• 한국통신학회논문지
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• 제24권10B호
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• pp.1824-1831
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• 1999

본 논문에서는 연속 패킷 손실 환경에서 systematic erasure code를 적용하였을 경우의 손실 복구율에 관하여 분석하고 손실 특성에 따른 부가 전송량의 추정방법에 대하여 제시한다. 연속 패킷 손실환경은 Gilbert 모델로 설정하였고, 기존의 연속 손실 환경에서의 erasure code의 손실 복구율 분석방안을 이용하여 systematic erasure code를 사용하였을 경우의 성능을 분석하고, 평균 패킷 손실율, 손실의 평균 길이 등의 주어진 패킷 손실 특성으로부터 주어진 손실 특성을 만족시키는 부가 전송량의 추정 방법을 제시한다.

• ETRI Journal
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• 제31권5호
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• pp.518-524
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• 2009

Single parity check (SPC) product codes are simple yet powerful codes that are used to correct errors and/or recover erasures. The focus of this paper is to evaluate the performance of such codes under erasure scenarios and to develop a closed-form tight upper bound for the post-decoding erasure rate. Closed-form exact expressions are derived for up to seven erasures. Previously published closed-form bounds assumed that all unrecoverable patterns should contain four erasures in a square. Additional non-square patterns are accounted for in the proposed expressions. The derived expressions are verified using exhaustive search. Eight or more erasures are accounted for by using a bound. The developed expressions improve the evaluation of the recoverability of SPC product codes without the need for simulation or search algorithms, whether exhaustive or novel.

• Journal of Information Processing Systems
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• 제15권1호
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• pp.55-66
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• 2019

Storage system often applies erasure codes to protect against disk failure and ensure system reliability and availability. Liberation code that is a type of coding scheme has been widely used in many storage systems because its encoding and modifying operations are efficient. However, it cannot effectively achieve fast recovery from single disk failure in storage systems, and has great influence on recovery performance as well as response time of client requests. To solve this problem, in this paper, we present HRSF, a Hybrid Recovery method for solving Single disk Failure. We present the optimal algorithm to accelerate failure recovery process. Theoretical analysis proves that our scheme consumes approximately 25% less amount of data read than the conventional method. In the evaluation, we perform extensive experiments by setting different number of disks and chunk sizes. The results show that HRSF outperforms conventional method in terms of the amount of data read and failure recovery time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권11호
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• pp.5290-5304
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• 2016

With the growth of the massive amount of data, the failure probability of the cloud storage node is becoming more and more big. A single fault tolerance strategy, such as replication and erasure codes, has some unavoidable disadvantages, which can not meet the needs of the today's fault tolerance. Therefore, according to the file access frequency and size, an adaptive hybrid redundant fault tolerance strategy is proposed, which can dynamically change between the replication scheme and erasure codes scheme throughout the lifecycle. The experimental results show that the proposed scheme can not only save the storage space(reduced by 32% compared with replication), but also ensure the fast recovery of the node failures(increased by 42% compared with erasure codes).

• 한국통신학회논문지
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• 제30권9C호
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• pp.877-886
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• 2005

Various frame recovery algorithms have been suggested to overcome the communication quality degradation problem due to Internet-typical impairments on Voice over IP(VoIP) communications. In this paper, we propose a new receiver-based recovery method which is able to enhance recovered speech quality with almost free computational cost and without an additional increment of delay and bandwidth consumption. Most conventional recovery algorithms try to recover the lost or erroneous speech frames by reconstructing missing coefficients or speech signal during speech decoding process. Thus they eventually need to modify the decoder software. The proposed frame recovery algorithm tries to reconstruct the missing frame itself, and does not require the computational burden of modifying the decoder. In the proposed scheme, the Vector Quantization(VQ) codebook indices of the erased frame are directly estimated by referring the pre-computed VQ Codebook Index Interpolation Tables(VCIIT) using the VQ indices from the adjacent(previous and next) frames. We applied the proposed scheme to the ITU-T G.723.1 speech coder and found that it improved reconstructed speech quality and outperforms conventional G.723.1 loss recovery algorithm. Moreover, the suggested simple scheme can be easily applicable to practical VoIP systems because it requires a very small amount of additional computational cost and memory space.

• 전자공학회논문지
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• 제51권2호
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• pp.85-91
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• 2014

클라우드 스토리지 시스템은 데이터의 저장과 관리를 위해서 분산 파일시스템을 사용한다. 기존 분산 파일시스템은 데이터 디스크의 손실 발생시 이를 복구하기 위해서 3개의 복제본을 만든다. 그러나 데이터 복제 기법은 저장공간을 원본 파일의 복제 횟수만큼 필요로하고 복제과정에서 입출력 발생이 증가하는 문제가 있다. 본 논문에서는 SSD 기반 클라우드 스토리지 시스템에서 저장공간 효율성 향상과 입출력 성능 향상을 위하여 Erasure Codes를 이용한 데이터 복제 기법을 제안한다. 특히, 데이터 접근 빈도에 따라 복제 횟수를 줄이더라도 Erasure Codes를 사용하여 데이터 복구 성능을 동일하게 유지하였다. 실험 결과 제안한 기법이 HDFS 보다 저장공간 효율성은 최대 약40% 향상되었으며, 읽기성능은 약11%, 쓰기성능은 약10% 향상됨을 확인하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제4권1호
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• pp.62-77
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• 2010

Emerging applications with high data rates will need to transport bulk data reliably in wireless sensor networks. ARQ (Automatic Repeat request) or Forward Error Correction (FEC) code schemes can be used to provide reliable transmission in a sensor network. However, the naive ARQ approach drops the whole frame, even though there is a bit error in the frame and the FEC at the bit level scheme may require a highly complex method to adjust the amount of FEC redundancy. We propose a bulk data transmission scheme based on erasure-resilient code in this paper to overcome these inefficiencies. The sender fragments bulk data into many small blocks, encodes the blocks with LT codes and packages several such blocks into a frame. The receiver only drops the corrupted blocks (compared to the entire frame) and the original data can be reconstructed if sufficient error-free blocks are received. An incidental benefit is that the frame error rate (FER) becomes irrelevant to frame size (error recovery). A frame can therefore be sufficiently large to provide high utilization of the wireless channel bandwidth without sacrificing the effectiveness of error recovery. The scheme has been implemented as a new data link layer in TinyOS, and evaluated through experiments in a testbed of Zigbex motes. Results show single hop transmission throughput can be improved by at least 20% under typical wireless channel conditions. It also reduces the transmission time of a reasonable range of size files by more than 30%, compared to a frame ARQ scheme. The total number of bytes sent by all nodes in the multi-hop communication is reduced by more than 60% compared to the frame ARQ scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권10호
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• pp.5058-5077
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• 2019

Traditional regenerating codes are designed to tolerate node failures with optimal bandwidth overhead. However, there are many types of partial failures inside the node, such as latent sector failures. Recently, proposed regenerating codes can also repair intra-node failures with node-level redundancy but incur significant bandwidth and I/O overhead. In this paper, we construct a new scheme of regenerating codes, called IR-RBT codes, which employs intra-node redundancy to tolerate intra-node failures and serve as the help data for other nodes during the repair operation. We propose 2 algorithms for assigning the intra-node redundancy and RBT-Helpers according to the failure probability of each node, which can flexibly adjust the helping relationship between nodes to address changes in the actual situation. We demonstrate that the IR-RBT codes improve the bandwidth and I/O efficiency during intra-node failure repair over traditional regenerating codes but sacrifice the storage efficiency.

• International Journal of Internet, Broadcasting and Communication
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• 제10권3호
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• pp.11-25
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• 2018

While being believed that decrypting any RSA ciphertext is as hard as factorizing the RSA modulus, it was also shown that, if additional information is available, breaking the RSA cryptosystem may be much easier than factoring. For example, Coppersmith showed that, given the 1/2 fraction of the least or the most significant bits of one of two RSA primes, one can factorize the RSA modulus very efficiently, using the lattice-based technique. More recently, introducing the so called cold boot attack, Halderman et al. showed that one can recover cryptographic keys from a decayed DRAM image. And, following up this result, Heninger and Shacham presented a polynomial-time attack which, given 0.27-fraction of the RSA private key of the form (p, q, d, $d_p$, $d_q$), can recover the whole key, provided that the given bits are uniformly distributed. And, based on the work of Heninger and Shacham, this paper presents a different approach for recovering RSA private key bits from decayed key information, under the assumption that some random portion of the private key bits is known. More precisely, we present the algorithm of recovering RSA private key bits from erased key material and elaborate the formula of describing the number of partially-recovered RSA private key candidates in terms of the given erasure rate. Then, the result is justified by some extensive experiments.

• 한국차세대컴퓨팅학회논문지
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• 제15권3호
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• pp.7-15
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• 2019

세계적으로 ICT(Information & Communication Technology)를 통한 비용절감 및 업무혁신이 이루어지면서 클라우드 컴퓨팅(이하 클라우드) 시장이 급성장하고 있다. 이러한 패러다임에 맞춰 우리나라는 다양한 연구를 통해 공공부문, 국방 분야 등 다양한 분야에 클라우드를 도입시키기 위해 노력하고 있다. 특히 국방 분야에서는 2015년 육·해·공·군 전산소를 통합하여 국방통합데이터센터(DIDC, Defense Integrated Data Center)를 설립하였으며, 센터 내 일부 시스템을 대상으로 IaaS(Infrastructure as a Service) 형태의 클라우드 서비스를 제공하고 있다. 국방통합데이터센터 및 추후 도입될 국방 분야의 다양한 클라우드 시스템에서 네트워크 지연, 시스템 자원 고장 등과 같은 시스템 장애가 발생하게 되면 전장의 결과와 직결되기 때문에 국방 부문의 클라우드 시스템에 가용성을 보장하는 것은 중요한 이슈라 할 수 있다. 그러나 국방 클라우드의 모든 시스템을 대상으로 최고 수준의 가용성을 확보하는 것은 비효율적일 수 있으며, 클라우드 시스템 구축으로 얻을 수 있었던 효율성이 감소할 수 있다. 본 논문에서는 국방 클라우드 시스템의 가용성 확보 수준을 단계별로 분류 및 정의하고, 각 가용성 확보 수준에 따른 Erasure Coding 및 장애 허용 시스템, 재난 복구 시스템 기술 도입 전략을 제안한다.