• The KIPS Transactions:PartA
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• v.12A no.7 s.97
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• pp.613-620
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• 2005

To provide reliable differentiated service for internet clients, many studies on differentiated service are widely done. According to the types of the request of the clients in cluster-based web systems, SLA (Service Level Agreement) between service provider and the clients is considered. In this Paper, we study primary-backup web switch in the web systems that distribute the request of clients to each of web servers and also study performance isolation and admission control schemes of heterogeneous web systems which distinguish the servers into each different function domains. We analyze the availability, the response time and the performance of admission control through various simulated experiments on the proposed web systems.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2001.10a
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• pp.195-198
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• 2001

인터넷의 사용자가 급증하면서 고가용성(High Availability)과 확장성(Scalability)를 지닌 고성능 인터넷 서버들이 요구되고 있다. 클러스터 시스템은 이러한 요구사항을 만족시킬 수 있는 시스템으로 실제 작업을 처리하는 서버(Server)와 시스템 외부에서 유입되는 사용자 요구를 시스템에 속한 서버 노드에 분배하는 디렉터 (Director)로 이루어져 있다. 디렉터는 사용자가 요구한 작업을 서버노드에 분배하는 로드밸런서(Load-Balancer)의 역할을 하게 되는데, 작업을 분배하는 방법으로는 Round-Robin, Least-Connection 등의 방법이 주로 사용되고 있다. 본 논문에서는 각 작업분배 방법 중 효과적인 방법을 비교 선택하기 위해 대기이론을 적용하여 시뮬레이션을 통해 검증하였다.

• Journal of Aerospace System Engineering
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• v.18 no.1
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• pp.11-20
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• 2024

In the recent era of NewSpace, unlike high-reliability satellites of the past, low-reliability satellites are being developed and mass-produced at a lower cost to launch constellations satellites. To achieve cost-effective cluster satellite development, satellite users and developers need to assess the feasibility of maintaining mission performance over the expected lifespan when cluster satellites are launched. Plans for replacements due to random failures should also be established to maintain performance. This study proposed a method for assessing system reliability and availability to maintain mission performance and establish replacement strategies for Earth observation constellation satellites. In this study, a constellation reliability and availability model considering mission performance required for a satellite constellation, situations of satellite backup, and additional ground backups was established. The reliability model was structured based on the concept of a k-out-of-n system and the availability model used a Markov chain model. Based on the proposed reliability model, the minimum number of satellites required to meet mission requirements was defined and satellites needed in orbit during the required mission period to satisfy mission reliability were calculated. This research also analyzed the number of spare satellites in orbit and on the ground required to meet the desired availability during required service period through availability analysis.

• Journal of Digital Convergence
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• v.6 no.2
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• pp.117-125
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• 2008

High-volume web sites often use clusters of servers with load balancing as a way to increase the performance, scalability, and availability of the sites. Load balancing, usually performed by load balancer in front of such clusters, is a technique to spread workload between several computers or resources, in order to get optimal resource utilization or response time. In this paper we examine the performance for several configurations of cluster-based web servers using a simulation approach. We investigate two types of buffering scheme (common and local) for web clusters and three load balancing policies (uniformly random, round robin, and least queue first), using response time as a performance measure. We also examine two basic approaches of scaling web clusters: adding more servers of same type or upgrading the capacity of the servers in the clusters.

• Proceedings of the Korean Information Science Society Conference
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• 2002.10c
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• pp.253-255
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• 2002

최근 인터넷 서버의 역할을 위해 24 시간 무정지 서비스가 요구되면서 여러 개의 단일 서버를 고속의 네트웍으로 연결한 클러스터 DMBS 에 관한 연구가 국내외적으로 활발히 진행중이다. 그러나, 이러한 클러스터 DBMS를 효율적으로 관리할 수 있는 관리 도구에 대한 연구는 미흡한 실정이다. 본 논문에서는 각 서버의 상태를 모니터링한 정보를 바탕으로 서버의 오류를 감지하고 복구함으로써, 전체 클러스터 DBMS가 정상적인 서비스를 할 수 있도록 지원할 수 있는 고가용성 클러스터 관리기률 설계하고 구현한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.11
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• pp.5323-5343
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• 2018

Mobile applications and social networks tend to enhance the need for high-quality content access. To address the rapid growing demand for data services in mobile networks, it is necessary to develop efficient content caching and distribution techniques, aiming at significantly reduction of redundant content transmission and thus improve content delivery efficiency. In this article, we develop optimal cooperative content cache and distribution policy, where a geographical cluster model is designed for content retrieval across the collaborative small cell base stations (SBSs) and replacement of cache framework. Furthermore, we divide the SBS storage space into two equal parts: the first is local, the other is global content cache. We propose an algorithm to minimize the content caching delay, transmission cost and backhaul bottleneck at the edge of networks. Simulation results indicates that the proposed neighbor SBSs cooperative caching scheme brings a substantial improvement regarding content availability and cache storage capacity at the edge of networks in comparison with the current conventional cache placement approaches.

• Journal of the Korea Computer Industry Society
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• v.5 no.1
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• pp.101-108
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• 2004

As the dependency to network system and demands of efficient storage systems rapidly grows in every networking filed, the current trends initiated by explosive networked data grow due to the wide-spread of internet multimedia data and internet requires a paradigm shift from computing-centric to data-centric in storagesystems. Furthermore, the new environment of file systems such as NAS(Network Attached Storage) and SAN(Storage Area Network) is adopted to the existing storage paradigm for Providing high availability and efficient data access. We describe the design issues and system components of SANiqueTM, which is the cluster file system based on SAN environment. SANiqueTM has the capability of transferring the user data from the network-attached SAN disk to client applications directly We, especially, present the protocol and functionality of the global buffer manager in our cluster file system.

• The Journal of the Korea Contents Association
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• v.12 no.2
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• pp.19-29
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• 2012

Currently, cloud computing technology is being supplied in various service forms and it is becoming a ground breaking service which provides usage of storage service, data and software while user is not involved in technical background such as physical location of service or system environment. cloud computing technology has advantages that it can use easily as many IT resources as it wants freely regardless of hardware issues required by a variety of systems and service level required by infrastructure. Also, since it has a strength that it can choose usage of resource about business model due to various internet-based technologies, provisioning technology and virtualization technology are being paid attention as main technologies. These technologies are ones of important technology elements which help web-based users approach freely and install according to user environment. Therefore, this thesis introduces software-related technologies and architectures in an aspect of grid for building up high availability cloud computing environment by analysis about cloud computing technology trend.

• KIPS Transactions on Computer and Communication Systems
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• v.6 no.11
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• pp.453-462
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• 2017

OpenDaylight is an SDN (Software Defined Networking) open source framework, which is popular in network fields recently. This paper analyzes the performance of a controller cluster architecture by focusing on distributed datastore and Raft leader election algorithm. In addition, we propose an enhanced version of Raft algorithm in order to improve the performance of distributed datastore by distributing shard leaders over controller cluster. This paper compares the conventional Raft algorithm with the proposed version of the Raft algorithm. Moreover, we compare the performance of distributed datastore according to shard roles such as leader and follower. Experimental results show that Shard leaders provide better performance than followers and Shard updating requests need to be distributed over multiple controllers. So, by using proposed version of Raft algorithm, controller performance can be improved. The details of the experiment results are cleary described.

• Proceedings of the Korea Contents Association Conference
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• 2004.11a
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• pp.395-401
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• 2004

In the current high network-centralized computing and enterprising environment, it is getting essential to transmit data reliably at very high rates. Until now previous client/server model based NFS(Network File System) or AFS(Andrew's Files System) have met the various demands but from now couldn't satisfy those of the today's scalable high-performance computing environment. Not only performance but data sharing service redundancy have risen as a serious problem. In case of NFS, the locking issue and cache cause file system to reboot and make problem when it is used simply as ip-take over for H/A service. In case of AFS, it provides file sharing redundancy but it is not possible until the storage supporting redundancy and equipments are prepared. Lustre is an open source based cluster file system developed to meet both demands. Lustre consists of three types of subsystems : MDS(Meta-Data Server) which offers the meta-data services, OST(Objec Storage Targets) which provide file I/O, and Lustre Clients which interact with OST and MDS. These subsystems with message exchanging and pursuing scalable high-performance file system service. In this paper, we compare the transmission speed of gigabytes file between Lustre and NFS on the basis of concurrent users and also present the high availability of the file system by removing more than one OST in operation.