• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.11a
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• pp.438-442
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• 1999

More and more residential and mobile users are requiring access to the Internet. This paper presents an architecture of the network solution for cost-effective Internet/intranet access between users and Network Service Providers(NSPs). It also presents a functional architecture of Internet access router in the integrated access node system. The proposed Internet access router provides the functionality that users select any of a number of NSPs and mutiple user PPP calls are multiplexed over each secure tunnel between the Internet access router and NSP.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4B
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• pp.323-332
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• 2006

In this paper, we consider a WDM based metro ring connecting broadband access networks by using FT-TR (Fixed Transmitter-Tunable Receiver) type access nodes and a new MAC protocol for fair transmission is proposed. The basic channel access scheme is CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) and the transferred optical slot is changed to be empty slot by SS(Source-Stripping) which drops a packet from ring-rotated slot. This empty slot can be either used to send head-of-line packet in buffer or transmitted to next access node. In former cases, there is the improvement of network throughput, but latter case leads unfairness problem of transmission. Thus the proposed MAC protocol exploits the advantages form tow cases. It gives downstream access nodes chance to use empty slots and limits the unconditional usage of empty slots at upstream access nodes with probability as called p-Persistent MAC protocol. We use a numerical analysis to evaluate bandwidth efficiency and maximum node throughput and compares simulation results in terms of node throughput, fairness factor, transfer delay depending on probability. Under two different FT-TR type architectures for metro ring network the proposed MAC protocol is evaluated and compared.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11a
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• pp.334-336
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• 2005

이동적응망(MANET: Mobile Ad-hoc Network)은 네트워크 하부 구조를 필요로 하지 않은 무선 단말들로 구성된 네트워크이다. 이러한 특성은 네트워크 단절 가능성을 높게 하기 때문에 이동단말들의 데이터 액세스률이 낮아지게 된다는 문제점을 갖는다. 이를 해결하기 위하여 이동 노드들은 데이터의 중복사본을 갖는다. 이동 노드가 갖는 중복사본은 데이터 일관성을 유지하기 위하여 별도의 중복관리 기법이 필요하다. 하지만 MANET을 구성하는 이동 노드들은 일반적으로 제한된 전력을 가지고 있고 단절될 가능성이 높기 때문에 중복 사본의 일관성 보장은 어려운 문제로 지적되고 있다. 기존에 제안된 MANET에서의 데이터 중복관리 기법은 데이터 액세스 빈도수를 계산하여 액세스률을 높이는 방법에 주안점을 두고 있고 갱신 데이터의 일관성 보장은 그 어려움 때문에 주로 판독 연산만 고려하였다. 갱신 트랜잭션을 지원하는 경우 대부분 높은 통신비용을 이유로 데이터 일관성을 보장하지 않는다. 또한 이동 노드가 다수의 서버를 통해서 갱신 연산을 실행하기 때문에 통신 오버헤드로 인하여 전력소모가 크다. 본 논문에서는 주사본 노드를 통하여 갱신을 가능하게 함으로써 데이터 일관성을 유지할 수 있는 데이터 중복 기법을 제안한다. 제안된 기법은 이동 노드들의 에너지 특성을 고려하여 더 않은 에너지를 가진 노드에게 갱신 전파 및 일관성 유지를 의뢰함으로써 상대적으로 낮은 에너지를 갖는 이동 노드의 에너지 효율을 고려하였다.

• Journal of KIISE:Software and Applications
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• v.26 no.2
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• pp.223-233
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• 1999

데이터베이스 공유 시스템(Database Sharing System : DSS) 은 고성능의 트랜잭션 처리를 위해 제안된 구조이다. DSS에서 고속의 통신망으로 연결된 노드들은 별도의 메모리와 운영체제, 그리고 DBMS를 가지며, 데이터베이스르 저장하고 있는 디스크는 모든 노드에 의해 공유된다. 빈번한 디스크 액세스를 피하기 위해 각 노드는 자신의 메모리 버퍼에 최근에 액세스한 페이지들을 캐싱한다. 본 논문에서는 레코드와 같은 미세 단위의 로킹을 지원하는 DSS에서 데이터베이스를 정확한 상태로 복구할 수 있는 회복 기법인 DRCP(Database Recovery using Cached Pages)를 제안한다. DRCP는 정상적으로 동작하고 있는 다른 노드에 캐싱된 페이지의 내용을 참조하여 회복 작업을 수행함으로써 디스크 액세스 수와 회복 과정에서 필요한 로그 스캔의 범위를 줄일 수 있고 , 그 결과 데이터베이스를 빨라 복구할 수 있다는 장점을 갖는다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4A
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• pp.330-335
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• 2007

This paper proposes a multichannel random access channel allocation scheme for multihop cellular networks to guarantee the stable throughput of a random access. The fundamental contribution is a mathematical formula for an optimal partition ratio of shared random access channels between a base station and a relay station. In addition, the proposed scheme controls the retransmission probability of random access packets under heavy load condition. Simulation results show that the proposed scheme can guarantee the required random access channel utilization and packet transmission delay even if the a random access packet arrival rate is higher than 0.1.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10a
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• pp.36-38
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• 2000

데이터베이스 공유 시스템(Database Sharing System: DSS)은 고성능 트랜잭션 처리를 위해 다수 개의 컴퓨터를 연동하는 방식으로, 각 노드들은 디스크 계층에서 데이터베이스를 공유한다. DSS에서 각 노드는 빈번한 디스크 액세스를 피하기 위해 최근에 액세스한 데이터 페이지와 인덱스 페이지들을 자신의 지역 메모리 버퍼에 캐싱한다. 이때 노드가 항상 최신의 페이지를 사용할 수 있기 위해서는 지역 버퍼에 캐싱된 페이지들의 일관성을 지원하여야 한다. 본 논문에서는 데이터 페이지에 비해 빈번히 엑세스되는 인덱스 페이지의 정확성을 보장할 수 있는 캐쉬 일관성 제어 기법을 제안한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.1 s.343
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• pp.111-120
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• 2006

In this paper, a node architecture of WDM metro network for connecting broadband access networks to converge wire/wireless networks. In consideration of the proposed node architecture and network requirements we proposed and evaluated medium access control protocols. We review WDM related technologies of sub-carrier multiplexing and optical components in order to resolve the bottleneck between optical backbone networks md access networks, and a access node architecture sharing common wavelength is introduced. Source-stripping (SS) MAC protocol Is evaluated under the proposed functional node architecture. DS+IS (Destination-Stripping and Source-Stripping) and DS+IS (Destination-Stripping and Intermediate-Stripping) MAC protocols are described to increase the slot-reuse factor which is low on SS MAC protocol. The key function of new MAC protocols regards the optical switch module of proposed node architecture and helps intermediate or source access nodes for dropping slots to destinations of different wavelength group. Thus, slot-reuse factor increases as the MAC protocols reduce the unnecessary ring-rotation of transferred slots. We use a numerical analysis to expect bandwidth efficiency and maximum throughput by slot-reuse factor Throughput network simulation, the verification of throughput, queuing delay, and transmission fairness are compared among MAC protocols.

• Journal of Korea Multimedia Society
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• v.11 no.5
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• pp.673-684
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• 2008

In this paper, we propose a signaling protocol which can support QoS for multimedia applications continuously after handover of a mobile node in the network environment where IP-based wireless access networks co-exist. Since existing RSVP-based signaling protocols can cause the waste of network resources due to double reservation and do not provide fast resource reservation/release, they are not suitable for mobile networks. The proposed QoS signaling protocol can support QoS for multimedia applications using the fast reservation of necessary resources after handover and avoid the waste of resources by resolving the double reservation problem. This paper presents design and implementation architectures of the proposed signaling protocol and analyzes its performance via a physical testbed. Based on the analysis results, it was shown that the proposed protocol is able to support seamless QoS for multimedia applications.

• Journal of KIISE:Databases
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• v.35 no.6
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• pp.469-480
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• 2008

A shared disk (SD) cluster couples multiple nodes for high performance transaction processing, and all the coupled nodes share a common database at the disk level. To reduce the number of disk accesses, each node caches database pages in its memory buffer. Since a particular page may be cached simultaneously in different nodes, cache consistency should be maintained to ensure that nodes can always access the most recent version of database pages. Most cache consistency schemes proposed in the SD cluster adopted LRU as a buffer replacement algorithm. In this paper, we first present four buffer replacement algorithms that consider the characteristics of the SD cluster. Then we compare the performance of the buffer replacement algorithms. We perform the experiments on a variety of cluster configurations and database workloads. The experiment results show that the proposed algorithms achieve performance improvement up to 5 times of LRU algorithm.

• The KIPS Transactions:PartC
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• v.15C no.5
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• pp.383-390
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• 2008

The mobile sink is most suitable to guarantee the real time processing to events in ubiquitous environment. However it brings many challenges to wireless sensor networks. In particular, the question of how to transfer the collected data to the mobile sink is an important topic in the aspect of effective management of wireless sensor nodes. In this paper, a new data dissemination model is proposed. Since this method uses the home agent and the access node concepts, it provides reliable and efficient data delivery to mobile sink with minimum overhead. In this proposed method, the information of the mobile sink which is constantly moving is informed only to the home agent node and the access node, instead of all sensor nodes. Thus, the collected data from sensor nodes are transferred to the fixed home agent and it sends these data to the mobile sink. Since the confliction phenomenon between data packets in wireless networks could be reduced, the success ratio of data arriving in the mobile sink is highly enhanced. In our experiments, the proposed method reduces the number of broadcast packets so that it saves the amount of energy consumed for transmitting and receiving the data packets. This effect contributes to prolong the lifetime of the wireless sensor networks operated by batteries.