| Summary: | 碩士 === 國立交通大學 === 資訊科學與工程研究所 === 94 === WLAN has been widely deployed over public and private areas in recent years and has become one of the most popular access technologies for mobile Internet services. Handoffs between WLAN access points (APs) that introduce packet loss and delay during a network session is one of the critical issues for real-time communication services. Unfortunately, most of the previous studies in reducing handoff latency and packet loss in WLANs rely on WLAN infrastructure upgrades, and those solutions suffer from deployment problems in the well-established WLAN hotspots. In this work, a pure station (STA)-side approach which only requires the firmware or software upgrade on WLAN STAs without the enhancements of the WLAN standards and infrastructures is presented. The proposed mechanism developed from a time division duplex concept maintains both connections with the serving and target AP simultaneously using two different medium access control (MAC) addresses. Thus, an STA can perform WLAN association, authentication, security key handshake procedures with the target AP, or further acquires an IP address in a new subnet while transmitting and receiving real-time packets through the serving AP at the same time. Simulation results demonstrate that seamless handoffs for real-time communications in secured WLANs can be easily achieved by the proposed mechanism.
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