• KSII Transactions on Internet and Information Systems (TIIS)
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• 제6권9호
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• pp.2136-2152
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• 2012

The growth of Internet technologies and the widespread use of mobile devices have been paving the way for the increasing use of conferencing services. Two types of systems have been designed to provide conferencing services: 1) a conferencing system using session control over a peer-to-peer (P2P) network and 2) an IP Multimedia Subsystem (IMS) conferencing system. The IMS conferencing system was developed to adapt to a server-based centralized system, whereas the benefits of the P2P operational model in providing such conference services are widely acknowledged. However, each system provides conferencing services only to its own users. Therefore, in this paper, we propose an interworking model to support multimedia conferencing service between the P2P environment and IMS networks. We also introduce protocol architecture and some service scenarios. To verify this system model and the design architecture, we perform an actual implementation and show experienced test results.

• Journal of Communications and Networks
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• 제18권2호
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• pp.135-149
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• 2016

Cloud radio access network (C-RAN) refers to the virtualization of base station functionalities by means of cloud computing. This results in a novel cellular architecture in which low-cost wireless access points, known as radio units or remote radio heads, are centrally managed by a reconfigurable centralized "cloud", or central, unit. C-RAN allows operators to reduce the capital and operating expenses needed to deploy and maintain dense heterogeneous networks. This critical advantage, along with spectral efficiency, statistical multiplexing and load balancing gains, make C-RAN well positioned to be one of the key technologies in the development of 5G systems. In this paper, a succinct overview is presented regarding the state of the art on the research on C-RAN with emphasis on fronthaul compression, baseband processing, medium access control, resource allocation, system-level considerations and standardization efforts.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권10호
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• pp.4787-4807
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• 2016

Although the dense interconnection datacenter networks (DCNs) (e.g. FatTree) provide multiple paths and high bisection bandwidth for each server pair, the single-path TCP (SPT) and ECMP which are widely used currently neither achieve high bandwidth utilization nor have good load balancing. Due to only one available transmission path, SPT cannot make full use of all available bandwidth, while ECMP's random hashing results in many collisions. In this paper, we present OFPT, an OpenFlow based Parallel Transport framework, which integrates precise routing and scheduling for better load balancing and higher network throughput. By adopting OpenFlow based centralized control mechanism, OFPT computes the optimal path and bandwidth provision for each flow according to the global network view. To guarantee high throughput, OFPT dynamically schedules flows with Seamless Flow Migration Mechanism (SFMM), which can avoid packet loss in flow rerouting. Finally, we test OFPT on Mininet and implement it in a real testbed. The experimental results show that the average network throughput in OFPT is up to 97.5% of bisection bandwidth, which is higher than ECMP by 36%. Besides, OFPT decreases the average flow completion time (AFCT) and achieves better scalability.

• 한국식품조리과학회지
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• 제3권2호
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• pp.87-99
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• 1987

병원급식의 관능적인 품질, 특히 적온 관리 실태를 평가하기 위해, 서울시내 소재한 종합병원 20개 병원의 급식제도, 식품운반체계 조사 및 식품생산과정 중 소요시간-온도상태를 조사하였다. 또한 대부분의 병원들이 중앙배선화 되어가는 현시점에서 중앙 및 병동 배선의 장.단점을 비교.분석하기 위하여 두 가지 배선방법을 함께 실시하는 H병원을 대상으로 조사하였고, H병원의 특수한 상황을 배제한 보편적인 실태 비교를 위해 H병원과 병상규모가 유사한(360~520병상) 7개 병원(병동배선 : 4, 중앙배선 : 3)의 배선방법을 비교하여 다음과 같은 결과를 얻었다. 1. 조사대상 20개 병원의 노동관리 실태를 조사한 결과, 병상당 종업원 수를 외국과 비교했을 때 현저히 적었으며, 주당노동시간은 미국의 경우보다 2배 많았다. 또한 사용하는 급식제도는 모두 전통적인 급식제도를 이용했고, 식품운반체계는 최근 1~2년 내에 대부분의 병원들이 중앙배선화 되어 현재 중앙배선 실시 병원은 60%에 달하였으며, 35%가 중앙배선으로 이행해 가는 과도기에 있었고, 단지 5%만이 병동배선을 실시하고 있었다. 그러나 전통적인 급식제도와 중앙배선체계의 단점인 적온관리를 위한 기기 도입을 통해 특별한 배려를 하는 병원은 단지 3개 병원에서 일부 음식에 제한되어 실시되고 있는 실정이었다. 2. 서울시내에 소재한 20개 종합병원에서 제공되는 밥, 국, 육찬(또는 어찬)의 소요시간-온도상태를 조사한 결과, 병동배선 실시 병원의 I, II group의 국과 III group의 밥만이 미각기준온도를 만족시키며, 나머지는 모두 미달하는 수준이었다. 특히 조리후 급식까지 장시간 동안 방치되는 육찬 또는 어찬의 경우는 최저 99.1분에서 최고 199.1분까지 소요되어 급식온도 는 $20.6^{\circ}C$에서 $25.7 ^{\circ}C$로 미각 만족 온도에 크게 미달하는 온도로 급식되고 있었다. 또한 중앙배선방법을 이용하는 병원은 밥의 경우 $^45.3{\circ}C$~52.9$^{\circ}C$, 국의 경우 $43.1^{\circ}C$~ $54.0^{\circ}C$의 범위로 급식되었고, 병동배선을 이용하는 병원도 특별한 적온관리의 배려가 없는 III group 은 55.8$^{\circ}C$로 미각기준온도인 밥 : $65^{\circ}C$, 국 : $70^{\circ}C$에 미달된 것으로 나타났다. 그리고 급식당시의 온도에 영향을 미치는 변수들의 상관관계를 분석한 결과는 중앙 배선시 정량후 급식까지 소요시간이 -.78로 가장 높게, 병동배선의 경우는 정량시 온도가 .61로 가장 높게 나타났다. 3. 중앙배선 및 병동배선 비교연구 결과 중 소요시간-온도상태의 비교연구 결과, 병동배선이 유의적으로 높은 온도를 나타냈으나, 두 배선방법 모두 미각 만족온도에는 미달되는 수준이었다. H병원에서 조사한 환자수응도 비교연구 결과는 배선방법간에 유의적인 차이가 없었다. 또한 노동가 연구 결과 H병원의 경우 중앙배선시 병동배선에 비해 노동시간이 21.0% 절약되었고, 노동임금도 17.9%가 낮았으며, 서울시내 7개 병원의 조사결과는 중앙배선시 병동배선보다 노동시간이 38.4%, 노동임금이 21.35%가 절약된 것으로 집계되었다. 즉 중앙배선을 실시하는 경우 노동임금이 절약되는 잇점이 있으나, 급식되는 온도는 병동배선시보다 유의적으로(P<.01) 낮게 나타나 효과적인 적온관리를 위한 적절한 배려가 절실히 요청된다.

• 한국지열·수열에너지학회논문집
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• 제9권3호
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• pp.11-18
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• 2013

Small and medium-size buildings employ a multi-distributed individual air-conditioning system utilizing package air conditioners instead of centralized cooling systems, which can allow easier building management and maintenance along with a diversification of facility use. Inverter driven system heat pumps have been developed to achieve not only easy distribution control allowing free combination of indoor units with different models and different capacities, but also wide applications to an intelligent air conditioning. In this study, the transient performance of a system heat pump was analysed with the variation of compressor speed and EEV openings. The superheat was selected as a control parameter of the system, because the variation of it was consistent with each indoor unit capacity.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제15권2호
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• pp.580-599
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• 2021

Software-Defined Networking (SDN) has three key features: separation of control and forwarding, centralized control, and network programmability. While improving network management flexibility, SDN has many security issues. This paper systemizes the security threats of SDN using spoofing, tampering, repudiation, information disclosure, denial of service, and elevation of privilege (STRIDE) model to understand the current security status of SDN. First, we introduce the network architecture and data flow of SDN. Second, we analyze security threats of the six types given in the STRIDE model, aiming to reveal the vulnerability mechanisms and assess the attack surface. Then, we briefly describe the corresponding defense technologies. Finally, we summarize the work of this paper and discuss the trends of SDN security research.

• 설비공학논문집
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• 제25권7호
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• pp.398-405
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• 2013

Small and medium-size buildings employ a multi-distributed individual air-conditioning system that utilizes package air conditioners instead of centralized cooling systems, which can allow easier building management and maintenance, along with a diversification of facility use. Inverter driven system heat pumps have been developed to achieve not only an easy distribution control, allowing free combination of indoor units with different models and different capacities, but also wide applications to intelligent air conditioning. However, the control algorithms of the system heat pump are limited in the open literature, due to complicated operating conditions. In this paper, an inverter-driven system heat pump having two indoor units with electronic expansion valves (EEV) was simulated in the cooling mode. An integral optimum regulating controller employing the state space control method was also simulated, and applied to the system-heat pump system, to obtain efficient control of the MIMO (multi input multi output) system. The simulation model for the controller yielded satisfactory prediction results. The new control model can be successfully utilized as a basic tool in controller design.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1172-1173
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• 2008

At the moment, the control ability of wind farms is a prime research concern for the grid integration of large wind farms, due to their required active role in the power system. As more wind turbines are installed, the power from wind energy will start to replace conventional generation units and its influence on power systems cannot be neglected. Besides, because of the intermittent nature of wind the output power of wind turbines fluctuates according to wind speed variation. Especially an isolated power system with small capacity such like Jeju needs more systematic solutions and regulations(grid code). This paper presents the idea of approach for centralized operating wind farm strategy to regulate the wind farm power production to the reference power ordered by the system operator. The doubly fed induction generator(DFIG) can control active and reactive power in feasible range. So wind farm comprised of DFIG has the possibility of a controllable component in the power system. The presented wind farm control has a hierarchical structure with both a wind farm control level and a wind turbine control level.

• Journal of Communications and Networks
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• 제13권4호
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• pp.319-326
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• 2011

Beamforming techniques have been successfully utilized for traffic channels in order to solve the interference problem. However, their use for control channels has not been sufficiently investigated. In this paper, a (semi-) centralized beamforming strategy that adaptively changes beam patterns and controls the total transmit power of cells is proposed for the performance enhancement of the common channel in hierarchical cell structure (HCS) networks. In addition, some examples of its practical implementation with low complexity are presented for two-tier HCS networks consisting of macro and pico cells. The performance of the proposed scheme has been evaluated through multi-cell system-level simulations under optimistic and pessimistic interference scenarios. The cumulative distribution function of user geometry or channel quality has been used as a performance metric since in the case of common control channel the number of outage users is more important than the sum rate. Simulation results confirm that the proposed scheme provides a significant gain compared to the random beamforming scheme as well as conventional systems that do not use the proposed algorithm. Finally, the proposed scheme can be applied simultaneously to several adjacent macro and pico cells even if it is designed primarily for the pico cell within macro cells.

• 융합보안논문지
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• 제2권2호
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• pp.109-121
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• 2002

정보기술의 발달로 보안사고가 증가되면서 침입차단 시스템, 침입탐지 시스템 및 가상 사설망 등의 기능이 통합된 보안 관리 시스템(ESM)의 개발에 대한 요구가 증가되고 있다. 그러나, 불행하게도 개발자들은 관련 표준의 미비로 어려움을 겪어왔다. 최근 ISTF가 침입차단 시스템 및 침입탐지 시스템의 로그 형식 표준을 발표하였으나 실제적으로 효율적인 ESM을 위해서는 이벤트 및 제어 메시지 등의 추가적인 표준 개발이 요구된다. 본 연구는 ISTF 표준을 분석하고 침입차단 시스템 및 침입탐지 시스템의 이벤트 및 제어 표준을 제안하고자 하며, 본 연구 결과는 ESM의 개발과 지속적인 관련 표준 개발에 도움이 될 것이다.