Wireless devices must discover and connect to an AP or wireless router. Wireless clients connect to the AP using a scanning (probing) process. This process can be:

Figure 1 illustrates how passive mode works with the AP broadcasting a beacon frame every so often.

Figure 2 illustrates how active mode works with a wireless client broadcasting a probe request for a specific SSID. The AP with that SSID responds with a probe response frame.

A wireless client could also send a probe request without an SSID name to discover nearby WLAN networks. APs configured to broadcast beacon frames would respond to the wireless client with a probe response and provide the SSID name. APs with the broadcast SSID feature disabled do not respond.