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LoRaWAN® Specification v1.0.3

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LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 47 of 72 The authors reserve the right to change specifications without notice. 13 Class B Downlink slot timing 1254 13.1 Definitions 1255 To operate successfully in Class B the end-device MUST open reception slots at precise 1256 instants relative to the infrastructure beacon. This section defines the required timing. 1257 The interval between the start of two successive beacons is called the beacon period. The 1258 beacon frame transmission is aligned with the beginning of the BEACON_RESERVED 1259 interval. Each beacon is preceded by a guard time interval where no ping slot can be placed. 1260 The length of the guard interval corresponds to the time on air of the longest allowed frame. 1261 This is to insure that a Class B downlink initiated during a ping slot just before the guard time 1262 will always have time to complete without colliding with the beacon transmission. The usable 1263 time interval for ping slot therefore spans from the end of the beacon reserved time interval to 1264 the beginning of the next beacon guard interval. 1265 1266 Figure 14: Beacon timing 1267 Beacon_period 128 s Beacon_reserved 2.120 s Beacon_guard 3.000 s Beacon-window 122.880 s Table 13: Beacon timing 1268 The beacon frame time on air is actually much shorter than the beacon reserved time interval 1269 to allow appending network management broadcast frames in the future. 1270 The beacon window interval is divided into 2 12 = 4096 ping slots of 30 ms each numbered from 1271 0 to 4095. 1272 An end-device using the slot number N MUST have its receiver on Ton seconds after the start 1273 of the beacon where: 1274 Ton = beacon_reserved + N * 30 ms 1275 N is called the slot index. 1276 The latest ping slot starts at beacon_reserved + 4095 * 30 ms = 124 970 ms after the beacon 1277 start or 3030 ms before the beginning of the next beacon. 1278

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