• The KIPS Transactions:PartB
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• v.12B no.7 s.103
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• pp.775-782
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• 2005

In this paper, we propose multicast technique in order to reduce the required network bandwidth by n times, by merging the adjacent multicasts depending on the number of HENs (Head-End-Nodes) n that request the same video. Allowing new clients to immediately join an existing multicast through patching improves the efficiency of the multicast and offers services without any initial latency. A client might have to download data through two channels simultaneously, one for multicast and the other for patching. The more the frequency of requesting the video is, the higher the probability of caching it among HENs increases. Therefore, the requests for the cached video data can be served by HENs. Multicast from server is generated when the playback time exceeds the amount of cached video data. Since the interval of multicast can be dynamically expanded according to the popularity of videos, it can be reduced the server's workload and the network bandwidth. We perform simulations to compare its performance with that of conventional multicast. From simulation results, we confirm that the Proposed multicast technique offers substantially better performance.

• Proceedings of the Korean Information Science Society Conference
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• 2012.06a
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• pp.98-100
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• 2012

모바일 웜의 전파 속도는 시간이 지날수록 급격히 빨라진다. 급속도로 전파하는 웜을 억제하기 위한 연구가 계속 진행되어 왔다. 기존 연구 중 하나로 소셜 네트워크를 그래프(Graph)로 표현하고 분할한 뒤 각 파티션의 대표노드(Key Node)를 선택해 웜 패치를 전파하는 기법이 있다. 이 기법은 패치 전파 속도를 웜 전파 속도보다 빠르게 해서 웜을 억제 시킨다. 하지만 이 기법에서는 대표노드에 가중치(Weight)가 낮은 간선(Edge)이 연결 될 수 있거나 대표노드가 없는 파티션이 생길 수 있다. 잘못된 대표노드 선정은 패치 전파속도를 저하시키고 웜 억제를 지연시킬 수 있다. 본 논문에서는 페이지랭크를 이용해서 대표노드를 선정하는 개선된 소셜 네트워크 기반의 웜 패칭 기법을 제안한다. 제안 기법은 웜 패칭 전략에 사용할 수 있도록 수정한 페이지랭크를 각 파티션에 적용해서 대표노드를 선정한다. 파티션마다 전파 능력이 가장 높은 노드가 대표노드로 선정되기 때문에 웜 패치 전파 속도를 향상시킬 수 있다.

• Journal of KIISE:Software and Applications
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• v.32 no.11
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• pp.1084-1098
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• 2005

In this paper, we propose a migration technique for autonomous mobile agents suitable to dynamic environments. The proposed migration technique dynamically creates the itinerary of agents that considers states of networks and systems. In the migration of the agent, it first sends prefetching message to the next system. The system receives necessary data for migration in advance. Through this, we reduce the amount of the sending data and save the time for creating the instance of the agent. And it improves the execution efficiency by using the checkpoint-based recovery method that does not execute the agent again and recovers the process states even though the errors take place. To show superiority of the proposed technique, we compare the proposed method with the existing methods through various simulations.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1116-1119
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• 2009

최근 그룹 통신 분야에서 전통적으로 대표되는 IP 멀티캐스트의 대안기술로서 호스트기반 멀티캐스트 및 P2P시스템은 기존의 IP 멀티캐스트의 단점을 극복하고자 하는 연구이다. 이러한 호스트기반 멀티캐스트는 사용자 중심의 서비스를 제공함으로써 다양한 네트워크 환경에서 누구나 사용자들이 효율적으로 데이터를 공유하게 해주고 있다. 본 논문에서는 이러한 협동 기반의 호스트 멀티캐스트를 사용하여 미디어 서비스를 제공하는 VOD 시스템 전반에 관한 연구를 수행하고 이러한 VOD의 서비스를 고도화 하고자 한다. 보다 구체적으로는 패칭 기법을 사용하여 사용자간의 전달 지연을 최소화 할 수 있는 효율적인 자료 전송 경로를 설정 방법과 주문형 비디오 서버를 위한 현실적인 호스트 기반 멀티캐스트 트리 구성 모델을 제시하고자 한다.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.77-81
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• 2009

This study was performed to evaluate applicability of patching materials for underwater dam concrete structure. Two kinds of patching materials was investigated. Laboratory experimentals were conducted by workability, compressive strength, bond strength, chloride ion penetration, abrasion resistance. Test results showed that the most performances are relatively good except chloride ion penetration.

• Journal of KIISE:Databases
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• v.32 no.4
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• pp.405-415
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• 2005

Indexing techniques are used to implement selective tuning in wireless environments Indices are broadcast together with data to help mobile clients locate the required information. As a result, clients stay in doze mode most of the time. The drawback of this solution is that broadcast cycles are lengthened due to additional index information. In location-aware mobile services(LAMSs), it is important to reduce the query response time, since a late query response nay contain out-of-date information. In this paper, we present a broadcast-based spatial query processing method (BBS) designed to support k-NN query processing. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients and the size of the service area.

• Journal of KIISE
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• v.44 no.5
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• pp.545-552
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• 2017

Because of the explosive growth of mobile devices and development of network technologies, HTTP (Hypertext Transfer Protocol) adaptive streaming has become a new trend in video delivery to provide efficient multimedia streaming services. As interest in personalized broadcasting grows, the study of interactive multimedia has been actively pursued. The interactive multimedia service is a method of playing media according to a scenario selected by the user. Providing the interactive multimedia service with the existing HTTP adaptive streaming causes switching delay and buffer underflow according to the point in time when the user selects the scenario while the client streams the interactive multimedia and therefore decreases the user QoE (Quality of Experience). In this paper, we propose an adaptive streaming scheme for interactive multimedia service in HTTP adaptive streaming to provide seamless playback. We design the architecture and prefetching scheme for interactive multimedia streaming.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.48-57
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• 2007

The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by usiag the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.1
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• pp.137-149
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• 2004

A new software paradigm is required on the development of network and various service requirements. With this, many studies on a mobile agent have been made. For the execution of the mobile agent, migration is the most important factor that influences the performance of the mobile agent. In this paper we propose the method that leads to high migration efficiency in order to improve the performance. The features of our migration technique are as follows. First, the migration technique creates the dynamic itinerary that appropriately copes with the network conditions and the platform changes to improve the agent execution efficiency. Second, it perfecters an executed code to reduce the amount of the mobile data and reduces the execution time by instantiating the agent in advance. Third, it improves the execution efficiency by using the checkpoint-based recovery method that does not execute the agent again and recovers the process states even though the errors take place. Though the simulation we compare the proposed method with the existing methods. The simulation result shows that the proposed method outperform the existing methods in terms of migration.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.512-514
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• 1998

요약 최근 들어 인터넷 데이터를 사용자와 가까운 위치 복사해 놓음으로써 인터넷 병목현상을 줄이는 인터넷 캐시 서버의 사용이 증가되고 있다. 캐시 서버의 성능은 캐시 적중률과 캐시된 데이터의 신선도에 의해 좌우된다고 할 수 있다. 데이터의 신선도는 캐싱된 데이터가 가장 최근에 갱신된 데이터와 일치할 확률이다. 신선도 유지를 위해 가장 많이 사용되고 있는 방법은 데이터마다 만료시간을 부여하여 만료시간이 지났을 때 새로운 데이터를 요청하는 방법이다. 하지만, 적절하지 않은 만료시간의 설정은 네트웍 교통량 증가나 사용자에게 신선하지 않은 데이터를 전달하는 무제가 생긴다. 본 논문에서는 각 데이터의 접근 주기와 실제 갱신주기에 기초하여 그 페이지의 리프레시 시간을 설정함으로써 요청될 가능성이 높은 페이지들만을 선택하여 프리패칭이 될 수 있도록 하는 기법을 제안한다.