• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1B
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• pp.22-30
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• 2007

In this paper, to achieve consistency maintenance as well as stable service execution, we build a Fault-Tolerant Object Group framework that provides both of the group management service and the load scheduling service. The group management service supports the object management such as registration and authentication, and provides two schemes for failure recovery using the service priority and the checkpointing. In the load scheduling servile, we improve the effectiveness of service execution through the reasoning process of object loads based on the ANFIS architecture. The effectiveness in the performance of the developed framework is validated through a virtual home-network simulation based on the FTOG framework.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.39 no.2
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• pp.1-9
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• 2002

The use of Object-Oriented Distributed Programming(OODP) environment such as DCOM, DSOM, Java RMI, CORBA to implement distributed applications is becoming increasingly popular. However, absence of a fault-tolerance feature in these middleware platforms complicates the design and implementation of reliable distributed object-based applications, although they greatly enhance the quality and reusability of the distributed object-based applications. In this paper, we propose a fault-tolerant programming environment based on RMI, namely Evergreen, for the reliable distributed computing with checkpoints and rollback-recovery mechanism. Based on a series of experiments, we evaluate the performance of Evergreen and find its possibility of extension to fully support our optimal design goal.

• Journal of KIISE:Software and Applications
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• v.32 no.11
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• pp.1084-1098
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• 2005

In this paper, we propose a migration technique for autonomous mobile agents suitable to dynamic environments. The proposed migration technique dynamically creates the itinerary of agents that considers states of networks and systems. In the migration of the agent, it first sends prefetching message to the next system. The system receives necessary data for migration in advance. Through this, we reduce the amount of the sending data and save the time for creating the instance of the agent. And it improves the execution efficiency by using the checkpoint-based recovery method that does not execute the agent again and recovers the process states even though the errors take place. To show superiority of the proposed technique, we compare the proposed method with the existing methods through various simulations.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.11a
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• pp.215-218
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• 2012

스팟 인스턴스(Spot instance)는 클라우드 환경에서 사용자가 제시한 입찰 가격으로 클라우드 내의 자원을 이용하여 작업을 수행할 수 있게 하는 새로운 방식이다. 사용자는 자신의 입찰 금액이 클라우드 내의 스팟 인스턴스 가격을 초과하는 한 인스턴스를 실행할 수 있다. 그러나 입찰 가격이 스팟 가격보다 낮다면 작업 실패가 발생하고, 이로 인해 작업 완료 시간은 지연되며 서비스 품질은 저하된다. 이 문제를 해결하기 위해, 본 논문에서는 스팟 인스턴스에서 사용자 비드가 초과되어 작업 수행이 중지된 VM에 대하여 체크포인트 기법과 VM 이주(migration) 기법을 이용함으로써 작업 대기 시간을 줄이는 방법을 제안한다. 이는 작업 중인 스팟 인스턴스에서 작업 실패가 발생할 경우 다른 인스턴스로 이주하여 작업을 재수행하는 기법이다. 실험 결과는 제안하는 VM 이주 기법이 작업을 수행할 수 있는 스팟 인스턴스의 가용성을 증가시킬 수 있음을 보여준다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.156-157
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• 2011

In this work, we study the checkpoint/restart problem for message-passing parallel applications running on cloud computing environment. This is a new direction which arises from the trend of enabling the applications to run on the cloud computing environment. The main objective is to propose an efficient checkpoint algorithm for message-passing parallel applications considering communications with external systems. We further implement the novel algorithm by modifying gSOAP and OpenMPI (the open source libraries) which support service calls and checkpoint message-passing parallel programs, especially. The simulation showed that additional costs to the executing and checkpointing application of the algorithm are negligible. Ultimately, the algorithm supports efficiently the checkpoint/restart service for message-passing parallel applications, that send requests to external services.

• Journal of the Korea Society of Computer and Information
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• v.17 no.12
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• pp.187-198
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• 2012

International standard for software quality evaluation, ISO/IEC 9126 defines the quality characteristics and sub-characteristics consisting of quality of the software. Also, in this standard, the quality assessment items are presented in metrics based on maturity, fault tolerance, recoverability and compliance which are sub-characteristics of reliability. However, this reliability assessment items which are presented are not applied now due to the mathematical difficulties and the problems caused by collection of data. In order to resolve these problems, this study introduces measures to develop a specific test technique by quality attributes and to measure the quality. In other words, the detailed guidelines are presented to be utilized as a standard by summarizing test activities and techniques by each development life the most commonly used. The SW quality results are derived by assigning weights to software in order of the most important quality characteristics of respective software using checklist that can be easily utilized and applying test technique that can be utilized for detailed evaluation items and checklist. This improves problems that include reliability assessment item of ISO/IEC 9126 as the measures to measure new reliability quality of software.

• Journal of Korea Multimedia Society
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• v.8 no.7
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• pp.953-960
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• 2005

The Network can be easily damaged in the mobile computing environment. Mobile Support Station (MSS) which supports the Mobile Host(MH) could also be unstable too. Therefore, when a critical error occurs the repairing cost can be high. For stable repair, the hand-off strategy should be considered to save the continuing message and checkpoint information, and to reduce the cost of network repair. In this paper, we propose the Switching Trickle(ST) strategy which reduces the repairing cost for the MH's mobility. ST strategy changes the way which stores the information in connection with the number of write events(r) that occur from the hands-off strategy. Accumulated cost by increased mobility has been simulated too. From the results of simulation, the proposed strategy has shown more cost effective than the conventional strategy. The proposed strategy also has shown very supportive in saving checkpoint and message log information stably.

• Proceedings of the Korea Contents Association Conference
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• 2003.05a
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• pp.92-101
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• 2003

The accessibility evaluation of ten web-based loaming content in Korea was performed with the following procedure : (1) A primitive metric of the compliance of those contents to the WCAG (Web Content Accessibility Guidelines) 1.0 was obtained using Bobby, a widely used accessibility checker. (2) SGML validation test was carried out. (3) The contents were rendered with various browsers including a text-mode browser. (4) They were manually checked as to whether they satisfy the accessibility criteria proposed by W3C. Most of the tested contents scored low marks in all the test categories partly because they were apparently developed with little attention paid to web standard conformance, browser compatibility, and device-independence. They also put heavy emphasis on audio-visual effects catering only to the best-equipped users and offering no alternate access route for those in restricted environment. As more information and learning materials are delivered through the Internet, these low accessible contents would lead to a deeper information divide. The accessibility needs to be regarded as an important factor in evaluating the quality of loaming content.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.137-149
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• 2004

A new software paradigm is required on the development of network and various service requirements. With this, many studies on a mobile agent have been made. For the execution of the mobile agent, migration is the most important factor that influences the performance of the mobile agent. In this paper we propose the method that leads to high migration efficiency in order to improve the performance. The features of our migration technique are as follows. First, the migration technique creates the dynamic itinerary that appropriately copes with the network conditions and the platform changes to improve the agent execution efficiency. Second, it perfecters an executed code to reduce the amount of the mobile data and reduces the execution time by instantiating the agent in advance. Third, it improves the execution efficiency by using the checkpoint-based recovery method that does not execute the agent again and recovers the process states even though the errors take place. Though the simulation we compare the proposed method with the existing methods. The simulation result shows that the proposed method outperform the existing methods in terms of migration.

• Korean Journal of Optics and Photonics
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• v.27 no.4
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• pp.133-142
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• 2016

This paper presents the design and simulation of a three-dimensional pixel-by-pixel scanning light detection and ranging (LIDAR) system with a microelectromechanical system (MEMS) scanning mirror and direct sequence optical code division multiple access (DS-OCDMA) techniques. It measures a frame with $848{\times}480$ pixels at a refresh rate of 60 fps. The emitted laser pulse waves of each pixel are coded with DS-OCDMA techniques. The coded laser pulse waves include the pixel's position in the frame, and a checksum. The LIDAR emits the coded laser pulse waves periodically, without idle listening time to receive returning light at the receiver. The MEMS scanning mirror is used to deflect and steer the coded laser pulse waves to a specific target point. When all the pixels in a frame have been processed, the travel time is used by the pixel-by-pixel scanning LIDAR to generate point cloud data as the measured result.