Browsing by Author "Tsai, Ya-Hsuan"

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Fast Handoff among IEEE 802.11r Mobility Domains
(2010-07-01)
Chi, Kuang-Hui
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Tseng, Chien-Chao
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Tsai, Ya-Hsuan
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資訊工程學系
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Department of Computer Science
This paper deals with secure fast handoff among access points (APs) of different IEEE 802.11r mobility domains. We leverage standard IEEE 802.11i mechanisms to let a station preauthenticate and establish a pairwise transient key with some target AP beforehand. Upon reassociation, the new AP aware of the preauthenticated station can thus complete handoff sooner than would otherwise be required. In order to resolve target APs timely, we introduce a location server that maintains network topology of an autonomous system covering multiple mobility domains. The location server assesses with which AP(s) the mobile station may reassociate next using its migration tendency. Accordingly the station is instructed to preauthenticate with fewer potential next APs than unnecessary. Performance discussions indicate that our proposal is effective in practice. Our approach is not only complementary to emerging IEEE 802.11r-based techniques but also useful to any network-layer fast handoff schemes for streamlined communication.
Modeling Resilience Enhancement Strategies for International Express Logistics
(2013)
Chen, Cheng-Chieh (Frank)
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Feng, Cheng-Min
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Tsai, Ya-Hsuan
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Wu, Pei-Ju
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運輸與物流管理系註：原交通所+運管所
International express is a most time-sensitive industry, and members of this industry must be able to respond to disruptions quickly to ensure service quality and to avoid a loss of their competitiveness with other logistics service providers. Instead of a method that arbitrarily makes rushed decisions during the postdisruption phase, this paper describes a method for quantifying and optimizing resilience strategies based on concepts of integrated resource assignment, regardless of where the available resources are located in the logistics network studied or how much capacity can be rented from others. The study started with the use of a typical transportation network modeling approach and then incorporated nonlinear time-dependent cargo value functions into a multiobjective mixed-integer nonlinear programming problem. A set of optimal actions from resilience strategies, such as the selection of alternative routes, switching of shipping modes, rental of other carriers' capacities, reallocation of local trucks, and prioritization of the order of shipments because of limited capacities, was considered. Decisions should be based on overall trade-off considerations and, at the same time, joint maximization of the product of the total time-dependent cargo value and the corresponding throughput and minimization of the costs incurred with resilience enhancement strategies.