Issue link: https://read.uberflip.com/i/1428383
LoRaWAN 1.0.3 Specification ©2018 LoRa™ Alliance Page 45 of 72 The authors reserve the right to change specifications without notice. 12 Beacon acquisition and tracking 1222 Before switching from Class A to Class B, the end-device MUST first receive one of the 1223 network beacons to align his internal timing reference with the network. 1224 Once in Class B, the end-device MUST periodically search and receive a network beacon to 1225 cancel any drift of its internal clock time base, relative to the network timing. 1226 A Class B device may be temporarily unable to receive beacons (out of range from the network 1227 gateways, presence of interference, ..). In this event, the end-device has to gradually widen 1228 its beacon and ping slots reception windows to take into account a possible drift of its internal 1229 clock. 1230 Note: For example, a device which internal clock is defined with a +/- 1231 10ppm precision may drift by +/-1.3mSec every beacon period. 1232 12.1 Minimal beacon-less operation time 1233 In the event of beacon loss, a device SHALL be capable of maintaining Class B operation for 1234 2 hours (120 minutes) after it received the last beacon. This temporary Class B operation 1235 without beacon is called "beacon-less" operation. It relies on the end-device's own clock to 1236 keep timing. 1237 During beacon-less operation, Class B unicast, multicast and beacon reception slots MUST 1238 all be progressively expanded to accommodate the end-device's possible clock drift. 1239 1240 1241 Figure 13 : beacon-less temporary operation 1242 12.2 Extension of beacon-less operation upon reception 1243 During this 120 minutes time interval the reception of any beacon directed to the end-device, 1244 should extend the Class B beacon-less operation further by another 120 minutes as it allows 1245 to correct any timing drift and reset the receive slots duration. 1246 Note: Device should also use classB pingSlots downlinks to 1247 resynchronize its' internal clock. 1248 12.3 Minimizing timing drift 1249 The end-devices MAY use the beacon's (when available) precise periodicity to calibrate their 1250 internal clock and therefore reduce the initial clock frequency imprecision. As the timing 1251 End-device End-device receives the beacon Beacon reception window End-device temporarily stop receiving beacon End-device receives a beacon and resets the reception window length Reception window enlarges to accommodate clock drift