Nonlinear performance evaluation model for throughput of AQM scheme using full factorial design approach

The performance of active queue management (AQM) is measured in terms of throughput, delay, queue size, and loss rate. We have carried out the optimized performance measure of throughput for AQM scheme random early detection (RED) using full factorial design (FDD) technique that is a new approach of performance analysis particularly for congestion control algorithms. We have considered the input factors, viz, buffer size, maximum threshold, and the number of file transfer protocol (FTP) sources for the evaluation of RED that can be used for other AQM schemes, viz, adaptive RED, three‐section RED (TRED), and adaptive queue management with random dropping (AQMRD). The effect of each input factor as well as their interactions are evaluated using factorial design technique that results to obtain the nonlinear equation for performance measure in terms of input factors buffer size, maximum threshold, and the number of FTP sources. Finally, we show the contour plots for variation of performance measure throughput (steady state) from minimum to maximum values with respect to the different setting of input parameters.     

A resilient buffer allocation scheme in active queue management: a stochastic cooperative game theoretic approach

During the last decade, a plentiful number of active queue management schemes have been proposed, but their main objectives are simply allocating the buffer resource to all flows evenly, or protecting responsive flows from being degraded by unresponsive flows. However, the sending rates of the responsive flows can be determined diversely, and not all unresponsive flows have aggressively high sending rates. Furthermore, it is rational to reserve a portion of the buffer resource for certain privileged traffic. Grounded by these evidences, in this paper, we present a resilient active queue management algorithm, named Prior‐Core‐based Buffer Allocation considering diverse congestion control algorithms, fair‐unresponsive flows, and some privileged traffic. Our approach is based on stochastic cooperative game theory, where the payoffs yielded by cooperation are described by random variables, and the core is defined only over the distribution of these random payoffs; the core in this situation is called the prior‐core. As a result, it is shown that our buffer allocation, yielded by the prior‐core, achieves completely fair allocation for those flows whose requirement does not exceed the fair‐share regardless of the responsiveness, whereas aggressive flows are restricted according to availability of the buffer; all these are verified through ns‐2 simulation experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

基于消息队列的通信系统异步传送控制仿真

传统方法对通信系统异步传送控制效果不佳,存在信号干扰及传送时间间隔较长等问题。为此引入消息队列技术,提出一种新的传送控制方法来解决以上问题。对通信系统的空时信道进行空时编码设计,实现空时信道的编码增益与分集增益;利用空时编码实现通信系统中继节点的空间分集,根据空间分集结果制订异步空时传送方案;采用消息队列技术构建通信系统异步传送控制模型,实现通信系统的异步传送控制。为了验证所提方法异步传送控制效果,设计对比实验。实验结果表明,上述方法的传送时间间隔较短,抗干扰能力强,平均分集增益高,说明所提方法更适用于通信系统的异步传送控制。     

NoC中负载均衡的AVOQ路由器设计

针对片上网络中使用虚拟输出队列(VOQ)机制的路由器在网络拥塞时存在的头阻塞问题,提出负载均衡的AVOQ路由器架构。首先,输入缓冲区仍使用VOQ机制来处理头阻塞问题。其次,在路由计算模块自适应地选择输出端口,确保数据从较不拥塞的端口输出;在单个虚通道内自适应地读取数据包,确保下游不拥塞的流量能够在网络里流通。实验结果表明,相较于虚通道路由器和VOQ路由器,AVOQ路由器平均延时最多减少83.2%和57.1%,吞吐率最多增加72.7%和33.3%,功耗和面积开销可接受。该方案通过两个层级的自适应均衡全网的流量分布,缓解拥塞,进而降低头阻塞出现的可能性,并在头阻塞出现时消除其影响,提升网络性能。     

基于不可靠通信链路的数据共享模块

随着企业规模的逐步扩大和计算机网络与企业信息技术的飞速发展，大中型企业陆续建立了很多业务系统，对各个系统之间数据同步的安全性提出了更高的需求。针对此需求，基于RabbitMQ消息队列中间件，本文设计并实现基于不可靠通信链路的数据共享模块，解决在企业内部两级数据中心之间的双向数据同步问题，并通过RabbitMQ的消息确认机制和持久化机制，保证数据的安全送达、无丢失。经过实践证明，该数据共享模块功能稳定，可提高两级数据中心的数据传输效率并保证其安全性。     

连续时间完全服务与门限服务两级轮询系统性能研究

在信息分组以连续时间规律到达系统的基础上，对于轮询系统中不同优先级的业务问题，提出区分优先级的两级轮询服务模型。首先，在该模型中，低优先级站点采用门限服务，高优先级站点采用完全服务；然后，在高优先级转低优先级时，将传输服务与转移查询并行处理来降低服务器在查询转换期间所耗费的时间，提高轮询系统的效率；最后，运用马尔可夫链和概率母函数的方法建立了系统的数学模型，通过对数学模型精确解析，得到了连续时间两级服务系统每个站点的平均排队队长和平均等待时间的表达式，精确解析出平均排队队长和平均等待时间的值。仿真实验结果表明：理论计算值与实验仿真值近似相等，说明理论分析正确合理。该模型既能保障低优先级站点服务质量，又能为高优先级站点提供优质服务。     

Optimal assignment of human resources for maintenance departments using fuzzy queuing systems

Maintenance-related costs are one of the main components of overhead costs and constitute an important part of a product’s actual cost. Therefore, making proper efforts to reduce and optimise maintenance costs could be one way of gaining competitive advantages. A major part of maintenance-related costs is the salaries paid to the workforce in the maintenance department. This paper seeks the optimal assignment of human resources to the maintenance department to reduce the related costs. First, we model the maintenance department using fuzzy queue models. Then, a cost function is proposed which includes the costs of workforce shortage and workforce overload. The optimal size of workforce is obtained by considering different numbers and choosing the one which minimises the total costs. Some parameters are fuzzy outputs of the queue models, which make fuzzy results of the cost function. In order to find the minimum fuzzy cost function, we use Lee and Li fuzzy ranking method. Finally, our model is tested in a spiral-tube company and a sensitivity analysis is performed.     

Performance evaluation of a transportation-type bulk queue with generally distributed inter-arrival times

This paper is motivated by the performance evaluation of circulating vertical conveyor systems (CVCSs). CVCSs are bulk queues of transportation type. These material handling systems feature generally distributed inter-arrival times, which can be longer than the bulk service time. This leads to interdependencies between the number of arrivals in consecutive service intervals and the number of loads in the queue. We propose a new discrete-time approach for the steady-state analysis of such bulk service queues of transportation type with general arrival and service processes and finite server and limited queue capacities. The approach is based on a finite Markov chain that generates complete probability distributions for the key performance measures, including the queue length, waiting time and departing batch size. The proposed approach is exact in the cases of discrete-time slots, e.g. as in communication systems. We investigate the discretisation error that arises if the approach is used as an approximation for the continuous time using a numerical comparison to a discrete-event simulation. Moreover, we examine the impact of arrival stream variability on the system performance and compare the positive effects of a higher frequency of server visits with the effects arising from larger pickup capacities.     

The approximation analysis of the discrete-time Geo/Geo/1 system with additional optional service

This paper analyses a discrete-time Geo/Geo/1 queueing system, where all arriving customers demand the first essential service and some of them may further demand an additional optional service. The interarrival times, the service times of the essential service and the second optional service for arrivals are assumed to be random variables with Geometric distributions. Such a model has potential applications in computer or digital communication network systems. We model this system by the level-dependent and independent quasi-birth-death processes and develop efficient computation algorithms of the stationary distribution of the number of customers in the system using matrix analytic method. A cost model is derived to determine the optimal values of the two different service rates simultaneously at the minimal total expected cost per unit time. Illustrative numerical examples demonstrate the optimization approach.     

基于令牌漏桶法的数据记录技术

针对实时系统记录数据会引起系统运行速度缓慢、瘫痪、甚至＂死机＂的问题,提出了具有特色的令牌漏桶法。该方法通过创建循环队列数据池并根据数据池的数据量适时发放令牌和拥有令牌的任务自动选择CPU空闲时执行等技术实现。通过试验验证,在保证整个系统实时性、可靠性的前提下,该方法实现了实时记录数据的功能。