This section provides details on the MAC frame formats. The information provided here is sufficiently detailed to act as a reference for the topics discussed in this book, but it does not provide an exhaustive list of all field elements, particularly in the management frames. For a detailed treatment of the frame formats refer to the actual specification (IEEE 2007a, 2007b).

General frame format

Each MAC frame consists of the following:

• a MAC header

• a variable length frame body that contains information specific to the frame type or subtype

• a frame check sequence or FCS that contains a 32-bit CRC.

This frame format consists of a set of fields that occur in a fixed order as illustrated in Figure 11.1. Not all fields are present in all frame types.

Frame Control field

The Frame Control field is shown in Figure 11.2 and is composed of a number of subfields described below.

Protocol Version field

This field is 2 bits in length and is set to 0. The protocol version will only be changed when a fundamental incompatibility exists between a new revision and the prior edition of the standard, which to date has not happened.

Type and Subtype fields

The Type and Subtype fields together identify the function of the frame. There are three frame types defined: control, data, and management. Each frame type has several subtypes defined and the combinations are listed in Table 11.1.