Based On The Ieee 802.11 Wireless Lan Communication Protocol

This thesis researches the central MAC protocols of IEEE802.11 WLAN. Each functional module of Distributed Coordination Function (DCF) and Point Coordination Function (PCF) in MAC protocol has been designed and implemented in software. Finally, the design and implementation of Signal Dispatching System which is supporting protocol stack have been given.Firstly, the basic framework of WLAN is built on the basis of the introduction of elements and related conceptions of IEEE802.11 WLAN. The services of IEEE802.11 are introduced in two types, which are distribution services and station services. Their relationships and messages to support them are also presented.Secondly, the functional architecture of MAC sublayer is discussed. The whole functional architecture, the distributed coordination function and the point coordination function are introduced. In DCF, the special emphasis is put on the carrier-sense mechanism, MAC-Level acknowledgments, inter-frame space, random back-off time, and DCF access procedure. In PCF, the effort is put into CFP structure and timing, PCF access procedure, PCF transfer procedure, polling list operation. The fragmentation and defragmentation and multiple rate support are also presented.Thirdly, according to the data flow of IEEE802.11 MAC protocol, the control mechanism and protocol flow of Finite State Machine (FSM) are described systematically and each functional module of DCF is implemented in software with C language. Based on this work, according to the protocol flow of 802.11 MAC, the Point coordination function mechanism and Distributed coordination function mechanism are implemented systematically in software with C code. The following functions of IEEE 802.11 protocol stack has been finished, which are the encapsulation and resolution of MAC protocol data unit, frame fragmentation and data encryption/decryption, insertion and access operation of data frame queue, data frame exchange and retransmission, and back-off time process. When receiving, the operation of CRC validation and filtering and decryption, defragmentation of data frame, and real-time checking of channel status have also been implemented.Finally, in order to implement communications between modules of protocol stack, the signal dispatching system is been designed and implemented. The module partition and data structure of this system, and the software design flow of every module are given. The function of signal dispatching system contains message queue management such as adding, deletion and update. The message services have also been implemented, for example, message registration, message node searching, and message dispatching. In addition, the process registration and deregistration of IEEE 802.11 protocol stack have been given.