IEEE802.11b的DCF退避算法实现技术探究

An Inquiry into the Random Escape Mechanism of DCF in IEEE802.11b

本文研究了无线局域网IEEE802.11b的MAC层基于随机竞争的分布式协调功能(DCF:Distributed Coordination Funct0ion)的基本信道访问方式的实现技术。DCF主要包括载波侦听机制、随机退避机制、帧优先级机制等。它定义了两种工作方式,一种是基本访问方式CSMA/CA,基于物理信道的载波侦听;另外一种是基于RTS/CTS虚拟载波侦听,这种方式在CSMA/CA的基础上增加两个长度特别小的数据包RTS和CTS来克服"隐藏终端"问题。可以通过对这两种载波侦听机制的研究,并利用SDL图和状态转移图,完成退避算法的软件实现。

This paper focuses on the technology of basic channel access of the random competitive DCF （Distributed Coordination Function） on MAC layer of WLAN IEEE802.11b. DCF mainly includes carrier monitoring mechanism, random escape mechanism and frame-level priority mechanism. It defines two access modes. One is the basic access mode called CSMA/CA, which is based on carrier monitoring mechanism of physical communication channel. The other mode is virtual carrier monitoring on the base of RTS/CTS. This mode adds two small-length data packages ＂RTS＂ and ＂CTS＂ to overcome the ＂Hidden Terminal＂ problem other than the base mode CSMA/CA. After my research on the two carrier monitoring mechanisms, I finished the software reality of random escape mechanism by using SDL and State-transfer diagrams.