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Chapter 10. Wireless Ethernet > Media Access Control Protocol

10.1. Media Access Control Protocol

The wireless Ethernet MAC defined in the 802.11 standards is common for all different implementations of RF transmission methods including FHSS, DSS, HRDSS, and OFDM, as well as for the infrared implementation. The main CDMA/CA protocol is defined as a distributed coordination function (DCF) and also sometimes called the frame exchange protocol. This protocol defines different MAC frames and procedures for exchanging frames. These MAC frames are to be encapsulated with different preambles and packet headers in accordance with particular transmission methods. A polling system using a point coordinator is also defined as the point coordination function (PCF) for timing-sensitive applications. PCF is built upon DCF, and they can simultaneously share the same transmission medium. To fight against the possibility of eavesdropping, a WEP is also defined using encryption with shared keys distributed through secure channels other than over the air.

10.1.1. Frame Format

Figure 10.1 shows the general format of a wireless Ethernet MAC frame as defined by the IEEE 802.11 standards. A particular version of wireless Ethernet packet is formed by encapsulating the MAC frame with a physical layer–dependent preamble and header. Therefore, no preamble is defined for the wireless Ethernet frame.


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