• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.595-598
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• 2014

In order to provide the Mobile Stations operating in IEEE 802.11 Wireless LAN network with seamless handover, a comprehensive study on the functions of handover considering various networking environments and characteristics of Mobile Stations is required. Note that the channel scan process finding a new AP takes the major portion of handover time, and this is the most significant issue with seamless handover for real-time multimedia service in WLAN environment. In this paper the functions required to provide seamless handover in IEEE 802.11 WLAN network are identified, and a new scanning technique is proposed with which the Mobile Stations can selectively scan the channels to reduce the channel scan time in various network environments. Here each Mobile Station awares of the channels the neighbor APs are using by scanning them in advance according to the proposed technique. Afterwards, when handover is actually required, the optimal AP is decided quickly by scanning only the predetemined group of channels and order of scan without unnecessary scan of all the channels. In addition, proposes to enter the Scan Trigger Value and Handover Threshold Value in mobile phones in order to prevent the phenomenon can not handover.

• Proceedings of the Korean Information Science Society Conference
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• 2004.04a
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• pp.664-666
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• 2004

최근 멀티미디어 인터넷의 확산으로 인해 SIP를 비롯한 음성 및 화상 패킷 전송에 대한 관심이 증대되고 있으며, 이에 대해 인터넷을 통한 음성통신서비스가 전개되고 있다. 또한, 노트북, 핸드폰과 같은 무선 기기에 이러한 음성통신서비스를 제공함으로써 이를 효율적으로 연동하고 제어하기 위한 다양한 표준들이 나타나고 있다. 본 논문에서는 급속하게 발전되고 있는 VoIP 기술 중 세션 제어를 위한 기본 프로토콜 표준인 SIP를 살펴보고, 무선 환경에 이를 적용함으로써 SIP단말이 홈 망을 나간 후 다시 홈 망으로 들어왔을 때의 패킷 손실 및 중단 시간을 이동 단말의 속도에 따라 측정함으로써 무선 환경에서의 음성 트래픽 성능이 어느 정도의 결과를 산출할 수 있는지를 측정한다. 실험 결과 이동 단말이 좀 더 빠르게 움직일 때 더 적은 패킷 손실률이 나왔음을 볼 수 있다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.5
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• pp.996-1002
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• 2009

The EDCA scheme in IEEE 802.11 MAC protocols was adopted to support QoS of each traffic. The impact of legacy DCF stations on EDCA voice service is studied using extensive simulations. The maximum number of voice sessions are obtained in cases that IEEE 802.11b and IEEE 802.11a physical layers are used.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1228-1233
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• 2004

Character of the technology that is going to lead the next generation convergence network which has been discussed recently can be represented by Integrating and Convergence. As Wireless Telecommunication and Broadband Transport Technology make rapid progress for several years, and those of two important technical advance, Integrating, Convergence will combine with the latest terminal technology. so it becomes a big issue of utmost importance. This paper, therefore, investigates the network deployment strategies and relating technology toward Broadband Convergence Network(BcN) and makes a survey of up-to-date technique based on Telecom Service businesses which have been required.

• The KIPS Transactions:PartC
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• v.13C no.4 s.107
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• pp.427-434
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• 2006

Broadband Convergence Network(BcN) is a critical infrastructure to provide wired-and-wireless high-quality multimedia services by converging communication and broadcasting systems, However, there exist possible danger to spread the damage of an intrusion incident within an individual network to the whole network due to the convergence and newly generated threats according to the advent of various services roaming vertically and horizontally. In order to cope with these new threats, we need to analyze the vulnerabilities of BcN in a system architecture aspect and classify them in a systematic way and to make the results to be utilized in preparing proper countermeasures, In this paper, we propose a new classification of vulnerabilities which has been extended from the ITU-T recommendation X.805, which defines the security related architectural elements. This new classification includes system elements to be protected for each service, possible attack strategies, resulting damage and its criticalness, and effective countermeasures. The new classification method is compared with the existing methods of CVE(Common Vulnerabilities and Exposures) and CERT/CC(Computer Emergency Response Team/Coordination Center), and the result of an application to one of typical services, VoIP(Voice over IP) and the development of vulnerability database and its management software tool are presented in the paper. The consequence of the research presented in the paper is expected to contribute to the integration of security knowledge and to the identification of newly required security techniques.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.3
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• pp.569-575
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• 2014

These days as smart TVs or android set top boxes have come into wide use, VoIP(Voice over Internet Protocol) services such as the Skype which can beused on computer system, can be also accessed by smart TVs or set top boxes. and the various kinds of distance learning programs have been developed on smart TVs or set top boxes. but when users have utilized a webcam with smart TVs or set top boxes, users have to go in front of smart TVs or set top boxes In this research paper, the new technology can be solved the problem of webcam use according to chaned environment. This tech is related with the wireless webcam one which can be applicable to open spaces such as living room with some distance between user and smart TV. There are few problems in long distance the test results show high reliability in living room with some distance.

• Journal of the Korean Society for Railway
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• v.19 no.4
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• pp.456-467
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• 2016

Wireless Access in Vehicular Environments (WAVE) communication technology, which provides vehicleto-vehicle and vehicle-to-infrastructure communication and offers safe and convenient service, has been developed for application to an Intelligent Transport System (ITS). This paper provides field test results on a study of the feasibility of WAVE technology application to railway communication systems. A test railway communication system based on WAVE technology has been built along the Daebul line and a newly developed EMU. Field tests have been carried out according to the communication function requirements for LTE - R. The test results show that the railway communication system based on WAVE technology meets the functional requirements: maximum transmission length is 730m, maximum transfer delay is 5.69ms, and maximum interruption time is 1.36s; other tests including throughput test, video data transmission test, VoIP data test, and channel switching test also produced results that meets the functional requirements. These results suggest that WAVE technology can be applied to the railway communication system, enabling Vehicle-to-Wayside communication.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.9 no.6
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• pp.599-603
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• 2016

Recently the wireless LAN system is substituting wired LAN system notably as the number of mobile users increases greatly along the advancement of technology. But the wireless LAN has a critical weakness in the security such as data leakage. Thus a safe security system is imperative to avoid threatening from hackers with offering the best convenience to inner users. In this research, we have developed a RADIUS wireless LAN security system for industrial applications, which performs the EAP authentication with the compatibility for any maker of wireless LAN. The system has interfaces based on WEB, providing DB access function for user management so that users can perform authentication of 802.1x in their computers.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.5 s.347
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• pp.77-83
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• 2006

In this paper, we designed, constructed and evaluated the system for the FTTH suited to a residence and apartment using CWDM-PON techniques. These systems have capacity to service at 100Mbps rate to 384 users in the same breath. Also, the services include the internet, CATV, IPTV and wireless LAN. In the case of ire network, the data could be transmitted by UTP cable and optical fiber and case of wireless one, the data transmitted using WLAN. The distance between the cental office and the user is 20km and the data rate is 100Mbps maximum. Of course, the optical network used just one fiber optical core. For the basic material, we obtained the characteristics of optical transceiver module, Mux/Demux and transmission qualities depends on the environment.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.130-139
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• 2010

Environmental issues and the need to reduce energy consumption for lowering operating costs have pushed power efficiency to become one of the major issues of current research in the field of wireless networks. This paper addresses a number of multiple input multiple output (MIMO) precoding and scheduling techniques across the PHY and MAC layers that can operate under a reduced link budget and collectively improve the transmit power efficiency of a base station, while maintaining the same levels of service. Different MIMO transmission and precoding schemes proposed for LTE, achieving varying degrees of multiuser diversity in both the time, frequency as well as the space domain, are examined. Several fairness-aware resource allocation algorithms are applied to the considered MIMO schemes and a detailed analysis of the tradeoffs between power efficiency and quality of service is presented. This paper explicitly examines the performance of a system serving real-time, VoIP traffic under different traffic loading conditions and transmit power levels. It is demonstrated that by use of efficient scheduling and resource allocation techniques significant savings in terms of consumed energy can be achieved, without compromising QoS.