Connecting to the Network

The wireless host (station) needs to associate with an Access Point (AP) before it can send/receive network-layer data. This is a basic 802.11 system management function.

Association is the creation of a 'virtual' ethernet wire between the station and the switch.

The basic three-step procedure followed by the station:

  1. Locate an AP to associate with; this process can involve passive or active scanning as discussed below.
  2. Authenticate itself to the AP (and possibly the infrastructure).
  3. Associate with the AP (create the 'virtual' blue cable).

Now, the station can retrieve an IP address from the subnet and begin TCP/UDP socket communications.

Locate

The first step is to locate the AP you wish to join. The algorithm for locating/selecting an AP is not defined by the 802.11 standards, but by your application. There are two methods provided in 802.11 to discover APs near the station: passive and active scanning, which are illustrated below.

connecting-to-the-network-locate.png

In a typical application, one of the several possible commissioning methods is deployed to get a specific AP's network parameters into your application (channel, SSID, security).

After copying these parameters to your Wi-Fi® sub-system's connection profile, your application will call a WiFi_Connect() API which uses an active scanning method to connect to this specific AP.

Authenticate

Next, the station attempts to authenticate itself to the AP (at a minimum) and possibly the network.

Authentication Protocols:

  • Based on 802.11 (1997)
    • Open System Authentication (see WEP)
    • Shared Key Authentication (see WEP)
  • Based on 802.11i (2004)
    • Open System Authentication (see WEP)
    • Wi-Fi™ Protected Access (see WPA/2)
connecting-to-the-network-authenticate.png
Click image to enlarge.

Associate

The final step in the creation of the 'virtual blue wire'.

After the association is complete, the DHCP process can begin to assign an IP address to the station and enable the application to connect with other hosts on the network.

  • Association request/response frames are exchanged.
  • Final bit rates and security parameters are agreed upon.
  • Now, 802.11 data frames can be sent between the station and AP.
connecting-to-the-network-associate.png
Click image to enlarge.
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