• 한국정보처리학회논문지
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• 제7권4호
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• pp.1201-1210
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• 2000

In order to tolerate faults which may occur during the execution of distributed tasks in high-performance parallel computer systems, tasks are duplicated on different processors. In this paper, by utilizing the task duplication based scheduling algorithm, a new task scheduling algorithm which duplicates each task on more than two different processors with the minimum schedule length is presented, and the number of processors required for the duplication is analyzed with the ratio of communication cost to computation time and the workload of the system. A simulation with various task graphs reveals that the number of processors required for the full-duplex fault-tolerant task scheduling with the obtainable minimum schedule length increases about 30% to 75% when compared with that of the task duplication based scheduling algorithm.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.289-293
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• 2000

We propose two new algorithms for parallelism-independent scheduling. The machine code generated from the compiler using these algorithms in its scheduling phase is parallelism-independent code, executable in minimum time regardless of the number of the processors in the parallel computer. Our new algorithms have the following phases: finding the minimum number of processors on which the program can be executed in minimal time, scheduling by an heuristic algorithm for this predefined number of processors, and serialization of the parallel schedule according to the earliest start time of the tasks. At run time tasks are taken from the serialized schedule and assigned to the processor which allows the earliest start time of the task. The order of the tasks decided at compile time is not changed at run time regardless of the number of the available processors which means there is no out-of-order issue and execution. The scheduling is done predominantly at compile time and dynamic scheduling is minimized and diminished to allocation of the tasks to the processors. We evaluate the proposed algorithms by comparing them in terms of schedule length to the CP/MISF algorithm. For performance evaluation we use both randomly generated DAGs (directed acyclic graphs) and DACs representing real applications. From practical point of view, the algorithms we propose can be successfully used for scheduling programs for in-order superscalar processors and shared memory multiprocessor systems. Superscalar processors with any number of functional units can execute the parallelism-independent code in minimum time without necessity for dynamic scheduling and out-of-order issue hardware. This means that the use of our algorithms will lead to reducing the complexity of the hardware of the processors and the run-time overhead related to the dynamic scheduling.

• 한국통신학회논문지
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• 제18권2호
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• pp.279-287
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• 1993

본 논문은 다중등급의 통화유량에 대해 효율적인 처리를 위하여 동적 우선순위 스케쥴링이 가능한 2중이완성 한계치를 갖는 최소이완성한계 (Minimum Laxity Threshold:MLT)알고리즘과 2중 대기행열 한계치를 갖는 대기 행열간격한계(Queue Length Threshold QLT) 알고리즘을 제안하였다. 그리고 제안한 알고리즘의 성능을 컴퓨터 시뮬레이션을 통하여 분석하였다. 시뮬레이션 결과, 실시간서비스 중 지연민감도가 다른 2개 등급 이상의 통화유량 처리시2중 이완성 한계치를 갖는 MLT알고리즘을 적용함으로써 MLT알고리즘 자체보다 처리 효율성이 개선됨을 확인하고, 또2개 등급 이상의 비실시간 통화유량에 대해서는 2중 대기행열 한계치를 갖는 QLT알고리즘이 QLT보다 우수함을 알 수 있었다.

• 정보처리학회논문지A
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• 제11A권7호
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• pp.511-520
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• 2004

P2P(peer-to-peer) 모델은 클라이언트-서버 모델의 서버 링크 병목현상을 해결하기 위한 대안으로 고려되고 있다. 본 연구에서, 우리는 P2P 네트웍에서 연속형 미디어의 배포 문제 중 두 가지를 다루었다. 첫째는 다중-소스 스트리밍 세션을 위한 미디어 데이터의 전송 스케쥴링 문제이다. 버퍼링 지연을 최소화시키는 정교한 분산 전송 스케쥴링으로서FSS(fixed-length slotted scheduling)라는 기법을 제안한다. 두 번째 문제는 스스로 성장하는 P2P 시스템에서 미디어 컨텐츠의 배포 속도 향상 문제이다. 이를 위해 우리는 시스템의 스트리밍 용량이 증가하는 속도를 가속시키는 FAST라 불리는 기술을 제안한다.

• Journal of Communications and Networks
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• 제11권5호
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• pp.489-499
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• 2009

We describe the fundamental issue of scheduling the allocation of wireless network resources and provide several formulations of the associated problems. The emphasis is on scheduling transmission attempts. We place this problem in the context of existing approaches, like information theoretic and traditional network theoretic ones, as well as novel avenues that open up the possibility of addressing this issue for non-stationary and non-ergodic environments. We summarize concrete recent results for specific special cases that include unicast and multicast traffic, different objective functions, and reduced complexity versions of the problem. We conclude with some thoughts for future work. We identify and single out the cross-layer nature of the problem and include a simple physical-layer criterion in what is mostly a medium access control (MAC) problem.

• Journal of Communications and Networks
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• 제6권2호
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• pp.147-155
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• 2004

In this paper, we propose an efficient sequencing technique, namely minimum Row time scheduling (MFTS), to manage variable-Iength message transmissions for single-hop passive starcoupled WDM optical networks. By considering not only the message length but also the state of the receivers and the tuning latency, the proposed protocol can reduce the average delay of the network greatly. This paper also introduces a new channel assignment technique latency minimizing scheduling (LMS), which aims to reduce the scheduling latency. We evaluate the proposed algorithm, using extensive discrete-event simulations, by comparing its performance with shortest job first (SJF) algorithm. We find that significant improvement in average delay could be achieved by MFTS algorithm. By combining the proposed message sequencing technique with the channel selection technique, the performance of the optical network could be further improved.

• 한국정보과학회논문지:정보통신
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• 제28권3호
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• pp.447-453
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• 2001

본 논문에서는 방향성 커플러를 이용하여 구성한 광 베니언-형 교환 망에 있어 교환소자를 달리하는 멀티캐스팅의 스케줄링을 고려한다. 임의의 주어진 시각에 최대한 하나의 접속만이 각각의 교환소자를 점유하기 때문에 블록킹은 물론 누화가 발생하지 않도록 보장된다. 이러한 멀티캐스팅에서는 대개 수차례 걸친 라우팅이 수반되므로 라우팅 횟수를 최소한으로 하는 것이 바람직하다. 먼저 일-대-다 접속 능력을 제공하는 광 베니언-형 망에서 접속들이 동일한 교환소자를 경유하기 위한 필요충분 조건을 제시한다. 멀티캐스트 접속을 일정한 부분접속들로 분할 하는 규칙을 정의하고 부분접속들간의 누화 관계를 그래프로 표현한다. 최악의 경우의 누화를 분석하기 위해 그래프차수의 상한을 제시한다. 후속 논문(제2부)[14]에서는 스케줄링 알고리즘과 스케줄링 길이의 상한을 고찰하고 관련 연구결과와의 상세한 비교를 다룬다.

• 한국통신학회논문지
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• 제23권7호
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• pp.1785-1796
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• 1998

본 논문에서는 WDM(wavelength division multiplexing) 수동 성형망(passive star network) 환경에서 TDM(time d division multiplexing) 방법을 기반으로 한 타임슬롯 스케률링시의 최적파장수와 파장조정시간{tuning time)과의 관계에 대해 분석한다. 여기서는 각 노드들이 한 개 씩의 파장조정 송신기(tunable transmitter)와 파장고정 수신기(fixed receiver)를 갖추고 있고, 전송 트래픽은 비균등(nonuniform)이며, 각 노드들은 자신을 제외한 나머지 모든 노드들로 패킷을 전솜함을 가정한다. 기존의 스케률링 방법[7, 8, etc.]에서는 주어진 파장수를 전부 이용하였으나, 본 논문에 서는 부하균형(load balancing)을 포함한 순서 스케줄링(list scheduing) 사용시 프레임 길이를 최소로 하는 '최적 파 장수'가 이용 가능한 파장수 이하의 범위에서 존재함을 실험을 통해 보이고, 파장조정시간과의 관계를 분석한다. 또한 각 노드의 송신기(transmitter)와 수신기(receiver) 수의 증가에 의한 프레임 길이 단축 가능성에 대해 분석한다.

• 산업경영시스템학회지
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• 제25권2호
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• pp.92-101
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• 2002

The Job Shop Scheduling Problem(JSSP) is concerned with schedule of m different machines and n jobs where each job consists of a chain of operations, each of which needs to be processed during an uninterrupted time period of a given length on a given machine. The purpose of this paper is to develop the efficient heuristic method for solving the minimum makespan problem of the large scale job shop scheduling. The proposed heuristic method is based on a Tabu Search(TS) and on a Constraint Satisfaction Technique(CST). In this paper, ILOG libraries is used to embody the job shop model, and a CST is developed for this model to generate the increased solution. Then, TS is employed to overcome the increased search time of CST on the increased problem size md to refine the next-current solution. Also, this paper presents the new way of finding neighbourhood solution using TS. On applying TS, a new way of finding neighbourhood solution is presented. Computational experiments on well known sets of MT and LA problem instances show that, in several cases, our approach yields better results than the other heuristic procedures discussed In literature.

• 한국컴퓨터정보학회논문지
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• 제21권6호
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• pp.47-53
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• 2016

This paper deals with the capacity constrained time slot assignment problem(CTSAP) that a satellite switches to traffic between $m{\times}n$ ground stations using on-board $k{\leq}_{min}\{m,n\}$ k-transponders switching modes in SS/TDMA time-division technology. There was no polynomial time algorithm to solve the optimal solution thus this problem classified by NP-hard. This paper suggests a heuristic algorithm with O(mn) time complexity to solve the optimal solution for this problem. Firstly, the proposed algorithm selects maximum packet lengths of $\({mn \atop c}\)$ combination and transmits the cut of minimum packet length in each switching mode(MSMC). In the case of last switching mode with inefficient transmission, we applies a compensation strategy to obtain the minimum number of switching modes and the minimum makespan. The proposed algorithm finds optimal solution in polynomial time for all of the experimental data.