The IEEE 802.11-2012 standard requires VHT capable devices to be backward compatible with devices using which other 802.11 physical layer specification (PHY)?

You were previously onsite at XYZ's facility to conduct a pre-deployment RF site survey. The WLAN has been deployed according to your recommendations and you are onsite again to perform a post-deployment validation survey.
When performing this type of post-deployment RF site survey for voice over Wi-Fi. what is an action that must be performed?

What security method is commonly used for VoIP handsets when the infrastructure does not support OKC or FT roaming?

What factor will have the most significant impact on the amount of wireless throughput available to each station within a BSS?

In an 802.11n 2.4 GHz BSS, what prevents each station from using the full network data rate (e.g. 216.7 Mbps) for user data when multiple clients are actively exchanging data with the AP?