Which one of the following is the frame type sent to discover APs within the signal range of a wireless client?
The frame type sent to discover APs within the signal range of a wireless client is Probe.
Probes are frames that are sent by a wireless device trying to connect to an access point (AP). The probe frame contains the name of the desired network, which is broadcasted in order for any AP within range to respond with a beacon frame, which contains the network information for a given AP.
If the wireless device receives multiple beacon frames, it will select an appropriate AP to connect to based on the signal quality, encryption method, and other factors. Probes are also used by access points to detect and authenticate connected clients.
In this case, the probe frame is sent by the AP and is responded to by the client with an authentication frame. This process is known as 802.11 authentications.