• Journal of Korea Multimedia Society
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• v.12 no.1
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• pp.31-40
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• 2009

Call centers have become the prevalent contact points between companies and their customers. By virtue of recent advances in communication technology, the number and size of call centers have grown dramatically. As a large portion of the operating costs are related to the labor costs, efficient design and workforce staffing are crucial for the economic success of call centers. Therefore it is very important to determine the adequate number of agents. In this context, the workforce staffing level can be modeled as mathematical optimization problem using queueing theory. In this paper, we deal with an approximate analysis of an N-design call center with two finite queues and two types of reneging customers by using the state decomposition method. We also represent some numerical examples and show the impact of the system parameters on the performance measures of the call center.

• Journal of the Korean Operations Research and Management Science Society
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• v.34 no.3
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• pp.137-153
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• 2009

In this paper, we present an analytic model that evaluates the performance of B-MAC protocol under contention transmission conditions of two senders in a single-hop wireless sensor network. Our model considers the impact of several important factors such as sleep cycle, the backoff mechanism and incoming traffic loads. After obtaining the service delay distribution of a sending node and expected delay of a receiving node, an iterative algorithm is presented for calculating the performance measures such as expected energy consumption usage per packet and latency. Simulation results show that the proposed analytic model can accurately estimate the performance measures under different traffic conditions.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.7
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• pp.1-16
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• 1994

In this paper, we propose a new multiple access scheme for VSAT(Very Small Aperture Terminal) data communications. The proposed scheme has better performance in terms of delay throughput than Controlled Multiaccess Scheme which has excellent performance. The proposed scheme use the spare reservation method, adaptation method to offered load, and fixed bandwidth reservation method. In this paper, we analyze the performance using simple queueing model and present the simulation results. When network traffic is very low, the new scheme and the controlled multiaccess scheme have almost the same access delay characteristic. As the network load becomes higher, the new scheme's access delay gain becomes larger. Futhermore, even when the network traffic is very high it is possible to access satellite link within the delay similar to one round-trip delay. In addition to access delay performance enhancement, the new scheme has facility that supports fixed bandwidth reservation. So it shows more enhanced performance in the environment that stream traffic is dominant such as in VSAT communication environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.10
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• pp.2014-2027
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• 1994

A queueing model with two input streams of different service priorities is studied. Specifically, IBP+BP/D/1 with head-of-line priority is analyzed. IBP and BP stand for Interrupted Bernoulli Process and Bernoulli Process respectively. The BP-stream customers have the higher service priority over the IBP-stream customers. An exact analysis of this priority queue is presented to derive the distributions of the state of the system at steady state, the waiting time distributions for each class of customers, and the interdeparture time distributions. The numerical results of the analysis are presented to show how the various parameters of the low and high priority arrival processes affect the performance of the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1289-1295
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• 1999

본 논문에서는 스위치의 운용 알고리즘에 따라 시뮬레이션 프로그램을 이용하여 입/출력 버퍼의 셀 손실율을 측정하였다. 그 결과 셀 손실에 영향을 주는 요소로서, 셀 도착 간격 시간(k(a))과 SPEEDUP FACTOR(SF) en 가지 요소에 따라 셀손실을 평가할 수 있음을 알 수 있었다. 셀 도착 간격 시간 혹은 주기성은 비트가 셀로 모이는데 걸리는 시간을 의미하며 스위치 속도 SF는 임의의 한 슬롯내에서 한 입력단에서 출력단으로 서비스 가능한 셀의 수를 나타내고 있다. 시뮬레이션의 결과에서 보면 입력 버퍼에서는 주지성에 따라, 출력 버퍼에서는 SF의 크기에 따라 셀손실율이 커진다는 사실을 알 수 있었다. 따라서 보다 정확한 고속 스위칭 향상을 위해서는 입/출력 버퍼의 크기 결정이 중요하다. 본 논문의 시뮬레이션 결과에서는 입력 버퍼가 100x셀 일 때 출력 버퍼가 40x셀 정도의 크기가 적합하다는 것을 얻어내었다. 물론 입/출력 버퍼를 크게 한다면 셀 손실이 작아지지만, 하드웨어를 구성하는데 문제점이 발생될 것이기 때문이다. 그리고 본 논문 결과치중 셀 도착 분포 상황은 변동계수 모델링 성정에 따라 SF가 처리하는 서비스의 셀 도착 분포에 의 \ulcorner달라지지만, 변동계수가 전혀 없는 이상적인 경우(CV=1)를 제외한 경우의 SF값을 만족한다고 하겠다. 끝으로 입/출력 버퍼를 가진 스위치 구조는 단지 출력 버퍼를 갖는 스위치 보다 지연이 크지만, VLSI의 발달로 셀의 처리 속도가 증가하므로 더 많은 장점을 갖게 될 것이다.

• Journal of Korean Institute of Industrial Engineers
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• v.28 no.2
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• pp.139-146
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• 2002

The third generation mobile communication needs to provide multimedia service with increased data rates. Thus an efficient allocation of radio and network resources is very important. This paper models the 'burst switching' as an efficient radio resource allocation scheme and the performance is compared to the circuit and packet switching. In burst switching, radio resource is allocated to a call for the duration of data bursts rather than an entire session or a single packet as in the case of circuit and packet switching. After a stream of data burst, if a packet does not arrive during timer2 value ($\tau_{2}$), the channel of physical layer is released and the call stays in suspended state. Again if a packet does not arrive for timerl value ($\tau_{1}$) in the suspended state, the upper layer is also released. Thus the two timer values to minimize the sum of access delay and queuing delay need to be determined. In this paper, we focus on the decision of $\tau_{2}$ which minimizes the access and queueing delay with the assumption that traffic arrivals follow Poison process. The simulation, however, is performed with Pareto distribution which well describes the bursty traffic. The computational results show that the delay and the packet loss probability by the burst switching is dramatically reduced compared to the packet switching.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.3
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• pp.416-420
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• 2002

Traditional queueing analyses are very useful for designing a network's capacity and predicting there performances, however most of the predicted results from the queueing analyses are quite different from the realistic measured performance. And recent empirical studies on LAN, WAN and VBR traffic characteristics have indicated that the models used in the traditional Poisson assumption can't properly predict the real traffic properties due to under estimation of the long range dependence of network traffic and self-similarity In this parer self-similar characteristics over statistical approaches and real time network traffic measurements are estimated It is also shown that the self- similar traffic reflects network traffic characteristics by comparing source model.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.6
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• pp.1158-1168
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• 1994

The paper proposes a distributed control self-healing algorithm for a line failure to improve the restoration time. This proposed self-healing algorithm acquired the fast restoration time by reducing the number of control messages and the queueing delay. And the reduction of queueing delay was attained by the ASC_NULL(Available Spare Channel_NULL) message which informs neighbor nodes that a source node has no available spare channel to reduce the waste of time during the rerouting. It is difficult for this proposed self-healing algorithm to be compared with other self-healing algorithms, because each self-healing algorithm has different simulation conditions. So, the performance of the proposed self-healing algorithm was compared with only NETRATS(NETwork Restoration Algorithm for Telecommunication Systems). The results of the simulation showed that the proposed self-healing algorithm was better than NETRATS in the restoration time.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.5C
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• pp.435-444
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• 2002

In this paper, a novel packet scheduling algorithm, so-called the CSL algorithm is discussed, whereby the firewall property as well as the deterministic delay bound guarantee are supported in session level. Lots of simulation studies validate those properties of the CSL algorithm. The CSL algorithm is distingushable from the well- known EDD scheme in terms of the firewall property. Regarding the implementation complexity, the CSL algorithm turns out to be of 0(1) besides the sorting overhead. Owing to the maintained generic fair queueing structure in the CSL algorithm, a various fair queueing schemes can be applied with minor modification. For the TCP/IP network which is vulnerable to the misbehaving traffic sources, the firewall property of the CSL algorithm is quite useful for the advanced quality of services.

• Journal of the Korea Society for Simulation
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• v.16 no.2
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• pp.75-81
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• 2007

Previous queue inference has been studied with some limits. Larson's inference engine, which is the basis for this paper, also processed with basic assumption that arrival process is poisson process. Our inference method, which relaxes the poisson process assumption, must be a useful tool for looking into unobservable inside of queueing systems, as well as calculating accurate system performance. This paper employs these inference methods and proves the validity. Then we apply this method to system analysis for more complicated models. At first, we suggest methods to system with known number of servers, then expand to unknown number of servers. For validating our inference approach, we run some simulation models and compare true values with our results.