Issue link: https://read.uberflip.com/i/1428353
LoRaWAN Application Layer Clock Synchronization v1.0.0 Specification ©2018 LoRa Alliance™ Page 8 of 13 The authors reserve the right to change specifications without notice. If the AnsRequired bit is set to 1 the end-device expects an answer whether its clock is well 189 synchronized or not. If this bit is set to 0, this signals to the AS that it only needs to answer if 190 the end-device clock is de-synchronized. 191 192 The application server MAY respond to the AppTimeReq command with an AppTimeAns 193 with the following payload: 194 195 196 Field TimeCorrection Param Size (bytes) 4 1 Table 5: AppTimeAns 197 Where: 198 199 Param Fields RFU TokenAns Size (bits) 4bits 4bits Table 6: Param fields 200 201 TimeCorrection is a signed 32-bit integer, stipulating the time delta correction in seconds. 202 203 If the AnsRequired bit is 0 the application server MAY respond if the end-device indicated 204 current clock timing drifts above a certain application specific threshold. If the end-device's 205 clock is well synchronized, the application server does not need to answer. The application 206 server uses the network time stamp of the uplink frame to compute the required timing 207 correction. 208 If the AnsRequired bit is 1 the application server SHOULD respond to the AppTimeReq 209 command. Not responding to the end-device very probably triggers a retransmission of 210 AppTimeReq by the end-device until it receives an answer. This retransmission strategy is 211 application specific. 212 213 When the application server answers: 214 TokenAns MUST match the TokenReq value of the AppTimeReq message which is being 215 answered. If the TokenAns & TokenReq fields do not match the end-device SHALL ignore 216 the AppTimeAns message. 217 218 If the two tokens match, then the end-device SHALL increment its TokenReq internal 219 counter (modulo 16) and TimeCorrection MUST be added to the current end-device clock to 220 be synchronous with the network clock. The end-device SHALL immediately perform the 221 correction on its clock. Any following transmission of the AppTimeReq message SHALL 222 reflect the timing correction and the incremented TokenReq value to avoid unnecessary 223 downlinks. 224 3.3 DeviceAppTimePeriodicityReq & Ans 225 226 Each end-device's application MAY come with a different default periodicity for the 227 transmission of the AppTimeReq message. 228 229 The DeviceAppTimePeriodicityReq command is used by the application server to modify 230 this periodicity and/or get an instant reading of the end-device's clock value. The message 231 payload is: 232 233