• Journal of applied mathematics & informatics
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• 제25권1_2호
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• pp.389-405
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• 2007

In this paper, we study a k-out-of-n system with single server who provides service to external customers also. The system consists of two parts:(i) a main queue consisting of customers (failed components of the k-out-of-n system) and (ii) a pool (of finite capacity M) of external customers together with an orbit for external customers who find the pool full. An external customer who finds the pool full on arrival, joins the orbit with probability ${\gamma}$ and with probability $1-{\gamma}$ leaves the system forever. An orbital customer, who finds the pool full, at an epoch of repeated attempt, returns to orbit with probability ${\delta}\;(<\;1)$ and with probability $1-{\delta}$ leaves the system forever. We compute the steady state system size probability. Several performance measures are computed, numerical illustrations are provided.

• 대한수학회지
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• 제32권2호
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• pp.211-236
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• 1995

The purpose of this paper is to provide a transient diffusion approximation of queue size distribution for M/G/m/N system. The M/G/m/N system can be expressed as follows. The interarrival times of customers are exponential and the service times of customers have general distribution. The system can hold at most a total of N customers (including the customers in service) and any further arriving customers will be refused entry to the system and will depart immediately without service. The queueing system with finite capacity is more practical model than queueing system with infinite capacity. For example, in the design of a computer system one of the important problems is how much capacity is required for a buffer memory. It its capacity is too little, then overflow of customers (jobs) occurs frequently in heavy traffic and the performance of system deteriorates rapidly. On the other hand, if its capacity is too large, then most buffer memories remain unused.

• 산업경영시스템학회지
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• 제40권3호
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• pp.66-75
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• 2017

Priority disciplines are an important scheme for service systems to differentiate their services for different classes of customers. (N, n)-preemptive priority disciplines enable system engineers to fine-tune the performances of different classes of customers arriving to the system. Due to this virtue of controllability, (N, n)-preemptive priority queueing models can be applied to various types of systems in which the service performances of different classes of customers need to be adjusted for a complex objective. In this paper, we extend the existing (N, n)-preemptive resume and (N, n)-preemptive repeat-identical priority queueing models to the (N, n)-preemptive repeat-different priority queueing model. We derive the queue-length distributions in the M/G/1 queueing model with two classes of customers, under the (N, n)-preemptive repeat-different priority discipline. In order to derive the queue-length distributions, we employ an analysis of the effective service time of a low-priority customer, a delay cycle analysis, and a joint transformation method. We then derive the first and second moments of the queue lengths of high- and low-priority customers. We also present a numerical example for the first and second moments of the queue length of high- and low-priority customers. Through doing this, we show that, under the (N, n)-preemptive repeat-different priority discipline, the first and second moments of customers with high priority are bounded by some upper bounds, regardless of the service characteristics of customers with low priority. This property may help system engineers design such service systems that guarantee the mean and variance of delay for primary users under a certain bounds, when preempted services have to be restarted with another service time resampled from the same service time distribution.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 1999년도 가을 학술발표논문집 Vol.26 No.2 (3)
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• pp.423-426
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• 1999

In offering a statistical end-to-end bandwidth guarantee service, typically called Assured Service, in Differentiated Serviced (Diff-Serv) framework, the biggest issue is its inconsistency. Larger profile TCP flows fail to achieve the guaranteed rate when competing with many smaller profile flows. This phenomenon, which we call "bandwidth skew", stems from the fact that larger profile flows take longer time to recover from the congestion window size backoff after a packet drop. Proposed solutions to this problem, therefore, are focused on modifying the TCP behavior. However, TCP modification is not practicable, mainly due to its large installation base. We look to other mechanisms in the Diff-Serv framework to find more realistic solutions. In particular, we demonstrate that RIO, the de facto standard packet differentiation mechanism used for Assured Service, also contributes to the bandwidth skew. Based on this new finding, we design a modified RIO mechanism called RI+O. RI+O uses OUT queue length in addition to IN and IN+OUT queue length to calculate OUT packet drop probability. We show through extensive simulation that RI+O significantly alleviates the bandwidth skew, expanding the operating regime for Assured Service.d Service.

• 한국산업정보학회논문지
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• 제11권3호
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• pp.1-9
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• 2006

IEEE 802.11 WLAN은 핸드오프 과정에서 일시적인 통신로의 단절이 발생하는 하드 핸드오프을 적용한다. 이 방식은 핸드오프 과정에서 트래픽의 유실을 초래하며, 트래픽 유실을 복구하기 위해 old AP에서 new AP로 트래픽을 포위딩하는 방식을 사용하나 실시간 서비스에는 적용이 어렵다. 본 연구에서는 무선 LAN 기반 홈네트워크의 실시간서비스의 핸드오프에서 트래픽 유실 및 전송시컨스 에러를 줄이기 위한 방식을 제안한다. 이를 위해 IEEE 802.11e에서 권고하는 priority queue scheme을 적용하고, 실시간 서비스의 핸드오프 트래픽에 대해 priority queue의 사용 우선권을 주어 핸드오프시 트래픽 유실 및 전송시컨스 에러를 줄이는 방식을 제안하고, 시뮬레이션을 통해 성능을 분석하였다

• Journal of Communications and Networks
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• 제13권2호
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• pp.132-141
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• 2011

IEEE 802.15.4 networks are a feasible platform candidate for connecting all health-care-related equipment dispersed across a hospital room to collect critical time-sensitive data about patient health state, such as the heart rate and blood pressure. To meet the quality of service requirements of health-care systems, this paper proposes a multi-priority queue system that differentiates between various types of frames. The effect of the proposed system on the average delay and throughput is explored herein. By employing different contention window parameters, as in IEEE 802.11e, this multi-queue system prioritizes frames on the basis of priority classes. Performance under both saturated and unsaturated traffic conditions was evaluated using a novel analytical model that comprehensively integrates two legacy models for 802.15.4 and 802.11e. To improve the accuracy, our model also accommodates the transmission retries and deferment algorithms that significantly affect the performance of IEEE 802.15.4. The multi-queue scheme is predicted to separate the average delay and throughput of two different classes by up to 48.4% and 46%, respectively, without wasting bandwidth. These outcomes imply that the multi-queue system should be employed in health-care systems for prompt allocation of synchronous channels and faster delivery of urgent information. The simulation results validate these model's predictions with a maximum deviation of 7.6%.

• Journal of applied mathematics & informatics
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• 제30권5_6호
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• pp.749-757
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• 2012

We consider the M/PH,G/1 queue with two classes of customers in which class-1 customers have deterministic impatience time and have preemptive priority over class-2 customers who are assumed to be infinitely patient. The service times of class-1 and class-2 customers have a phase-type distribution and a general distribution, respectively. We obtain performance measures of class-2 customers such as the queue length distribution, the waiting time distribution and the sojourn time distribution, by analyzing the busy period of class-1 customers. We also compute the moments of the queue length and the waiting and sojourn times.

• Journal of applied mathematics & informatics
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• 제16권1_2호
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• pp.469-481
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• 2004

In this paper, we investigate the mean queue length and the mean packet delay of a dynamic bandwidth allocation(DBA) scheme in an Ethernet passive optical network(EPON). We focus on the interleaved polling system with a gated service discipline. We assume that input packets arrive at an optical network unit(ONU) according to Poisson process. We use a continuous time queueing model in order to find the queue length distribution of the gated interleaved polling system with the first stage input queue and the second stage transmission queue. We give some numerical results to investigate the mean queue lengths and mean packet delays for the symmetric polling system with statistically identical stations.

• 한국시뮬레이션학회논문지
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• 제8권1호
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• pp.51-61
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• 1999

A cell scheduling method of Queue for the ATM switch is proposed and simulated. In this paper, we present the cell scheduling method proper to the proposed queue and the improved queue with Queue Sharing(QS) structure for CBR, VBR, ABR traffic. The proposed QS structure minimizes the CLS(Cell Loss Ratio) of ABR traffic and decreases the CLR of bursty VBR traffic. Also we propose a cell scheduling method using VRR(Variable Round Robin) scheme proper to the high-speed(ATM) switch. The VRR scheme provides a fairness in terms of service chance for the queues in the ATM switch as well as QOS of their cell delay characteristic of CBR and VBR traffic, QOS of ABR CLR. The simulation results show the proposed method achieves excellent CLR and average cell delay performance for the various ATM traffic services in the Queue Sharing structure.

• 대한수학회보
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• 제47권6호
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• pp.1251-1258
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• 2010

For an M/G/1 processor-sharing queue with batch arrivals, Avrachenkov et al. [1] conjectured that the conditional mean sojourn time is concave. However, Kim and Kim [5] showed that this conjecture is not true in general. In this paper, we show that this conjecture is true if the service times have a hyperexponential distribution.