• Journal of KIISE:Computer Systems and Theory
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• v.33 no.9
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• pp.615-625
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• 2006

Nonvolatile memory technology is evolving continuously and commercial products such as FeRAM and PRAM are now challenging their markets. As NVRAM has properties of both memory and storage, it can store persistent data objects while allowing fast and random access. To utilize NVRAM for general purpose storing of frequently updated data across power disruptions, some essential features of the file system including naming, recovery, and space management are required while exploiting memory-like properties of NVRAM. Conventional file systems, including even recently developed NVRAM file systems, show very low space efficiency wasting more than 50% of the total space in some cases. To efficiently utilize the relatively expensive NVRAM, we design and implement a new extent-based space-thrifty file system, which we call NEBFS (NVRAM Extent-Based File System). We analyze and compare the space utilization of conventional file systems with NEBFS and validate the results with experimental results observed from running the file system implementations on a system with actual NVRAM installed as well as on systems emulating NVRAM. We show that NEBFS has high space efficiency compared to conventional file systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.4B
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• pp.661-674
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• 2000

The main memory DBMS(MMDBMS) efficiently supports various database applications that require high performance since it employs main memory rather than disk as a primary storage. In this paper, we discuss theexperiences obtained in developing the index manager of the Tachyon, a next-generation MMDBMS. The indexmanager is an essential sub-component of the DBMS used to speed up the retrieval of objects from a largevolume of a database in response to a certain search condition. Previous research efforts on indexing proposed various index structures. However, they hardly dealt with the practical issues occured in implementating an index manager on a target DBMS. In this paper, we touch these issues and present our experiences in developing the index manager on the Tachyon as solutions. The main issues touched are (1) compact representation of an indexentry, (2) support of variable-length keys, (3) support of multiple-attribute keys, (4) support of duplicated keys,(5) definition of external APls, (6) concurrency control, and (7) backup and recovery. We believe that ourcontribution would help MMDBMS developers highly reduce their trial-and-errors.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.192.2-192.2
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• 2016

최근 차세대 휴대용 전자기기나 전기자동차의 상용화 연구가 활발히 이루어짐에 따라 리튬이온 배터리가 주력 에너지 저장장치로써 활발히 개발되고 있다. 이러한 리튬이온 배터리의 음극 물질로써 주로 탄소재료가 많이 사용되어 왔지만 낮은 이론용량 (372 mAh/g)으로 인하여 좀더 높은 용량을 가지는 금속이나 합금 등이 주목을 받게 되었다. 그 중에서도 주석이 탄소재료에 비해 3배 정도 높은 이론 용량 (993 mAh/g)을 가지고 있어 많은 연구가 진행되고 있다. 하지만 주석의 경우 리튬이온 배터리의 충방전 과정 중에 급격한 부피 변화가 발생하여 음극이 손상되고 이에 따라 용량이 급격하게 감소하는 한계점이 있다. 이 한계를 극복하기 위한 많은 방법들 중 하나가 구리-주석 합금을 음극으로 사용하는 것이다. 구리는 비활성 금속으로 충방전 중의 부피 변화에 완충제 역할을 하고, 연성과 전기전도성이 있어서 배터리의 전기화학적 성능 또한 향상시켜 준다. 이에 따라, 본 연구에서는 주석이 풍부한 구리-주석 합금 도금을 통하여 구조적으로 튼튼한 리튬이온 배터리의 음극을 만들었고 그 성능을 확인하기 위하여 반쪽전지 실험을 통하여 500회 충방전 동안의 싸이클 특성 및 효율을 확인하였고 순환전압전류 실험 또한 진행하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.11a
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• pp.30-32
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• 2014

최근 낸드 플래시 메모리는 임베디드 저장 장치로 많이 사용되고 있다. 비휘발성인 플래시 메모리는 기존의 하드디스크와 달리 저 전력, 좋은 내충격성 및 집적도 등 많은 장점이 있지만 데이터 업데이트 시 덮어쓰기가 안 되어 쓰기 연산 전 해당 블록을 지우는 작업이 선 진행되어야 하며 이로 인해 부분 페이지 업데이트가 자주 일어난다. 이런 플래시메모리와 더불어 최근 차세대 메모리연구가 많이 진행 중인데, 이 중에서 PCM 이라는 메모리는 비휘발성으로 정전 시 데이터가 날라 가버리는 DRAM에 반해 전원이 공급 안 되더라도 데이터가 보존되는 특성이 있다. 하지만 PCM 역시 플래시 메모리와 마찬가지로 블록 당 쓰기연산 작업이 제한되어 있어서 근래에 DRAM과 같이 사용하는 하이브리드 구조를 채택하여 많은 연구가 진행되고 있다. 따라서 본 논문에서는 플래시 메모리의 문제점을 해결함으로서 수명을 연장시키고 정 전시 데이터가 보존되지 않는 DRAM의 단점을 하이브리드 메모리를 기반으로하여 데이터의 신뢰성을 높이는 FTL알고리즘을 제안한다.

• Convergence Security Journal
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• v.19 no.1
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• pp.3-10
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• 2019

The 5G network is a next-generation converged network that combines various ICT technologies to realize the need for high speed, hyper connection and ultra low delay, and various efforts have been made to address the security vulnerabilities of the previous generation mobile networks. However, the standards released so far still have potential security vulnerabilities, such as USIM deception and replication attack, message re-transmission attack, and race-condition attack. In order to solve these security problems, this paper proposes a new 5G-AKA protocol with PUF technology, which is a physical unclonable function. The proposed PUF-based 5G-AKA improves the security vulnerabilities identified so far using the device-specific response for a specific challenge and hash function. This approach enables a strong white-list policy through the addition of inexpensive PUF circuits when utilizing 5G networks in areas where security is critical. In addition, since additional cryptographic algorithms are not applied to existing protocols, there is relatively little burden on increasing computational costs or increasing authentication parameter storage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.6
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• pp.1696-1704
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• 2008

The conventional hard disk has been the dominant database storage system for over 25 years. Recently, hybrid systems which incorporate the advantages of flash memory into the conventional hard disks are considered to be the next dominant storage systems. Their features are satisfying the requirements like enhanced data I/O, energy consumption and reduced boot time, and they are sufficient to hybrid storage systems as major database storages. However, we need to improve traditional index management schemes based on B-Tree due to the relatively slow characteristics of hard disk operations, as compared to flashmemory. In order to achieve this goal, we propose a new index management scheme called FNC-Tree. FNC-Tree-based index management enhanced search and update performance by caching data objects in unused free area of flash leaf nodes to reduce slow hard disk I/Os in index access processes. Based on the results of the performance evaluation, we conclude that our scheme outperforms the traditional index management schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.8
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• pp.1486-1491
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• 2017

In this paper, we propose a private multimedia caching scheme based on wireless local area network (WLAN) to improve the quality of service for high capacity and high quality multimedia streaming services which are recently increasing and to reduce the traffic load of core networks. The proposed caching scheme stores multimedia in the storage device mounted on WLAN APs and provides streaming services on its own without Internet connection in accordance with the request from clients. We have implemented a test network based on real commercial networks and measured the performance of the proposed caching scheme in terms of frames per second (FPS) and buffering time. According to the performance measurement results, the proposed caching scheme can reduce the average buffering time by 73.3% compared to the conventional streaming scheme. In addition, the proposed caching scheme can also improve the average FPS by 71.3% compared to the conventional streaming scheme.

• Proceedings of the Korean Information Science Society Conference
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• 2006.10a
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• pp.261-266
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• 2006

최근 낸드 플래시 메모리는 임베디드 저장 장치로서 많이 사용되고 있을 뿐만 아니라 플래시 메모리의 저장 용량의 대용량화로 하드 디스크를 대체하는 SSD(solid state disk) 같은 제품이 출시되고 있다. 플래시 메모리는 하드디스크에 비하여 저전력, 빠른 접근성, 물리적 안정성 등의 장점이 있지만 읽기와 쓰기의 연산의 불균형적인 비용과 덮어 쓰기가 안 되고 쓰기 전에 해당 블록을 지워야하는 부가적인 작업을 수행해야 한다. 이와 같은 특징은 플래시 메모리의 쓰기 성능을 저하 시키고 기존의 하드디스크를 대체하는 것을 어렵게 만든다. 이와 같은 플래시 메모리의 단점을 해결하기 위해서 본 논문에서 비휘발성 메모리와 플래시 메모리를 함께 사용하는 방법을 제안한다. 최근 MRAM, FeRAM, PRAM과 같은 차세대 메모리 기술의 발전과 배터리 백업 메모리의 가격 하락으로 인하여 비휘발성 메모리의 상품적 가치가 높아지고 있다. 하지만 아직까지 용량 대비 가격이 비효율적이기 때문에 소용량의 비휘발성 메모리를 활용하여 플래시 메모리의 쓰기 연산에 대한 단점을 보완하는 방법을 제안한다. 본 논문에서는 FTL 에서 비휘발성 메모리를 쓰기 버퍼로 이용한 여러 가지 버퍼 관리 정책을 실험하였고 각 관리 정책에 따른 플래시 메모리의 성능 향상을 측정하였다. 실험을 통하여 최대로 읽기의 횟수는 90% 감소, 쓰기 횟수는 33% 감소, 소거 횟수는 50% 감소 효과를 보였다.

• The KIPS Transactions:PartD
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• v.18D no.3
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• pp.157-168
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• 2011

Recently flash memory has been being utilized as a main storage device in mobile devices, and flashSSDs are getting popularity as a major storage device in laptop and desktop computers, and even in enterprise-level server machines. Unlike HDDs, on flash memory, the overwrite operation is not able to be performed unless it is preceded by the erase operation to the same block. To address this, FTL(Flash memory Translation Layer) is employed on flash memory. Even though the modified data block is overwritten to the same logical address, FTL writes the updated data block to the different physical address from the previous one, mapping the logical address to the new physical address. This enables flash memory to avoid the high block-erase cost. A flashSSD has an array of NAND flash memory packages so it can access one or more flash memory packages in parallel at once. To take advantage of the internal parallelism of flashSSDs, it is beneficial for DBMSs to request I/O operations on sequential logical addresses. However, the B-tree structure, which is a representative index scheme of current relational DBMSs, produces excessive I/O operations in random order when its node structures are updated. Therefore, the original b-tree is not favorable to SSD. In this paper, we propose AS(Always Sequential) B-tree that writes the updated node contiguously to the previously written node in the logical address for every update operation. In the experiments, AS B-tree enhanced 21% of B-tree's insertion performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.7B
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• pp.605-619
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• 2003

The main memory DBMS(MMDBMS) efficiently supports various database applications that require high performance since it employs main memory rather than disk as a primary storage. In this paper, we discuss the index manager of the Tachyon, a next-generation MMDBMS. Recently, the gap between the CPU processing and main memory access times is becoming much wider due to rapid advance of CPU technology. By devising data structures and algorithms that utilize the behavior of the cache in CPU, we are able to enhance the overall performance of MMDBMSs considerably. In this paper, we address the practical implementation issues and our solutions for them obtained in developing the cache-conscious index manager of the Tachyon. The main issues touched are (1) consideration of the cache behavior, (2) compact representation of the index entry and the index node, (3) support of variable-length keys, (4) support of multiple-attribute keys, (5) support of duplicated keys, (6) definition of the system catalog for indexes, (7) definition of external APIs, (8) concurrency control, and (9) backup and recovery. We also show the effectiveness of our approach through extensive experiments.