• The KIPS Transactions:PartD
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• v.14D no.5
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• pp.565-572
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• 2007

In this paper, we developed a VoWLAN(Voice over WLAN) system based on an open source software. The system aims to provide VoIP service over wireless LAN with an IP-PBX server. The features of system presented in this paper are as follows. First, the initial cost for the development is reduced since the system is developed based on open source software. Second, the system provides various additional services such as Voice Mail, Conference Call, and Interactive Voice Response with a software IP-PBX server. Third, the VoWLAN terminal provides high-level user applications with minimal system resources using lightweight open software solutions. Finally, it is highly scalable since it is based on the open source software.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10c
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• pp.217-219
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• 2001

WLAN은 다양한 정보와 자원을 공유할 수 있게 하는 LAN의 장점과, 제약 없는 연결성 제공이라는 편리성을 동시에 제공하고, 신뢰성 있는 data전송뿐만 아니라 유연성과 설치의 용이성을 장점으로 갖고 있다. 그러나 WLAN 이용하여 여러 어플리케이션을 사용할 때 제기되는 문제로 WLAN은 셀룰라 폰의 soft handover와 같은 mobility가 완전하게 지원되지 않으므로 WLAN 환경에서 VoIP 서비스 같은 실시간 서비스에 제약이 있다는 단점이 있다. 본 논문에서는 WLAN의 제약을 극복하기 위해 WLAN환경에서 이동단말의 이동성을 지원하기 위한 handover 방안을 제시하였다.

• 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 Institute of Information and Commucation Sciences Conference
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• 2010.10a
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• pp.456-458
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• 2010

VoIP services are growing fast and WLAN VoIP phones are being used in widespread. Emergency services are very critical in WLAN VoIP as in other traditional networks. This paper summarize recent standards of IEEE 802.11 supporting emergency services in WLANs. Two standards are discussed. The 11u deals with the aspect of access in WLAN emergency services, and the 11v deals with the location services.

• Journal of the Korea Society for Simulation
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• v.15 no.3
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• pp.87-91
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• 2006

With the growth of the internet, the number of wireless internet users has increased continuously up to date. However, mobile communications could not support high speed transmission rate with cheap communication fee and wireless LAN has problems in providing terminal mobility and wide area connectivity, respectively. So the WMAN standard has been newly designed to make up for these limits. The initial 802.16 specification effectively offers a solution for providing fixed users with high speed wireless communication but it does not offer terminal mobility. So the 802.16d and 802.16e have been developed as the next generation solution that can support various PHY layer (SC, SCa, OFDM, OFDMA) and offer the terminal mobility. In this paper, we propose an effective uplink scheduling algorithm for VoIP with using UGS, and we show that our proposed algorithm is superior in view of average delay and management of uplink bandwidth to conventional rtPS algorithm and the scheme in reference, with using NS-2 network simulator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1A
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• pp.33-43
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• 2010

Recently, users want to use real-time multimedia services, such as internet, VoIP, etc., using their IEEE 802.11 wireless lan mobile stations. In order to provide such services, a handoff among access points is essential to support the mobility of a node, in such an wide area. However, the legacy handoff methods of IEEE 802.11 technology are easy to lose connections. Also, the recognition of a disconnection and channel re-searching time make the major delay of the next AP to connect. In addition, because IEEE 802.11 decides the selection of an AP depending only on received signal strength, regardless of a node direction, position, etc., it cannot guarantee a stable bandwidth for communication. Therefore, in order to provide a real-time multimedia service, a node must reduce the disconnection time and needs an appropriate algorithm to support a sufficient communication bandwidth. In this paper, we suggest an algorithm which predicts a handoff point of a moving node by using GPS location information, and guarantees a high transmission bandwidth according to the signal strength and the distance. We implemented the suggested algorithm, and confirmed the superiority of our algorithm by reducing around 3.7ms of the layer-2 disconnection time, and guaranteed 24.8% of the communication bandwidth.