USB-PD specifies the architecture used for data transfer and power programming. It utilizes standard computer-to-computer and network communication protocols. For the USB-PD power adapters, the standard specifies how the output voltage and power levels can be determined by the end equipment it is used with. Specific pins are used for the end device to provide signals that will determine the specific output power and voltage levels needed for that device. A USB power adapter, when unconnected (No USB cable), or if connected to a device lacking the USB-PD capability, will default to a safe operating level of 5 volts @ 900 milliamps.