• Journal of KIISE:Information Networking
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• v.34 no.6
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• pp.466-474
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• 2007

Asymmetric networks that the downlink bandwidth is larger than the uplink bandwidth may cause the degradation of the TCP performance due to the uplink congestion. In order to solve this problem, this paper designs and implements the Dynamic Segment Size Control mechanism which offers a suitable segment size for current networks. The proposed mechanism does not require any changes in customer premises but suppress the number of ACKs using segment reassembly technique to avoid the uplink congestion. The gateway which adapted the Dynamic Segment Size Control mechanism, detects the uplink congestion condition and dynamically measures the bandwidth asymmetric ratio and the packet loss ratio. The gateway reassembles some of segments received from the server into a large segment and transmits it to the client. This reduces the number of corresponding ACKs. In this mechanism, the SACK option is used when occurs the bit error during the transmission. Based on the simulation in the GEO satellite network environment, we analyzed the performance of the Dynamic Segment Size Control mechanism.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.1
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• pp.259-264
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• 2014

IEEE 802.15.4 has been emerging as the popular choice for various monitoring and control applications. In this paper, a fault management system for DC power-lines has been designed using IEEE 802.15.4, in order to monitor DC power-lines in real time, and to rapidly detect faults and shut off the line where such faults occur. Numbers were allocated for each node and unslotted CSMA-CA method of IEEE 802.15.4 was used, the performance of which was analyzed by a simulation. For such purpose, a total of 60 bits of the control data consisting of 16 bits of the current, 16 bits of the amplitude, 28 bits of the terminal state data were sent out, and the packet transfer rate and the transmission delay time of the fault management system for DC power-lines were measured and analyzed. When the traffic load was 330 packets per second or lower, the average delay time was shown to be shorter than 0.02 seconds, and when the traffic load was 260 packets per second or lower, the packet transfer rate was shown to be 99.99% or higher. Therefore, it was confirmed that the stringent condition of US Department of Energy (DOE) could be satisfied if the traffic load was 260 packets per second or lower, The results of this study can be utilized as basic data for the establishment of the fault management system for DC power-lines using IEEE 802.15.4.

• Journal of KIISE:Information Networking
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• v.31 no.1
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• pp.20-26
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• 2004

A congestion control algorithm to prevent buffer overflow in MSR(Mobility Support Router) for I-TCP is proposed. Due to high bit error rate and frequent hand-offs over wireless environment, the current congestion control scheme in TCP Reno over mixed(wired and wireless) network exhibits lower throughput than the throughput achieved over wired only network. I-TCP has been proposed to address this by splitting a TCP connection into two TCP connections over wired section and wireless section, respectively. However, buffer overflow in MSR may occur whenever there are excessive bit errors or frequent hand-offs. This may lead to the loss of packets acked by MSR(resident in buffer) to the sender, but not received by the receiver, breaking TCP end-to-end semantics. In this Paper, a new scheme is proposed to prevent the MSR buffer from overflow by introducing “flow control” between the sender and the MSR. Advertised window for the TCP connection between the sender and the MSR is tied to the remaining MSR buffer space, controlling the flow of packets to the MSR buffer before overflow occurs.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.47-56
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• 2018

National-scale industrial control systems for gas, electric power, water processing, nuclear power, and traffic control systems increasingly use open networks and open standards protocols based on advanced information and communications technologies. The frequency of cyberattacks increases steadily because of the use of open networks and open standards protocols, but follow-up actions are limited. Therefore, the application of security solutions to an industrial control system is very important. However, it is not possible to apply security solutions to a real system because of the characteristics of industrial control systems. And a security system that can detect attacks without affecting the existing system is imperative. Therefore, in this paper, we propose an intrusion detection system based on packet analysis that can detect anomalous behaviors without affecting the industrial control system, and we verify the effectiveness of the proposed intrusion detection system by applying it in a test bed simulating a real environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1B
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• pp.154-161
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• 2010

In wireless sensor networks, due to the many-to-one convergence of upstream traffic, congestion more probably appears. The existing congestion control protocols avoid congestion by controlling incoming traffic, but the duty-cycle operation of MAC(Medium Access Control) layer has not considered. In this paper, we propose DCA(Duty-cycle Based Congestion Avoidance), an energy efficient congestion control scheme using duty-cycle adjustment for wireless sensor networks. The DCA scheme uses both a resource control approach by increasing the packet reception rate of the receiving node and a traffic control approach by decreasing the packet transmission rate of the sending node for the congestion avoidance. Our results show that the DCA operates energy efficiently and achieves reliability by its congestion control scheme in duty-cycled wireless sensor networks.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10c
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• pp.301-303
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• 2003

본 논문에서는 인터넷 혼잡제어를 위한 새로운 방법을 제안한다. 라우터 큐에 예측제어함수를 적용하여 미래의 혼잡상황을 예측하고 소스에게 미리 피드백을 수행하여 혼잡제어를 한다. 예측제어함수는 실제 큐와 예측된 큐의 오차를 계산하여 주기적으로 예측함수를 갱신하는 NLMS 방식의 예측제어함수를 적용한다. 피드백 정보의 전송지연으로 인한 혼잡상황 악화가 발생하기 전에 혼잡상황에 대응할 수 있으므로 라우터 버퍼 사용효율의 최적함을 유지할 수 있으며 버퍼 오퍼플로우로 발생하는 패킷의 손실을 최소화 할 수 있다. 혼잡상황을 야기하도록 과도한 트래픽을 생성하여 라우터에서 예측함수를 적용하는 경우와 단지 혼잡알림제어를 수행하는 경우를 비교하여 시뮬레이션을 수행하였다. 예측함수를 적용하는 경우는 시스템 성능효율을 증가시키며 라우터 버퍼 크기를 최적하게 사용할 뿐만 아니라 오퍼플로우가 발생하지 않았으나 예측함수를 적용하지 않고 혼잡알림제어를 수행하는 경우는 과도한 큐 크기와 오버플로우가 발생하였음을 시뮬레이션을 통해서 보인다.

• Annual Conference of KIPS
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• 2002.11b
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• pp.1277-1280
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• 2002

화상회의 시스템들은 여러 명의 사람들에게 멀티미디어 데이터를 공유하여 전송하기 때문에 안정적인 대역폭을 보장받지 못하며, 계속적으로 변화하는 네트워크 상태에서 최적의 서비스를 제공하기 위해서는 동적 흐름제어 기법이 필요하게 된다. 동적 흐름제어 기법은 최적의 서비스를 제공하기 위해서 사용 대역폭이 클 경우에는 데이터의 량이 많은 고품질의 데이터를, 사용 가능한 대역폭이 낮을 경우에는 데이터의 량이 적은 저품질의 데이터를 생성한다. 본 논문에서는 기존의 두 가지 흐름제어 기법에서 사용된 측정 요소인 패킷 손실율과 왕복 시간외의 성능을 개선시킬 수 있는 요소인 네트워크 상태에 따른 제어 메시지의 빈도수와 데이터의 량을 이용한 동적 흐름제어 기법을 제안한다. 또한 실험을 통하여 기존의 동적 흐름제어 기법과 제안한 동적 흐름제어기법의 성능을 비교하였다.

• Journal of Broadcast Engineering
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• v.10 no.4 s.29
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• pp.548-556
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• 2005

In wireless network environments, wireless channels are characterized by time-varying fading and interference conditions, which may lead to burst packet corruptions and delay variation. This can cause severe quality degradation of streaming media. To guarantee successful transmission of media over the hostile wireless networks, where channel conditions are highly fluctuating, a flexible and network-adaptive transport method is required. Thus, we propose a network-adaptive transport error control consisting of packet-level interleaved FEC and delay-constrained ARQ, which acts as an application-level transport method of streaming media to alleviate burst packet losses while adapting to the changing channel condition in wireless networks. The performances of the proposed network-adaptive transport error control, general error control schemes, and hybrid schemes are evaluated by a developed simulator at the transport-level and video quality of streaming media. Simulation results show that the proposed mechanism provides the best overall performance among compared other schemes in terms of the transport-level performance of error control and the performance of video quality for streaming media.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.717-720
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• 2003

본 연구에서는 인터넷통신에서 트래픽의 혼잡 제어를 억압하여 성능을 향상시키는데 중점을 둔다. 무선통신에서 미디어 액세스 제어를 제공하지 않기 때문에, ATM이나 인터넷 네트워크에 혼잡이 발생하면 쓰루풋이 낮아지는 것이 경우가 있다. 이런 효과를 입증하기 위해서 인터넷 네트워크 혼잡 발생 시 트래픽에서 TCP 쓰루풋 반응을 발생하기 때문에 링크사용 및 버퍼점유에 정보를 사용하여 혼잡을 알릴 수 있고, ACK 지연을 다양한 네트워크 노드를 통하여 트래픽 제어를 구현하며 버퍼에서 패킷 손실을 RTOr을 응용해 성능을 평가하고 시뮬레이션을 응용하여 안정적인 성능 향상을 입증한다.

• Annual Conference of KIPS
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• 2005.11a
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• pp.1527-1530
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• 2005

스마트 홈은 홈 내의 여러 장치와 서비스가 서로 협력함으로써 최적의 가정환경을 만들고, 거주자가 원격지에서 홈 내의 특정 가전을 제어할 수 있도록 발전하였다. 현재 가장 많이 사용되어지고 있는 웹 서버를 이용하는 방법은 고정 IP(Internet Protocol)를 가지고 있지 않고, 푸쉬(Push) 기능의 부재로 인해 거주자가 지시한 내용이 잘 진행되어지고 있는지 알기 위해 새로운 플랫폼을 구축하거나, 다시 접속을 하여야만 진행상황을 알 수 있다. 또한, 제어를 원하는 정보가전의 상태를 먼저 받아야만 제어가 가능하기 때문에 실내에서는 그 상태를 사용자가 알고 있지만, 패킷의 오류 발생은 제어의 지연 원인이 된다. 유비쿼터스는 인간친화적인 형태의 제어 장비를 제안하여 오고 있다. 본 논문에서는 메신저와 자연어 처리의 구문 분석을 활용하여 정보 가전을 제어할 수 있는 방법을 제안한다.