• The KIPS Transactions:PartA
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• 제14A권2호
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• pp.99-106
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• 2007

Grid computing, a mechanism which uses heterogeneous systems that are geographically distributed, draws attention as a new paradigm for the next generation operation of parallel and distributed computing. The importance of grid computing concerning communication cost is very huge because grid computing furnishes uses with integrated virtual computing service, in which a number of computer systems are connected by a high-speed network. Therefore, to reduce the execution time, the scheduling algorithm in grid environment should take communication cost into consideration as well as computing ability of resources. However, most scheduling algorithms have not only ignored the communication cost by assuming that all tasks were dealt in one cluster, but also did not consider the overhead of communication cost when the tasks were processed in a number of clusters. In this paper, the functions of original scheduling algorithms are analyzed. More importantly, the functions of algorithms are compared and analyzed with consideration of communication cost within the co allocation environment, in which a task is performed separately in many clusters.

• The KIPS Transactions:PartC
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• 제16C권5호
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• pp.621-628
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• 2009

Wireless sensor networks (WSNs) have been considered as a promising method for reliably monitoring both civil and military environments under hazardous or dangerous conditions. Due to the special property and difference from the traditional wireless network, the lifetime of the whole network is the most important aspect. The bottleneck nodes widely exist in WSNs and lead to decrease the lifetime of the whole network. In order to find out the bottleneck nodes, the traditional centralized bottleneck detection method MINCUT has been proposed as a solution for WSNs. However they are impractical for the networks that have a huge number of nodes. This paper first proposes a distributed algorithm called DBND (Distributed Bottleneck Node detection) that can reduce the time for location information collection, lower the algorithm complexity and find out the bottleneck nodes quickly. We also give two simple suggestions of how to solve the bottleneck problem. The simulation results and analysis show that our algorithm achieves much better performance and our solutions can relax the bottleneck problem, resulting in the prolonging of the network lifetime.

• Journal of the Korea Institute of Information Security & Cryptology
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• 제17권4호
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• pp.131-136
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• 2007

Ad hoc networks enable efficient resource aggregation in decentralized manner, and are inherently scalable and fault-tolerant since they do not depend on any centralized authority. However, lack of a centralized authority prompts many security-related challenges. Moreover, the dynamic topology change in which network nodes frequently join and leave adds a further complication in designing effective and efficient security mechanism. Security services for ad hoc networks need to be provided in a scalable and fault-tolerant manner while allowing for membership change of network nodes. In this paper, we investigate distributed certification mechanisms using a threshold cryptography in a way that the functions of a CA(Certification Authority) are distributed into the network nodes themselves and certain number of nodes jointly issue public key certificates to future joining nodes. In the process, we summarize one interesting report [5] in which the recently proposed RSA-based ad hoc signature scheme, called URSA, contains unfortunate yet serious security flaws. We then propose new scheme by fixing their security flaws.

• Journal of the Korean Society of Marine Environment & Safety
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• 제25권2호
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• pp.178-188
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• 2019

When using a distributed system, it is very important to know the intention of a target ship in order to prevent collisions. The action taken by a certain ship for collision avoidance and the action of the target ship it intends to avoid influence each other. However, it is difficult to establish a collision avoidance plan in consideration of multiple-ship situations for this reason. To solve this problem, a Distributed Stochastic Search Algorithm (DSSA) has been proposed. A DSSA searches for a course that can most reduce cost through repeated information exchange with target ships, and then indicates whether the current course should be maintained or a new course should be chosen according to probability and constraints. However, it has not been proven how the parameters used in DSSA affect collision avoidance actions. Therefore, in this paper, I have investigated the effect of the parameters and weight factors of DSSA. Experiments were conducted by combining parameters (time window, safe domain, detection range) and weight factors for encounters of two ships in head-on, crossing, and overtaking situations. A total of 24,000 experiments were conducted: 8,000 iterations for each situation. As a result, no collision occurred in any experiment conducted using DSSA. Costs have been shown to increase if a ship gives a large weight to its destination, i.e., takes selfish behavior. The more lasting the expected position of the target ship, the smaller the sailing distance and the number of message exchanges. The larger the detection range, the safer the interaction.

• The KIPS Transactions:PartB
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• 제11B권5호
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• pp.611-618
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• 2004

This paper addresses the design and implementation of class distribution in distributed object-oriented databases. The proposed strategy of distribution consists of two-step design of fragments. One is class fragmentation and the other is allocation of fragments. In step of class fragmentation, we have defined partitioning algorithms to reflect the characteristics of object-oriented databases such as method, inheritance and composite-object. In step of allocation, we have defined the objective function for allocation considering system operating cost including storage, query processing and communication and implemented it using Genetic Algorithm.

• Journal of Korea Game Society
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• 제19권3호
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• pp.5-14
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• 2019

The gaming server is based on a distributed server. In order to distribute workloads of gaming servers, distributed gaming servers apply some algorithms which divide each of gaming server's workload into balanced workload among the gaming servers and as a result, efficiently manage response time and fusibility of server requested by the clients. In this paper, we propose a load balancing agent using PPO(Proximal Policy Optimization) which is one of the methods from a greedy algorithm and Policy Gradient which is from Reinforcement Learning. The proposed load balancing agent is compared with the previous researches based on the simulation.

• The Journal of Korean Association of Computer Education
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• 제9권1호
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• pp.107-118
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• 2006

Load redistribution algorithm is a critical factor in computer system. In a receiver-initiated load redistribution algorithm, receiver(underloaded processor) continues to send unnecessary request messages for load transfer until a sender(overloaded processor) is found while the system load is light. Therefore, it yields many problems such as low cpu utilization and system throughput because of inefficient inter-processor communications until the receiver receives an accept message from the sender in this environment. This paper presents an approach based on genetic algorithm(GA) for dynamic load redistribution including self-adjustable in heterogeneous distributed systems. In this scheme the processors to which the requests are sent off are determined by the proposed GA to decrease unnecessary request messages.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제14권5호
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• pp.2457-2464
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• 2013

In this paper, we design and analyze a mutual exclusion algorithm, based on the Token and Failure detector, in asynchronous distributed systems. A Failure Detector is an independent module that detects and reports crashes of other processes. There are some of advantages in rewriting the Token-based ME algorithm using a Failure Detector. We show that the Token-based ME algorithm, when using Failure Detector, is more effectively implemented than the classic Token-based ME algorithm for synchronous distributed systems.

• Journal of The Korean Association of Information Education
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• 제2권2호
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• pp.269-277
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• 1998

In most of the distributed deadlock detection algorithms using messages called probes, only a portion of the generated messages are effectively used, and hence the wasted probes cause heavy communication traffic. In this paper, a distributed deadlock detection algorithm is proposed which can efficiently detect deadlocks making use of those residue probes. Our algorithm is complete in the sense that they detect not only those deadlocks in which the initiator is involved as most other algorithms do, but all the other deadlocks that are present anywhere in a connected wait-for-graph. To detect all the deadlocks, the algorithms known to be most efficient require O(ne) messages, where e and n are the number of edges and nodes in the graph, respectively. The single execution of the presented algorithm can accomplish the same task with O(e) messages.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제28권10A호
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• pp.838-846
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• 2003

In Bluetooth networks, the scatternet is defined as the internetworking of multiple piconets. Currently, Bluetooth standardization does not include the formation issue of scatternet by piconets. The existing formation algorithms of scatternet do not support the features of ad-hoc networks, which cause the performance degradation of systems when the nodes have certain degree of mobility. Therefore, as the formation of scatternet gets complicated, the throughput is lowered and the delay increases due to the inefficient architectural problems. In this paper, we propose the distributed formation scheme for bluetooth in scatternet, in which the nodes are spread out to form scatternet. Simulation results show that the proposed algorithm outperforms the conventional schemes.