• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.223-225
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• 2003

Session Initiation Protocol(이하 SIP)은 H.323 network에서 제기된 문제점을 해결하고 다양한 multimedia service를 제공하기위해 IETF에서 정의된 protocol로서, 3GPP의 IP Multimedia Subsystem(이하 IMS)의 기반 protocol로 채택되었다. IMS는 multimedia service를 제공하기 위한 infrastructure로서 CSCF, HSS, MRF, MGCF, IM-GW등 기능적으로 분리된 여러 entity로 구성되며, 향후 추가될 다양한 부가 service에 유연하게 대처할 수 있는 Application Server(이하 AS) mechanism을 포함하고 있다. 현재 AS mechanism을 이용하여 3GPP규격 상에 정의된 대표적 서비스는 presence service이며, presence service network은 presence server, presence agent, presence proxy, watcher등으로 구성된다. 마지막으로 상기에 언급한 규격을 바탕으로 실제 구축된 Instant messaging/presence service network을 제시한다. (본문 참조)

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.334-336
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• 2004

If Network에서 mobility의 보장은 효과적인 network 동작을 위해 중요하다. Mobile IP와 SIP를 사용할 경우 MH가 위치변경 시 마다 MH로부터 먼 곳에 위치할 가능성이 있는 MH의 Home network내 Home Agent나 Redirect Server에 registration을 수행해야 하는데 이 경우 이전 subnet에서 새로운 subnet으로의 registration이 완료되기 전까지는 correspondent node에 대한 연결성을 잃어 버리게 되어 이로 인해 발생되는 Packet 손실과 delay 생기게 된다. 이런 Registration Problem을 효과적으로 해결하기 위해 Presence System을 이용한 효율적인 network architecture를 제안한다.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 2005.10a
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• pp.189-206
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• 2005

Much of work on network externality assumed network effects are dependent on the network size. Therefore, very little consideration is given to the view that marginal benefits from joining the network may not increase with the network size if consumer benefits come from the direct interaction with neighbors, namely local network. In this study, we used the agent-based simulation method to reexamine the effectiveness of the traditional network market strategy under the presence of the local network where two incompatible technologies compete. We found that the strategy of growing an initial customer base is not effective under the presence of the local network. Our study also showed that targeting customers based on their technology Preference is not as effective as targeting customers within the same local network. As a result, the focus of a network market strategy should be directed to taking advantage of the customer network.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1997.10a
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• pp.177-180
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• 1997

Outliers, unexpected extraordinary observations that look discordant from most observation in a data set are commonplace in various kinds of data analysis. Since the effect of outliers on model identification could be serious, the aim of this paper is to present some ways of handling outliers in given data set and to specify a model in the presence of outliers. A procedure based on neural network which identifies outliers, removes their effects, and specifies a model for the underlying process is proposed. In contrast with traditional parametric methods requiring to estimate the model's structure and parameters before detecting outliers, the proposed procedure is a nonparametric method without the estimation of model's structure and parameters before handling outliers and could be applied for real problems in the presence of outliers. The proposed methodology is performed as followings. Firstly, outliers are detected and the detected outliers replace the prediction values using outliers detection neural network. The data set removing the effect of outliers is retraining using neural network. Therefore the effects of outliers are removed and the modeling precision can be improved. Experimental results show that the proposed method is suitable for predicting data set in the presence of outliers.

• Journal of Korea Technology Innovation Society
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• v.3 no.3
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• pp.36-52
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• 2000

This study takes an issue of efficiency analysis in the presence of network effect utilizing the DEA (Data Envelopment Analysis) framework. Network effect has important policy implication for the regulation of local monopolies which undertake their business through physical network, such as electricity, natural gas, local telephony, etc. If the difference in spatial condition between companies is not controlled properly, the performance comparison and associated incentive regulation bear significant bias. In this study, we propose a methodology to measure the true managerial or technical efficiency apart from efficiency difference accruing from the difference in spatial condition. A series of modified DEA efficiency models are combined to investigate the extent of exogenous and endogenous efficiency component in the Korean natural gas distribution companies. Empirical results show that the network effect plays significant role in determining superficial performance difference.

• Journal of Communications and Networks
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• v.9 no.4
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• pp.356-367
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• 2007

In large networks, maintaining precise global network state information is impossible. The imprecise network state information has significant impacts on Quality-of-Service(QoS) routing and path establishment. In this paper, we develop analytical models for investigating the QoS routing schemes that are designed to tolerate imprecise network state information, and study the performance of various QoS routing schemes, including randomized routing, multi-path routing, and probability based routing, using both the models and simulations. We further propose a new mechanism, called local rerouting, that improves the effectiveness of QoS path establishment in the presence of imprecise global network state information. Local rerouting is orthogonal to existing schemes for dealing with imprecise state information and can be used in conjunction with them to alleviate the impacts of the imprecise information. The results of our performance study indicate that local rerouting is robust and effective.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.6
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• pp.2128-2147
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• 2021

Cognitive radio systems are being implemented recently to tackle spectrum underutilization problems and aid efficient data traffic. Spectrum sensing is the crucial step in cognitive applications in which cognitive user detects the presence of primary user (PU) in a particular channel thereby switching to another channel for continuous transmission. In cognitive radio systems, the capacity to precisely identify the primary user's signal is essential to secondary user so as to use idle licensed spectrum. Based on the inherent capability, a new spectrum sensing technique is proposed in this paper to identify all types of primary user signals in a cognitive radio condition. Hence, a spectrum sensing algorithm using improved convolutional neural network and long short-term memory (CNN-LSTM) is presented. The principle used in our approach is simulated annealing that discovers reasonable number of neurons for each layer of a completely associated deep neural network to tackle the streamlining issue. The probability of detection is considered as the determining parameter to find the efficiency of the proposed algorithm. Experiments are carried under different signal to noise ratio to indicate better performance of the proposed algorithm. The PU signal will have an associated modulation format and hence identifying the presence of a modulation format itself establishes the presence of PU signal.

• Korean Management Science Review
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• v.11 no.1
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• pp.187-196
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• 1994

Time-Space-Time(T-S-T) switching network is modeled as a graceful degrading system. Call blocking probability is defined as a measure of performance. Several performance related measures are suggested under the presence of failure. An optimization model is proposed, which determines optimal values of system parameters of the switching network.

• Journal of Korea Multimedia Society
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• v.25 no.8
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• pp.1188-1202
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• 2022

This study aims to investigate what communication phenomenon social viewing is associated with, and how satisfaction with using live commerce affects, taking into account that live commerce is a form of content consumption based on social viewing. In particular, social viewing is classified in this study as message production and sharing activities that influence users' satisfaction with live commerce viewing, as well as how two-dimensional social viewing behaviors are associated with users' perception of social presence. Then, the impact of these factors on improving viewing satisfaction is determined. It is also designed to investigate the moderating effect of social presence and viewing satisfaction as a function of the size of users' social networks by taking into account how social viewing affects the degree of social exchange among users. The findings of the analysis are as follows. First, social viewing behaviors. i.e., sharing and production behavior were identified as strong factors that have a direct impact on social presence and viewing satisfaction. Second, social presence plays a moderating role in the relationship between social viewing behavior and viewing satisfaction. Third, the impact of sharing behavior on social presence and viewing satisfaction was greater than the that of production behavior. Fourth, network size (number of followers and followings) had no direct effect on social reality or viewing satisfaction, but it had a moderating effect on the relationship between production behavior and social presence. Based on the findings, the implications and recommendations were discussed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.11
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• pp.2678-2684
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• 2014

In this paper a new message control method that can reduce server load and network traffic in XMPP/SIP presence service system has been proposed. This presence service system can process both XMPP(Extensible Massaging and Presence Protocol) based presence information and SIP(Session Initiation Protocol) based presence information. A new XMPP stanza architecture with added elements for presence stanza and IQ stanza has been designed, and a new presence information data processing method which can reduce size of SIP notification message and SIP PUBLISH message has been suggested. Furthermore a messages exchanging procedure that can transfer presence information between XMPP domain and SIP domain has been also suggested. The performance of the proposed system has been analysed by simulation.