How the STA get into the wireless access Process?

Three phases: 1. Scan; 2.authentication; 3.Association
1. Scan: When the STA works in infrastructure mode, the STA scans APs in either of the following methods:
a. Active scan. STA sends a Probe Request frame through 11 channels in turn. It keeps searching for the AP that has the same SSID as itself until it finds one.
b. Passive scan. The STA using this mode consumes low power, but requires a long time to find the AP. STA waits for the Beacon frame sent by the AP. The AP uses the Beacon frame to notify the STA of its BSS information.
2 Authentication: If the STA finds multiple APs with the same SSID as itself, it selects the AP that has the strongest signal, and enters the authentication phase. Only the authenticated STAs can access APs. Huawei AP supports the following authentication methods:
a. Open-system authentication
b. Shared-key authentication
c. WPA pre-shared key (PSK) authentication
d. 802.1X EAP authentication
3 Association: After the STA is successfully authenticated by the AP, the STA enters the association phase. The STA sends an association request to the AP, and the AP returns a response. Then the course of open mode has been finished. The wireless access process is complete, and the STA can transmit data to the AP. And the encryption mode need to finish the exchange of keys. Then the wireless access process is complete, and the STA can transmit data to the AP.
document name security-level
2013-1-25 Huawei Confidential Page29, total36
4.2 Why the users cannot pass the WEP authentication
The possible causes are as follows::
1. No WEP SSID is added to the STA. Many STAs associate with WEP SSIDs by using encryption without authentication. However, the AP uses both authentication and encryption. Therefore, the STA cannot associate with the SSID. The SSID must be manually configured on the STA. At last, set the encryption type to share mode.
2. The key index configured on the AP is different from the key index on the STA. By default, the key index of an AP is 0 (ranging from 0 to 3), and the key index of STA is 1 (ranging from 1 to 4). Key index 0 on the AP matches key index 1 on the STA.