802.11 WLAN Frames (Management, Control, Data frames)

There are 3 types of frames used in the 802.11 MAC layer 2 communications happening over the air which manages and controls the wireless link.

They are Management Frames, Control Frames and Data frames. 

Management Frame:

1)    Authentication frame

2)    Deauthentication frame

3)    Association request frame

4)    Association response frame

5)    Reassociation request frame

6)    Reassociation response frame

7)    Disassociation frame

8)    Beacon frame

9)    Probe request frame

10) Probe response frame

Control Frames:

802.11 control frames assist in the delivery of data frames between stations. The following are common 802.11 control frame subtypes:

·         Request to Send (RTS)/Clear to Send(CTS) frame: The RTS/CTS function is optional and reduces frame collisions present when hidden stations have associations with the same access point. A station sends a RTS frame to another station as the first phase of a two-way handshake necessary before sending a data frame.

RTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem. Originally the protocol fixed the exposed node problem as well, but modern RTS/CTS includes ACKs and does not solve the exposed node problem.

Frame Format:

The RTS frame contains five fields, which are:

1.     Frame Control

2.     Duration

3.     RA (Receiver Address)

4.     TA (Transmitter Address)

5.     FCS

The CTS frame contains four fields, which are:

1.     Frame Control

2.     Duration

3.     RA (Receiver Address)

4.     FCS

The ACK frame contains four fields, which are:

1.     Frame Control

2.     Duration

3.     RA (Receiver Address)

4.     FCS

RA - Receiver Address indicating the MAC Address of the station that shall receive frame.
TA - Transmitter Address indicating the MAC address of the station which has transmitted frame.
FCS - Frame Check Sequence.

Acknowledgement (ACK) frame: After receiving a data frame, the receiving station will utilize an error checking processes to detect the presence of errors. The receiving station will send an ACK frame to the sending station if no errors are found. If the sending station doesn't receive an ACK after a period of time, the sending station will retransmit the frame.

Data Frames:

These at the frames which come later in the game after the basic wlan communication is already established between the Mobile station and the Access point. We will always reach to this 802.11 data frame for analysis typically to verify and analyze over the air if the protocols and data from higher layers within the frame body is getting through to the wire. These frames transport data packets from higher layers, such as web pages, printer control data, etc., within the body of the frame.