Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 60 of 90 The authors reserve the right to change specifications without notice. The BEACON_WINDOW time interval is divided into 2 12 = 4096 ping slots of 30 ms each, 1851 numbered from 0 to 4095. 1852 An end-device using the slot number N SHALL turn its receiver on T on s after the start of the 1853 beacon, where 1854 T on = BEACON_RESERVED + N × 30 ms. 1855 N is called the slot index. 1856 The latest ping slot starts at BEACON_RESERVED + 4095 × 30 ms = 124,970s after the 1857 beacon starts or 3030 ms before the beginning of the next beacon. 1858 11.2 Slot Randomization 1859 To avoid systematic collisions or overhearing problems, the slot index is randomized and 1860 changed at every beacon period. 1861 The following parameters are used: 12 1862 1863 DevAddr Device 32-bit network unicast or multicast address PingNb Number of ping slots per beacon period. This is a power of 2 integer: PingNb = 2 7 −Periodicity PingPeriod Period of the end-device receiver wake-up expressed in number of slots: PingPeriod = 2 5 +Periodicity PingOffset Randomized offset computed at each BEACON_PERIOD start. Values can range from 0 to (PingPeriod−1) BeaconTime The time carried in the field BCNPayload. SlotLen Length of a unit ping slot = 30 ms Table 59: Class B slot randomization algorithm parameters 1864 1865 1866 1867 At each beacon period, the end-device and the server SHALL compute a new pseudo-random 1868 offset to align the reception slots. An AES encryption with a fixed key of 16 all-zero octets 1869 SHALL be used to randomize: 1870 Key = 16 × 0x00 1871 Rand = aes128_encrypt(Key, BeaconTime | DevAddr | pad16) 1872 PingOffset = (Rand[0] + Rand[1] × 256) modulo PingPeriod 1873 The slots used for this beacon period SHALL be 1874 PingOffset + N × PingPeriod with N=[0:PingNb−1] . 1875 1876 1877 1878 1879 12 Periodicity is defined in Section 12.1.