IEEE 802.11 MAC Frame Format

IEEE 802.11 MAC Frame:

The 802.11 standard defines three kinds of frames: data frame, control frame and management frame. The IEEE 802.11 MAC Frame Format for data frame is given below:

IEEE-802.11-MAC-Frame-Format

Frame Control: This field has 11 subfields.

Version: Version of the protocol used in a cell.

Type: Type of frame (Example – Data, control and management)

Subtype: Subtype of the type (Example – RTS or CTS)

To DS: Whether frame is coming from inter cell distribution system.

MF: Whether more fragments will follow.

Retry: It indicates retranmission of a frame sent earlier.

Power: It is used by a base station to make the receiver asleep or awake.

More: It indicates that sender has more frames for the receiver.

W: It specifies that body has been encrypted using Wired Equivalent Privacy.

O: It tells the receiver that frames with this bit-on must be processed in the order.

Address 1, 2, 3, 4: Two addresses are for source and destination and the remaining two are for base stations for inter-cell communication.

Sequence: It used for numbering the frames and fragments. 12 bits are used for indicating the frame and the remaining 4 bits are used for indicating the fragment.

Data: This field contains payload of upto 2312 bytes.
Checksum: This field is used for error detection.

Control Frame: Control Frames have only one or two addresses, no data field and no sequence field. The important field here is the subtype field.

Management Frame: Management Frame has the same structure except without one base station’s address because Management Frames are restricted to a single frame only.