Implementation of NTP clock synchronization based on NB-IoT Internet of things
NTP clock synchronization based on NB-IoT Internet of things is actually using the NTP protocol algorithm to achieve wireless timing. In fact, that is NTP timing, the following is a detailed description of the algorithm.
1 clock synchronization principle (time difference calculation)
The time difference calculation assumes that the network transmission delay is equal.
Device local time | Server time | |
Device send | 1000 (deviceSendTime) | One trillion and five hundred and forty-three billion four hundred and seventy-five million seven hundred and sixty-two thousand nine hundred and eighty-five |
Server reception | One thousand and twenty-five | 1543475763010 (serverRecvTime) |
Server send | One thousand and thirty-five | 1543475763020 (serverSendTime) |
Device reception | 1060 (deviceRecvTime) | One trillion and five hundred and forty-three billion four hundred and seventy-five million seven hundred and sixty-three thousand and forty-five |
After synchronization | One trillion and five hundred and forty-three billion four hundred and seventy-five million seven hundred and sixty-three thousand and forty-five | One trillion and five hundred and forty-three billion four hundred and seventy-five million seven hundred and sixty-three thousand and forty-five |
Schematic diagram
Note: the error exists in the transmission and receiving process.
Synchronization of device and server clock on 2.IoT platform
2.1 device terminal Pub Topic
2.2 device terminal receives Sub Topic
Topic format /ext/ntp/${productKey}/${deviceName}/response cloud responds to Payload content: {"deviceSendTime": "1000", "serverRecvTime": "1543475763010", "serverSendTime": "1543475763020"}.
2.3 device terminal receives the local timestamp of Sub.
"DeviceRecvTime":1060
2.4 the synchronization time between device terminal and server clock.
DeviceTime = serverTime = (serverRecvTime + serverSendTime + deviceRecvTime deviceSendTime) / 2, 1543475763045= (1543475763010+1543475763020+1060-1000) /2
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