• Proceedings of the Korea Information Processing Society Conference
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• 2002.04b
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• pp.1373-1376
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• 2002

인터넷 환경에서 멀티캐스팅 서비스를 제공하기 위한 응용프로그램과 양질의 서비스를 받고자 하는 사용자들의 요구를 만족시키기 위해 네트워크 관리에 관한 정책이 필요하며, 정책시스템은 네트워크에서 QoS를 가능하게 하는 요소이다. 본 논문에서는 리눅스 기반 환경에서 정책을 적용할 수 있는 정책서버에 해당하는 PDP와 클라이언트인 PEP구현, 디렉토리 서비스 프로토콜인 LDAP 사용 환경 구축에 초점을 두어 설계 및 구현하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2008.11a
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• pp.1272-1275
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• 2008

클러스터 VOD 시스템에서 한정된 자원을 사용하여 많은 사용자에게 안정적인 QoS를 제공하기 위해서는 클러스터 노드들 간의 효율적인 부하 분산이 필요하다. 본 연구에서는 효율적인 부하 분산 방법으로 윈도우즈 환경에서 클러스터 각 노드의 정보를 WMI를 이용하여 부하 분배 서버가 필요할 때마다 원격 질의를 통해 네트워크의 오버헤드를 줄이면서 각 클러스터 노드의 장애 상황을 파악하고 복구하는 방법에 대해 연구한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.12
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• pp.5712-5728
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• 2017

Recently, there are many studies, that considering green wireless cellular networks, have taken the energy consumption of the base station (BS) into consideration. In this work, we first introduce an energy consumption model of multi-mode sharing BS powered by multiple energy sources including renewable energy, local storage and power grid. Then communication load requests of the BS are transformed to energy demand queues, and battery energy level and worst-case delay constraints are considered into the virtual queue to ensure the network QoS when our objective is to minimize the long term electricity cost of BSs. Lyapunov optimization method is applied to work out the optimization objective without knowing the future information of the communication load, real-time electricity market price and renewable energy availability. Finally, linear programming is used, and the corresponding energy efficient scheduling policy is obtained. The performance analysis of our proposed online algorithm based on real-world traces demonstrates that it can greatly reduce one day's electricity cost of individual BS.

• Journal of Digital Convergence
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• v.12 no.10
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• pp.317-327
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• 2014

To improve the efficiency of wireless channel, IEEE 802.11ac uses the DL MU-MIMO MAC scheme through which an AP transmits multiple frames to different mobile nodes simultaneously. IEEE 802.11ac DL MU-MIMO MAC needs a new step, called as TXOP sharing, between legacy IEEE 802.11n DL SU-MIMO's two operations, the obtaining an EDCA TXOP and the transmitting multiple frames for EDCA TXOP. In the TXOP sharing operation, both wireless channel destinations and frames transmitted for its TXOP period should are determined. So this paper deals with the TXOP sharing for improving IEEE 802.11ac MAC performance. However, the EDCA priority based method mentioned by IEEE 802.11ac standard document not fair among the buffers and the frames of buffers, and occurs in high_loss rate and high_delay about specific buffers. In this paper, we propose a new scheme of the TXOP sharing with sequencing p-AC, s-AC in similar properties, and all S-AC. This method provides a differentiated service without damage of EDCA characteristics.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.10
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• pp.2376-2394
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• 2013

In order to ensure both of the whole system capacity and users QoS requirements in heterogeneous wireless networks, admission control mechanism should be well designed. In this paper, Multi-agent Q-learning based Admission Control Mechanism (MQACM) is proposed to handle new and handoff call access problems appropriately. MQACM obtains the optimal decision policy by using an improved form of single-agent Q-learning method, Multi-agent Q-learning (MQ) method. MQ method is creatively introduced to solve the admission control problem in heterogeneous wireless networks in this paper. In addition, different priorities are allocated to multiple services aiming to make MQACM perform even well in congested network scenarios. It can be observed from both analysis and simulation results that our proposed method not only outperforms existing schemes with enhanced call blocking probability and handoff dropping probability performance, but also has better network universality and stability than other schemes.

• Journal of Digital Convergence
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• v.13 no.11
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• pp.179-185
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• 2015

In this paper, we research the IPTV that is the convergence technique of TV and network technique and performed the performance evaluation of picture quality of IPTV in the situation of increasing the network traffic in the Internet environment. To do this, we constructed the mock Internet network similar to the real Internet environment and measured the quality of received video using V-Factor model according to the increase of network traffic, and analyzed the result of the experiment. Making use of the result of this paper for the threshold value of V-Factor, the measured factor of network performance, the measured factor of video performance in the watchable IPTV video quality.

• Journal of Digital Convergence
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• v.10 no.6
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• pp.197-203
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• 2012

In this paper, researching for the video quality estimation of IPTV in the situation that increase the broadcasting network traffic on the IPTV multicasting service using the ETSI TR 101 290 that is the European digital video quality standard estimating method and present the experiment result. Proving that the intimate relation is between IPTV video quality and ETSI TR 101 290 estimation, also ETSI TR 101 290 can detect the video quality factors which can't be detected by the exist video estimation methods.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2005.11a
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• pp.121-124
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• 2005

The High Rate Wireless Personal Area Networks (WPAN) is mainly targeted to consumer electronics and portable communication devices which need high rates and QoS. To achieve these goals, the WPAN provides data rates up to 1Gbps and adopts a Time Division Multiple Access (TDMA) MAC protocol. Since IEEE 802.15.3 MAC is based on TDMA scheme, it has good performance in dealing with real traffics. But it does not give better results for dynamic traffic. For dynamic traffic, IEEE 802.15.3 MAC needs a kind of request and response policy that brings about the degradation of performance in order to adapt to network changes. To overcome this problem and enhance the data throughput, this paper proposes a superframe structure which uses the Enhanced Contention Access Period (ECAP) to transmit data during sleep-CTA in PM mode.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4165-4187
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• 2016

As an emerging technology, cloud computing is a revolution in information technology that attracts significant attention from both public and private sectors. In this paper, we proposed a dynamic approach for live migration to obviate overloaded machines. This approach is applied on OpenStack, which rapidly grows in an open source cloud computing platform. We conducted a cost-aware dynamic live migration for virtual machines (VMs) at an appropriate time to obviate the violation of service level agreement (SLA) before it happens. We conducted a preemptive migration to offload physical machine (PM) before the overload situation depending on the predictive method. We have carried out a distributed model, a predictive method, and a dynamic threshold policy, which are efficient for the scalable environment as cloud computing. Experimental results have indicated that our model succeeded in avoiding the overload at a suitable time. The simulation results from our solution remarked the very efficient reduction of VM migrations and SLA violation, which could help cloud providers to deliver a good quality of service (QoS).

• Journal of the Korea Computer Industry Society
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• v.5 no.9
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• pp.911-920
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• 2004

Intensive studies have been made in the area of VOD server. Multimedia files in the VOD sever are characterized with the large volume of data, the requirements of synchronization and real-time playback of streams. The basic goal of the study is to find an efficient mechanism to allow maximum number of users under the limited resources such as Bu11er size and disk bandwidth. we propose a efficient user-grouping policy for multi-casting services with dynamic monitoring and management of VOD sever resources. Simulation results show that the rate of buffer usage and QOS change of proposed scheme are about 23% performance improved than that of traditional methods. This implies that our method can allow much more users for given resources.