• Journal of information and communication convergence engineering
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• v.5 no.2
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• pp.93-97
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• 2007

In this paper, centralized access control and slot allocation algorithm is proposed for wireless networks. The proposed algorithm is characterized by the contention-based reservation. In order to reduce the collision probability of reservation request, the base station calculates and broadcasts the transmission probability of reservation requests, and the wireless terminal transmits its reservation request with the received transmission probability. The scheduler allocates the uplink data slots based on the successful reservation requests. Simulation results show that the proposed algorithms can provide high channel utilization, and furthermore, maintains constant delay performance in the heavy traffic environment.

• Journal of the Korean Operations Research and Management Science Society
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• v.22 no.2
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• pp.31-44
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• 1997

This paper presents an approximate analytical model to estimate the mean packet walting times at the stations in the IEEE 802, 6 subnetwork of a metropolitan area network. Each station is modeled as a two queue single server system, which serves data packets and requests from downstream stations according to the DQDB protocol. The model estimates the mean waiting time of the requests and in turn, using the discrete time work conservation law, estimates the mean waiting time for packets. Simulation experiments shows that the model accurately works even under very high traffic loads.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.12
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• pp.2981-2986
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• 2015

In this paper, there are m servers to carry out broadcasts and the scheduling problem to serve the requests with deadlines is studied. If a server broadcasts a page, then all the requests which require the page are satisfied. A scheduling algorithm shall determine which pages are broadcasted on servers at a time. Its goal is to maximize the sum of weights of requests satisfied within their deadlines. The performance of an on-line algorithm is compared with that of the optimal off-line algorithm which can see all the inputs in advance. In general, the off-line algorithms outperform the on-line algorithms. So we will use the resource augmentation analysis in which the on-line algorithms can utilize more resources. We consider the case that the on-line algorithms can use more servers in this paper.

• Journal of Computing Science and Engineering
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• v.6 no.3
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• pp.179-192
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• 2012

This paper presents novel statistical algorithms for protecting the iTrust information retrieval network against malicious attacks. In iTrust, metadata describing documents, and requests containing keywords, are randomly distributed to multiple participating nodes. The nodes that receive the requests try to match the keywords in the requests with the metadata they hold. If a node finds a match, the matching node returns the URL of the associated information to the requesting node. The requesting node then uses the URL to retrieve the information from the source node. The novel detection algorithm determines empirically the probabilities of the specific number of matches based on the number of responses that the requesting node receives. It also calculates the analytical probabilities of the specific numbers of matches. It compares the observed and the analytical probabilities to estimate the proportion of subverted or non-operational nodes in the iTrust network using a window-based method and the chi-squared statistic. If the detection algorithm determines that some of the nodes in the iTrust network are subverted or non-operational, then the novel defensive adaptation algorithm increases the number of nodes to which the requests are distributed to maintain the same probability of a match when some of the nodes are subverted or non-operational as compared to when all of the nodes are operational. Experimental results substantiate the effectiveness of the detection and defensive adaptation algorithms for protecting the iTrust information retrieval network against malicious attacks.

• Journal of Korea Multimedia Society
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• v.7 no.3
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• pp.357-367
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• 2004

In VOD systems the number of channels available to a video server is limited since the number of channels, the video server can support, is determined by the communication bandwidth of the video server. Multicast techniques such as batching, patching and batch-patching have been proposed to reduce I/O demand on the video server by sharing multicast data. In this paper, we propose a channel reservation batch-patching technique that first applies the batching technique to hot video requests and then applies the patching technique to the batches of the hot video requests. And the proposed technique reserves a part of the channel capacity of the video server for many hot video requests, so that the hot video requests can be served without defection. The performance of the proposed technique is compared with those of Patching and Batch-Patching techniques in terms of average service latency, defection rate, fairness and frame reduction rate by simulations.

• Journal of KIISE:Computing Practices and Letters
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• v.15 no.5
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• pp.400-404
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• 2009

Native Command Queueing is a technology to maximize throughput of disk system by reordering requests in its command queue. Recent S-ATA 2 standard specifies a protocol for the purpose of dealing with NCQ feature, making most vendors implementing it in their disk devices. However, the new feature, NCQ, may lead to information gap between OS and disk drive. 05 considers that disk will service I/O requests in the order as OS has dispatched. Unfortunately, it isn't true any more since NCQ would simply ignore the policy of OS and reorder the sequence OS has expected. Let us define the term as expectation-discord. Due to the discord, serious performance anomalies or starvation of requests may occur in I/O subsystem. In this paper, we confirm that the expectation-discord actually brings about starvation of requests. We propose a solution to settle it. Our solution is very simple, effective, cheap(not requiring any hardware modification) and portable across various OS. Experimental results show that our solution can balance throughput and response time very well.

• Journal of Information Management
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• v.40 no.4
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• pp.73-92
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• 2009

Generally, we used to provide ILL to users for overcoming the limited resource and satisfying user's desires for information. ILL makes library service's paradigm change from ownership to sharing. K-university Library has been providing Campus inter-library loan as ILL to users for long time and continually trying to improve the service's quality. This case study is to analysis the performance of campus inter-library loan in the past 9 years. As the related automation system was developed and upgraded, the service requests have been increasing annually. Campus inter-library loan requests were 12% of total book requests in 2001, and then were 75% of total book requests in 2008. The transaction time was reduced until 17% of 2004.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.2
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• pp.175-182
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• 2008

Context-aware service environment should provide many kinds of services according to users' requests. Users want a great variety of services. In response to their demands the service provider should make a new service every time. But making a new service every time may be inefficient even for a small number of users' requests. So, there are studies on how to efficiently support various and complex requests fFom users. In many researches, service compositions have lately attracted considerable attention. However, existing researches have mainly focused on Web services. So they are not proper to rapidly providing services in response to users' requests, especially In context-aware service environment. This paper proposes a rapid service composition using case-based reasoning. For evaluating the proposed algorithm we implement 'purchasing seTvice agent'. With this system, we compare our algorithm and the existing service composition algorithms.

• Journal of KIISE:Computer Systems and Theory
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• v.31 no.9
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• pp.527-535
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• 2004

Handling mixed workload in digital set-top box or streaming server becomes an important issue as integrated file system gets momentum as the choice for the next generation file system. The next generation file system is required to handle real-time audio/video playback while being able to handle text requests such as web page, image file, etc. Legacy file system provides only best effort I/O service and thus cannot properly support the QoS of soft real-time I/O. In this paper, we would like to present our experience in developing the file system which fan guarantee the QoS of multimedia stream. We classify all application I/O requests into two category: periodic I/O and sporadic I/O. The QoS requirement of multimedia stream could be guaranteed by giving a higher priority to periodic requests than sporadic requests. The proto-type file system(Qosfs) is developed on Linux Operating System.

• Journal of the Korea Institute of Building Construction
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• v.3 no.1
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• pp.161-168
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• 2003

This study has researched upon customers' request in the remodelling of residential buildings, and that the research results could be used as a reference data when the remodelling work is under implementation. This study also has collected the residents' upgrading request on their residential buildings, and graded the requests according to their importance. For those purposes, this study classified the problem items through classified analyses and, built the census items, based on the results. Then, the residents' requests on the residential building were presented by importance rates through coupled analysis census. Also, the importance rates have been related to the construction items which predict the importance of each construction item. The main purposes of this study are setting up the direction of the remodelling of residential buildings and predicting the customer requests in the future, even though the remodelling of residential building in Korea has not been activated yet. The research results are expected to be used as a basic data in the remodelling and construction of residential buildings.