• Communications for Statistical Applications and Methods
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• 제13권3호
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• pp.577-585
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• 2006

This paper presents a method for reliability evaluation of a telecommunication network with variable link-capacities when the simple paths of the network are known. The LP-EM, suggested by Lee and Park (2001), identifies a composite path as a subnetwork and adds only a minimal set of links at each step which gives maximal increase on the maximum capacity flow of the subnetwork. Thereby the LP-EM reduces the possible occurrence of redundant composite paths significantly over other existing methods. Based on the LP-EM, our method further reduces the possible redundancy by identifying such simple paths that could give no increase of maximum capacity flow on the current subnetwork and excluding those simple paths from consideration in the process of constructing composite paths.

• 한국항공우주학회지
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• 제45권2호
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• pp.133-139
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• 2017

틸트로터 무인기의 비행제어컴퓨터는 신뢰도 향상을 위하여 주 채널과 보조 채널을 갖는 이중화 시스템으로 설계되었다. 이중화 기능은 채널 전환과 데이터 복원으로 구성된다. 채널 전환 기능은 교차채널 데이터링크를 이용한 소프트웨어 방식과 워치독 타이머를 이용한 하드웨어 방식으로 구성되었다. 데이터 복원 기능은 운용 중 비행제어컴퓨터가 비정상적으로 재시작 되었을 때 비행 상태를 유지하기 위한 기능이다. 이중화 기능은 비행제어컴퓨터 벤치 시험, 체계 통합 시험 그리고 HILS 시험을 통해 검증되었다. 본 논문에서는 틸트로터 무인기 비행제어컴퓨터에 구현된 이중화 기능과 시험-검증 방법에 대해서 기술하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 춘계종합학술대회 A
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• pp.1003-1007
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• 2008

HF대 SSB 해상 데이터통신 서비스를 운용하는 회사는 가입 선박을 대상으로 하지만, 무선프로토콜의 미비로 접속을 요구하는 선박이 많아지면 calling redundancy가 증가되는 문제가 있다. 선박국과 링크접속을 위하여 자유신호를 이용하는 경우가 있지만 선박국들의 호출에 의한 서로간의 충돌을 회피하기가 어렵다. HF대 SSB 통신은 특성상 채널의 트래픽을 고려하여 자동적으로 무선링크가 설정되어야 하며, 트래픽의 과부하시에는 적응적으로 채널의 안정성을 확보하며 운용되어야 한다. 이에 대하여 자유접속, 그룹자유접속, 폴링(polling)의 3가지 접속링크 방식을 순차적으로 구동하는 새로운 무선프로토콜에 대하여 연구하였다

• ETRI Journal
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• 제41권4호
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• pp.473-482
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• 2019

High availability and reliability have been considered promising requirements for the support of seamless network services such as real-time video streaming, gaming, and virtual and augmented reality. Increased availability can be achieved within a local area network with the use of the virtual router redundancy protocol that utilizes backup routers to provide a backup path in the case of a master router failure. However, the network may still lose a large number of packets during a failover owing to a late failure detections and lazy responses. To achieve an efficient failover, we propose the implementation of fast detection with virtual router redundancy protocol (FDVRRP) in which the backup router quickly detects a link failure and immediately serves as the master router. We implemented the FDVRRP using open neutralized network operating system (OpenN2OS), which is an open-source-based network operating system. Based on the failover performance test of OpenN2OS, we verified that the FDVRRP exhibits a very fast failure detection and a failover with low-overhead packets.

• 한국정보통신설비학회:학술대회논문집
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• 한국정보통신설비학회 2008년도 정보통신설비 학술대회
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• pp.350-354
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• 2008

IP-based mobile communication system is one of the key research items in the mobile networks for a long time. But, due to some technical issues and no need of markets, it is still not full-fledged. Recently, CDMA and WCDMA service providers want to introduce IP-based network connectivity. Even though their efforts, the main network intra-structure depends on ATM or HDLC technology. This article describes a good example of commercialization of IP-based mobile communication systems. Our research is not experimental system but a in-service system - replacing the existing equipments with new IP-based systems. In this paper, we introduce IP related technologies used in our research such as IP-based ATCA(Advanced Telecommunications Computing Architecture) platform, HA(High Availability) redundancy, IP multicast, network redundancy techniques, multi-link bundling and IP header compression. These are already well-known to internet domain. We mix them with mobile communication systems concretely.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권9호
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• pp.3449-3467
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• 2015

A broadcast operation is the fundamental transmission technique in mobile ad-hoc networks (MANETs). Because a broadcast operation can cause a broadcast storm, only selected forwarding nodes have the right to rebroadcast a broadcast message among the one-hop and two-hop neighboring nodes of a sender. This paper proposes the maximum intersection self-pruning (MISP) algorithm to minimize broadcasting redundancy. Herein, an example is given to help describe the main concept of MISP and upper bounds of forward node have been derived based on induction. A simulation conducted demonstrated that when conventional blind flooding (BF), self-pruning (SP), an optimized link state routing (OLSR) multipoint relay (MPR) set, and dominant pruning (DP), are replaced with the MISP in executing Strong duplicate address detection (DAD), the performances in terms of the energy consumption, upper bounds of the number of forward nodes, and message complexity have been improved. In addition, to evaluate the performance in reference to the link error probability, P_e, an enhancement was achieved by computing a proposed retransmission limit, S, for error recovery based on this probability. Retransmission limit control is critical for efficient energy consumption of MANET nodes operating with limited portable energy where Strong DAD reacts differently to link errors based on the operational procedures.

• Journal of Communications and Networks
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• 제14권6호
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• pp.653-661
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• 2012

High-availability seamless redundancy (HSR) is a redundancy protocol for Ethernet networks that provides two frame copies for each frame sent. Each copy will pass through separate physical paths, pursuing zero fault recovery time. This means that even in the case of a node or a link failure, there is no stoppage of network operations whatsoever. HSR is a potential candidate for the communications of a smart grid, but its main drawback is the unnecessary traffic created due to the duplicated copies of each sent frame, which are generated and circulated inside the network. This downside will degrade network performance and might cause network congestion or even stoppage. In this paper, we present two approaches to solve the above-mentioned problem. The first approach is called quick removing (QR), and is suited to ring or connected ring topologies. The idea is to remove the duplicated frame copies from the network when all the nodes have received one copy of the sent frame and begin to receive the second copy. Therefore, the forwarding of those frame copies until they reach the source node, as occurs in standard HSR, is not needed in QR. Our example shows a traffic reduction of 37.5%compared to the standard HSR protocol. The second approach is called the virtual ring (VRing), which divides any closed-loop HSR network into several VRings. Each VRing will circulate the traffic of a corresponding group of nodes within it. Therefore, the traffic in that group will not affect any of the other network links or nodes, which results in an enhancement of traffic performance. For our sample network, the VRing approach shows a network traffic reduction in the range of 67.7 to 48.4%in a healthy network case and 89.7 to 44.8%in a faulty network case, compared to standard HSR.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.895-901
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• 1993

This paper present controller designs based on the configuration control framework for a redundant manipulator to accomplish the basic task of desired, end-effector motion, while utilizing the redundancy to achieve the additional tasks such as joint motion control, obstacle avoidance, singularity avoidance. etc. A task based decentralized adaptive scheme is then applied for the configuration variables to track some reference trajectories as close as possible. Simulation results for a direct-drive three-link arm in the vertical plane demonstrate its capabilities for performing various useful tasks.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1993년도 한국자동제어학술회의논문집(국내학술편); Seoul National University, Seoul; 20-22 Oct. 1993
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• pp.902-907
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• 1993

An efficient dynamic control algorithm that outperforms existing local torque optimization techniques for redundant manipulators is presented. The method resolves redundancy at the acceleration level. In this method, a systematic switching technique as a trade-off means between local torque optimization and global stability is proposed based on the stability condition proposed by Maciejewski [1]. Comparative simulations on a three-link planar arm show the effectiveness of the proposed method.

• 동력기계공학회지
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• 제5권2호
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• pp.79-86
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• 2001

A method is presented for generating the path which significantly reduces residual vibration of the redundant, flexible robot manipulator in the presence of obstacles. The desired path is optimally designed so that the system completes the required move with minimum residual vibration, avoiding obstacles. The dynamic model and optimal path are effectively formulated and computed by using special moving coordinate, called VLCS, to represent the link flexibility. The path to be designed is developed by a combined Fourier series and polynomial function to satisfy both the convergence and boundary condition matching problems. The concept of correlation coefficients is used to select the minimum number of design variables. A planar three-link manipualtor is used to evaluate this method. Results show that residual vibration can be drastically reduced by selecting an appropriate path, in the presence of obstacles.