• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.7
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• pp.680-695
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• 1991

In this paper, the conditions on the number of required copies of a self-routing network with and without extra stages in back-to-back manner are presented respectively for a nonblocking $Multi-Log_2N$ multiconnection network. Actually the obained results hold regardless of connection patterns, i.e., whether a network deploys on-to-one connections or multiconnections. Thus open problems on the nonblocking condition for a multi $Multi-Log_2N$ multiconnection network are solved. Interestingly some of the given formulas comprise the Benes network and the Canto network as a special case repectively. A novel switching system architecture deploying a distributed calls-distribution algorithm is provided to design a nonblocking $Multi-Log_2N$ photonic switching network using a directional coupler. And a directional couplex based call holding demultiplexer is introduced to hold a call until blocking disappears in a switching network and let it enter to a network, provided that the number of switching networks is less than that of required switching networks for a nonblocking $Multi-Log_2N$ network.

• Journal of Advanced Navigation Technology
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• v.23 no.5
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• pp.460-465
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• 2019

In this study, we aim to derive a solution from the structural analysis for electrical failure of single board computers for computing navigation information. By analyzing the characteristic factor, we identify that crack occur on the central processing unit board due to a certain structural problem, and that the physical effect by the crack make communication function be impossible to perform, which it causes booting error. In order to find the location of excessive stress causing the crack, structural analysis for the single board computer is done. From the structural analysis, the areas where stress concentration occurs are identified, and improvement methods changing the structures are developed. As a result, we shows that stresses are reduced entirely on the stress distribution for the improved structure. In addition, heat analysis shows that changing the structure to reduce stresses is not affect to the heat radiation, and the thermal resistance of the actual equipment is verified by measuring the temperature of the heat sink applied with the improved structure.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.4
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• pp.89-100
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• 2011

Physical memory analysis has been an issue on a field of live forensic analysis in digital forensics until now. It is very useful to make the result of analysis more reliable, because record of user behavior and data can be founded on physical memory although process is hided. But most memory analysis focuses on windows based system. Because the diversity of target system to be analyzed rises up, it is very important to analyze physical memory based on other OS, not Windows. Mac OS X, has second market share in Operating System, is operated by loading kernel image to physical memory area. In this paper, We propose a methodology for physical memory analysis on Mac OS X using symbol information in kernel image, and acquire a process information, mounted device information, kernel information, kernel extensions(eg. KEXT) and system call entry for detecting system call hooking. In additional to the methodology, we prove that physical memory analysis is very useful though experimental study.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.12
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• pp.1134-1149
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• 2013

Pub/sub system enables data users to access any necessary data without knowledge of the data producer and synchronization with the data producer. It is widely used as the middleware technology for the data-centric services. DDS (Data Distribution Service) is a standard middleware supported by the OMG (Object Management Group), one of global standardization organizations. It is considered quite useful as a standard middleware for US military services. However, it is well-known that it takes considerably long time in searching the Participants and Endpoints in the system, especially when the system is booting up. In this paper, we propose a discovery scheme to reduce the latency when the participants and Endpoints are densely distributed in a small area. We propose to modify the standard DDS discovery process in three folds. First, we integrate the Endpoint discovery process with the Participant discovery process. Second, we reduce the number of connections per participant during the discovery process by adopting the concept of successors in Distributed Hashing scheme. Third, instead of UDP, the participants are connected through TCP to exploit the reliable delivery feature of TCP. We evaluated the performance of our scheme by comparing with the standard DDS discovery process. The evaluation results show that our scheme achieves quite lower discovery latency in case that the Participants and the Endpoints are densely distributed in a local network.

• Journal of Broadcast Engineering
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• v.11 no.1 s.30
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• pp.66-79
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• 2006

As constant development of digital broadcasting and data broadcasting system, new technology will be introduced to digital broadcasting and new broadcasting service will be appeared. These services need to be changed and processed to suit each services and the software of the receiver need to be upgraded. Though, generally the digital broadcasting receivers are not getting updated once it's delivered to home for long time and it need to be done by hand or collected each one of them with trouble. Therefore this paper suggests a way to overcome these difficulties via broadcasting stream. This research is to describe how three modules-namely (1) Downloader, downloads new software from data carrousel stream, (2) Update Loader, installs the software received by downloader; and (3) Recoverer, recovers the former version of the software if some serious problem has been occurred during downloading and installing the software. This paper tries to realize the accommodation of terrestrial STB based on the new technique and service following ATSC A-97 agreement.

• Journal of KIISE:Computer Systems and Theory
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• v.37 no.6
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• pp.330-338
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• 2010

Flash storage devices are very popularly used in portable devices such as cell phones, PDAs and MP3 players. As technology is improved, users want much bigger and faster storage system. Paradoxically, people have to wait more and more time proportionally to the capacity of their storage devices when these are trying to be recovered after file system crash. It is serious problem because booting time of devices is dominated by crash recovery of flash file system. In this paper, we design a crash recovery mechanism, named 'Working Area(WA hereafter)' technique, which has bounded crash recovery execution time. With WA technique, write operations to flash memory are only performed in WA. Therefore, by simply scanning the latest WA. We can recover a file system crash because every change for flash memory is occured only in latest WA. We implement the WA technique based on YAFFS2 and evaluate by comparing with traditional techniques. As a result, WA technique shows that its crash recovery execution time is 25 times faster than Log-based Method when we use 1 gig a bytes NAND flash memory in worst case. This gap will be futher and futher as storage capacity grows.

• Journal of KIISE:Computing Practices and Letters
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• v.14 no.3
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• pp.256-260
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• 2008

This paper describes an improvement of mount-time delay in NAND Flash file systems. To improve file system mount performance, this work configures a hierarchical storage system with byte-addressable NVRAM and NAND Flash memory, and let the meta data of a file system allocated in the NVRAM. Since the meta data are stored in NVRAM supporting data integrity some of the items, which are stored in Spare area and Object Header area of NAND Flash memory to control meta data of NAND Flash file system, could be eliminated. And also, this work eliminates the scanning operation of the Object Header area of previous work FRASH1.0. The scanning operation is definitely required to find out the empty Object Header address for storing the Object Header data and provokes a certain amount of performance loss in file generation and deletion. In this work, an implemented file system, so-called FRASH1.5, is demonstrated, featuring new data structures and new algorithms. The mount time of FRASH1.5 becomes twice as fast as that of the FRASH1.0. The performance in file generation gets improved by about $3{\sim}8%$. In particular, for most large-size files, the FRASH1.5 has 8 times faster mount time than YAFFS, without any performance loss as seen in the file generation.

• Journal of Platform Technology
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• v.11 no.2
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• pp.39-53
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• 2023

Non-installation program (hereinafter referred to as "portable program") is a program that can be used without an installation process, unlike general software. Since there is no separate installation process, portable programs have high mobility and are used in various ways. For example, when initial setup of multiple PCs is required, a portable program can be stored on one USB drive to perform initial setup. Alternatively, when a problem occurs with the PC and it is difficult to boot normally, Windows PE can be configured on the USB drive and portable programs can be stored for PC recovery. And the portable program does not directly affect PC settings, such as changing registry values, and does not leave a trace. This means that the portable program has high security. If a portable program is deleted after using it, it is difficult to analyze behavior in a general way. If a user used a portable program for malicious behavior, analysis in a general way has limitations in collecting evidence. Therefore, portable programs must have a new way of behavioral analysis that is different from ordinary installation software. In this paper, after installing the Windows 10 operating system on a virtual machine, we proceed with the scenario with a portable program of Opera and Notepad++. And we analyze this in various ways such as file analysis of the operating system and memory forensics, collect information such as program execution time and frequency, and conduct specific behavioral analysis of user.