How can i Rejoin with the previously paired network after power goes off ?

Hi,

The OpenThread stack should store the network dataset in flash during the commissioning procedure. When you power cycle the device, your application should be able to utilize the existing credentials to rejoin the network. See this post for more details.

You can use the function otDatasetIsCommissioned() to check if the dataset is commissioned, to determine if you should start joiner process or not.

Best regards,
Jørgen

is dataset stored in flash automatically after successfully got paired?

if once we paired, is it needs to be pair again while joining into the network?
Very first time i am pairing the devices by pressing the key but i don't wanted to press key while device tries to rejoin into same network after got disconnect once. Device should join automatically.
How it would be possible?

No, you do not need to pair again if you have reset the device and want to rejoin the network. Dataset and keys are stored in flash during commissioning. See Chapter 10.12 (Persistent data) in Thread 1.1.1 specifications for more details.

In your application, you can call otDatasetIsCommissioned() to see if the dataset is commissioned. If the dataset is not commissioned, you can choose to start the joiner, or call otThreadSetEnabled() to join the network if dataset is commissioned.

otDatasetIsCommissioned() this function accept otinstance as a parameter . Very 1st time while i am pairing device one otinstance gets created . I have used this function otDatasetIsCommissioned() with the otinstace and i can see this function returned TRUE that's mean data gets commissioned. now i  do reset my device and i wanted to use those data . How can i faced those data? so that i can use the stored dataset and key for join again.

otDatasetIsCommissioned() this function accept otinstance as a parameter . Very 1st time while i am pairing device one otinstance gets created . I have used this function otDatasetIsCommissioned() with the otinstace and i can see this function returned TRUE that's mean data gets commissioned. now i  do reset my device and i wanted to use those data . How can i faced those data? so that i can use the stored dataset and key for join again.

Unless you call otInstanceFactoryReset()/otInstanceErasePersistentInfo() after joining, the dataset should be stored in non-volatile memory (flash) and loaded when you call otInstanceInitSingle()/otInstanceInit() after the reset. When you call otThreadSetEnabled() to enable the Thread stack, the previously commissioned dataset should be used to attach to the previously joined network.

I can see now my device is getting reconnecting into the network. One issue i am facing now with this implementation. i.e while i am trying to change few parameters of the device, i observed in sniffer that sometimes parameters are getting changed and some times not, getting time out error. what may the cause would you let me know?

Please post a new ticket where you describe the issue in detail and include the sniffer logs. Then we will help you resolve it.

There is still issues while reconnecting into network. Some times device not getting connected. I can see in debugging the network key getting changed. 

I have attached sniffer data pls check and let me know.

Network key : ca fe ca fe ca fe ca fe ca fe ca fe ca fe ca fe

Following up this issue in the other thread.