Devices USE channel
Devices USE channel to receive messages and send commands over channel’s connections.
Application: parent account can group devices. In this case, devices can’t have the same ident (e.g. it is not possible that two companies connect a device with the same IMEI to one IP:port).
Channels and devices USE stream
Stream can subscribe for messages from child’s channels and devices.
Application: only parent account can manage stream subscriptions and turn on or off subscription for specified channels or devices.
Devices USE several modems to send SMS
Child account uses its own modem to send settings to devices and if it fails to deliver the message, then the parent account modem tries to send the SMS. (Subaccount is created without modem, so by default, it uses parent account's modem.)
Application: Parent account allows subaccount to use its own SMS service account but guarantees delivery of the SMS by backing up the modem if subaccount’s modem is not working properly.
Note: Channels use modems to send channel commands via SMS, so all of the above applies to channels as well.