Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 57 of 90 The authors reserve the right to change specifications without notice. 10 Class B Beacon Acquisition and Tracking 1785 Before enabling Class B operation, the end-device SHOULD first synchronize with the network 1786 beacons to align its internal timing reference with the network. 1787 Once Class B is enabled, the end-device SHOULD periodically search and receive a network 1788 beacon to cancel any drift of its internal clock time base, relative to the network timing. 1789 A Class B-enabled end-device may be temporarily unable to receive beacons (out of range 1790 from the network gateways, presence of interference, etc.). In this event, the end-device 1791 SHOULD gradually widen its beacon and ping-slot reception windows to accommodate a 1792 possible drift of its internal clock. 1793 1794 Note: For example, an end-device whose internal clock is defined with 1795 a precision of ±10 ppm may drift by ±1.3 ms every beacon period. 1796 10.1 Minimal Beaconless Operation Time 1797 In the event of beacon loss, an end-device SHALL be capable of maintaining Class B operation 1798 for 2 hours (120 minutes) after it received the last beacon. This temporary Class B operation 1799 without beacon is called beaconless operation. It relies on the end-device's own clock to keep 1800 time. 1801 During beaconless operation, Class B unicast, multicast and beacon reception slots SHALL 1802 be progressively expanded to accommodate the end-device's possible clock drift. 1803 1804 1805 1806 Figure 4: Beaconless temporary operation 1807 1808 1809 1810 10.2 Extension of Beaconless Operation upon Receipt 1811 During the 120-minute time interval described above, the receipt of any beacon directed to the 1812 end-device SHOULD extend Class B beaconless operation by another 120 minutes allowing 1813 the end-device to correct any timing drift and reset the duration of the receive slots. 1814 1815 Note: An end-device can also use Class B ping-slot downlinks to 1816 resynchronize its internal clock. 1817 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