• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.286-288
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• 2005

최근 기지국(Base Station)의 도움 없이 이동 단말기 간의 다중 무선 홉을 사용하여 송,수신자 간의 데이터 전송을 가능하게 하는 Ad-hoc 통신망에 관한 연구가 활발히 진행되고 있다. 유선망과 달리 Ad-hoc 통신망은 무선 전송 매체를 사용하기 때문에 신호의 페이딩(Fading), 간섭(Interference), 잡음(Noise) 등에 의해 높은 BER(Bit Error Rate)이 발생하는 특징을 가지고 있다. 하지만, 현재 인터넷 상에서 광범위하게 사용되고 있는 전송 규약인 TCP(Transmission Control Protocol)는 유선망의 신뢰적인 전송 매체를 고려하여 개발된 프로토콜이기 때문에 TCP를 수정 없이 Ad-hoc 통신망에 적용할 경우 전송 성능이 저하되는 문제를 가지고 있다. 전송 성능이 저하되는 문제는 기존 TCP가 에러 발생의 원인을 혼잡에 의한 것으로 인식하고 불필요한 혼잡 제어를 하기 때문이다. 본 논문에서는 송신자가 에러 발생 원인을 구별하고, 그에 따라 전송률을 조절함으로써 Ad-hoc 망에서의 TCP성능 향상을 위한 방법을 제시하였다. 또한 ns-2 시뮬레이터를 이용한 실험을 통해 TCP의 성능이 제안된 알고리즘에 의해 향상되었음을 확인하였다

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.912-919
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• 2005

The Growth in wireless Internet has made Networking possible at anytime and anywhere. So mobile devices like cellular phone and PDA are now used in various fields. In particular, the mobility of mobile devices has a great advantage in remote control. This paper designed and implemented a Mobile VNC system that transmitted the screen image of a remote computer, control the remote computer GU and monitor all by cellular phone. The proposed system consists of a Mobile Viewer un on the cellular phone, VNC Server m on a number of remote computers and a VNC Monitor. For communication between the VNC Server and the Mobile Viewer the MRFB protocol is used. The screen image transmitted to the Mobile Viewer is encoded in the PNG format supported by SK-VM, the Java execution environment of the Cellular phone. According to implementation results, the image is about $2KB\~8KB$. According to the 65 times transmission test, the average frame per second is 4.93fps in the emulator and a real cellular phone takes 0.8fps. Therefore, the proposed system is more efficient than existing systems.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.95-98
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• 2006

Data collected by sensors in field are transmitted to the base station gathering all of data. Because sensors have to gather data in surroundings and periodically transmit data to the base station, it makes energy consumed much. In this paper, we propose the scheme that is to avoid traffic congestion with achievement of energy efficiency, so collected data is transmitted efficiently. This is to adjust transmission rate differently in case of increasing or decreasing traffic and minimize the energy consumption with setting ideal options up basic CSMA(Carrier Sense Multiple Access) protocol in each sensor. Through the simulation, we find the ideal CSMA options and apply the proposed scheme of traffic control mechanism to them, then show energy efficiency and effective traffic control mechanism.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2000.10a
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• pp.463-467
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• 2000

In this paper, we have implemented the Web Server Patient Monitoring System using PPP. It is composed of two parts. The first part is the Analog board for acquiring ECG signals. The second part is the module for processing and transmitting the acquired signal. The second part is using PPP for dial-up networking, TCP/IP for Internet, HTTP for web browser and JAVA program for a Patient Monitoring Program in one chip. In home, it is not need to establish another network line because it uses a telephone line. And a user who want to monitor a patient's biosignal can monitor a patient without wholly open network because it is the network sewer. The Patient Monitoring Program runs on a web browser by downloaded JAVA codes when a user connect to this system. It can make the Home Patient Monitoring Program decrease cost. It can help to avoid the limitation of monitoring a patient.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.8A
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• pp.791-800
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• 2010

Recently wireless sensor networks as a field of ubiquitous computing technology was in the limelight. To use and collect the necessary information, Sink node mobility is essential. TTDD(Two-Tier Data Dissemination) proposed most common technique associated with Mobile sink node in wireless sensor networks, but issues exist that the use of many control packet falls into the energy efficiency. The technique for solving problems is Cluster-Based Energy-efficient Routing protocol (CBPER). But CBPER does not transmit the data correctly to sink node or source node. In this paper, we propose An Energy-Efficient Routing Protocol based on Static Grid using mobile sink nodes in order to solve the data transmission failure and reduce the energy consumption in Wireless Sensor Networks. We have evaluated it with the NS-2 simulator. Our results show that the proposed protocol saves the energy consumption up to 34% in comparison with CBPER. We also prove that the proposed protocol can transmit more accurate data to the sink de than CBPER.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.1
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• pp.39-45
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• 2008

High-Rate Wireless Personal Area Networks (HR-WPANs) in IEEE 802.15.3 standard use a TIme Devision Multiple Access (TDMA) protocol to support isochronous traffic. Isochronous traffic requires a delay-bounded service. However, the HR-WPAN standard suffers from long access delay and association delay. In this paper, we propose an enhanced MAC protocol for the delay-bounded traffic. This proposed protocol provides a way that a central node is able to collect traffic status on all member nodes. Furthermore, by utilizing the information, a scheduling algorithm is also proposed in order to synchronize the instant of a packet transmission with that of the packet arrival. With the proposed protocol and algorithm, the delay of access and association can be reduced. Performance analysis is carried out and the significant performance enhancement is observed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2811-2817
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• 2010

In this paper we propose the QAC-MAC that supports Quality of Service(QoS) and saves energy resources of the sensor node, and hence prolonging the lifetime of the sensor network with multiple sink nodes. Generally, the nodes nearest to the sink node often experience heavy congestion since all data is forwarded toward the sink through those nodes. So this critically effects on the delay-constraint data traffics. QAC-MAC uses a hybrid mechanism that adapts scheduled scheme for medium access and scheduling and unscheduled scheme based on TDMA for no data collision transmission. Generally speaking, characteristics of the real-time traffic with higher priority tends to be bursty and has same destination. QAC-MAC adapts cross-layer concept to rearrange the data transmission order in each sensor node's queue, saves energy consumption by allowing few nodes in data transmission, and prolongs the network lifetime.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.4
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• pp.35-44
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• 2004

Recently announced TCP Vegas predicts the degree of congestion in the network and then control the congestion window size. Thus it shows better performance than TCP Reno. however, TCP vegas does not assume any network model, its congestion window control is very limited. Because or this limitation, TCP vegas still can not adapt to fast changing available bandwidth. In this paper, we introduce a new TCP algorithm which adapts to fast changing available bandwidth well. To devise such a TCP, we model the end to end network of TCP connection as a queueing system and finds congestion window size which can utilize the available bandwidth sufficiently but not make the network congested. The simulation results show that our algorithm adapts to the avaliable bandwidth faster than TCP vegas and as a results, when the available bandwidth is changing rapidly, our algorithm not only operates more stably than TCP Vegas, but also it shows higher thruput than TCP Vegas.

• Proceedings of the KIEE Conference
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• 2008.10b
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• pp.497-498
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• 2008

모바일 폰에서 IrDA를 통하여 개인정보 (전화번호부, 동영상, 사진등) 송수신시 IrMC, IrOBEX 그리고 HDLC 프로토콜 기반위의 IrLAP등의 프로토콜 스택을 사용하고 있다. Primary, secondary 두 mobile phone 간에 IrLAP layer의 payload data 송수신시 이용되는 3가지 physical layer schemes 중 전송속도 1l5.2kbps data rate의 제안된 표준인 Asynchronous(Async) frame 방식을 이용한다. [1] 현재의 모바일 폰에서는 Async frame scheme을 구현하기 위한 인터페이스 방식 중 UART 인터페이스를 이용하여 구현하고 있다. 현 모바일 폰에 이미 구현 되어 있는 기존 UART의 FIFO 제어 방법과 Interrupt service routine의 제어 알고리즘을 개선하여 기존 제어 방식과 비교하고 향상된 성능의 결과는 Throughput로 도출한다. 현 모바일 폰에서 사용자가 개인 정보 data등을 저장할 수 메모리 공간이 점점 늘어나고 있는 추세이다. Camera의 해상도 현 5Mega pixel까시 지원되고 동영상 파일 등도 근거리 무선통신인 IrDA로 송수신할 수 있으므로 본 성능비교 file의 size는 100Mega 이상도 비교할 수 있도록 하였다.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 2003.07a
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• pp.182-187
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• 2003

액티브 네트워크 환경에서 액티브 노드(라우터 또는 스위치)의 기능은 액티브 익스텐션(active extension)에 의해 다이나믹하게 확장될 수 있다 즉, 액티브 노드 기능을 확장하는 소프트웨어 모듈을“익스텐션”이라 할 수 있다. 이러한 융통성(flexible)이 강한 구조는 새로운 네트워크 프로토콜과 서비스들을 활성화시키고 있으나, 다른 한편으로는 매우 심각한 안전성(safety)과 보안(security) 문제를 야기 시키게 된다. 본 논문에서 다루는 액티브 익스텐션 관련 보안 문제는 하나의 액티브 노드상의 익스텐션이 다른 액티브 노드에 접근하려 할 경우 이에 대한 제어 방법이 반드시 제공되어야 한다는 것이다. 특히, 이 문제에서는 액티브 노드들간의 인증(authentication)이 매우 중요하다. 여기에서는 액티브 노드들간의 접근 정책 전송을 위해 각 객체가 갖는 고유 정보인 아이덴티티(identity)를 이용한다. 우리는 본 논문에서 아이덴티티를 통하여 액티브 노드들간의 인증(authentication)을 행하는 새로운 방식의 접근 정책(access policy) 전송 방법을 제안한다.