• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.237-252
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• 2017

In recent years, data centers have become the core infrastructure to deal with big data processing. For these big data applications, network transmission has become one of the most important factors affecting the performance. In order to improve network utilization and reduce job completion time, in this paper, by real-time monitoring from the application layer, we propose job-aware priority scheduling. Our approach takes the correlations of flows in the same job into account, and flows in the same job are assigned the same priority. Therefore, we expect that flows in the same job finish their transmissions at about the same time, avoiding lagging flows. To achieve load balancing, two approaches (Flow-based and Spray) using ECMP (Equal-Cost multi-path routing) are presented. We implemented our scheme using NS-2 simulator. In our evaluations, we emulate real network environment by setting background traffic, scheduling delay and link failures. The experimental results show that our approach can enhance the Hadoop job execution efficiency of the shuffle stage, significantly reduce the network transmission time of the highest priority job.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권2호
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• pp.846-864
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• 2017

Software Defined Network (SDN) realizes management and control over the underlying forwarding device, along with acquisition and analysis of network topology and flow characters through south bridge protocol. Data path Identification (DPID) is the unique identity for managing the underlying device, so forged DPID can be used to attack the link of underlying forwarding devices, as well as carry out DoS over the upper-level controller. This paper proposes a dynamic defense method based on Client-Puzzle model, in which the controller achieves dynamic management over requests from forwarding devices through generating questions with multi-level difficulty. This method can rapidly reduce network load, and at the same time separate attack flow from legal flow, enabling the controller to provide continuous service for legal visit. We conduct experiments on open-source SDN controllers like Fluid and Ryu, the result of which verifies feasibility of this defense method. The experimental result also shows that when cost of controller and forwarding device increases by about 2%-5%, the cost of attacker's CPU increases by near 90%, which greatly raises the attack difficulty for attackers.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.3775-3788
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• 2014

With the increasing number of the wireless and mobile networks, the way that people use the Internet has changed substantively. Wireless multimedia services, such as wireless video streaming, mobile video game, and mobile voice over IP, will become the main applications of the future wireless Internet. To accommodate the growing volume of wireless data traffic and multimedia services, cognitive radio (CR) and Information-Centric Network (ICN) have been proposed to maximize the utilization of wireless spectrum and improve the network performance. Although CR and ICN have high potential significance for the future wireless Internet, few studies have been conducted on collaborative operations of CR and ICN. Due to the lack of infrastructure support in multi-hop ad hoc CR networks, the problem is more challenging for video streaming services. In this paper, we propose a Cross-layer Video Streaming Mechanism (CLISM) for Cognitive Radio Ad Hoc Information Centric Networks (CRAH-ICNs). The CLISM included two distributed schemes which are designed for the forwarding nodes and receiving nodes in CRAH-ICNs. With the cross-layer approach, the CLISM is able to self-adapt the variation of the link conditions without the central network controller. Experimental results demonstrate that the proposed CLISM efficiently adjust video transmission policy under various network conditions.

• Journal of Electrical Engineering and information Science
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• 제2권3호
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• pp.29-40
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• 1997

Two asymptotic analyses of the queue length distribution at a statistical multiplexor supporting heterogeneous exponential on-off sources are considered. The first analysis is performed by approximating the cell generation rates as a multi-dimensional Ornstein-Uhlenbeck process and then applying the Benes queueing formula. In the second analysis, w state with a system of linear equations derived from the exact expressions of the dominant eigenvalue of the matrix governing the queue length distribution. Assuming that there are a large number of sources, we obtain asymptotic approximations to the dominant eigenvalue. Based on the analyses, we define a traffic descriptor to include the mean and the variance of the cell generation rate and a burstiness measure. A simple expression for the quality of service (QoS) in cell loss rate is derived in terms of the traffic descriptor parameters and the multiplexor parameters (output link capacity and buffer size). The result is then used to quantify the factors determining the required capacity of a call taking the statistical multiplexing gain into consideration. As an application of the analyses, we can use the required capacity calculation for simple yet effective connection admission control(CAC) algorithms.

• 한국식물학회:학술대회논문집
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• 한국식물학회 1998년도 The 12th Symposium on Plant Biotechnology Vol.12
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• pp.61-70
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• 1998

Genome and chromosome analyses in plants using fluorescence in situ hybridization (FISH) and immuno-staining (IMS) methods are reviewed by presenting the recent results obtained by the Chromosome Link, a group of chromosome and genome researchers. FISH is now effective to detect unique nucleotide sequences with 153 bp on the extended DNA fibers. Genomic in situ hybridization (GISH) also allows painting plant chromosomes of different genomes. GISH is quite effective to detect the genomic differentiation in the individual chromosomes within a nucleus. Three dimensional (3D) analyses are now available by confocal microscopy and a deconvolution system. These techniques are invaluable to visualize both the structural and functional dynamics within a nucleus. 3D-FISH revealed the spatial differentiation of different genomees within a nucleus. 3D-FISH also proved structural partition of centromeric and telomeric domains within a barely nucleus. The dynamic acetylation of histone H4 at the specific regions of a genome during a cell cycle is also analyzed using 3D-IMS. It is anticipated that these methods will provide us powerful tools to understand the structural and functional significance of plant chromosomes and genomes.

• Composites Research
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• 제16권6호
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• pp.1-9
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• 2003

본 논문에서는 웨이블 분포 함수를 이용한 확률 파손 해석을 통해 복합재 압력 용기의 섬유 강도를 예측하였다. 그리고 섬유 강도의 크기 효과를 확인하고 해석의 타당성을 입증하기 위하여 섬유 인장 시편, 한 방향 복합재 시편과 복합재 압력 용기를 이용만 강도 시험이 수행되었다. 해석적 방법으로 웨이블 최약 링크 파손 모델과 다단계 연속 파손 모델을 이용하였고, 해석 결과를 상호 비교하였다. 크기 효과에 의해, 시편의 부피가 증가함에 따라 섬유 인장 강도가 감소하는 경향을 나타내었다. 해석을 통해 예측한 한 방향 복합재 시편과 복합재 압력 용기의 후프 층 섬유 강도 분포는 시험 값과 좋은 일치를 보였다. 섬유 강도의 크기 효과는 소재와 제작 공정 변수의 함수로서, 다른 소재 및 제작 공정에 대해서는 다른 크기 효과를 보이게 된다.

• Journal of Communications and Networks
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• 제13권2호
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• pp.160-166
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• 2011

In u-healthcare services based on wireless body sensor networks, reliable connection is very important as many types of information, including vital signals, are transmitted through the networks. The transmit power requirements are very stringent in the case of in-body networks for implant communication. Furthermore, the wireless link in an in-body environment has a high degree of path loss (e.g., the path loss exponent is around 6.2 for deep tissue). Because of such inherently bad settings of the communication nodes, a multi-hop network topology is preferred in order to meet the transmit power requirements and to increase the battery lifetime of sensor nodes. This will ensure that the live body of a patient receiving the healthcare service has a reduced level of specific absorption ratio (SAR) when exposed to long-lasting radiation. We propose an efficientmethod for delivering delay-intolerant data packets over multiple hops. We consider forward error correction (FEC) in an erasure correction mode and develop a mathematical formulation for packet-level scheduling of delay-intolerant FEC packets over multiple hops. The proposed method can be used as a simple guideline for applications to setting up a topology for a medical body sensor network of each individual patient, which is connected to a remote server for u-healthcare service applications.

• 한국통신학회논문지
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• 제35권1B호
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• pp.136-143
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• 2010

본 논문에서는 임의로 분포되어 있는 레일리 페이딩(Rayleigh fading) 채널 하에서 소스노드와 목적지 노드 사이의 직접 경로가 존재하고 복호 후 전송(decode-and-forward) 방식을 사용하여 중계하는 시스템을 고려한다. 이때, 다수의 릴레이 가운데 베스트 릴레이를 선택하여 이중 홉을 사용하여 통신하는 경우와 다중 홉을 사용하여 통신하는 경우의 아웃티지 확률을 구하고, 이를 통해 그 성능을 비교한다. 여기서 소스 노드와 릴레이들로부터 목적지 노드가 받은 모든 신호는 maximum ratio combining (MRC) 기법을 사용하여 결합하였고, 모든 경우에 대하여 목적지 노드에서 받은 수신 신호의 SNR이 갖는 확률 밀도 함수(probability density function, PDF)와 누적 확률 변수(cumulative density function, CDF)를 유도하였다. 이와 같이 구한 아웃티지 확률을 통해 릴레이의 개수가 2개일 때를 가정하고 실험한 결과, 채널 상태가 나쁠수록 다중 홉을 사용하여 통신하는 기법이 베스트 릴레이 선택 기법보다 좋은 성능을 보였다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2017년도 전력전자학술대회
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• pp.433-434
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• 2017

기존의 전력 시스템에서 큰 부피를 차지하는 계통 주파수(50/60Hz) 변압기를 대체하기 위해서, 최근 전력용 반도체 변압기 SST(Solid State Transformer)에 대한 연구가 많이 수행되고 있다. AC/DC 컨버터는 높은 시스템 입력 전압에 대응 가능한 기존의 다양한 멀티레벨 컨버터 중 CHB (Cascaded H-bridge) 컨버터는 시스템 모듈화의 용이성과 상용 소자의 정격전압을 고려했을 때 반도체 변압기 시스템에 가장 많이 적용되고 있는 토폴로지이지만 각각의 H-bridge 컨버터 DC-link 전압의 불평형 문제가 발생한다. 본 논문에서는 CHB 컨버터의 전압 불평형을 해결하기 위하여 추가적인 센서가 필요없는 간단하고 실용적인 전압 불평형 보상 제어기를 제안한다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 G
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• pp.3064-3066
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• 1999

The existing equipment with wire communication can expect the stability of data transmission. However, according to increasing a number of DTE (Data Terminal Equipment), wiring work becomes a heavy burden. Restriction to application about portable DTE and the lack of flexibility are another drawback of wire communication. This paper presents the design and implementation of a RF (Radio Frequency) based wireless communication system. The RF based module is designed to the multi communication between DTEs. The RF based module consists of RF circuit and microprocessor. The main properties of RF circuit are maximum 5Kbps transmission rate, maximum 90m transmission distance and 433MHz frequency band. The microprocessor rearrange the data into AHDLC(Advanced High level Data Link Control) format and then instructs RF circuits to transmit/receive the data. The RF module have a wide application field such as fire/security alarm, remote control/measurement etc..