The Research Of Mobile VOIP Handoff And APs Load Balance In Wireless Local Area Networks

Mobile VOIP handoff and load unbalance among APs are common issues on the research of WLAN. The Quality of Service correlates with these two issues. It may cause huge handoff latency and high packets dropping rate during a mobile node implements handoff procedure in WLAN; in addition, the AP with the strongest signal will be selected by the mobile node to re-association with, which may cause load differences among APs, thus, the handoff will influence load balance among APs. In order to solve these two issues, this paper will conduct related research and simulate with OPNET. The research contents are:(1) Give a brief introduction about the issues of handoff and load unbalance among APs which is caused by handoff. Summarize current research situations about the two issues, and then introduce related technologies.(2) In order to solve the problems of huger handoff latency and higher packet dropping rate of current handoff technologies, a new handoff technology, i.e. pre-disposal for handoff is proposed. In this handoff technology, pre-divert and pre-recover packets will be implemented based on channels scanning when the pre-disposal condition appeared before handoff. In this handoff technology, not only the scanning phase was eliminated during handoff, but also the packets destined for MN were pre-transferred to destination AP from current AP, thus, this technology reduces the influence on real-time applications, and achieves the goal of lower packets dropping and smaller handoff latency.(3) In order to solve the problem of load balance feint which caused in current load balance technologies, a new load balance technology, i.e. a hierarchy load balance technology is proposed. In this load balance technology, appropriate mobile nodes will be selected based on compartmentalizing APs to be a layer structure, and then load balance will be extended from regional to entire system, thus, this technology eliminate the phenomenon of load balance feint and enhances load balance exponential and throughput. (4) Give a brief introduction of OPNET, and implement simulation on the handoff technologies and the load balance technologies. From the analysis and comparison of the experiment results, we can educe the conclusion that the pre-disposal for handoff technology can reduce handoff latency and packet dropping rate more effectively compared with current handoff technologies; the hierarchy load balance technology can resolve the load unbalance problem among APs more effectively compared with current load balance technologies.