Stochastic bounds for queueing systems with limited service schedules

Motivated by the study of cyclic service queue processor schedules and token ring local area networks, upper and lower stochastic bounds for a GI/G/1 vacation model with limited service are developed. The limited service vacation model is compared with the Bernoulli schedule vacation model. For the case of Poisson arrivals and infinitely divisible vacation durations simple, closed-form expressions are given for upper and lower bounds of the first two moments of the waiting time. Some upper and lower bounds are also derived for cyclic queues with limited service. The quality of the bounds is illustrated through numerical examples.     

Adaptive control of service in queueing systems

We consider the service-rate selection problem in an M/G/1 queueing system with unknown arrival rate and average cost criterion. An optimal adaptive policy is determined using recently developed results on parameter estimation and adaptive control of semi-Markov processes.     

Queueing systems with service interruptions: An approximation model

We present a single queueing model which can be used to analyse queueing systems with service interruptions. The model is based on a diffusion approximation using an instantaneous return process which reflects the particular queueing system under consideration. Applications to queueing systems with preemptive resume priority and breakdowns are given in this paper as well as numerical results showing the accuracy of the approximation.     

An approximation method for a class of queueing systems

We consider a queueing system with an ordered hunt. Specifically, we consider a communication system in which messages arrive at a node that has n output links numbered 1,…,n, and an arriving message is processed by the lowest numbered idle link. Obtaining such steady-state parameters as the expected delay of an arbitrary message and the utilization factor of each link requires knowledge of the complete state space of the system and the solution of 2ⁿ linear equations. In this paper we develop a method of computing the approximate values of these parameters without the need for the knowledge of the complete state space and the solution of 2ⁿ linear equations.     

Structured priority queueing systems with applications to packet-radio networks

In this paper we investigate a certain class of systems containing dependent discrete time queues. This class of systems consists of N nodes transmitting packets to each other or to the outside of the system over a common shared channel, and is characterized by the fact that access to the channel is assigned according to priorities that are preassigned to the nodes. To each node a given probability distribution is attached, that indicates the probabilities that a packet transmitted by the node is forwarded to one of the other nodes or to the outside of the system.

Using extensively the fact that the joint generating function of the queue lengths distribution is an analytic function in a certain domain, we obtain an expression for this joint generating function. From the latter any moment of the queue lengths and also average time delays can be obtained.

The main motivation for investigating the class of systems of this paper is its applicability to several packet-radio networks. We give two examples: The first is a certain access scheme for a network where all nodes can hear each other, and the second is a three-node tandem packet-raido network.     

A DFO technique to calibrate queueing models

A crucial step in the modeling of a system is to determine the values of the parameters to use in the model. In this paper we assume that we have a set of measurements collected from an operational system, and that an appropriate model of the system (e.g., based on queueing theory) has been developed. Not infrequently proper values for certain parameters of this model may be difficult to estimate from available data (because the corresponding parameters have unclear physical meaning or because they cannot be directly obtained from available measurements, etc.). Hence, we need a technique to determine the missing parameter values, i.e., to calibrate the model.As an alternative to unscalable “brute force” technique, we propose to view model calibration as a non-linear optimization problem with constraints. The resulting method is conceptually simple and easy to implement. Our contribution is twofold. First, we propose improved definitions of the “objective function” to quantify the “distance” between performance indices produced by the model and the values obtained from measurements. Second, we develop a customized derivative-free optimization (DFO) technique whose original feature is the ability to allow temporary constraint violations. This technique allows us to solve this optimization problem accurately, thereby providing the “right” parameter values. We illustrate our method using two simple real-life case studies.     

Analysis on queueing systems with synchronous vacations of partial servers

We study an M/M/c queue with server vacations. In this queueing system, d (≤c) of c servers take synchronous vacations when these d servers become idle at a service completion instant. This type of queueing model captures the major characteristics of a stochastic service system which processes both random arriving jobs and constantly available jobs. In this paper, the multi-server vacation queueing system has been analyzed as a quasi-birth and death process. Using matrix geometric method, we obtain the stationary distributions of queue length and waiting time and demonstrate the conditional stochastic decomposition property of the queue length and waiting time in this system.     

Approximate solution to multichain queueing networks with state dependent service rates

An approximation scheme for solving non-product form queueing networks with multiple chains and state dependent service rates is described. Estimates of the steady state probability distribution are obtained using less computational requirements than the standard solution techniques.The approximation scheme is based on a property called chain conditional balance, which leads to a decomposition of the global balance equations into smaller sets of equations. A technique for combining conditional distributions is examined and used to combine the solutions of conditional balance equations into the final estimates. Expressions for the storage and computational requirements of the approximation algorithm are given and an example is provided.An error analysis is described in which the approximation is tested on a large number of randomly generated queueing networks. The experimental results indicate that the approximation yields good estimates of the steady state distribution, as well as several important performance measures of these networks.     

Performance comparison of some discrete service time systems

This paper analyzes and compares the slotted time operation and the non-slotted time operation of a singleserver system with deterministic service time. These two operations are commonly used to model discrete service time systems in computer or digital communications. But due to the similarity in their operations and performance, the two models may be mixed up with each other. This paper examines by means of queueing analysis the performance of a few classes of systems that differ in the service order of their customers. The means and variances of the queue lengths, waiting times and interdeparture times of FCFS systems using the slotted time operations are first obtained from their respective LST and generating function equations. These are then used for comparison with those in non-slotted time systems. The results show that although the slotted time operation in the FCFS systems can be approximated by the non-slotted time operations under heavy traffic condition, the performances under other regions and service disciplines (e.g., the LCFS and the priority systems) may deviate significantly. They must be properly adjusted if one wishes to use the simpler equations of the non-slotted time operations to approximate the slotted time operations. The comparison graphs provided in this paper supply adjustments guidelines for the careful designers.     

An analytical model for delivery evaluation of multimodal contents in pervasive computing

Recent advance of mobile and interactive devices, such as smart phones, PDAs, and handheld computers, enables to deliver multimodal contents based on users and their environments. In pervasive computing, multimodal contents are mainly composed of multiple components which are often delivered from distributed multiple sources. Therefore, how appropriate contents can be provided to users and how computing resources can be effectively exploited are critical issues. In this paper, an analytical model for multimodal contents is developed based on a queueing theory for the purpose of delivery evaluation of the contents. The model can be applied to estimate how delivery parameters of multimodal contents, such as arrival rates, drop rates, and the number of packets, can impact overall the quality of services in terms of temporal aspects. A numerical example of weather information delivery is provided to illustrate the effectiveness of the proposed model.     

基于ITIL的高校IT服务管理模型

高校信息化实践过程中普遍存在着"重建设、轻应用、轻管理"的现象,已经严重影响了信息化的建设效果。解决此问题的关键途径是建立一套IT服务管理体系。本文结合ITIL理论和中国大学的实际情况得出了高校IT服务管理的组织模型、流程模型、技术模型。     

An enhanced algorithm to solve multiserver retrial queueing systems with impatient customers

The homogenization of the state space for solving retrial queues refers to an approach, where the performance of the M/M/c retrial queue with impatient customers and c servers is approximated with a retrial queue with a maximum retrial rate restricted beyond a given number of users in the orbit. As a consequence, the stationary distribution can be obtained by the matrix-geometric method, which requires the computation of the rate matrix. In this paper, we revisit an approach based on the homogenization of the state space. We provide the exact expression for the conditional mean number of customers based on the computation of the rate matrix R with the time complexity of O(c). We develop simplified equations for the memory-efficient implementation of the computation of the performance measures. We construct an efficient algorithm for the stationary distribution with the determination of a threshold that allows the computation of performance measures with a specific accuracy.     

A novel algorithm for performance prediction of web-based software systems

Performance metrics can be predicted with appropriate performance models and evaluation algorithms. The goal of our work is to adapt the Mean-Value Analysis evaluation algorithm to model the behavior of the thread pool. The computation time and the computational complexity of the proposed algorithm have been provided. The limit of the response time and the throughput sequences computed by the novel algorithm has been determined. It has been shown that the proposed algorithm can be applied to performance prediction of web-based software systems in ASP.NET environment. The proposed algorithm has been validated and the correctness of performance prediction with the novel algorithm has been verified with performance measurements. Error analysis has been performed to verify the correctness of performance prediction.     

系统通信模型执行性研究

针对可执行体系结构中系统数据交换是如何最终落实到具体的通信网络或设备,并进行具体数据传输问题,提出了系统通信模型执行方法.该方法描述了系统通信模型具有的基本元素及相关属性、模型元素之间的关系和表示,阐述了系统通信模型与系统接口描述模型、系统数据交换描述以及系统状态转移/系统时序图之间的关系,说明了系统功能驱动系统数据交换的具体步骤以及系统通信模型执行的过程.系统通信模型的执行使系统体系结构模型在整体上形成一个内在的一致性执行体,充实并完善了可执行体系结构,为可执行体系结构的执行奠定基础.     

RRM: An incentive reputation model for promoting good behaviors in distributed systems

Reputation systems represent soft security mechanisms that complement traditional information security mechanisms. They are now widely used in online e-commerce markets and communities in order to stimulate good behaviors as well as to restrain adverse behaviors. This paper analyzes the limitations of the conversational reputation models and proposes an incentive reputation model called the resilient reputation model （RRM） for the distributed reputation systems. The objective of this reputation model is not only to encourage the users to provide good services and, therefore, to maximize the probability of good transaction outcomes, but also to punish those adverse users who are trying to manipulate the application systems. The simulation results indicate that the proposed reputation model （RRM） could effectively resist against the common adverse behaviors, while protecting the profits of sincere users from being blemished by those adversaries.     

An norm-driven state machine model for CSCW systems

In order to improve the feasibility of the CSCW systems, we utilize the methods in organizational Semiotics and put forward the organizational model and the organizational state machine (OSM) to describe the norms in the systems. According to the general form of norm, we classify the norm into three kinds of rules expressed by the logical predications. Combining with cooperative theory and speech-act theory, we first propose an organizational relationship graph of role, behavior and rule of CSCW systems and then a logical predication-based model. This model is referred to as the organizational model that is used to describe the relationship graph. In addition, we present the OSM, which can check the logical conflict among the rules and insure semantic completeness. And the dynamical changes of rules and roles can be delineated exactly by the OSM.     

Developing a maturity model for service systems in heavy equipment manufacturing enterprises

Heavy equipment manufacturing firms are increasingly challenged by the integration of service planning and execution in their established product-centred information systems (IS) environment. Despite a few standardisation efforts, there is no common understanding of service systems in industry goods companies and the corresponding requirements for the appropriation of information systems. We address this need by developing a maturity model. The design of the model is grounded in extant literature, focus group and case study research involving eleven organisations over 1.5 years. The evaluation confirms that the maturity model makes a novel and useful contribution to the design of service systems.     

Expected service time model for a rotary parking system

This paper deals with rotary parking system. For retrieval and storage request, an expected service time model is developed based on the continuous Markov process. The validity of the model is illustrated through simulation studies.