Choose participating gateways to receive multicast downlink messages - AWS IoT Wireless
Choose gateways for multicast downlink (console)Choose gateways for multicast downlink (CLI)Next steps

Choose participating gateways to receive multicast downlink messages

A multicast group that consists of multiple devices can have the devices associated with multiple gateways. When a downlink message is sent to the multicast group, it will be sent to all the gateways that are associated with the devices in the group. This can potentially lead to the message that the device receives getting corrupted, such as when a device is in the vicinity of two gateways and receives the same multicast downlink from both gateways at the same time.

Image showing how a multicast downlink message from AWS IoT Core for LoRaWAN can get corrupted to the device.

To avoid this message corruption, you can specify the gateways that you want to use for receiving the downlink message and the transmission interval between them. To provide this information, use the following fields using the console or CLI.

Note

This feature is different from the participating gateways feature that you can use for general downlink data traffic from AWS IoT Core for LoRaWAN to your device. For more information, see Choosing gateways to receive the LoRaWAN downlink data traffic.

  • Gateway list

    The list of gateways that you want to use for sending the multicast downlink message. Each downlink message will be sent to all the gateways in the list in the order that you provided them. If the gateway list is empty, then AWS IoT Core for LoRaWAN will use the gateways that were used for the most recent uplink message from the device.

  • Transmission interval

    The time duration in milliseconds for which AWS IoT Core for LoRaWAN will wait before transmitting the multicast payload to the next gateway in the list.

    Note

    If you are performing FUOTA for a multicast group for which you added participating gateways when creating the group, make sure that the fragment interval is less than or equal to the transmission interval for the gateways.

Choose gateways for multicast downlink (console)

In the AWS IoT console, you can choose the gateways that you want to use for receiving the multicast downlink message when creating the multicast group and adding your devices to the groups. For information about creating a group, see Create multicast groups and add devices to the group.

  1. Go to the Multicast groups page of the AWS IoT console and choose Create multicast group.

  2. Specify a name for the multicast group, and optionally provide a description and tags for your group.

  3. Choose Next to add devices to your multicast group.

  4. Specify the RFRegion, and whether to add devices individually using their Device ID, or in bulk using their device profile.

  5. Add the gateways that you want to use for receiving the downlink message using their Gateway ID, and the transmission interval.

  6. Choose Create to create the multicast group.

Choose gateways for multicast downlink (CLI)

To specify the gateways for receiving the downlink messages, use the CreateMulticastGroup API operation or the create-multicast-group CLI command.

aws iotwireless create-multicast-group \
    --name "MC_group_FUOTA" \ 
    --cli-input-json file://input.json

The following shows the contents of the input.json file.

Contents of input.json

{
    "LoRaWAN": {
    "DlClass": "ClassB",
    "ParticipatingGateways": {
        "GatewayList": [ 
            "a01b2c34-d44e-567f-abcd-0123e445663a", 
             "12345678-a1b2-3c45-67d8-e90fa1b2c34d" 
          ],
         "TransmissionInterval": 1200
      },
      "RfRegion": "US915"
   }
}

In this example, the downlink message will be sent to the gateway with ID a01b2c34-d44e-567f-abcd-0123e445663a, and the same message will then be sent to the gateway with ID 12345678-a1b2-3c45-67d8-e90fa1b2c34d after 1200 ms.

Next steps

After you've chosen the gateways to use, you can add devices to the multicast group and proceed to schedule a multicast session. For more information, see Schedule a downlink message for your multicast group.

If you want to update the firmware of the devices in the multicast group, you can perform Firmware Updates Over-The-Air (FUOTA) with AWS IoT Core for LoRaWAN. In this case, as the FUOTA uses this multicast group, the FUOTA message will be sent to the gateways in the list that you specified. For more information about FUOTA, see Firmware update over-the-air (FUOTA) for AWS IoT Core for LoRaWAN.