Downlink Queue Operations

The Things Stack keeps a queue of downlink messages per device. Applications can keep pushing downlink messages or replace the queue with a list of downlink messages.

You can schedule a downlink using the CLI, MQTT or HTTP webhooks.

To schedule downlinks using MQTT, see MQTT Server. To schedule downlinks using webhooks, see Scheduling Downlinks with Webhooks.

Note:

See the Confirmed Downlinks Behavior section to learn how confirmed downlinks behavior for class B and class C devices differs from confirmed downlinks behavior for class A devices.

This guide shows how to interact with the downlink queue from the command-line interface (CLI).

Command-line interface only

The instructions below use the command-line interface (CLI).

Learn how to install the CLI

If there are more application downlink messages in the queue, the Network Server sets the LoRaWAN® FPending bit to indicate end devices that there is more downlinks available. In class A downlink, this typically triggers the device to send an uplink message to receive the downlink message. In class C, the Network Server automatically transmits all queued downlink messages.

We define some user parameters that will be used below:

APP_ID="app1"
DEVICE_ID="dev1"
PAYLOAD="01020304"
PRIORITY="NORMAL"
F_PORT="42"

Make sure to modify these according to your setup.

Push and replace downlink queue

To push downlink to the end of the queue:

ttn-lw-cli end-devices downlink push $APP_ID $DEVICE_ID \
  --frm-payload $PAYLOAD \
  --priority $PRIORITY \
  --f-port $F_PORT

You must pass an FPort with the --f-port flag. Confirmed downlinks can be set using --confirmed.

To replace the existing queue with a new item:

ttn-lw-cli end-devices downlink replace $APP_ID $DEVICE_ID \
  --frm-payload $PAYLOAD \
  --priority $PRIORITY \
  --f-port $F_PORT

The Things Stack limits the application downlink queue on 10k messages per end device. When this limit is reached, no more scheduled downlinks can be placed in the queue and The Things Stack will drop them. In order to avoid hitting the application downlink queue limit and loosing downlinks, we advise scheduling downlink messages in batches.

List queue

To see currently scheduled downlink messages:

ttn-lw-cli end-devices downlink list $APP_ID $DEVICE_ID

Clear queue

To clear scheduled downlink messages:

ttn-lw-cli end-devices downlink clear $APP_ID $DEVICE_ID

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