Subject: Mobile Communication and Computing

Topic: Wireless Local Area Networks

Difficulty: High

IEEE 802.11 MAC Sublayer

IEEE 802.11:

1. It is a set of standards for implementing Wireless Local Area Network(WLAN).
2. It operates in 2,4,3.6 and 5Ghz frequency bands.
3. They are created and maintained by the Institute of Electrical and electronics engineers (IEEE) LAN/MAN Standards Committee (IEEE 802).
4. 802.11 has various versions such as 802.11a, 802.11b, 802.11g etc.

IEEE 802.11 MAC Sublayer:

1. IEEE 802.11 MAC Sublayer is used to define addressing and frame format.
2. It is also used to handle access mechanism
3. IEEE 802.11 defines two MAC Sublayer i.e DCF and PCF.
4. DFC: a. DCF stands for Distributed Coordination function. b. It provides Asynchronous Data Service. c. It is mandatory traffic services.

MAC sublayer Frame format

1. Frame format: it carries the instruction on the nature of the packet. It contain several sub field. a. Protocol version: it shows the current protocol version.

b. Type: it determines the function of a frame.

c. Sub type: it determine the sub function of a frame.

d. To DS/From DS : it is used to control meaning of the address field.

e. More fragments: it should be set to1 to provide more fragments.

f. Retry: it is used to retry the re-transmission of previous frame.

g. Power management: it is used to control the power set 1 for power save mode.

h. More data: this field indicates a receiver that sender has more data to send than the current frame.

i. Wired equivalent privacy (WEP): it indicates the standard security mechanism.

j. Order: it indicates that the received frame must be proceeds in strict over when it is set to 1.

1. Duration/ID : This field is used to define the period of time.
2. Address 1 to 4: Four address field are used to identify the source, destination and access point.
3. Sequence control: it is used to control sequence numbering.
4. Checksum : it is used to protect frame.