• Journal of KIISE
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• v.43 no.6
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• pp.613-620
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• 2016

This paper presents a MOHA(Many-Task Computing on Hadoop) framework which aims to effectively apply the Many-Task Computing(MTC) technologies originally developed for high-performance processing of many tasks, to the existing Big Data processing platform Hadoop. We present basic concepts, motivation, preliminary results of PoC based on distributed message queue, and future research directions of MOHA. MTC applications may have relatively low I/O requirements per task. However, a very large number of tasks should be efficiently processed with potentially heavy inter-communications based on files. Therefore, MTC applications can show another pattern of data-intensive workloads compared to existing Hadoop applications, typically based on relatively large data block sizes. Through an effective convergence of MTC and Big Data technologies, we can introduce a new MOHA framework which can support the large-scale scientific applications along with the Hadoop ecosystem, which is evolving into a multi-application platform.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.17-24
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• 2004

This paper proposes an efficient technique to protect e-mail server from DDoS attack using the CBQ (Class Based Queuing) algorithm The proposed method classifies incoming trafic to an e-mail server into three classes: 'more important mail traffic', 'less important traffic' and 'unknown traffic' and assigns bandwidths differently to the traffics. By differentiating the bandwidths of classes, normal mail traffic may flow even under DDoS attack in the proposed technique. The proposed technique is implemented on an embedded system which hires a switching processor with the WFHBD(Weighted Fair Hashed Bandwidth Distribution) engine that has been known as an efficient algorithm to distribute a given bandwidth to multiple sources, and it is verified that it can be an efficient way to protect e-mail server from DDoS attack.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.844-851
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• 2004

Various types of error are caused due to many factors of various environment in air interface channel of wireless communications. In this case, the reliability of the channel is much lower than that of wired case. IEEE 802.15.3 high-rate WPAN, which operates in an ad hoc networking environment, is more susceptible to such errors. The problem has been investigated for wireless LANs, for example, as follows. If the queue size of a certain node is longer than that of other nodes, the node estimates that its channel state is bad and the resource of the node is decreased. However this method has a disadvantage that a central controller must always monitor the status. To avoid this disadvantage, in this paper, a new MAC protocol that the throughput of overall piconet is increased by LDS (Link-status Dependent Scheduling) is proposed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2811-2817
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• 2010

In this paper we propose the QAC-MAC that supports Quality of Service(QoS) and saves energy resources of the sensor node, and hence prolonging the lifetime of the sensor network with multiple sink nodes. Generally, the nodes nearest to the sink node often experience heavy congestion since all data is forwarded toward the sink through those nodes. So this critically effects on the delay-constraint data traffics. QAC-MAC uses a hybrid mechanism that adapts scheduled scheme for medium access and scheduling and unscheduled scheme based on TDMA for no data collision transmission. Generally speaking, characteristics of the real-time traffic with higher priority tends to be bursty and has same destination. QAC-MAC adapts cross-layer concept to rearrange the data transmission order in each sensor node's queue, saves energy consumption by allowing few nodes in data transmission, and prolongs the network lifetime.

• The KIPS Transactions:PartC
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• v.9C no.1
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• pp.21-30
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• 2002

Nowadays the fair queuing field is studied actively for solving the unfair queuing problem which degrades the service performance of various applications on network. Above all DRR is a scheme that has lower work complexity and can be implemented easily. It guarantees the fair service by serving each queue every round Service Quantum(SQ) that includes the service deficit of the previous round. But it increases the delay by the numbers of unnecessary resetting of SQ or round circulation for the service that have the packet size over maximum several kbyte. In this paper, We propose the method that sets SQ dynamically to minimize this problem and the method that minimizes the work complexity on processing of packet. The proposed scheme minimizes the delay on various applications in enterprise environment by setting SQ dynamically and processing the packet simply.

• Proceedings of the Korea Society for Simulation Conference
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• 1992.10a
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• pp.3-3
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• 1992

컴퓨터 시스템의 개발 및 분석에 많이 활용되는 시뮬레이션 모델을 구축하는데 있어서 SIMSCRIT, GISS, SIMAN, SLA II등과 같은 시뮬레이션 전용언어가 많이 사용되지만, 이들은 새로운 전용언어의 습득, 시스템 프로그램과의 접속, 시뮬레이션 수행 속도면에서 부담을 주어왔다. 본 연구에서는 기존의 C언어 사용자들이 손쉽게 시뮬레이션 모델을 구축할 수 있도록 기존의 smpl을 확장하여 SMPLE(smpl extended)를 개발하였다. SMPLE의 모체의 smpl은 컴퓨터 시스템의 시뮬레이션 모델을 구현하기 위해 MIT에서 C언어를 이용하여 고안되었으며, C언어의 기능적인 확장으로서 라이브러리 함수들의 집합 형태를 갖는 시뮬레이션 서브 시스템이다. 이러한 라이브러리 함수들의 집합인 smpl 시뮬레이션 서브 시스템은 C언어 자체와 더불어 사건중심(event-oriented) 시뮬레이션 언어를 구성하며, smpl 시뮬레이터는 C 언어 프로그램으로 구현되다. smpl은 시뮬레이션하기 위한 설비(facility)들을 정의, 예약, 해제하거나 상태를 알아보는 함수를 제공하며, 시간의 관점에서 보면 토큰의 흐름은 일련의 대기시간과 활동시간에 의하여 나타낼 수 있게 된다. smpl은 사건의 스케쥴링(scheduling), 확률변수의 생성, 통계자료 수집 등에 관한 함수의 제공과, 시뮬레이션 시간의 전진과 사건발생의 순서를 조절해주는 기능을 제공한다. smpl 시뮬레이션 프로그램은 초기화루틴, 제어루틴 및 결과출력루틴으로 구성된다. 기존의 smpl에서 사용되는 프로그램의 자료구조(data structure)는 배열과 인덱스 구조가 사용되었다. 이러한 구조는 이미 완성되어 있는 프로그램 내에서는 효율성 면에서 좋겠지만, 변경이나 확장하기 위해 이 프로그램을 분석한다거나 필요한 기능을 추가하기 위해서는 매우 많은 어려움이 따르게 된다. 본 논문에서는 배열을 기반으로 하고 있는 smpl의 자료구조를 C의 structure와 pointer를 기반으로 하게끔 변경시키고 이에 따르는 제반 변경 사항을 수정 보완하여 프로그램의 분석을 용이하게 하며 기능의 변경 및 추가가 수월하게 하였고 메모리를 동적으로 관리할 수 있게 하였다. 또한 기존의 smpl에 디버깅용 함수 및 설비(facility) 제어용 함수를 추가하여 시뮬레이션 프로그램 작성을 용이하게 하였다. 예를 들면 who_server(), who_queue(), pop_Q(), push_Q(), pop_server(), push_server(), we(), wf(), printfct() 같은 함수들이다. 또한 동시에 발생되는 사건들의 순서를 조종하기 위해, 동시에 발생할 수 있는 각각의 사건에 우선순위를 두어 이 우선 순위에 의하여 사건 리스트(event list)에서 자동적으로 사건들의 순서가 결정되도록 확장하였으며, 설비 제어방식에 있어서도 FIFO, LIFO, 우선 순위 방식등을 선택할 수 있도록 확장하였다. SIMPLE는 자료구조 및 프로그램이 공개되어 있으므로 프로그래머가 원하는 기능을 쉽게 추가할 수 있는 장점도 있다. 아울러 SMPLE에서 새로이 추가된 자료구조와 함수 및 설비제어 방식등을 활용하여 실제 중형급 시스템에 대한 시뮬레이션 구현과 시스템 분석의 예를 보인다.

• The Transactions of the Korea Information Processing Society
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• v.7 no.8
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• pp.2484-2496
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• 2000

High speed switches have been developing to interconnect a large number of nodes. It is important to analyze the switch performance under various conditions to satisfy the requirements. Queueing analysis, in general, has the intrinsic problem of large state space dimension and complex computation. In fact, The petri net is a graphical and mathematical model. It is suitable for various applications, in particular, manufacturing systems. It can deal with parallelism, concurrence, deadlock avoidance, and asynchronism. Currently it has been applied to the performance of computer networks and protocol verifications. This paper presents a framework for modeling and analyzing ATM switch using stochastic activity networks (SANs). In this paper, we provide the ATM switch model using SANs to extend easily and an approximate analysis method to apply A TM switch models, which significantly reduce the complexity of the model solution. Cell arrival process in output-buffered Queueing A TM switch with finite buffer is modeled as Markov Modulated Poisson Process (MMPP), which is able to accurately represent real traffic and capture the characteristics of bursty traffic. We analyze the performance of the switch in terms of cell-loss ratio (CLR), mean Queue length and mean delay time. We show that the SAN model is very useful in A TM switch model in that the gates have the capability of implementing of scheduling algorithm.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.793-805
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• 2001

In the recent priority system, high-priority packet will be served first and low-priority packet will be served when there isn\`t any high-priority packet in the system. By the way, even high-priority packet can be blocked by HOL (Head of Line) contention in the input queueing System. Therefore, the whole switching performance can be improved by serving low-priority packet even though high-priority packet is blocked. In this paper, we study the performance of preemptive priority in an input queueing switch for high speed switch system. The analysis of this switching system is taken into account of the influence of priority scheduling and the window scheme for head-of-line contention. We derive queue length distribution, delay and maximum throughput for the switching system based on these control schemes. Because of the service dependencies between inputs, an exact analysis of this switching system is intractable. Consequently, we provide an approximate analysis based on some independence assumption and the flow conservation rule. We use an equivalent queueing system to estimate the service capability seen by each input. In case of the preemptive priority policy without considering a window scheme, we extend the approximation technique used by Chen and Guerin [1] to obtain more accurate results. Moreover, we also propose newly a window scheme that is appropriate for the preemptive priority switching system in view of implementation and operation. It can improve the total system throughput and delay performance of low priority packets. We also analyze this window scheme using an equivalent queueing system and compare the performance results with that without the window scheme. Numerical results are compared with simulations.