• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.229-231
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• 2001

최근 VOD 시스템에서 cost를 줄이기 위해 사용되는 멀티캐스트 전송 방법은 각 사용자의 대화형 서비스를 지원하기에는 많은 어려움이 있다. 따라서 본 논문에서는 많은 사용자를 서비스하는 VOD 시스템에서 VCR 기능을 보장하고 동시에 초기지연을 줄일 수 있는 프레임 기반 멀티캐스트 전송 기법을 제안한다. 이 기법은 일반 재생과 VCR 재생 모두를 동일한 채널로 지원한다. 이때 세그먼트를 구성하고 있는 프레임의 종류에 따라 개별적인 채널로 프레임을 전송하고 있다. 실험 결과를 통해 제안한 기법이 다른 기법보다 VCR blocking 확률 면에서 보다 나은 성능을 가짐을 보여준다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1A
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• pp.1-9
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• 2010

This paper offers performance analysis of selection decode and forward (DF) networks with differential modulation/demodulation for an arbitrary number of relays in independent but not identically distributed Rayleigh fading channels. We have shown that the selection DF protocol with differential modulation can achieve full diversity in both independent identically distributed (i.i.d.) and independent but not identically distributed (i.n.d.) Rayleigh fading channels, and the performance loss due to using non-coherent detection is not substantial. Furthermore, we study the impact of combining techniques on the performance of the system by comparing a system that uses selection combining (SC) to one that uses maximum ratio combining (MRC). Simulations are performed and show that they match exactly with analytic ones in high SNR regime.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1110-1114
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• 1998

The crystallization behaviors and electrical conductivities of the glasses heat-treated at various times and temperatures in the CuO-Bi$_2$O$_3$-V$_2$O$_{5}$ glass system were investigated. Among glass samples with various compositions, the highest conductivity obtained in the 31CuO-14Bi$_2$O$_3$-55V$_2$O$_{5}$ (mol%) glass sample. The 31CuO-14Bi$_2$O$_3$-55V$_2$O$_{5}$ (mol%) glass sample crystallized by heat treatment at 358$^{\circ}C$ for 8h had 2.67$\times$10$^{-2}$ $\Omega$$^{-1}$ $cm^{-1}$ /, which was much high value as a solid electrolyte. Compared to the glass sample, the heat- treated glass sample was increased in conductivity by an order of 10$^3$-10$^4$due to the formation and growth of BiVO$_4$ and CuVO$_3$crystals.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.12
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• pp.660-673
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• 2001

In Video-on-Demand (VoD) servers, disk throughput is an important system design parameter because it is directly related to the number of user requests that can be served simultaneously. In this paper, we propose an efficient periodic request grouping scheme for disk array-based VoD servers that reduces the disk seek time, thus improving the disk throughput of VoD disk arrays. To reduce the disk seek time, the proposed scheme groups the periodic requests that access data blocks stored in adjacent regions into one, and arranges these groups in a pre-determined order (e.g., in left-symmetric or right-symmetric fashion). Our simulation result shows that the proposed scheme reduces the average disk bandwidth required by a single video stream and can serve more user requests than existing schemes. For a data block size of 192KB, the number of simultaneously served user requests is increased by 8% while the average waiting time for a user request is decreased by 20%. We also propose an adaptation technique that conforms the proposed scheme to the user preference changes for video streams.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.437-440
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• 2011

IP 기반은 VoD, 인터넷 등의 통신 서비스와 실시간 방송 프로그램을 제공하는 통신과 방송의 속성을 모두 가진 융합서비스를 의미한다. 이러한 IP 기반을 통해 본 논문은 사용자의 요청에 따라 양방향으로 다양한 멀티미디어 콘텐츠를 제공할 수 있도록 미디어 데이터의 유연성과 적응성이 고려된 멀티미디어 시스템 설계 및 구현을 하고자 한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.9A
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• pp.704-711
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• 2009

In this paper, we report the results of the field trial test of 1GbpsX16channels Injection locking FP-LD based WDM-PON system which could guarantee 40Mbps minimum bandwidth per subscriber, We have confirmed the system reliability, also verified that the system could reliably deliver the service such as internet, VoD through the systems during the field trial test.

• Proceedings of the Optical Society of Korea Conference
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• 2008.07a
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• pp.421-422
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• 2008

In this paper, we will present the results of 1Gbps x 16 channels RSOA remodulation based WMD-PON field trial test. We have confirmed the system reliability, also verified the system could reliably deliver the service such as internet, VoD through the system during the field trial test.

• Proceedings of the Korea Information Processing Society Conference
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• 2001.10b
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• pp.1435-1438
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• 2001

MGCP는 IETF에서 제안한 VoIP기술의 표준 프로토콜로서 특유의 단순함(Simplicity)을 이용하여 다른 프로토콜과의 연동을 용이하게 구현할 수 있도록 설계되었으며, 현재 다양한 시스템과 프로토콜로 구성되어 있는 망을 통합하기 위한 적절한 해결책으로 부각되고 있다. 본 논문에서는 MGCP기반의 AX-Gateway 시스템의 설계기법에 관하여 기술한다. MGCP기반의 AX-Gateway 시스템은 H.323과의 연동을 위하여 내부적으로 자신에게 연결된 Endpoint의 상태정보를 유지하도록 설계하였다. 이러한 구조를 통해 자신에게 전달되는 호처리 요청에 대한 유효성을 MG 차원에서 검사함으로써, Call Agent의 부하를 줄여 시스템의 안정성과 성능 향상을 기대할 수 있다. 이렇게 구현된 AX-Gateway 시스템의 성능을 측정하기 위하여 통화음질과 지연, 최대 동시 통화 사용자의 수를 측정한 결과를 나타내었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11C
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• pp.51-63
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• 2001

According to the popular use of the multimedia services in distributed environments, the need for the variable multimedia communication technologies have been presented today. In order to support the efficient transmission multimedia streams, the multicasting, and the interoperability between multimedia applications in distributed environments, the development of the open exclusive multimedia communication systems and the provision of the control and management methodologies for media streams have been required. In order support the realtime transmission of multimedia stream in distributed environments. the protocols such as RTP, RSVP, and RTSP have been standardized. For supporting the interoperability between multimedia applications and the control and management of streams, the distributed processing platforms such as CORBA by OMG and DSM-CC by DAVIC were published. In this paper, we introduce the CORBA-based distributed multimedia communication system which support the realtime transmission, control, and management of multimedia streams and provide the interoperability between multimedia applications. Finally, we present the QoS measurement results by the interoperability between our systems and VoD systems.

• Journal of Digital Contents Society
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• v.10 no.1
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• pp.61-71
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• 2009

While the broadband network and multimedia technology are being developed, the commercial market on digital contents as well as IPTV has been widely spreading. Especially IPTV is providing various useful services since it makes using multimedia contents easier and more convenient by combining the strong points of both TV and PC system. Until now, IPTV system has been focused on VoD service as a general usages. However, various IPTV services are recently demanded since they can have special features for some specific places and occasions. So in this paper, we propose a design of the download based IPTV system using user-specific channel management. At first, program contents previously scheduled by users are downloaded and are played at settop-box according to the prescribed time table. This system has some advantages of giving users easy access to any wanted media contents in anytime that is IPTV's characteristics. And we can increase stability of services by using time slot distributed download for contents. Because this service can be constructed and maintained at relatively low cost, we confirm that this service model is more suitable to some companies with small infrastructure and special purposes. Accordingly, in this paper, we look into necessary elements and define some protocols for system in order to help other developer build this system.