ATM ABR服务的流量控制

由于数据流量的突发性，流量控制对于ＡＴＭ ＡＢＲ服务比其它服务更复杂。文中综述了现有主要流量控制方案，介绍了一种新的智能控制策略。     

A new state space control scheme for Host-Gate Way Rate Control Protocol within intranets using ATM ABR service

In this paper, a new control strategy based on Host-Gate Way Rate Control Protocol is proposed for intranet congestion management. A more sophisticated optimal control algorithm based on a state space approach will be proposed via using the Available Bit Rate (ABR) service of an Asynchronous Transfer Mode (ATM) backbone network. The stability of the proposed control algorithm will be analyzed and the benefits of the algorithm are investigated thoroughly. Simulations confirm that the proposed new algorithm will produce lower queue level variance at the gateway. This implies that smaller buffers can fulfill the requirement for a given loss probability. Moreover, the queue level variance is less sensitive to variations in the ABR bandwidth model. This is true even when a self-similar long-range dependent trace is used to represent the ABR bandwidth in simulations, which is encouraging in view of the known self-similar nature of both LAN traffic and compressed video streams that will be sharing the ATM network.     

主动网络中CPU和带宽资源分配的公平性

传统的包调度方案能实现单一资源分配的公平性,但不能直接应用于主动网络中的主动节点上,因为主动节点包含多种相互关联的资源。提出一种能实现在主动节点中公平分配资源的包调度算法。仿真实验结果显示,该算法能在主动流之间实现CPU和带宽资源的有效公平分配。     

ATM网络ABR业务流量控制算法的研究

目前,已经有许多基于速率的流量控制方法,这些方法中大多都能提高连接的公平分配带宽以及利用率。本文在ERICA算法的基础之上提出了一种新的计算虚连接数量的计算方法。该方法的改进方法能够更加快速、准确地计算出处于活动状态的源端数,并将未用带宽在ATM网络ABR连接之间公平且准确地进行分配。     

模糊控制在ATM流量管理中的应用

应用模糊控制理论,研究了ATM网络的流量管理问题。将ABR（Available Bit Rate)业务的流量控制抽象为一时滞系统的控制问题,指出了一种模糊速率流量控制算法,实现了带宽在各个ABR虚连接中公平有效地分配。仿真结果表明算法具有良好的综合性能。     

ABR流量控制中的变结构控制器

自适应比特(available bit rate,简称ABR)业务的流量控制是ATM网络中一种有效的拥塞控制机制和流量管理手段.在高速的ATM网络中,算法的简洁性在很大程度上决定着交换机的性能.尽管二进制ABR流量控制的简洁性具有相当大的吸引力,但标准的EFCI算法控制的队列长度和允许信元速率(allowed cell rate,简称ACR)却容易出现大幅振荡的现象,这势必会降低链路的利用率,严重影响交换机的性能.进而又有了相对复杂却有效的显式速率反馈机制.在此研究中,以已有的ABR流量控制模型为基础,应用概率拥塞判定机制,并借助鲁棒控制理论中滑模变结构控制器的设计方法,为ABR流量控制设计了一种新的二进制算法,避免了标准EFCI算法中非线性环节诱发的自激振荡,这对于充分发挥二进制流控算法的简洁性以及优化交换机的性能是极为有利的.仿真实验表明:二进制流量控制中的滑模变结构算法大幅度地抑制了ACR和队列的振荡,平滑了由此而引入的时延抖动,为实现ATM网络中的服务质量提供了可靠的实现机制.     

Correctness and performance of the ATM ABR rate control scheme

We study both correctness and performance of the source/destination protocols of the available bit rate (ABR) service in asynchronous transfer mode (ATM) networks. Although the basic protocol for rate-based congestion management is relatively simple, the protocol specification has to cope with several “real-world” cases such as failures and delayed/lost feedback which introduce complexity. Rigorous proof of the correct functioning of the protocol based on a formal specification is necessary. We use a formal model to show that the ABR source/destination protocol is free of livelocks, so that under all conditions both resource management (RM) and data cells will be transmitted. Furthermore, if there are data cells available, then the ABR protocol is deadlock free; otherwise, the system goes to a desirable sleep state waiting for data cells, as long as certain parameters are set appropriately at connection setup. We also show that the network options of explicit forward congestion indication (EFCI) and explicit rate (ER) interoperate correctly.In addition to ensuring the correct functioning of the protocol, it is essential that pathological situations do not result in very poor performance, which we view as another form of “incorrect operation”. We derive conditions that ensure that the source's allowed cell rate (ACR) is stable in the presence of delayed or lost feedback RM cells. We arrive at bounds on the number of consecutive RM cell losses tolerated while the ACR rate remains stable. We also provide an asymptotic estimate of ACR and the allowable RM cell loss probability to ensure that ACR is stable, statistically.The ABR protocol contributes to the feedback delay in two ways: the source delay of sending out the probe forward RM (FRM) cells and the destination delay of turning around the backward RM (BRM) cell. We provide a worst-case analysis of the delay in turning around RM cells at the destination station and the worst-case inter-departure time of FRM cells from the source.     

因特网拥塞控制的公平性研究综述

将网络拥塞控制的公平性研究划分为在同质流网络中的公平性和在异质流网络中的公平性两个方面,公平性研究在两类网络中均有重大的意义.依此划分,分别介绍了近年来拥塞控制公平性研究的重要进展.同质流网络中公平性研究主要是围绕解决TCP流的RTT歧视这一问题而展开和深入的;异质流网络中公平性研究主要是围绕保护正当行为流的问题而不断推进的,目前的研究热点是对用户公平的AQM算法.最后对拥塞控制公平性研究领域未来有价值的研究问题给出了预测,并阐述了对这几个问题的理解.     

ATM网络流量控制中的活动VC计算方法

ATM网络ABR业务流量控制是一种基于速率的流量控制机制。在ERICA算法的基础上,提出有效活动虚连接的计算方法,根据它们的活动度计算活动连接的有效数值,从而准确计算出处于活动状态的源端数,将未用带宽在ATM网络ABR连接之间公平且准确地进行分配,体现了Max-Min公平分配准则,能保证算法的高效性和带宽分配的公平性。     

Design and analysis of a merging algorithm for multipoint-to-point ABR service in ATM networks

In this paper, we propose a merging algorithm, which can provide efficient support for multipoint-to-point ABR service in ATM networks. By forwarding the FRM cells belonging to the VC with the largest FRM-cell arrival rate in a merge point, the proposed algorithm can achieve better link utilization than existing merging algorithms. In addition, the proposed algorithm reduces the number of FRM cells forwarded by a merge point. As a result, it can reduce the control overhead of ABR service. Most importantly, it does not incur extra complexity in switches. We also discuss the impact of different network topologies on our algorithm. Simulation results show that the proposed algorithm is able to achieve better performance while requiring significantly fewer RM cells.     

Fairness in dataflow scheduling in the cloud

Expensive dataflow queries which may involve large-scale computations operating on significant volumes of data are typically executed on distributed platforms to improve application performance. Among these, cloud computing has emerged as an attractive option for users to execute dataflows allowing them to select proper configurations (e.g., number of machines) to achieve desired trade-offs between execution time and monetary cost. Discovering dataflow schedules that exhibit the best trade-offs within a plethora of potential solutions can be challenging, especially in a heterogeneous environment where resource characteristics like performance and price can be varied. To increase resource utilization, users may also submit multiple dataflows for execution concurrently. Traditionally, building fair schedules (schedules where the slowdown of all dataflows due to resource sharing is similar) while achieving good performance is a major concern. However, considering fairness in the cloud computing setting where monetary cost is part of the optimization objectives significantly increases the difficulty of the scheduling problem. This paper proposes an algorithm for the scheduling of multiple dataflows on heterogeneous clouds that identifies Pareto-optimal solutions (schedules) in the three-dimensional space formed from the different trade-offs between overall execution time, monetary cost and fairness. The results show that in most cases the proposed approach can provide solutions with fairer schedules without significantly impacting the quality of the execution time to monetary cost skyline compared to the state of the art where the fairness of a solution is not taken into account.     

多时滞ATM网络中ABR流量的积分滑模控制

针对含有多个时滞的异步传输模式(ATM)网络的拥塞问题,设计了积分滑模控制器,对可用比特率(ABR)业务流量进行控制,并引入预估器来补偿输入时滞.所设计的控制算法不但能够克服变化的ABR带宽给闭环系统带来的不利影响,而且还能保证含有多输入时滞闭环系统的稳定性,同时还可实现带宽按权重分配和缓冲队列长度的跟踪.     

ATM网络中ABR服务的流控方式

对ＡＴＭ的ＱｏＳ进行简要介绍之后，重点讨论了在ＡＢＲ服务中为实现ＱｏＳ而可以采用的两种流量控制方式，并提出了一种改进的基于速率的流控机制，这种方式在广域网中显得更为公平。     

ATM网络中ABR业务的拥塞控制

基于信用的拥塞控制和基于速率的拥塞控制方式各有优缺点,本文在讨论了几种主要的拥塞控制方式之后,提出了对OSU算法的改进方案。     

Z＆G协议公平性的形式化验证

Zhou和Gollmann设计的公平非否认协议(Z&G协议)旨在为电子商务交易的双方提供非否认证据和公平性.提出一种基于状态转换的方法对其公平性进行分析.与以往方法不同,它是一种针对电子商务协议的专门分析工具:用状态转换系统为电子商务系统建模;用基于状态的形式系统描述协议,将协议的信任假设显式表示为协议的一部分.该方法按进程是否背离协议或者背离协议的程度将协议在系统中的执行序列定义为三类模式:遵守型、欺骗型和中断型.验证了Z&G协议在三种模式下的执行序列都满足公平性.     

WMN网络中TCP公平性仿真研究

本文主要对无线网格网中的TCP公平性进行仿真分析研究。文中给出了仿真模型和公平性指数公式,模拟了多条TCP业务流的传输过程并对其公平性指数进行定量计算,为今后进一步的改进研究奠定了基础。     

基于ANN的空气处理单元换热器的动态性能预测

应用人工神经网络技术对安装在空气处理单元（Air Handler Unit,AHU）中的换热器建立了动态神经网络模型。该模型的所有预测值基本都在实际测量值的95%~105%之间。实际测量值和神经网络模型预测值之间的平均相对误差（Mean Relative Error,MRE）小于2.5%,充分说明模型逼近实际对象的精确性。实验结果显示,神经网络,尤其是BP神经网络,可以作为一个很容易的建模工具来获得空气处理单元中换热器的神经网络模型,同时也很容易应用在类似的热系统中。     

Analysis of Source Rate Adaption for ATM networks using a dynamic flow model

This paper focuses on using Source Rate Adaption (SRA) as a viable flow control scheme in Asynchronous Transfer Mode (ATM) networks. A modeling technique related to conducting performance evaluation studies using a dynamic flow model has been developed. SRA control strategies at node, domain or network levels have been proposed. Computer simulations verify the validity of the model and strategies.     

A novel congestion control in hybrid ATM/TDMA networks

A new congestion control scheme is analyzed for an ATM multiplexer node. This scheme is based on the leaky bucket and virtual leaky bucket techniques, and utilizes the interaction between the ATM and higher layers, in a hybrid asynchronous transfer mode/time division multiple access (ATM/TDMA) network. The transport users are assumed to be generic ATM sources, who modulate their end-to-end flow control parameters, i.e. protocol data unit size in case of video and voice users, and window size in case of data users, based on the congestion status. Simple analytical formulas are derived for congestion criteria, to represent the required bandwidth to support various classes of service, i.e. video, voice, data, etc. with their own performance requirements. An ATM multiplexer node buffer is analyzed using a modulated poisson process queuing model with bulk arrival and bulk service of cells. The ATM multiplexer node congestion performance criteria, i.e. the mean probabilities of ATM multiplexer node congestion, cell generation, cell discarding, buffer content and buffer overflow, are evaluated with and without the congestion control schemes.