In future mobility support will require handling roaming in heterogeneousaccess networks. In order to enable seamless roaming it is necessary tominimize the impact of the vertical handoffs. Localized mobility managementschemes such as FMIPv6 and HMIPv6 do not provide sufficient handoffperformance, since they have been designed for horizontal handoffs. In thispaper, we propose the SafetyNet protocol, which allows a Mobile Node to performseamless vertical handoffs. Further, we propose a handoff timing algorithmwhich allows a Mobile Node to delay or even completely avoid upward verticalhandoffs. We implement the SafetyNet protocol and compare its performance withthe Fast Handovers for Mobile IPv6 protocol in our wireless test bed andanalyze the results. The experimental results indicate that the proposedSafetyNet protocol can provide an improvement of up to 95% for TCP performancein vertical handoffs, when compared with FMIPv6 and an improvement of 64% overFMIPv6 with bicasting. We use numerical analysis of the protocol to show thatits signaling and data transmission overhead is comparable to Fast Mobile IPv6and significantly smaller than that of FMIPv6 with bicasting.
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