• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.682-684
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• 2004

IPv4 주소공간의 고갈 문제를 해결하기 위해 많은 사람들은 IPv6의 도입을 추진하고 있다. 따라서 본격적인 보급을 눈앞에 두고 있는 IPv6은 6BONE과 같은 실험망에서 IPv6을 이용하여 개발된 여러 응용프로그램들로 그 성능 및 효용성을 테스트 받고 있다. IPv6 기반 P2P 확장 프로토콜 연구 및 응용 서비스 개발의 일환으로 Distributed Hash Table(DHT)을 이용한 P2P 오버레이 네트워크를 형성하는 툴을 소개한다. 이 툴은 인스턴트 메신저 기능을 함과 동시에 로그인한 사용자 모두를 대상으로 하는 파일 검색 및 공유 기능도 제공한다. 본 논문에서는 P2P 오버레이 네트워크의 구축 과정과 인스턴트 메신저의 친구 목록을 이용한 효과적인 파일 검색 기법을 중점적으로 설명한다.

• Information and Communications Magazine
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• v.28 no.10
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• pp.11-18
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• 2011

최근 다양한 유형의 모바일 클라우드 서비스가 활성화 됨에 따라 서비스 제공을 위한 하부구조에 대한 논의가 증대되고 있다. 모바일 환경에 적합한 클라우드 컴퓨팅 서비스를 제공하기 위해서는 미디어 변환, 처리와 같은 표현(presentation) 계층뿐만 아니라 네트워크 계층에서 서비스를 지원하기 위한 기능이 요구된다. 이러한 기능은 서비스기능 측면에서 QoS, 인증, 로밍 등의 기능이 필요할 뿐만 아니라 클라우드 사업자 내부 시스템의 통합(integration) 및 사업자간 연합(federation) 의 필요성을 증대시킨다. 본고에서는 NGSON 에서 논의되고 있는 서비스 오버레이 구조를 소개하고, 클라우드 컴퓨팅과 통합되는 구조와 특정을 제시하며 끝으로 NGSON 기반 모바일 클라우드 컴퓨팅 서비스를 제공하는 주요사례와 장점을 알아본다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.5
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• pp.139-145
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• 2009

Recently P2P (Peer-to-Peer) networks and applications have been expanded to various field. However, because the construction of P2P network did not influence a underlying network topology or property, it may be inefficient. Especially, this inefficiency is more serious in MANET because MANET has narrow bandwidth and energy constraint. When we use a proactive routing protocol in MANET, we can know hop counts between two nodes. And, we can construct a P2P overlay network using this hop count information. However, In case of using hop count only, we can avoid a interference path selection problem and a zig-zag problem. We propose a method of improving P2P contents distribution using virtual positions. We calculate virtual positions from hop counts using the trigonometry. This method solves a interference path selection problem and a zig-zag problem. This method also allows a P2P network to influence underlying network topology. We adopt this method to a network which uses a virtual geographic routing, a proactive routing protocol, or a reactive routing protocol. We show that our proposed methods improve P2P contents distribution performance over MANET through a simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.4
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• pp.737-747
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• 1997

performance of the cellular CDMA overlay system is analyzed which shares the same band with existing microwave narrowband system to enhance the spectral efficiency. To suppress the interfreence from narrowband system, we used a linear predicition filter that adopts the adaptive least mean square algorithm. Alalyzing the performance in the Personal Communication Services channel, characterized as a multipath Rician fadng channels, we considered the power control to solve the near-far problem, and-off and multipath diversity. We also considered interleaving and channel coding to improve BER performance of the CDMA system.

• Proceedings of the Korean Information Science Society Conference
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• 2008.06d
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• pp.62-65
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• 2008

Mobile IPv6에서 단말이 이동을 하게 되면 경로 최적화를 위한 바인딩 업데이트를 하게 된다. 안전한 바인딩 업데이트를 위해 RFC 3775에서 Return Routability가 제안 되었다. 그러나 Return Routability는 MN과 HA 사이에는 IPSec으로 Secure Path를 보장 받지만, MN과 CN 사이에는 바인딩 업데이트 과정에 공격자가 개입할 경우 다양한 공격에 노출될 수 있다. 이에 본 논문에서는CN도 MN과 같이 HA와 Secure Channel을 보유한 이동 단말일 경우, 각 HA 사이에 커버로스 서버를 이용한 키 분배를 통해 바인딩 업데이트 메시지가 전달되는 전 구간에 걸쳐 안전한 경로를 확보하는 아키텍쳐를 제안한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.35-40
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• 2019

It is important to constantly provide service in real-time multimedia applications using multicast. Transmission path reconstruction occurs in hybrid multicast using Internet Protocol (IP) multicast and ALM in order to adapt the network status to things like congestion. So, there is a problem in which real-time QoS is reduced, caused by an increase in end-to-end delay. In this paper, we want to solve this problem through multi-layer transmission path construction. In the proposed method, we deploy the control server and application layer overlay host (ALOH) in each multicast domain (MD) for hybrid multicast construction. After the control server receives the control information from an ALOH that joins the MD, it makes a group based on the hop count and sends it to the ALOH in each MD. The ALOH in the MD performs the role of sending the packet to another ALOH and constructs the multi-layered transmission path in order of priority by using control information that is received from the control server and based on the delay between neighboring ALOHs. When congestion occurs in, or is absent from, the ALOH in the upper MD, the ALOH selects the path with the highest priority in order to reduce end-to-end delay. Simulation results show that the proposed method could reduce the end-to-end delay to less than 289 ms, on average, under congestion status.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.345-348
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• 2001

The paper describes the physical design flow & verification of Digital Video Broadcasting(DVB) compliant satellite receiver chip. It includes problems and issues of earth design flow, verification process for physical layout.

• Journal of Korea Foundry Society
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• v.43 no.6
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• pp.330-333
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• 2023

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.11
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• pp.42-50
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• 2016

Overlay welding affects the chemical components and weld hardness by dilution of the lamination layer thickness, which determines the surface properties. This study experimentally investigates different numbers of layers for overlay welding monel materials, which are anti-corrosion materials. The Fe content, weldability of the base metal and monel materials, hardness, and surface flatness were examined. Each evaluation was carried out after overlay welding with three layers on the base material and pipe base material of the plate. The Fe content was evaluated by analyzing the constituents of each layer. The Fe content was satisfactory in the three layers. The weldability of the laminate specimens was evaluated by a bending test. The hardness and bead flatness of the laminate specimens were evaluated by micro Vickers and 3D measurements. The hardness was highest in the heat-affected zone with one layer, and it decreased with increasing lamination. In the case of bead flatness, there is a sharp difference in the deviation with increasing numbers of laminations, which should be considered carefully.

• The KIPS Transactions:PartC
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• v.14C no.2
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• pp.163-170
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• 2007

The next generation communication environment consists of various wireless access networks with distinct features that are configured as an overlay topology. In the network environments, the frequency of hand overs should be minimized and the error propagation should be solved in order to provide high-quality multimedia services to mobile users. Therefore, we propose an performance enhancement approach, based on mSCTP, that provides high quality multimedia services to mobile users by ameliorating the error propagation problem. We utilizes the following four functions: 1) the separation of transmission paths according to the types of frames. 2) retransmission strategy to minimize the loss rate of frames, 3) Foced vertical handover execution by utilizing bicasting, 4) using the stability period in order to reduce the effect of the ping pong phenomenon. The simulation results show that the proposed approach provides seamless multimedia service to mobile users by achieving error resilience.