• The Journal of the Korea institute of electronic communication sciences
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• v.17 no.6
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• pp.1047-1054
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• 2022

With the advent of SDN, a next-generation network technology that separates the hardware and software areas of network equipment and defines the network using open source-based software, it solves the problems of complexity and scalability of the existing network system. It is now possible to configure a custom network according to the requirements. However, it has a structural disadvantage that a load on the network may occur due to a lot of control communication occurring between the controller and the switch, and many studies on network load distribution to effectively solve this have been preceded. In particular, in previous studies of load balancing techniques related to flow tables, many studies were conducted without consideration of flow entries, and as the number of flows increased, the packet processing speed decreased and the load was increased. To this end, we propose a new network load balancing technique that monitors flows in real time and applies dynamic flow management techniques to control the number of flows to an appropriate level while maintaining high packet processing speed.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.3
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• pp.50-57
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• 2009

We propose a network node search scheme to address the network fragmentation due to high node mobility in the VANET. VANET is very similar to MANET in that a multi-hop ad-hoc network is configured by wireless communication between vehicles without any network infrastructure. However, high speed mobility, high node density, and frequent topology change induce frequent network fragmentation so that overall network traffic can be increased. In this paper, new broadcasting protocol called an adaptive relay node search protocol is proposed to decrease the network fragmentation. It reduces the network fragmentation and network traffic by researching nodes outside the dangerous area only in case of network fragmentation. Simulation results show that the proposed protocol decreases network fragmentation by up to 39.9% and increase informed rate by up to 41.9% compared to the existing broadcasting protocol.

• Journal of the Korea Society for Simulation
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• v.15 no.3
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• pp.69-77
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• 2006

Geocasting is a form of communication that transmits messages to all nodes within a given geographical region(i.e., the geocasting region). Most of conventional onery aware protocols were based on shortest-hop routing that is, they minimized the cost in terms of the distance and total transmission energy not considering both the residual energy at each node and the link error ratio when selecting the routes for communication. In this paper we propose a MLRG(Maximum Lifetime Reliable Geocast) protocol for energy-efficient and reliable geocasting in Ad-hoc networks. The proposed MLRG, a position-based and routing-based geocasting algorithm, maximizes the network lifetime using newly defined cost function and selecting the energy balanced routes on the basis of each node's residual energy, and provides a reliable communication considering the link error ratio.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.9A
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• pp.868-877
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• 2006

Sensor network applications need synchronized time to the highest degree such as object tracking, consistent state updates, duplicate detection, and temporal order delivery. In addition, reliability issues and fault tolerance in sophisticated sensor networks have become a critical area of research today. In this paper, we proposed a fault tolerant clock management scheme in sensor networks considering two cases of fault model such as network faults and clock faults. The proposed scheme restricts the propagation of synchronization error when there are clock faults of nodes such as rapid fluctuation, severe changes in drift rate, and so on. In addition, it handles topology changes. Simulation results show that the proposed method has about $1.5{\sim}2.0$ times better performance than TPSN in the presence of faults.

• Proceedings of the Korean Information Science Society Conference
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• 2007.10b
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• pp.313-318
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• 2007

위치기반서비스에서 사용자의 정확한 위치가 요구되면서 측위와 추적에 대한 연구가 활발히 진행되고 있다. 측위 방법에는 위성기반 방법[1, 2], 로컬네트워크기반 방법[3-6], 센서기반 방법[1, 7, 8, 9]등이 있다. 본 연구에서는 로컬네트워크 중 WLAN (Wireless Local Area Network) 환경의 옥내에서 사용자의 위치를 추적하는 기존의 방법의 정확성을 제고하는 방안을 제안한다. 제안하는 방법은 WLAN 환경에서 RSS를 측정하여 K-NN방식으로 현재 위치를 판단한 다음, 칼만필터를 사용하여 사용자의 위치와 이동경로를 예측한다는 점에서 기존의 방법과 비슷하다. 제안하는 방법의 특징은 도면 정보를 이용하는 것이다. 제안하는 방법은 도면정보로부터 갈림길 영역을 파악하고, 갈림길 영역에서는 측정치에 가중치를 두고 갈림길이 아닌 지역에서는 시스템 모델에 가중치를 두도록 파라메타의 값을 조절한다. 제안하는 방법의 효율성을 실험적으로 증명하기 위한 실험 결과와 분석 내용도 제시한다.

• Proceedings of the Korea Multimedia Society Conference
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• 2002.05c
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• pp.437-442
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• 2002

이 논문에서는 WLAN 네트워크 환경에서 이동 호스트에게 QoS가 보장된 실시간 멀티미디어 서비스를 제공하기 위한 방법론을 제안한다. 이동무선 환경에서 MH(Mobile Host)의 이동특성은 실시간 멀티미디어 어플리케이션에게 제공되어야 하는 QoS에 심각한 영향을 주게 된다. MH의 이동성에 영향을 받지 않는 QoS를 제공하기 위해서 MH가 가까운 장래에 이동할 것으로 예상되는 영역에 미리 자원을 예약함으로서 요구되는 QoS를 제공할 수 있다. 기존의 유선환경에서 제안된 RSVP은 유선환경을 고려하여 개발된 프로토콜로써 이동무선 환경에 적용하기에는 부적절하며, 이를 개선한 MRSVP는 많은 자원의 낭비를 가져오고 있다. 본 논문에서는 기존의 MRSVP 프로토콜에 링크계층의 핸드오프 정보를 적용하여 최소한의 자원만을 예약하도록 하는 방법론을 제안한다. 이는 미리 자원을 예약하는 영역을 능동적으로 최적화함으로써 불필요한 자원의 낭비를 막고, MRSVP와 같은 수준의 QoS를 제공할 수 있다.

• Korean Journal of Comparative Education
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• v.28 no.1
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• pp.1-24
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• 2018

The objective of the article is to find the research trends and the main traits presented in the keywords on abstracts of research articles of "International Journal of Education Development" from 2002 to 2017. To do this, Text Network Analysis(TNA) was applied targeting 966 papers on the journal and the major research outcomes are as follows. First, the frequency analysis on the keywords showed that the keywords like Administration of education program, Schools and instruction, Regional public administration, Educational support service, Elementary education, and Elementary and secondary school were analyzed more than 100 times and also high in centrality degree. Second, the analysis results of the keywords presented in those research articles by development goal periods showed that several new keywords like Elementary education, Elementary and secondary school, Education quality, Secondary education, Educational planning have emerged frequently after SDGs and these keywords showed high in their centrality analysis. Third, the analysis on education level showed that the keywords like Elementary education, Administration of education program, School children were high in frequency and centrality degree in Elementary level. In secondary level, Schools and instruction, Administration of education program, Academic achievement were high, and in high level, college and university was high, respectively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.5
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• pp.2150-2156
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• 2013

This study attempts to identify how the value network of mobile industry has evolved in the value creating process. The longitudinal case study on SK Telecom was conducted by measuring the SK Telecom's investment structure during from 1999 to 2008. Results show that the convergence services based on the advanced mobile networks changed the revenue structure, and enabled SK Telecom to reposition as a media company. For the value creation, SK Telecom's value network has flexibly adapted to convergence environment through dynamic asset reconfiguration.

• Proceedings of the Korea Multimedia Society Conference
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• 2002.05c
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• pp.449-454
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• 2002

네트워크 혼잡으로 인한 패킷 손실은 인터넷 망에서는 필수 불가결이고, 압축된 비디오 비트 스트림을 인터넷 망에 전송할 경우 공-시간적 도메인상에 에러 전파을 야기하므로 화질에 심각한 화질열화를 초래한다. 본 논문에서는 수신측에서 손상된 영상 일부분을 복구하기 위하여 새로운 에러 은닉 알고리즘인 EBMA(Edge detecting for Boundary Matching Algorithm)를 제안한다. 기존 BMA는 부호화된 인접한 블록의 움직임벡터들이 상당히 높은 유사도 혹은 상관도 (correlation)를 갖고 있다는 점과 손실블록과 인접블록 경계에 존재하는 화소간의 유사도를 이용하기 때문에 비교적 신뢰할 수 있지만, 손실블록과 정확히 복원된 인접블록 화소간의 방향성을 고려하지 않는 단점이 있다. 따라서 제안한 알고리즘은 에지영역을 검출하고, 검출된 에지영역에서 방향성을 조사하므로 기존 BMA 방법 보다 성능이 향상되었다. 실험결과는 제안한 알고리즘이 기존 BMA 방법보다 계산 및 화질측면에서 우월하였을 뿐만 아니라, PSNR 값과 주관적인 화질상에서도 좋은 결과를 나타내었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.1B
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• pp.8-17
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• 2004

In this paper: we propose the adaptive error concealment technique for scalable video coding over wireless network error prove environment. We prove it is very effective that Error concealment techniques proposed in this paper are applied to scalable video data. In this paper, we propose two methods of error concealment. First one is that the en·or is concealed using the motion vector of base layer and previous VOP data. Second one is that according to existence of motion vector in error position, the error is concealed using the same position data of base layer when the motion vector is existing otherwise using the same position data of previous VOP when the motion vector is 0(zero) adaptively. We show that according to various error pattern caused by condition of wireless network and characteristics of sequence, we refer decoder to base layer data or previous enhancement layer data to effective error concealment. Using scalable coding of MPEG-4 In this paper, this error concealment techniques are available to be used every codec based on DCT.