• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6A
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• pp.802-812
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• 2000

Multihop lightwave networks are the optical-fiber based local communication systems that employ WDM(Wavelength Division Multiplexing) technology to fully use the enormous fiber bandwidth without requiring any tunable tranceives. In this paper, we introduce a novel ShuffleNet topology, asymmetric bilayered ShuffleNet(ABS) topology as a multihop WDM network technique. For 1Gb/s transmission system, we compared ABS topology with previously reported ones in terms of common network parameters such as average number of hops, throughput, time delay, and network power function. Through the analysis, the performance of ABS topology was proven to be superior to the existing ones. To decrease the amount of hardware required for implementing ABS system, we also proposed a new WDM channel sharing scheme. For (2, 3) ShuffleNet topology system, the number of wavelengths needed in the system can be reduced dramatically from 96 to 4 by using new scheme.

• Journal of Communications and Networks
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• v.10 no.4
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• pp.455-464
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• 2008

To provide network services consistently under various network failures, enterprise networks increasingly utilize path diversity through multi-homing. As a result, multi-homed non-transit autonomous systems become to surpass single-homed networks in number. In this paper, we address an inevitable problem that occurs when networks with multiple entry points deploy firewalls in their borders. The majority of today's firewalls use stateful inspection that exploits connection state for fine-grained control. However, stateful inspection has a topological restriction such that outgoing and incoming traffic of a connection should pass through a single firewall to execute desired packet filtering operation. Multi-homed networking environments suffer from this restriction and BGP policies provide only coarse control over communication paths. Due to these features and the characteristics of datagram routing, there exists a real possibility of asymmetric routing. This mismatch between the exit and entry firewalls for a connection causes connection establishment failures. In this paper, we formulate this phenomenon into a state-sharing problem among multiple fire walls under asymmetric routing condition. To solve this problem, we propose a stateful inspection protocol that requires very low processing and messaging overhead. Our protocol consists of the following two phases: 1) Generation of a TCP SYN cookie marked with the firewall identification number upon a SYN packet arrival, and 2) state sharing triggered by a SYN/ACK packet arrival in the absence of the trail of its initial SYN packet. We demonstrate that our protocol is scalable, robust, and simple enough to be deployed for high speed networks. It also transparently works under any client-server configurations. Last but not least, we present experimental results through a prototype implementation.

• Journal of the Korean Geotechnical Society
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• v.37 no.10
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• pp.55-63
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• 2021

The construction of shield tunnels is being expanded from the small-bore tunnels such as power, telecommunications, water supply, and sewerage pipes to the large bore tunnels such as road and railway tunnels with the advancement of the shield TBM (Tunnel Boring Machine) manufacturing technology. Accordingly, the construction of twin shield tunnels is increasing. Peck (1969) reported that the surface settlement trough is well described by a Gaussian distribution on a single shield tunnel. Hereafter, many studies about the surface settlement trough were performed by the field measurement, laboratory model test, and numerical analysis. This study confirmed that the additional surface settlement trough induced by the 2^nd tunneling were well described by using each Gaussian curve for the right and left sides of the settlement trough.

• International Area Studies Review
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• v.20 no.1
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• pp.3-22
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• 2016

In this study, I examine mutual shock spillover effects among interest rate differences, won-dollar foreign exchange change rates, and stock market returns in Korea during the daily sample period from the beginning of 1995 to the October 16, 2015, using the multivariate GARCH (generalized autoregressive conditional heteroscedasticity) BEKK (Baba-Engle-Kraft-Kroner) model framework. Major findings are as follows. Throughout the 6 model estimation results of variance equations determining return spillovers covered from symmetric and asymmetric models of total sample period and two crisis sub-sample periods composed of Korean FX Crisis Times and Global Financial Crisis Times, shock spillovers are shown to exist mainly from stock market return shocks. Stock market shocks including down-shocks from the asymmetric models are shown to transfer to those other two markets most successfully. Therefore it is most important to maintain stable financial markets that a policy design for stock market stabilization such as mitigating stock market volatility.

• Journal of Korea Trade
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• v.25 no.3
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• pp.1-20
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• 2021

Purpose - The purpose of this paper is to examine the welfare effects of standards harmonization between technologically asymmetric countries, and to determine optimal harmonization strategies for a country with mid-level technological advancement. Design/methodology - Following Salop's circular city model (Salop, 1979), this study constructs a simple, horizontally-differentiated oligopoly model in which three firms and three countries exist. Each country adopts different compatibility standards and each firm incurs conversion costs for foreign market access due to differences in standards. The conversion costs are related to technology; standards harmonization removes these costs between participating countries. The paper considers three cases: i) no harmonization; ii) harmonization with the more technologically-advanced country and iii) harmonization with the less technologically-advanced country. Findings - The paper first considers a scenario in which all three firms occupy some share of the market in each country. It shows that standards harmonization with both the technologically moreor less-advanced country always increases consumer surplus and social welfare. In addition, the producer surplus will increase if the harmonization partner has a higher technology level, whereas it may decrease if the partner has a lower technology level. It also shows that if most domestic export goods are in sectors with conversion costs above a certain level, harmonizing standards with a technologically more-advanced country should be prioritized. Such strategies, moreover, should be emphasized when there exists a large technology gap among countries. Lastly, the paper considers another scenario, in which harmonization leads to the foreclosure of the non-member firm from the member countries' markets. It shows that harmonization improves the social welfare of a mid-level technology country regardless of its partner's technology. It also shows that the country should prioritize harmonization with the technologically less-advanced country. Originality/value - Though some of the existing studies consider the welfare effects of harmonization, their main assumption is that firms have the same conversion technology. Since complying with standards often requires substantial technological advancement and technical expertise, harmonization of compatibility standards between countries with gaps in technological ability carries different implications. This paper investigates the welfare effects of this harmonization and determines an optimal harmonization strategy while considering technological asymmetry among countries in standards compliance.

• Applied Chemistry for Engineering
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• v.19 no.6
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• pp.633-639
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• 2008

Polysulfone membranes were prepared via the phase inversion process. Toluene was added as a nonsolvent additive in the casting solution containing a mixture of polysulfone and n-methylpyrrolidone. When prepared via the diffusion-induced process using isopropanol as a precipitation nonsolvent, the solidified membranes revealed a similar asymmetric structure irrespective of the addition of toluene, presenting both a dense skin layer and a sponge-like support layer. The added toluene played a role of enhancing liquid-liquid phase separation of the casting solution, and skin layer thickness of a prepared membrane increased with toluene content in the casting solution. On membrane performance, the solute rejection showed a uniform behavior irrespective of the addition of toluene. However, in spite of the significant increase in dense skin layer thickness, the water permeation through the membrane prepared with 60 wt% toluene revealed five times as much flux, compared with that of the membrane prepared without toluene additive.

• Journal of Digital Contents Society
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• v.7 no.3
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• pp.161-168
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• 2006

Wibro(Wibro - Wireless Broadband Internet ) is a system that can accept effectively the IP-based Wireless data traffic with upward / downward asymmetric transfer characteristic by using a Wirelss broadband transfer technology in OFDMA/TDD (Orthogonal frequency Division Multiple Access/Time Division Duplex). Wibro service should support handover to maintain connection continuously in movement because the service is based on If system which is different from cellular system. Current Micro Mobility system and general Mobile If system has got a problem of delayed speed and lost packets during handover. IETF protocol has been proposed for minimizing this problem and its standardization is under process, mainly focused on Mip4, Mip6 and Mipshop WG. This article studies and analyzes an effective method of minimizing handover delay to improve the problem of WiBro system and its revitalization & outlook.

• Particle and aerosol research
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• v.9 no.2
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• pp.103-110
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• 2013

The electrostatic precipitator (ESP) has been used for degrading atmospheric pollutants. These devices induce the electrical forces to facilitate the removal of particulate pollutants. The ions travel from the high voltage electrode to the grounded electrode by Coulomb force induced by the electric field when a high voltage is applied between two electrodes. The ions collide with gas molecules and exchange momentum with each other thus inducing fluid motion, electrohydrodynamic (EHD) flow. In this study, for the simulation of electric field and EHD flow in ESPs, an open source EHD solver, "espFoam", has been developed using open source CFD toolbox, OpenFOAM(R) (Open Field Operation and Manipulation). The electric potential distribution and ionic space charge density distribution were obtained with the developed solver, and validated with experimental results in the literature. The comparison results showed good agreement. Turbulence model is also incorporated to simulate turbulent flow; hence the developed solver can analyze laminar and turbulent flow. In distributions of electric potential and space charge, the distributions become distorted and asymmetric as the flow velocity increases. The effect of electrical drift flow was investigated for different flow velocities and the secondary flow in a flow of low velocity is successfully predicted.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.103-105
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• 2008

차세대 양방향데이터방송 (BIFS: BInary Format for Scenes) 서비스에서는 하향링크(downlink) 데이터 전송률에 상응하는 높은 상향링크(uplink) 데이터 전송률이 요구되고 있다. 이에 무선 전송 채널의 한정된 자원 환경 속에서 상향링크 전송용량 증대를 위한 주파수 효율성 제고 기술의 필요성이 대두되고 있다. 본 논문에서는 차세대 양방향데이터방송을 위한 다중 모바일(mobile) 사용자의 클러스터(cluster) 기반 상향링크 협동 다이버시티(cooperative diversity) 기법을 제안한다. 제안된 기법은 하나의 단일 안테나(single antenna) 방송 기지국과 다수의 단일 안테나 모바일 사용자가 있는 상향링크 시분할다중접속 (TDMA: Time Division Multiple Access) 시스템에서 데이터 지연허용(delay-tolerant)에 따라 클러스터를 구성하고 제곱 다이버시티 차수(square diversity order)의 협동 프로토콜(cooperative protocol)을 통해 높은 공간다이버시티 이득(spatial diversity gain)을 얻는다. 또한, 비대칭(asymmetric) 무선 채널 환경에서 공정성(fairness)을 보장한다.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.229-232
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• 2000

Orthogonal frequency division multiplexing(OFDM) has meanwhile become part of several telecommunicati ons standards, such as satellite and terrestrial digital audio broadcasting(DAB), digital terrestrial TV broad casting(DVB), asymmetric digital subscriber line(ADSL) for high-bit-rate digital subscriber services on twisted-pair channels, and broadband indoor wireless systems. In his paper, we show that OFDM signals contain sufficient structure to accomplish blind channel estimation using second order statistics only. This method doesn't require redundancy as cp in transmitter. And the result is compared with PSAM channel estimation as least square, linear minimum mean square, singular value decomposition.