[LoRaWAN] Behaviour of Joins and LinkChecks

For EU 868 products:

1. When they are powered, the transmitters send a JOIN *.
2. After 24 hours, they send a LinkCheckReq message which should be confirmed by a LinkCheckAck. And so on every 24 hours. As long as the LinkCheckReq are confirmed by a LinkCheckAck, the transmitter will not send a new JOIN.
3. If the LinkCheckReq message does not receive a LinkCheckAck response, then new LinkCheckReq will be sent in the process. If 6x LinkCheckReq receive no response, then the transmitter initiates a new JOIN procedure. If the JOIN procedure is not successful, the transmitter will enter sleep mode and reinitiate a JOIN procedure after 24 hours.

For US 915 products:

1. When they are powered, the transmitters send a JOIN *.
2. After 37 hours, they send a LinkCheckReq message which should be confirmed by a LinkCheckAck. And so on every 37 hours. As long as the LinkCheckReq are confirmed by a LinkCheckAck, the transmitter will not send a new JOIN.
3. If the LinkCheckReq message does not receive a LinkCheckAck response, then new LinkCheckReq will be sent in the process. If 6x LinkCheckReq, spaced by the periodicity with which the transmitter is configured, receive no response, then the transmitter initiates a new JOIN procedure. If the JOIN procedure is not successful, the transmitter will enter sleep mode and reinitiate a JOIN procedure after 37 hours.

*JOIN: This is a network access phase LoRaWAN network that allows the network parameters to be dynamically renewed between the end device and the LoRa Server.