• Journal of Communications and Networks
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• v.12 no.1
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• pp.52-66
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• 2010

Since large objects consume substantial resources, web proxy caching incurs a fundamental trade-off between performance (i.e., hit-ratio and latency) and overhead (i.e., resource usage), in terms of caching and relaying large objects to users. This paper investigates how and to what extent the current dedicated-server based web proxy caching scheme is affected by large file transfers in a high bandwidth campus network environment. We use a series of trace-based performance analyses and profiling of various resource components in our experimental squid proxy cache server. Large file transfers often overwhelm our cache server. This causes a bottleneck in a web network, by saturating the network bandwidth of the cache server. Due to the requests for large objects, response times required for delivery of concurrently requested small objects increase, by a factor as high as a few million, in the worst cases. We argue that this cache bandwidth bottleneck problem is due to the fundamental limitations of the current centralized web proxy caching model that scales poorly when there are a limited amount of dedicated resources. This is a serious threat to the viability of the current web proxy caching model, particularly in a high bandwidth access network, since it leads to sporadic disconnections of the downstream access network from the global web network. We propose a peer-to-peer cooperative web caching scheme to address the cache bandwidth bottleneck problem. We show that it performs the task of caching and delivery of large objects in an efficient and cost-effective manner, without generating significant overheads for participating peers.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.426-430
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• 2005

The computer practicing class advances to reach the ultimate goal of learning through the comprehensive learning of theory. Moreover, the improved function and environment of computer makes it easy for students to access a variety of information. However, students are likely to get into the internet and other things mainly for fun during the computer practicing class, and the multi-tasking may distract the concentration of students and degrade their performance. Computers for practice purpose need to be controlled to minimize such distraction. In this dissertation, we monitor and control computers which are used by students for the purpose of practicing, realize the function of transfer and deletion of file, whole shutdown of computer and screen capture. We also applied the class based on current way and realized program, and assigned the practice work on the basis of what was learned during the class. We intend to understand the relation between the concentration of students and their performance by assigning practice work related to survey after the class, capture file and log file

• Smart Media Journal
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• v.4 no.3
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• pp.38-43
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• 2015

The increased number of smart devices leads users to share multimedia contents with others. Smart device users transmit multimedia files using apps. For multimedia file transfer under NAT (Network Address Translator), a lot of apps exploit a server with public IP or short range communication technologies such as WiFi Direct or Bluetooth because smart devices with private IP address cannot communicate each other directly. We first proposed the push service based file transmission scheme without an additional server and distance limitation. Second, for the push service based transmission, we proposed congestion control scheme to adapt transmission rate to the receiver's link bandwidth. Third, we considered bandwidth aware transmission for senders with different bandwidth. We implemented apps to evaluate the proposed scheme, and conducted experiments with smart devices.

• The Journal of the Korea Contents Association
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• v.4 no.4
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• pp.123-131
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• 2004

Internet is absolutely contributed to information technology revolution nowadays. Internet services such as voice and data, etc. are provided home or small office via home gateway. The development of communication equipment via home gateway is implemented rapidly, and its product various. This paper presents the design and implementation of the VoIP equipment including the telephone function based on the embedded environment and being connected to the home gateway and the PC because of taking 2-ethernet LAN ports. As developing environment, the STLC1502 developed at ST Microelectronics as single chip solution, VxWorks as RTOS, and C language as coding mechanism are used. The verification of the developed systems for the voice test is carried out for the gatekeeper via Internet. The performance parameter is considered as the call processing capacity measuring the time of the call setup and clearing, and the data processing capacity for the file transfer. As a call setup and clearing is about 95ms, the call processing capacity is about 10 calls per second. The data processing capacity is 5.7Mbps in case of file transfer of server and client environment. Therefore the performance result is satisfied in the aspect of the call processing time and the data transfer time in Internet.

• Journal of the Korean Society of Radiology
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• v.12 no.6
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• pp.785-791
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• 2018

Recently, Disk array is widely used as a long term storage device in PACS, but reliability is not enough in relation to annual failure rate of disk. Between October 2016 and February 2017, we scanned the serial port of the hard disk while reading or storing medical images on a PACS reader. The data rate was calculated from the data stored in HDD 99ea that were used in the PCAS image storage device and in HDD 101ea that were used in the Personal Computer. When a CT image was read from a PACS reader, Reading was 87.8% and Writing was 12.2% in units of several tens of megabytes or less. When the CT image was stored in the PACS reader, Reading was 11.4% and Writing was 88.6% in units of several tens of megabytes or less. While reading the excel file on the personal computer, Reading was 75% and Writing was 25% in less than 3 MB, and In the process of storing the excel file on the personal computer, Reading was carried out by 38% and Writing was carreid out 62% in the units of 3 MB or less. The transfer rate of the hard disk used in the PACS image storage device was 10 GB/h, and the transfer rate per hour of the hard disk of the personal computer was 5 GB / h. Annual failure rate of hard disk of image storage system is 0.97 ~ 1.13%, Annual failure rate of Hard Disk of personal computer is 0.97 ~ 1.13%. the higher transfer rate is, the higher annual failure rate is. These results will be used as a basis for predicting the life expectancy of the hard disk and the annual failure rate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2801-2806
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• 2011

During data transmissions via Bluetooth networks, data to be encrypted, or plain text between the application layer and the device layer, can be hacked similar to a key-logger by the major function hooking technique of Windows Kernel Driver. In this paper, we introduce an improved protection module which provides data encryption transmission by modifying the data transmission driver of the Bluetooth device layer, and also suggest a self-protecting scheme which prevents data exposure by various hacking tools. We implement the protection module to verify the confidentiality guarantee. Our protection module which provides data encryption with minimal latency can be expected the widespread utilization in Bluetooth data transmission.

• Journal of the Korea Society of Computer and Information
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• v.4 no.2
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• pp.46-60
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• 1999

Recently, CTI (Computer Telephony Integration) technology has been widely applied to various area such as video conference, file transfer, voice mail, automatic message transfer and automatic redial, integrated messaging and network fax. In this paper, an administrative affairs supporting system using call control mode of CTI is designed. To improve inefficient processing of job due to heavy calling from entrance candidates during entrance examination of a college, the system is developed. The database of the system is desigend using object modeling technique. Also, the automatic calling and response system using CTI call control mode is implemented. Especially, to interface with voice of candidates who ask whether they pass or fail the entrance examination of the college, TTS(Text To Speech) module is developed.

• International Journal of Quality Innovation
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• v.10 no.1
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• pp.115-126
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• 2009

Video transmission effectiveness in the Ad Hoc network is becoming important recently, if different routing protocols are applied. Some researchers conclude that the reactive protocols are better for file transfer protocol (FTP) and constant bit rate (CBR) or hypertext transfer protocol (HTTP) transmission in an Ad Hoc wireless network but the performance report of video transmission is not much. This study adopts Qualnet (Network Simulator) as a simulation tool for environmental designing and performance testing, and employs an experimental design with eight groups. Our experiment shows that: (1) The performance of AODV (reactive) protocol is better than DSDV, ZRP and DSR when the transmission load has only one video stream; (2) Proactive (DSDV) and Hybrid protocols (ZRP) are better for a smaller Ad Hoc network when it transmits a video stream with some applications (VoIP, FTP and CBR). We conclude that packet loss rate is sensitive to the quality of video transmission and it has negative relationship with Peak Signal-to-Noise Ratio (PSNR) value. In addition, our experiment also shows that PSNR is a simple Metric for the performance evaluation of video transmission.

• Journal of Internet Computing and Services
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• v.9 no.4
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• pp.143-156
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• 2008

Grid-based PACS can provide an advanced medical information services such as remote image file transfer, collaboration, remote diagnosis, and virtual hospital. In this paper, we have implemented Grid-PACS which guarantees both storage safety and extendability for virtual large scale storage system. The experimental results showed that the virtual storage system provided more efficient and faster data transfer than the conventional PACS. The proposed Grid data management system can be utilized to improve the effectiveness of the PACS data management and transmission between medical institutions.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.712-718
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• 2005

In this study, a translator for transferring structural analysis data among commercial structural analysis programs was developed. The translator adopted the neutral format type based on ISO standard STEP AP 209 not only for the international standardization and robustness but also for the efficient management of structural analysis data Additional load entity is developed and added to AP 209 for the prevention of loss of information in retrieving exact loading condition. A modulization which is needed for efficient management and extension of the translator was made for the encapsulation of file format of each commercial code. Pilot tests peformed with 3-D frame analysis data of Sung-su bridge show that the developed translator guarantees the integrated management of analysis information as well as the exact transferring and retrieving of analysis data and related information.