ABP Class C Node (RAK3172) - Downlinks Delayed After Gateway Reconnection Until Next Uplink (ChirpStack)

Devices
1

Hi all,

I’m working with a RAK3172 node configured in ABP mode and Class C, connected to ChirpStack.

I’ve observed a specific behavior:

  1. The gateway loses internet connectivity.
  2. The gateway regains internet connectivity and reconnects to ChirpStack.
  3. At this point, my Class C node does not receive any pending or new downlinks from ChirpStack.
  4. However, as soon as the node sends a new uplink after the gateway is stable, it immediately starts receiving downlinks as expected.

My question is: Why doesn’t ChirpStack (or is this a general LoRaWAN behavior for ABP Class C?) proactively send downlinks to the Class C node as soon as the gateway is back online? Why does it seem to wait for a new uplink from the device to “re-establish” the downlink path or trigger queued messages?

Is this expected behavior, and what’s the underlying mechanism or reasoning for this? Are there any configurations in ChirpStack that might influence this for ABP Class C devices?

Thanks for any insights!