• 산업공학
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• 제25권4호
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• pp.450-457
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• 2012

This study addresses the call admission control(CAC) problem for OFDMA wireless communication systems in which both subcarriers and power should be considered together as the system resources. To lessen the exccessive allocation of radio resources for protecting handoff calls, the proposed CAC allows the less data rate than their requirements to handoff calls. The CAC problem is formulated as a semi-Markov decision process(SMDP) with constraints on the blocking probabilities of handoff calls. Some extensive experiments are conducted to show the usefulness of the proposed CAC model.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권5호
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• pp.546-553
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• 2015

Recently, flash cache is widely adopted as the performance accelerator of legacy storage systems. Unlike other cache media, flash cache should be carefully managed as it has peculiar characteristics such as long write latency and limited P/E cycles. In particular, we make two prominent observations that can be utilized in managing flash cache. First, a serious worn-out problem happens when the working-set of a system is beyond the capacity of flash cache due to excessively frequent cache replacement. Second, more than 50% of data has no hit in flash cache as it is a second level cache. Based on these observations, we propose a cache admission control policy that does not cache data when it is first accessed, and inserts it into the cache only after its second access occurs within a certain time window. This allows the filtering of data disruptive to flash cache in terms of endurance and performance. With this policy, we prolong the lifetime of flash cache 2.3 times without any performance degradations.

• 대한산업공학회지
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• 제34권4호
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• pp.445-459
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• 2008

This paper addresses a call admission control(CAC) scheme giving handoff calls a priority over new calls for OFDMA wireless communication systems. The characteristics of OFDMA system and a variety of user QoS (Quality of Service) requirements are incorporated into the proposed CAC scheme which consists of several optimization modules for the system resource(subcarriers and power) allocations. The mathematical models and its solution methods for the embedded resource allocation problems are proposed. Some extensive computational experiments are conducted to illustrate the superiority of our CAC.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2010년도 한국컴퓨터종합학술대회논문집 Vol.37 No.1(D)
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• pp.26-29
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• 2010

네트워크 대역폭 소모 위주로 발생했던 DDoS 공격이 최근에는 웹서비스 대상 시스템 부하 유발을 통해 가용성을 떨어뜨리는 응용계층에서의 DDoS 공격 위주로 발생하고 있다. 이러한 DDoS 공격에 대응하기 위해 History, IP 분산도, GRT, Behavior 기반 등 다양한 대응 메커니즘이 연구되고 있지만 연구초기 단계에 머물러 있다. 본 논문에서는 Admission Control 기반 DDoS 공격대응 메커니즘을 제안하고, 시스템 개발을 통해 성능을 검증하였다. 제안된 메커니즘은 지금까지 발생한 모든 응용계층 DDoS 공격유형에 대응 가능하며, 기존 Behavior 기반 대응기법은 오탐지 가능성이 있으나 제안하는 메커니즘은 오탐지가 발생하지 않는 장점이 있어, 상용 환경에 바로 적용할 수 있을 것으로 예상된다.

• 한국통신학회논문지
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• 제38B권7호
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• pp.535-542
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• 2013

Coordinated multi-point transmission (CoMP) is considered to be a promising technique to improve the throughput for LTE-Advanced systems. One important approach for CoMP is Joint Transmission (JT). However, the analytical model of JT has not been fully studied, as user equipments (UEs) receiving the desired signals from an adjacent base station (BS) as well as serving BS, or only serving BS were not distinguished. We derive a new analytical model to describe the call admission control in JT based systems. The performance measures of interest are the call blocking probability, and resource utilization. Furthermore, we compare the performance of JT-based systems and non-JT- based systems. The analytical results are in reasonable agreement with the simulation results.

• Journal of Communications and Networks
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• 제12권6호
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• pp.568-576
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• 2010

The paper presents a control architecture aimed at implementing bandwidth optimization combined with call admission control (CAC) over a digital video broadcasting (DVB) return channel satellite terminal (RCST) under quality of service (QoS) constraints. The approach can be applied in all cases where traffic flows, coming from a terrestrial portion of the network, are merged together within a single DVB flow, which is then forwarded over the satellite channel. The paper introduces the architecture of data and control plane of the RCST at layer 2. The data plane is composed of a set of traffic buffers served with a given bandwidth. The control plane proposed in this paper includes a layer 2 resource manager (L2RM), which is structured into decision makers (DM), one for each traffic buffer of the data plane. Each DM contains a virtual queue, which exactly duplicates the corresponding traffic buffer and performs the actions to compute the minimum bandwidth need to assure the QoS constraints. After computing the minimum bandwidth through a given algorithm (in this view the paper reports some schemes taken in the literature which may be applied), each DM communicates this bandwidth value to the L2RM, which allocates bandwidth to traffic buffers at the data plane. Real bandwidth allocations are driven by the information provided by the DMs. Bandwidth control is linked to a CAC scheme, which uses current bandwidth allocations and peak bandwidth of the call entering the network to decide admission. The performance evaluation is dedicated to show the efficiency of the proposed combined bandwidth allocation and CAC.

• 한국정보과학회논문지:정보통신
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• 제29권1호
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• pp.1-14
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• 2002

이동 컴퓨팅 환경에서 멀티미디어 트래픽 제공에 관련된 가장 중요한 이슈는 이동 호스트(클라이언트)에게 지속적인 QoS(Quality of Service)를 보장하는 것이다. 그러나, 핸드-오프를 초래하는 클라이언트의 이동성으로 인해 클라이언트와 네트워크간에 협상된 QoS가 보장되지 못할 수도 있다. 본 논문에서는 이동 컴퓨팅 환경에서 멀티미디어 트래픽에 대해 지속적인 QoS를 지원하기 위한 호 수락 제어 메커니즘을 제안한다. 각 셀은 핸드-오프 호를 위해 이웃 셀로부터 대역폭을 예약한다. 만약, 핸드-오프 호를 위해 필요 이상으로 대역폭이 예약된다면 신규 호의 블록킹 확률이 증가하므로, 핸드-오프 호를 위해 예약할 대역폭의 크기를 정확히 결정하는 것이 중요하다. 본 논문에서는 예약할 대역폭의 정확한 크기를 결정하고, 네트워크 상태에 다라 이 크기를 적응적으로 조정하기 위해 MPP(Mobility Pattern Profile)와 2-계층 셀 구조를 기반으로 한 적응적 대역폭 예약을 제안한다. 또한, MPP를 이용한 다음-셀 예측 기법과 적응적 대역폭 예약을 기반으로 한 호 수락 제어 메커니즘을 제안한다. 본 논문에서 제시된 호 수락 제어 메커니즘의 성능을 평가하기 위해, 신규 호 블록킹률, 핸드-오프 호 종료율, 대역폭 이용률을 측정하였다. 시뮬레이션 결과, 본 논문의 호 수락 제어 메커니즘의 성능이 NR-CAT1, FR-CAT1, AR-CAT1과 같은 기존의 메커니즘들보다 우수함을 알 수 있었다.

• 한국경영과학회지
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• 제35권1호
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• pp.83-95
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• 2010

This paper considers a firm that operates make-to-stock and make-to-order facilities in successive stages. The make-to-stock facility produces components which are consumed by the external market demand as well as the internal make-to-order operation. The make-to-order facility processes customer orders with the option of acceptance or rejection. In this paper, we address the problem of coordinating how to allocate the capacity of the make-to-stock facility to internal and external demands and how to control incoming customer orders at the make-to-order facility so as to maximize the firm's profit subject to the system costs. To deal with this issue, we formulate the problem as a Markov decision process and characterize the structure of the optimal inventory allocation and customer order control. In a numerical experiment, we compare the performance of the optimal policy to the heuristic with static inventory allocation and admission control under different operating conditions of the system.

• 정보교육학회논문지
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• 제15권3호
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• pp.493-503
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• 2011

사이버대학 학생정원의 증원은 학생 규모에 따른 교육여건의 확보, 신입생 충원율 등을 감안하여 결정되는데 정원 관리를 위해 고려되는 항목들이 사이버대학의 특수성을 충분히 반영하지 못하고 있으며, 항목별 기준도 미약하여 증원에 대한 자율 통제, 학습권 보호, 교육의 질 담보를 제대로 수행하지 못하고 있다. 본 연구는 사이버대학 학생정원 관리 정책의 취약점을 보완하고 사이버대학의 특장점을 살려서 고등교육기관으로서의 교육의 질을 담보할 수 있는 학생정원 관리 방안을 제안하기 위하여 수행되었다. 본 연구를 통해 사이버대학의 현황 및 질 제고 요소 분석, 전문가 의견조사 등을 통하여 사이버대학 학생정원 관리모형을 도출하였다.

• 대한간호학회지
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• 제2권1호
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• pp.141-157
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• 1971

The peripheral infection is one of the major causes of maternal death, and although it is preventable through an effective prenatal as well as postnatal care its morbidity is increasing due to bacterial resistant to an effective antibiotics. The primary purpose of this study was to investigate the peripheral morbidity of 949 parturients who were admitted to the Obstetrics and Gynecologic department of Ewha Woman's University Hospital from January 1971 to September 1971. Among the 949 parturients, especially 40 normal parturients were selected (20, control soup was given complete aseptic care during labor and delivery and post delivery: 20, compare group was given the ordinary care practiced during labor and delivery and maternal ward of Ewha Woman's University Hospital) for bacteriologic test on vaginal flora twice, on admission and on complete cervical dilatation of each parturient. The results obtained from this study were as follows; 1. Majority of parturients age were 21 to 35 years old(90.83%), and educational level of 949 parturients was above high school. A large number of parturients socioeconomic level (according to their husbands' job) were moderate. 2, Among the 949 parturients, multipara (55.9%) were a little more than primipara (44. 1%) and 38.84% of parturients had experienced aborition. 3. In deliverty types, normal deliveries (804 cases) were more than cesarean section deliveries (145 cases) The peripheral morbidity after normal deliveries was 0.5%, and cesarean section deliveries, 23.45%. 4. Among 949 parturients incidence of hemorrhage eases (500cc or more bleeding) showed the higher peripheral morbidity (24.86%) than other cases (bleeding less than 500cc, 7.83%). 5. The majority of parturients (81.03%) had teen taking antenatal care, but most of them were taken irregular antenatal care. On the other hand, on admission, the parturients with complication were 30.32%, and their peripheral morbidity showed much higher (7.02%) than those with no complication (2.71%). 6. The incidence of peripheral morbidity in premature ruptured membrane was higher (10.91%) than normal parturienta (1.73%). 7. In the result of aseptic care during labor and delivery and post delivery, the number of cultured bacteria was legs in control group than Compare group (in control group, on admission 17, on complete cervical dilatation 12: in compare group, on admission 21 on complete cervical dilatation 21) . The most common bacteria were Staphylococcus (control group 14 on admission, compare group 16 on admission), and next Streptococcus, E- Coil, Bacillus Subtilis, in order. Also in control group the number. of colony were reduced (43%) more than in Compare group. Transient temperature elevation from 37℃ to 37.4℃ were noted in compare group (50%) than in control group (30%), and there was no one indicated above 38℃. In conclusion, the aseptic care is the test way of preventing peripheral infection as well as decreasing the puerperal morbidity. Therefore the most important nursing care is the aseptic care for each parturient during labor and delivery and peat delivery and also all the instruments must be cleaned and sterilized.