802.11 Wireless

The IEEE 802.11 standard uses the same 802.2 LLC and 48-bit addressing scheme as other 802 LANs. However, there are many differences at the MAC sublayer and physical layer. In a wireless environment, the environment requires special considerations. There is no definable physical connectivity; therefore, external factors may interfere with data transfer and it is difficult to control access. To meet these challenges, wireless standards have additional controls.

The IEEE 802.11 standard is commonly referred to as Wi-Fi. It is a contention-based system using a CSMA/CA media access process. CSMA/CA specifies a random backoff procedure for all nodes that are waiting to transmit. The most likely opportunity for medium contention is just after the medium becomes available. Making the nodes back off for a random period greatly reduces the likelihood of a collision.

802.11 networks also use data link acknowledgements to confirm that a frame is received successfully. If the sending station does not detect the acknowledgement frame, either because the original data frame or the acknowledgment was not received intact, the frame is retransmitted. This explicit acknowledgement overcomes interference and other radio-related problems.

Other services supported by 802.11 are authentication, association (connectivity to a wireless device), and privacy (encryption).

As shown in the figure, an 802.11 frame contains these fields: