Virtual Carrier Sensing and Network Allocation vector

Carrier sensing is used to determine if the medium is available. In addition to the physical carrier sensing, 802.11 employs also virtual carrier sensing functions. If either one of them indicates that the medium is busy, the station defers the transmission. Virtual carrier sensing is provided by the network allocation vector, Most 802.11 frames carry a duration field, which can be used to reserve the medium for a fixed time period. Stations set the NAV to the time for which they expect to use the medium including any frames necessary to complete the current operation. Other stations that receive the frame set their NAV timer which is a timer that indicates the amount of time the medium will be reserved and count down from the NAV to 0. Read More