• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.754-756
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• 2004

CBMC는 ANSI-C 프로그램과 베릴로그 서킷사이의 일치성을 검증하는 툴이다. 입력된 서킷과 코드를 CNF로 변환 과정에서 C 코드는 중첩 루프, pointer, dynamic memory allocation등에 대한 변환의 문제점이 있다. 본 논문에서는 CBMC에서 C 코드의 CNF로 변환하는 과정의 문제점들을 동일한 식(equation)의 변환 과정에 대하여 설명하고 상용적인 트리플 DES를 CBMC로 검증하는 과정을 제시한다

• The Transactions of the Korea Information Processing Society
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• v.2 no.3
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• pp.364-373
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• 1995

We propose a probabilistic design method and performance analysis in the area of dynamic data structures. We assign two stacks to a block which consists of m contiguous memory cells. Frequencies of delete and insert operations are not fixed, but depend on stack heights. We present various probabilistic schema and a rigorous performance analysis for a random memory allocation. Especially, stack coillision problem is studied and exponential increase of the mean of collision time as mlongrightarrow$\infty$is showed. We also present general mathematical schema which can be applied to the performance problems of finite automata and other computer information systems.

• Journal of KIISE:Databases
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• v.36 no.5
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• pp.374-385
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• 2009

Flash memory becomes increasingly popular as data storage for various devices because of its versatile features such as non-volatility, light weight, low power consumption, and shock resistance. Flash memory, however, has some distinct characteristics that make today's disk-based database technology unsuitable, such as no in-place update and the asymmetric speed of read and write operations. As a result, most traditional disk-based database systems may not provide the best attainable performance on flash memory. To maximize the database performance on flash memory, some approaches have been proposed where only the changes made to the database, i.e., logs, are written to another empty place that has born erased in advance. In this paper, we propose an efficient log management scheme for flash-based database systems. Unlike the previous approaches, the proposed approach stores logs in specially allocated blocks, called log blocks. By evenly distributing logs across log blocks, the proposed approach can significantly reduce the number of write and erase operations. Our performance evaluation shows that the proposed approaches can improve the overall system performance by reducing the number of write and erase operation compared to the previous ones.

• The Transactions of the Korea Information Processing Society
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• v.4 no.6
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• pp.1625-1635
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• 1997

An extension of the weighted buddy system, called the extended-weighted buddy system, for dynamic memory allocation in an object-oriented computer is presented. The extended-weighted buddy system allows block sizes of $2^k,\;3*2^k,\;5*2^k,\;7*2^k$, whereas the original weighted buddy system allowed block sizes of $2^k\;and\;3*2^k$. This extension is achieved at only the cost of additional 3 bits per block for memory management unit. Simulation results are presented which compare our method with the weighted buddy system. These results indicate that, for uniform request distributions, our system has less internal memory fragmentation than the weighted buddy system(approximately 60%). And, for exponential request distributions, it has less internal memory fragmentation than the weighted buddy method (approximately 50%). The external fragmentation is greater for this system than the weighted buddy system. But, our system has less total memory fragmentation for exponential request distributions, and two systems take a similar total memory fragmentation for uniform request distributions, so we can substitutes the extended-weighted buddy system for weighted buddy system.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.767-774
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• 2010

Due to advantages of NAND flash memory such as non-volatility, low access latency, low energy consumption, light weight, small size and shock resistance, it has become a better alternative over traditional magnetic disk drives, and has been widely used. Traditional DBMSs including mobile DBMSs may run on flash memory without any modification by using Flash Translation Layer (FTL), which emulates a random access block device to hide the characteristics of flash memory such as "erase-before-update". However, most existing FTLs are optimized for file systems, not for DBMSs, and traditional DBMSs are not aware of them. Also, traditional DBMSs do not consider the characteristics of flash memory. In this paper, we propose a flash-conscious storage system for DBMSs that utilizes flash memory as a main storage medium, and carefully put the characteristics of flash memory into considerations. The proposed flash-conscious storage system exploits log records to avoid costly update operations. It is shown that the proposed storage system outperforms the state.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6C
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• pp.614-622
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• 2006

In this paper, we propose an efficient packetization method to reduce the packetization overhead. For the purpose, we firstly verify the relationship between packet length and packet loss rate. The empirical results show that as the packet length is larger than the path MTU, the packet loss rate is drastically increased, producing poor visual quality at the receiver side. However, as the length of the packet is reduced, we should transmit more packets per frame and the packetization overhead will be increased. This increase in the packetization overhead reduces the number of bits allocated to the video data, resulting in the low visual quality. Therefore, each packet should be packetized to have the packet length close to the path MTU. In this paper, we show that the this process of the packetization with the constraint on the packet length is very similar to the dynamic storage allocation in the operating system. We had thoroughly surveyed the dynamic storage allocation methods used in the recent operating systems and propose to use the allocation methods for the video packetization. We empirically show that the proposed method can reduce the packetization overhead upto 28.3%, compared with the conventional sequential packetization method which have been widely used in Internet video transmission.

• Journal of KIISE:Information Networking
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• v.32 no.4
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• pp.443-451
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• 2005

Stateful inspection devices must maintain flow information. These devices create the flow information also for network attack packets, and it can fatally inflate the dynamic memory allocation on stateful inspection devices under network attacks. The memory inflation leads to memory overflow and subsequent performance degradation. In this paper, we present a guideline to set the flow entry timeout for a stateful inspection device to remove harmful embryonic entries created by network attacks. Considering Transmission Control Protocol (TCP) if utilized by most of these attacks as well as legitimate traffic, we propose a parsimonious memory management guideline based on the design of the TCP and the analysis of real-life Internet traces. In particular, we demonstrate that for all practical purposes one should not reserve memory for an embryonic TCP connection with more than (R+T) seconds of inactivity where R=0, 3, 9 and $1\leqq{T}\leqq{2}$ depending on the load level.

• Journal of the Korea Computer Graphics Society
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• v.14 no.1
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• pp.27-33
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• 2008

Mobile systems have relatively limited resources such as low memory, slow CPU, or low power comparing to desktop systems. In this paper, we present a new 3D mesh connectivity coding algorithm especially optimized for mobile systems(i.e., mobile phones). By using adaptive octree data structure for vertex positions, a new distance-based connectivity coding is proposed. Our algorithm uses fixed point arithmetic and minimizes dynamic memory allocation, appropriate for mobile systems. We also demonstrate test data to show the utility of our mobile 3D mesh codec.

• The Journal of Asian Finance, Economics and Business
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• v.8 no.8
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• pp.297-309
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• 2021

In this study, to capture the skewness and kurtosis detected in both conditional and unconditional return distributions of the stock markets of Kazakhstan and Russia, two versions of normal mixture GARCH models are employed. The data set consists of daily observations of the Kazakhstan and Russia stock prices, and world crude oil price, covering the period from 1 June 2006 through 1 March 2021. From the empirical results, incorporating the long memory effect on the returns not only provides better descriptions of dynamic behaviors of the stock market prices but also plays a significant role in improving a better understanding of the return dynamics. In addition, normal mixture models for time-varying volatility provide a better fit to the conditional densities than the usual GARCH specifications and has an important advantage that the conditional higher moments are time-varying. This implies that the volatility skews implied by normal mixture models are more likely to exhibit the features of risk and the direction of the information flow is regime-dependent. The findings of this study contain useful information for diverse purposes of cross-border stock market players such as asset allocation, portfolio management, risk management, and market regulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.3
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• pp.896-915
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• 2023

The network function virtualization (NFV) uses virtualization technology to separate software from hardware. One of the most important challenges of NFV is the resource management of virtual network functions (VNFs). According to the dynamic nature of NFV, the resource allocation of VNFs must be changed to adapt to the variations of incoming network traffic. However, the significant delay may be happened because of the reallocation of resources. In order to balance the performance between delay and quality of service, this paper firstly made a compromise between VNF migration and energy consumption. Then, the long short-term memory (LSTM) was utilized to forecast network traffic. Also, the asymmetric loss function for LSTM (LO-LSTM) was proposed to increase the predicted value to a certain extent. Finally, an experiment was conducted to evaluate the performance of LO-LSTM. The results demonstrated that the proposed LO-LSTM can not only reduce migration times, but also make the energy consumption increment within an acceptable range.