Network allocation vector
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The Network Allocation Vector (NAV) is a method to avoid colisions in a shared transmission medium. Each station wishing to transmit through the shared medium performs a RTS (Request To Send) with a NAV that indicates the time required to complete the whished transmission. If no collision is detected and after the acknowledge published by the receiving station in a CTS (Clear To Send) packet, every connected station consider the shared medium allocated to the sending station during the time specified in the NAV.
This technique is used within IEEE 802.11 (Wi-Fi) and IEEE 802.16 (WiMax) networks.