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LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 7 of 90 The authors reserve the right to change specifications without notice. 1 Introduction 275 This document describes the LoRaWAN ® network protocol, which is optimized for battery- 276 powered end-devices that may be either mobile or mounted at a fixed location. 277 LoRaWAN networks are typically laid out in a star-of-stars topology in which gateways 1 relay 278 transmissions between end-devices and a central Network Server at the backend. Gateways 279 are connected to a Network Server via standard IP connections, whereas end-devices use 280 single-hop radio-frequency (RF) communication to one or many gateways. All communication 281 is generally bi-directional, although uplink communication from an end-device to a Network 282 Server is expected to be the predominant traffic. 283 Communication between end-devices and gateways is distributed over different frequency 284 channels and data rates. Selecting the data rate is a tradeoff between communication range 285 and transmission duration; communications with different LoRa data rates do not interfere with 286 each other. To maximize both the battery life of end-devices and the overall network capacity, 287 the LoRaWAN network infrastructure MAY manage the data rate and RF transmit power for 288 each end-device individually by means of an adaptive data rate (ADR) scheme. 289 An end-device may transmit on any channel available at any time using any available data 290 rate, as long as the following rules are observed: 291 The end-device changes channels in a pseudo-random fashion for every transmission. The 292 resulting frequency diversity makes the system more robust to interference. 293 The end-device pseudo-randomly changes its transmit periodicity to prevent systematic 294 synchronization of populations of end-device transmissions. 295 The end-device complies with all local regulations governing its behavior in the band and 296 sub-bands in which it is currently operating including, but not limited to, duty-cycle and dwell- 297 time (transmit-duration) limitations. 298 All LoRaWAN end-devices SHALL implement at least Class A functionality as described in 299 this document. In addition, they MAY implement Class B and/or Class C as also described in 300 this document. 301 End-devices implementing Class B are referred to as Class B-capable. When operating in 302 Class B, end-devices are referred to as Class B-enabled. Transition from Class B-disabled to 303 Class B-enabled is called switching to Class B. 304 End-devices implementing Class C are referred to as Class C-capable. When operating in 305 Class C, end-devices are referred to as Class C-enabled. Transition from Class C-disabled to 306 Class C-enabled is called switching to Class C. 307 In all cases, end-devices remain compatible with Class A. 308 1 Gateways are also known as concentrators, routers, access points, or base stations.