1.  Beacons are frames broadcast by the access point to
advertise the SSID of the WLAN to wireless clients
 Probes are frames used by WLAN clients to find a
WLAN network
 Authentication and Association is the process for
establishing the data link between an access point and
a WLAN client

2. The Join Process:
 Beacons are broadcast at regular intervals by an access
point. Beacons allow a client to discover what WLANS are
available in the current location.
◦ It populates the Wireless connection list on a Windows host
 Probes are sent by client stations on multiple channels. The
probe request contains the SSID of the WLAN the client
wants to join and supported bit rates.
◦ A client can send out a probe request with no SSID specified. All
access points that receive the probe will respond except those with
broadcast SSID disabled.
 The access point responds with a probe response that
includes the SSID, supported data rates and security
standard e.g. WPA2

3. To authenticate the wireless client to the access point
 Open authentication (NULL request)
◦ The client device requests authentication to the access point
◦ Four hello packets with NULL verification (no password or keys are provided or
expected) exchanged and the access points responds with YES
◦ Open authentication allows the device to start the join process – Choose OPEN to
allow WPA and WPA2 security protocols provide strong authentication at a later
stage
◦ This is the current default method
 Shared key authentication
◦ This method uses a WEP Wired Equivalency Protection key
 The client device sends an authentication request to the access point.
 The access point sends a challenge back to the client
 The client encrypts the challenge with the shared WEP key and sends it back to the
access point.
 The access point decrypts the encrypted challenge and if it matches the original challenge
the access point authenticates the client
◦ WEP was an interim security protocol used while WPA was in development.
◦ Don’t use WEP as it can be broken very quickly

4. Association
 The client device scans all channels and listens for beacons
and responses to probes
 The client device associates to the access point with the
strongest signal (if EBSS)
 The SSID, MAC address and security settings are sent from
the client device to the access point
 The access point maps a logical port called the association
identifier AID for the WLAN to the clients MAC address (its
like a port on a switch)
The wireless device has joined the WLAN