Bound analysis for WRR scheduling in a statistical multiplexer with bursty sources

Among various cell scheduling schemes for ATM networks, weighted round‐robin (WRR) seems a promising algorithm for explicit bandwidth allocation [15]. In this paper, we present a method for analyzing a discrete‐time queueing model of a statistical multiplexer with contiguous slot assignments, deterministic vacations, and bursty input sources, which serves as a bound analysis for WRR scheduling in ATM networks. Similar models have been studied as well in the context of TDMA (time division multiple access) schemes with multiple contiguous slots assigned per frame [3,16]. For the model under study, after establishing an expression for the probability generating function (pgf) of the system contents, we derive closed‐form expressions for performance measures such as the expected value, and an asymptotic approximation for the tail probabilities of the system contents distribution. Also, after examining the cell delay, we formulate the pgf of the cell delay in a closed form in terms of the system contents pgf. The numerical results obtained for the system contents and cell delay distributions illustrate that they match with simulation results extremely well, especially in the low probability area. We also discuss the impact of the slot assignment cycle of WRR on the system performance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analysis of secondary user performance in cognitive radio networks with reactive spectrum handoff

Cognitive radio networks use dynamic spectrum access of secondary users (SUs) to deal with the problem of radio spectrum scarcity . In this paper, we investigate the SU performance in cognitive radio networks with reactive-decision spectrum handoff. During transmission, a SU may get interrupted several times due to the arrival of primary (licensed) users. After each interruption in the reactive spectrum handoff, the SU performs spectrum sensing to determine an idle channel for retransmission. We develop two continuous-time Markov chain models with and without an absorbing state to study the impact of system parameters such as sensing time and sensing room size on several SU performance measures. These measures include the mean delay of a SU, the variance of the SU delay, the SU interruption probability, the average number of interruptions that a SU experiences, the probability of a SU getting discarded from the system after an interruption and the SU blocking probability upon arrival.     

Discrete-time buffers with variable-length train arrivals

An infinite capacity single server queueing system is considered, to which messages consisting of a variable number of fixed-length packets arrive at the rate of one packet per slot (`train arrivals'). Assuming geometrically distributed message lengths. An exact closed-form expression for the probability generating function (pgf) of the buffer contents is obtained     

A queuing model for meteor burst packet communication systems

A discrete-time queuing model for the performance of a meteor-burst packet communication system is analyzed using matrix analytic methods. Not only is the system subject to interruptions due to the intermittence of the ionization layer, but its analysis is further complicated by the necessity to retransmit packets that have error or that occur at the tail end of a period of availability of the system. The authors' model takes such complexities into account. It is also of independent methodological interest in that it provides an exact analysis of a general queuing model with service interruptions. For the application at hand, the authors demonstrate the feasibility of the algorithms by a selected set of numerical examples. The algorithm can be used to ascertain the effects of the packet size, the bit error rate, the sync acquisition time, and other variables on system performance     

Performance optimization of distributed-system models withunreliable servers

Models of distributed systems with servers subject to breakdown and repair are investigated for optimization of performance measures. The optimization problems are the cost minimization, response time minimization, and throughput maximization. The system is modeled by a preemptive-resume priority queuing network. The mean-value analysis algorithm is applied to derive a relationship between the multiprogramming level and performance measure formulas. Based on this relationship the Lagrange multiplier technique is applied to carry out the optimization of performance measures. Optimal service rates are obtained that reach a target throughput while minimizing the total cost. Servers are also treated individually in order to minimize the mean response time of a particular server in the system in order to find the optimal service rates which minimize the response time of a particular server while reaching a target throughput. Formulas are derived for determining the maximum throughput of the system; unfortunately, it has no closed-form solution. However, it can be solved using the binary search and insert value method. Numerical examples illustrate the solutions     

Distributed and Energy-Aware MAC for Differentiated Services Wireless Packet Networks: A General Queuing Analytical Framework

We present a novel queuing analytical framework for the performance evaluation of a distributed and energy-aware medium access control (MAC) protocol for wireless packet data networks with service differentiation. Specifically, we consider a node (both buffer-limited and energy-limited) in the network with two different types of traffic, namely, high-priority and low-priority traffic, and model the node as a MAP (Markovian arrival process)/PH (phase-type)/1/K nonpreemptive priority queue. The MAC layer in the node is modeled as a server and a vacation queuing model is used to model the sleep and wakeup mechanism of the server. We study standard exhaustive and number-limited exhaustive vacation models both in multiple vacation case. A setup time for the head-of-line packet in the queue is considered, which abstracts the contention and the back-off mechanism of the MAC protocol in the node. A nonideal wireless channel model is also considered, which enables us to investigate the effects of packet transmission errors on the performance behavior of the system. After obtaining the stationary distribution of the system using the matrix-geometric method, we study the performance indices, such as packet dropping probability, access delay, and queue length distribution, for high-priority packets as well as the energy saving factor at the node. Taking into account the bursty traffic arrival (modeled as MAP) and, therefore, the nonsaturation case for the queuing analysis of the MAC protocol, using phase-type distribution for both the service and the vacation processes, and combining the priority queuing model with the vacation queuing model make the analysis very general and comprehensive. Typical numerical results obtained from the analytical model are presented and validated by extensive simulations. Also, we show how the optimal MAC parameters can be obtained by using numerical optimization     

远程故障诊断系统的排队论分析

引入随机服务系统,分析了远程故障诊断系统,建立了基于等待制的M/M/C/∞排队系统模型,并由此分析得到排队队长和等待时间等系统运行的指标。为平衡客户对故障诊断及时性的要求与系统维护费用之间的关系,根据排队等待时间和诊断服务器数量的关系,结合服务器的有效利用率,提出确定服务器最佳配置数量的方法。并以变频器的远程故障诊断系统为例,根据客户要求的等待时间数量级确定了服务器的合理配置。     

The effects of correlated arrivals at a server with credit‐based traffic policing

In this paper we observe the steady state and transient behaviour of correlated cell arrivals into a server with credit‐based traffic policing. We derive expressions for the lag‐k correlations of the departure process from the traffic policing mechanism, and observe how dependencies in the departure stream affect cell loss at the server. The results illustrate the impact of the second‐order statistics and the higher moments of the cell arrival processes on the traffic policing mechanism performance. Copyright © 2001 John Wiley & Sons, Ltd.     

The optimum adjustment of motor protection relays in an industrial complex

In this paper a distribution network is considered supplying electricity to a number of factories belonging to one industrial complex. The costs of interruption may vary more than one order of magnitude from one factory to another. The problem studied in this paper is how to adjust the time lags of the undervoltage protection relays in each factory in order to obtain a minimum in the total costs of interruptions of all factories together. By properly adjusting the time lags of the relays it may be provoked that factories with low interruption costs are disconnected from the network rather fast after the occurrence of a short circuit through which action the chance that a factory with high interruption cost is switched off is decreased.     

Traffic performance analysis of handover in GMPCS systems

This paper presents an analysis of handover process and its effect on the traffic performance in global mobile personal communications by satellite (GMPCS) systems. With the nongeostationary satellite used for the system, the handover scheme needs to be applied to make calls completed without any interruption. An analytical model is developed for the analysis of the handover process. We derive the mean number of handovers and handover delay with various satellite antenna patterns and different settings of handover parameter. A suitable traffic model of the whole system is also derived after due considerations of the handover process. The system performance measures include new call blocking probability, call dropping probability, and mean number of handovers per call. A computer simulation is developed and used. We also analyze the system performance with a number of handover priority schemes applied. Based on the study results, the handover parameters are selected to maximize the traffic performance. It is shown that we can improve the overall traffic performance of GMPCS system by setting handover parameters properly and using the handover priority scheme     

Analysis of Erlangian network services

This paper presents two equivalent analytical models to study the performance of finite queuing systems with Erlangian network services. Erlangian services are commonly seen in the processing of received network packets by many network servers. Our models allow us to derive equations for key features and performance measures of engineering and design significance. These features and measures include throughput, packet loss, packet delay, and server CPU availability. Numerical examples are given to study the performance while varying the number of service stages and the size of finite buffer. Discrete-event simulation has been used to verify the proposed analytical models.     

An Analytical Approach to Obtain the Interdeparture Time Characteristics in a Multistage VoIP Network

In this paper, we investigate the evolution of the interarrival and interdeparture times between voice packets when they are proceeding through a number of network nodes. We model the arrival process in a node as the superposition of a single tagged stream and an independent background process that aggregates the remaining traffic sources. Because we assume that the load of a single voice stream is very low compared to the load of the aggregate traffic, we can represent the tagged voice packets as markers (packets with size zero). We will establish an expression for the probability generating function (pgf) of the interdeparture time of the voice packets after one stage and use this interdeparture-time pgf as the pgf of the interarrival time of the voice packets in the next stage, in order to assess the evolution of the interarrival-time characteristics throughout the network.     

Validating complex computer system availability models

The authors report on experiences in validating complex computer-system availability models. A validation process, the availability models, and the data-collection process are described. An iteration of the model validation process emphasizing discrepancies between observed system behavior from data and from the model assumptions is presented. Analysis of data from five sites revealed that interruption dependencies on a device and across devices within a system exist. Furthermore, the frequency of, dependencies between, and downtime of device interruptions constitute differentiating characteristics of the causes of device interruptions. Data on partially available machine states, nonexponentially distributed machine downtimes, and nonstationarity of the machine interruption process are included. Validating the model assumptions is essential to model interpretation. Model accuracy is assessed. Exponentially distributed times between interruptions on a device and exponentially distributed device downtimes are not significant with respect to average measures of availability. The benefits of and issues for availability-model validation are summarized     

Performance management for cluster-based web services

We present an architecture and prototype implementation of a performance management system for cluster-based web services. The system supports multiple classes of web services traffic and allocates server resources dynamically so to maximize the expected value of a given cluster utility function in the face of fluctuating loads. The cluster utility is a function of the performance delivered to the various classes, and this leads to differentiated service. In this paper, we will use the average response time as the performance metric. The management system is transparent: it requires no changes in the client code, the server code, or the network interface between them. The system performs three performance management tasks: resource allocation, load balancing, and server overload protection. We use two nested levels of management. The inner level centers on queuing and scheduling of request messages. The outer level is a feedback control loop that periodically adjusts the scheduling weights and server allocations of the inner level. The feedback controller is based on an approximate first-principles model of the system, with parameters derived from continuous monitoring. We focus on SOAP-based web services. We report experimental results that show the dynamic behavior of the system.     

A novel performance analysis model for an IEEE 802.11 wireless LAN

This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF.     

Performance analysis of the IEEE 802.16e sleep mode for correlated downlink traffic

In this paper, we evaluate the performance of the IEEE 802.16e sleep mode mechanism in wireless access networks. This mechanism reduces the energy consumption of a mobile station (MS) by allowing it to turn off its radio interface (sleep mode) when there is no traffic present at its serving base station (BS). After a sleep period expires, the MS briefly checks the BS for data packets and switches off for the duration of another sleep period if none are available. Specifically for IEEE 802.16e, each additional sleep period doubles in length, up to a certain maximum. Clearly, the sleep mode mechanism can extend the battery life of the MS considerably, but also increases the delay at the BS buffer. For the performance analysis, we use a discrete-time queueing model with general service times and multiple server vacations. The vacations represent the sleep periods and have a length depending on the number of preceding vacations. Unlike previous studies, we take the (short-range) traffic correlation into account by assuming a D-BMAP arrival process, i.e. the distribution of the number of packet arrivals per slot is modulated by the transitions in a Markov chain with N background states. As results, we obtain the distribution of the number of packets in the queue at various sets of time epochs, the distribution of the packet delay and the antenna activity rate. We apply these results to the IEEE 802.16e sleep mode mechanism with correlated downlink traffic. By means of some examples, we show the influence of both the configuration parameters and the traffic correlation on the delay and the energy consumption.     

Response Time Analysis in a Data Broadcast System with User Cache

Data broadcast has been considered a promising way of information dissemination to a massive number of users in a wireless communication environment. Reducing user-waiting time is a major problem in developing a data broadcast system. There are two approaches for this problem; One is to design a broadcast schedule at the server side which reduces the mean response time, and the other is to utilize a local cache at the user side which may respond to a user request instantly. Though these two approaches were addressed separately in the literature, they may be taken jointly for better performance. The performance of system with joint approach depends on several factors such as broadcast schedule, cache size, cache management strategy, etc. In this paper we analyze response time in a data broadcast system with joint approach in which information items are structurally related with each other as in WWW. Based on the worst-case assumption, we derive a lower bound on the system performance for a given set of broadcast schedule, cache size, and cache management strategy. This result will be of help for designing and developing a data broadcast system. We support our analysis by carrying out an extensive simulation on some interesting proposed broadcast schedules and cache management strategies.     

Experimental performance of soil monitoring system using IoT technique for automatic drip irrigation

This paper proposes an IoT-enabled soil monitoring system using wireless sensor network for automatic irrigation in agricultural applications, especially for lemongrass plants, where an automated control system is required for irrigation applications. This can solve the problem of the water crisis, which is faced by the farmers during the cultivation of the crop in the field. This controls the water supply in the irrigation process using an IoT communication system. A system architecture for soil monitoring and controlling irrigation using IoT technique is designed where the different sensors and actuators like humidity, soil moisture, temperature, pump, and so forth are connected with a node microcontrol unit and message queuing telemetry transport (MQTT) protocol for enhancing communication capabilities. This wireless sensor network gives feedback to the system. This provides automation by the on/off pump system during drip irrigation. The sensor data are displayed on a PC or mobile phone through wireless communication and an IoT cloud platform. An experimental testing setup is developed and the experimental performance of a soil monitoring system using IoT technique for automatic drip irrigation has been carried out and soil moisture data are also stored in a cloud server for analytics. The performance shows that the MQTT protocol sends data within 48 s to the IoT cloud so that the data can be acquired in a faster manner. This shows that this kind of soil monitoring system is suitable for automatic drip irrigation, which enhances the farming process and overcomes the water crises in the agricultural system by reducing the wastage of water.     

网络存储系统I/O响应时间边界性能研究

为了对网络存储系统性能进行预测和改进,利用定量分析法研究了系统I/O响应时间与各性能影响因素之间的关系。通过分析网络RAID存储系统的数据传输原理,建立了该系统的闭合排队网络模型,并研究了其I/O响应时间的性能边界。实验表明,理论性能边界反映了实际系统性能的变化趋势和性能边界。进一步分析发现,当并发任务数较低时,存储中心服务器CPU处理能力和缓冲区命中率是影响I/O响应时间的关键因素。     

基于收益的认知无线电多信道阶梯排队接入机制分析

为了简化分析认知无线电系统中授权用户享有更高优先级对认知用户造成的影响,该文将2维生灭排队过程等效为1维非占先排队模型进行分析;并在多信道情景下,提出了一种基于信道收益的阶梯式排队接入方案,给出了由队列结构系数决定的系统性能参数阻塞概率及强制中断率的解析结果。仿真与数值计算验证了等效1维非占先排队模型的有效性;同时比较几种排队机制的性能参数,该文接入方案有较低的阻塞率,并且可根据系统环境自适应调整队列结构将强制中断率控制在较低范围内,不会随系统负荷率增高而增高。