# Create multicast groups to send a downlink payload to multiple devices Create multicast groups To send a downlink payload to multiple devices, create a multicast group. Using multicast, a source can send data to a single multicast address, which is then distributed to an entire group of recipient devices. Devices in a multicast group share the same multicast address, session keys, and frame counter. By using the same session keys, devices in a multicast group can decrypt the message when a downlink transmission is initiated. A multicast group only supports downlink. It doesn't confirm whether the downlink payload has been received by the devices. With AWS IoT Core for LoRaWAN's multicast groups, you can: + Filter your list of devices by using the device profile, RFRegion, or device class, and then add these devices to a multicast group. + Schedule and send one or more downlink payload messages to devices in a multicast group, within a 48-hour distribution window. + Have devices temporarily switch to Class B or class C mode at the start of your multicast session for receiving the downlink message. + Monitor your multicast group setup and the state of its devices, and also troubleshoot any issues. + Use Firmware Updates-Over-The-Air (FUOTA) to securely deploy firmware updates to devices in a multicast group. The following video describes how AWS IoT Core for LoRaWAN multicast groups can be created and walks you through the process of adding a device to the group and schedule a downlink message to the group. [![AWS Videos](http://img.youtube.com/vi/https://www.youtube.com/embed/LcCR-1eKX1w/0.jpg)](http://www.youtube.com/watch?v=https://www.youtube.com/embed/LcCR-1eKX1w) The following shows how to create your multicast group and schedule a downlink message. **Topics** + [ # Create multicast groups and add devices to the group ](lorawan-create-multicast-groups.md) + [ # Choose participating gateways to receive multicast downlink messages ](lorawan-multicast-choose-gateways.md) + [ # Monitor and troubleshoot your multicast groups ](lorawan-multicast-status.md) + [ # Schedule a downlink message for your multicast group ](lorawan-multicast-schedule-downlink.md) # Create multicast groups and add devices to the group Create multicast groups and add devices You can create multicast groups by using the console or the CLI. If you're creating your multicast group for the first time, we recommend that you use the console to add your multicast group. When you want to manage your multicast group and add or remove devices from your group, you can use the CLI. After exchanging signaling with the end devices you added, AWS IoT Core for LoRaWAN establishes the shared keys with the end devices and sets up the parameters for the data transfer. ## Prerequisites Before you can create multicast groups and add devices to the group: + Prepare your devices for multicast and FUOTA setup by specifying the FUOTA configuration parameters `GenAppKey` and `FPorts`. For more information, see [Prepare devices for multicast and FUOTA configuration](lorawan-prepare-devices-multicast.md). + Check whether the devices support class B or class C modes of operation. Depending on the device class that your device supports, choose a device profile that has one or both **Supports Class B** or **Supports Class C** modes enabled. For information about device profiles, see [Add profiles to AWS IoT Core for LoRaWAN](lorawan-define-profiles.md). At the start of the multicast session, a class B or class C distribution window is used to send downlink messages to the devices in your group. ## Create multicast groups by using the console Create multicast groups (console) To create multicast groups by using the console, go to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose **Create multicast group**. 1. **Create a multicast group** To create your multicast group, specify the multicast properties and tags for your group. 1. **Specify multicast properties** To specify multicast properties, enter the following information for your multicast group. + **Name**: Enter a unique name for your multicast group. The name must contain only letters, numbers, hyphens, and underscores. It can't contain spaces. + **Description**: You can provide an optional description for your multicast group. The description length can be up to 2,048 characters. 1. **Tags for multicast group** You can optionally provide any key-value pairs as **Tags** for your multicast group. To continue creating your multicast group, choose **Next**. 1. **Add devices to a multicast group** You can add individual devices or a group of devices to your multicast group. To add devices: 1. **Specify RFRegion** Specify the **RFRegion** or frequency band for your multicast group. The **RFRegion** for your multicast group must match the **RFRegion** of devices that you add to the multicast group. For more information about the **RFRegion**, see [Consider selection of LoRa frequency bands for your gateways and device connection](lorawan-rfregion-permissions.md#lorawan-frequency-bands). 1. **Select a multicast device class** Choose whether you want devices in the multicast group to switch to a class B or class C mode at the start of the multicast session. A class B session can receive downlink messages at regular downlink slots and a class C session can receive downlink messages at anytime. 1. **Choose your devices to add to the group** Choose whether you want to add devices individually or in bulk to the multicast group. + To add devices individually, enter the wireless device ID of each device that you want to add to your group. + To add devices in bulk, you can filter the devices you want to add by device profile or tags. For device profile, you can add devices with a profile that supports class B, class C, or both device classes. 1. **(Optional) Choose participating gateways** Optionally, you can choose the gateways that you want to use for receiving the downlink message and the transmission interval between them. For more information, see [Choose participating gateways to receive multicast downlink messages](lorawan-multicast-choose-gateways.md). 1. To create your multicast group, choose **Create**. The multicast group details and the devices you added appear in the group. For information about the status of the multicast group and your devices and for troubleshooting any issues, see [Monitor and troubleshoot your multicast groups](lorawan-multicast-status.md). After creating a multicast group, you can choose **Action** to edit, delete, or add devices to the multicast group. After you've added the devices, you can schedule a session for the downlink payload to be sent to the devices in your group. ## Create multicast groups by using the API Create multicast groups (CLI) To create multicast groups and add devices to the group by using the API: 1. **Create a multicast group** To create your multicast group, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_CreateMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_CreateMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/create-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/create-multicast-group.html) CLI command. You can provide an `input.json` file as input to the `create-multicast-group` command. **Note** When creating a multicast group, you can optionally specify the gateways that you want to use for receiving the multicast downlink message using the `ParticipatingGateways` parameter. For more information, see [Choose participating gateways to receive multicast downlink messages](lorawan-multicast-choose-gateways.md). ``` aws iotwireless create-multicast-group \ --cli-input-json file://input.json ``` where: **Contents of input.json** ``` { "Description": "Multicast group to send downlink payload and perform FUOTA.", "LoRaWAN": { "DlClass": "ClassB", "RfRegion": "US915" }, "Name": "MC_group_FUOTA" } ``` After you create your multicast group, you can use the following API operations or CLI commands to update, delete, or get information about your multicast groups. + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_UpdateMulticastGroup](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_UpdateMulticastGroup) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/update-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/update-multicast-group.html) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_UpdateMulticastGroup](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_UpdateMulticastGroup) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/get-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/get-multicast-group.html) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_ListMulticastGroups](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_ListMulticastGroups) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/list-multicast-groups.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/list-multicast-groups.html) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DeleteMulticastGroup](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DeleteMulticastGroup) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/delete-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/delete-multicast-group.html) 1. **Add devices to a multicast group** You can add devices to your multicast group individually or in bulk. + To add devices in bulk to your multicast group, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartBulkAssociateWirelessDeviceWithMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartBulkAssociateWirelessDeviceWithMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-bulk-associate-wireless-device-with-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-bulk-associate-wireless-device-with-multicast-group.html) CLI command. To filter the devices you want to associate in bulk to your multicast group, provide a query string. The following shows how you can add a group of devices that has a device profile with the specified ID linked to it. ``` aws iotwireless start-bulk-associate-wireless-device-with-multicast-group \ --id "12abd34e-5f67-89c2-9293-593b1bd862e0" \ --cli-input-json file://input.json ``` where: **Contents of input.json** ``` { "QueryString":"DeviceProfileName: MyWirelessDevice AND DeviceProfileId: d6d8ef8e-7045-496d-b3f4-ebcaa1d564bf", "Tags": [ { "Key": "Multicast", "Value": "ClassB" } ] } ``` Here, `multicast-groups/d6d8ef8e-7045-496d-b3f4-ebcaa1d564bf/bulk` is the URL that's used to associate devices with the group. + To add devices individually to your multicast group, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_AssociateWirelessDeviceWithMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_AssociateWirelessDeviceWithMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/associate-wireless-device-with-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/associate-wireless-device-with-multicast-group.html) CLI. Provide the wireless device ID for each device you want to add to your group. ``` aws iotwireless associate-wireless-device-with-multicast-group \ --id "12abd34e-5f67-89c2-9293-593b1bd862e0" \ --wireless-device-id "ab0c23d3-b001-45ef-6a01-2bc3de4f5333" ``` After you create your multicast group, you can use the following API operations or CLI commands to get information about your multicast group or to disassociate devices. + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DisassociateWirelessDeviceFromMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DisassociateWirelessDeviceFromMulticastGroup.html) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/disassociate-wireless-device-from-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/disassociate-wireless-device-from-multicast-group.html) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartBulkDisassociateWirelessDeviceFromMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartBulkDisassociateWirelessDeviceFromMulticastGroup.html) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-bulk-disassociate-wireless-device-from-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-bulk-disassociate-wireless-device-from-multicast-group.html) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_ListWirelessDevices](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_ListWirelessDevices) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/list-wireless-devices.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/list-wireless-devices.html) **Note** The `ListWirelessDevices` API operation can be used to list wireless devices in general, and wireless devices that are associated with a multicast group or a FUOTA task. To list wireless devices associated with a multicast group, use the `ListWirelessDevices` API operation with `MulticastGroupID` as the filter. To list wireless devices associated with a FUOTA task, use the `ListWirelessDevices` API operation with `FuotaTaskID` as the filter. ## Next steps After you've created a multicast group and added devices, you can continue adding devices and monitor the status of the multicast group and your devices. If your devices have been added successfully to the group, you can configure and schedule a downlink message to be sent to the devices. Before you can send a downlink message, your devices' status must be **Multicast setup ready**. After you schedule a downlink message, the status changes to **Session attempting**. For more information, see [Schedule a downlink message for your multicast group](lorawan-multicast-schedule-downlink.md). 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. For more information, see [Firmware update over-the-air (FUOTA) for AWS IoT Core for LoRaWAN](lorawan-mc-fuota-overview.md). If your devices weren't added or if you see an error in the multicast group or device statuses, you can hover over the error to get more information and resolve it. If you still see an error, for information about how to troubleshoot and resolve the issue, see [Monitor and troubleshoot your multicast groups](lorawan-multicast-status.md). # Choose participating gateways to receive multicast downlink messages Choose gateways for multicast downlink 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. ![\[Image showing how a multicast downlink message from AWS IoT Core for LoRaWAN can get corrupted to the device.\]](http://docs.aws.amazon.com/iot-wireless/latest/developerguide/images/iot-lorawan-multicast-gateways.png) 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](lorawan-gateway-participate.md). + **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](lorawan-create-multicast-groups.md). 1. Go to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose **Create multicast group**. 1. Specify a name for the multicast group, and optionally provide a description and tags for your group. 1. Choose **Next** to add devices to your multicast group. 1. Specify the RFRegion, and whether to add devices individually using their Device ID, or in bulk using their device profile. 1. Add the gateways that you want to use for receiving the downlink message using their Gateway ID, and the transmission interval. 1. Choose **Create** to create the multicast group. ## Choose gateways for multicast downlink (CLI) To specify the gateways for receiving the downlink messages, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_CreateMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_CreateMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/create-multicast-group.html](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/create-multicast-group.html) 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](lorawan-multicast-schedule-downlink.md). 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](lorawan-mc-fuota-overview.md). # Monitor and troubleshoot your multicast groups Monitor and troubleshoot multicast groups After you've added devices and created your multicast group, open the AWS Management Console. Navigate to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose the multicast group you created to view its details. You'll see information about the multicast group, the number of devices that have been added, and device status details. You can use the status information to track progress of your multicast session and troubleshoot any errors. ## Multicast group status Your multicast group can have one of the following status messages displayed in the AWS Management Console. + **Pending** This status indicates that you've created a multicast group but it doesn't yet have a multicast session. You'll see this status message displayed when your group has been created. During this time, you can update your multicast group, and associate or disassociate devices with your group. After the status changes from **Pending**, additional devices can't be added to the group. + **Session attempting** After your devices have been added successfully to the multicast group, when your group has a scheduled multicast session, you'll see this status message displayed. During this time, you can't update or add devices to your multicast group. If you cancel your multicast session, the group status changes to **Pending**. + **In session** When it's the earliest session time for your multicast session, you'll see this status message displayed. A multicast group also continues to be in this state when it's associated with a FUOTA task that has an ongoing firmware update session. If you don't have an associated FUOTA task in session, and if the multicast session is canceled because the session time exceeded the time out or you canceled your multicast session, the group status changes to **Pending**. + **Delete waiting** If you delete your multicast group, its group status changes to **Delete waiting**. Deletions are permanent and can't be undone. This action can take time and the group status will be **Delete\$1Waiting** until the multicast group has been deleted. After your multicast group enters this state, it can't transition to one of the other states. ## Status of devices in multicast group The devices in your multicast group can have one of the following status messages displayed in the AWS Management Console. You can hover over each status message to get more information about what it indicates. + **Package attempting** After your devices have been associated with the multicast group, the device status is **Package attempting**. This status indicates that AWS IoT Core for LoRaWAN has not yet confirmed whether the device supports multicast setup and operation. + **Package unsupported** After your devices have been associated with the multicast group, AWS IoT Core for LoRaWAN checks whether your device's firmware is capable of multicast setup and operation. If your device doesn't have the supported multicast package, its status is **Package unsupported**. To resolve the error, check whether your device's firmware is capable of multicast setup and operation. + **Multicast setup attempting** If the devices associated with your multicast group are capable of multicast setup and operation, the status is **Multicast setup attempting**. This status indicates that the device hasn't completed the multicast setup yet. + **Multicast setup ready** Your device has completed the multicast setup and has been added to the multicast group. This status indicates that the devices are ready for a multicast session and a downlink message can be sent to those devices. The status also indicates when you can use FUOTA to update the firmware of the devices in the group. + **Session attempting** A multicast session has been scheduled for the devices in your multicast group. At the start of a multicast group session, the device status is **Session attempting**, and requests are sent for whether a class B or class C distribution window can be initiated for the session. If the time it takes to set up the multicast session exceeds the timeout or if you cancel the multicast session, the status changes to **Multicast setup done**. + **In session** This status indicates that a class B or class C distribution window has been initiated and your device has an ongoing multicast session. During this time, downlink messages can be sent from AWS IoT Core for LoRaWAN to devices in the multicast group. If you update your session time, it overrides the current session and the status changes to **Session attempting**. When the session time ends or if you cancel the multicast session, the status changes to **Multicast setup ready**. ## Next steps Now that you've learned the different statuses of your multicast group and the devices in your group, and how you can troubleshoot any issues such as when a device is not capable of multicast setup, you can schedule a downlink message to be sent to the devices and your multicast group will be in **In session**. For information about scheduling a downlink message, see [Schedule a downlink message for your multicast group](lorawan-multicast-schedule-downlink.md). # Schedule a downlink message for your multicast group Schedule multicast downlink message After you've successfully added devices to your multicast group, you can start a multicast session and configure a downlink message to be sent to those devices. The downlink message must be scheduled within 48 hours and the start time for the multicast must be at least 30 minutes later than the current time. **Note** Devices in a multicast group can't acknowledge when a downlink message has been received. ## Prerequisites Before you can send a downlink message, you must have created a multicast group and successfully added devices to the group for which you want to send a downlink message. You can't add more devices after a start time has been scheduled for your multicast session. For more information, see [Create multicast groups and add devices to the group](lorawan-create-multicast-groups.md). If any of the devices weren't added successfully, the multicast group and device status will contain information to help you resolve the errors. If the errors still persist, for information about troubleshooting these errors, see [Monitor and troubleshoot your multicast groups](lorawan-multicast-status.md). ## Schedule a downlink message by using the console To send a downlink message by using the console, go to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose the multicast group you created. In the multicast group details page, choose **Schedule downlink message** and then choose **Schedule downlink session**. 1. **Schedule downlink message window** You can set up a time window for a downlink message to be sent to the devices in your multicast group. The downlink message must be scheduled within 48 hours. To schedule your multicast session, specify the following parameters: + **Start date** and **Start time**: The start date and time must be at least 30 minutes after and 48 hours before the current time. **Note** The time that you specify is in UTC so consider checking the time difference with your time zone when scheduling the downlink window. + **Session timeout**: The time after which you want the multicast session to timeout if no downlink message has been received. The minimum timeout allowed is 60 seconds. The maximum timeout value is 2 days for class B multicast groups and 18 hours for class C multicast groups. **Note** We recommend that you provide a timeout value that is a power-of-two (such as 64, 128, 256). If a non-power-of-two value is provided, it will automatically be rounded up to the next supported power-of-two within the allowed range. 1. **Configure your downlink message** To configure your downlink message, specify the following parameters: + **Data rate**: Choose a data rate for your downlink message. The data rate depends on RFRegion and payload size. The default data rate is 8 for the US915 region and 0 for the EU868 region. + **Frequency**: Choose a frequency for sending your downlink message. To avoid messaging conflicts, choose an available frequency depending on the RFRegion. + **FPort**: Choose an available frequency port for sending the downlink message to your devices. + **Payload**: Specify the maximum size of your payload depending on the data rate. Using the default data rate, you can have a maximum payload size of 33 bytes in the US915 RfRegion and 51 bytes in the EU868 RfRegion. Using larger data rates, you can transfer up to a maximum payload size of 242 bytes. To schedule your downlink message, choose **Schedule**. ## Schedule a downlink message by using the API To schedule a downlink message by using the API, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartMulticastGroupSession.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartMulticastGroupSession.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-multicast-group-session](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-multicast-group-session) CLI command. You can use the following API operations or CLI commands to get information about a multicast group and to delete a multicast group. + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_GetMulticastGroupSession.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_GetMulticastGroupSession.html) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/get-multicast-group-session](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/get-multicast-group-session) + [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DeleteMulticastGroupSession.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_DeleteMulticastGroupSession.html) or [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/delete-multicast-group-session](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/delete-multicast-group-session) To send data to a multicast group after the session has been started, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_SendDataToMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_SendDataToMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/send-data-to-multicast-group](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/send-data-to-multicast-group) CLI command. ## Next steps After you've configured a downlink message to be sent to the devices, the message is sent at the start of the session. The devices in a multicast group can't confirm whether the message has been received. ### Configure additional downlink messages You can also configure additional downlink messages to be sent to the devices in your multicast group: + To configure additional downlink messages from the console: 1. Go to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose the multicast group you created. 1. In the multicast group details page, choose **Schedule downlink message** and then choose **Configure additional downlink message**. 1. Specify the parameters **Data rate**, **Frequency**, **FPort**, and **Payload**, similar to how you configured these parameters for your first downlink message. + To configure additional downlink messages using the API or CLI, call the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_SendDataToMulticastGroup.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_SendDataToMulticastGroup.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/send-data-to-multicast-group](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/send-data-to-multicast-group) CLI command for each additional downlink message. ### Update session schedule You can also update the session schedule to use a new start date and time for your multicast session. The new session schedule will override the previously scheduled session. **Note** Update your multicast session only when required. These updates can cause a group of devices to wake up for a long duration and drain the battery. + To update the session schedule from the console: 1. Go to the [Multicast groups](https://console.aws.amazon.com/iot/home#/wireless/multicastGroups) page of the AWS IoT console and choose the multicast group you created. 1. In the multicast group details page, choose **Schedule downlink message** and then choose **Update session schedule**. 1. Specify the parameters **State date**, **Start time**, and **Session timeout**, similar to how you specified these parameters for your first downlink message. + To update the session schedule from the API or CLI, use the [https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartMulticastGroupSession.html](https://docs.aws.amazon.com/iot-wireless/latest/apireference/API_StartMulticastGroupSession.html) API operation or the [https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-multicast-group-session](https://docs.aws.amazon.com/cli/latest/reference/iotwireless/start-multicast-group-session) CLI command.