Do all devices which use Wi-Fi (802.11) use CSMA/CA?

Question

I know this is quite trivial, but I just want to know if all devices which support Wi-Fi through interface cards/hardware (like laptops/PCs/phones..etc) use CSMA/CA irrespective of their router/network if they share the same space?

Suppose there are three WAPs. How do each of these WAPs know which sub-carrier frequencies to use, so that it does not cause interference?

Will all the devices (which are labelled with 802.11x) use CSMA/CA? As in when started, will they start sensing which frequencies are busy in the 2.4/5GHz frequencies and thereby choose one which is empty?

Answer 1

Will all the devices (which are labelled with 802.11x) use CSMA/CA?

On a shared medium, you need something like CSMA/CD or CSMA/CA. Because Wi-Fi devices cannot both send and receive at the same time, they cannot use CSMA/CD to detect the collisions, so the use CSMA/CA to try to avoid collisions.

How do each of these WAPs know which sub-carrier frequencies to use, so that it does not cause interference?

That depends on how they are configured by the network administrators, whether manually, or by using a WLC. Some WAPs can tell if a channel is crowded and try to find a less crowded channel, but businesses really want a bit more control over it than that, and perform wireless site surveys and configure the WAPs for best performance.