows that after a transmission slot a Class A device 250 turns on its receiver for two short receive windows that are offset 251 from the end of the transmission window. The frequencies and data 252 rate chosen for the first of these receive windows depends on those 253 used for the transmit window. The frequency and data-rate for the 254 second receive window are configurable. If a downlink message 255 preamble is detected during a receive window, then the end-device 256 keeps the radio on in order to receive the frame. 258 End-devices can only transmit a subsequent uplink frame after the end 259 of the associated receive windows. When a device joins a LoRaWAN 260 network, there are similar timeouts on parts of that process. 262 |----------------------------| |--------| |--------| 263 | Tx | | Rx | | Rx | 264 |----------------------------| |--------| |--------| 265 |---------| 266 Rx delay 1 267 |------------------------| 268 Rx delay 2 270 Figure 2: LoRaWAN Class A transmission and reception window 272 Given the different regional requirements the detailed specification 273 for the LoRaWAN physical layer (taking up more than 30 pages of the 274 specification) is not reproduced here. Instead and mainly to 275 illustrate the kinds of issue encountered, in Table 1 we present some 276 of the default settings for one ISM band (without fully explaining 277 those here) and in Table 2 we describe maxima and minima for some 278 parameters of interest to those defining ways to use IETF protocols 279 over the LoRaWAN MAC layer. 281 +------------------------+------------------------------------------+ 282 | Parameters | Default Value | 283 +------------------------+------------------------------------------+ 284 | Rx delay 1 | 1 s | 285 | | | 286 | Rx delay 2 | 2 s (must be RECEIVE_DELAY1 + 1s) | 287 | | | 288 | join delay 1 | 5 s | 289 | | | 290 | join delay 2 | 6 s | 291 | | | 292 | 868MHz Default | 3 (868.1,868.2,868.3), date rate: 0.3-5 | 293 | channels | kbps | 294 +------------------------+------------------------------------------+ 296 Table 1: Default settings for EU868MHz band 298 +-----------------------------------------------+--------+----------+ 299 | Parameter/Notes | Min | Max | 300 +-----------------------------------------------+--------+----------+ 301 | Duty Cycle: some but not all ISM bands impose | 1% | no-limit | 302 | a limit in terms of how often an end-device | | | 303 | can transmit. In some cases LoRaWAN is more | | | 304 | stringent in an attempt to avoid congestion. | | | 305 | | | | 306 | EU 868MHz band data rate/frame-size | 250 | 50000 | 307 | | bits/s | bits/s : | 308 | | : 59 | 250 | 309 | | octets | octets | 310 | | | | 311 | US 915MHz band data rate/frame-size | 980 | 21900 | 312 | | bits/s | bits/s : | 313 | | : 19 | 250 | 314 | | octets | octets | 315 +-----------------------------------------------+--------+----------+ 317 Table 2: Minima and Maxima for various LoRaWAN Parameters 319 Note that in the case of the smallest frame size (19 octets), 8 320 octets are required for LoRa MAC layer headers leaving only 11 octets 321 for payload (including MAC layer options). However, those settings 322 do not apply for the join procedure - end-devices are required to use 323 a channel that can send the 23 byte Join-request message for the join 324 procedure. 326 Uplink and downlink higher layer data is carried in a MACPayload. 327 There is a concept of "ports" (an optional 8 bit value) to handle 328 different applications on an end-device. Port zero is reserved for 329 LoRaWAN specific messaging, such as the join procedure. 331 The header also distinguishes the uplink/downlink directions and 332 whether or not an acknowledgement ("confirmation") is required from 333 the peer. 335 All payloads are encrypted and ciphertexts are protected with a 336 cryptographic Message Integrity Check (MIC) - see Section 6 for 337 details. 339 In addition to carrying higher layer PDUs there are Join-Request and 340 Join-Response (aka Join-Accept) messages for handling network access. 341 And so-called "MAC commands" (see below) up to 15 bytes long can be 342 piggybacked in an options field ("FOpts"). 344 LoRaWAN end-devices can choose various different data rates from a 345 menu of available rates (dependent on the frequencies in use). It is 346 however, recommended that end-devices set the Adaptive Data Rate 347 ("ADR") bit in the MAC layer which is a signal that the network 348 should control the data rate (via MAC commands to the end-device). 349 The network can also assert the ADR bit and control data rates at 350 it's discretion. The goal is to ensure minimal on-time for radios 351 whilst increasing throughput and reliability when possible. Other 352 things being equal, the effect should be that end-devices closer to a 353 gateway can successfully use higher data rates, whereas end-devices 354 further from all gateways still receive connectivity though at a 355 lower data rate. 357 Data rate changes can be validated via a scheme of acks from the 358 network with a fall-back to lower rates in the event that downlink 359 acks go missing. 361 There are 16 (or 32) bit frame counters maintained in each direction 362 that are incremented on each transmission (but not re-transmissions) 363 that are not re-used for a given key. When the device supports a 32 364 bit counter, then only the least significant 16 bits are sent in the 365 MAC header, but all 32 bits are used in cryptographic operations. 366 (If an end-device only supports a 16 bit counter internally, then the 367 topmost 16 bits are set to zero.) 369 There are a number of MAC commands for: Link and device status 370 checking, ADR and duty-cycle negotiation, managing the RX windows and 371 radio channel settings. For example, the link check response message 372 allows the network server (in response to a request from an end- 373 device) to inform an end-device about the signal attenuation seen 374 most recently at a gateway, and to also tell the end-device how many 375 gateways received the corresponding link request MAC command. 377 Some MAC commands are initiated by the network server. For example, 378 one command allows the network server to ask an end-device to reduce 379 it's duty-cycle to only use a proportion of the maximum allowed in a 380 region. Another allows the network server to query the end-device's 381 power status with the response from the end-device specifying whether 382 it has an external power source or is battery powered (in which case 383 a relative battery level is also sent to the network server). 385 The network server can also inform an end-device about channel 386 assignments (mid-point frequencies and data rates). Of course, these 387 must also remain within the bands assigned by local regulation. 389 A LoRaWAN network has a short network identifier ("NwkID") which is a 390 seven bit value. A private network (common for LoRaWAN) can use the 391 value zero. If a network wishes to support "foreign" end-devices 392 then the NwkID needs to be registered with the LoRA Alliance, in 393 which case the NwkID is the seven least significant bits of a 394 registered 24-bit NetID. (Note however, that the methods for 395 "roaming" are currently being enhanced within the LoRA Alliance, so 396 the situation here is somewhat fluid.) 398 In order to operate nominally on a LoRaWAN network, a device needs a 399 32-bit device address, which is the catentation of the NwkID and a 400 25-bit device-specific network address that is assigned when the 401 device "joins" the network (see below for the join procedure) or that 402 is pre-provisioned into the device. 404 End-devices are assumed to work with one or a quite limited number of 405 applications, which matches most LoRaWAN use-cases. The applications 406 are identified by a 64-bit AppEUI, which is assumed to be a 407 registered IEEE EUI64 value. 409 In addition, a device needs to have two symmetric session keys, one 410 for protecting network artefacts (port=0), the NwkSKey, and another 411 for protecting appliction layer traffic, the AppSKey. Both keys are 412 used for 128 bit AES cryptpgraphic operations. (See Section 6 for 413 details.) 415 So, one option is for an end-device to have all of the above, plus 416 channel information, somehow (pre-)provisioned, in which case the 417 end-device can simply start transmitting. This is achievable in many 418 cases via out-of-band means given the nature of LoRaWAN networks. 419 Table 3 summarises these values. 421 +---------+---------------------------------------------------------+ 422 | Value | Description | 423 +---------+---------------------------------------------------------+ 424 | DevAddr | DevAddr (32-bits) = NwkId (7-bits) + device-specific | 425 | | network address (25 bits) | 426 | | | 427 | AppEUI | IEEE EUI64 naming the application | 428 | | | 429 | NwkSKey | 128 bit network session key for use with AES | 430 | | | 431 | AppSKey | 128 bit application session key for use with AES | 432 +---------+---------------------------------------------------------+ 434 Table 3: Values required for nominal operation 436 As an alternative, end-devices can use the LoRaWAN join procedure in 437 order to setup some of these values and dynamically gain access to 438 the network. 440 To use the join procedure, an end-device must still know the AppEUI. 441 In addition to the AppEUI, end-devices using the join procedure need 442 to also know a different (long-term) symmetric key that is bound to 443 the AppEUI - this is the application key (AppKey), and is distinct 444 from the application session key (AppSKey). The AppKey is required 445 to be specific to the device, that is, each end-device should have a 446 different AppKey value. And finally the end-device also needs a 447 long-term identifier for itself, syntactically also an EUI-64, and 448 known as the device EUI or DevEUI. Table 4 summarises these values. 450 +---------+----------------------------------------------------+ 451 | Value | Description | 452 +---------+----------------------------------------------------+ 453 | DevEUI | IEEE EUI64 naming the device | 454 | | | 455 | AppEUI | IEEE EUI64 naming the application | 456 | | | 457 | AppKey | 128 bit long term application key for use with AES | 458 +---------+----------------------------------------------------+ 460 Table 4: Values required for join procedure 462 The join procedure involves a special exchange where the end-device 463 asserts the AppEUI and DevEUI (integrity protected with the long-term 464 AppKey, but not encrypted) in a Join-request uplink message. This is 465 then routed to the network server which interacts with an entity that 466 knows that AppKey to verify the Join-request. All going well, a 467 Join-accept downlink message is returned from the network server to 468 the end-device that specifies the 24-bit NetID, 32-bit DevAddr and 469 channel information and from which the AppSKey and NwkSKey can be 470 derived based on knowledge of the AppKey. This provides the end- 471 device with all the values listed in Table 3. 473 There is some special handling related to which channels to use and 474 for multiple transmissions for the join-request which is intended to 475 ensure a successful join in as many cases as possible. Join-request 476 and Join-accept messages also include some random values (nonces) to 477 both provide some replay protection and to help ensure the session 478 keys are unique per run of the join procedure. If a Join-request 479 fails validation, then no Join-accept message (indeed no message at 480 all) is returned to the end-device. For example, if an end-device is 481 factory-reset then it should end up in a state in which it can re-do 482 the join procedure. 484 In this section we describe the use of cryptography in LoRaWAN. This 485 section is not intended as a full specification but to be sufficient 486 so that future IETF specifications can encompass the required 487 security considerations. The emphasis is on describing the 488 externally visible characteristics of LoRaWAN. 490 All payloads are encrypted and have data integrity. Frame options 491 (used for MAC commands) when sent as a payload (port zero) are 492 therefore protected. MAC commands piggy-backed as frame options 493 ("FOpts") are however sent in clear. Since MAC commands may be sent 494 as options and not only as payload, any values sent in that manner 495 are visible to a passive attacker but are not malleable for an active 496 attacker due to the use of the MIC. 498 For LoRaWAN version 1.0.x, the NWkSkey session key is used to provide 499 data integrity between the end-device and the network server. The 500 AppSKey is used to provide data confidentiality between the end- 501 device and network server, or to the application "behind" the network 502 server, depending on the implementation of the network. 504 All MAC layer messages have an outer 32-bit Message Integrity Code 505 (MIC) calculated using AES-CMAC calculated over the ciphertext 506 payload and other headers and using the NwkSkey. 508 Payloads are encrypted using AES-128, with a counter-mode derived 509 from IEEE 802.15.4 using the AppSKey. 511 Gateways are not expected to be provided with the AppSKey or NwkSKey, 512 all of the infrastructure-side cryptography happens in (or "behind") 513 the network server. 515 When session keys are derived from the AppKey as a result of the join 516 procedure the Join-accept message payload is specially handled. 518 The long-term AppKey is directly used to protect the Join-accept 519 message content, but the function used is not an aes-encrypt 520 operation, but rather an aes-decrypt operation. The justification is 521 that this means that the end-device only needs to implement the aes- 522 encrypt operation. (The counter mode variant used for payload 523 decryption means the end-device doesn't need an aes-decrypt 524 primitive.) 526 The Join-accept plaintext is always less than 16 bytes long, so 527 electronic code book (ECB) mode is used for protecting Join-accept 528 messages. 530 The Join-accept contains an AppNonce (a 24 bit value) that is 531 recovered on the end-device along with the other Join-accept content 532 (e.g. DevAddr) using the aes-encrypt operation. 534 Once the Join-accept payload is available to the end-device the 535 session keys are derived from the AppKey, AppNonce and other values, 536 again using an ECB mode aes-encrypt operation, with the plaintext 537 input being a maximum of 16 octets. 539 4.2. Narrowband IoT (NB-IoT) 541 [[Text here is from [I-D.ratilainen-lpwan-nb-iot].]] 543 4.2.1. Provenance and Documents 545 Narrowband Internet of Things (NB-IoT) is developed and standardized 546 by 3GPP. The standardization of NB-IoT was finalized with 3GPP 547 Release-13 in June 2016, but further enhancements for NB-IoT are 548 worked on in the following releases, for example in the form of 549 multicast support. For more information of what has been specified 550 for NB-IoT, 3GPP specification 36.300 [TGPP36300] provides an 551 overview and overall description of the E-UTRAN radio interface 552 protocol architecture, while specifications 36.321 [TGPP36321], 553 36.322 [TGPP36322], 36.323 [TGPP36323] and 36.331 [TGPP36331] give 554 more detailed description of MAC, RLC, PDCP and RRC protocol layers 555 respectively. 557 4.2.2. Characteristics 559 [[Editor notes: Not clear if all the radio info here is needed. Not 560 clear what minimum MTU might be. Many 3GPP acronyms/terms to 561 eliminate or explain.]] 563 Specific targets for NB-IoT include: Less than 5$ module cost, 564 extended coverage of 164 dB maximum coupling loss, battery life of 565 over 10 years, ~55000 devices per cell and uplink reporting latency 566 of less than 10 seconds. 568 NB-IoT supports Half Duplex FDD operation mode with 60 kbps peak rate 569 in uplink and 30 kbps peak rate in downlink, and a maximum size MTU 570 of 1600 bytes. As the name suggests, NB-IoT uses narrowbands with 571 the bandwidth of 180 kHz in both, downlink and uplink. The multiple 572 access scheme used in the downlink is OFDMA with 15 kHz sub-carrier 573 spacing. On uplink multi-tone SC-FDMA is used with 15 kHz tone 574 spacing or as a special case of SC-FDMA single tone with either 15kHz 575 or 3.75 kHz tone spacing may be used. 577 NB-IoT can be deployed in three ways. In-band deployment means that 578 the narrowband is multiplexed within normal LTE carrier. In Guard- 579 band deployment the narrowband uses the unused resource blocks 580 between two adjacent LTE carriers. Also standalone deployment is 581 supported, where the narrowband can be located alone in dedicated 582 spectrum, which makes it possible for example to refarm the GSM 583 carrier at 850/900 MHz for NB-IoT. All three deployment modes are 584 meant to be used in licensed bands. The maximum transmission power 585 is either 20 or 23 dBm for uplink transmissions, while for downlink 586 transmission the eNodeB may use higher transmission power, up to 46 587 dBm depending on the deployment. 589 For signaling optimization, two options are introduced in addition to 590 legacy RRC connection setup, mandatory Data-over-NAS (Control Plane 591 optimization, solution 2 in [TGPP23720]) and optional RRC Suspend/ 592 Resume (User Plane optimization, solution 18 in [TGPP23720]). In the 593 control plane optimization the data is sent over Non Access Stratum, 594 directly from Mobility Management Entity (MME) in core network to the 595 UE without interaction from base station. This means there are no 596 Access Stratum security or header compression, as the Access Stratum 597 is bypassed, and only limited RRC procedures. 599 The RRC Suspend/Resume procedures reduce the signaling overhead 600 required for UE state transition from Idle to Connected mode in order 601 to have a user plane transaction with the network and back to Idle 602 state by reducing the signaling messages required compared to legacy 603 operation 605 With extended DRX the RRC Connected mode DRX cycle is up to 10.24 606 seconds and in RRC Idle the DRX cycle can be up to 3 hours. 608 NB-IoT has no channel access restrictions allowing up to a 100% duty- 609 cycle. 611 3GPP access security is specified in [TGPP33203]. 613 +--+ 614 |UE| \ +------+ +------+ 615 +--+ \ | MME |------| HSS | 616 \ / +------+ +------+ 617 +--+ \+-----+ / | 618 |UE| ----| eNB |- | 619 +--+ /+-----+ \ | 620 / \ +--------+ 621 / \| | +------+ Service PDN 622 +--+ / | S-GW |----| P-GW |---- e.g. Internet 623 |UE| | | +------+ 624 +--+ +--------+ 626 Figure 3: 3GPP network architecture 628 Mobility Management Entity (MME) is responsible for handling the 629 mobility of the UE. MME tasks include tracking and paging UEs, 630 session management, choosing the Serving gateway for the UE during 631 initial attachment and authenticating the user. At MME, the Non 632 Access Stratum (NAS) signaling from the UE is terminated. 634 Serving Gateway (S-GW) routes and forwards the user data packets 635 through the access network and acts as a mobility anchor for UEs 636 during handover between base stations known as eNodeBs and also 637 during handovers between other 3GPP technologies. 639 Packet Data Node Gateway (P-GW) works as an interface between 3GPP 640 network and external networks. 642 Home Subscriber Server (HSS) contains user-related and subscription- 643 related information. It is a database, which performs mobility 644 management, session establishment support, user authentication and 645 access authorization. 647 E-UTRAN consists of components of a single type, eNodeB. eNodeB is a 648 base station, which controls the UEs in one or several cells. 650 The illustration of 3GPP radio protocol architecture can be seen from 651 Figure 4. 653 +---------+ +---------+ 654 | NAS |----|-----------------------------|----| NAS | 655 +---------+ | +---------+---------+ | +---------+ 656 | RRC |----|----| RRC | S1-AP |----|----| S1-AP | 657 +---------+ | +---------+---------+ | +---------+ 658 | PDCP |----|----| PDCP | SCTP |----|----| SCTP | 659 +---------+ | +---------+---------+ | +---------+ 660 | RLC |----|----| RLC | IP |----|----| IP | 661 +---------+ | +---------+---------+ | +---------+ 662 | MAC |----|----| MAC | L2 |----|----| L2 | 663 +---------+ | +---------+---------+ | +---------+ 664 | PHY |----|----| PHY | PHY |----|----| PHY | 665 +---------+ +---------+---------+ +---------+ 666 LTE-Uu S1-MME 667 UE eNodeB MME 669 Figure 4: 3GPP radio protocol architecture 671 The radio protocol architecture of NB-IoT (and LTE) is separated into 672 control plane and user plane. Control plane consists of protocols 673 which control the radio access bearers and the connection between the 674 UE and the network. The highest layer of control plane is called 675 Non-Access Stratum (NAS), which conveys the radio signaling between 676 the UE and the EPC, passing transparently through radio network. It 677 is responsible for authentication, security control, mobility 678 management and bearer management. 680 Access Stratum (AS) is the functional layer below NAS, and in control 681 plane it consists of Radio Resource Control protocol (RRC) 682 [TGPP36331], which handles connection establishment and release 683 functions, broadcast of system information, radio bearer 684 establishment, reconfiguration and release. RRC configures the user 685 and control planes according to the network status. There exists two 686 RRC states, RRC_Idle or RRC_Connected, and RRC entity controls the 687 switching between these states. In RRC_Idle, the network knows that 688 the UE is present in the network and the UE can be reached in case of 689 incoming call. In this state the UE monitors paging, performs cell 690 measurements and cell selection and acquires system information. 691 Also the UE can receive broadcast and multicast data, but it is not 692 expected to transmit or receive singlecast data. In RRC_Connected 693 the UE has a connection to the eNodeB, the network knows the UE 694 location on cell level and the UE may receive and transmit singlecast 695 data. RRC_Connected mode is established, when the UE is expected to 696 be active in the network, to transmit or receive data. Connection is 697 released, switching to RRC_Idle, when there is no traffic to save the 698 UE battery and radio resources. However, a new feature was 699 introduced for NB-IoT, as mentioned earlier, which allows data to be 700 transmitted from the MME directly to the UE, while the UE is in 701 RRC_Idle transparently to the eNodeB. 703 Packet Data Convergence Protocol's (PDCP) [TGPP36323] main services 704 in control plane are transfer of control plane data, ciphering and 705 integrity protection. 707 Radio Link Control protocol (RLC) [TGPP36322] performs transfer of 708 upper layer PDUs and optionally error correction with Automatic 709 Repeat reQuest (ARQ), concatenation, segmentation and reassembly of 710 RLC SDUs, in-sequence delivery of upper layer PDUs, duplicate 711 detection, RLC SDU discard, RLC-re-establishment and protocol error 712 detection and recovery. 714 Medium Access Control protocol (MAC) [TGPP36321] provides mapping 715 between logical channels and transport channels, multiplexing of MAC 716 SDUs, scheduling information reporting, error correction with HARQ, 717 priority handling and transport format selection. 719 Physical layer [TGPP36201] provides data transport services to higher 720 layers. These include error detection and indication to higher 721 layers, FEC encoding, HARQ soft-combining. Rate matching and mapping 722 of the transport channels onto physical channels, power weighting and 723 modulation of physical channels, frequency and time synchronization 724 and radio characteristics measurements. 726 User plane is responsible for transferring the user data through the 727 Access Stratum. It interfaces with IP and consists of PDCP, which in 728 user plane performs header compression using Robust Header 729 Compression (RoHC), transfer of user plane data between eNodeB and 730 UE, ciphering and integrity protection. Lower layers in user plane 731 are similarly RLC, MAC and physical layer performing tasks mentioned 732 above. 734 Under worst-case conditions, NB-IoT may achieve data rate of roughly 735 200 bps. For downlink with 164 dB coupling loss, NB-IoT may achieve 736 higher data rates, depending on the deployment mode. Stand-alone 737 operation may achieve the highest data rates, up to few kbps, while 738 in-band and guard-band operations may reach several hundreds of bps. 739 NB-IoT may even operate with higher maximum coupling loss than 170 dB 740 with very low bit rates. 742 4.3. SIGFOX 744 [[Text here is from [I-D.zuniga-lpwan-sigfox-system-description].]] 746 4.3.1. Provenance and Documents 748 The SIGFOX LPWAN is in line with the terminology and specifications 749 being defined by the ETSI ERM TG28 Low Throughput Networks (LTN) 750 group [etsi_ltn]. As of today, the SIGFOX LPWAN/LTN has been fully 751 deployed in 6 countries, with ongoing deployments on 14 other 752 countries, which in total will reach 316M people. 754 4.3.2. Characteristics 756 SIGFOX LPWAN autonomous battery-operated devices send only a few 757 bytes per day, week or month, allowing them to remain on a single 758 battery for up to 10-15 years. 760 The radio interface is compliant with the following regulations: 762 Spectrum allocation in the USA [fcc_ref] 764 Spectrum allocation in Europe [etsi_ref] 766 Spectrum allocation in Japan [arib_ref] 768 The SIGFOX LTN radio interface is also compliant with the local 769 regulations of the following countries: Australia, Brazil, Canada, 770 Kenya, Lebanon, Mauritius, Mexico, New Zealand, Oman, Peru, 771 Singapore, South Africa, South Korea, and Thailand. 773 The radio interface is based on Ultra Narrow Band (UNB) 774 communications, which allow an increased transmission range by 775 spending a limited amount of energy at the device. Moreover, UNB 776 allows a large number of devices to coexist in a given cell without 777 significantly increasing the spectrum interference. 779 Both uplink and downlink communications are possible with the UNB 780 solution. Due to spectrum optimizations, different uplink and 781 downlink frames and time synchronization methods are needed. 783 The main radio characteristics of the UNB uplink transmission are: 785 o Channelization mask: 100 Hz (600 Hz in the USA) 787 o Uplink baud rate: 100 baud (600 baud in the USA) 789 o Modulation scheme: DBPSK 791 o Uplink transmission power: compliant with local regulation 793 o Link budget: 155 dB (or better) 794 o Central frequency accuracy: not relevant, provided there is no 795 significant frequency drift within an uplink packet 797 In Europe, the UNB uplink frequency band is limited to 868,00 to 798 868,60 MHz, with a maximum output power of 25 mW and a maximum mean 799 transmission time of 1%. 801 The format of the uplink frame is the following: 803 +--------+--------+--------+------------------+-------------+-----+ 804 |Preamble| Frame | Dev ID | Payload |Msg Auth Code| FCS | 805 | | Sync | | | | | 806 +--------+--------+--------+------------------+-------------+-----+ 808 Figure 5: Uplink Frame Format 810 The uplink frame is composed of the following fields: 812 o Preamble: 19 bits 814 o Frame sync and header: 29 bits 816 o Device ID: 32 bits 818 o Payload: 0-96 bits 820 o Authentication: 16-40 bits 822 o Frame check sequence: 16 bits (CRC) 824 The main radio characteristics of the UNB downlink transmission are: 826 o Channelization mask: 1.5 kHz 828 o Downlink baud rate: 600 baud 830 o Modulation scheme: GFSK 832 o Downlink transmission power: 500 mW (4W in the USA) 834 o Link budget: 153 dB (or better) 836 o Central frequency accuracy: Centre frequency of downlink 837 transmission are set by the network according to the corresponding 838 uplink transmission. 840 In Europe, the UNB downlink frequency band is limited to 869,40 to 841 869,65 MHz, with a maximum output power of 500 mW with 10% duty 842 cycle. 844 The format of the downlink frame is the following: 846 +------------+-----+---------+------------------+-------------+-----+ 847 | Preamble |Frame| ECC | Payload |Msg Auth Code| FCS | 848 | |Sync | | | | | 849 +------------+-----+---------+------------------+-------------+-----+ 851 Figure 6: Downlink Frame Format 853 The downlink frame is composed of the following fields: 855 o Preamble: 91 bits 857 o Frame sync and header: 13 bits 859 o Error Correcting Code (ECC): 32 bits 861 o Payload: 0-64 bits 863 o Authentication: 16 bits 865 o Frame check sequence: 8 bits (CRC) 867 The radio interface is optimized for uplink transmissions, which are 868 asynchronous. Downlink communications are achieved by querying the 869 network for existing data from the device. 871 A device willing to receive downlink messages opens a fixed window 872 for reception after sending an uplink transmission. The delay and 873 duration of this window have fixed values. The LTN network transmits 874 the downlink message for a given device during the reception window. 875 The LTN network selects the BS for transmitting the corresponding 876 downlink message. 878 Uplink and downlink transmissions are unbalanced due to the 879 regulatory constraints on the ISM bands. Under the strictest 880 regulations, the system can allow a maximum of 140 uplink messages 881 and 4 downlink messages per device. These restrictions can be 882 slightly relaxed depending on system conditions and the specific 883 regulatory domain of operation. 885 +--+ 886 |EP| * +------+ 887 +--+ * | RA | 888 * +------+ 889 +--+ * | 890 |EP| * * * * | 891 +--+ * +----+ | 892 * | BS | \ +--------+ 893 +--+ * +----+ \ | | 894 DA -----|EP| * * * | SC |----- NA 895 +--+ * / | | 896 * +----+ / +--------+ 897 +--+ * | BS |/ 898 |EP| * * * * +----+ 899 +--+ * 900 * 901 +--+ * 902 |EP| * * 903 +--+ 905 Figure 7: ETSI LTN architecture 907 Figure 7 depicts the different elements of the SIGFOX architecture. 909 The architecture consists of a single core network, which allows 910 global connectivity with minimal impact on the end device and radio 911 access network. The core network elements are the Service Center 912 (SC) and the Registration Authority (RA). The SC is in charge of the 913 data connectivity between the Base Station (BS) and the Internet, as 914 well as the control and management of the BSs and End Points. The RA 915 is in charge of the End Point network access authorization. 917 The radio access network is comprised of several BSs connected 918 directly to the SC. Each BS performs complex L1/L2 functions, 919 leaving some L2 and L3 functionalities to the SC. 921 The devices or End Points (EPs) are the objects that communicate 922 application data between local device applications (DAs) and network 923 applications (NAs). 925 EPs (or devices) can be static or nomadic, as they associate with the 926 SC and they do not attach to a specific BS. Hence, they can 927 communicate with the SC through one or many BSs. 929 Due to constraints in the complexity of the EP, it is assumed that 930 EPs host only one or very few device applications, which communicate 931 to one single network application at a time. 933 The radio protocol provides mechanisms to authenticate and ensure 934 integrity of the message. This is achieved by using a unique device 935 ID and a message authentication code, which allow ensuring that the 936 message has been generated and sent by the device with the ID claimed 937 in the message. 939 Security keys are independent for each device. These keys are 940 associated with the device ID and they are pre-provisioned. 941 Application data can be encrypted by the application provider. 943 4.4. WI-SUN 945 [[Add text here when available. Source = bheile@ieee.org]] 947 5. Gap Analysis 949 [[Add text here from [I-D.minaburo-lpwan-gap-analysis].]] 951 6. Security Considerations 953 7. IANA Considerations 955 There are no IANA considerations related to this memo. 957 8. Contributors 959 As stated above this document is mainly a collection of content 960 developed by the full set of contributors listed below. The main 961 input documents and their authors were: 963 o The text on LoRaWAN was based on [I-D.farrell-lpwan-lora-overview] 964 co-authored by Alper Yegin and Stephen Farrell. 966 o Text for Section 4.2 was provided by Antti Ratilainen in 967 [I-D.ratilainen-lpwan-nb-iot]. 969 o Text for Section 4.3 was provided by Juan Carlos Zuniga and Benoit 970 Ponsard in [I-D.zuniga-lpwan-sigfox-system-description]. 972 o Text for Section 5 was provided by Ana Minabiru, Carles Gomez, 973 Laurent Toutain, Josep Paradells and Jon Crowcroft in 974 [I-D.minaburo-lpwan-gap-analysis]. Additional text from that 975 draft is also used elsewhere above. 977 The full list of contributors are: 979 Jon Crowcroft 980 University of Cambridge 981 JJ Thomson Avenue 982 Cambridge, CB3 0FD 983 United Kingdom 985 Email: jon.crowcroft@cl.cam.ac.uk 987 Carles Gomez 988 UPC/i2CAT 989 C/Esteve Terradas, 7 990 Castelldefels 08860 991 Spain 993 Email: carlesgo@entel.upc.edu 995 Ana Minaburo 996 Acklio 997 2bis rue de la Chataigneraie 998 35510 Cesson-Sevigne Cedex 999 France 1001 Email: ana@ackl.io 1003 Josep PAradells 1004 UPC/i2CAT 1005 C/Jordi Girona, 1-3 1006 Barcelona 08034 1007 Spain 1009 Email: josep.paradells@entel.upc.edu 1011 Benoit Ponsard 1012 SIGFOX 1013 425 rue Jean Rostand 1014 Labege 31670 1015 France 1017 Email: Benoit.Ponsard@sigfox.com 1018 URI: http://www.sigfox.com/ 1020 Antti Ratilainen 1021 Ericsson 1022 Hirsalantie 11 1023 Jorvas 02420 1024 Finland 1026 Email: antti.ratilainen@ericsson.com 1028 Laurent Toutain 1029 Institut MINES TELECOM ; TELECOM Bretagne 1030 2 rue de la Chataigneraie 1031 CS 17607 1032 35576 Cesson-Sevigne Cedex 1033 France 1035 Email: Laurent.Toutain@telecom-bretagne.eu 1037 Alper Yegin 1038 Actility 1039 Paris, Paris 1040 FR 1042 Email: alper.yegin@actility.com 1044 Juan Carlos Zuniga 1045 SIGFOX 1046 425 rue Jean Rostand 1047 Labege 31670 1048 France 1050 Email: JuanCarlos.Zuniga@sigfox.com 1051 URI: http://www.sigfox.com/ 1053 9. Acknowledgements 1055 Thanks to all those listed in Section 8 for the excellent text. 1056 Errors in the handling of that are solely the editor's fault. 1058 Thanks to [your name here] for comments. 1060 Stephen Farrell's work on this memo was supported by the Science 1061 Foundation Ireland funded CONNECT centre . 1063 10. Informative References 1065 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1066 Requirement Levels", BCP 14, RFC 2119, 1067 DOI 10.17487/RFC2119, March 1997, 1068 . 1070 [I-D.farrell-lpwan-lora-overview] 1071 Farrell, S. and A. Yegin, "LoRaWAN Overview", draft- 1072 farrell-lpwan-lora-overview-01 (work in progress), October 1073 2016. 1075 [I-D.minaburo-lpwan-gap-analysis] 1076 Minaburo, A., Gomez, C., Toutain, L., Paradells, J., and 1077 J. Crowcroft, "LPWAN Survey and GAP Analysis", draft- 1078 minaburo-lpwan-gap-analysis-02 (work in progress), October 1079 2016. 1081 [I-D.zuniga-lpwan-sigfox-system-description] 1082 Zuniga, J. and B. PONSARD, "SIGFOX System Description", 1083 draft-zuniga-lpwan-sigfox-system-description-00 (work in 1084 progress), July 2016. 1086 [I-D.ratilainen-lpwan-nb-iot] 1087 Ratilainen, A., "NB-IoT characteristics", draft- 1088 ratilainen-lpwan-nb-iot-00 (work in progress), July 2016. 1090 [TGPP36300] 1091 3GPP, "TS 36.300 v13.4.0 Evolved Universal Terrestrial 1092 Radio Access (E-UTRA) and Evolved Universal Terrestrial 1093 Radio Access Network (E-UTRAN); Overall description; Stage 1094 2", 2016, 1095 . 1097 [TGPP36321] 1098 3GPP, "TS 36.321 v13.2.0 Evolved Universal Terrestrial 1099 Radio Access (E-UTRA); Medium Access Control (MAC) 1100 protocol specification", 2016. 1102 [TGPP36322] 1103 3GPP, "TS 36.322 v13.2.0 Evolved Universal Terrestrial 1104 Radio Access (E-UTRA); Radio Link Control (RLC) protocol 1105 specification", 2016. 1107 [TGPP36323] 1108 3GPP, "TS 36.323 v13.2.0 Evolved Universal Terrestrial 1109 Radio Access (E-UTRA); Packet Data Convergence Protocol 1110 (PDCP) specification (Not yet available)", 2016. 1112 [TGPP36331] 1113 3GPP, "TS 36.331 v13.2.0 Evolved Universal Terrestrial 1114 Radio Access (E-UTRA); Radio Resource Control (RRC); 1115 Protocol specification", 2016. 1117 [TGPP36201] 1118 3GPP, "TS 36.201 v13.2.0 - Evolved Universal Terrestrial 1119 Radio Access (E-UTRA); LTE physical layer; General 1120 description", 2016. 1122 [TGPP23720] 1123 3GPP, "TR 23.720 v13.0.0 - Study on architecture 1124 enhancements for Cellular Internet of Things", 2016. 1126 [TGPP33203] 1127 3GPP, "TS 33.203 v13.1.0 - 3G security; Access security 1128 for IP-based services", 2016. 1130 [etsi_ltn] 1131 "ETSI Technical Committee on EMC and Radio Spectrum 1132 Matters (ERM) TG28 Low Throughput Networks (LTN)", 1133 February 2015. 1135 [fcc_ref] "FCC CFR 47 Part 15.247 Telecommunication Radio Frequency 1136 Devices - Operation within the bands 902-928 MHz, 1137 2400-2483.5 MHz, and 5725-5850 MHz.", June 2016. 1139 [etsi_ref] 1140 "ETSI EN 300-220 (Parts 1 and 2): Electromagnetic 1141 compatibility and Radio spectrum Matters (ERM); Short 1142 Range Devices (SRD); Radio equipment to be used in the 25 1143 MHz to 1 000 MHz frequency range with power levels ranging 1144 up to 500 mW", May 2016. 1146 [arib_ref] 1147 "ARIB STD-T108 (Version 1.0): 920MHz-Band Telemeter, 1148 Telecontrol and data transmission radio equipment.", 1149 February 2012. 1151 [LoRaSpec] 1152 LoRa Alliance, "LoRaWAN Specification Version V1.0.2", Nov 1153 2016, . 1155 [LoRaSpec1.0] 1156 LoRa Alliance, "LoRaWAN Specification Version V1.0", Jan 1157 2015, . 1160 Author's Address 1162 Stephen Farrell (editor) 1163 Trinity College Dublin 1164 Dublin 2 1165 Ireland 1167 Phone: +353-1-896-2354 1168 Email: stephen.farrell@cs.tcd.ie