In this paper, we address the problem of choosing a disk admission algorithm for continuous media streams where each stream may have a different bit rate, and more importantly, where the bit rate within a single stream may vary considerably. We evaluate several different Variable Bit Rate (VBR) disk admission control algorithms for continuous media. An algorithm which accepts too few streams under-utilizes the server resources, while an algorithm which accepts too many streams over-utilizes the resources resulting in inadequate service (i.e. missing or delayed data) to the clients. The evaluation process is based on a representative set of video streams encoded in MJPEG. We conclude that one particular algorithm, the VBR simulation algorithm, performs the best among realizable algorithms in terms of system utilization and delivery guarantees and performs close to an optimal algorithm,

In conventional commerce, customer groups with similar interests or behaviours can be observed. Similarly, customers in E-commerce naturally form groups. These groups allow the organization to provide quality of service (QoS) and perform capacity planning. From a system point of view, overall server performance can be improved and resources managed considering customer session behaviour.Previous studies have grouped customers using clustering techniques. Different data metrics have been selected as criteria for grouping, in order to analyze different problems. The limitation for these approaches is that problems are analyzed separately. In order to manage an E-commerce server well, we must analyze many related problems comprehensively rather than separately. For example, we would like to know the impact on resource usage when optimizing revenue. Thus, we must understand the differences and similarities between session groups chosen by different metrics. This paper characterizes customer groups for an E-rental business and compares customer groups created according to different criteria including services requested, navigation pattern and resource usage. A significant finding of this study shows that using each of the three criteria independently yields roughly similar results, since customers looking for similar services tend to have similar navigation pattern as well as similar server resource usage. Thus, it is sufficient to group customers in only one of these ways. Grouping customers by services requested is suggested since this method yields relatively better results and is simple to implement.

Abstract. Real-time monitoring applications for sensor networks can require high sampling rates and low-delay forwarding of the sensor values to a sink node at which the data is to be further processed. High data collection rates can be efficiently supported by aggregating data as it is being forwarded to the sink. Since aggregation requires that some sensor data be delayed at intermediate nodes, while waiting for other data to be received, a key issue in the context of real-time monitoring is how to achieve effective aggregation with minimal forwarding delay. Previous work has advocated synchronous aggregation, in which a node's position in the aggregation tree determines when it transmits to its parent. This paper shows that asynchronous aggregation, in which the time of each node's transmission is determined adaptively based on its local history of past packet receptions from its children, outperforms synchronous aggregation by providing lower delay for a given end-to-end loss rate.

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One of a Software Engineer's most important skills is the ability to define the scope of the problem and ascertain the requirements from general and vague specifications. Teaching this skill is known to be difficult and is made more complex because students are conditioned to expect that this portion of programming projects is already complete. This paper reports on experience in teaching a second year computer science class designed to give an appreciation for the need for requirements engineering and to provide students an opportunity to engage in the activity. We found that the student response was bimodal, and while some students met the challenge, more felt betrayed by the experience. We conclude that students gained the requisite knowledge using this approach but that a less traumatic approach may produce better results.