基于混合服务策略轮询系统的性能分析

周期轮询系统已被广泛运用于各个领域,如计算机网络、工业制造系统等。在周期轮询系统中,最基本的队列调度策略有门限服务、限定服务以及完全服务。这些调度策略各有其优缺点,文章提出了一种基于混合服务的调度策略,对一些队列采用门限服务,对另一些队列采用限定服务,这样既可以避免在单一的完全服务中低优先级队列有可能出现的队列饥饿现象,又可以对不同的队列提供不同的服务质量。该文通过嵌入马尔可夫链和概率母函数的方法对基于混合服务的轮询系统进行分析,推导出队列的平均队长,并与采用门限服务的轮询系统进行比较,从而说明混合服务系统的优点。     

Heavy traffic analysis of polling models by mean value analysis

In this paper we present a new approach to derive heavy-traffic asymptotics for polling models. We consider the classical cyclic polling model with exhaustive or gated service at each queue, and with general service-time and switch-over time distributions, and study its behavior when the load tends to one. For this model, we explore the recently proposed mean value analysis (MVA), which takes a new view on the dynamics of the system, and use this view to provide an alternative way to derive closed-form expressions for the expected asymptotic delay; the expressions were derived earlier in [R.D. van der Mei, H. Levy, Expected delay in polling systems in heavy traffic, Adv. Appl. Probab. 30 (1998) 586–602], but in a different way. Moreover, the MVA-based approach enables us to derive closed-form expressions for the heavy-traffic limits of the covariances between the successive visit periods, which are key performance metrics in many application areas. These results, which have not been obtained before, reveal a number of insensitivity properties of the covariances with respect to the system parameters under heavy-traffic assumptions, and moreover, lead to simple approximations for the covariances between the successive visit times for stable systems. Numerical examples demonstrate that the approximations are accurate when the load is close enough to one.     

基于广播SNMP的网络管理并行轮询算法*

面对网络融合环境下网络规模大、分布广、设备多的实际需求,传统网络管理系统通过依次轮询设备进行数据采集存在轮询周期长、实时性低、轮询数据量多等缺点,提出了一种基于广播SNMP的数据采集并行轮询算法。该算法在轮询时,通过向每个网段发送广播SNMP数据包的方式并行轮询被管设备,减少轮询数据包的数量,减轻管理站的负担,缩短轮询周期;在接收设备回复数据包时,针对接收和处理速度不匹配的情况,采用多线程自适应并行处理环形缓存的方法,达到高速数据接收的目的。系统测试结果表明,通过广播方式的轮询可以有效缩短轮询周期,减少轮     

A duplex cyclic polling system for mixed queues

We consider a new mathematical model that adequately represents the workings of a cyclic polling system in high-speed wireless MESH-networks. The queues are serviced by two processing units (servers) in a cyclic fashion. Part of the queues are available for cyclic polling for both servers; each of the remaining queues is attached to its “own” processing unit in the servicing cycle. To study this system, we have applied the mean value approach and have obtained analytic expressions for average waiting times of claims in the queues and other characteristics. The paper also presents numerical examples.     

An efficient quality-of-service MAC protocol for infrastructure WLANs

In this paper, we propose a new efficient MAC protocol, named quality-of-service MAC (QMAC), which is an integrated solution for providing QoS guarantees to real-time multimedia applications in infrastructure WLANs. In addition, QMAC has the following attractive features: (i) its reservation scheme ensures that real-time stations enter the polling list in bounded time, (ii) it supports multiple priority levels and guarantees that high-priority stations always join the polling list earlier than low-priority stations, (iii) it employs the distributed pre-check technique such that the access point can admit as many newly flows as possible, while not violating admitted flows' guarantees, (iv) its dynamic bandwidth allocation scheme provides real-time traffic transmission with per-flow probabilistic bandwidth assurances, and (v) it uses a multipoll frame to poll all stations on the polling list at a time, therefore, the bandwidth can be utilized more efficient. Through simulations, we demonstrate the advantage of our QMAC.     

Optimal polling in communication networks

Polling is the process in which an issuing node of a communication network (polling station) broadcasts a query to every other node in the network and waits to receive a unique response from each of them. Polling can be thought of as a combination of broadcasting and gathering and finds wide applications in the control of distributed systems. In this paper, we consider the problem of polling in minimum time. We give a general lower bound on the minimum number of time units to accomplish polling in any network and we present optimal polling algorithms for several classes of graphs, including hypercubes and recursively decomposable Cayley graphs     

Multicycle Polling Scheduling Algorithms for FieldBus Networks

The paper deals with the scheduling of periodic information flow in a FieldBus environment. The scheduling problem is defined from an analytical point of view, giving a brief survey of the most well-known solutions. One of these is called multicycle polling scheduling, which is based on the hypothesis that all the production periods of the periodic processes to be scheduled are harmonic. Although in some process control or manufacturing scenarios, this hypothesis may be acceptable, there are many real industrial processes to which it cannot be applied. The aim of the paper is to make a contribution towards solving the scheduling problem. It essentially concerns extension of the theory on which multicycle polling scheduling is based to a much more realistic and general scenario, where the periods of all the processes to be scheduled have arbitrary values. The authors present a new formulation of multicycle polling scheduling, called extended multicycle polling scheduling, and demonstrate that it comprises the scenario currently considered in the literature. Two algorithmic solutions for extended multicycle polling scheduling are then proposed, giving a computational complexity analysis which will highlight the capability of the algorithmic scheduling solutions to be performed on-line. The paper concludes by comparing the multicycle polling scheduling approach known in literature and the one presented in the paper. Comparison is performed by evaluating the use of available bandwidth to serve both periodic and asynchronous traffic in the two approaches.     

一种基于SNMP网管系统的动态轮询算法研究

提出了一种基于SNMP网管系统的动态轮询算法TAP,该算法通过获取网络设备的ARP表信息进行分析比较,得到管理域内设备增加和删除等结构变化信息,然后增加和停止相应设备的轮询来适应这种变化。测试表明,TAP算法能够自适应管理域内设备的增加和删除,同时也能在网络拥塞时缩减轮询通信量。     

基于SNMP的自陷的传递轮询算法

提出了一种基于SNMP网管系统的自陷的传递轮询算法TTP。该算法对传统的自陷的轮询算法进行了改进，引入了传递和分组的思想，在每个分组内部由被管设备的代理来控制轮询数据报的传递，减轻了在轮询过程中管理站的工作，有利于提高大型网络网管系统的工作效率。     

一种应用于Ad Hoc无线局域网的预约多址协议

本文通过对AdHoc无线局域网的预约多址(PRMA)控制方式进行了分析,即通过一个中央站点依次轮询各站点传输信息,采用嵌入Markov链和概率母函数的分析方法,给出了轮询系统的数学模型。然后给出一种轮询调度策略的改进方法,将传输服务与转移查询做了并行处理,给出系统平均排队队长的精确解析,通过仿真实验讨论了改进方法对网络性能的提高。     

Performance analysis of Markovian polling systems with single buffers

In this paper, we analyze the Markovian polling system with single buffers, asymmetric arrival rates, service times, and switchover times. A virtual buffer model is introduced to derive the relationship of the joint generating function for the queue length of each station at a polling instant. The Laplace-Stieltjes transforms of the cycle time and the intervisit time are obtained from the marginal generating function. We analyze the cyclic, load-oriented-priority, and symmetric random polling schemes which are classified by adjusting the transition probabilities, and compare the merits and demerits of each scheme for the performance measures. In particular, we prove that the mean queue lengths at the polling instants are the same for all stations in case of the load-oriented-priority polling scheme for the buffer relaxation system in which a new message is stored as soon as the transmission of the message currently in the buffer is initiated.     

Modelling and performance analysis of an adaptive state-transition approach for power saving in Bluetooth

In this paper, an approach is developed to improve the power efficiency of Bluetooth. The better efficiency is achieved by reducing the unnecessary polling operations in the Basic Rate/Enhanced Data Rate (BR/EDR) controllers. An analysis of the current low power modes in the Bluetooth BR/EDR controller indicates that their activation requires a critical and challenging parameter negotiation phase. These parameters have a wide range of choices and as a result the associated low power modes are typically ignored by the Bluetooth application developers. The new approach is based upon multiple polling intervals. It is shown that three different polling intervals: small, medium and large are sufficient for a broad range of data traffic scenarios. As the kernel idea, each controller runs a common algorithm to choose among the three polling intervals and adaptively switches link state between the active data transfer state and idle. The state-transition rules are derived, and a system model is established based on the Hidden Markov Model (HMM), which is used to analyze and design the new Bluetooth link state-transition algorithm. The simulation and analysis demonstrates significant power saving and relatively low average end-to-end packet delay for this state-transition based approach, in comparison to the conventional polling system and the low power sniff mode. Moreover, the state-transition approach enables easier parameter setting that can be further optimized for a specific Bluetooth scenario.     

网格资源监控中的自适应轮询策略

目前大多数网格资源监控系统的轮询策略采用固定周期,很少考虑动态调整的轮询周期。该文提出了自适应轮询策略,采用了经典的一元线性回归预测模型,解决了固定轮询周期的不足之处,并进行了仿真测试。     

基于虚拟OID计算的WSN网络管理方法

为降低无线传感器网络(WSN)管理过程中代理节点的能量消耗,提出基于本地轮询和虚拟对象标示符(OID)计算的网络管理方法,并实现相应的网络管理操作原语。利用虚拟OID技术降低网络管理过程中的信息传递量,通过本地轮询策略减少网络管理站和代理节点的信息交换量。实验结果表明,该方法可降低代理节点的能量消耗,设计的操作原语符合WSN管理的需求。     

一种基于双令牌的蓝牙调度算法

调度算法是短距离无线通信技术的主要问题。蓝牙网络中使用的Round Robin (RR)轮询调度算法严重影响了系统的性能，本文针对这个问题提出了一种改进的蓝牙调度算法——双令牌随机(DTPR)轮询算法．此算法有两个重要特点：一是访问采用随机次序解决从设备之间的不公平性；二是采用优先级调度策略，对拥有令牌的主从设备对进行调度，缩短了轮询周期。并对本文提出的算法与现已提出的算法进行了仿真实验，结果表明，本文提出的算法在系统的吞吐量、传输时延和公平性方面都优于现有的其它算法。     

A Hopfield neural network approach to decentralized self-synchronizing sensor networks

Decentralized inference of a sensor network in the difficult case of a nonreciprocal nonlinear context is investigated by transforming the sensor network into a Hopfield neural network. Equilibrium states of the latter correspond to situations of global consensus in the sensor network, characterized by suitable regions (consensus regions) in the space of its parameters. The said transformation was recently proposed by the author and applied to the simple case of three sensors. The general case of more than three sensors is investigated in the present paper. A procedure is developed for determining the structure and the properties of the consensus regions.     

分忙闲站点的限定(K=2)轮询控制系统分析研究

为了保障系统公平性并提高轮询控制系统的工作效率,提出了区分忙闲站点的限定(K=2)轮询控制系统。系统在限定(K=2)轮询服务的基础上,依托站点忙闲状态,采用并行调度控制方式仅对有数据分组的忙站点提供发送服务。采用概率母函数和嵌入式马尔科夫链的方法建立了系统的数学模型,并精确解析了系统平均排队队长和平均等待时延等重要性能参数。仿真实验结果表明:理论计算值与模拟仿真值近似相等,说明理论分析正确合理。该模型既能保障系统公平性,又能避免对空闲站点查询,同时还能节省转换查询时间,从而提高了系统利用率和工作效率。与已有限定(K=1)轮询控制方式相比,所提系统具有更好的QoS保障。     

中心站点和普通站点完全服务排队系统分析

通过对具有最高优先级的排队轮询系统的分析,用物理方法及其机理原理,提出最高优先级及普通队列都采用完全服务的统一服务机制,得出系统平均排队长和平均查询周期的解析式。     

CORBA异步Polling模型的研究与实现

基于CORBA异步消息中的抽象Polling模型提出了一种Polling模型实现方案，讨论了其中的核心算法，该算法能分解耦合请求和应答并确保at-most-once语义。在分布对象中间件平台StarBus上实现了该模型和算法，实现结果表明该模型和算法为在CORBA中实现异步Polling机制提供了一种有效的参考方案。     

Seamless handover supported by parallel polling and dynamic multicast group in connected WLAN micro-cells system

WLAN (Wireless Local Area Network) has been seen to be one of the promising access technologies that adapts to 4G cellular network systems in providing very high speed connection with QoS guarantee through the polling function. However, when the handover happens, the contention-based medium access mechanism which is mainly used in WLAN is invoked and introduces unbounded transmission delay due to idle time periods and retransmission because of collision during the handover. If this technique is expanded to use in a microcellular network such as connected WLAN micro-cells, contention-based mechanism, therefore, should not be used to handle the MT’s handover, especially for vehicular users who change access point every few seconds. To overcome these difficulties in handover, we introduce parallel polling scheme in dynamic LMC (Logical Macro Cell) which can reduce delays much and remove packet loss rate. LMC is a virtual single macro cell which is built on a multicast group of adjacent micro-cells. In the same LMC, polling signals are sent from every BS (base station) to give MT (mobile terminal) permission to access one of these BSs. Instead of wasting much time to contend for resources of a new BS during handover, the MT answers the polling as an acknowledgment to connect to that new BS. The polling response is controlled to multicast to all BSs of the same LMC via the core network to synchronize for the next polling cycle. LMC is controlled to dynamically change when the MT comes in a new BS to make polling signals be continuous in a new LMC. Through analytical and simulation results, we show that the parallel polling scheme can achieve no handover latency, no packet loss and maintain mobile users’ throughput stably in the high traffic load condition though it causes overhead on the neighboring cells in both of wired and wireless sections. At speeds of up to70 m/s, the MT can still maintain its stable connection. OMNeT++ simulator with INET project is used to evaluate our proposal.