• Journal of Communications and Networks
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• 제18권1호
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• pp.105-111
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• 2016

Trust models in the literature of MANETs commonly assume that packets have different security requirements. Before a node forwards a packet, if the recipient's trust level does not meet the packet's requirement level, then the recipient must perform certain security association procedures, such as re-authentication. We present in this paper an analysis of the epidemic broadcast delay in such context. The network, mobility and trust models presented in this paper are quite generic and allow us to obtain the delay component induced only by the security associations along a path. Numerical results obtained by simulations also confirm the accuracy of the analysis. In particular, we can observe from both simulation's and analysis results that, for large and sparsely connected networks, the delay caused by security associations is very small compared to the total delay of a packet. This also means that parameters like network density and nodes' velocity, rather than any trust model parameter, have more impact on the overall delay.

• 한국통신학회논문지
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• 제19권3호
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• pp.434-441
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• 1994

본 논문에서는 생산 자동화 네트워크인 MAP에서 네트워크 관리 기능을 실현하기 위해 중용한 변수인 전송 지연과 버퍼크기 그리고 시스템의 안정도등의 트래픽 성능을 분석하였다. 네트워크 관리는 네트워크 상에서 통신이 정상적으로 수행되도록 자원의 제어 및 감독을 담당하는 것으로 네트워크 운영시 필수적으로 요구되는 기능이다. 그러나 MAP 네트워크는 운영시 빠른 응담성을 요구하기 때문에 네트워크 관리 시스템을 구현하여 운영하기 위해서는 네트워크 관리 활동으로 인한 영향을 고려하여야 한다. 네트워크 관리 시스템 동작시 발생하는 불균일한 트래픽을 분석하기 위해, 사이클릭 큐잉 모델을 이용해 해석적 방법과 시뮬레이션을 수행하여 대기 지연 시간과 버퍼 크기를 구했으며, 네트워크 관리 활동에 따른 시스템의 안정도를 분석하였다.

• Journal of Information Processing Systems
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• 제13권6호
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• pp.1544-1553
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• 2017

The network coding mechanism has attracted much attention because of its advantage of enhanced network throughput which is a desirable characteristic especially in a multi-hop wireless network with limited link capacity such as the device-to-device (D2D) communication network of 5G. COPE proposes to use the XOR-based network coding in the two-hop wireless network topology. For multi-hop wireless networks, the Distributed Coding-Aware Routing (DCAR) mechanism was proposed, in which the coding conditions for two flows intersecting at an intermediate node are defined and the routing metric to improve the coding opportunity by preferring those routes with longer queues is designed. Because the routes with longer queues may increase the delay, DCAR is inefficient in delivering real-time multimedia traffic flows. In this paper, we propose a network coding-aware routing protocol for multi-hop wireless networks that enhances DCAR by considering traffic load distribution and link quality. From this, we can achieve higher network throughput and lower end-to-end delay at the same time for the proper delivery of time-sensitive data flow. The Qualnet-based simulation results show that our proposed scheme outperforms DCAR in terms of throughput and delay.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 학술대회 논문집 정보 및 제어부문
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• pp.657-659
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• 2004

CAN is a serial communication bus for real-time controls and automations in distributed control systems. In distributed control systems, occasionally a sensor module and a controller are not in the same node and physically separated. In order for the signal from a sensor node to reach the controller node, the signal must travel through network. CAN has a certain capabilities to deal with real-time data. However, when many nodes on the networks try to send data on the same network, the arbitration mechanism to solve the data collision problem is necessary. This situation causes the time delay which has detrimental effects on the performance of the control systems. This paper proposes a method to solve the problem due to the time delay in distributed control system using CAN. Time delay is approximated to an element with a rational transfer function using Pade approximation and Mu~synthesis method is applied. Since time delay in the network is not constant, the time delay element is considered to be an uncertainty block with a bound. The proposed method is applied to the experimental system with CAN and proved to be effective.

• 한국산업정보학회논문지
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• 제17권2호
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• pp.33-43
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• 2012

디지털 사이니지란 멀티미디어 기반의 정보와 광고를 소비자에게 전달하는 스마트 전자 디스플레이 시스템을 일컫는다. 대부분의 디지털 사이니지는 일련의 멀티미디어 콘텐츠를 원격 네트워크 스토리지로부터 로컬 디스크로 다운로드 한 후에 재생을 시작한다. 하지만 모든 콘텐츠를 다운로드 한 후 재생할 경우에 긴 초기 지연시간을 초래한다. 본 논문에서는 디지털 사이니지에서 이러한 초기 지연시간 문제를 정의하고, 주어진 네트워크 대역폭 및 멀티미디어 콘텐츠의 품질과 크기에 따라서 최소한으로 필요한 초기 지연시간을 계산하는 방법을 제시한다. 또한, 디지털 사이니지 상의 다양한 멀티미디어 콘텐츠들을 이용하여 본 제안 기법의 성능을 분석한다.

• 대한전자공학회논문지SD
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• 제47권2호
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• pp.51-59
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• 2010

드모르간 및 재대입 논리변환은 unate gate network (UGN)을 보다 일반적인 balanced inversion parity (BIP) network으로 전환하는데 충분하다. 이러한 회로계층에 대해서도 자세히 논의하고 있다. 우리는 드모르간 및 재대입 논리변환이 경로지연고장 테스트집합을 유지한다는 것을 증명하였다. 본 논문의 결과를 이용하여 함수 z를 구현하는 모든 UGN에서 모든 경로지연고장을 검출하는 상위수준 테스트집합은 함수 z의 어떠한 BIP realization에서도 모든 경로지연고장을 검출한다는 것을 보일 수 있다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4977-4996
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• 2016

The existence of excessively large and too filled network buffers, known as bufferbloat, has recently gained attention as a major performance problem for delay-sensitive applications. Researchers have made three types of suggestions to solve the bufferbloat problem. One is End to End (E2E) congestion control, second is deployment of Active Queue Management (AQM) techniques and third is the combination of above two. However, these solutions either seem impractical or could not obtain good bandwidth utilization. In this paper, we propose a Transmission Control Protocol（TCP）delayed window update mechanism which uses a congestion detection approach to predict the congestion level of networks. When detecting the network congestion is coming, a delayed window update control strategy is adopted to maintain good protocol performance. If the network is non-congested, the mechanism stops work and congestion window is updated based on the original protocol. The simulation experiments are conducted on both high bandwidth and long delay scenario and low bandwidth and short delay scenario. Experiment results show that TCP delayed window update mechanism can effectively improve the performance of the original protocol, decreasing packet losses and queuing delay while guaranteeing transmission efficiency of the whole network. In addition, it can perform good fairness and TCP friendliness.

• International Journal of Control, Automation, and Systems
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• 제6권2호
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• pp.186-193
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• 2008

The Internet's low cost and ubiquity present an attractive option for real-time distributed control of processes on the factory floor. When integrated with the Internet, the LonWorks open control network can give ubiquitous accessibility with the distributed control nature of information on the factory floor. One of the most important points in real-time distributed control of processes is timely response. There are many processes on the factory floor that require timely response. However, the uncertain time delay inherent in the network makes it difficult to guarantee timely response in many cases. Especially, the transmission characteristics of the LonWorks/IP network show a highly stochastic nature. Therefore, the time delay problem has to be resolved to achieve high performance and quality of the real-time distributed control of the process in the LonWorks/IP Virtual Device Network (VDN). It should be properly predicted and compensated. In this paper, a new distributed control scheme that can compensate for the effects of the time delay in the network is proposed. It is based on the PID controller augmented with the Smith predictor and disturbance observer. Designing methods for output feedback filter and disturbance observer are also proposed. Tracking position control experiment of a geared DC Servo motor is performed using the proposed control method. The performance of the proposed controller is compared with that of the Internal Model Controller (IMC) with the Smith predictor. The result shows that the performance is improved and guaranteed by augmenting a PID controller with both the Smith predictor and disturbance observer under the stochastic time delay in the LonWorks/IP VDN.

• 디지털콘텐츠학회 논문지
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• 제15권1호
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• pp.1-9
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• 2014

지연-허용 네트워크 (Delay-Tolerant Network; DTN)는 안정적인 통신 연결성이 보장되지 않는 네트워킹 환경에서 전개할 수 있는 비대칭 네트워킹 기술로써, 저장 공간에 수신한 데이터를 저장하고 통신 경로가 확보될 때 경우에만 데이터를 전송한다. DTN은 위성간의 통신을 지원하는 우주 통신 뿐만 아니라 센서 네트워크와 MANET (Mobile Ad-Hoc Network)에도 적용되고 있다. DTN 네트워킹 환경에서는 오버헤드가 작으면서도 라우팅 신뢰성이 높아서, 라우팅 속도와 성능을 전반적으로 향상시킬 수 있는 방안을 제공하는 것이 매우 중요하다. 본 논문에서는, 시간 주기를 가지는 이동 노드들이 존재하는 네트워크에서 데이터를 효과적으로 전송하기 위하여, 라우팅 경로를 예측할 수 있는 시간 정보 기반의 DTN라우팅 기법을 제안한다. Omnet++ 시뮬레이션 도구를 이용한 성능 분석 결과, 제안된 시간 정보 기반의 DTN 라우팅 알고리즘이 기존의 DTN 라우팅 알고리즘들에 비해 적은 라우팅 오버헤드를 가지고도 라우팅 속도와 신뢰성을 높일 수 있는 기법임을 검증하였다.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2007년도 학술대회
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• pp.136-141
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• 2007

The frequency accuracy and phase alignment is necessary for ensuring the quality of service (QoS) for applications such as voice, real-time video, wireless hand-off, and data over a converged access medium at the telecom network. As telecom networks evolve from circuit to packet switching, proper synchronization algorithm should be meditated for IP networks to achieve performance quality comparable to that of legacy circuit-switched networks. The Time of Packet (ToP) specified in IEEE 1588 is able to synchronize distributed clocks with an accuracy of less than one microsecond in packet networks. But, The ToP can be affected by impairments of a network such as packet delay variation. This paper proposes the efficient method to minimize the expectable delay variation when ToP synchronizes the distributed clocks. The simulation results are presented to demonstrate the improved performance case when the efficient ToP transmit algorithm is applied.