Network Allocation Vector (NAV) - A timer mechanism that maintains a prediction of future traffic on medium based on duration value information seen in previous frame transmission. When a radio is not transmitting it's listening. When listening it and hears frame from another station it looks at the header and determines the Duration/ID contains a duration value or ID Value. If it contains duration value the listening station will set it's NAV timer to this value. Listening station will then use the NAV as a countdown timer, knowing that the RF medium should be busy until the countdown reaches 0."