Wireless channels vary drastically over time and mobility adds further difficulties to the engineering problem of providing stable and robust communication performance. Handovers occur regularly in mobile environments and the increasing heterogeneity of present networks leads to the requirement for seamless vertical handovers. An important practical problem is the lack of a generic interface that enables applications, such as a vertical handover decision engine, to retrieve comparable link-layer information independently of the deployed technology or the used software and hardware platform. In this paper we propose the Unified Link-Layer API (ULLA) as a solution to this problem. We describe its architecture, how it can be utilized for vertical handover scenarios and introduce our Linux prototype. The prototype performance proves that ULLA is appropriate for mobility management.
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