基于扩充的GIX/M/1/N排队系统的主动队列管理算法性能评价模型

为了评价主动队列管理(AQM Active Queue Management)算法的性能,通过在标准的排队系统GIX/M/1/N中嵌入主动队列管理(AQM)算法的方法,建立了一个扩充的GIX/M/1/N排队系统。利用该扩充的GIX/M/1/N排队系统和Internet业务流量自相似性的特征,提出了一种评价AQM算法在非响应业务流量下的性能的分析方法,并据此评价了TD,RED,GRED和Adaptive RED等4个经典的AQM算法。为了验证该分析方法的合理性,利用NS2进行了一系列的仿真实验。结果表明,该分析方法所得结果与仿真实验所得结果一致,因此该分析方法能用于评价AQM算法的性能。     

改进的排队系统三阶段法及其仿真

通过对M/M/C/N/∞排队模型下机场排队场景的分析,提出运用三阶段法仿真策略设计仿真系统时,用于处理由于附加条件限制使B类事件变为C类事件的规则,同时对已有的三阶段仿真流程进行改进,使三阶段法仿真描述更加清晰,设计更容易。利用C#.NET和LINQ（Language IntegratedQuery）语言实现该三阶段法排队仿真系统,将TPA排队仿真系统中参数设置成track≥1,queue≥1,就可以输出任何M/M/C/N/∞排队系统的仿真结果,最后对仿真结果进行简单的分析。     

基于CPN的空竭服务单重休假M/G/1型排队系统建模与分析

空竭服务单重休假M/G/1型排队系统是经典排队系统的推广,在许多领域有着广泛的应用.到目前为止对其的处理方法还都是建立在概率论和数理统计的基础上,运用马尔可夫随机过程求解,推导十分复杂,没有直观的模型描述.因此,利用着色Petri网对空竭服务单重休假M/G/1型排队系统进行建模,并对主要性能指标进行仿真分析是迫切以及可行地.仿真软件选用CPNTools[1],仿真结果证明该方法具有较高的精确度以及实用价值.     

码头装卸服务G／M／1排队模型及仿真研究

研究码头装卸仿真服务系统,M/M/1排队模型有严格的理论条件,在工程应用中对不满足理论条件的情况,模型分析结果的准确性会受到影响。为提高控制序列的准确性,提出了等间隔到达和随机到达的混合序列到达时间间隔概率分布,假定该混合到达顾客到达时间间隔相互独立同分布,采用G/M/1排队模型得出了排队服务系统的系统参数。编写MAT-LAB仿真程序,结合实例比较了G/M/1与M/M/1模型分析结果和仿真结果,表明比M/M/1模型能更准确地描述系统的各项参数,结果证明可为排队系统设计提供参考依据。     

基于超爱尔兰分布的自相似网络排队模型研究

现有网络的业务流研究表明,多种通信业务中普遍存在自相似特性,但是如何对自相似业务流进行建模和分析一直是个难解问题。基于超爱尔兰拟合算法,建立了到达为泊松分布,服务时间为超爱尔兰分布的M/HErD/1/K自相似排队模型,推导得到呼叫损失概率、平均排队队长等排队性能的解析解。在实际业务环境下和传统的M/M/1/K排队模型进行了仿真对比,结果表明M/HErD/1/K模型不仅可有效表征业务流的快挂业务特性,而且能仿真出该网络在业务负荷较重时潜在的运营风险,对实际网络运营管理具有重要的指导作用。     

大型M/P/C/C排队系统仿真研究

理论上推测Erlang B 公式对服务时问为任意分布的M/G/C/C系统的呼叫损失概率是有效的但缺乏严格证明.据此,对服务时间呈 Pareto 分布的M/P/C/C排队系统的仿真问题进行了研究,特别是对排队系统中服务装置数目很大的情况进行了研究.采用一种名为红黑树的数据结构较好地解决了超长序列、超大C值所造成的计算时间问题,并采用基于事件驱动的时间调度法进行排队仿真,结果与 Erlang-B 公式相符.表明Erlang B公式对M/P/C/C系统的呼叫损失概率是有效的.为采用仿真方法对自相似流下的网络性能进行深入研究打下了基础.     

基于排队网络的流水线模拟器任务缓存新分析模型

流水线软件模拟器是嵌入式微处理器软件仿真系统的关键技术,提出对嵌入式微处理器流水线仿真系统的排队网络建模与缓存大小分析方法.对SPARC-V8流水线模拟器建立M/M/1/N型排队网络模型,分析指令到达及服务阻塞机制.为了解决模型计算中的阻塞问题,在排队网络模型中增加“保持节点”,得到扩展的等价排队网络模型.采用近似计算迭代算法,得到系统性能评价指标,并建立排队网络节点性能关系曲线,确定各功能模块的任务缓存大小.根据得出的任务缓存计算值设置流水线软件模拟器实际缓存大小,实验表明模型计算数据与实际运行数据基本一致.该评价方法对嵌入式微处理器流水线仿真系统的建模与性能分析具有重要的指导意义.     

网络分组交换中的排队论模型分析

排队论模型在计算机网络通信系统中具有广泛应用,如评价网络性能,设计计算机网络等。作者通过对M/M/l和M/D/1模型的深入分析,得出了M/G/1模型中的最佳排队系统模型。     

网络分组交换中的排队论模型分析

排队论模型在计算机网络通信系统中具有广泛应用,如评价网络性能,设计计算机网络等.作者通过对M/M/1和M/D/1模型的深入分析,得出了M/G/1模型中的最佳排队系统模型.     

基于仿真模型的集装箱码头排队系统分析

基于Witness仿真软件建立了集装箱码头桥吊服务系统的排队系统仿真模型,通过对M/M/m排队系统参数分析,发现随着服务台数量的增大,排队系统的性能逐渐变好。各指标的变化曲线存在拐点,拐点之后变化幅度不再明显,此拐点对应的x坐标值就是桥吊配置数量的最佳值。通过对比不同排队模型进行仿真分析,认为集装箱码头桥吊服务系统的M/M/m排队系统的工作能力和效率都更高,且性能更容易改善。研究结果对码头其它节点的排队系统的分析也有参考价值。     

On approximating the generalized occupancy of the G/M/K queueing system

The G/M/K is one of very few multiserver queueing systems for which analytical results exist. In 1951 Kendall [4] showed how to compute the steady-state probabilities of a G/M/K queueing system. Later, Takacs [6] suggested an iterative procedure for the evaluation of a needed component in Kendall's scheme; namely, the generalized occupancy ω^*. However, Takàcs' algorithm requires the computation of a general integral for each of its interations.In this paper we propose a simple and explicit approximation for the generalized occupancy of the G/M/K system. Several numerical results are also included.     

Control Policies of an M/G/1 Queueing System with a Removable and Non-reliable Server

This paper considers a single non-reliable server in the ordinary M/G/1 queueing system whose arrivals form a Poisson process and service times are generally distributed. We also study a single removable and non-reliable server in the controllable M/G/1 queueing systems operating under the N policy, the T policy and the Min( N , T ) policy. It is assumed that the server breaks down according to a Poisson process and the repair time has a general distribution. In three control policies, we show that the probability that the server is busy in the steady-state is equal to the traffic intensity. It is shown that the optimal N policy and the optimal Min( N , T ) policy are always superior to the optimal T policy. Sensitivity analysis is also investigated.     

Markovian queueing systems with retrials and heterogeneous servers

The asymptotic performances of a random access and an ordered entry G/M/K/Oqueueing system with a stationary counting arrival process, K heterogeneous parallel servers, no waiting room and retrials are approximated based on a two-parameter method. In a random access system, units upon arrival are randomly assigned to one of the servers. In an ordered entry system, servers are indexed from 1 to K, and units first arrive at server i and if the server is found to be busy, those units arrive at server (i + 1), for i = 1 to K − 1. In both queueing systems, if units are not processed by one of the servers, those units are not lost, instead they retry to receive service by merging with the incoming arrival units.

To approximate the asymptotic performance of the above queueing systems, a recursive algorithm is suggested, and appropriate performance measures are presented to be used as comparison criteria at the design stage. Furthermore, numerical results are provided and approximation outcomes are compared against those from a simulation study.     

The complete analysis of the discrete time finite DBMAP/G/1/N queue

A comprehensive analysis of the DBMAP/G/1/N queueing system for both the “arrival first” and “departure first” policies is given including detailed proofs and latest results on an algorithmic recipe to compute the z-transform of the waiting time probability function as well as the probability function itself. Additionally, expressions for the probability of simultaneous arrivals and departures and an algorithm to compute them are presented for the first time. The framework presented allows dealing with a superposition DMAP+DBMAP as an input process. For both streams in the superposition, per stream waiting time probability functions are given for the case of a deterministic service time, which is relevant for the modeling of ATM networking (both wired and wireless). Together with findings for the continuous time case, this paper completes the insights into finite queueing systems of the M/G/1-type. In comparison with the method of the unfinished work, which can be used to analyze finite queueing systems with deterministic service-time only and, besides other semi-Markovian input processes, with the DBMAP as an input, the M/G/1-paradigm provides much faster algorithms to compute loss probabilities and waiting time moments, due to the smaller system matrix. Note that the D[B]MAP has proved a versatile stochastic process, which can also be tuned to represent periodic correlation functions and not only geometrically decaying ones.     

Regulating an M/G/1 queue when customers know their demand

Customers do not necessarily join a queue at a socially optimal rate. Hence, queueing systems may call for regulation. For customers in an M/G/1 unobservable (not necessarily FCFS) queue and homogeneous with respect to waiting costs and service rewards, we show how queueing systems can be regulated by imposing an entry fee, a holding fee (based on time in the system), or a service fee (based on the required service time) when customers know their service requirements. We start with a unified approach and state the socially optimal fees. We show that customers are always worse off under a flat entry fee in comparison with holding and service fees. As for holding vs. service fees, the answer depends on the queueing regime and/or the service length itself. For example, under FCFS, service fees are preferred by all. Details are given on some common service regimes. We also review the case where customers know only the common distribution of service times, but not their actual requirements.     

基于非饱和负载的802.15.4网络能耗分析

为了优化802.15.4 MAC协议能耗性能,提出了一种基于退避时提前休眠的时隙CSMA/CA机制,并建立了该协议的Markov链模型。然后使用M/G/1排队系统理论对非饱和网络负载建模,并对协议主要参数进行了数学推导。最后基于该模型对网络节点能耗进行数值分析。理论分析和仿真结果表明,该模型较好的描述基于非饱和负载的802.15.4 MAC协议,网络节点能耗得到有效改善。     

窄带Ad hoc网络端到端拥塞控制机理分析

基于窄带半双工信道的军用无线网络限制了ACK反馈信息的及时性和有效性,使得单程时延和交付概率等端到端传输指标成为发现网络拥塞的有效途径。利用M/G/1模型的排队方法分析和揭示了无线自组织网络中节点拥塞程度、链路层参数以及业务层面的性能参数之间的量化关系,从而为窄带无线自组织网络的拥塞控制协议设计提供了理论依据。     

Performance modelling of an integrated assembly line system with inspection stations and finite capacity local storages; an approximation algorithm

To control the bottleneck in a flexible assembly line system consisting of a set of tandem flexible workstations, a set of automated inspection stations, a loading station, and an unloading station, linked by a material handling system, a perturbation (e.g., parametric) approach is presented. The performances of each workstation and each transporter station have been modelled by compatible finite capacity G/M/I queueing systems with generally distributed inter-arrival time, a single Markovian processer, and the first-come-first-served queueing discipline. Finally, an example is presented and the relative accuracy of the proposed approximation algorithm is investigated by a simulation study     

A conservation law for G/G/m queueing systems

Summary Conservation laws are useful in the investigation of physical systems. There exists a special conservation law for priority queueing systems: a preferential treatment given to one class of jobs is afforded at the expense of other jobs. This fundamental relationship has been proved previously for G/G/1 queueing systems. In the present paper the conservation law is extended to G/G/m queueing systems and a useful application of this extension is given.     

Analysis of a G/M/K/O queueing loss system with heterogeneous servers and retrials

Consider a G/M/K/O queueing loss system with K heterogeneous servers, exponentially distributed service times, no waiting room, a stationary counting arrival process, and an ordered entry. The ordered entry rule implies that, if the servers are indexed from 1 to K, units first arrive at the first server, then at the second server, and finally at the Kth server. In this queueing system, units that find the servers busy are not lost. Those units re-try to receive service by merging with the incoming units to be reconsidered for service by one of the free servers. This queueing system is analysed in terms of approximating the flows of units inside the system by a two parameter method. An example is introduced and approximation results are compared with those from a simulation study.