• Journal of KIISE:Computer Systems and Theory
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• v.31 no.9
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• pp.495-502
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• 2004

A rapid growth of the Internet user and rich media content cause an excessive server load and high network traffic, and thus it decreases the quality of service. A solution to this problem is to distribute the content on multiple replicated servers. However, in this circumstance, clients face additional task of selecting the best server to provide proper so${\gamma}$vice which clients request. This paper is intended to propose an adaptive server selection mechanism for a client request based on distance and server load. This will offer a fast and scalable service in response to the increase of massive and realtime multimedia content and contribute to floating a new business model of digital content service.

• Spatial Information Research
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• v.13 no.3 s.34
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• pp.221-237
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• 2005

This study attempts at building a GIS computing environment that incorporates object-relational spatio-temporal database for the time geography model with space-time path, space-time prism and space-time accessibility. The proposed computing environment is composed of ( i ) mobile GIS application for collecting spatio-temporal trajectory data of an individual, ( ii ) spatio-temporal database server that includes time geography model, and (iii) geovisualization client that performs time geographic queries to the spatio-temporal database. The spatio-temporal trajectory data collected by GPS-PDA client is automatically processed and sent to server through data management middleware. The spatio-temporal database implemented by extending a generic DBMS provides spatio-temporal objects, functions, and SQL. The geovisualization client illustrates 3D visual results of the queries about space-time path, space-time prism, and space-time accessibility. This study confirms the possibility of integrating mobile GIS and DBMS for time geography model, and it presents the appropriate database model with spatio-temporal objects and functions that may handle very large data for time geography application.

• The Transactions of the Korea Information Processing Society
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• v.7 no.2S
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• pp.733-743
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• 2000

This paper describes design and implementation of a content manager in the Integrated Steaming Framework Architecture (ISSA) that is proposed by the authors. The ISSA can provide an environment to develop multimedia streaming applications under heterogeneous distributed systems. The goal of ISSA is to extend the limitations of existing streaming systems. It can support diverse media formats and high level programming environment for streaming application developers. Moreover, it is independent from underlying networks and operating systems, and compatible with the global real-time multimedia database system(BeeHive) so that streaming media is efficiently retrieved, stored, and serviced. The role of a content manager is important in the ISSA environment since it manages an information of media that are provided by the server, and allow users to access media more easily by means of conveying that information to the streaming server, Web server, and client efficiently. The proposed content manager is not only to meed these requirements, but also to provide streaming information to media source and transport manager in order to be an efficient streaming. Furthermore, it supports database transaction processing by using the database connector.

• Journal of the Korea Society of Computer and Information
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• v.13 no.5
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• pp.1-10
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• 2008

In this paper, we discuss the development of an integrated HMI system based on OPC(OLE for Process Control) to control and monitor an automation equipment in the diverse environment. We implement an embedded OPC server according to the OPC standard which is proposed as the communication standard mechanism in the process control field, and design the interface module in which the output data of the OPC server can be connected to various HMI environment such as the local application, intranet client and Web page. This paper will be contributed in the HMI system implementation for the ubiquitous environment because it is possible to make remote control on the network and Web monitoring as well as the connection and data exchange of heterogeneous equipments by applying to various control systems.

• The KIPS Transactions:PartD
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• v.8D no.2
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• pp.132-144
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• 2001

The broadcast environment is asymmetric communication aspect that is typically much greater communication capacity available from server to clients than in the opposite direction. In addition, most of mobile computing systems only allow the generation of read-only transactions from mobile clients for retrieving different types of information such as stock data, traffic information and news updates. Since previous concurrency control protocols, however, do not consider such a particular characteristics, the performance degradation occurs when those schemes are applied to the broadcast environment having quite a high data contention. In this paper, we propose OCC/2VTS (Optimistic Concurrency Control based on 2-Version and TimeStamp) that is most appropriate for broadcast environment. OCC/2VTS lets each client process and commit query transactions for itself by using two version data in cache. If the values of appropriate data items are not changed twice by invalidation report after a query transaction starts, the query transaction is committed safely independent of commitment of update transactions. OCC/2VTS decreases the number of informing server for the purpose of commitment. Due to broadcasting the validation reports including updated recent values, it reduces the opportunity of requesting a recent data values of server as well. As a result, OCC/2VTS makes full use of the asymmetric bandwidth. It also improves transaction throughput by increasing the query transaction commit ratio as much as possible.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.7
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• pp.399-412
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• 2006

A clustering based wireless internet proxy server with cooperative caching has a problem of minimizing overall performance because some servers become overloaded if client request pattern is Hot-Spot or uneven. We propose a self-learning based adaptive clustering scheme to solve the poor performance problems of the existing clustering in case of Hot-Spot or uneven client request pattern. In the proposed scheme, requests are dynamically redistributed to the other servers if some servers supposed to handle the requests become overloaded. This is done by a self-learning based method based dynamic weight adjustment algorithm so that it can be applied to a situation with even various request pattern or a cluster of hosts with different performance. We performed experiments in a clustering environment with 16 PCs and a load balancer. Experimental results show the 54.62% performance improvement of the proposed schemes compared to the existing schemes.

• Journal of KIISE:Databases
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• v.31 no.2
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• pp.140-149
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• 2004

Data broadcast has received much attention as a very efficient method for disseminating data items in mobile environment with large number of mobile clients. In this approach, a database server periodically and continuously broadcasts data items through wireless channels and clients perform read-only transactions by accessing necessary data items from the air. While broadcasting, the server must also process update transactions on the database, which raises an obstacle for client's accessing consistent data. In this research, we propose a new algorithm SCDSC(Serialization Checking with DirtySet on Commit) which is an alternative for solving the concurrency control problem efficiently. The SCDSC is a kind of optimistic concurrency control in that a client checks the consistency of data using a DirtySet as a part of data broadcast when it commits its transaction. In each broadcast cycle, the server updates and disseminates the DirtySet with newly changed data items for last few cycles in the sliding window approach. We perform an analysis and a simulation study to evaluate the performance of our SCDSC algorithm in terms of data consistency and data currency.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.6
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• pp.1480-1490
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• 2007

This study implemented a remote control system using PDA based on WINDOWS CE. NET. In existing remote control systems, the user generally controls remote objects and obtain data using a computer, which is a local system connected to the internet, and the remote objects are connected to server computers. In order to control remote objects, the user has to have a computer, a space to use the Internet, and wired internet. The system proposed in this study uses an embedded board as a server and PDA as a client. Thus, the user can control remote objects at any place as long as wireless internet is available. In addition, because an embedded board is used as a server, the system has the characteristics of high performance and low power consumption. The proposed system provides not only remote control environment using PDA but also conventional control environment using a computer as a client. In case PDA is not available, remote objects still can be controlled from any place as long as there are wired internet and a computer.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.2
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• pp.811-829
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• 2015

One-way authenticated key agreement protocols, aiming at solving the problems to establish secure communications over public insecure networks, can achieve one-way authentication of communicating entities for giving a specific user strong anonymity and confidentiality of transmitted data. Public Key Infrastructure can design one-way authenticated key agreement protocols, but it will consume a large amount of computation. Because one-way authenticated key agreement protocols mainly concern on authentication and key agreement, we adopt multi-server architecture to realize these goals. About multi-server architecture, which allow the user to register at the registration center (RC) once and can access all the permitted services provided by the eligible servers. The combination of above-mentioned ideas can lead to a high-practical scheme in the universal client/server architecture. Based on these motivations, the paper firstly proposed a new one-way authenticated key agreement scheme based on multi-server architecture. Compared with the related literatures recently, our proposed scheme can not only own high efficiency and unique functionality, but is also robust to various attacks and achieves perfect forward secrecy. Finally, we give the security proof and the efficiency analysis of our proposed scheme.

• The Journal of the Korea Contents Association
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• v.5 no.2
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• pp.79-85
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• 2005

In order to handle client's requests while multiple servers seamlessly work in the web server cluster environment, it is vital to implement a router that execute a routing using TCP information and requested target content. The implemented package software measured packet volume that was generated from data generator, virtual server, and server 1, 2, 3, and could find out traffic distribution toward Server 1, 2, 3. As the result of the study shows, Round Robin Algorithm ensured definite traffic distribution, unless incoming data loads differ much. Although error levels were high in some partial cases, they were eventually alleviated by repeated tests for a longer time.