4 The IEEE 802.11 standard
4.2 802.11 MAC Frame

The IEEE 802.11 standard MAC frame, as shown in Figure 1.12, consists of a MAC header, the frame body, and a frame check sequence (FCS). The MAC frame format comprises a set of nine fields that occur in a fixed order in all frames.

Frame Control Field

The Frame Control Field, see Figure 1.12, contains control information used for defining the type of 802.11 MAC frame and providing information necessary for the following fields to understand how to process the MAC frame.

A description of each Frame Control field subfield is given below:

Duration/ID Field

This field is used for all control type frames, except with the subtype of Power Save (PS) Poll, to indicate the remaining duration needed to receive the next frame transmission. When the sub-type is PS Poll, the field contains the association identity (AID) of the transmitting STA.

Address Fields

Depending upon the frame type, the four address fields will contain a combination of the following address types:

For more information about the address types and the contents of the address fields in the 802.11 MAC header, see the IEEE 802.11 standard at the IEEE Web site [6].

Sequence Control

The Sequence Control field contains two subfields, the Fragment Number field and the Sequence Number field, as shown in Figure 1.12.

A description of each Sequence Control field subfield is as follows:

Frame Body

The frame body contains the data or information included in either management type or data type frames.

Frame Check Sequence

The transmitting STA uses a cyclic redundancy check (CRC) over all the fields of the MAC header and the frame body field to generate the FCS value. The receiving STA then uses the same CRC calculation to determine its own value of the FCS field to verify whether or not any errors occurred in the frame during the transmission.

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Figure 1.12 The 802.11 standard MAC frame format. Frame control and sequence control fields are detailed.