As mentioned previously, an STA is considered a device equipped with a wireless network interface controller. An STA will always be listening for active communication in a specific channel. The first phase of connecting to Wi-Fi is the scanning phase. There are two types of scan mechanisms employed:

• Passive scanning: This form of scanning uses beacons and probe requests. After a channel is selected, the device performing the scan will receive beacons and probe requests from nearby STAs. An access point may transmit a beacon, and if the STA receives the transmission, it may progress to join the network.
• Active scanning: In this mode, the STA will attempt to locate an access point by instantiating probe requests. This mode of scanning uses more power but allows for faster network joins. The AP may respond to a probe request with a probe request response, which is similar to a beacon message. 

Beacons are always broadcast at the lowest basic rates to ensure every STA in the range has the ability to receive the beacon even if it can't connect to that particular network. After a beacon is processed, the next phase of Wi-Fi connectivity is the synchronization phase. This phase is necessary to keep clients attuned to the access point. The beacon packet contains information needed by the STA:

• SSID: Service Set ID. 1 to 32-character network name (this field can optionally be hidden by setting the SSID length to zero. Even if it is hidden the other portions of the beacon frame are transmitted as usual. Generally, speaking, using a hidden SSID offers no additional network security.
• BSSID: Basic Service Set ID. Unique 48-bit following layer-2 MAC address conventions. Formed by the combination of the 24-bit Organization Unique Identifier and the manufacturer's assigned 24-bit identifier for the radio chipset.
• Channel width: 20 MHz, 40 MHz, and so on
• Country: List of supported channels (country-specific)
• Beacon interval: TBTT time mentioned previously
• TIM/DTIM: Wake-up times and intervals to retrieve broadcast messages—allows for advanced power management.
• Security services: WEP, WPA, and WPA2 abilities

If the STA does find an AP or another STA to make a connection with, it then enters an authentication phase. More will be discussed on the variety of security standards used in 802.11 later in this chapter. 

If the security and authentication process succeeds, the next phase is association. The device will send an association request frame to the AP. The AP will subsequently reply with an association response frame that will allow the STA to join the network or be excluded. If the STA is included, the AP will release an association ID to the client and add it to the list of connected clients. 

At this point, data can be exchanged with the AP and vice versa. All data frames will be followed by an acknowledgment.