3 - Receiving Messages
Messages sent from a network server to an end device are referred to as downlinks. These are sent to the end device via a single gateway. If there are multiple gateways near a device, the network server will select the most suitable gateway to broadcast from. This means the end device does not need to consider de-duping.
Devices operating in Class A mode only receive downlinks during the receive windows opened following an uplink, as described in the section Opening Receive Windows of the Sending Messages Book.
Devices that support Class B mode as well as Class A can receive additional downlinks in receive windows opened at fixed time slots. Read more about Class B mode in the Class B Book.
Devices that support Class C mode as well as Class A can receive additional downlinks at any time. Read more in the Class C: Continuously Listening for Downlinks book.
Todo
Fix link
In this book, you learn how to receive and handle downlink packets using the LoRaWAN® 1.0.4 specification.
Processing the Downlink Packet
Verify the Frame Type (FType)
Find the value in the three-bit FType field, located within the MAC Header at position [7:5], as shown in Figure 1.
Figure 1: FType field highlighted in the LoRaWAN® downlink packet structure
If FType is set to 011 (unconfirmed data downlink) or 101 (confirmed data downlink) then this message is a downlink and should be handled, as described in this section.
The end device may also receive a packet with FType 001, which is a Join-Accept message. Learn more about joining a network and handling Join-Accept messages in our paper In-Depth: LoRaWAN® End Device Activation.
If FType is set to 101, and this message was received in one of the Class A receive windows, the end device must respond with an acknowledgement on its next uplink, described in section Uplink Bit Fields of the Sending Messages Book.