Channel configuration is defined using the ANT serial message protocol. A network key must be defined and sent as the start of the channel set-up, as well as a channel ID of 32 bits, made up of the device ID, device type and transmission type. This ID is the basis of device association. The device ID is a sixteen bit field that is often the variable used to distinguish a device within the network. The device type is used in ANT+, the interoperable application extension, to narrow search variables by pre-defining which device class is transmitting. Transmission type is mostly used to define certain transmission characteristics. In a private network application transmission type offers another unique eight bits of ID. Power output levels are also defined at this stage using the message protocol.