【作者】 罗超；

【导师】 李凤华； 吴振强；

【作者基本信息】 西安电子科技大学 ， 计算机系统结构， 2010， 硕士

【摘要】 近年来,由于WLAN技术的迅速发展,在WLAN中大规模部署多媒体实时业务已经成为WLAN发展的趋势。实时业务对切换过程中的时延非常敏感,现有的基于IEEE 802.11协议的WLAN很难满足其要求。因此,尽可能的减小切换过程中的时延具有重要的现实意义。WLAN切换时延由扫描阶段时延、认证阶段时延、关联阶段时延三部分组成。现有的研究成果表明：扫描阶段所引起的时延最长。IEEE组织于2008年发布的802.11r快速切换标准虽然改善了STA与AP的关联过程,却没有规定STA(Station)扫描AP(Access point)的方式,因此并没有从根本上解决切换时延的问题。基于此,论文的研究工作主要围绕如何有效减小扫描阶段时延进行。论文通过对基于802.11协议的无线局域网快速切换的理论与技术的深入研究,并针对无线局域网中基于STA的传统快速切换机制在效率、QoS等方面的缺陷,结合邻居图算法提出了一种基于AP的快速切换方案。论文主要针对以下几个方面进行研究：(1)由AP取代STA完成对切换目标AP的选择,在改善传统切换机制的效率的同时,有效减少了STA的工作负担；(2)结合邻居图算法提出了在AP构建邻居AP信息表的思想,从而减小AP选择目标AP时扫描信道的数量,提高选择目标AP时的工作效率；(3)添加切换决策触发条件,在STA触发切换之前,提前进行目标AP的决策,从而将扫描阶段提前,有效减小切换过程中的时延；最后,论文利用网络仿真工具OPNET对所提出的方案进行了仿真,并根据该方案设计了WLAN原型实验平台。仿真和实验结果表明：基于AP的快速切换方案能够有效减小快速切换过程中的时延。更多还原

【Abstract】 Recently, with the development of WLAN technology, the massive deployment of multimedia real-time service in WLAN has become the trend in development. Handoff latency is sensitive to real-time service. However, the IEEE 802.11 protocol is hard to meet the demand of latency. Therefore, it is very important to reduce the handoff latency as much as possible.The handoff latency of the WLAN consists of the latency of scan phase, the latency of authentication phase, and the latency of association phase. Previous studies have shown that the latency of the scan phase account for the most of the total latency.802.11r protocol issued by IEEE in 2008 has improved the association between STA and AP, but it doesn’t define the method how to scan AP, which does not solve the handoff latency fundamentally. For this, the research work of this thesis mainly focuses on how to reduce the latency of scan phase effectively.The thesis does some research on the theory and mechanism of WLAN fast handoff based on IEEE802.11 protocol, in allusion to the limitation of efficiency, QoS and security of STA-based fast handoff mechanism for WLAN, by integrating Neighbor Graphs algorithm, proposing a novel AP-based security fast handoff scheme, including the follows:1) AP completes the choose of target AP instead of STA, which not only improves the handoff efficiency but also reduce the workload of STA;2) Proposing the ideal of building the AP infomation table by integrating Neighbor Graphs algorithm, which not only reduce the number of scanning channel when chosing target AP, but also improves the working efficiency;3) By adding handoff decision triggering threshold and utilizing dynamic Neighbor AP information table to choose the target AP in advance, bringing forward scanning stage before handoff triggering stage, which reduce the handoff latency and increase the fast handoff efficiency.Finally, the proposed mechanism is simulated by network simulation tool—OPNET, which the WLAN platform environment is built based on. The simulation and experiment results show that the fast handoff mechanism based on AP can reduce the handoff latency effectively.更多还原