• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.1
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• pp.182-189
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• 2010

This paper defines the quorum-based fault-tolerant mutual exclusion problem in a message-passing asynchronous system and determines a failure detector to solve the problem. This failure detector, which we call the modal failure detector star, and which we denote by $M^*$, is strictly weaker than the perfect failure detector P but strictly stronger than the eventually perfect failure detector ◇P. The paper shows that at any environment, the problem is solvable with $M^*$.

• The Transactions of the Korea Information Processing Society
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• v.6 no.5
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• pp.1203-1211
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• 1999

Checkpointing is the one of fault-tolerant techniques to restore faults and to restart job fast. Checkpointing algorithms in distributed systems have been studied for many years. These algorithms can be classified into synchronous Checkpointing algorithms and asynchronous Checkpoiting algorithms. In this paper, we propose an independent Checkpointing algorithm that has a minimum Checkpointing counts equal to periodic Checkpointing algorithm, and relatively short rollback distance at faulty situation. Checkpointing count is directly related to task completion time in a fault-free situation and short rollback distance is directly related to task completion time in a faulty situation. The proposed algorithm is compared with the previously proposed asynchronous Checkpointing algorithms using simulation. In the simulation, the proposed Checkpointing algorithm produces better results than other algorithms in terms of task completion time in fault-free as well as faulty situations.

• Journal of the Korea Society of Computer and Information
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• v.21 no.8
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• pp.41-48
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• 2016

In this paper, we propose an election protocol based on mobile ad-hoc network. In distributed systems, a group of computer should continue to do cooperation in order to finish some jobs. In such a system, an election protocol is especially practical and important elements to provide processes in a group with a consistent common knowledge about the membership of the group. Whenever a membership change occurs, processes should agree on which of them should do to accomplish an unfinished job or begins a new job. The problem of electing a leader is very same with the agreeing common predicate in a distributed system such as the consensus problem. Based on the termination detection protocol that is traditional one in asynchronous distributed systems, we present the new election protocol in distributed systems that are based on MANET, i.e. mobile ad hoc network.

• Journal of KIISE:Computing Practices and Letters
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• v.5 no.6
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• pp.738-747
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• 1999

본 논문에서는 분산 실시간 시스템의 특징인 분산 처리 과정의 신뢰성을 지원하기 위한 동적 트랜잭션 처리 구조를 연구하였다. 실시간 분산 처리 환경에서 동적으로 발생하는 실시간 분산 트랜잭션 처리를 위하여 트랜잭션 내에 필수적인 3가지 언어적 특성들을 제시하였다. 첫째는 트랜잭션 내에 실시간 시스템의 가장 중요한 특징인 시간적인 제약 조건들을 정의 할 수 있는 방안을 제시하고, 둘째는 비동기적인 처리 성격을 지닌 실시간 특성을 고려한 비동기적 트랜잭션 처리 방법을 제시한다. 또한, 분산 처리 과정에서 발생되는 예외 사항들을 처리하기 위하여 긴급성을 고려한 다중레벨 우선순위 스케줄링 (Multi-Level Priotiry Scheduling)이라 부르는 트랜잭션 스케줄링 방안을 제시한다. 그리고, 제시한 실시간 분산 트랜잭션 처리 구조의 타당성 및 가능성을 입증하기 위한 실시간 트랜잭션 처리 과정을 시물레이션을 통하여 제시한 언어적 특성에 대한 고려 사항들을 보여준다.Abstract We propose a dynamic transaction processing model that supports a reliability for distributed real-time processing. For the dynamic processing in distributed real-time transaction systems, we suggest three features that are defined in programming language. First, we propose a specification model to explicitly define the time constraints, needs in real-time distributed processing. Second, we describe an asynchronous transaction processing mechanism based on the real-time characteristics. So, we suggest three communication primitives to support asynchronous transaction processing. Lastly, a scheduling policy based on urgent transaction is suggested to manage the exception occurred during the distributed processing. This scheduling policy is called multi-level priotiry scheduling (MPLS). Based on three features and scheduling policy, we describe a direction to manage a dynamic transaction processing in distributed real-time systems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.05a
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• pp.257-262
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• 2000

Recently, though there are many REES(Remote Education Estimation Systems), they have some tied and complete testing method not considering for the student individual specification and characteristic. This paper proposes the education model of the distributed asynchronous communication method which making a test without me and place limits using web estimation system from problem bank database, and attach effective method could improve student achievement, quality of estimation later problem filtering using user profile in order to consider the student individual difference and characteristic that not considered pre-Remote Education Estimation Systems. This is a adaptive DAC method improving the pre-DAC method.

• ETRI Journal
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• v.26 no.5
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• pp.413-422
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• 2004

This paper investigates the impacts of array weight errors (AWE) in an antenna array (AA) on a parallel interference cancellation (PIC) receiver in uplink synchronous and asynchronous direct sequence code division multiple access (DS-CDMA) systems. The performance degradation due to an AWE, which is approximated by a Gaussian distributed random variable, is estimated as a function of the variance of the AWE. Theoretical analysis, confirmed by simulation, demonstrates the tradeoffs encountered between system parameters such as the number of antennas and the variance of the AWE in terms of the achievable average bit error rate and the user capacity. Numerical results show that the performance of the PIC with the AA in the DS-CDMA uplink is sensitive to the AWE. However, either a larger number of antennas or uplink synchronous transmissions have the potential of reducing the overall sensitivity, and thus improving its performance.

• Journal of the Korea Society for Simulation
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• v.5 no.2
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• pp.13-24
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• 1996

Workflow is an ordered sequence of interdependent component data activities each of which can be executed on an integrated information system by accessing a remote information system. In our previous research [4], we proposed a distributed CIM Workflow system which consists of a workflow execution model called DAF-Net and an agent-based information systems called AIMIS. Given a component data activity, there needs an interaction protocol among agents which allocates the component data activity to a relevant information systems exist. The objective of this research is to propose and test two protocols: ARR(Asynchronous Request and Response)protocol and NCL(Negotiation with Case based Learning) protocol. To test the effectiveness of the protocols, we applied the PVM(Parallel Virtual Machine) software to simulate the distributed CIM Workflow system. PVM provides a distributed computing environment in which users can run different software processes in different computers while allowing communication among the processes.

• 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.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.2
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• pp.45-50
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• 2017

Micro-service Architecture is a service architecture optimized for large-scale distributed systems such as real-time realistic broadcasting systems, so that are fiercely adopted by Global leading service platform vendors such as Netflix and Twitter due to the merit of horizontal performance scalability enabling the scale-out technique. In addition, micro-service architecture makes it possible to execute image processing and real-time data analysis using an asynchronous-based processing that are difficult to handle in Web API such as REST. In this paper, an event stream processing framework applicable to asynchronous based micro services is proposed in the sense that the accountability of event processing order is not guaranteed in the events such as IoT sensor data analysis or cloud-based image editing because these are the situations where the real-time media editing generates multiple event streams and asynchronous processes in the platform.

• Journal of KIISE:Computer Systems and Theory
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• v.27 no.5
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• pp.518-528
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• 2000

Messages in distributed real-time systems are categorized into two groups: synchronous messages and asynchronous messages. Synchronous messages, such as sampled audio and image data,are generated periodically with delivery time constraints. Protocols should guarantee the end-to-enddeadlines for such messages. Asynchronous messages are non-periodic and may arrive in a randomway with no strict time constraints.In this paper, we propose TTP/C(timed token protocol with concession), an extension of TTPprotocol, to achieve higher timeliness guarantee for synchronous messages in distributed real-timesystems. In TTP/C, a node concedes the allocated bandwidth to other nodes with urgent synchronousmessages to be sent provided that the node has no urgent messages, TTP/C works very well evenif the synchronous messages are generated with some jittering by nodes. The simulation results showthe improved performance of TTP/C protocol for guaranteeing synchronous messages deadlinescomeared to the existing TTP protocols.