Network Allocation Vector

The network allocation vector (NAV) is a virtual carrier-sensing mechanism used with wireless network protocols such as

IEEE 802.11 IEEE 802.11 is part of the IEEE 802 set of local area network (LAN) technical standards, and specifies the set of media access control (MAC) and physical layer (PHY) protocols for implementing wireless local area network (WLAN) computer commu ...

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Wi-Fi Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio w ...

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IEEE 802.16 IEEE 802.16 is a series of wireless broadband standards written by the Institute of Electrical and Electronics Engineers (IEEE). The IEEE Standards Board established a working group in 1999 to develop standards for broadband for wireless metrop ...

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WiMax Worldwide Interoperability for Microwave Access (WiMAX) is a family of wireless broadband communication standards based on the IEEE 802.16 set of standards, which provide physical layer (PHY) and media access control (MAC) options. The WiMA ...

). 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 In IEEE 802 LAN/MAN standards, the medium access control (MAC, also called media access control) sublayer is the layer that controls the hardware responsible for interaction with the wired, optical or wireless transmission medium. The MAC sublay ...

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 medium read the ''Duration'' field and set their NAV, which is an indicator for a station on how long it must defer from accessing the medium. The NAV may be thought of as a counter, which counts down to zero at a uniform rate. When the counter is zero, the virtual carrier-sensing indication is that the medium is idle; when nonzero, the indication is busy. The medium shall be determined to be busy when the station (STA) is transmitting. In IEEE 802.11, the NAV represents the number of

microsecond A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 100 ...

s the sending STA intends to hold the medium busy (maximum of 32,767 microseconds). When the sender sends a Request to Send the receiver waits one SIFS before sending Clear to Send. Then the sender will wait again one SIFS before sending all the data. Again the receiver will wait a SIFS before sending ACK. So NAV is the duration from the first SIFS to the ending of ACK. During this time the medium is considered busy. Wireless stations are often battery-powered, so to conserve power the stations may enter a power-saving mode. A station decrements its NAV counter until it becomes zero, at which time it is awakened to sense the medium again. The NAV virtual carrier sensing mechanism is a prominent part of the

CSMA/CA Carrier-sense multiple access with collision avoidance (CSMA/CA) in computer networking, is a network multiple access method in which carrier sensing is used, but nodes attempt to avoid collisions by beginning transmission only after the channel ...

MAC Mac or MAC most commonly refers to: * Mac (computer), a family of personal computers made by Apple Inc. * Mackintosh, a raincoat made of rubberized cloth * A variant of the word macaroni, mostly used in the name of the dish mac and cheese * Mac, ...

protocol used with

WLANs. NAV is used in DCF, PCF and HCF. {{compu-network-stub Media access control Computer networking