• KIPS Transactions on Computer and Communication Systems
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• v.2 no.6
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• pp.265-278
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• 2013

With the recent advancements in various wireless communication technologies, the importance of mobile multicasting is coming to the fore, in an effort to use network resources more efficiently. In the past, when various mobile IP-based multicast techniques were proposed, the focus was put on the costs needed for network delivery for providing multicast services, as well as on minimizing the multicast handover delay. For techniques using MIPv6 (Mobile IPv6), a host-based mobility management protocol, however, it is fundamentally difficult to resolve the problems of handover delay and tunnel convergence. To resolve these problems, a network-based mobility management protocol called PMIPv6 (Proxy Mobile IPv6) was standardized. Although performance is improved in PMIPv6 over MIPv6, it still suffers from the problems of handover delay and tunnel convergence. In this paper, to overcome these limitations, a technique called LFH (Low-cost and Fast Handoff) is proposed for fast and low-cost mobility management with multicasting support in PMIPv6 networks. To reduce the interactions between the complex multicast routing protocol and the multicast messages, a simplified proxy method called MLD (Multicast Listener Discovery) is implemented and modified. Furthermore, a TCR (Tunnel Combination and Reconstruction) algorithm was used in the multicast handover procedure within the LMA (Local Mobility Anchor) domain, as well as in the multicast handover procedure between domains, in order to overcome the problem of tunnel convergence. As a result, it was found that LFH has reduced multicast delay compared to other types of multicast techniques, and that it requires lower costs as well.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.6B
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• pp.615-622
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• 2009

In this paper, we consider the problem of applying NEMO in PMIPv6, and propose a method to support network mobility. When an MR enters a PMIPv6 domain, an MAG recognizes the MR to access using the BU message. And the MAG makes a tunnel between the MAG and the MR. The MR do not make tunnel fundamentally except for handover. Therefore, the PMIPv6 protocol needs to modify the original algorithm and the BCE data filed. However, the proposed method can use NEMO without protocol modification. To show verification, we implement our proposed algorithm with added BCE data filed using C program, and configure a testbed network. Through a network connectivity procedure, we can see that our proposed method can support network mobility within the PMIPv6 network.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.43-50
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• 2020

We have developed an algorithm for tracking coronal mass ejection (CME) propagation that allows us to estimate CME speed and its arrival time at Earth. The algorithm may be used either to forecast the CME's arrival on the day of the forecast or to update the CME tracking information for the next day's forecast. In our case study, we successfully tracked CME propagation using the algorithm based on g-values of interplanetary scintillation (IPS) observation provided by the Institute for Space-Earth Environmental Research (ISEE). We were able to forecast the arrival time (Δt = 0.30 h) and speed (Δv = 20 km/s) of a CME event on October 2, 2000. From the CME-interplanetary CME (ICME) pairs provided by Cane & Richardson (2003), we selected 50 events to evaluate the algorithm's forecast capability. Average errors for arrival time and speed were 11.14 h and 310 km/s, respectively. Results demonstrated that g-values obtained continuously from any single station observation were able to be used as a proxy for CME speed. Therefore, our algorithm may give stable daily forecasts of CME position and speed during propagation in the region of 0.2-1 AU using the IPS g-values, even if IPS velocity observations are insufficient. We expect that this algorithm may be widely accepted for use in space weather forecasting in the near future.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.106-109
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• 2000

The virtual reality - haptic device is developed for the purpose used in the work that human cannot approach and that need elaborate exercises. To render haptic, the total system is constituted master, haptic device, and slave, remote manipulator. Human operates the remote manipulator. Human operates the remote manipulator relying on the hapti devices and stereo graphic. And then the force and scene of the remote manipulator is fed-back from each haptic devices and virtual devices. The feedback information gets system gain exactly. The system gain provides the most exact haptic and virtual devices. The feedback information gets system gain exactly. The system gain provides the most exact haptic and scene to human by the location, the graphic rendering and the haptic rendering algorithm on real-time. In this research, 3D haptic device is developed for common usage and make human feel the haptic when human contacts virtual object rendered by computer graphic. The haptic device is good for tracing location and producing devices because of the row structure. Also, openGL and Visual Basic is utilized to the algorithms for haptic rendering. The haptic device of this research makes the interface possible not only with virtual reality but also with the real remote manipulator.

• Journal of KIISE:Information Networking
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• v.33 no.3
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• pp.231-246
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• 2006

A server load balancer is used to accept and distribute client requests to one of servers in a wireless internet proxy server cluster. LVS(Linux Virtual Server), a software based server load balancer, can support several load balancing algorithms where client requests are distributed to servers in a round robin way, in a hashing-based way or in a way to assign first to the server with the least number of its concurrent connections to LVS. An improved load balancing algorithm to consider server performance was proposed where they check upper and lower limits of concurrent connection numbers to be allowed within each maximum server performance in advance and apply the static limits to load balancing. However, they do not apply run-time server load information dynamically to load balancing. In this paper, we propose a dynamic load balancing scheme where the load balancer keeps each server CPU load information at run time and assigns a new client request first to the server with the lowest load. Using a cluster consisting of 16 PCs, we performed experiments with static content(image and HTML). Compared to the existing schemes, experimental results show performance improvement in the cases of client requests requiring CPU-intensive processing and a cluster consisting of servers with difference performance.

• Proceedings of the IEEK Conference
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• 2003.07d
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• pp.1661-1664
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• 2003

The transcoding is a method which converts a multimedia stream to an adaptive format, such as frame rate and resolution, that can be played in the mobile devices. Due to the heavy consumption of CPU power for transcoding, the server in charge cannot supply all streams requested from clients if it is already occupied by several streams. The load balancing among proxies is a common approach for solving such problem. In addition to collaborative works for load balancing, the mobility must be taken into account in the mobile environments. Thus, the wired-network based algorithm is not suitable for the streams service in the mobile environments. In this paper, we propose an alternative scheme for cooperative proxy architecture that considers the case in which mobile devices are moving over other zones.

• Proceedings of the Korean Information Science Society Conference
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• 2004.10c
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• pp.412-414
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• 2004

대용량의 멀티미디어 데이터들을 다수의 시용자가 동시에 요구할 경우 접속이 끊기거나 데이터의 손실과 같은 접속 성능이 현저하게 저하되는 문제가 발생할 수 있다. 이는 대부분의 사용자들의 요청을 원거리의 Central Server가 단독으로 처리하기 때문에 발생하는 문제이다. 띠라서 Central Sever의 Load 감소와 초기 지연시간 및 비디오 패킷의 손실의 문제점을 해결하기 위해 프록시 서버를 사용자의 근거리에 위치시키는 방법을 이용한다. 대용랑의 멀티미디어 데이터들을 복잡한 인터넷의 중간경로를 거치지 않고 다수의 사용자들에게 직접 전달함으로써 데이터의 손실을 방지함과 동시에 보다 안정적이고 빠른 속도로 제공하는 것이 가능하다. 특징적으로 프록시 서버는 Central Server에 비해 비교적 제한된 용랑을 가지고 있다. 따라서 본 논문에서는 사용자의 선호도를 기반으로 하여 앞으로 요구학 것이라고 예측되는 비디오 데이터들만을 선별적으로 저장하도록 하는 알고리즘을 제안한다. 시뮬레이션을 통해 제안하는 캐쉬 교환 알고리즘을 기존의 알고리즘과 비교, 관찰한 결과 상대적으로 높은 Hit rate가 나타남을 확인하였다.

• Journal of KIISE:Computer Systems and Theory
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• v.26 no.6
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• pp.729-741
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• 1999

WWW의 사용량이 대단히 빠르게 늘어남에 따라 웹 프락시 서버의 캐싱 기능은 그 중요성이 날로 증가하고 있다. 본 논문에서는 이러한 웹 프락시 캐시의 교체 정책을 웹 요구의 특성과 프락시 서버환경자체를 고려하여 주어진 환경에 맞는 교체 정책이 되도록 유전 알고리즘을 사용하여 설계하는 방법을 제시하였다. 이 방법은 대부분의 기존 연구에서처럼 특정한 교체 정책 자체를 제시하는 것이 아니라, 주어진 프락시 환경에 적합한 교체 정책을 동적으로 설계할 수 있는 방법을 제시한다는 점메서 기존의 연구보다 일반성이 높다.

• Proceedings of the Korean Information Science Society Conference
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• 2006.06a
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• pp.292-294
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• 2006

최근 수년간 클라이언트 모델에서 발생하는 문제인 서버 병목 현상, Dos공격, 그리고 시스템의 확장성에 따른 비용 증가 등의 문제를 해결하는 방법으로 P2P 방식이 활발히 연구되고 있으며, 그 중 사용자간 파일 공유하는 분야에 적용된 P2P가 가장 널리 알려져 있다. 본 논문에서는 플랫폼에 독립적이고, 네트워크 디바이스에 독립적인 환경을 지원하는 JXTA 네트워크 환경에서 분산된 자원의 효율적인 검색을 하는 DHT(Distributed Hash Table) 알고리즘을 제안하고자 한다.

• Proceedings of the Korean Information Science Society Conference
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• 2005.07a
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• pp.649-651
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• 2005

본 논문에서는 실제 모바일 환경에서의 멀티미디어 컨텐츠의 요청 패턴을 분석하고 그 결과를 반영한 캐싱 알고리즘을 제안한다. 로그 데이터를 분석한 결과 컨텐츠의 연속적인 요청이 매우 짧은 시간 동안 이루어지는 시간적인 특성을 발견했으며, 컨텐츠의 다른 버전 사이의 요청 시간이 짧음을 통해서 버전별 컨텐츠의 요청이 응집되어 나타남을 확인했다. 제안된 알고리즘에서는 시간적인 특성과 컨텐츠의 인기도 특성을 반영하기 위해 측정 시간 윈도우 내에서 컨텐츠의 요청 횟수를 측정하고, 요청 횟수의 임계값 이상의 컨텐츠에 대해서 유지 시간 단위만큼의 컨텐츠 만료 시간을 정한다. 또한 공간적인 특성을 이용하여 컨텐츠가 캐시에서 제거될 때, 만료시간이 지난 컨텐츠의 다른 버전을 동시에 캐시에서 제거하는 방법을 사용한다 실험 결과 캐시의 크기가 작은 경우 제안된 알고리즘이 기존 알고리즘에 비해 $1-5\%$ 정도 성능향상을 보였다.