In this paper, we propose a cache invalidation scheme called Invalidation by Absolute Validity Interval (IAVI) for mobile computing systems. In IAVI, we define an absolute validity interval (AVI), for each data item based on its dynamic property such as the update interval. A mobile client can verify the validity of a cached item by comparing the last update time and its AVI. A cached item is invalidated if the current time is greater than the last update time plus its AVI. With this self-invalidation mechanism, the IAVI scheme uses the invalidation report to inform the mobile clients about changes in AVIs rather than the update event of the data items. As a result, the size of the invalidation report can be reduced significantly. Through extensive simulation experiments, we have found that the performance of the IVAI scheme is significantly better than other methods such as bit sequence and timestamp.

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In this paper, we present the Buffer Sens(tive Rate-Based (BSRB) algorithm, which provides a fair scheduling scheme to serve video playback requests, while maximizing the performance of individual playback. In BSRB, the amount of bandwidth allocated to serve a video request depends on the buffer leve[ of the req~estingclient, and the expected and minimum bandwidth requirements of the video. By maintaining a high video buffer level at a client, the quality of the playbacks can be maintained and its performance will be more adapJive to the changing playback conditions. By employing the rate-based policy in BSRB, the performance of the requests is less affected by the poor performance ofa single client and hence fair services can be provided to the clients.

In this paper, we propose the Adaptive Buffer Sensitive (ABS) algorithm for scheduling the transmission of video packets from multiple video streams in a mobile multimedia system. Two important considerations in the design of the ABS are: .(1) to maximize the mobile network bandwidth utilization and at the same time to minimize the impact of transient overloading on video playback; and (2) to minimize the impact of a video playback by other video requests. The second objective is very important to mobile multimedia systems since the clients may request videos with great differences in workload characteristics. In the ABS, the allocation of network ' bandwidth to serve client requests is divided into two phases.Firstly, each client receives equal share of network bandwidth or at least enough bandwidth to support the average playback of its requested video. Secondly, the extra bandwidth after the first allocation will be distributed to clients based on its playback status, i.e., buffer playback duration, to deal with the problem of transient overloading. A selective packet transmission scheme is adopted in ABS to deal with heavy overloading situation.