MAC Layer

The MAC layer is responsible for providing the following services:
• Asynchronous data service, which provides peer IEEE 802.2 entities
with the ability to exchange MSDUs;
• Security services, which in IEEE 802.11 are provided by the authentication
service and the wired-equivalent privacy (WEP) mechanism;
• MSDU ordering, whose sole effect, for the set of MSDUs received at
the MAC service interface of any single station, is a change in the
delivery order of broadcast and multicast MSDUs, relative to
directed MSDUs, originating from a single source station address. The general MAC frame format is shown in Figure 4.4 and consists of the
following components:
• A MAC header, which comprises frame control, duration, address,
and sequence control information;
• A variable length frame body, which contains information specific
to the frame type;
• A frame check sequence (FCS), which contains an IEEE 32-bit CRC.
It is important to remark that there are four address fields in the MAC
frame format. These fields are used to indicate the BSS identifier (BSS_ID),
source address, destination address, transmitting station address, and receiving
station address.