• Proceedings of the Korean Information Science Society Conference
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• 2002.04a
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• pp.613-615
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• 2002

본 논문에서는 멀티미디어 데이터의 증가로 인한 네트워크 전송량 폭주 현상 및 서비스 비용의 증가를 감소시키기 위한 방법으로, 부하분산과 관련된 가상서버의 개념에 대해서 알아보고, 대표적인 가상 서버중 하나인 리눅스 가상 서버 (LVS : Linux Virtual Server)의 성능 측정을 통해 멀티미디어 컨텐츠 전송에 사용되는 CDD 시스템에 가장 적합한 가상서버의 구성 및 알고리즘을 도출하였다. 이를 위해서 리눅스 가상서버 시스템을 구축하고, 3가지 구성방식과 8가지 스케줄링 알고리즘에 대한 성능 평가를 수행하였으며, 각 경우에 대한 비교분석을 하였다. 이를 토대로, 추후 CDD 시스템과의 접목을 통하여 네트워크 부하량을 감소시키고, 서버로부터 발생할 수 있는 병목현상을 적은 비용으로 해결할 수 있는 방향을 제시하고자 하였다.

• THE INTERNATIONAL COMMERCE & LAW REVIEW
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• v.16
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• pp.295-329
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• 2001

The wonderful new world of shopping - being able to order items you need by just one click. However, there is one factor that has not changed at all - customers, whether they are private individuals or public companies, want to have the product delivered to their address, and usually as fast as possible too. To achieve this, the operators of virtual shops must make use of a fully operational and efficient delivery service. The internet and its potential for creating a virtual market for millions of buyers and sellers, has generated a lot of excitement in the express delivery industry. Clearly e-commerce will cause greater growth in the business-to-residential package market. Korean express delivery industry is not an exception to this trend. Currently, while major three service providers enjoy a lion's share in Korea, a lot of small and medium companies are struggling to capture more shipments in express parcel market. Nevertheless, it will be forecasted that Korean parcel market will be consolidated and become an oligopoly market in the near future.

• Proceedings of the Korea Information Processing Society Conference
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• 2002.04a
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• pp.381-384
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• 2002

This paper describes the motivation, design and performance of bi-active Load balancer in Linux Virtual Server. The goal of bi-active Load balancer is to provide a framework to build highly scalable, fault-tolerant services using a large cluster of commodity servers. The TCP/IP stack of Linux Kernel is extended to support three IP load balancing techniques, which can make parallel services of different kinds of server clusters to appear as a service on a single IP address. Scalability is achieved by transparently adding or removing a node in the cluster. and high availability is provided by detecting node or daemon failures and reconfiguring the system appropriately. Extensive simulation reveals that the proposed approach improves the reply rate about 20% compared to earlier design.

• Computers and Concrete
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• v.7 no.2
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• pp.87-102
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• 2010

This paper discusses new capabilities developed for the Virtual Penetration Laboratory (VPL) software package to address the challenges of determining Penetration Resistance (PR) equations for concrete materials. Specifically, the paper introduces a three-invariant concrete constitutive model recently developed by the authors. The Advanced Fundamental Concrete (AFC) model was developed to provide a fast-running predictive model to simulate the behavior of concrete and other high-strength geologic materials. The Continuous Evolutionary Algorithms (CEA) automatic fitting algorithms used to fit the new model are discussed, and then examples are presented to demonstrate the effectiveness of the new AFC model. Finally, the AFC model in conjunction with the VPL software package is used to develop a PR equation for a concrete material.

• Educational Technology International
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• v.24 no.2
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• pp.295-329
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• 2023

The recent development of metaverse-related technology has led to efforts to overcome the limitations of time and space in education by creating a virtual educational environment. To make use of this platform efficiently, applying learning analytics has been proposed as an optimal instructional and learning decision support approach to address these issues by identifying specific rules and patterns generated from learning data, and providing a systematic framework as a guideline to instructors. To achieve this, we employed an inductive, bottom-up approach for framework modeling. During the modeling process, based on the activity system model, we specifically derived the fundamental components of the learning analytics framework centered on learning activities and their contexts. We developed a prototype of the framework through deduplication, categorization, and proceduralization from the components, and refined the learning analytics framework into a 7-stage framework suitable for application in the metaverse through 3 steps of Delphi surveys. Lastly, through a framework model evaluation consisting of seven items, we validated the metaverse learning analytics framework, ensuring its validity.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1326-1331
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• 2009

The sensor data measured by the legged robot are used to recognize the physical environment or information that controls the robot's posture. Therefore, a robot's ambulation can be advanced with the use of such sensing information. For the precise control of a robot, highly accurate sensor data are required, but most sensors are expensive and are exposed to excessive load operation in the field. The seriousness of these problems will be seen if the prototype's practicality and mass productivity, which are closely related to the unit cost of production and maintenance, will be considered. In this paper, the use of a virtual sensor technology was suggested to address the aforementioned problems, and various ways of applying the theory to a walking robot obtained through training with an actual sensor, and of various hardware information, were presented. Finally, the possibility of the replacement of the ground reaction force sensor of legged robot was verified.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.10
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• pp.4703-4723
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• 2018

In recent years, dense small cell network has been deployed to address the challenge that has resulted from the unprecendented growth of mobile data traffic and users. It has proven to be a cost efficeient solution to offload traffic from macro-cells. Software defined heterogeneous wireless network can decouple the control plane from the data plane. The control signal goes through the macro-cell while the data traffic can be offloaded by small cells. In this paper, we propose a framework for cell virtualization and user association in order to satisfy versatile requirements of multiple tenants. In the proposed framework, we propose an interference graph partioning based virtual-cell association and customized physical-cell association for multi-homed users in a software defined small cell network. The proposed user association scheme includes 3 steps: initialization, virtual-cell association and physical-cell association. Simulation results show that the proposed virtual-cell association outperforms the other schemes. For physical-cell association, the results on resource utilization and user fairness are examined for mobile users and infrastructure providers.

• Proceedings of the Korea Society for Simulation Conference
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• 1999.04a
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• pp.1-5
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• 1999

An ATM switch is the basic component of an ATM network, and its functioning is to switch incoming cells arriving at an input port to the output port associated with an appropriate virtual path. In case of an ATM switch with buffer sharing scheme, the performance analysis is very difficult due to the interactions between the address queues. In this paper, the influences of the degree of traffic burstiness and some traffic routing properties are investigated by using the simulation. Also, some cell access strategies including priority access and cell dropping are compared in terms of cell loss probability.

• The KIPS Transactions:PartC
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• v.16C no.5
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• pp.653-660
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• 2009

A research for middleware of WSN can provide sensor applications with avoiding tight coupling of hardware, ease of development, and abstract data access. However, previous works have some limitations which should install their own middleware onto the all sensor nodes resulting in computational and communication overhead. In order to address it, we proposed a virtual sensor overlay network, called TinyONet-Lite which introduced virtual sensors to model a virtual counterpart of physical sensors. These virtual sensors dynamically grouped into an overlay network, Slice, which provides middleware services. We implemented TinyONet-Lite on mote class hardware with TinyOS. In accordance with experiments and comparison with existing researches, TinyONet-Lite was proved to show advantages of extensibility, dynamic service composition and reducing overhead.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.2892-2913
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• 2016

Network virtualization promises to play a dominant role in shaping the future Internet by overcoming the Internet ossification problem. However, due to the injecting of additional virtualization layers into the network architecture, several new security risks are introduced by the network virtualization. Although traditional protection mechanisms can help in virtualized environment, they are not guaranteed to be successful and may incur high security overheads. By performing the virtual network (VN) embedding in a security-aware way, the risks exposed to both the virtual and substrate networks can be minimized, and the additional techniques adopted to enhance the security of the networks can be reduced. Unfortunately, existing embedding algorithms largely ignore the widespread security risks, making their applicability in a realistic environment rather doubtful. In this paper, we attempt to address the security risks by integrating the security factors into the VN embedding. We first abstract the security requirements and the protection mechanisms as numerical concept of security demands and security levels, and the corresponding security constraints are introduced into the VN embedding. Based on the abstraction, we develop three security-risky modes to model various levels of risky conditions in the virtualized environment, aiming at enabling a more flexible VN embedding. Then, we present a mixed integer linear programming formulation for the VN embedding problem in different security-risky modes. Moreover, we design three heuristic embedding algorithms to solve this problem, which are all based on the same proposed node-ranking approach to quantify the embedding potential of each substrate node and adopt the k-shortest path algorithm to map virtual links. Simulation results demonstrate the effectiveness and efficiency of our algorithms.