• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.5
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• pp.108-116
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• 1989

The simulator described here-LOSIM(LOgic SIMulator)-was developed to verify the logic design for VLSI(Very Large Scale Integrated) circuits at mixed level. In this paper, we present a modeling approach to obtain more accurate results than conventional logic simulators [5-6,9] for general elements, functional elements, transmission gates and tri-state gates using eight signal values and two gignal strengths. LOSIM has the capability which can perform timing and hazard analysis by using assignable rise and fall delays. We also prosent an efficient algorithm to accurately detectdynamic and static hazards which may be caused by the circuit delays. Our approach is based on five logic values and the scheduled time. LOSIM has been implemented on a UN-3/160 workstation running Berkeley 4.2 UNIX, and the program is written in C language. Static RAM cell and asynchronous circuit are illustrated as an example.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.4
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• pp.35-44
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• 2004

Recently announced TCP Vegas predicts the degree of congestion in the network and then control the congestion window size. Thus it shows better performance than TCP Reno. however, TCP vegas does not assume any network model, its congestion window control is very limited. Because or this limitation, TCP vegas still can not adapt to fast changing available bandwidth. In this paper, we introduce a new TCP algorithm which adapts to fast changing available bandwidth well. To devise such a TCP, we model the end to end network of TCP connection as a queueing system and finds congestion window size which can utilize the available bandwidth sufficiently but not make the network congested. The simulation results show that our algorithm adapts to the avaliable bandwidth faster than TCP vegas and as a results, when the available bandwidth is changing rapidly, our algorithm not only operates more stably than TCP Vegas, but also it shows higher thruput than TCP Vegas.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.1
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• pp.73-82
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• 2004

As a new service category to better support TCP traffic in ATM networks, the Guaranteed Frame Rate (GFR) service category aims to support minimum cell rate guarantee, fairly distribute available bandwidth while keeping the simplicity of Unspecified Bit Rate (UBR). In this paper, we proposed a buffer management scheme which uses the per-VC accounting of single FWO queue and capable of supporting both GFR.1 and GFR.2 conformance definition. The proposed buffer management deal with GFR.1 and GFR.2 conformance definitions differentially by controlling the number of CLP=0 cell and CLP=1 cell which are occupying buffer space. The simulation results show that our proposed scheme satisfies the requirements of GFR services as well as improves total fairness index and each conformance definition fairness index.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.10
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• pp.4754-4773
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• 2018

In sensor medium access control (SMAC) protocol, sensor nodes can only access the channel in the scheduling and listening period. However, this fixed working method may generate data latency and high conflict. To solve those problems, scheduling duty in the original SMAC protocol is divided into multiple small scheduling duties (micro duty MD). By applying different micro-dispersed contention channel, sensor nodes can reduce the collision probability of the data and thereby save energy. Based on the given micro-duty, this paper presents an adaptive duty cycle (DC) and back-off algorithm, aiming at detecting the fixed duty cycle in SMAC protocol. According to the given buffer queue length, sensor nodes dynamically change the duty cycle. In the context of low duty cycle and low flow, fair binary exponential back-off (F-BEB) algorithm is applied to reduce data latency. In the context of high duty cycle and high flow, capture avoidance binary exponential back-off (CA-BEB) algorithm is used to further reduce the conflict probability for saving energy consumption. Based on the above two contexts, we propose an improved SMAC protocol, micro duty adaptive SMAC protocol (MDA-SMAC). Comparing the performance between MDA-SMAC protocol and SMAC protocol on the NS-2 simulation platform, the results show that, MDA-SMAC protocol performs better in terms of energy consumption, latency and effective throughput than SMAC protocol, especially in the condition of more crowded network traffic and more sensor nodes.

• The Journal of the Acoustical Society of Korea
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• v.19 no.8
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• pp.3-11
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• 2000

This paper considers the performance of a dynamic priority control function (DPCF) of a threshold-based Bernoulli priority jump (TBPJ) scheme. Loss-sensitive and delay-sensitive traffics are applied to a system with a TBPJ scheme that is a general state-dependent Bernoulli scheduling scheme. Loss-sensitive and delay-sensitive traffics represent sound and data, respectively. Under the TBPJ scheme, the first packet of the loss-sensitive traffic buffer goes into the delay-sensitive traffic buffer with Bernoulli probability p according to system states which represent the buffer thresholds and the number of packets waiting for scheduling. Performance analysis shows that TBPJ scheme obtains large performance build-up for the delay-sensitive traffic without performance degradation for the loss-sensitive traffic. TBPJ scheme shows also better performance than that of HOL scheme.

• Journal of IKEEE
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• v.13 no.3
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• pp.7-17
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• 2009

WiMedia UWB technology is a fully distributed data communication technology developed for the application demanding a high data transmission rate in the wireless PAN area. In general, devices can send data either by reserving time slots or by using prioritized CSMA/CA. If the PCA protocol of prioritized CSMA/CA is used, they are suffered congestion as the number of devices increases. In this paper, we propose a Deterministic Access Protocol(DAP) in WiMedia WPANs. A DAP is a method to transmit data in the non-reserved DRP period without competition as each device informs the beacon order information in the beacon period and the queue information. In addition, the problem that the devices with a lower beacon slot number have more transmission opportunities is addressed by introducing the reference point. Simulation results are given to demonstrate that a DAP can improve the throughput and reduce the packet loss rate.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.5
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• pp.83-90
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• 2012

This paper is a research on the design and implementation of a small real-time radio broadcasting system by using smart phone based on Android. It was designed as the server-client structure, and used the progressive download of HTTP as methods of transferring data to further simplify the system. In order to realize the real-time broadcasting, the original audio source was divided with a short interval and captured to be compressed and stored into files. Then the client receives and plays the compressed files sequentially as it is downloaded. However, this method occurs two problems each of which is the loss of capturing the original source in the server and the discontinuity of playing the files in the client. We solved the problem in the server by separating the thread into two parallel threads of which is each captured and compressed/stored, also by using the double buffering method. The problem in the client was solved using MediaPlayer in Android and the file queue to store the multiple files.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.13 no.2
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• pp.1-7
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• 2013

Big data management is becoming increasingly important in both industry and academia of information science community. One of the important categories of big data generated from software systems is log data. Log data is generally used for better services in various service providers and can also be used as information for qualification. This paper presents a big data management architecture specialized for log data. Specifically, it provides the aggregation of log messages sent from multiple clients and provides intelligent functionalities such as analyzing log data. The proposed architecture supports an asynchronous process in client-server architectures to prevent the potential bottleneck of accessing data. Accordingly, it does not affect the client performance although using remote data store. We implement the proposed architecture and show that it works well for processing big log data. All components are implemented based on open source software and the developed prototypes are now publicly available.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.126-134
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• 2006

Traditional TCP implementations have the under-utilization problem in large bandwidth delay product networks especially during the startup phase. In this paper, we propose a delay-based congestion control(DCC) mechanism to solve the problem. DCC is subdivided into linear and exponential growth phases. When there is no queueing delay, the congestion window grows exponentially during the congestion avoidance period. Otherwise, it maintains linear increase of congestion window similar to the legacy TCP congestion avoidance algorithm. The exponential increase phase such as the slow-start period in the legacy TCP can cause serious performance degradation by packet losses in case the buffer size is insufficient for the bandwidth-delay product, even though there is sufficient bandwidth. Thus, the DCC uses the RTT(Round Trip Time) status and the estimated queue size to prevent packet losses due to excessive transmission during the exponential growth phase. The simulation results show that the DCC algorithm significantly improves the TCP startup time and the throughput performance of TCP in large bandwidth delay product networks.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.6 s.324
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• pp.17-24
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• 2004

This paper proposes an efficient technique to protect e-mail server from DDoS attack using the CBQ (Class Based Queuing) algorithm The proposed method classifies incoming trafic to an e-mail server into three classes: 'more important mail traffic', 'less important traffic' and 'unknown traffic' and assigns bandwidths differently to the traffics. By differentiating the bandwidths of classes, normal mail traffic may flow even under DDoS attack in the proposed technique. The proposed technique is implemented on an embedded system which hires a switching processor with the WFHBD(Weighted Fair Hashed Bandwidth Distribution) engine that has been known as an efficient algorithm to distribute a given bandwidth to multiple sources, and it is verified that it can be an efficient way to protect e-mail server from DDoS attack.