Embedded Hosts and peripherals are supported through the USB OTG and Embedded Host Supplement to the USB 3.0 specification. Protocols The USB OTG and Embedded Host Supplement to the USB 2.0 specification introduced three new communication protocols: Attach Detection Protocol (ADP): Allows an OTG device, embedded host or USB device to determine attachment status in the absence of power on the USB bus, enabling both insertion-based behavior and the capability to display attachment status. It does so by periodically measuring the capacitance on the USB port to determine whether there is another device attached, a dangling cable, or no cable. When a large enough change in capacitance is detected to indicate device attachment, an A-device will provide power to the USB bus and look for device connection. At the same time, a B-device will generate SRP (see below) and wait for the USB bus to become powered. Session Request Protocol (SRP): Allows both communicating devices to control when the link's power session is active; in standard USB, only the host is capable of doing so. That allows fine control over the power consumption, which is very important for battery-operated devices such as cameras and mobile phones. The OTG or embedded host can leave the USB link unpowered until the peripheral (which can be an OTG or standard USB device) requires power. OTG and embedded hosts typically have little battery power to spare, so leaving the USB link unpowered helps in extending the battery runtime. Host Negotiation Protocol (HNP): Allows the two devices to exchange their host/peripheral roles, provided both are OTG dual-role devices. By using HNP for reversing host/peripheral roles, the USB OTG device is capable of acquiring control of data-transfer scheduling. Thus, any OTG device is capable of initiating data-transfer over USB OTG bus. The latest version of the supplement also introduced HNP polling, in which the host device periodically polls the peripheral during an active session to determine whether it wishes to become a host. The main purpose of HNP is to accommodate users who have connected the A and B devices (see below) in the wrong direction for the task they want to perform. For example, a printer is connected as the A-device (host), but cannot function as the host for a particular camera, since it does not understand the camera's representation of print jobs. When that camera knows how to talk to the printer, the printer