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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 LPWAN Working Group JC. Zuniga 3 Internet-Draft B. Ponsard 4 Intended status: Informational SIGFOX 5 Expires: December 15, 2017 June 13, 2017 7 SIGFOX System Description 8 draft-zuniga-lpwan-sigfox-system-description-03 10 Abstract 12 This document presents an overview of the network architecture and 13 system characteristics of a typical SIGFOX Low Power Wide Area 14 Network (LPWAN), which is in line with the terminology and 15 specifications defined by ETSI. It is intended to be used as 16 background information by the IETF LPWAN group when defining system 17 requirements of different LPWAN technologies that are suitable to 18 support common IP services. 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 December 15, 2017. 37 Copyright Notice 39 Copyright (c) 2017 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. System Architecture . . . . . . . . . . . . . . . . . . . . . 3 57 4. Radio Spectrum . . . . . . . . . . . . . . . . . . . . . . . 5 58 5. Radio Protocol . . . . . . . . . . . . . . . . . . . . . . . 5 59 5.1. Uplink . . . . . . . . . . . . . . . . . . . . . . . . . 6 60 5.1.1. Uplink Physical Layer . . . . . . . . . . . . . . . . 6 61 5.1.2. Uplink MAC Layer . . . . . . . . . . . . . . . . . . 6 62 5.2. Downlink . . . . . . . . . . . . . . . . . . . . . . . . 7 63 5.2.1. Downlink Physical Layer . . . . . . . . . . . . . . . 7 64 5.2.2. Downlink MAC Layer . . . . . . . . . . . . . . . . . 7 65 5.3. Synchronization between Uplink and Downlink . . . . . . . 8 66 6. Network Deployment . . . . . . . . . . . . . . . . . . . . . 8 67 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 68 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 69 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 70 10. Informative References . . . . . . . . . . . . . . . . . . . 9 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 73 1. Introduction 75 This document presents an overview of the network architecture and 76 system characteristics of a typical SIGFOX LPWAN, which is in line 77 with the terminology and specifications defined by ETSI [etsi_unb]. 78 It is intended to be used as background information by the IETF LPWAN 79 group when defining system requirements of different LPWANs that are 80 suitable to support common IP services. 82 LPWAN technologies are a subset of IoT systems which specifically 83 enable long range data transport (e.g. distances up to 50 km in open 84 field), are capable to communicate with underground equipment, and 85 require minimal power consumption. Low throughput transmissions 86 combined with advanced signal processing techniques provide highly 87 effective protection against interference. LPWAN technologies can 88 also cooperate with cellular networks to address use cases where 89 redundancy, complementary or alternative connectivity is needed. 91 Because of these characteristics, LPWAN systems are particularly well 92 adapted for low throughput IoT traffic. SIGFOX LPWAN autonomous 93 battery-operated devices send only a few bytes per day, week or month 94 in an asynchronous manner and without the needed for central 95 coordination, which allows them to remain on a single battery for up 96 to 10-15 years. 98 2. Terminology 100 The following terms are used throughout this document: 102 Base Station (BS) - A Base Station is a radio hub, relaying 103 messages between DEVs and the SC. 105 Device Application (DA) - An application running on the DEV or EP. 107 Device (DEV) - A Device (aka end-point) is a leaf node of a LPWAN 108 that communicates application data between the local device 109 application and the network application. 111 End Point (EP) - An End Point (aka device) is a leaf node of a 112 LPWAN that communicates application data between the local device 113 application and the network application. 115 Low-Power Wide-Area Network (LPWAN) - A system comprising several 116 BSs and millions/billions of DEVs, characterized by the extreme 117 low-power consumption, long-range of transmission, and typically 118 connected in a star network topology. 120 Network Application (NA) - An application running in the network 121 and communicating with the device(s). 123 Registration Authority (RA) - The Registration Authority is a 124 central entity that contains all allocated and authorized Device 125 IDs. 127 Service Center (SC) - The SIGFOX network has a single service 128 centre. The SC performs the following functions: 130 * DEVs and BSs management 132 * DEV authentication 134 * Application data packets forwarding 136 * Cooperative reception support 138 3. System Architecture 140 Figure 1 depicts the different elements of the system architecture: 142 +---+ 143 |DEV| * +------+ 144 +---+ * | RA | 145 * +------+ 146 +---+ * | 147 |DEV| * * * * | 148 +---+ * +----+ | 149 * | BS | \ +--------+ 150 +---+ * +----+ \ | | 151 DA -----|DEV| * * * | SC |----- NA 152 +---+ * / | | 153 * +----+ / +--------+ 154 +---+ * | BS |/ 155 |DEV| * * * * +----+ 156 +---+ * 157 * 158 +---+ * 159 |DEV| * * 160 +---+ 162 Figure 1: SIGFOX network architecture 164 SIGFOX has a "one-contract one-network" model allowing devices to 165 connect in any country, without any need or notion of either roaming 166 or handover. 168 The architecture consists of a single cloud-based core network, which 169 allows global connectivity with minimal impact on the end device and 170 radio access network. The core network elements are the Service 171 Center (SC) and the Registration Authority (RA). The SC is in charge 172 of the data connectivity between the Base Stations (BSs) and the 173 Internet, as well as the control and management of the BSs and 174 Devices. The RA is in charge of the Device network access 175 authorization. 177 The radio access network is comprised of several BSs connected 178 directly to the SC. Each BS performs complex L1/L2 functions, 179 leaving some L2 and L3 functionalities to the SC. 181 The Devices (DEVs) or End Points (EPs) are the objects that 182 communicate application data between local device applications (DAs) 183 and network applications (NAs). 185 Devices can be static or nomadic, as they associate with the SC and 186 they do not attach to any specific BS. Hence, they can communicate 187 with the SC through one or multiple BSs without needing to signal for 188 handover or roaming. 190 Due to constraints in the complexity of the Device, it is assumed 191 that Devices host only one or very few device applications, which 192 most of the time communicate each to a single network application at 193 a time. 195 4. Radio Spectrum 197 The coverage of the cell depends on the link budget and on the type 198 of deployment (urban, rural, etc.). The radio interface is compliant 199 with the following regulations: 201 Spectrum allocation in the USA [fcc_ref], 203 Spectrum allocation in Europe [etsi_ref], 205 Spectrum allocation in Japan [arib_ref]. 207 At present, the SIGFOX radio interface is also compliant with the 208 local regulations of the following countries: Australia, Brazil, 209 Canada, Kenya, Lebanon, Mauritius, Mexico, New Zealand, Oman, Peru, 210 Singapore, South Africa, South Korea, and Thailand. 212 5. Radio Protocol 214 The radio interface is based on Ultra Narrow Band (UNB) 215 communications, which allow an increased transmission range by 216 spending a limited amount of energy at the device. Moreover, UNB 217 allows a large number of devices to coexist in a given cell without 218 significantly increasing the spectrum interference. 220 Since the radio protocol is connection-less and optimized for uplink 221 communications, the capacity of a SIGFOX base station depends on the 222 number of messages generated by devices, and not on the actual number 223 of devices. Likewise, the battery life of devices depends on the 224 number of messages generated by the device. Depending on the use 225 case, devices can vary from sending less than one message per device 226 per day, to dozens of messages per device per day. 228 Both uplink and downlink are supported, although the system is 229 optimized for uplink communications. Due to spectrum optimizations, 230 different uplink and downlink frames and time synchronization methods 231 are needed. 233 5.1. Uplink 235 5.1.1. Uplink Physical Layer 237 The main radio characteristics of the UNB uplink transmission are: 239 o Occupied bandwidth: 100 Hz / 600 Hz (depending on the region) 241 o Uplink baud rate: 100 baud / 600 baud (depending on the region) 243 o Modulation scheme: DBPSK 245 o Uplink transmission power: compliant with local regulation 247 o Link budget: 155 dB (or better) 249 o Central frequency accuracy: not relevant, provided there is no 250 significant frequency drift within an uplink packet transmission 252 For example, in Europe the UNB uplink frequency band is limited to 253 868.00 to 868.60 MHz, with a maximum output power of 25 mW and a 254 maximum mean transmission time of 1%. 256 5.1.2. Uplink MAC Layer 258 The format of the uplink frame is the following: 260 +--------+--------+--------+------------------+-------------+-----+ 261 |Preamble| Frame | Dev ID | Payload |Msg Auth Code| FCS | 262 | | Sync | | | | | 263 +--------+--------+--------+------------------+-------------+-----+ 265 Figure 2: Uplink Frame Format 267 The uplink frame is composed of the following fields: 269 o Preamble: 19 bits 271 o Frame sync and header: 29 bits 273 o Device ID: 32 bits 275 o Payload: 0-96 bits 276 o Authentication: 16-40 bits 278 o Frame check sequence: 16 bits (CRC) 280 5.2. Downlink 282 5.2.1. Downlink Physical Layer 284 The main radio characteristics of the UNB downlink transmission are: 286 o Occupied bandwidth: 1.5 kHz 288 o Downlink baud rate: 600 baud 290 o Modulation scheme: GFSK 292 o Downlink transmission power: 500 mW / 4W (depending on the region) 294 o Link budget: 153 dB (or better) 296 o Central frequency accuracy: Centre frequency of downlink 297 transmission are set by the network according to the corresponding 298 uplink transmission 300 For example, in Europe the UNB downlink frequency band is limited to 301 869.40 to 869.65 MHz, with a maximum output power of 500 mW with 10% 302 duty cycle. 304 5.2.2. Downlink MAC Layer 306 The format of the downlink frame is the following: 308 +------------+-----+---------+------------------+-------------+-----+ 309 | Preamble |Frame| ECC | Payload |Msg Auth Code| FCS | 310 | |Sync | | | | | 311 +------------+-----+---------+------------------+-------------+-----+ 313 Figure 3: Downlink Frame Format 315 The downlink frame is composed of the following fields: 317 o Preamble: 91 bits 319 o Frame sync and header: 13 bits 320 o Error Correcting Code (ECC): 32 bits 322 o Payload: 0-64 bits 324 o Authentication: 16 bits 326 o Frame check sequence: 8 bits (CRC) 328 5.3. Synchronization between Uplink and Downlink 330 The radio interface is optimized for uplink transmissions, which are 331 asynchronous. Downlink communications are achieved by devices 332 querying the network for available data. 334 A device willing to receive downlink messages opens a fixed window 335 for reception after sending an uplink transmission. The delay and 336 duration of this window have fixed values. The network transmits the 337 downlink message for a given device during the reception window, and 338 the network also selects the base station (BS) for transmitting the 339 corresponding downlink message. 341 Uplink and downlink transmissions are unbalanced due to the 342 regulatory constraints on the ISM bands. Under the strictest 343 regulations, the system can allow a maximum of 140 uplink messages 344 and 4 downlink messages per device. These restrictions can be 345 slightly relaxed depending on system conditions and the specific 346 regulatory domain of operation. 348 6. Network Deployment 350 As of today, SIGFOX's network has been fully deployed in 12 351 countries, with ongoing deployments on 26 other countries, giving in 352 total a geography of 2 million square kilometers, containing 512 353 million people. The one-contract one-network model allows devices to 354 connect in any country, without any notion of roaming or handover. 356 The vast majority of the current applications are sensor-based, 357 requiring solely uplink communications, followed by actuator-based 358 applications, which make use of bidirectional (i.e. uplink and 359 downlink) communications. 361 Similar to other LPWAN technologies, the sectors that currently 362 benefit from the low-cost, low-maintenance and long battery life are 363 agricultural and environment, public sector (smart cities, education, 364 security, etc.), industry, utilities, retail, home and lifestyle, 365 health and automotive. 367 7. IANA Considerations 369 N/A. 371 8. Security Considerations 373 Due to the nature of low-complexity devices, it is assumed that 374 Devices host only one or very few device applications, which most of 375 the time communicate each to a single network application at a time. 377 The radio protocol provides mechanisms to authenticate and ensure 378 integrity of the message. This is achieved by using a unique device 379 ID and a message authentication code, which allow ensuring that the 380 message has been generated and sent by the device with the ID claimed 381 in the message. 383 Security keys are independent for each device. These keys are 384 associated with the device ID and they are pre-provisioned. 385 Application data can be encrypted at the application level or not, 386 depending on the criticality of the use case, allowing hence to 387 balance cost and effort vs. risk. 389 9. Acknowledgments 391 The authors would like to thank Olivier Peyrusse for the useful 392 inputs and discussions about ETSI. 394 10. Informative References 396 [arib_ref] 397 "ARIB STD-T108 (Version 1.0): 920MHz-Band Telemeter, 398 Telecontrol and data transmission radio equipment.", 399 February 2012. 401 [etsi_ref] 402 "ETSI EN 300-220 (Parts 1 and 2): Electromagnetic 403 compatibility and Radio spectrum Matters (ERM); Short 404 Range Devices (SRD); Radio equipment to be used in the 25 405 MHz to 1 000 MHz frequency range with power levels ranging 406 up to 500 mW", May 2016. 408 [etsi_unb] 409 "ETSI TR 103 435 System Reference document (SRdoc); Short 410 Range Devices (SRD); Technical characteristics for Ultra 411 Narrow Band (UNB) SRDs operating in the UHF spectrum below 412 1 GHz", February 2017. 414 [fcc_ref] "FCC CFR 47 Part 15.247 Telecommunication Radio Frequency 415 Devices - Operation within the bands 902-928 MHz, 416 2400-2483.5 MHz, and 5725-5850 MHz.", June 2016. 418 Authors' Addresses 420 Juan Carlos Zuniga 421 SIGFOX 422 425 rue Jean Rostand 423 Labege 31670 424 France 426 Email: JuanCarlos.Zuniga@sigfox.com 427 URI: http://www.sigfox.com/ 429 Benoit Ponsard 430 SIGFOX 431 425 rue Jean Rostand 432 Labege 31670 433 France 435 Email: Benoit.Ponsard@sigfox.com 436 URI: http://www.sigfox.com/