• Journal of information and communication convergence engineering
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• v.7 no.3
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• pp.309-313
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• 2009

In this paper, end-to-end VoIP(Voice over Internet Protocol) performance is evaluated by simulation with NS-2 simulation tool. There are many results studied and published for VoIP performance over TCP/IP networks. But, almost all of them were focused on wired or wireless Internet environments. About MANET (Mobile Ad Hoc Network), VoIP is currently studying several points of research. In this paper, analysis of VoIP performance is done with focusing on the mobility of MANETs. MOS(Mean Opinion Score), network delay, packet loss rates are considered as end-to-end QoS performance parameters.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.53 no.7
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• pp.501-508
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• 2004

In this paper, a coordinated scheduling algorithm is proposed to reduce end-to-end delay in distributed control of systems. For the algorithm, the analysis of practical end-to-end delay in the worst case is performed priory with considering implementation of the systems. The end-to-end delay is composed of the delay caused by multi-task scheduling of operating systems, the delay caused by network communications, and the delay caused by asynchronous timing between operating systems and network communications. Through some simulation tests based on CAN(Controller Area Network), the proposed worst case end-to-end delay analysis is validated. Through the simulation tests, it is also shown that a real-time distributed control system designed to existing worst case delay cannot guarantee end-to-end time constraints. With the analysis, a coordinated scheduling algorithm is proposed here. The coordinated scheduling algorithm is focused on the reduction of the delay caused by asynchronous timing between operating systems and network communications. Online deadline assignment strategy is proposed for the scheduling. The performance enhancement of the distributed control systems by the scheduling algorithm is shown through simulation tests.

• Journal of Astronomy and Space Sciences
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• v.24 no.1
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• pp.69-78
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• 2007

The international EARTHSHINE mission is to measure 1% anomaly of the Earth global albedo and total solar irradiance using Amon-Ra instrument around Lagrange point 1. We developed a new ray truing based integrated end-to-end simulation tool that overcomes the shortcomings of the existing end-to-end performance simulation techniques. We then studied the in-orbit radiometric performance of the breadboard Anon-Ra visible channel optical system. The TSI variation and the Earth albedo anomaly, reported elsewhere, were used as the key input variables in the simulation. The output flux at the instrument focal plane confirms that the integrated ray tracing based end-to-end science simulation delivers the correct level of incident power to the Amon-Ra instrument well within the required measurement error budget of better than ${\pm}0.28%$. Using the global angular distribution model (ADM), the incident flux is then used to estimate the Earth global albedo and the TSI variation, confirming the validity of the primary science cases at the L1 halo orbit. These results imply that the integrated end-to-end ray tracing technique, reported here, can serve as an effective and powerful building block of the on-line science analysis tool in support of the international EARTHSHINE mission currently being developed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10B
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• pp.1852-1860
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• 1999

This paper studied performance of the AAL2 for variable rate real time services in ATM network with discrete-time simulation model. In this simulation, input parameters are packet fill delay for AAL2 PDU generation, guard time for ATM cell generation, burstness and number of channels. Though variation of the above mentioned parameters, we obtained end-to end delay variations and throughput, analyzed performance effect of the each parameter for voice packet service.

• Proceedings of the KSRS Conference
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• v.1
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• pp.274-277
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• 2006

KARI is currently developing a geostationary ocean color imager (GOCI) for COMS. We report the progress in integrated optical modeling and analysis for stray light suppression and the end-to-end instrument performance verification including in-orbit calibration. The Sun is modeled as the emitting light source and the selected area around Korean peninsular as the observation target that scatters the sun light towards GOCI in orbit. The optical ray tracing employing active geometric scaling was then used for precise characterization of the spatial and radiometric performance at the instrument focal plane. The analysis results show positive reduction in the simulated stray light level with the design improvement including baffles. It also indicates that the ray traced in-orbit radiometric performances are effective tools for the independent assessment of more traditional linear and quadratic equation based estimation of water leaving radiance. The concept of integrated GOCI optical model and the computational method are presented.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.274-287
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• 2009

In the Internet environment in which best-effort services are provided, we need to guarantee end-to-end performance rather than hop performance to provide services with a variety of QoS(Quality of Service) requirements. The end-to-end performance is affected by many factors along the path of traffic flow. Most existing simulation studies are concentrated on a single node or a few nodes. We need much different approach considering the simulation execution time to simulate a large-scale network. In this paper, we derive requirements and present methodologies for the implementation of the simulator to simulate it. Then, we design and implement our simulator using OPNET. Performance evaluation is carried out using the simulator for large-scale KII (National Information Infrastructure in Korea). We use a self-similar traffic model and present some results on the end-to-end performance metric for the networks.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.69-72
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• 2002

The geometry parameter of tool such as rake angle and clearance angle is defined clearly to solve the difference in communication between design and measurement stage. Using the developed simulation program, wheel is properly determined and end mill can be manufactured accurately. The performance test with well defined end mill provides sufficient information to decide optimal geometry. For machining hardened steel, end mills are designed and manufactured. Optimal rake angle and clearance angle is obtained from performance test. A specific software for automatic end mill production is developed far simulation and fur generation of NC code as Cad/CAM system.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.248-255
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• 2011

An investigation has been carried out, by computer simulation, to evaluate the impact of dispersion compensation configurations on 960 Gbps wavelength division multiplexed (WDM) system with optical phase conjugator (OPC). The considered dispersion compensation configurations in this research are conventional one-end type and bi-end type. One-end and bi-end type are made by using one dispersion compensating fiber (DCF) and two DCFs to decrease dispersion accumulated in one single mode fiber (SMF) span, respectively. It is found that bi-end compensation configuration offers the equal performance with that of one-end configuration in WDM system with residual dispersion per span (RDPS) of 400 ps/nm if net residual dispersion (NRD) had to be optimized in each cases.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.677-680
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• 2003

In this paper, the analysis of practical end-to-end delay in worst case is performed for distributed control system considering the implementation of the system. The control system delay is composed of the delay caused by multi-task scheduling of operating system, the delay caused by network communication, and the delay caused by the asynchronous between them. Through simulation tests based on CAN(Controller Area Network), the proposed end-to-end delay in worst case is validated. Additionally, online clock synchronization algorithm is proposed here for the control system. Through another simulation test, the online algorithm is proved to have better performance than offline one in the view of network bandwidth utilization.

• Journal of the Korea Society for Simulation
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• v.10 no.2
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• pp.15-24
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• 2001

In this paper we study the delay patterns of voice traffic for end-to-end users Caused by serving the whole bunch of applications traffic at the same time on the Voice over Internet Protocol (VoIP) network. Given the current situation that voice traffic is served along with other application services on the VoIP network, it is quite necessary to figure out how and by what the voice traffic requiring high QoS is delayed. We compare the delay performance of voice traffic on the VoIP network under FIFO with the one under Weighted Fair Queuing(WFQ), and discover the differences of the delay performance resulting from the use of different voice codec algorithms. The results of our study show that using the voice codec algorithm with a higher coding rate nd the queuing algorithm of WEQ can provide users with high-quality voice traffic.