A Non-Preemptive Priority Queueing System with a Single Server Serving Two Queues M/G/1 and M/D/1 with Optional Server Vacations Based on Exhaustive Service of the Priority Units

We study a vacation queueing system with a single server simultaneously dealing with an M/G/1 and an M/D/1 queue. Two classes of units, priority and non-priority, arrive at the system in two independent Poisson streams. Under a non-preemptive priority rule, the server provides a general service to the priority units and a deterministic service to the non-priority units. We further assume that the server may take a vacation of random length just after serving the last priority unit present in the system. We obtain steady state queue size distribution at a random epoch. Corresponding results for some special cases, including the known results of the M/G/1 and the M/D/1 queues, have been derived.

On One Model of Multichannel Queuing System with Unreliable Repairable Servers and Input Memory

The work deals with the development of analytical model of multichannel technical queuing system with unreliable servers and input memory where server failure flows and incoming request flows comply with Poissonian laws, while the flows of failed facilities repairs and flows of incoming requests comply with exponential laws of probability distribution. Random process of system change-over is a Markovian process with continuous time and discrete states. Relations binding basic parameters and output characteristics of the system indicated are obtained as probabilities of system staying in the given moment in one of the possible states. The proposed model is the most generalized compared to some models known in literature which could be considered as special cases of the considered model.

Unemployment Period Approach with Infinite Servers Queue Systems

With results on the infinite servers queue systems with Poisson arrivals - M｜G｜∞ queues - busy period, it is displayed an application of those queue systems in the unemployment periods time length parameters and distribution function study. These queue systems are adequate to the study of many population processes, and this quality is brought in here. The results presented are mainly on unemployment periods length and their number in a certain time interval. Also, some questions regarding the practical applications of the outlined formulas are briefly discussed.

Effects of Reneging, Server Breakdowns and Vacation on a Batch Arrival Single Server Queueing System with Three Fluctuating Modes of Service

This article examines the effects of reneging, server breakdown and server vacation on the various states of the batch arrivals queueing system with single server providing service to customers in three fluctuating modes. In this queueing system, any batch arrival joins the queue if the server is busy or on vacation or under repair. However, if the server is free, one customer from the arriving batch joins the service immediately while others join the queue. In case of server breakdown, the customer whose service is interrupted returns back to the head of the queue. As soon as the server has is repaired, the server attends to the customer in mode 1. For this queueing system, customers that are impatient due to breakdown and server vacation may renege (leave the queue without getting service). Due to fluctuating modes of service delivery, the system may provide service with complete or reduced efficiency. Consequently, we construct the mathematical model and derive the probability generating functions of the steady state probabilities of several states of the system including the steady state queue size distribution. Further, we discuss some particular cases of the proposed queueing model. We present numerical examples in order to demonstrate the effects of server vacation and reneging on the various states of the system. The study revealed that an increase in reneging and a decrease in server vacation results in a decrease in server utilization and an increase in server’s idle time provided rates of server breakdown and repair completion are constant. In addition, the probability of server vacation, the probability of system is under repair and the probabilities that the server provides service in three fluctuating modes decreases due to an increase in reneging and a decrease in vacation completion rates.

Customer Joining Behavior and Regulation Strategy in Visible Multi-Server Queues with Synchronous Vacations of Partial Servers

This paper studies customer joining behavior and system regulation strategy in nonexhaustive visible M/M/m queues with synchronous vacations of a part of the servers.Once this part of the servers are idle,they take multiple vacations simultaneously(vacation period).Until there are customers waiting in the queue,they are reactivated and all servers are busy or idle(busy period).The authors call this part of the servers as“partial servers”.In view of the fully visible queue and the almost visible queue,the authors obtain customers’equilibrium joining threshold strategies and their socially optimal joining threshold strategies,respectively,and observe that customer joining behavior in equilibrium generally makes the system overcrowded,which makes the equilibrium social welfare lower than the optimal social welfare.After regulation,interestingly,for optimizing social welfare,the system manager hopes not only customers arriving in vacation period pay attention to the number of partial servers,but also customers arriving in busy period should care about it rather than ignore.Moreover,arranging more servers for vacation does not necessarily lead to the decrease of social welfare on condition that the number of partial servers is close to m.As for the information advantage of the fully visible case,it is not obvious for increasing social welfare and even unfavorable to servers’profit unless the number of partial servers is big enough.Furthermore,given the different composition of social welfare,there exists the optimal number of partial servers and the optimal arrival rate of customers for maximizing social welfare.

THE QUEUE-LENGTH DISTRIBUTION FOR M^x/G/1 QUEUE WITH SINGLE SERVER VACATION

This paper studies the bulk-arrival M-x/G/1 queue with single server vacation. By introducing the server busy period and using the Laplace transform, the recursion expression of the Laplace transform of the transient queue-length distribution is derived. Furthermore, the distribution and stochastic decomposition result of the queue length at a random point in equilibrium are obtained. Especially some results for the single-arrival M/G/1 queue with single server vacation and bulk-arrival M-x/G/1 queue but with no server vacation can be derived directly by the results obtained in this paper.

AN M/G/1 RETRIAL QUEUE WITH SECOND MULTI-OPTIONAL SERVICE,FEEDBACK AND UNRELIABLE SERVER

An M/G/1 retrial queue with two-phase service and feedback is studied in this paper, where the server is subject to starting failures and breakdowns during service. Primary customers get in the system according to a Poisson process, and they will receive service immediately if the server is available upon arrival. Otherwise, they will enter a retrial orbit and are queued in the orbit in accordance with a first-come-first-served （FCFS） discipline. Customers are allowed to balk and renege at particular times. All customers demand the first “essential” service, whereas only some of them demand the second “multi-optional” service. It is assumed that the retrial time, service time and repair time of the server are all arbitrarily distributed. The necessary and sufficient condition for the system stability is derived. Using a supplementary variable method, the steady-state solutions for some queueing and reliability measures of the system are obtained.

THE TRANSIENT SOLUTION FOR M/G/1 QUEUEWITH SERVER VACATIONS

In this paper, the transient solutions for M/G/1 queues with single server vacation and multiple server vacations are firstly studied, and the recursion expressions of their Laplace transform are given. Further the distribution and stochastic decomposition result of the queue length at a random point in equilibrium are directly obtained from the transient solution. As will be seen this paper provides a intuitive and elegant method for studying transient solutions for M/G/1 queues with single server.

Appointment scheduling with customer impatience based on operating cost model

An appointment scheduling problem is studied with the consideration of customer impatience.On the assumption that both the time of leaving queue and the time of service are exponentially distributed,in order to minimize the joint cost,the optimal appointment schedule of the fixed number of customers is studied.The joint cost function is composed of customers expected delay time and service availability time.The expected delay time of each customer in the queue is recursively computed in terms of customer interarrival time.Furthermore,the effect of impatience on the optimal schedule as well as the total operating cost is studied.The results show that as the impatience rate increases,the optimal interarrival time becomes shorter and the interarrival time of the last few customers gradually approaches that of the customers in the middle.In addition,impatient behaviors can increase the joint cost.

Analysis of the WWW System Performance

A simple, high-level, open queueing network model is presented from which several general performance results for WWW server on the Internet are derived. Multiple-Server systems are also analyzed.A theoretical upper bound on the serving capacity of WWW server is defined. The effects of file size,server speed, and network bandwidth on response time are also investigated. In addition, the relative merits of several methods of improving server performance are evaluated.

On One Analytical Model of a Probability Estimation of Quality and Efficiency of Functioning of Complex Technical Queuing Systems

The work is dedicated to the development of analytical model of probability estimation of reliability, productivity, quality and efficiency of functioning of the complex technical queuing system consisting of the arbitrary number of marked groups of the service devises (channels, facilities, servers) differing with reliable characteristics (parameters of refusals and restorations) of forming their composition (also of arbitrary number) marked, identical, unreliable and restorable serving channels in which for serving come in requirements with intensities depending on marking of channels. In the considered system it is supposed that the currents of refusals of serving devices and currents of coming requirements are subdued to Poisson, and the currents of restorations of refused devices and the currents of services of coming requirements—exponential laws of distribution of probabilities. A stochastic process of transfers of a system by that is Markovian process with continuous time and discrete states. Correlations linking the basic parameters and exit characteristics of the systems of the pointed out type are obtained in a view of probabilities of the system location in the given moment of time in one of the possible states.

A Single Server Queue with Coxian-2 Service and One-Phase Vacation (M/C-2/M/1 Queue)

In this paper, we study a single server queueing system with Coxian-2 service. In Particular, we study M/C-2/M/1 queue with Coxian-2 service and exponential vacation. We assume that units (customers) arrive at the system one by one in a Poisson process and the server provides one-by-one service based on first in first out (FIFO) rule. We obtained the steady state queue size distributions in terms of the probability generating functions, the average number of customers and their average waiting time in the system as well as in the queue.

一种基于区块链的MQTT协议优化算法

通信协议的设计已然成为实现设备与互联网通信的重要支撑,其覆盖了整个物联网系统的各个环节。针对传统物联网协议中关键数据被伪造或篡改的安全问题,文章设计了一种在数据传输过程中使用区块链技术来保证传输数据安全的改进消息队列遥测传输(message queue telemetry transmission,MQTT)协议,进而保证了存储在broker的数据不被恶意篡改。通过仿真实验证明,该方法具有高效、轻量以及易实现等多方面的特点,在保护物联网的数据安全方面效果十分显著。

部分服务台同步多重休假的排队库存系统

本文研究了(s,S)库存策略的多服务台排队库存系统,其中库存为空时有部分服务台同步多重休假,休假时间服从指数分布。顾客到达为泊松过程,每个服务台的服务时间和补货时间均服从指数分布。利用拟生灭过程和矩阵几何解法,计算了系统稳态概率和一些性能指标,并给出了系统单位时间的平均费用函数。最后,通过数值算例分析了参数对费用函数的影响,并得到最优库存策略和最优平均费用。

具有耐烦服务员和N-策略的M/G/1可中断休假排队系统

考虑具有耐烦服务员和N-策略的M/G/1休假排队系统,其中服务员的假期可中断.运用全概率分解技术、更新理论和拉普拉斯变换工具,分析了系统的瞬态队长分布和稳态队长分布,获得了瞬态队长分布的拉普拉斯变换表达式和稳态队长分布的递推表达式,并进一步证明了稳态队长的随机分解性质.最后,通过建立费用结构模型,结合数值实例,讨论了使系统在长期单位时间内的期望费用最小的最优控制策略N*.

Python Server Page Performance Analysis and Modeling

Today, in the field of computer networks, new services have been developed on the Internet or intranets, including the mail server, database management, sounds, videos and the web server itself Apache. The number of solutions for this server is therefore growing continuously, these services are becoming more and more complex and expensive, without being able to fulfill the needs of the users. The absence of benchmarks for websites with dynamic content is the major obstacle to research in this area. These users place high demands on the speed of access to information on the Internet. This is why the performance of the web server is critically important. Several factors influence performance, such as server execution speed, network saturation on the internet or intranet, increased response time, and throughputs. By measuring these factors, we propose a performance evaluation strategy for servers that allows us to determine the actual performance of different servers in terms of user satisfaction. Furthermore, we identified performance characteristics such as throughput, resource utilization, and response time of a system through measurement and modeling by simulation. Finally, we present a simple queue model of an Apache web server, which reasonably represents the behavior of a saturated web server using the Simulink model in Matlab (Matrix Laboratory) and also incorporates sporadic incoming traffic. We obtain server performance metrics such as average response time and throughput through simulations. Compared to other models, our model is conceptually straightforward. The model has been validated through measurements and simulations during the tests that we conducted.

路径规划及信号灯控制的智能优化

由于全智能化的交通控制系统尚未得到完全普及,道路交通资源占用时空二维不够均衡、城市交通规划策略与通行车辆规模不够匹配,导致城市交通拥塞、车辆准点率低等问题。针对上述问题,首先构建了基于服务员休假的多队列多服务员排队模型和级联队列的多跳排队模型,分析了在十字路口处及一般道路情况下车辆流量、信号灯时长与通勤时延的理论关系;然后提出了基于近端策略优化的路径规划及信号灯控制的智能优化方法,通过动态感知城市实时交通拥塞状态,联合规划车辆最优路径和控制信号灯最优时长,从而最大化车辆准点率。仿真结果表明,所提方法比于自适应高效联邦对比方法在时延性能方面提升了3倍以上,在车辆准点率方面提升了18%左右。

WEB服务器集群系统中负载平衡的设计与实现

在In ternet和In tranet上,随着客户机数量和密集性任务的增加,单个W eb服务器受到处理能力的限制,已经成为网络访问的新瓶颈。如果W eb服务器集群系统具备高可用性和负载平衡性将成为解决这一问题的最佳方法。本文重点研究了服务器集群负载平衡的原理和实现技术。文中用排队论的方法分析集群系统的性能,通过对服务器负载性能数据的实时采集和对轻载服务器的周期性判决做到动态的负载平衡。测试结果表明,本文提出的负载平衡方法应用于W eb服务器集群系统中,其吞吐量提高了30%以上。

分布式系统中异地数据库的数据一致性维护

大型分布式系统通常需要在异地的数据库中存储同一数据的不同副本,不同副本之间需要维护数据的一致性。文章讨论了维护数据一致性的两种方法:消息队列法和复制控制法,并分别介绍了使用IBMMQSeries消息队列和MicrosoftSQLServer复制机制来维护数据一致的实现过程,对比分析了二者在实际应用中各自的特点,以及在理论上的技术差异。