Study Of Fast Handoff Mechanism Based On Ap In Wlan

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.