| Summary: | 碩士 === 國立臺灣大學 === 資訊工程學研究所 === 94 === In recent years, network technologies such as WLAN, GPRS, and 3G are getting more and more popular. There is high probability that signal coverage of these coexisting networks overlaps with each other. For a user roaming among these networks, it is desirable that his or her mobile device can have anytime connectivity, and therefore vertical handoff becomes an important issue.
To achieve high performance, a user may want to choose the best network to connect to. However, properties such as signal coverage area, maximum data rate, monetary cost, and power consumption on end devices vary largely among these networks. Moreover, different types of services require various combinations of these properties. While most vertical handoff schemes are based on single optimization policy in which service difference is not taken into consideration, we propose a service-based handoff decision model. Through this decision model, weight of the parameters in the cost function is adjustable based on the type of service in use, and therefore we can make a more appropriate decision on network selecting.
In recent research, mobile IP is a generally used handoff scheme. However, to facilitate vertical handoff, help from a home agent and a foreign agent is required in the mobile IP scheme, which induces overloading on the agents themselves. In our handoff scheme, only with mobile host itself can handoff be realized, hence the overall handoff scheme is simplified. Moreover, through our implementation, handoff latency can probably be even shorter than that in the mobile IP scheme.
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