• 산업경영시스템학회지
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• 제45권1호
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• pp.1-9
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• 2022

The PoN (Proof of Nonce) distributed consensus algorithm basically uses a non-competitive consensus method that can guarantee an equal opportunity for all nodes to participate in the block generation process, and this method was expected to resolve the first trilemma of the blockchain, called the decentralization problem. However, the decentralization performance of the PoN distributed consensus algorithm can be greatly affected by the network transaction transmission delay characteristics of the nodes composing the block chain system. In particular, in the consensus process, differences in network node performance may significantly affect the composition of the congress and committee on a first-come, first-served basis. Therefore, in this paper, we presented a problem by analyzing the decentralization performance of the PoN distributed consensus algorithm, and suggested a fairness control algorithm using a learning-based probabilistic acceptance rule to improve it. In addition, we verified the superiority of the proposed algorithm by conducting a numerical experiment, while considering the block chain systems composed of various heterogeneous characteristic systems with different network transmission delay.

• Journal of information and communication convergence engineering
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• 제17권3호
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• pp.167-173
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• 2019

This study investigates the problem of leader-following consensus for multi-agent systems with output saturations. This study assumes that the agents are described as a neutrally stable system, and the leader agent generates the bounded trajectory within the saturation level. Then, the objective of the leader-following consensus is to track the trajectory of the leader by exchanging information with neighbors. To solve this problem, we propose an observer-based distributed consensus algorithm. Then, we provide a consensus analysis by applying the Lyapunov stability theorem and LaSalle's invariance principle. The result shows that the agents achieve the leader-following consensus in a global sense. Moreover, we can achieve the consensus by choosing any positive control gain. Finally, we perform a numerical simulation to demonstrate the validity of the proposed algorithm.

• 산업경영시스템학회지
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• 제41권4호
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• pp.179-188
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• 2018

Recently, blockchain technology has been recognized as one of the most important issues for the 4th Industrial Revolution which can be represented by Artificial Intelligence and Internet of Things. Cryptocurrency, named Bitcoin, was the first successful implementation of blockchain, and it triggered the emergence of various cryptocurrencies. In addition, blockchain technology has been applied to various applications such as finance, healthcare, manufacturing, logistics as well as public services. Distributed consensus algorithm is an essential component in blockchain, and it enables all nodes belonging to blockchain network to make an agreement, which means all nodes have the same information. For example, Bitcoin uses a consensus algorithm called Proof-of-Work (PoW) that gives possession of block generation based on the computational volume committed by nodes. However, energy consumption for block generation in PoW has drastically increased due to the growth of computational performance to prove the possession of block. Although many other distributed consensus algorithms including Proof-of-Stake are suggested, they have their own advantages and limitations, and new research works should be proposed to overcome these limitations. For doing this, above all things, we need to establish an evaluation method existing distributed consensus algorithms. Based on this motivation, in this work, we suggest and analyze assessment items by classifying them as efficiency and safety perspectives for investigating existing distributed consensus algorithms. Furthermore, we suggest new assessment criteria and their implementation methods, which can be used for a baseline for improving performance of existing distributed consensus algorithms and designing new consensus algorithm in future.

• 품질경영학회지
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• 제49권4호
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• pp.527-537
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• 2021

Purpose: The purpose of this study was to suggest an improved version of Proof-of-Nonce (PoN) algorithm, which is a distributed consensus algorithm used for block chain system. Methods: First, we used response surface method for design of experiment that is to generate experimental points considering non-linear relationship among variables. Then, we employed overlapped contour plots for visualizing the impact of control variables to performance target. Results: First, we modified the consensus procedure of the existing PoN algorithm by diminishing the content of the exchanged message. Then, we verified the performance improvement of the new PoN algorithm by performing a numerical experiment and paired t-test. Finally, we established new regression models for consensus time and Transactions per second (TPS) and proposed a method for optimizing control variables for obtaining performance target. Conclusion: We could improve the performance of the previous version of PoN algorithm by modifying the content of the exchanged message during 4-steps of consensus procedure, which might be a stepping stone for designing an efficient and effective consensus algorithm for blockchain system with dynamic operation environment.

• 전자통신동향분석
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• 제37권1호
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• pp.63-72
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• 2022

Recently, blockchain has been attracting attention as a high-reliability technology in various fields. However, the Proof-of-Work-based distributed consensus algorithm applied to representative blockchains, such as Bitcoin and Ethereum, has limitations in applications to various industries owing to its excessive resource consumption and performance limitations. To overcome these limitations, various distributed consensus algorithms have appeared, and recently, hybrid distributed consensus algorithms that use two or more consensus algorithms to achieve decentralization and scalability have emerged. This paper introduces the technological trends of the latest high-performance distributed consensus algorithms by analyzing representative hybrid distributed consensus algorithms.

• ETRI Journal
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• 제42권6호
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• pp.872-885
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• 2020

Distributed consensus requires the consent of more than half of the congress to produce irreversible results, and the performance of the consensus algorithm deteriorates with the increase in the number of nodes. This problem can be addressed by delegating the agreement to a few selected nodes. Since the selected nodes must comply with the Byzantine node ratio criteria required by the algorithm, the result selected by any decentralized node cannot be trusted. However, some trusted nodes monopolize the consensus node selection process, thereby breaking decentralization and causing a trilemma. Therefore, a consensus node selection algorithm is required that can construct a congress that can withstand Byzantine faults with the decentralized method. In this paper, an algorithm based on the Byzantine agreement among decentralized agents to facilitate agreement between decentralization nodes is proposed. It selects a group of random consensus nodes per block by applying the proposed proof of nonce algorithm. By controlling the percentage of Byzantine included in the selected nodes, it solves the trilemma when an arbitrary node selects the consensus nodes.

• 예술인문사회 융합 멀티미디어 논문지
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• 제7권2호
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• pp.267-277
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• 2017

견고한 분산 서비스를 개발하는 데 있어 주요 문제점 중 하나는 분산 그룹의 참여자들이 공유하는 데이터에 대한 동의를 보장하는 분산 컨센서스를 어떻게 달성하는가에 대한 문제이다. 분산 컨센서스를 위한 알고리즘 중 Raft는 분산 컨센서스 문제를 3가지(리더 선거, 로그 복제, 안정성)로 나누어 해결한 간단하고 이해하기 쉬운 컨센서스 알고리즘이다. 하지만 Raft는 컨센서스 그룹을 구성하고 있는 참여 노드의 추가나 제거같은 노드의 동적 구성에 대하여 전혀 언급하지 않고 있다. 본 논문에서는 Raft를 확장하여 참여 노드의 동적 구성을 허용하는 새로운 컨센서스 알고리즘, Raft-D에 대해 기술한다. 이를 위하여, Raft-D는 참여 노드가 가지는 정보를 확장하고 컨센서스 그룹에 속해있는 노드들의 연결 상태를 확인하기 위한 기법을 제공하며, 이를 바탕으로 컨센서스 그룹의 참여 노드 추가 및 삭제 작업을 다루기 위한 상태와 조건에 대하여 정의한다. 이러한 상태와 조건을 기반으로, Raft-D는 Raft의 로그 업데이트 과정을 통한 컨센서스 그룹의 동적 구성 작업을 수행한다.

• 한국컴퓨터정보학회논문지
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• 제26권12호
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• pp.99-104
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• 2021

블록체인 기술은 분산 네트워크에 연결된 다수의 노드 간 원장을 공유하는 분산 원장기술이다. 기존 중앙 서버를 통하여 관리되던 데이터들이 블록체인을 통하여 관리되며 거래 데이터에 대한 투명성과 정확성 및 무결성이 높아지며 블록체인을 통한 데이터관리의 필요성이 높아지고 있다. 본 논문에서는 금융업에서 신뢰 기반의 기관 간 신뢰 기반의 데이터 공유가 필요하다는 점을 인지하고 블록체인을 통한 데이터관리 효율성 증대를 높이는 방법으로 프라이빗 블록체인 합의 알고리즘인 Raft의 리더 노드 선출과정의 처리 과정을 수정한 합의 알고리즘을 제시하였다. 본 논문에서 제시한 수정 합의 알고리즘과 일반적인 Raft 합의 알고리즘에 대하여 트랜잭션 처리시간을 기준으로 성능을 비교·분석하였으며 제안한 합의 알고리즘 적용을 통하여 합의 과정의 효율성이 높아짐을 확인하였다.

• 제어로봇시스템학회논문지
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• 제18권7호
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• pp.617-621
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• 2012

This paper studies asymptotic consensus problem for linear multi-agent systems. We propose a distributed state feedback control algorithm for solving the problem under fixed and undirected network communication. In contrast with the conventional algorithms that use global information (e.g., graph connectivity), the proposed algorithm only uses local information from neighbors. The principle for achieving asymptotic consensus is that, for each agent, a distributed update law gradually increases the coupling gain of LQR-type feedback and thus, the overall stability of the multi-agent system is recovered by the gain margin of LQR.

• 인터넷정보학회논문지
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• 제23권4호
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• pp.73-85
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• 2022

인공지능으로 자동화와 연결성이 극대화되는 4차 산업혁명 시대를 맞이하여 모델의 업데이트를 위한 데이터 수집과 활용의 중요성이 점차 높아지고 있다. 인공지능 기술을 사용하여 모델을 생성하기 위해서는 일반적으로 데이터를 한곳에 모아야 업데이트할 수 있으나, 이런 경우 사용자의 개인정보를 침해할 수 있다. 본 논문에서는 분산 저장된 데이터를 직접 공유하지 않으면서 서로 협력하여 모델을 업데이트할 수 있는 분산형 기계학습 방법인 연합학습을 소개하며, 기존의 서버 없이 참여자들 간의 분산 합의 최적화를 이루는 연구를 소개한다. 또한, Kirkman Triple System을 기반으로 한 패턴 및 그룹을 생성하는 알고리즘을 이용하며, 병렬적인 업데이트 및 통신을 하는 패턴 및 그룹 기반 분산 합의 최적화 알고리즘을 제안한다. 이러한 알고리즘은 기존의 분산 합의 최적화 알고리즘 이상의 프라이버시를 보장하며, 모델이 수렴할 때까지의 통신시간을 감소시킨다.