Network Allocation Vector
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The Network Allocation Vector (NAV) is virtual carrier sensing mechanism used with wireless network protocols such as IEEE 802.11 and IEEE 802.16 (WiMax). The virtual carrier sensing is a logical abstraction which limits the need for physical carrier sensing at the air interface in order to save power. The MAC layer frame headers contain a Duration field that specifies the transmission time required for the frame, in which time the medium will be busy. The stations listening on the wireless media reads the Duration field and sets their NAV, which is an indicator for the station on how long it must defer from accessing the media.
Wireless stations are often battery powered, so in order to conserve power the stations may enter a power-saving mode. The stations decrement its NAV counter until it becomes zero, at which time they awaken to sense the medium again.
The NAV virtual carrier sensing mechanism is a prominent part of the CSMA/CA random access protocol used with IEEE 802.11 WLANs.