• Journal of the Korean Society for Railway
• /
• v.15 no.3
• /
• pp.278-285
• /
• 2012

The Service Availability (SA) in the viewpoint of passenger is used as the key performance indicator (KPI) of quality of service in Light Rail Transit (LRT) Public-Private Partnerships projects. But there are many disputes on the target value of SA because of the lack of experience in SA. The target value of SA should be set at an early stage of the project to be specified on the system specifications and operation plan. Therefore, this paper developed the quantitative prediction model of SA to set the reasonably achievable target value of SA at an early stage of the LRT project. Also this paper analyzed the relationship and differentiation of SA and Train Punctuality (TP) that is mostly compared with SA.

• Journal of KIISE:Computer Systems and Theory
• /
• v.31 no.9
• /
• pp.503-513
• /
• 2004

In large distributed systems, replications of data and service are needed to decrease communication cost, increase availability, and avoid single server bottleneck. Tree Quorum protocol is a representative replication protocol, which exploits a logical structure. Tree quorum protocol is one of the replication protocols allowing low read cost only in the best case, while the number of replicas exponentially increases as the level grows. In this paper, thus, we propose a new replication protocol, called symmetric tree protocol which efficiently solves the problem. The proposed symmetric tree protocol also requires much smaller read cost than previous protocols. We conduct cost and availability analysis of the protocols, and the proposed protocol displays comparable read availability to the tree protocol using much smaller number of nodes. Also, the symmetric tree protocol has much smaller response time than the logarithmic protocol.

• Journal of Digital Convergence
• /
• v.20 no.3
• /
• pp.1-8
• /
• 2022

Despite increasing damages caused by violations of COVID-19 precautions, studies on violations of precautions have not yet received much attention. This study identified antecedents that could theoretically influence the intention to violate COVID-19 precautions based on the black swan theory, and collected 215 responses by conducting an online survey from February 11, 2021 to March 10, 2021. As a result of the regression analysis, this study found that dissonance with COVID-19 preventive information, representativeness bias, and availability bias increase the intention to violate COVID-19 precautions. However, optimistic bias did not have a significant effect on the intention to violate precautions. This study not only provides new antecedents but also suggests theoretical evidence for decreasing intention to violate precautions. This study also proposes the necessity to identify differences in violation intention by regions, countries, and theories.

• The Journal of the Korea Contents Association
• /
• v.10 no.7
• /
• pp.49-54
• /
• 2010

In these days, Internet environment are very quickly development as well On-line service have been using a online for the mission critical business around the world. As the amount of information to be processed by computers has recently been increased there has been cluster computing systems developed by connecting workstations server using high speed networks for high availability. As a result, this study on a cluster based DBMS and common solution of DBMS venders has been studying with a wide range, as well as It is not good study a management skill for the cluster-based DBMS efficiently and optimization. accordingly, This study find out optimization managements skill and theory of he High availability solution on cluster-based DBMS.

• Journal of KIISE:Computer Systems and Theory
• /
• v.30 no.10
• /
• pp.533-543
• /
• 2003

With the increase of interests in cluster, there have been a number of research efforts to address the high availability issues on cluster. However, there are no kernel-level group communication systems to support the development of kernel-level application programs and it is not easy to use traditional user-level group communication systems for the kernel-level applications. This paper presents the design and implementation issues of KCGCS(Kernel-level Cluster Group Communication System), which is a kernel-level group communication module for linux cluster. Unlike traditional user-level group communication systems, the KCGCS uses light-weight heartbeat messages and a ring-based heartbeat mechanism, which allows users to implement scalable failure detection mechanisms. Moreover, the KCGCS improves the reliability by using distributed coordinators to maintain membership information.

• Journal of KIISE:Computer Systems and Theory
• /
• v.30 no.5_6
• /
• pp.290-298
• /
• 2003

Internet-based computer systems have to provide both high-availability and high-performance. Cluster technology has been used to obtain availability and performance simultaneously Generally, high-availability cluster systems tolerate a failure of a cluster node and cost-effectively solve it. In this paper, we study availability and downtime cost of (n,k) cluster systems. By considering performance, we model state transition of (n,k) cluster systems and apply software rejuvenation technique to improve availability of the system. We find that software rejuvenation can be used to improve availability of (n,k) cluster systems.

• Proceedings of the Safety Management and Science Conference
• /
• 2010.04a
• /
• pp.573-585
• /
• 2010

최근 철도차량은 안전성과 신뢰성 향상을 위해 점차 복잡하게 설계 제작되고, 품질에 대한 기대와 요구수준이 점차 높아짐에 따라 운영기관에서는 과학적이고 체계적인 예방 정비를 통한 안전성과 가용성 향상을 위해 노력하고 있다. 이러한 목적을 달성하기 위하여 여러 방안들이 연구되고 있으며, 대표적으로 신뢰성 기반 유지보수(RCM; Reliability Centered Maintenance)가 철도분야에 지속적으로 도입되고 있는 추세이다. 본 연구에서는 새로운 예방정비 기술로 대두되고 있는 RCM의 기본이론에 대한 고찰과 RCM의 일반적 실시 절차를 소개하고, RCM의 국제규격인 IEC 60300-3-11, NAVAIR 00-25-403, MIL-STD-2173을 비교 분석하여 이를 바탕으로 철도차량에 RCM 도입 시 효과적이고 적합한 절차 및 방안을 제시하고자 한다.

• Journal of KIISE:Computer Systems and Theory
• /
• v.28 no.3
• /
• pp.173-180
• /
• 2001

고가용도 클러스터 시스템에서 가동되는 인터넷 기반 소프트웨어의 복잡도가 증가됨에 따라 소프트웨어의 설계, 구현, 또는 그 밖의 여러 가지 원인과 관련된 결함으로 인하여 시스템 서비스의 오동작 또는 수행 중단으로 이어지는 사례가 늘어나고 있다. 특히 대량 트랜잭션을 처리하는 인터넷 기반 컴퓨팅 소프트웨어는 빈번한 통신 두절과 데이터 유실로 인하여, 이들이 탑재된 클러스터 시스템의 결함 발생이 더욱 심각할 가능성이 높다. 본 연구는 소프트웨어 재활 결함 허용 기법을 활용하여, 별도의 추가되는 하드웨어 없이도 가용도를 개선할 수 있다는 '소프트웨서 재활 기법을 적용한 다중계 시스템 가용도 분석'에 관한 논문에서 언급된 문제점들에 대한 해결 방안을 제시하였으며, 구체적으로는 1) 주서버의 고장 발생시 여분서버로의 작업전이(switchover) 상태를 클러스터 시스템 모델링에 포함시켰으며, 2) 작업전이 상태와 재활(rejuvenation) 상태에서 머무는 시간을 지수분포 대신에 k-stage Erlangian 분포를 사용하여 확정시간(deterministic time)을 표현할 수 있도록 하였다. 즉 본 논문에서는 고가용도 cold standby 클러스터 시스템의 운영 상태에 대한 상태전이도(state transition diagram)에서, 임의의 상태에서 머무는 시간분포가 memoryless 성질을 만족하지 않아도 되는 semi-Markov 프로세스 문제를 해결하였다.

• Journal of KIISE:Computer Systems and Theory
• /
• v.36 no.3
• /
• pp.140-148
• /
• 2009

Recent advances in communication and multimedia technologies make it possible to provide video-on-demand(VOD) services and people can access video servers over the Internet at any time using their electronic devices, such as PDA, mobile phone and digital TV. Each device has different processing capabilities, energy budgets, display sizes and network connectivities. To support such diverse devices, multiple versions of videos are needed to meet users' requests. In general cases, VOD servers cannot store all the versions of videos due to the storage limitation. When a device requests a stored version, the server can send the appropriate version immediately, but when the requested version is not stored, the server first converts some stored version to the requested version, and then sends it to the client. We call this conversion process transcoding. If transcoding occurs frequently in a VOD server, the CPU resource of the server becomes insufficient to response to clients. Thus, to admit as many requests as possible, we need to maximize the CPU availability. In this paper, we propose a new algorithm to select versions from those stored on disk using a branch and bound technique to maximize the CPU availability. We also explore the impact of these storage management policies on streaming to heterogeneous users.

• Information and Communications Magazine
• /
• v.26 no.3
• /
• pp.9-15
• /
• 2009

전쟁양상이 네트워크 중심 전으로 발전되기 위해서는 기동중에도 멀티미디어 등 대용량의 정보를 실시간으로 소통할 수 있는 정보통신기반체계가 필수적으로 요구된다. 이러한 기반을 구축하기 위해 개발 중인 전술정보통신체계(TICN: Tactical Information and Communication Network)의 부체계 중 하나인 전술이동통신체계는 이동하는 전장가입자에게 음성서비스이외 전장상황 공유를 위한 대용량의 데이터 서비스를 제공해야 하므로, 주파수 효율성이 좋은 Mobile WiMAX 기술을 기반으로 구현되었다. 구현된 장비는 전장 환경과 비슷한 산악지형의 테스트베드에 설치되어서 운용 가능성을 검증하였다. 본고에서는 Mobile WiMAX기반의 전술이동통신체계의 가용성을 확인하기 위해 수행한 이론적인 분석과 테스트베드에서 확인한 성능에 대해 소개한다.