• Journal of KIISE:Information Networking
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• v.32 no.1
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• pp.80-88
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• 2005

In ubiquitous spaces, a user wants to be provided with a VOD service while moving one space to another freely. Since the traditional VOD system is dependent on user location, the VOD server transmits video data to a single client during a session. If the user moves to another space, he/she should close the old session and make a new request for the same video. However, the location-aware VOD system supports user mobility by closing and opening the session automatically. That is, the VOD system automatically perceives the movement of a user and allows the server to change the data flow so that a client near the user can receive the video data. This paper proposes a location-aware VOD service architecture and a session handoff scheme to provide a mobile user with continuous video delivery and implements a location-aware VOD prototype system based on Jini and Java. In experiment, we show that the proposed handoff scheme has a smaller handoff delay than the other handoff scheme.

• Journal of Industrial Technology
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• v.24 no.B
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• pp.177-186
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• 2004

The main bottleneck for a VOD system is bandwidth of storage or network I/O due to the high bandwidth requirements and long-lived nature of digital video. Patching is one of the most efficient techniques to overcome the bottleneck of the VOD system through the use of multicast scheme. In this paper, we propose a new patching scheme, P2P proxy patching, for improving the typical patching technique by jointly using the proxy prefix caching scheme and the P2P proxy. In our proposed scheme, each client play a role in a proxy for multicasting a regular stream to other clients that request the same stream. Due the use of the P2P proxy and the prefix caching, the server bandwidth is required significantly less than that of the typical patching technique. In the performance study, we show that our patching scheme can reduce the server bandwidth requirements compared with the existing patching techniques.

• Convergence Security Journal
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• v.7 no.2
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• pp.135-143
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• 2007

This study proposes a DRM system for VOD streaming services in a mobile environment. The proposed system consists of DRM client manager (Consumer), in which core components for client services are independently constructed to be used in a mobile environment, and DRM server, which provides DRM services. Consumer independently exists in the client to maximize efficiency and processing capacity in such a mobile environment, and consists of license service, content service, access service, and tracking service. DRM server consists of streaming server for VOD streaming, distributor, license server, and provider. The proposed system has an architecture suitable for a mobile environment that is difficult to process in the existing DRM system and can solves the super-distribution using license manager in client manager.

• Proceedings of the Korean Information Science Society Conference
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• 2001.04a
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• pp.277-279
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• 2001

VOD 서비스를 원활히 제공하기 위해서는, 대용량의 멀티미디어 데이터를 전송할 수 있는 고속의 네트워크의 구축과 더불어, 날로 증가하는 사용자들의 요구를 수용할 수 있는 서버가 요구된다. 그러나 단일서버의 VOD 시스템은 고장 발생 시, 서비스를 중단해야 할 뿐만 아니라, 늘어나는 서비스 요청에 효과적으로 대응할 수 있는 확장성 또한 유연하지 않아서, 클러스터링 기술을 적용한 VOD 서버가 그 대안으로 인식되고 있다. 본 논문에서는 리눅스를 이용한 클러스터링 VOD 서버와 관련하여, 미디어 스트라이핑 방법과 서버 설계 및 구현 과정에 대하여 기술한다.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.301-303
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• 2003

비디오 서버는 제한된 자원을 이용하여 보다 많은 사용자에게 안정적인 005(Quality of Service)를 제공하는 것이 중요하다. 본 논문에서는 안정적인 QoS를 지원하기 위한 서버 진입 제어에 관한 연구를 클러스터 형태의 VOD 서버에서 수행하였다. 리눅스 환경에서 구축된 VOD 서버의 성능을 분산 저장 노드의 수와 일반 재생 및 고속 재생의 비율을 변화시키며 측정하였다. 측정한 결과를 토대로 클러스터 VOD 서버의 성능 제한의 원인을 분석하고, 그에 따른 대책을 제안한다. 분석된 자료는 클러스터 VOD 서버에서 진입 제어의 기준을 결정하는 변수들로 사용되어 진다.

• Journal of Korea Multimedia Society
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• v.7 no.3
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• pp.357-367
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• 2004

In VOD systems the number of channels available to a video server is limited since the number of channels, the video server can support, is determined by the communication bandwidth of the video server. Multicast techniques such as batching, patching and batch-patching have been proposed to reduce I/O demand on the video server by sharing multicast data. In this paper, we propose a channel reservation batch-patching technique that first applies the batching technique to hot video requests and then applies the patching technique to the batches of the hot video requests. And the proposed technique reserves a part of the channel capacity of the video server for many hot video requests, so that the hot video requests can be served without defection. The performance of the proposed technique is compared with those of Patching and Batch-Patching techniques in terms of average service latency, defection rate, fairness and frame reduction rate by simulations.

• Journal of the Korea Society for Simulation
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• v.9 no.3
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• pp.65-75
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• 2000

In recent years, significant advances in computers and communication technologies have made multimedia services feasible. As a result, various queuing models and cost models on architecture and data placement for multimedia server have been proposed. However, these analytical techniques use only probabilistic models to represent the behavior of a system, and then they have several limitations like accuracy. Simulation is a viable alternative to analytical model. It avoids many of the limitations associated with analytical techniques, allowing for more precise representation of system attributes like workload in program code. In this paper, we propose a simulation test bed that can evaluate performance of real-time multimedia server by using simulation model.

• Journal of Korea Multimedia Society
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• v.11 no.5
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• pp.685-691
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• 2008

Recently with the rapid evolution of the mobile computing and communication technologies, mobile VOD service becomes increasingly important for wireless mobile users. The VOD service is being widely used in various areas of application, such as education, entertainment and business, because it provides users convenience in easily having access to video information at any time in any places. However, in reality, the mobile system has many difficulties in providing the smooth VOD service owing to frequent transfers and cutoffs of clients. The importance of a technique to transmit broadcasting is being stressed as a method for providing stabler mobile VOD service to a large number of clients. This paper is aimed at showing how to reduce demands for server bandwidth and delay of earlier service through performance analysis by suggesting an effective VOD broadcasting transmission technique through channel division in the mobile atmosphere. Many researches have been made about regular broadcasting techniques in particular. This study divides the methods used for assigning channels which have been decided by the size of segments into a group of regular channels and assistant channels using wireless gap-fillers to provide effective VOD services to a large number of clients at the mobile environment using small bandwidth resources. The regular channels transfer regular streams, while assistant channels repeatedly transfer the first segment to reduce early service delay time to receive regular streams. In this way, the study suggests a technique to reduce server bandwidth demand and early service delay time. Through the proposed technique, the server bandwidth demand could be reduced by more than 30 percent and the study continuously shows reduced early service delay time through conducting performance analysis.

• The KIPS Transactions:PartA
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• v.12A no.5 s.95
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• pp.341-354
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• 2005

The main bottleneck for large scale VOD systems is bandwidth of storage or network I/O due to the large number of client requests simultaneously, and then efficient techniques are required to solve the bottleneck problem of the VOD system. Patching is one of the most efficient techniques to overcome the bottleneck of the VOD system through the use of multicast scheme. In this paper, we propose a new patching scheme, called P2P proxy patching, for improving the typical patching technique by jointly using the prefix caching and P2P proxy. In our proposed scheme, each client plays a role in a proxy to multicast a regular stream to other clients that request the same video stream. Due to the use of the P2P proxy and the prefix caching, the client requests that ive out of the patching window range can receive the regular stream from other clients in the previous patching group without allocating the new regular channels from the VOD server to the clients. In the performance study, we show that our patching scheme can reduce the server bandwidth requirement about $33\%$ less than that of the existing patching technique with respect to prefix size and request interval.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.11
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• pp.797-809
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• 2006

To support the QoS streams for large scale clients, the internal resources of VOD servers should be utilized based on the characteristics of the streaming media service. Among the various resources in the server, the main memory is used for the buffer space to the media data loaded from the disks and the buffer hit ratio has a great impact upon the server performance. However, if the buffer data with high hit ratio are replaced for the new media data as a result of the number of clients and the required movie titles are increased, the negative impact on the scalability of server performance is occurred. To address this problem, the buffer replacement policy considers the intrinsic characteristics of the streaming media such as the sequential access to large volume data and the highly disproportionate preference to specific movies. In this paper, the preference-based segment buffer replacement policy is proposed in the cluster-based VOD server to exploit the characteristics of the streaming media. Since the proposed method reflects both the temporal locality by the clients' preference and the spatial locality by the sequential access to media data, the buffer hit ratio would be improved as compared to the existing buffer replacement policy. The enhanced buffer hit ratio causes the fact that the performance scalability of the cluster-based VOD server is linearly improved as the number of cluster nodes is increased.