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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: June 7, 2018 December 04, 2017 7 SIGFOX System Description 8 draft-zuniga-lpwan-sigfox-system-description-04 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). It is intended to be used as background information 15 by the IETF LPWAN group when defining system requirements of 16 different LPWAN technologies that are suitable to support common IP 17 services. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on June 7, 2018. 36 Copyright Notice 38 Copyright (c) 2017 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. System Architecture . . . . . . . . . . . . . . . . . . . . . 3 56 4. Radio Spectrum . . . . . . . . . . . . . . . . . . . . . . . 5 57 5. Radio Protocol . . . . . . . . . . . . . . . . . . . . . . . 5 58 5.1. Uplink . . . . . . . . . . . . . . . . . . . . . . . . . 6 59 5.1.1. Uplink Physical Layer . . . . . . . . . . . . . . . . 6 60 5.1.2. Uplink MAC Layer . . . . . . . . . . . . . . . . . . 6 61 5.2. Downlink . . . . . . . . . . . . . . . . . . . . . . . . 7 62 5.2.1. Downlink Physical Layer . . . . . . . . . . . . . . . 7 63 5.2.2. Downlink MAC Layer . . . . . . . . . . . . . . . . . 7 64 5.3. Synchronization between Uplink and Downlink . . . . . . . 8 65 6. Network Deployment . . . . . . . . . . . . . . . . . . . . . 8 66 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 67 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 68 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 69 10. Informative References . . . . . . . . . . . . . . . . . . . 9 70 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 72 1. Introduction 74 This document presents an overview of the network architecture and 75 system characteristics of a typical SIGFOX LPWAN, which is in line 76 with the terminology and specifications defined by ETSI [etsi_unb]. 77 It is intended to be used as background information by the IETF LPWAN 78 group when defining system requirements of different LPWANs that are 79 suitable to support common IP services. 81 LPWAN technologies are a subset of IoT systems which specifically 82 enable long range data transport (e.g. distances up to 50 km in open 83 field), are capable to communicate with underground equipment, and 84 require minimal power consumption. Low throughput transmissions 85 combined with advanced signal processing techniques provide highly 86 effective protection against interference. LPWAN technologies can 87 also cooperate with cellular networks to address use cases where 88 redundancy, complementary or alternative connectivity is needed. 90 Because of these characteristics, LPWAN systems are particularly well 91 adapted for low throughput IoT traffic. SIGFOX LPWAN autonomous 92 battery-operated devices send only a few bytes per day, week or month 93 in an asynchronous manner and without the needed for central 94 coordination, which allows them to remain on a single battery for up 95 to 10-15 years. 97 2. Terminology 99 The following terms are used throughout this document: 101 Base Station (BS) - A Base Station is a radio hub, relaying 102 messages between DEVs and the SC. 104 Device Application (DA) - An application running on the DEV or EP. 106 Device (DEV) - A Device (aka end-point) is a leaf node of a LPWAN 107 that communicates application data between the local device 108 application and the network application. 110 End Point (EP) - An End Point (aka device) is a leaf node of a 111 LPWAN that communicates application data between the local device 112 application and the network application. 114 Low-Power Wide-Area Network (LPWAN) - A system comprising several 115 BSs and millions/billions of DEVs, characterized by the extreme 116 low-power consumption, long-range of transmission, and typically 117 connected in a star network topology. 119 Network Application (NA) - An application running in the network 120 and communicating with the device(s). 122 Registration Authority (RA) - The Registration Authority is a 123 central entity that contains all allocated and authorized Device 124 IDs. 126 Service Center (SC) - The SIGFOX network has a single service 127 centre. The SC performs the following functions: 129 * DEVs and BSs management 131 * DEV authentication 133 * Application data packets forwarding 135 * Cooperative reception support 137 3. System Architecture 139 Figure 1 depicts the different elements of the system architecture: 141 +---+ 142 |DEV| * +------+ 143 +---+ * | RA | 144 * +------+ 145 +---+ * | 146 |DEV| * * * * | 147 +---+ * +----+ | 148 * | BS | \ +--------+ 149 +---+ * +----+ \ | | 150 DA -----|DEV| * * * | SC |----- NA 151 +---+ * / | | 152 * +----+ / +--------+ 153 +---+ * | BS |/ 154 |DEV| * * * * +----+ 155 +---+ * 156 * 157 +---+ * 158 |DEV| * * 159 +---+ 161 Figure 1: SIGFOX network architecture 163 SIGFOX has a "one-contract one-network" model allowing devices to 164 connect in any country, without any need or notion of either roaming 165 or handover. 167 The architecture consists of a single cloud-based core network, which 168 allows global connectivity with minimal impact on the end device and 169 radio access network. The core network elements are the Service 170 Center (SC) and the Registration Authority (RA). The SC is in charge 171 of the data connectivity between the Base Stations (BSs) and the 172 Internet, as well as the control and management of the BSs and 173 Devices. The RA is in charge of the Device network access 174 authorization. 176 The radio access network is comprised of several BSs connected 177 directly to the SC. Each BS performs complex L1/L2 functions, 178 leaving some L2 and L3 functionalities to the SC. 180 The Devices (DEVs) or End Points (EPs) are the objects that 181 communicate application data between local device applications (DAs) 182 and network applications (NAs). 184 Devices can be static or nomadic, as they associate with the SC and 185 they do not attach to any specific BS. Hence, they can communicate 186 with the SC through one or multiple BSs without needing to signal for 187 handover or roaming. 189 Due to constraints in the complexity of the Device, it is assumed 190 that Devices host only one or very few device applications, which 191 most of the time communicate each to a single network application at 192 a time. 194 4. Radio Spectrum 196 The coverage of the cell depends on the link budget and on the type 197 of deployment (urban, rural, etc.). The radio interface is compliant 198 with the following regulations: 200 Spectrum allocation in the USA [fcc_ref], 202 Spectrum allocation in Europe [etsi_ref], 204 Spectrum allocation in Japan [arib_ref]. 206 At present, the SIGFOX radio interface is also compliant with the 207 local regulations of the following countries: Australia, Brazil, 208 Canada, Kenya, Lebanon, Mauritius, Mexico, New Zealand, Oman, Peru, 209 Singapore, South Africa, South Korea, and Thailand. 211 5. Radio Protocol 213 The radio interface is based on Ultra Narrow Band (UNB) 214 communications, which allow an increased transmission range by 215 spending a limited amount of energy at the device. Moreover, UNB 216 allows a large number of devices to coexist in a given cell without 217 significantly increasing the spectrum interference. 219 Since the radio protocol is connection-less and optimized for uplink 220 communications, the capacity of a SIGFOX base station depends on the 221 number of messages generated by devices, and not on the actual number 222 of devices. Likewise, the battery life of devices depends on the 223 number of messages generated by the device. Depending on the use 224 case, devices can vary from sending less than one message per device 225 per day, to dozens of messages per device per day. 227 Both uplink and downlink are supported, although the system is 228 optimized for uplink communications. Due to spectrum optimizations, 229 different uplink and downlink frames and time synchronization methods 230 are needed. 232 5.1. Uplink 234 5.1.1. Uplink Physical Layer 236 The main radio characteristics of the UNB uplink transmission are: 238 o Occupied bandwidth: 100 Hz / 600 Hz (depending on the region) 240 o Uplink baud rate: 100 baud / 600 baud (depending on the region) 242 o Modulation scheme: DBPSK 244 o Uplink transmission power: compliant with local regulation 246 o Link budget: 155 dB (or better) 248 o Central frequency accuracy: not relevant, provided there is no 249 significant frequency drift within an uplink packet transmission 251 For example, in Europe the UNB uplink frequency band is limited to 252 868.00 to 868.60 MHz, with a maximum output power of 25 mW and a 253 maximum mean transmission time of 1%. 255 5.1.2. Uplink MAC Layer 257 The format of the uplink frame is the following: 259 +--------+--------+--------+------------------+-------------+-----+ 260 |Preamble| Frame | Dev ID | Payload |Msg Auth Code| FCS | 261 | | Sync | | | | | 262 +--------+--------+--------+------------------+-------------+-----+ 264 Figure 2: Uplink Frame Format 266 The uplink frame is composed of the following fields: 268 o Preamble: 19 bits 270 o Frame sync and header: 29 bits 272 o Device ID: 32 bits 274 o Payload: 0-96 bits 275 o Authentication: 16-40 bits 277 o Frame check sequence: 16 bits (CRC) 279 5.2. Downlink 281 5.2.1. Downlink Physical Layer 283 The main radio characteristics of the UNB downlink transmission are: 285 o Occupied bandwidth: 1.5 kHz 287 o Downlink baud rate: 600 baud 289 o Modulation scheme: GFSK 291 o Downlink transmission power: 500 mW / 4W (depending on the region) 293 o Link budget: 153 dB (or better) 295 o Central frequency accuracy: Centre frequency of downlink 296 transmission are set by the network according to the corresponding 297 uplink transmission 299 For example, in Europe the UNB downlink frequency band is limited to 300 869.40 to 869.65 MHz, with a maximum output power of 500 mW with 10% 301 duty cycle. 303 5.2.2. Downlink MAC Layer 305 The format of the downlink frame is the following: 307 +------------+-----+---------+------------------+-------------+-----+ 308 | Preamble |Frame| ECC | Payload |Msg Auth Code| FCS | 309 | |Sync | | | | | 310 +------------+-----+---------+------------------+-------------+-----+ 312 Figure 3: Downlink Frame Format 314 The downlink frame is composed of the following fields: 316 o Preamble: 91 bits 318 o Frame sync and header: 13 bits 319 o Error Correcting Code (ECC): 32 bits 321 o Payload: 0-64 bits 323 o Authentication: 16 bits 325 o Frame check sequence: 8 bits (CRC) 327 5.3. Synchronization between Uplink and Downlink 329 The radio interface is optimized for uplink transmissions, which are 330 asynchronous. Downlink communications are achieved by devices 331 querying the network for available data. 333 A device willing to receive downlink messages opens a fixed window 334 for reception after sending an uplink transmission. The delay and 335 duration of this window have fixed values. The network transmits the 336 downlink message for a given device during the reception window, and 337 the network also selects the base station (BS) for transmitting the 338 corresponding downlink message. 340 Uplink and downlink transmissions are unbalanced due to the 341 regulatory constraints on the ISM bands. Under the strictest 342 regulations, the system can allow a maximum of 140 uplink messages 343 and 4 downlink messages per device. These restrictions can be 344 slightly relaxed depending on system conditions and the specific 345 regulatory domain of operation. 347 6. Network Deployment 349 As of today, SIGFOX's network has been fully deployed in 17 350 countries, with ongoing deployments on 29 other countries, giving in 351 total a geography of 2.6 million square kilometers, containing 660 352 million people. The single core network model allows devices to 353 connect in any country, without any notion of roaming or handover. 355 The vast majority of the current applications are sensor-based, 356 requiring solely uplink communications, followed by actuator-based 357 applications, which make use of bidirectional (i.e. uplink and 358 downlink) communications. 360 Similar to other LPWAN technologies, the sectors that currently 361 benefit from the low-cost, low-maintenance and long battery life are 362 agricultural and environment, public sector (smart cities, education, 363 security, etc.), industry, utilities, retail, home and lifestyle, 364 health and automotive. 366 7. IANA Considerations 368 N/A. 370 8. Security Considerations 372 Due to the nature of low-complexity devices, it is assumed that 373 Devices host only one or very few device applications, which most of 374 the time communicate each to a single network application at a time. 376 The radio protocol authenticates and ensures the integrity of each 377 message. This is achieved by using a unique device ID and an AES-128 378 based message authentication code, ensuring that the message has been 379 generated and sent by the device with the ID claimed in the message. 381 Application data can be encrypted at the application level or not, 382 depending on the criticality of the use case, to provide a balance 383 between cost and effort vs. risk. AES-128 in counter mode is used 384 for encryption. Cryptographic keys are independent for each device. 385 These keys are associated with the device ID and separate integrity 386 and confidentiality keys are pre-provisioned. A confidentiality key 387 is only provisioned if confidentiality is to be used. 389 9. Acknowledgments 391 The authors would like to thank Olivier Peyrusse for the useful 392 inputs and discussions about ETSI UNB SRD. 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/