Issue link: https://read.uberflip.com/i/1428395
LoRaWAN ® L2 1.0.4 Specification © 2020 LoRa Alliance ® Page 73 of 90 The authors reserve the right to change specifications without notice. 14 Class B Unicast and Multicast Downlink Channel Frequencies 2217 The Class B downlink channel selection mechanism depends on the way the Class B beacon 2218 is broadcast. 2219 14.1 Single-Channel Beacon Transmission 2220 In certain regions (e.g., EU868), a beacon is transmitted on a single channel. In that case, all 2221 unicast and multicast Class B downlinks SHALL use a single frequency channel defined by 2222 the PingSlotChannelReq MAC command. The default frequency is defined in [RP002]. 2223 14.2 Frequency-Hopping Beacon Transmission 2224 In certain regions (e.g., US902-928 or CN470-510), a Class B beacon SHALL be transmitted 2225 following a frequency-hopping pattern. 2226 In certain regions (e.g., CN470-510), the default Class B downlink channel is subject to the 2227 definition in the "Regional Parameters" document [RP002]. 2228 In other regions with a hopping beacon, by default Class B ping slots SHALL use a channel 2229 that is a function of the Time field of the previous beacon (see Section 13.2) and the value of 2230 DevAddr. 2231 Class B ping − slot channel = [ DevAddr + floor ( BeaconTime BeaconPeriod ) ] modulo NbChannel , 2232 where 2233 BeaconTime is the 32-bit Time field of the current beacon period. 2234 BeaconPeriod is the length of the beacon period (defined as 128 s in the specification). 2235 floor designates rounding to the immediately lower integer value. 2236 DevAddr is the 32-bit network address of the end-device or multicast group. 2237 NbChannel is the number of channels over which the beacon is frequency hopping. 2238 Class B downlinks therefore hop across NbChannel channels (identical to the beacon 2239 transmit channels) in the ISM band, and all Class B end-devices are equally spread amongst 2240 the NbChannel downlink channels. 2241 If the PingSlotChannelReq command with a valid non-zero Frequency argument sets the 2242 Class B downlink frequency, then all subsequent ping slots SHOULD be opened on this single 2243 frequency independently of the previous beacon frequency. 2244 If the PingSlotChannelReq command with a zero Frequency argument is sent, the end- 2245 device SHOULD resume the default frequency plan, that is, Class B ping slots hopping across 2246 NbChannel channels. 2247 The underlying idea is to allow network operators to configure end-devices to use a single 2248 proprietary dedicated frequency band for Class B downlinks if available, and to maintain as 2249 much frequency diversity as possible when the ISM band is used. 2250