• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.12
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• pp.5744-5764
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• 2018

In Wireless Sensor Networks (WSNs) for Internet of Things (IoT) environment, fault tolerance is a most fundamental issue due to strict energy constraint of sensor node. In this paper, a robust energy saving data dissemination protocol for IoT-WSNs is proposed. Minimized energy consumption and dissemination delay time based on signal strength play an important role in our scheme. The representative dissemination protocol SPIN (Sensor Protocols for Information via Negotiation) overcomes overlapped data problem of the classical Flooding scheme. However, SPIN never considers distance between nodes, thus the issue of dissemination energy consumption is becoming more important problem. In order to minimize the energy consumption, the shortest path between sensors should be considered to disseminate the data through the entire IoT-WSNs. SPMS (Shortest Path Mined SPIN) scheme creates routing tables using Bellman Ford method and forwards data through a multi-hop manner to optimize power consumption and delay time. Due to these properties, it is very hard to avoid heavy traffic when routing information is updated. Additionally, a node failure of SPMS would be caused by frequently using some sensors on the shortest path, thus network lifetime might be shortened quickly. In contrast, our scheme is resilient to these failures because it employs energy aware concept. The dissemination delay time of the proposed protocol without a routing table is similar to that of shortest path-based SPMS. In addition, our protocol does not require routing table, which needs a lot of control packets, thus it prevents excessive control message generation. Finally, the proposed scheme outperforms previous schemes in terms of data transmission success ratio, therefore our protocol could be appropriate for IoT-WSNs environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.83-93
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• 2019

The purpose of this study is to suggest implications for maximizing the effectiveness and efficiency of IPP work-learning by studying the effects of the personal characteristics of trainees and firm's field teacher on trainees' employability. The following conclusions were drawn by verifying the causal relationship between factors based on a questionnaire (157 copies) distributed to 200 trainees (learning workers) of 9 universities participating in IPP work-learning training. First, in order to increase the employability of IPP trainees, it is necessary to select trainees with strong core competencies and failure tolerance by verifying individual characteristics of trainees. Secondly, companies should appoint senior staff with strong leadership and teaching capacity as corporate field teachers, and corporate field teacher training institutions should reinforce the training to improve their leadership. Third, work-learning companies should be selected as those with high social integration and absorption capacity, and those companies should try to build an organizational culture of acquiring and learning new technologies. The results of this study are expected to contribute to enhancing the effectiveness of work-learning training by establishing a training system that can systematically select trainees and participating companies and enhance the training capacity of companies and field teachers.

• Journal of Internet Computing and Services
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• v.21 no.1
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• pp.17-31
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• 2020

With the rapid development of block chain technology, attempts have been made to put the block chain technology into practical use in various fields such as finance and logistics, and also in the public sector where data integrity is very important. Defense Operations In addition, strengthening security and ensuring complete integrity of the command communication network is crucial for operational operation under the network-centered operational environment (NCOE). For this purpose, it is necessary to construct a command communication network applying the block chain network. However, the block chain technology up to now can not solve the security issues such as the 51% attack. In particular, the Practical Byzantine fault tolerance (PBFT) algorithm which is now widely used in blockchain, does not have a penalty factor for nodes that behave maliciously, and there is a problem of failure to make a consensus even if malicious nodes are more than 33% of all nodes. In this paper, we propose a Adaptive Consensus Bound PBFT (ACB-PBFT) algorithm that incorporates a penalty mechanism for anomalous behavior by combining the Trust model to improve the security of the PBFT, which is the main agreement algorithm of the blockchain.

• The KIPS Transactions:PartC
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• v.16C no.2
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• pp.245-256
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• 2009

Pastry overlay network is one of structured P2Ps using DHT(Distributed Hash Table). To reduce the number of messages among nodes, Rosary and LAR have been proposed by exploiting spatial locality and caching, respectively, in the Pastry. Rosary consists of Inter-Pastry and Intra-Pastry. A root node is assigned as a representative in each Intra-Pastry and it has the responsibility of Inter-Pastry and Intra-Pastry routing. Therefore, Rosary has several disadvantages; 1) low fault tolerance in case of root node failure 2) routing hop count increases because of the use of root nodes compared to the existing structured P2Ps, and 3) the communication load is concentrated in some specific areas. LAR has inefficient problems in that caching is not distributed among nodes in Intra-Pastry and caching is used by only nodes in the Intra-Pastry. In this paper, we propose an improved Pastry called Doughnut to overcome the above problems of Rosary and LAR. By dividing nodes with the local characteristics, the Doughnut consists of Inter-Pastry and Intra-Pastry, and all nodes have the responsibility of Inter-Pastry and Intra-Pastry routing. This results in that all nodes perform the role of the existing root node. This solves the problems of the reducing of fault-tolerance, the increasing of routing hop count, and the not-distributed communication load. Also Doughnut can use cache effectively because it guarantees the even cache distribution in local(Intra-Pastry) and the cache contents in local can be used in the other local. The proposed algorithm is implemented using simulator and the experimental results show the effectiveness of the proposed method compared to the existing method.

• The Journal of Korean Association of Computer Education
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• v.5 no.2
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• pp.21-28
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• 2002

This paper proposes a new approach to rollback-recovery using multi-agent in distributed computing system. Previous rollback-recovery protocols are dependent on inherent communication and operating system, which causes a decline of computing performance in distributed computing system. By using multi-agent, we propose rollback-recovery protocol that is independent on operating system. We define three kinds of agent. One is a recovery agent that performs rollback-recovery protocol after a failure. Other is an information agent that constructs domain knowledge as a rule of fault tolerance and information during failure-free operation. The other is facilitator agent that controls the efficient communication between agents. Also we propose rollback-recovery protocol using multi-agent and simulated the proposed rollback-recovery protocol using JAVA and agent communication language in CORBA environment.

• Journal of the Korean Society of Safety
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• v.27 no.5
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• pp.64-69
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• 2012

The concept of SIL is applied in the most of all standards relating to functional system safety. However there are problems for the people to apply SIL to their plants. as these standards don't include sufficient informations. In this regards, this paper will suggest the direction of SIL application and concept based on IEC 61508 and IEC 61511. A Safety Integrity Level(SIL) is the discrete level(one out of possible fours), corresponding to a range of the probability of an E/E/PE (Electric/Electrical/Programmable Electrical) safety-related system satisfactorily performing the specific safety functions under all the stated conditions within a stated period of time. SIL can be divided into the target SIL(or required SIL) and the result SIL. The target SIL is determined by the risk analysis at the analysis phase of safety lifecycle and the result SIL is calculated during SIL verification at the realization phase of safety lifecycle. The target SIL is determined by the risk analysis like LOPA(Layer Of Protection Analysis), Risk Graph, Risk Matrix and the result SIL is calculated by HFT(Hardware Fault Tolerance), SFF(Safe Failure Fraction) and PFDavg(average Probability of dangerous Failure on Demand). SIL is applied to various areas such as process safety, machinery(road vehicles, railway application, rotating equipment, etc), nuclear sector which functional safety is applied. The functional safety is the part of the overall safety relating to the EUC and the EUC control system that depends on the correct functioning of the E/E/PE safety-related systems and other risk reduction measures. SIL is applied only to the functional safety of SIS(Safety Instrumented System) in safety. EUC is the abbreviation of Equipment Under Control and is the equipment, machinery, apparatus or plant used for manufacturing, process, transportation, medical or other activities.

• Journal of KIISE:Computing Practices and Letters
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• v.7 no.2
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• pp.121-131
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• 2001

The failure of network and/or node on which server object is executed is a single point of system failure in the CORBA application. One of the possible ways to overcome such problem is to replicate server objects to several independent nodes. The replicated objects executing same tasks are called object group. In order to provide fault tolerance of server object, this paper proposes and implements new CORBA model that supports the object group based on active replication. The proposed model not only provides interoperability with existing CORBA application but also minimizes additional application interface required to support object group because it uses nop to exchange messages between client and server. And this paper extends IDL structure. Depending to application logic, it makes possible to prevent performance degradation caused by consistency maintenance. At present, this paper supports only active replication. But it can be easily extended to provide warm ancVor cold passive replication without modification of architecture required for active replication.

• Journal of Advanced Navigation Technology
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• v.14 no.2
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• pp.233-238
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• 2010

In this paper, we applied the forward and backward error recovery techniques to a reduced instruction set computer (risc) processor to develop two fault-tolerant processors, namely, fetch redundant risc (FRR) processor and a redundancy execute risc (RER) processor. To evaluate the fault-tolerance capability of three target processors, we developed the base risc processor, FRR processor, and RER processor in SystemC hardware description language. We performed fault injection experiment using the three SystemC processor models and the SystemC-based simulation fault injection technique. From the experiments, for the 1-bit transient fault, the failure rate of the FRR, RER, and base risc processor were 1%, 2.8%, and 8.9%, respectively. For the 1-bit permanent fault, the failure rate of the FRR, RER, and base risc processor were 4.3%, 6.5%, and 41%, respectively. As a result, for 1-bit fault, we found that the FRR processor is more reliable among three processors.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.768-770
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• 1998

동기적 검사점(synchronous checkpoiting)기법, 인과적 메시지 로깅(causal message logging)과 향상된 회복 비동기성(improved asynchronism during recovery)을 제공하는 복귀회복(rollback recovery) 기법을 적용하여 자바 메시지 전달 시스템(java massage passing system)에서 수행하는 병렬 에플리케이션들에게 저 비용의 결함 포용성에 따라, 통신망으로 연결된 이질형 (fault-tolerance)(heterogeneous) 컴퓨터들을 이용하는 대규모 분산 시스템들은 아주 효율적인 병렬 컴퓨팅 환경을 제공해준다. 그러나, 이러한 분산 시스템들의 규모가 커짐에 따라 고장률 (failure rate)도 그 만큼 중요하게 된다. 따라서, 고장률이 높은 대규모 분산 시스템들에게 좀더 효율적인 결함 포용성을 제공하는 기법들이 필요하다. 또한, 대규모분산 시스템들은 이질형 컴퓨터들로 구성되어 있기 때문에, 결함 포용성을 제공하는 소프트웨어 패키지들은 플랫폼 독립적(platform independent)이어야 한다. 이러한 문제점은 높은 이식성(portability)을 가지고 있는 자바 언어로 구현함으로써 해결될 수 있다. 따라서, 본 논문은 자바 메시지 전달 시스템에서 수행되는 병렬 애플리케이션들에게 동기적 검사점 기법, 인과적 메시지 로깅과 향상된 비동기성을 제공하는 복귀회복 기법을 높은 이식성을 가진 자바언어로 구현하여 저 비용으로 결함 포용성을 제공하고자 한다.

• Architectural research
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• v.15 no.4
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• pp.191-200
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• 2013

Since Modern Movement flexibility has been one of the most attractive words in architecture. However, "overprovision first, division later" has been the most prevailing design method for spatial flexibility, and many of buildings designed for flexible use are practically quite inflexible due to insufficient building systems or/and irresponsible planning. There have been two dominant strategies to achieve architectural flexibility: multi-functionality and polyvalence. These two approaches, which point contradictory directions, actually reflect the difficulty in providing a proper form of architectural flexibility. Multi-functionality can afford changeable environments with satisfying spatial conditions; however it lacks tolerance to accommodate other uses but intended functions by architects. Meanwhile, flexibility by a polyvalent form relies on the vague anticipation of user's various interpretations. In this study by looking up these two different standpoints and historical precedents flexibility in architecture is carefully scrutinized focused on the contradiction, and as an alternative for architectural flexibility contextual relations is proposed. Unlike both multi-functionality and polyvalence, which produce flexibility by changing its own properties, manipulating contextual relations infuses flexibility into space by changing the properties of a building, not of its individual room. By using this contextual relations method, a community-centered school in Manhattan, NY, which was in danger of being closed because of its academic failure, is represented as a flexible space.