• Journal of KIISE:Databases
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• v.30 no.6
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• pp.606-628
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• 2003

Recently, there have been many research efforts reported in the literature that focus on the cache consistency problems of mobile clients resulting from their frequent disconnections with a server in mobile environments. To cope with this problem, a number of methods based on the invalidation report scheme has been proposed. However, these proposed methods are sensitive to the disconnection time of mobile clients and independent of the frequency of data updates in the server. As a result, although the number of data updated in the server is small, the traditional methods can not guarantee the cache consistency of mobile clients if their disconnection time is over the time period the invalidation report is allowed to cover. In this paper, we propose an efficient cache consistency method called CCI(Cost-based Cache Invalidation) for mobile clients that take into account not only the disconnection time but also the frequencies of data updates in the server We also present an in-depth experimental analysis by comparing CCI method with BT(Broadcasting Time stamp) method based on Invalidation Report.

• Journal of KIISE:Computing Practices and Letters
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• v.7 no.1
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• pp.24-37
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• 2001

This paper deals with our experience for the design and implementation of Transport and Session managers in the Integrated Streaming Service Architecture (IS SA) that was developed by the authors. The ISSA is a streaming framework that allows to develop integrated multimedia streaming applications such as VOD system in unicast/multicast and real-time broadcastOive-cast). It also facilities standard real-time transport protocols such as RTp(Real-Time Transport Protocol)/RTCP(Real-time Control Protocol) and RTSP(Real-Time Streaming ProtocoD that allows to user openness. The ISSA supports diverse media fonnats and is independent from underlying networks and operating systems, and compatible with the global real-time multimedia database system (BeeHive) so that streaming media are efficiently retrieved, stored, and serviced. The role of the Transport Manager is to do packetization and depacketization for the different types of multimedia data and delivers the packetized media data in real-time. The Transport Manager uses RTP protocol. The role of the Session Manager is to establish and control the media channel by using RTSP protocol and to deliver the database transactions for the multimedia database by using RTTP(Real-Time Transaction Protocol) protocol. Both the Transport and Session Manager are doing their functions through the network interface in the ISSA that allows developers to various network programming interfaces and provides flexibility to the system.

• Journal of KIISE:Software and Applications
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• v.34 no.1
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• pp.40-51
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• 2007

To improve academic achievement, the most students not only participate in regular classes but also take various extra programs such as private lessons, private institutes, and educational TV programs. In this paper, we propose a data mining approach to identify which studying methods or usual life patterns during a school vacation affect changes in the academic achievement. First, we derive various studying methods and life patterns that are thought to be affecting changes in the academic achievement during a school vacation. Second, we propose the method of transforming and analyzing data to apply them to decision trees and association rules, which are representative data mining techniques. Third, we construct decision trees and find association rules from the real survey data of middle school students. We have discovered four representative results from the decision trees. First, for students in the higher rank, there is a tendency that private institutes give a positive effect on the academic achievement. Second, for the most students, the Internet teaming sites nay give a negative effect on the achievement. Third, private lessons that have thought to be making a large impact to the achievement, however, do not make a positive effect on the achievement. Fourth, taking several studying methods in parallel nay give a negative effect on the achievement. In association rules, however, we cannot find any meaningful relationships between academic achievement and usual life patterns during a school vacation. We believe that our approach will be very helpful for teachers and parents to give a good direction both in preparing a studying plan and in selecting studying methods during a school vacation.

• Journal of Broadcast Engineering
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• v.12 no.2
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• pp.80-92
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• 2007

IPTV Services that is representative union service of broadcasting and telecommunication need guarantee of QoS, efficiency of multicasting, and hish bandwidth on the network. Because typical TDM based metro transport network was designed by transporting fixed voice traffic with stable and recovering method, it has a defect of bottleneck and a waste of bandwidth for acceptance of data traffic with burst feature and then all of data are treated equally at the transport network because it cannot classify between advanced high end service and best effort low end service. for completely resolving this kind of problem about increasing burst traffic and QoS issues, firstly we need to new design for transport network. This paper presents transformation method from TDM based metro transport network to packet based transport network and advantage and effectiveness of packet based transport network and also indicates technical factor and characters about method of packet transport system. As a result of research, the Packet Transport System, which is a transmission network for packet delivery, take in not only a specific character of legacy TDM but QoS, Multicast and high bandwidth, then, it is able to keep an effective bandwidth and a stabilized performance of packet transmissions. Additionally, if a fault be occurred on an optical link, the system is able to guarantee a differential QoS by an each service class using an algorithm to make certain of a traffic existence and contain a protective mechanism.

• Journal of Digital Convergence
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• v.11 no.5
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• pp.299-305
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• 2013

Internet Data is hugely increased for high quality multimedia services and the related techniques is also developed rapidly. This paper is aimed to develop integrated internet data and Digital-Television receiving system with high performance and optimization, which is obtained by one-board integration with load control. It is applicable to various devices like computer, set-top box, home multimedia gateway etc. The performance is proved by evaluation test. It shows that the developed device can be TV tuner and internet AP for more robust multimedia services.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.187-194
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• 2011

In this paper, JPEG(Joint Photographic Experts Group) image data video decoding technique is presented, it is Huffman decoding method and fractal image method which is very complexive algorithm and the time required much it to implement this method and the first image is decoded to video frame image. This have defect of overlap decoding and transport work because of impossible to represent objective value of resemblance. The proposed method was calculated the mathematical absolute image resemblance and simplify the moving picture process to reducing the step of moving picture codefying. The results show that smoothed moving picture compared recent methods.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.4
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• pp.183-188
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• 2021

Collaborative filtering based recommender systems are currently indispensable function of commercial systems in various fields, being a useful service by providing customized products that users will prefer. However, there is a high possibility that the prediction of preferrable products is inaccurate, when the user's rating data are insufficient. In order to overcome this drawback, this study suggests a stepwise method for prediction of product ratings. If the application conditions of the prediction method corresponding to each step are not satisfied, the method of the next step is applied. To evaluate the performance of the proposed method, experiments using a public dataset are conducted. As a result, our method significantly improves prediction and precision performance of collaborative filtering systems employing various conventional similarity measures and outperforms performance of the previous methods for solving rating data sparsity.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1995.09a
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• pp.171-183
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• 1995

이 논문은 특정 기기산업의 기술적 구조와 현황의 분석 및 파악을 위한 제 품.기술 관련도라는 새로운 개념을 제시한다. 제품.기술 관련도란 분석대상산 업의 주요 제품들을 도출하고 각각의 제품에 관련된 기술들을 부품기술을 중심으로 파악하여 매트릭스의 형태로 도시한 것을 의미한다. 제품. 기술 관 련도상의 제품에 대해서는 전문가의 의견에 의해 측정된 기술수준과 주된 획득방법(국산화율)을 파악한다. 한편, 제품에 관련되는 기술은 기본적인 기능을 발휘하는 제품의 생산에 소요되는 기본기술과 제품의 성능향상을 위하여 필요한 성능관련기술 등으로 구분하여 분석된다. 이러한 제품.기술 관련도는 국내 기기산업의 각 분야별 기술수준, 부품군의 기술수준 등을 도출하고 상호관련성을 파악하는데 유용한 방법으로 활용될수 있다. 특히 제품군과 부품군간의 관계 도출, 기술수준 혹은 구산화율이 낮은 제품에 관련된 부품 및 기술의 파악, 국내의 기술수준이 낮은 부품에 관련되는 제품 및 제품군, 제품의 성능이 향상에 관련된 기술등의 파악이 용이하다. 본 논문에서는 제품.기술 관련도를 한국의 정보통신기기산업에 시험적으로 적용하여 정보통신 기기분야의 제품 및 기술 구조, 그리고 경쟁력을 분석하여 보았다. 국내 정보통신기기산업의 전체적인 기술수준은 자체적으로 기술을 보유하고 있으나 성능면에서 매우 미약한 소화 및 모방 단계의 수준이라고 해석할수 있다. 한편 부품기술은 아직도 소화및 모방단계에 머무르고 있으며, 개별소자와 수동부품의 기술수준이 매우 낮게 나타났다. 분야별로 볼 때 무선통신기기, 방송기기, 정보기기의 순으로 기술수준이 낮으며, 무선통신기기분야이 발전을 위해서는 고주파 부품의 기술 발전이 선행되어야 할것으로 보인다.라 제시된 외주위탁 전략과 현재의 외주위 탁 전략이 일치할 때 정보 시스템에 대한 사용자 만족도가 보다 높은 것으 로 나타났다. 할 수 있는 효율적인 distributed system를 개발하는 것을 제시하였다. 본 논문은 데이타베이스론의 입장에서 아직 정립되어 있지 않은 분산 환경하에서의 관계형 데이타베이스의 데이타관리의 분류체계를 나름대로 정립하였다는데 그 의의가 있다. 또한 이것의 응용은 현재 분산데이타베이스 구축에 있어 나타나는 기술적인 문제점들을 어느정도 보완할 수 있다는 점에서 그 중요성이 있다.ence of a small(IxEpc),hot(Tex> SOK) core which contains two tempegatlue peaks at -15" east and north of MDS. The column density of HCaN is (1-3):n1014cm-2. Column density at distant position from MD5 is larger than that in the (:entral region. We have deduced that this hot-core has a mass of 10sR1 which i:s about an order of magnitude larger those obtained by previous studies.previous studies.업순서들의 상관관계를 고려하여 보다 개선된 해를 구하기 위한 연구가 요구된다. 또한, 준비작업비용을 발생시키는 작업장의 작업순서결정에 대해서도 연구를 행하여, 보완작업비용과 준비비용을 고려한 GMMAL 작업순서문제를 해결하기 위한 연구가 수행되어야 할 것이다.로 이루어 져야 할 것이다.태를 보다 효율

• Information and Communications Magazine
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• v.13 no.8
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• pp.82-92
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• 1996

다양한 형태의 서비스에 대한 수요가 급증하면서 한정된 궤도와 주파수를 이용한 위성통신기술에 대한 효율적인 주파수 활용기술과 새로운 서비스의 개발이 필요하게 되었다. 위성통신시스템의 개발초기에 가장 널리 사용되었던 C대역은 거의 포화상태에 이르렀고, Ku대역도 역시 머지않아 포화상태에 이를 전망이다. 기존의 위성시스템은 주로 방송이나 기업간 사설데이타등의 서비스를 공급해왔는데, 최근에는 개인사용자를 위한 고속 대용량 데이터, 영상, 음성등의 멀티미디어 통신서비스의 공급의 필요가 대두되면서, 광대역통신을 할 수 있는 Ka대역을 이용한 위성통신시스템의 개발이 활발히 진행되고 있다. 서론부에서는 위성통신 주파수의 C대역, Ku대역, Ka대역별 이용현황이 간략히 소개되고, II장에서는 Ka대역의 전파특징에 대하여, III장에서는 Ka대역의 위성시스템 활용기술 및 서비스 발전방향에 관한 각국의 현황을 파악하고, IV장 결론에서는 국내 위성서비스를 위한 연구활동의 발전방향에 관한 의견을 제시하였다.

• ETRI Journal
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• v.5 no.1
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• pp.3-9
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• 1983

The pathsearching method in switchingmatrix of an electronic switching system depends upon the structure and function of the system. In this paper, an efficient way to construct the switching matrix and a pathsearching method under the full distributed traffic theory in an wideband switching system, which can control not only normal telephone call, but also TV telephone, data communication, videotex and sound, is proposed. And the effectiveness of the method is shown through an example of the pathsearching simulation program.