IEEE 802.11 Wi-Fi MAC Frame
- If a device wants to communicate to other devices it should have some medium like RF signals to communicate.
- To perform the transmission we need some kind of frame format & specifications.
- In IEEE 802.11 Wi-Fi MAC Frame format we have Frame header ,Frame Body and Frame check sequence(FCS).
| Frame Header | Frame Body | Frame check sequence (FCS) |
Frame Header
The frame header contains information about the where the frame is going, the data rate, cipher suite used to encrypt data frames etc.
Frame Body
Frame body contains the layer 3-7 information
Frame check sequence (FCS)
It is a 32-bit cyclic redundancy check (CRC) used to check the errors.
WiFi MAC Frame Header
| Frame control | Duration ID | Address 1 | Address 2 | Address 3 | Sequence Control | Address 4 | Qos Control | HT Control | Body | FCS |
- Frame control
- Duration ID
- Address 1
- Address 2
- Address 3
- Sequence Control
- Address 4
- Quality of service Control (Qos)
- HT Control
- Frame Body
- FCS (frame check sequence)
Frame control
We have three types of frames
- Management Frames : It is used to manage the Basic Service Set (BSS).
- Control Frames : It is used to control the access to the medium.
- Data Frames : It contains payload.
These Frame control consists of complete information about the frame.
| Protocol version | Type | Subtype | To DS | From DS | More fragmentation | Retry | Power management | More Data | Protected frame | Order |
- Protocol Version : It shows the current version like 802.11a ,b ,n,ac,ax etc. Default it is set to “zero”.
- Type : It defines the type of the frame whether it is management frame or control frame or Data frame
- Sub type : It defines the subtype of a frame, there are different subtypes for each type of frames like beacon, probe request and probe response in management frames and RTS and CTS in control frames etc.
- To DS : It is indicated as 1 If it’s destination is to Distributed system
- From DS : It is the indicated as 1 If it is starts from Distribution system
| To DS | From DS | Address 1 | Address 2 | Address 3 | Address 4 |
| 0 | 0 | RA=DA | TA=SA | BSSID | N/A |
| 0 | 1 | RA=DA | TA=BSS ID | SA | N/A |
| 1 | 0 | TA=BSS ID | TA=SA | DA | N/A |
| 1 | 1 | RA | TA | DA | SA |
6.More Fragmentation : If it is set to 1 there are more frames are available to receive.
7. Retry : It is set to 1 if current frame is re-transmitting.
8.Power Management : If it is set to 1 it is power save mode
9.More Data : If it set to 1 it indicates more data is there to transmit
10.Protected Frame :It indicates whether the frame is protected or not
11.Order : It indicates the order of the frame.
Types of frames
- Management frames
- Control frames
- Data frames
Management frames
They are used by stations. There is a total of 12 802.11 Management Frames
- Association Request
- Association Response
- Re-association request
- Re-association response
- Probe Request
- Probe Response
- Beacon
- Authentication Request
- Authentication Response
- De-authentication
- De-association
- Action
Control Frames
802.11 Control Frames assist with the delivery of data frames. There are 8 Control Frames
- Block Acknowledgment Request
- Block Acknowledgment
- Ps-poll
- Request to send
- Clear to send
- Acknowledgment
- CF end
- CF end Acknowledgment
Data Frames
802.11 Data Frames are mainly used to carry data. There is a total of 15 802.11 Data Frames
- Data
- Data+CF-Ack
- Data+CF-Poll
- Data+CF-Ack+CF-Poll
- Null
- CF-Ack
- CF-Poll
- CF-Ack+CF-Poll
- QoS Data
- QoS Data+CF-Ack
- QoS Data+CF-Poll
- QoS Data+CF-Ack+CF-Poll
- QoS Null
- QoS CF-Poll
- QoS CF-Ack+CF-Poll
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