• The Journal of the Acoustical Society of Korea
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• v.34 no.4
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• pp.310-315
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• 2015

A single channel VAD (Voice Activity Detection) algorithm for nonstationary noise environment is proposed in this paper. Threshold values of the feature parameter for VAD decision are updated adaptively based on estimates of means and standard deviations of past non-speech frames. The feature parameter, SPD-TE (Spectral Power Difference-Teager Energy), is obtained by applying the Teager energy to the WPD (Wavelet Packet Decomposition) coefficients. It was reported previously that the SPD-TE is robust to noise as a feature for VAD. Experimental results by using TIMIT speech and NOISEX-92 noise databases show that decision accuracy of the proposed algorithm is comparable to several typical VAD algorithms including standards for SNR values ranging from 10 to -10 dB.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11B
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• pp.1225-1233
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• 2009

ISPs and Enterprises are equipping their networks with sufficiently high speed facilities and provide large bandwidths members. However the high speed enterprise network does not have satisfying end-to-end network performance within the network in spite of under utilization. The root cause of this performance degradation is a micro-congestion, which is a short-live event of traffic congestion. A micro-congestion causes packet loss, delay and packet reodering, and finally results in end-to-end network performance degradation. In this paper, we propose a micro-congestion detection method and find out the characteristics of performance degradation by analyzing traffic archives which is collected from a network link when a micro-congestion occurs.

• The Journal of the Korea institute of electronic communication sciences
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• v.10 no.2
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• pp.289-296
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• 2015

Wireless multimedia sensor network senses and transfers mass multimedia data. Also, it is sensitive to latency. This thesis proposes a routing technique based on traffic priority in order to improve the network efficiency by minimizing latency. In addition, it proposes a congestion control mechanism that uses packet service time, packet inter-arrival time, buffer usage, etc. In this thesis, we verified the reduction of packet latency in accordance with the quality level of packet as a result of the performance analysis through the simulation method. Also, we verified that the proposed mechanism maintained a reliable network state by preventing packet loss due to network overload.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.2
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• pp.11-18
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• 1995

Error detection in ARQ(Automatic Repeat Request) protocols is very important in wireless data communication systems. The throughput efficiency of ARQ protocols can be improved by dynamically adapting the protocol packet length so that it approaches the optimum value for throuhput efficiency. In this paper, a simple and novel adaptive packet length allocation method is proposed which transmits the packets with variable length by dyanmically estimating the channel codition. The simulation results show that the average of throughput is improved by 315.4% in the stop-and-wait protocol, 41.4% in the go-back-N protocol and 155.9% in the selective repeat protocol respectively. And the throughput performances of adaptive packet length allocation method approximately approach the theoritically optimal throughput performances.

• Proceedings of the KIEE Conference
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• 2001.07c
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• pp.1832-1834
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• 2001

A new method of all optical packet header recognition scheme using a photorefractive hologram filter is presented. Wavelength encoded packet that has the header of a specific wavelength is assumed and the photorefractive filter can detect the wavelength. Concatenated electronics drives the optical switch to route the $\lambda$-encoded optical packet. The delay time at the switched signals are measured and compared with the original data stream.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.6
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• pp.11-22
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• 1996

We address an issue of channel sharing among users by using a random assignment-transmitter-based (RA-T) spread-spectrum transmission scheme which permits the contention mode only in the transmission of a header while avoiding collision during the data packet transmission. Once the header being successfully received, the data packet is ready for reception by switching to one of programmable matched-filters. But the receoption may be blocked due to limited number of matched-filters so that this effect is taken into account in our analysis. For realistic analysis, we integrate detection performance at the physical level with channel activity at the link level through a markov chain model. We also consider an acknowledgement scheme to notify whether the header is correctly detcted and the data packet can be processed continuously, which aims at reducing the interference caused unwanted data transmission. It is shown that receiver complexity can be greatly reduced by choosing a proper number of RA codes at the cost of only a little throughput degradation.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.4
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• pp.1006-1025
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• 2012

Improving the quality of service in IP networks is a major challenge for real-time voice communications. In particular, packet arrival-delay variation, so-called "jitter," is one of the main factors that degrade the quality of voice in mobile devices with the voice-over Internet protocol (VoIP). To resolve this issue, a receiver-based enhanced timing recovery algorithm combined with active jitter estimation is proposed. The proposed algorithm copes with the effect of transmission jitter by expanding or compressing each packet according to the predicted network delay and variations. Additionally, the active network jitter estimation incorporates rapid detection of delay spikes and reacts to changes in network conditions. Extensive simulations have shown that the proposed algorithm delivers high voice quality by pursuing an optimal trade-off between average buffering delay and packet loss rate.

• Annual Conference of KIPS
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• 2008.11a
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• pp.1012-1015
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• 2008

The packet capturing becomes a bottleneck in the network intrusion detection and monitoring system as the network performance developing. Many approaches, zero copy, interrupt coalescing and NAPI which attempt to improve packet capturing performance of Linux, are inefficient. PF_RING is a new type of network socket that dramatically improves the packet capture speed, but not perfect. This paper proposes some solutions which can improve the memory utilization and save some data copy time based on the commodity network adapters rather than on the commercial network adapters.

• The Journal of the Korea Contents Association
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• v.8 no.6
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• pp.54-65
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• 2008

When DDoS attack is achieved, malicious host discovering is more difficult on wireless network than existing wired network environment. Specially, because wireless network is weak on wireless user authentication attack and packet spoofing attack, advanced technology should be studied in reply. Integrated Access Device (IAD) that support VoIP communication facility etc with wireless routing function recently is developed and is distributed widely. IAD is alternating facility that is offered in existent AP. Therefore, advanced traffic classification function and real time attack detection function should be offered in IAD on wireless network environment. System that is presented in this research collects client information of wireless network that connect to IAD using AirSensor. And proposed mechanism also offers function that collects the wireless client's attack packet to monitoring its legality. Also the proposed mechanism classifies and detect the attack packet with W-TMS system that was received to IAD. As a result, it was possible for us to use IAD on wireless network service stably.

• The Journal of the Korea Contents Association
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• v.10 no.3
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• pp.101-112
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• 2010

The recent trend of the hacking deals with all the IT infrastructure related to the profit of the companies. Presently, they attack the service itself, the source of the profit, while they tried to access to the service infrastructure through the non-service port in the past. Although they affect the service directly, it is difficult to block them with the old security solution or the old system and they threaten more and more companies with the demand of money menacing the protection of customers and the sustainable management. This paper aims to design and implement multi-platform network packet scanner targeting the exception handling network intrusion detection system which determines normal, abnormal by traffic. Linux and unix have the various network intrusion detection and packet management tools like ngrep, snort, TCPdump, but most of them are based on CUI (Character based User Interface) giving users discomfort who are not used to it. The proposed system is implemented based on GUI(Graphical User Interface) to support the intuitive and easy-to-use interface to users, and using Qt(c++) language that supports multi-platform to run on any operating system.