• Communications for Statistical Applications and Methods
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• 제4권2호
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• pp.515-522
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• 1997

In this paper, we find the second derivative of mean busy cycle with respect to a parameter of inter-arrival time distribution. We show that this derivative can be estimated from single sample path. We do the similar thing for the mean number of arrivals during busy cycle.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권7호
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• pp.2512-2531
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• 2014

We propose a new Distributed Denial of Service (DDoS) defense mechanism that protects http web servers from application-level DDoS attacks based on the two methodologies: whitelist-based admission control and busy period-based attack flow detection. The attack flow detection mechanism detects attach flows based on the symptom or stress at the server, since it is getting more difficult to identify bad flows only based on the incoming traffic patterns. The stress is measured by the time interval during which a given client makes the server busy, referred to as a client-induced server busy period (CSBP). We also need to protect the servers from a sudden surge of attack flows even before the malicious flows are identified by the attack flow detection mechanism. Thus, we use whitelist-based admission control mechanism additionally to control the load on the servers. We evaluate the performance of the proposed scheme via simulation and experiment. The simulation results show that our defense system can mitigate DDoS attacks effectively even under a large number of attack flows, on the order of thousands, and the experiment results show that our defense system deployed on a linux machine is sufficiently lightweight to handle packets arriving at a rate close to the link rate.

• 한국시뮬레이션학회논문지
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• 제27권3호
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• pp.45-52
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• 2018

대기행렬에 고객 (또는 패킷 등)이 몰리는 오버로드(overload)가 발생하는 경우 긴 대기열이 발생하여 서비스 품질에 좋지 않은 영향을 줄 수 있다. 오버로드 상황에서 혼잡을 완화하기 위해 대기하는 고객숫자에 기반한 다양한 오버로드 제어 정책들이 고안, 적용되고 있다. 본 연구는 대기 중인 고객 숫자에 한계점 (threshold)을 두고, 한계점을 넘으면 서비스 속도를 빠르게 하거나 고객의 도착 간격(시간)을 증가시키는 제어정책을 대상으로 한다. 이러한 정책을 갖는 M/G/1 대기행렬에 대해 바쁜 기간(busy period)을 분석하는데, 연구결과는 비용구조가 주어졌을 때 최적 시스템 제어 정책을 찾는데 필수적이다.

• 한국경영과학회지
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• 제37권4호
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• pp.197-209
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• 2012

This paper studies an emergency service vehicle location problem, where minimum reliability level pre-specified at each demand point is assured. Several models are suggested depending on the busy fraction, which is the time proportion of unavailability for the ambulances. In this paper a new model on computing the busy fraction is suggested, where it varies depending on the distance between the demand point and ambulances, hence it may respond the more realistic situation. The busy fraction for the ambulance location determined by the optimization model is computed by the simulation, and updated through the iterative procedure. It has been shown that the performances of the solutions obtained by the algorithm suggested for the instances appeared in the literature.

• 한국산업정보학회논문지
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• 제23권1호
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• pp.53-63
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• 2018

본 논문에서는 D-정책을 갖는 이산시간 BMAP/G/1 대기행렬시스템의 대기시간을 분석한다. 고객(또는 패킷)들은 마코비안 도착과정을 따라 집단으로 시스템에 도착하며, 유휴한 서버는 시스템에 도착한 고객집단의 서비스시간의 총합이 이미 정해놓은 임계값 D를 초과하면 시스템에 더 이상 서비스할 고객이 없을 때까지 서비스를 제공한다. 시스템의 안정상태 대기시간 분포를 변환 형태로 구하고 성능척도로서 평균값을 유도하였다. 시뮬레이션을 통하여 이론값들의 타당성을 검증하고 간단한 수치예제를 보였다.

• 한방안이비인후피부과학회지
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• 제13권2호
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• pp.51-75
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• 2000

The result were as follows: 1. Apply the drug to the affected part can used every time of ulcer. 2. Apply the drug to the affected part is used cold drug on yang-syndrome, hot drug on yin-syndrome, regulate drug on ban yin and ban yang-syndrome. 3. Apply the drug to the affected part is used alcohol, water, allii radix(인), zingiberis rhizoma recens(姜), juice of chrysanthemi flos(菊花) and so forth. 4. Apply the drug to the affected part can't used hot drug on yang-syndrome, cold drug on yin-syndrome. 5. Apply the drug to the affected part is used to be very busy of YouYuiKimHoangSan(如意金黃散). 6. Apply the drug to the affected part is used to be very busy on the angelicae adhuricae radix(白芷) of disperse the edema and drain the pus, and on the arisaematis rhizoma(南星), rhei radix et rhizoma(大黃), olibanum(乳香), phellodendri cortex(黃柏), calomelas(輕粉), glycyrrhizae radix(甘草), angelicae gigantis radix(當歸), myrrha(沒藥) of clearing away heat, activating blood circulation and relieve pain. 7. Apply the drug to the affected part is clearing away heat, activating blood circulation 8. Apply the drug to the affected part is cold and hot. 9. Apply the drug to the affected part is pungent, bitter and sweet. 10. Apply the drug to the affected part is non-toxic. 11. Apply the drug to the affected part is used to be very busy on the chanel of liver, heart, spleen, lung, stomach.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권3호
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• pp.1301-1318
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• 2017

In order to utilize the licensed channel of cognitive radio (CR) when the primary user (PU) is detected busy, a benefit-exchange access mode based on cooperative communication is proposed to allow secondary user (SU) to access the busy channel through giving assistance to PU's communication in exchange for some transmission bandwidth. A holistic joint optimization problem is formulated to maximize the total throughput of CR system through jointly optimizing the parameters of cooperative spectrum sensing (CSS), including the local sensing time, the pre-configured sensing decision threshold, the forward power of cooperative communication, and the bandwidth and transmission power allocated to SUs in benefit-exchange access mode and traditional access mode, respectively. To solve this complex problem, a combination of bi-level optimization, interior-point optimization and exhaustive optimization is proposed. Simulation results show that, compared with the tradition throughput maximizing model (TTMM), the proposed holistic joint optimization model (HJOM) can make use of the channel effectively even if PU is busy, and the total throughput of CR obtains a considerable improvement by HJOM.

• 한국산업정보학회논문지
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• 제21권6호
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• pp.1-12
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• 2016

본 논문에서는 D-정책을 갖는 이산시간 BMAP/G/1 대기행렬시스템의 일량을 분석한다. 유휴한 서버는 시스템에 도착한 고객집단의 서비스시간의 총합이 이미 정해진 일량 임계값 D를 초과하면 시스템에 서비스할 고객이 없을 때까지 서비스를 제공한다. 시스템의 안정상태 일량변환벡터를 유도하고 성능척도로서 평균일량을 구하였다. 시뮬레이션을 통해 이론값들의 타당성을 검증하고 간단한 수치예제를 보였다.

• 환경위생공학
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• 제17권2호
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• pp.85-91
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• 2002

Workers who work at indoor and outdoor environment near busy road are suspected to be exposed to high-elevated air pollutant levels during working hours. This study evaluated the working-time nitrogen dioxide ($NO_2$) exposure for workers (repairmen and polishers) of shoe-stalls. Since shoe-stalls have particularly been located near busy road in Korea, workers might be high exposure to $NO_2$ from traffic exhaust as well as indoor sources of shoe-stall such as portable gas range (butane gas) during working hours. In this study, we measured the indoor and outdoor $NO_2$ concentrations of shoe-stalls. Simultaneously, outdoor $NO_2$ concentrations of building through sidewalk from shoe-stall were measured. High $NO_2$ exposure for workers of shoe-stalls was considered to be inflow of outdoor source of exhausted emission from vehicles and indoor source from usage of gas range to polish the shoe. Indoor/outdoor $NO_2$ concentration ratio ($0.94{\pm}0.22$) in Seoul was higher than that ($1.06{\pm}0.34$) in Asan, because ambient $NO_2$ level was high in Seoul and usage of gas range was prevalent in Asan. According to $NO_2$ concentrations by distance from roadside to building through sidewalk, $NO_2$ concentrations showed the decreased trend with distance. The results of this study can be utilized by municipal authorities in urban planning for evaluating effects of future traffic planning and land use.

• Journal of applied mathematics & informatics
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• 제5권1호
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• pp.1-12
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• 1998

We consider G/M/1 queues with multiple vacation disci-pline where at the end of every busy period the server stays idle in the system for a period of time called changeover time and then follows a vacation if there is no arrival during the changeover time. The vaca-tion time has a hyperexponential distribution. By using the methods of the shift operator and supplementary variable we explicitly obtain the queue length probabilities at arrival time points and arbitrary time points simultaneously.