• Journal of Internet Computing and Services
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• v.9 no.3
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• pp.141-158
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• 2008

In this paper, we developed the GML Map Server which visualized the map based on GML as international standard for exchanging the common format map and for interoperability of GIS information. And also, it should transmit effectively GML map into the mobile device by using dynamic map partition and caching. It manages a partition based on the visualization area of a mobile device in order to visualize the map to a mobile device in real time, and transmits the partition area by serializing it for the benefit of transmission. Also, the received partition area is compounded in a mobile device and is visualized by being partitioned again as four visible areas based on the display of a mobile device. Then, the area is managed by applying a caching algorithm in consideration of repetitiveness for a received map for the efficient operation of resources. Also, in order to prevent the delay in transmission time as regards the instance density area of the map, an adaptive map partition mechanism is proposed for maintaining the regularity of transmission time. GML Map Server can trace the position of mobile device with WIPI environment in this paper. The field emulator can be created mobile devices and mobile devices be moved and traced it's position instead of real-world. And we developed POIM(POI Management) for management hierarchically POI information and for the efficiency POI search by using the individual tagging technology with visual interface.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.10
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• pp.2750-2763
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• 2012

The Domain Name System (DNS) is a critical Internet infrastructure that provides name to address mapping services. In the past decade, Denial-of-Service (DoS) attacks have targeted the DNS infrastructure and threaten to disrupt this critical service. While the flooding DoS attacks may be alleviated by the DNS caching mechanism, we show in this paper that flooding DoS attacks utilizing name error queries is capable of bypassing the cache of resolvers and thereby impose overwhelming flooding attacks on the name servers. We analyze the impacts of such DoS attacks on both name servers and resolvers, which are further illustrated by May 19 China's DNS Collapse. We also propose the detection and defense approaches for protecting DNS servers from such DoS attacks. In the proposal, the victim zones and attacking clients are detected through monitoring the number of corresponding responses maintained in the negative cache. And the attacking queries can be mitigated by the resolvers with a sample proportion adaptive to the percent of queries for the existent domain names. We assess risks of the DoS attacks by experimental results. Measurements on the request rate of DNS name server show that this kind of attacks poses a substantial threat to the current DNS service.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.52 no.4
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• pp.386-393
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• 2016

It is essential to provide good environment for juvenile fish to grow and spawn in order to keep reproduction mechanism of fisheries resources. However, harvesting juvenile fish deprives adult fish of the opportunity to reproduce, thereby changing self-regulating renewable resources into non-renewable ones and preventing sustainable harvesting as well as reducing fishers' income. We reviewed the catch status of Korea on juvenile mackerel and analyzed how reducing the catch ratio of juvenile mackerel may affect the spawning stock and Korean fishermen's revenue. In addition, we analyzed the problem of caching juvenile mackerel in Korean fisheries and current efforts to protect and reduce the catch ratio of juvenile mackerel in Korea. Furthermore, we suggested future efforts to protect juvenile mackerel. The result of the study showed that reducing the catch ratio of juvenile mackerel from 44.4% to 30.0% would increase fishers' revenue by 60.6 billion KRW. We suggest the changing of purse seine fishery's catching methods from night operation to day operation, relocation of fishing vessels to move to other fishing grounds when fishing vessels meet high density of juvenile mackerel, and consumers' clever choice of consuming adult mackerel in order to accelerate the move toward protecting juvenile mackerel in Korea.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.11a
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• pp.131-134
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• 2002

초고속 네트워크에 연동된 고성능 컴퓨터 자원들을 효과적으로 활용하려는 그리드 컴퓨팅 연구는 네트워크를 통한 기존의 단순한 정보 공유보다 정보 및 자원의 공유를 더욱 더 밀접하게 결합시키는 것을 가능하게 한다. 이상적인 그리드 컴퓨팅 환경을 구축하기 위해서는 무엇보다도 그리드 환경에 속한 자원들의 정보를 통합적으로 관리 및 서비스하는 것이 무엇보다도 그리드 정보 서비스가 중요하다. 그리드 정보서비스의 역할은 그리드 사용자가 필요한 자원 및 그에 대한 정보를 쉽게 찾을 수 있도록 다양한 검색 기능을 제공하는 것 이외에도, 전세계에 분산된 자원들의 최신 정보를 빠르게 서비스하도록 하여야 한다. 이를 위해서는 그리드 환경의 특성을 고려하여 효율적인 그리드 정보 서비스 아키텍쳐를 구성하는 것이 필요하다. 본 논문에서는 그리드 미들웨어인 글로버스 툴킷(Globus $Toolkit^{TM}$)내에 포함된 그리드 정보 서비스를 기반으로 자원 정보의 적응형 캐슁 기법을 이용하여 그리드 정보 서비스 아키텍쳐를 재구성한다. 이를 통해 자원 정보의 일관성을 향상시키면서 기존의 그리드 정보 서비스의 빠른 응답 속도를 제공할 수 있다.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.6
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• pp.1113-1120
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• 2021

Content Central Network (CCN) appeared to improve network efficiency by transforming IP-based network into content name-based network structures. Each router performs caching mechanism to improve network efficiency in the CCN. And the cache replacement policy applied to the CCN router is an important factor that determines the overall performance of the CCN. Therefore various studies has been done relating to cache replacement policy of the CCN. In this paper, we proposed a cache replacement policy that improves the limitations of the LFU policy. The proposal algorithm applies real-time producer popularity-based variables. And through experiments, we proved that the proposed policy shows a better cache hit ratio than existing policies.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1285-1287
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• 2009

VoIP 통신에서 단말간의 세션을 수립하고 종료하는 역할을 하는 SIP는 기본적으로 서버-클라이언트 방식으로 이루어져있다. 하지만 이는 확장성과 설치비용, 단일실패 지점 측면에서 큰 단점을 갖는다. 최근에 DHT를 이용한 구조적인 P2P를 SIP와 결합하여 위의 단점들을 극복하기 위한 연구들이 활발히 진행되고 있다. 하지만 DHT를 이용한 방식은 기존 서버-클라이언트 방식에 비해 검색지연이 늘어난다는 큰 단점을 가지고 있다. 검색지연은 SIP에서 QoS의 중요한 지표중 하나인 호 설정 지연에 60~80% 정도의 큰 영향을 미치게 되므로 해결해야할 중요한 문제이다. P2PSIP에서는 종단 노드가 검색한 사용자의 주소를 캐싱하여 같은 사용자를 재 검색시에 사용하고 있다. 이는 네트워크 전체 오버헤드 감소에 큰 영향을 주지 못할뿐만 아니라 발생된 검색비용을 자신만이 사용할 수 있으므로 비효율적이다. 이에 본 논문에서는 도메인으로 구분된 계층적 P2PSIP네트워크에서 프록시 서버의 역할을 하는 슈퍼노드를 이용한 효과적인 캐싱 방법을 이용하여 호 설정 지연을 단축할 수 있는 방안을 제안하다.

• Journal of KIISE:Information Networking
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• v.27 no.2
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• pp.138-148
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• 2000

In the mobile computing environment, in order to make copies of important files available when being disconnected the mobile host(client) must store them in its local cache while the connection is maintained. In this paper, we propose the prefetching mechanism for the client to save files which may be accessed in the near future. Our mechanism utilizes analyzer, prefetch-list producer, and prefetch manager. The analyzer records file access patterns of the user in a FAP(File Access Patterns) profile. Using the profile, the prefetch-list producer creates the prefetch-list. The prefetch manager requests a file server to return this list. We set the parameter TRP(Threshold of Reference Probability) to ensure that only reasonably related files can be prefetched. The prefetch-list producer adds the files to a prefetch-list if their reference probability is greater than the TRP. We also use the parameter TACP(Threshold of Access Counter Probability) to reduce the hoarding size required to store a prefetch-list. Finally, we measure the metrics such as the cache hit ratio, the number of files referenced by the client after disconnection and the hoarding size. The simulation results show that the performance of our mechanism is superior to that of the LRU caching mechanism. Our results also show that prefetching with the TACP can reduce the hoard size while maintaining similar performance of prefetching without TACP.

• Journal of KIISE:Computer Systems and Theory
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• v.33 no.3
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• pp.193-204
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• 2006

In most existing distributed Web systems, incoming requests are distributed to servers via Domain Name System (DNS). Although such systems are simple to implement, the address caching mechanism easily results in load unbalancing among servers. Moreover, modification of the DNS is necessary to load considering the server's state. In this paper, we propose a new dynamic load balancing method using dynamic DNS update and round-robin mechanism. The proposed method performs effective load balancing without modification of the DNS. In this method, a server can dynamically be added to or removed from the DNS list according to the server's load. By removing the overloaded server from the DNS list, the response time becomes faster. For dynamic scheduling, we propose a scheduling algorithm that considers the CPU, memory, and network usage. We can select a scheduling policy based on resources usage. The proposed system can easily be managed by a GUI-based management tool. Experiments show that modules implemented in this paper have low impact on the proposed system. Furthermore, experiments show that both the response time and the file transfer rate of the proposed system are faster than those of a pure Round-Robin DNS.

• The Transactions of the Korea Information Processing Society
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• v.6 no.1
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• pp.1-10
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• 1999

A mobile computing environment is one that support user's mobility through the wireless communication technology. Users access the database and get results what they want by running mobile transactions. To run the mobile transaction correctly and to maintain the consistency I database, we need a concurrency control method to schedule transactions, a caching method to manage the cache, and a recovery method to construct a fault tolerant system. A mobile computing system is based on the existing distributed system, but we can't use recovery methods of the existing distributed system directly because of the user's mobility and the features of wireless media. So this paper presents a recovery mechanism to construct a fault tolerant mobile computing systems. Especially. we develop and analyze a recovery algorithm for server failure among types of failure which can arise in mobile computing environments.

• Journal of KIISE:Computer Systems and Theory
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• v.29 no.6
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• pp.318-330
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• 2002

This paper discusses the design and implementation of a video server which uses tertiary device, such as magneto-optical jukebox or tape library, as a source of media archiving. In order to handle the tertiary device in the framework of disk-based stream service model, a sophisticated streaming model is required for server and it should consider the device-specific performance characteristics of tertiary storage. We have carefully designed the streaming mechanism for server whose key functionalities include stream scheduling, disk caching and admission control. The proposed system has been implemented on Windows 2000 platform which is equipped with a magneto-optical jukebox. The design principles of the server are validated with the experiments and the performance characteristics is analyzed.