• The Transactions of the Korea Information Processing Society
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• v.4 no.6
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• pp.1464-1480
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• 1997

Distributed systems offer environments for attaining high performance, fault-tolerance, information sharing, resource sharing, etc. But we cannot benefit from these potential advantages without suitable management of events/states occurring in distributed systems. These events and states can be symptoms for performance degradation, erroneous functions, suspicious activities, etc. and are subject to further analysis. To properly manage events/states, we need to be able to specify and efficiently detect these events/states. In this paper we first describe an event/state specification language and a centralized algorithm for detecting events/states specified with this language. Then we describe an algorithm for distributing an event/state detection task in a distributed system which is hierarchically organized. The algorithm consists of decomposing an event/state detection task into subtasks and allocation these subtasks to the proper nodes. We also explain a method to make the distributed detection fault-tolerant.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.1
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• pp.206-215
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• 2007

Ad-Hoc network technology is a mobile internet technology of the future that will be used widely not only in Mobile Network but also in Wireless Personal Area Network (WPAN) and Ubiquitous Network For this to occur, distributed routing protocol design, loop prevention for link information reduction in overhead for control messages and route restoration algorithm must be improved or complemented. Security techniques that can guarantee safe com-munication between Ad-Hot nodes net also be provided. This study proposes and evaluates a new authentication mechanism for MANET. The mechanism segregates the roles of certification authority to keep with the dynamic mobility of nodes and handle rapid and random topological changes with minimal over-head. That is, this model is characterized by its high expandability that allows the network to perform authentication service without the influence of joining and leaving nodes. The efficiency and security of this concept was evaluated through simulation.

• Smart Media Journal
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• v.9 no.4
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• pp.91-96
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• 2020

A blockchain is a technology in which all nodes participating in a distributed network manage each transaction's contents without a central server managing the transaction, which is a record of the transaction. The block containing the transaction record of a specific period is connected to the blockchain by referring to the hash value for the previous block, and the chain with the new block added is shared with all nodes again. Transactions using existing certificates will pass through FinTech, and in the near future, applications using blockchains are expected to emerge. In this study, we analyze the problems of the existing model, and propose a transaction model that applies the blockchain to come. Among various applications, this study develops a trading model targeting the energy sales market among the topics that will lead the fourth industrial revolution. As a result of analyzing the proposed model, it was possible to be sure of the possibility of a safer energy sales transaction than the existing method.

• KNOM Review
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• v.23 no.1
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• pp.26-33
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• 2020

Bitcoin is an electronic money that does not rely on centralized institutions such as banks and financial institutions, unlike the world's paper currencies such as dollar, won, euro and yen. In Bitcoin network, a block with transaction details is generated by mining, and the message that the block has been created is broadcast to all participating nodes in a broadcasting method to secure reliability through verification. Likewise, the mining and block propagation methods in the Bitcoin network are greatly affected by the performance of the P2P network. For example, in the case of mining, the node receiving the reward for mining varies depending on whether the block is first mined in the network and the proof of mining is propagated faster. In this paper, we applied local characteristics and Round-to-Trip(RTT) measurement to solve the problems of the existing neighbor connection method and block propagation method performed in Bitcoin network. An algorithm to improve block propagation speed is presented. Through experiments, we compare the performance of the improved algorithm with the existing algorithm to verify that the overall block propagation time is reduced.

• Journal of Digital Convergence
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• v.17 no.12
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• pp.235-241
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• 2019

The structure of the IoT can be divided into devices, gateways, and servers. First, the gateway collects data from the device, and the gateway sends data to the server through HTTP protocol, Websocket protocol, and MQTT protocol. The processing server then processes, analyzes, and transforms the data, and the database makes it easy to store and use this data. These IoT services are basically centralized structures with servers, so attacks on the entire platform are concentrated only on the central server, which makes hacking more successful than distributed structures. One way to solve this problem is to develop IoT that combines blockchain. Therefore, the proposed research suggests that the blockchain is a distributed structure, in which blocks containing small data are connected in a chain form, so that each node agrees and verifies the data with each other, thereby increasing reliability and lowering the probability of data forgery.

• The KIPS Transactions:PartA
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• v.11A no.5
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• pp.355-364
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• 2004

These days, various clustering technologies have been adopted to construct web sites. High performance hardware switches have good performance, but have disadvantage of high cost for constructing small and middle-sized web sites. Now a days, many sites have been constructed with the LVS (Linux Virtual Server), which is free of charge and has good performance. Having a centralized load balancing with one front-end, the LVS causes a bottleneck when it receives all at once. In the paper, we suggest a way to remove the LVS bottleneck by providing multiple front-ends. In this architecture, all of cluster nodes act as both a front-end and a back-end. When the load of a node receiving requests is not large enough, the node responds to the client directly. When the load of a node is large enough, the node send the request to a node which is selected by a scheduling algorithm. The scheduling algorithm is discussed to balance loads between servers. While single front-end cluster raises the throughput curvedly, the multiple front-end cluster raises the throughput linearly.

• KIPS Transactions on Software and Data Engineering
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• v.4 no.9
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• pp.331-336
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• 2015

On the IoT-based sensor networks, users or sensor nodes must perform a Service Discovery (SD) procedure before access to the wanted service. Current approach uses a center-concentrated Resource Directory (RD) servers or P2P technique, but these can cause a point-of-failure or flooding of SD messages. In this paper, we proposes an improved SWoT SD approach for CoAP-based sensor networks, which integrates Social Web of Things (SWoT) concept to current CoAP-based SD approach that makes up for weak points of existing systems. This new approach can perform a function like a keyword or location-based search originated from SNS, which can enhances the usability. Finally, we implemented a real system to evaluate.

• The Journal of the Korea Contents Association
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• v.11 no.1
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• pp.65-71
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• 2011

In this paper, the RFID / USN-based ad-hoc network structure is presented for efficient operation of a container terminal yard. Communication between fixed or mobile devices in the container terminal yard is accomplished through the ad-hoc node, to collect the status information of a container in real time. Any outside shipper of the container as well as central server allows to share the status information of a container through ad-hoc communication. In addition, to predict the maximum wireless transmission range of nodes by RFID tag position in the yard, LAODV (Location based AODV) routing protocol is proposed. The validity is proved by performance evaluation via computer simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.134-141
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• 2010

In this paper, we propose a scheduling algorithm to improve the performance of IEEE 802.16 based wireless mesh networks using directional antenna. The performance is presented in terms of throughput of system and delay between each node by varying number of users. The result show that proposed scheduling algorithm improving the performance by reducing the delay of mesh network system. Our work may be useful as a guideline to control the fairness between SSs for multi-hop systems such as multi-hop relay and mesh networks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.10C
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• pp.902-911
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• 2002

A wireless ad-hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized adminstration or standard support services. Wireless ad-hoc networks may be quite useful in that they can be instantly deployable and resilient to change. In this environment, for many crucial distributed applications, it is necessary to design robust virtual infrastructures that are fault-tolerant, self-stabilized, and resource-efficient. For this task this paper proposes a scheme of maintaining robust spanning trees which are little affected by topological changes. By maintaining such a spanning tree and adapting it to the environments with frequent topological changes, one can improve the reliability and efficiency of many applications that use the spanning tree.