Network occupancy vector

The network allocation vector ( english network allocation vector , NAV ) is a tool for virtual carrier sense in the industry standard IEEE 802.11 for wireless local area networks (WLAN).

In a WLAN, all networked computers share a single communication medium. If several computers were to send data over the medium at the same time, this would lead to data collisions and thus to delays or even loss of information. The aim of the virtual carrier check is to prevent simultaneous attempts to send. For this purpose, each sender announces how long he will be using the medium before sending his data. The network computers manage this additional information in the network occupancy vector and can thus estimate when the medium will be available again at the earliest.

Each computer in the network internally manages its own network occupancy vector. If a computer receives information in the form "the medium is occupied for the next x seconds", the expected occupancy period is entered in the network occupancy vector. This value is regularly counted down over time until it reaches the value zero. The computer does not attempt to send as long as the network occupancy vector is not yet zero.

In WLANs, the time is not given in seconds or another time unit, but in the number of expected data frames . Contrary to its name, a network occupancy vector is not a vector in the mathematical sense, but a pure counting variable . After the introduction of the 802.11 standard, network occupancy vectors were also adopted in other network protocols, for example Sensor Media Access Control .