Certified Wireless Network Administrator (CWNA) Practice Test

The two carrier sense functions that determine if the wireless medium is busy are the virtual and physical carrier sense.

The physical carrier sense refers to the ability of a device to detect transmissions in the wireless medium using its hardware. This involves listening on the channel to check if there is an ongoing transmission—essentially, determining whether the medium is "busy" through listening for radio signals.

On the other hand, virtual carrier sense is a method used by wireless devices to keep track of network activity in a different way. It primarily relies on the Network Allocation Vector (NAV), which is a timer that indicates how long the medium is expected to be busy based on the information received in frames. This allows devices to make more informed decisions about when to transmit or defer their transmission based on the expected duration of current communications.

This combination of both physical and virtual sensing allows for more efficient use of the wireless medium and helps avoid collisions, which is particularly important in the context of wireless networking where multiple devices still share the same airwaves.