• Journal of KIISE:Software and Applications
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• v.26 no.8
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• pp.974-987
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• 1999

이동 컴퓨팅 환경에서 자주 접근하는 데이터에 대한 캐싱은 무선 채널의 좁은 대역폭에서 경쟁을 줄일 수 있는 유용한 기술이다. 그러나, 트랜잭션 캐시 일관성을 지원하는 전통적인 클라이언트/서버 전략은 클라이언트와 서버간에 많은 양의 통신을 필요로 하기 때문에 이동 클라이언트/서버 컴퓨팅 환경에서는 적절하지 않다. 본 논문에서는 브로드캐스트-기반 캐시 무효화 정책을 사용하면서 트랜잭션 캐시 일관성을 지원하는 OCC-UTS (Optimistic Concurrency Control with Update TimeStamp) 프로토콜을 제안한다. 접근한 데이터에 대한 일관성 검사 및 완료 프로토콜은 캐시 무효화 과정의 내부 과정으로 완전 분산 형태로 효율적으로 구현되며, 일관성 체크의 대부분이 이동 클라이언트에서 수행된다. 또한, 분석 모델에 기반한 성능 비교를 통해, 본 논문에서 제안하는 OCC-UTS 프로토콜이 다른 경쟁 프로토콜보다 높은 트랜잭션 처리율을 얻으며, 데이터 항목을 자주 접근하면 할수록 지역 캐시를 사용하는 OCC-UTS 프로토콜이 더 효율적임을 보인다. 이동 클라이언트의 접속 단절에 대해서는 무효화 브로드캐스트 윈도우를 크게 하여 접속 단절에 적절히 대처할 수 있다.Abstract In a mobile computing environment, caching of frequently accessed data has been shown to be a useful technique for reducing contention on the narrow bandwidth of the wireless channels. However, the traditional client/server strategies for supporting transactional cache consistency that require extensive communications between a client and a server are not appropriate in a mobile client/server computing environment. In this paper, we propose a new protocol, called OCC-UTS (Optimisitic Concurrency Control with Update TimeStamp), to support transactional cache consistency in a mobile client/server computing environment by utilizing the broadcast-based solutions for the problem of invalidating caches. The consistency check on accessed data and the commitment protocol are implemented in a truly distributed fashion as an integral part of cache invalidation process, with most burden of consistency check being downloaded to mobile clients. Also, our experiments based on an analytical model substantiate the basic idea and study the performance characteristics. Experimental results show that OCC-UTS protocol without local cache outperforms other competitor protocol, and the more frequent a mobile client accesses data items the more efficient OCC-UTS protocol with local cache is. With respect to disconnection, the tolerance to disconnection is improved if the invalidation broadcast window size is extended.

• Journal of the Korea Convergence Society
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• v.3 no.1
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• pp.1-5
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• 2012

In this paper, we developed real-tim video transfer system based on Android environment. After android device with embedded camera capture images, it sends image frames to video server system. And also video server transfer the images from client to peer client. Peer client also implemented on android environment. We can send 16 image frames per second without any loss in 3G mobile network environment.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.885-888
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• 1995

Virtual Manufacturing System(VMS) is a computer model that represents the precise and whole structure of manufacturing system and simulates their physical and logical behavior in operation. In this paper, a real time simulation for the virtual factory is proposed to integrate a process planning with scheduling under distributed environments. In order to communicate the information under distributed environment, weuse a sever/client concept and socket program. the VMS is implemented on the internet environment.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.579-582
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• 2004

File share system in client/server method requires server of High performance and capacity and this server is very expensive and management is complex and is been influenced much to flatform. Also, extension of correct memory or hard drive etc. causes a lot of expenses to server. While, may minimise human who happen by buying high-capacity server by dispersing file public ownership way unuse expensive server in client/serve. way who put up files in PC(client) to a sewer and manage files and make use of only client computers because public ownership of data and government official in P2P(peer to peer) environment, waste of material resources. Many people are interested to P2P by such reason, researches that use P2P to connection field to be Moba that have Gakgwangbatgo current are gone vigorously.

• The Journal of the Korea institute of electronic communication sciences
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• v.1 no.1
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• pp.36-41
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• 2006

P2P file sharing environment of the wireless environment of the client and server without using expensive, unlike the way from client to server, personla, you can minimize the waste of material resources. Operations also increase the number of users, such as increased collaboration and provide benefits.

• Journal of the Korea Society of Computer and Information
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• v.5 no.4
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• pp.161-165
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• 2000

In the past, the mutual saving finance service was managed by the Packages which consisted of the softwares managing data under the text mode environment. The data was mostly managed at only one place. So it becomes very important things that we efficiently deal various services and systematically support public-relation activities and efficient managements of a security mortgage. Therefor. we develope the system which efficiently manages customer service and management of a security mortgage by using GIS under the Client/server environment.

• Journal of KIISE:Databases
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• v.31 no.5
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• pp.457-467
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• 2004

The efficiency of algorithms managing data caches has a major impact on the performance of systems that utilize client-side data caching. In these systems, two versions of data can be maintained without an additional space overhead of the server by exploiting the replication of data in the server's buffer and clients' caches. In this paper, we present a new cache consistency algorithm employing versions: Two Versions-Callback Locking (2V-CBL). Our experimental results indicate that 2V-CBL provides good performance, particularly outperforms a leading cache consistency algorithm, Asynchronous Avoidance-based Gache Consistency, when some clients run only read-only transactions.

• Journal of Korea Spatial Information System Society
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• v.11 no.4
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• pp.56-64
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• 2009

As the Internet has been improved to Web 2.0, it introduces new approaches including Rich Internet Application (RIA) technology such as Flash, AJAX, Silverlight, etc. The RIA which is platform independent technology allows applications to provide rich client-side interfaces, and allows the browser to interact with users without communication to server. In this paper, we propose a method of spatial data service based on RIA technology. Internet map service using spatial data generally requires rich client-side interfaces and various interactions. These features can be provided by the RIA. The proposed method uses Flash developed by Macromedia as RIA technology. It can be applicable on any platform including mobile environment. The spatial data server makes Flash file known as SWF (Shock Wave File) with manipulation code for map and spatial data that is requested by user, and send it to the web browser. Once the web browser receives a SWF, client SWF manipulates user interactions, such as zooming and panning, without communication with server. Experiments that execute the application on various web browsers including mobile web browser and measure time of map interaction are carried out to compare with traditional bitmap based WMS (Web Map Service). As a result of experiments, we have confirmed improvement of interactivity and performance with RIA approach.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.6
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• pp.1343-1354
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• 2018

OAuth 2.0 bearer token and JWT(JSON web token), current standard technologies for authentication and authorization, use the approach of sending fixed token repeatedly to server for authentication that they are subject to eavesdropping attack, thus they should be used in secure communication environment such as HTTPS. In OAuth 2.0 MAC token which was devised as an authentication scheme that can be used in non-secure communication environment, server issues shared secret key to authenticated client and the client uses it to compute MAC to prove the authenticity of request, but in this case server has to store and use the shared secret key to verify user's request. Therefore, it's hard to provide stateless authentication service. In this paper we present a randomized token authentication scheme which can provide stateless MAC token authentication without storing shared secret key in server side. To remove the use of HTTPS, we utilize secure communication using server certificate and simple signature-based login using client certificate together with the proposed randomized token authentication to achieve the fully stateless authentication service and we provide an implementation example.

• The Transactions of the Korea Information Processing Society
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• v.6 no.1
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• pp.57-65
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• 1999

The simulation which is larger scale, complex and interactive with clients treat a lot of messages. It can be thinking more efficient distributed simulation than sequential one. The training simulation with multi-users is geographically distributed, and required high cost to operate and maintain system as increasing user requirements. The adaptation of web technology to the simulation can be a way to solves it without cost added. But dynamic web environment can causes causality error of events. This paper is concerned with client-server model, which supports interaction between distributed simulation server and web browser, and it is implemented by Java distributed object model. the result have shown that the distributed simulation is performed correctly on dynamic environment.