• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.7
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• pp.769-774
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• 2015

Sensor network as an infrastructure of IoT(Internet of Things) has reliability issue because sensor nodes have limited memory as well as bounded battery. To improve the reliability of network, this paper proposes a data distribution scheme. The proposed algorithm distributes the data which each sensor node periodically produces into neighbor nodes that have enough memory as well as battery. This distribution process goes on more than 1 hop for overcoming unexpected spatial crash. Through simulation, we have confirmed that the proposed scheme can improve the resilience of IoT without affecting the life time of sensor network.

• Journal of the Korea Society for Simulation
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• v.16 no.1
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• pp.59-68
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• 2007

IT (Intrusion Tolerant) technology is for guaranteeing the availability of service for certain amount time against the attacks which couldn't be prevented by the currently deployed information security countermeasures. IT (Intrusion Tolerant) technology mainly makes use of the replication of service and system fur enhancing availability, and voting scheme and GMP (Croup Management Protocol) are used for the correctness of service. This paper presents a scheme to analyze dependability of IT (Intrusion Tolerant) technology through probabilistic and simulation method. Using suggested analysis scheme, we can analyze the robustness and make a sensible trade-offs in of IT (Intrusion Tolerant) technology.

• KIISE Transactions on Computing Practices
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• v.22 no.1
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• pp.44-49
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• 2016

Recently, data has been growing dramatically along with the growth of social media and digital devices. A distributed memory processing system has been used to efficiently process large amounts of data. However, if a load is concentrated in a certain node in distributed environments, a node performance significantly degrades. In this paper, we propose a load balancing scheme to distribute load in a distributed memory environment. The proposed scheme replicates hot data to multiple nodes for managing a node's load and migrates the data by considering the load of the nodes when nodes are added or removed. The client reduces the number of accesses to the central server by directly accessing the data node through the metadata information of the hot data. In order to show the superiority of the proposed scheme, we compare it with the existing load balancing scheme through performance evaluation.

• Korean Journal of Microbiology
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• v.43 no.4
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• pp.285-291
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• 2007

According to the Baltimore Scheme, viruses are classified into 6 main classes based on their replication and coding strategies. Except for some small DNA viruses, most viruses code for their own polymerases: DNA-dependent DNA, RNA-dependent RNA and RNA-dependent DNA polymerases, all of which contain 4 common motifs. We undertook a phylogenetic study to establish the relationship between the Baltimore Scheme and viral polymerases. Amino acid sequence data sets of viral polymerases were taken from NCBI GenBank, and a multiple alignment was performed with CLUSTAL X program. Phylogenetic trees of viral polymerases constructed from the distance matrices were generally consistent with Baltimore Scheme with some minor exceptions. Interestingly, negative RNA viruses (Class V) could be further divided into 2 subgroups with segmented and non-segmented genomes. Thus, Baltimore Scheme for viral taxonomy could be supported by phylogenetic analysis based on the amino acid sequences of viral polymerases.

• Journal of the Korea Society of Computer and Information
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• v.17 no.5
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• pp.41-48
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• 2012

A Vehicular Ad-hoc Network (VANET) is a vehicular specific type of a mobile ad-hoc network, to provide temporary communications among nearby vehicles. Mobile node of VANET consumes energy and resource with participating in the member of network. In a VANET, data replication and cooperative caching have been used as promising solutions to improve system performance. Existing cooperative caching scheme in a VANET mostly focuses on weak consistency is not always satisfactory. In this paper, we propose an efficient cache management scheme to maintain strong data consistency in a VANET. We make an adaptive scheduling scheme to broadcast Invalidation Report (IR) in order to reduce query delay and communication overhead to maintain strong data consistency. The simulation result shows that our proposed method has a strength in terms of query delay and communication overhead.

• Journal of Korea Multimedia Society
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• v.9 no.11
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• pp.1410-1420
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• 2006

In this paper, a replica update propagation method for cost optimization of request forwarding in the Grid database is proposed,. In the Grid database, the data is replicated for performance and availability. In the case of data update, update information is forwarded to the neighbor nodes to synchronize with the others replicated data. There are two kinds of update propagation method that are the query based scheme and the log based scheme. And, only one of them is commonly used. But, because of dynamically changing environment through property of update query and processing condition, strategies that using one propagation method increases transmission cost in dynamic environment. In the proposed method, the three classes are defined from two cost models of query and log based scheme. And, cost functions and update propagation method is designed to select optimized update propagation scheme from these three classes. This paper shows a proposed method has an optimized performance through minimum transmission cost in dynamic processing environment.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.5_6
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• pp.273-279
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• 2003

Hypercube multicomputers have been drawing considerable attention from many researchers due to their regular structure and short diameter. One of keys to the performance of Hypercube is the efficiency of communication among processors. Among several communication patterns, multicast is important, which is found in a variety of applications as data replication and signal processing. As the number of processors increases, the probability of occurrences of fault components also increases. So it would be desirable to design an efficient scheme that multicasts messages in the presence of faulty component. In fault-tolerant routing and multicast, there are local information based scheme, global information based scheme and limited information based scheme in terms of information. In general, limited information is easy to obtain and maintain by compressing information in a concise format. In this paper, we propose a new routing scheme and a new multicast scheme using recently proposed fully reachability information scheme and new local information scheme. The proposed multicast scheme increases multicast success possibility and reduce deroute cases. Experiments show that multicast success possibility can increase at least 15% compared to previous method.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1996.10a
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• pp.93-95
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• 1996

A replication server is considered to be one of the most effective tools to cope with the problems that may be caused by the complex data replications in distributed database systems. In the distributed environment, locking a table is inevitable and it is the main reason to coerce the system practically. This paper presents an Asynchronous Replicator Scheme (ARS) that basically utilizes the system log as files named differential files to refresh the distributed data files with complicated queries, and that it prevents (normally, huge) base tables from being locked. We take join operations as the complicated queries, not only because the join operation covers almost all the operations, but also because it is one of the most time-consuming and data intensive operations in query processings.

• Annual Conference of KIPS
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• 2002.04a
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• pp.341-344
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• 2002

기존에 제안된 대부분의 중복 기법은 원본 트랜잭션을 완료한 후 비동기로 중복 사본에 대한 갱신 요구를 방송하는 지연 갱신 기법을 가정하였다. 지연 갱신 기법은 즉시 갱신 기법에서 발생하는 빈번한 교착상태 발생 문제를 해결할 수는 있지만 데이타 일관성 유지가 사용자 책임이라는 단점을 갖는다. 최근 그룹통신을 이용한 즉시 갱신 중복 기법들이 제안되고 있다. 이들 기법은 메시징 순서를 이용하여 교착상태 발생률을 줄였지만, 송신 노드는 갱신 요구 메시지를 방송한 후 전역 직렬성을 검증하는 낙관적 기법을 채택하기 때문에 통시성이 증가할수록 철회 트랜잭션의 실행 오버헤드가 증가한 다는 문제점을 갖는다. 본 논문에서는 철회 트랜잭션의 갱신 메시지 방송과 실행 오버헤드를 줄일 수 있는 즉시 갱신 기법을 제안한다. 제안한 기법은 갱신 요구 메시지를 방송하기 전에 전역 직렬성 검사가 이루어지기 때문에 완료 트랜잭션은 한번의 메시지 방송으로 처리할 수 있다. 뿐만 아니라, 철회 트랜잭션은 다른 노드로 방송할 필요가 없기 때문에 메시지 전송 횟수를 줄일 수 있으며, 철회 트랜잭션의 실행으로 인한 디스크 액세스 수와 로크 대기 시간을 줄임으로써 성능을 향상시킨다.

• Journal of information and communication convergence engineering
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• v.11 no.3
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• pp.173-178
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• 2013

To discover objects of interest in unstructured peer-to-peer networks, the peers rely on flooding query messages which create incredible network traffic. This article evaluates the performance of an unstructured Gnutella-like protocol over mobile ad-hoc networks and proposes modifications to improve its performance. This paper offers an enhanced mechanism for an unstructured Gnutella-like network with improved peer features to better meet the mobility requirement of ad-hoc networks. The proposed system introduces a novel caching optimization technique and enhanced ultrapeer selection scheme to make communication more efficient between peers and ultrapeers. The paper also describes an enhanced query mechanism for efficient searching by applying multiple walker random walks with a jump and replication technique. According to the simulation results, the proposed system yields better performance than Gnutella, XL-Gnutella, and random walk in terms of the query success rate, query response time, network load, and overhead.