Gratuitous Probe Response - To detect the presence of a WLAN, dual mode phones that support cellular and WLAN modes of operation consume significant battery power due to the amount of time the phone must wait passively while listening for beacons on each channel. Because beacon intervals are typically on the order of hundreds of milliseconds, these scans require that the phone's receiver is enabled for at least a typical beacon interval on each channel. The Gratuitous Probe Response feature helps to conserve battery power by providing a high rate packet on the order of 10ms. The GPR packet is transmitted from the AP at a predefined time interval (at intervals between 10 and 50ms).