• Journal of KIISE:Information Networking
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• v.36 no.2
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• pp.80-89
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• 2009

A DHT(Distributed Hash Table) based P2P is a method that compensates disadvantages of the existing unstructured P2P method. If a DHT algorithm is used, it can do fast data search and maintain search efficiency independent of the number of peers. The peers in a DHT method send messages periodically to keep the routing table updated. In a mobile environment, the peers in a DHT method should send messages more frequently to keep the routing table updated and reduce the failure of requests. However this results in increasing the overall network traffic. In this paper, we propose a method to reduce the update load of a routing table in the existing DHT by updating it in a reactive way. In the proposed reactive method, a routing table is updated only if a data request is coming whereas it is updated periodically in the existing proactive method. We perform experiments using Chord simulator(I3) made by UC Berkely. The experimental results show the performance improvement of the proposed method compared to the existing method.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2007.06a
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• pp.61-64
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• 2007

MPLS networks architectures have been prevailed as scalable approach to provide quality of service in the Internet. Many researches have been mainly focused on scalability and multi-path calculation scheme for failure restoration. However, the MPLS network have an scalability problem about traffic, and the existing failure restoration methods are wasted resources, and it has the problem that loss of a packet by a lot of delay occurs in too. Therefore in this paper, we propose a H-MPLS (Hierachical-Multiprotocol Label Switching)network for rapidly failure restorations and effective management of network extended. The proposed H-MPLS Network apply LSP multi-path routing algorithm and consists of several MPLS. After comparing the performance among the existing failure restoration methods with various network models, we use NS simulator in order to analyze the performance. Finally, we present an improvement scheme of the efficiency and scalability.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7B
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• pp.711-721
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• 2004

To provide the end-to-end service differentiation for assured services, the random early demotion and promotion (REDP) marker in the edge router at each domain boundary monitors the aggregate flow of the incoming in-profile packets and demotes in-profile packets or promotes the previously demoted in-profile packets at the aggregate flow level according to the negotiated interdomain service level agreement (SLA). The REDP marker achieves UDP fairness in demoting and promoting packets through random and early marking decisions on packets. But, TCP fairness of the REDP marker is not obvious as fur UDP sources. In this paper, to improve TCP fairness of the REDP marker, we combine a dropper with the REDP marker. To make packet transmission rates of TCP flows more fair, at the aggregate flow level the combined dropper drops incoming excessive in-profile packets randomly with a constant probability when the token level in the leaky bucket stays In demotion region without incoming demoted in-profile packets. It performs a dropping in the demotion at a domain boundary only if there is no prior demotion. The concatenate dropping at multiple domains is avoided to manifest the effect of a dropping at a domain boundary on TCP fairness. We experiment with the REDP marker with the combined dropper using ns2 simulator for TCP sources. The simulation results show that the REDP marker with the combined dropper improves TCP fairness in demoting and promoting packets by generating fair demoted in-profile traffic compared to the REDP marker. The effectiveness of the selected drop probability is also investigated with showing its impact on the performance of the REDP marker with the combined dropper.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11B
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• pp.1297-1304
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• 2011

SIP(Session Initiation Protocol) has some security vulnerability because it works on the Internet. Therefore, the proxy server can be affected by the flooding attack such as DoS and service interruption. However, traditional schemes to corresponding Denial of Service attacks have some limitation. These schemes have high complexity and cannot protect to the variety of Denial of Service attack. In this paper, we newly define the normal user who makes a normal session observed by verifier module. Our method provides continuous service to the normal users in the various situations of Denial of Service attack as constructing a whitelist using normal user information. Various types of attack/normal traffic are modeled by using OPNET simulator to verify our scheme. The simulation results show that our proposed scheme can prevent DoS attack and achieve a low false rate and fast searching time.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.2
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• pp.40-49
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• 2015

PicoCast is a recently proposed short-range wireless communications technology that supports both low rate sensor/control data and high speed data such as voice and video traffic in the personal space, defined by the user-centric space of radius tens of meters, with one unified protocol. When the users are in the same area, personal spaces defined by each user may overlap. Since these PicoCast piconets may simultaneously operate, mutual interference is unavoidable. It is necessary to investigate the effect of mutual interference on data transmission and to conduct research on minimizing the interference among PicoCast devices. In this paper we analyze the effect of mutual interference between PicoCast piconets based on data throughput using OPNET network simulator. We have implemented the PicoCast protocol and measured the average throughput and packet loss rate.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.17 no.4
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• pp.168-180
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• 2018

Due to the spread of mobile devices and the introduction of high-quality services, mobile traffic is expected to increase sharply and overload of cellular networks is expected. D2D communication is a way to reduce the load and evolve to 5th generation. Since D2D communication directly communicates between the terminals, it can reduce the overload of the cellular network and improve energy efficiency, data rate and network performance. This paper proposes a D2D handover scheme for D2D communication in cellular networks. The cellular network is a 3GPP EPS, and the proposed D2D handover method improves the existing EPS handover process considering compatibility between existing EPS and D2D communication. We also demonstrate the superiority of the proposed handover scheme using the network simulator ns-3. Simulation results show that the proposed handover scheme is superior to existing handover methods in terms of CUE variation, packet transmission delay time, and throughput.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.29 no.1
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• pp.77-83
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• 2005

In collision avoidance problem of a ship, collision risk model is usually set up using the interview results fron experts who sit on a simulator by varying parameters, in which DCPA and TCPA are commonly used. This method, however, has the weakness in that not only it is expensive but also it shows different results depending on the inerviewees and other navigational parameters. In this study, a fuzzy inference system is designed based on own ship's maneuverability verified fron simulation instead of interviewing navigators. The time and distance corresponding to the collision risk value on which avoidance maneuver should be started are set to the minimum marginal time at which own ship starts maneuvering and the minimum marginal distance suggested by marine traffic rules respectively. This system can be recorfigured as a nonlinearity-strengthened one by increasing the number of fuzzy membership functions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5B
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• pp.277-285
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• 2007

In this paper, we present a simulation model of Slammer worm propagation process which caused serious disruptions on Internet in the you of 2003 and analyze the process of Slammer by using NS-2. Recently introduced NS-2 modeling called "Detailed Network-Abstract Network Model" had enabled packet level analysis. However, it had deficiency of accommodating only small sized network. By extending the NS-2 DN-AN model to AN-AN model (Abstract Network-Abstract Network model), it is effectively simulated that the whole process from the initial infection to the total network congestion on hourly basis not only for the Korean network but also for the rest of the world networks. Furthermore, the progress of the propagation from Korean network to the other country was also simulated through the AN-AN model. 8,848 hosts in Korean network were infected in 290 second and 66,152 overseas hosts were infected in 308 second. Moreover, the scanning traffics of the worm at the Korean international gateway saturated the total bandwidth in 154 seconds for the inbound traffic and in 135 seconds for the outbound one.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.3
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• pp.47-61
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• 2012

parallel transmitting system with channel bonding method have been proposed to transmit mass content such as UHD(Ultra High Definition) in HFC(Hybrid Fiber Coaxial) networks. However, this system may lead to channel resource problem because the system needs many channels to transmit mass content. In this paper, we analyze three effective bandwidth approximation algorithms to use the bonding channel efficiently. These algorithms are the effective bandwidth of Gaussian approximation method algorithm proposed by Guerin, the effective bandwidth based on statistics of video frames proposed by Lee and the effective bandwidth based on Gaussian traffic proposed by Nagarajan. We also evaluate compatibility of algorithms to the mass broadcasting service. OPNET simulator is used to evaluate the performance of the algorithms. For accuracy of simulation, we make mass source from real HD broadcasting stream.

• Journal of Advanced Navigation Technology
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• v.10 no.4
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• pp.394-399
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• 2006

In this paper, we investigated performance for 5.8GHz dedicated short range communication system using OFDM which will be applied to Intelligent transportation system services. The maximum speed of a vehicle in DSRC channel is very fast as 180km/h, so a service time is very short to serve a various traffic information if hand-off is not occurred. Therefore higher bit rate is required to proved advanced and intelligent service to the drivers of various vehicle and the data transmission rate of the next generation DSRC system if being promoted over 10Mbps. The signals received in Clarke & Gans channel have been simulated using the computer simulator.