• The KIPS Transactions:PartA
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• v.8A no.3
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• pp.201-208
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• 2001

Explosive growth of the Web and the non-uniform characteristics of client requests result in the performance degradation of Web servers, and server cache has been recognized as the solution. We analyzed Web server accessing characteristics-repetition, size, and locality of access. Based on the result, we analyzed the cache removal policies and proposed a prefetch strategy to improve the hit ratio of server caches. In addition, through the trace-driven simulation based on the traces from real Web sites, we showed the performance improvement by our proposal.

• The KIPS Transactions:PartC
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• v.10C no.3
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• pp.325-334
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• 2003

In stateless server, if an asynchronous cache invalidation scheme attempts to support local processing of read-only transaction in mobile client/sever database systems, a critical problem may occur ; the asynchronous invalidation reports provide no guarantees of waiting time for mobile transactions requesting commit. To solve this problem, the server in our algorithm broadcasts two kind of messages, asynchronous invalidation report to reduce transaction latency and periodic guide message to avoid the uncertainty of waiting time for the next invalidation report. The asynchronous invalidation report has its own sequence number and the periodic guide message has the sequence number of the most recently broadcast asynchronous invalidation report. A mobile client checks its cache validity by using the sequence numbers of these messages.

• Journal of the Korea Society of Computer and Information
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• v.10 no.5 s.37
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• pp.217-226
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• 2005

In today's cyberworld, network performance is affected not only by an increased demand for legitimate content request, but also by an increase in malicious activity. In this Paper, we research that network performance was affected by an increase in malicious Hacker who make DoS Attack, DDoS Attack, SYN Flooding, IP Spoofing, etc. in using TCP/IP. We suggest that Packet filtering in Network Level, Gateway Level, Application Level against to Protect by Hacker's attack. Also, we suggest that content distribution in Web Server approaches to mitigate Hacker's activity using Cache Sever, Mirror Sever, CDN. These suggests are going to use useful Protection methode of Hacker's attack.

• Journal of KIISE:Databases
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• v.32 no.3
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• pp.276-284
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• 2005

In the mobile computing environment, caching data at the client's side is a useful technique for improving the performance. For caching to be effective, the cache contents must be consistent with those stored in the server. That is, unfortunately, difficult to enforce due to the frequent disconnection and mobility of clients. In the literature, the basic approach adopted is for the sever to periodically broadcast invalidation reports(IRs) that contain information about objects that have been updated recently. However IR-based cache maintenance scheme has a main drawback. Any client who has been disconnected longer than w seconds has to discard all cached items even some of them may still be valid. In this paper, we propose two main schemes which can adapt clients' losing IR messages by long disconnection. First, the client sends its disconnection time when connection is re-established, and the server uses this information to decide the size of broadcast window w dynamically. Second, the server maintains IR messages for a given period of time and a client who has been disconnected longer than w seconds can verify its cache consistency individually. Compared to previous IR-based schemes, our schemes can significantly reduce cache missing and uplink request and improve the throughput by reducing response time.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.412-414
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• 2004

대용량의 멀티미디어 데이터들을 다수의 시용자가 동시에 요구할 경우 접속이 끊기거나 데이터의 손실과 같은 접속 성능이 현저하게 저하되는 문제가 발생할 수 있다. 이는 대부분의 사용자들의 요청을 원거리의 Central Server가 단독으로 처리하기 때문에 발생하는 문제이다. 띠라서 Central Sever의 Load 감소와 초기 지연시간 및 비디오 패킷의 손실의 문제점을 해결하기 위해 프록시 서버를 사용자의 근거리에 위치시키는 방법을 이용한다. 대용랑의 멀티미디어 데이터들을 복잡한 인터넷의 중간경로를 거치지 않고 다수의 사용자들에게 직접 전달함으로써 데이터의 손실을 방지함과 동시에 보다 안정적이고 빠른 속도로 제공하는 것이 가능하다. 특징적으로 프록시 서버는 Central Server에 비해 비교적 제한된 용랑을 가지고 있다. 따라서 본 논문에서는 사용자의 선호도를 기반으로 하여 앞으로 요구학 것이라고 예측되는 비디오 데이터들만을 선별적으로 저장하도록 하는 알고리즘을 제안한다. 시뮬레이션을 통해 제안하는 캐쉬 교환 알고리즘을 기존의 알고리즘과 비교, 관찰한 결과 상대적으로 높은 Hit rate가 나타남을 확인하였다.

• Journal of KIISE:Software and Applications
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• v.26 no.8
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• pp.974-987
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• 1999

이동 컴퓨팅 환경에서 자주 접근하는 데이터에 대한 캐싱은 무선 채널의 좁은 대역폭에서 경쟁을 줄일 수 있는 유용한 기술이다. 그러나, 트랜잭션 캐시 일관성을 지원하는 전통적인 클라이언트/서버 전략은 클라이언트와 서버간에 많은 양의 통신을 필요로 하기 때문에 이동 클라이언트/서버 컴퓨팅 환경에서는 적절하지 않다. 본 논문에서는 브로드캐스트-기반 캐시 무효화 정책을 사용하면서 트랜잭션 캐시 일관성을 지원하는 OCC-UTS (Optimistic Concurrency Control with Update TimeStamp) 프로토콜을 제안한다. 접근한 데이터에 대한 일관성 검사 및 완료 프로토콜은 캐시 무효화 과정의 내부 과정으로 완전 분산 형태로 효율적으로 구현되며, 일관성 체크의 대부분이 이동 클라이언트에서 수행된다. 또한, 분석 모델에 기반한 성능 비교를 통해, 본 논문에서 제안하는 OCC-UTS 프로토콜이 다른 경쟁 프로토콜보다 높은 트랜잭션 처리율을 얻으며, 데이터 항목을 자주 접근하면 할수록 지역 캐시를 사용하는 OCC-UTS 프로토콜이 더 효율적임을 보인다. 이동 클라이언트의 접속 단절에 대해서는 무효화 브로드캐스트 윈도우를 크게 하여 접속 단절에 적절히 대처할 수 있다.Abstract In a mobile computing environment, caching of frequently accessed data has been shown to be a useful technique for reducing contention on the narrow bandwidth of the wireless channels. However, the traditional client/server strategies for supporting transactional cache consistency that require extensive communications between a client and a server are not appropriate in a mobile client/server computing environment. In this paper, we propose a new protocol, called OCC-UTS (Optimisitic Concurrency Control with Update TimeStamp), to support transactional cache consistency in a mobile client/server computing environment by utilizing the broadcast-based solutions for the problem of invalidating caches. The consistency check on accessed data and the commitment protocol are implemented in a truly distributed fashion as an integral part of cache invalidation process, with most burden of consistency check being downloaded to mobile clients. Also, our experiments based on an analytical model substantiate the basic idea and study the performance characteristics. Experimental results show that OCC-UTS protocol without local cache outperforms other competitor protocol, and the more frequent a mobile client accesses data items the more efficient OCC-UTS protocol with local cache is. With respect to disconnection, the tolerance to disconnection is improved if the invalidation broadcast window size is extended.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.847-854
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• 2001

The Web continues to grow fast rate in both a large aclae volume of traffic and the size and complexity of Web sites. Along with growth, the complexity of tasks such as Web site design Web server design and of navigating simply through a Web site have increased. An important input to these design tasks is the analysis of how a web site is being used. The is paper proposes a Page logging System(PLS) identifying reliably user sessions required in Web mining system PLS consists of Page Logger acquiring all the page accesses of the user Log processor producing user session from these data, and statements to incorporate a call to page logger applet. Proposed PLS abbreviates several preprocessing tasks which spends a log of time and efforts that must be performed in Web mining systems. In particular, it simplifies the complexity of transaction identification phase through acquiring directly the amount of time a user stays on a page. Also PLS solves local cache hits and proxy IPs that create problems with identifying user sessions from Web sever log.

• Journal of Internet Computing and Services
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• v.5 no.1
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• pp.15-23
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• 2004

This paper presents distributive web-caching technique on the Head-End-Network (HNET) to solve excessive load of multimedia sever and inefficient use of network resources, The proposed web-caching is not concentration of load for a specific Head-End-Node(HEN), and it has advantage that there is no copy of a specific item on distributive HENs. This technique distributively stores on HENs partial streams of requested videos from clients connected to HENs and the order of store streams follows the order of request of identical video items from HENs. Thus, storing streams on each HEN that requests sevice are different. When a client requests the cached video on some HENs, the HEN that connects him receives streams in the order of store from HENs which stored them and it transmits them to him. These procedures are performed under the control of SA. This technique uses cache replacement algorithm that the combination of LFU, LRU and the last remove for the first stream of videos In order to reduce end-to-end delay.