LoRaWan messages can be categorized into two types: uplink and downlink messages, depending on their direction of travel.
Uplink Messages: Uplink messages are transmitted by end devices and received by the Network Server, often through multiple gateways. In the case where the uplink message is intended for the Application Server or the Join Server, the Network Server forwards it to the appropriate recipient for further processing.
The LoRaWAN server integrated into Wattsense products demonstrates the capability to simultaneously receive data across 8 channels. In theory, we can represent this capability through the following schematic.
Note : Uplinks are randomly distributed among the 8 communication channels of the Lorawan server.
Downlink Messages: On the other hand, downlink messages are sent by the Network Server to individual end devices. This includes messages initiated by both the Application Server and the Join Server, ensuring targeted communication with specific devices.
Upon receiving a downlink command from the console, the Tower/Bridge (user, PLC, etc.) within the LoRaWAN network will enqueue it into a device-specific queue. The timing of when the downlink command is sent varies depending on the class of the end device:
For Class A devices: The downlink command will be transmitted after the LoRaWAN server receives an uplink message from the device. This class follows a scheduled communication pattern where downlink messages are transmitted only after an uplink transmission.
For Class C devices: The downlink command is directly sent by the LoRaWAN server immediately upon receiving the order. In this class, downlink messages can be sent at any time, even without waiting for an uplink transmission.
To visualize the process, we can conceptually illustrate the flow with the following schematic.
Important note :
- For Class A devices, if you program 2 downlinks one after the other and if the sensor has not sent an uplink (that would have triggered the first downlink). The latest downlink will overwrite the first one.
- In the case of Class C devices, if a single downlink is programmed, it is promptly transmitted without delay. However, when multiple downlinks are scheduled simultaneously, the LoRaWAN server can only send one downlink at a time. Therefore, these multiple downlinks will be scheduled with a fixed interval of 14 seconds between each transmission. This ensures a sequential and organized delivery of the scheduled downlink commands for optimal communication efficiency.
By distinguishing between uplink and downlink messages, the LoRaWAN protocol enables bidirectional communication within the network.