641995
An Admission Control Scheme for Predictable Server Response Time for Web Accesses
The diversity in web object types and their resource requirements contributes to the unpredictability of web service provisioning. In this paper, an eÆcient admission control algorithm, PACERS, is proposed to provide di erent levels of services based on the server workload characteristics. Service quality is ensured by periodical allocation of system resources based on the estimation of request rate and service requirements of prioritized tasks. Admission of lower priority tasks is restricted during high load periods to prevent denial-of-services to high priority tasks. A doublequeue structure is implemented to reduce the e ects of estimation inaccuracy and to utilize the spare capacity of the server, thus increasing the system throughput. Response delays of the high priority tasks are bounded by the length of the prediction period. Theoretical analysis and experimental study show that the PACERS algorithm provides desirable throughput and bounded response delay to the prioritized tasks, without any signi cant impact on the aggregate throughput of the system under various workload.
14347517
A Tiered System for Serving Differentiated Content
Contemporary Web sites typically consist of front–end Web servers, application servers, and back-end information systems such as database servers. There has been limited research on how to provide overload control and service differentiation for the back-end systems. In this paper we propose an architecture called tiered service (TS) for these purposes. In TS, there are several heterogeneous back-end systems to serve the Web applications. The Web applications communicate with a routing intermediary to intelligently route the queries to the appropriate back-end servers based on various policies such as client profiles and server load. In our system the back ends may store different qualities of data; lower quality data typically requires less overhead to serve. The main contributions of this paper include (i) a tiered content replication scheme that replicates tiered qualities of data on heterogeneous back ends with different capacity to satisfy clients with diverse requirements for latency and quality of data, and (ii) an application-transparent query routing architecture that automatically routes the queries to the appropriate back ends. The architecture was implemented in our test bed, and its performance was benchmarked. The experimental results demonstrate that TS offers significant performance improvement.
8488192
Session-based overload control in QoS-aware Web servers
With the explosive use of the Internet, contemporary Web servers are susceptible to overloads and their services deteriorate drastically and often cause denial of services. In this paper, we propose two methods to prevent and control overloads in Web servers by utilizing the session-based relationship among HTTP requests. We first exploited the dependence among session-based requests by analyzing and predicting the reference patterns. Using the dependency relationships, we have derived traffic conformation functions that can be used for capacity planning and overload prevention in Web servers. Second, we have proposed a dynamic weighted fair sharing (DWFS) scheduling algorithm to control overloads in Web servers. DWFS is distinguished from other scheduling algorithms in the sense that it aims to avoid processing of requests that belong to sessions that are likely to be aborted in the near future. The experimental results demonstrate that DWFS can improve server responsiveness by as high as 50% while providing QoS support through service differentiation for a class of application environment.
22537497
ACES: An efficient admission control scheme for QoS-aware web servers
The unpredictability of server response performance hinders the advance of new application on the Internet. In this paper, we present an efficient admission control algorithm, ACES, based on the server workload characteristics. The admission control algorithm ensures the bounded response time from a web server by periodical allocation of system resources according to the resource requirements of incoming tasks. By rejecting requests exceeding server capacity, the response performance of the server is well maintained even under high system utilization. The resource requirements of tasks are estimated based on their types. A double-queue structure is implemented to reduce the effects caused by estimation inaccuracy, and to exploit the spare capacity of the server, thus increasing the system throughput. The admission control algorithm can be used for server overload control and for QoS provisioning of service differentiating Internet servers. Response delays of accepted tasks are bounded by the desired predefined time period. Theoretical analyses and experimental studies show that the ACES algorithm provides desirable throughput and bounded response delay to the tasks, without any significant impact on the aggregate throughput performance of the system under various workload situations.
16884480
Overload control in QoS-aware web servers
With the explosive use of Internet, contemporary web servers are susceptible to overloads during which their services deteriorate drastically and often lead to denial of services. Overloads are of more serious concerns for QoS-aware servers. Evaluation of performance of QoS-aware servers in terms of the number of request completion is not very meaningful. A better measure would be the number of completed sessions. In this paper, we proposed two methods to prevent and control overloads in web servers by utilizing session-based relationship among HTTP requests. We first exploited the dependence among session-based requests by analyzing and predicting the reference patterns. Using the dependency relationships, we have derived traffic conformation functions that can be used for capacity planning and overload prevention in web servers. Second, we have proposed a dynamic weighted fair sharing (DWFS) scheduling algorithm to control overloads in web servers. DWFS is distinguished from other scheduling algorithms in the sense that it aims to avoid processing of requests that belong to sessions that are likely to be aborted in the near future. The experimental results demonstrate that DWFS can improve server responsiveness by as high as 50% while providing QoS support through service differentiation for a class of application environment.
4274853
Lifting based discrete wavelet transform architecture for JPEG2000
A lifting based 1-D discrete wavelet transform (DWT) core is proposed. It is re-configurable for 5/3 and 9/7 filters in JPEG2000. Folded architecture is adopted to reduce the hardware cost and achieve the higher hardware utilization. Multiplication is realized in hardwired multiplier with coefficients represented in canonic signed-digit (CSD) form. It is a compact and efficient DWT core for the hardware implementation of JPEG2000 encoder.
31295380
Intelligent Agents for Mobile and Embedded Devices
The pervasive computing environments of the near future will involve the interactions, coordination and cooperation of numerous, casually accessible, and often invisible computing devices. These devices, whether carried on our person or embedded in our homes, businesses and classrooms, will connect via wireless and wired links to one another and to the global networking infrastructure. The result will be a networking milieu with a new level of openness. The localized and dynamic nature of their interactions raises many new issues that draw on and challenge the disciplines of agents, distributed systems, and security. This paper describes recent work by the UMBC Ebiquity research group which addresses some of these issues.
24161285
Effects of Local-Lag Mechanism on Task Performance in a Desktop CVE System
Consistency maintenance is a kernel problem in Collaborative Virtual Environment (CVE) research. The approaches used in Networked Virtual Environments (e.g., DR algorithm) could not be used in CVEs, for they could not prevent short-term inconsistency. Therefore, local-lag mechanism has been proposed to eliminate short-term inconsistency in CVEs. Choosing a proper lag value is a key problem in local-lag mechanism. This paper studied the effects of lag value (0ms–900ms) on task performance in a desktop CVE system. Experimental results indicate that the effect of lag value on task performance is not linear. The effect could be separated into four segments by three dividing points: 150ms, 300ms and 600ms. Lag has no effect on task performance while ranging from 0ms to 150ms. From 150ms to 300ms, lag slightly affects task performance. Lag deteriorates task performance seriously while ranging from 300ms to 600ms. When lag is longer than 600ms, the task cannot be accomplished sometimes.
15665012
Progressive auction based resource allocation in service-oriented architecture
The emerging paradigm of distributed Web services has promised seamless business integration across the Internet that shares not only computing power but also applications. One major challenge is resource allocation to each end user in an economically efficient and low latency manner. A common solution is proportional sharing where each user gets his resource in proportion to the predetermined weight. However, this does not allow users to differentiate the value of their services and to dynamically adjust the weights. A resource reservation mechanism may improve the information and service sharing but usually introduces a high latency. In this paper, we propose a progressive auction based market mechanism for resource allocation that allows user differentiation of the service value and ensures the resource acquisition latency to be limited only to the communication delay in service-oriented architecture (SOA) systems. We present a service sharing prototype for selecting services for further business process composition or solution creation and show experimental results on the formation of reliable user ranking in resource sharing through the progressive auction.
15293705
Design and evaluation of a multi-agent collaborative Web mining system
Most existing Web search tools work only with individual users and do not help a user benefit from previous search experiences of others. In this paper, we present the Collaborative Spider, a multi-agent system designed to provide post-retrieval analysis and enable across-user collaboration in Web search and mining. This system allows the user to annotate search sessions and share them with other users. We also report a user study designed to evaluate the effectiveness of this system. Our experimental findings show that subjects' search performance was degraded, compared to individual search scenarios in which users had no access to previous searches, when they had access to a limited number (e.g., 1 or 2) of earlier search sessions done by other users. However, search performance improved significantly when subjects had access to more search sessions. This indicates that gain from collaboration through collaborative Web searching and analysis does not outweigh the overhead of browsing and comprehending other users' past searches until a certain number of shared sessions have been reached. In this paper, we also catalog and analyze several different types of user collaboration behavior observed in the context of Web mining.