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。     

Rate-based control schemes for ABR traffic — Design principles and performance comparison

A new ATM service category, the Available Bit Rate service, has been introduced in the ATM Forum. It dynamically allocates available bandwidth to users by controlling the flow of user traffic with feedback. The Forum has ratified the rate-based flow control framework for the support of this new service. In this paper, we provide a recipe for designing rate-based feedback schemes demonstrating the rich variety of available switch mechanisms. Each aspect of the feedback control loop mechanism is explored in detail and several available choices are investigated. Two example switch mechanisms are provided that illustrate the rate-based control design principles. The ability of these mechanims to support the desired objectives of an ABR service is compared using a reference network configuration. Simulation results show that the rate-based framework allows a great degree of architectural flexibility in the design of switch mechanisms. However, the explicit rate based approach is more capable than single bit feedback approaches in providing immediate access to available bandwidth in the presence of VBR sources. The rate-based framework provides switch vendors sufficient flexibility to choose a mechanism among several available options, based on their performance requirements and cost budges.     

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。     

基于种群生态的组播拥塞控制机制

针对现有TCP类组播拥塞控制机制不具有速率平滑性、往返时间(RTT)公平性以及在高速环境中传输效率低的问题,提出一种基于种群生态理论的自适应高速组播拥塞控制机制。该机制在每个接收端实现瓶颈链路带宽和背景流速率的测量,并将这两个测量值用于种群生态模型中以计算期望服务速率,然后使用一种简单的反馈抑制机制选取期望服务速率最小的接收端作为代表,该代表将其期望服务速率反馈给源端控制发送速率。仿真结果表明新机制发送速率平滑,具有RTT公平性,在低速网络和高速网络中都能与单播流公平共享带宽资源。     

多通道ATM 网络鲁棒拥塞控制

拥塞控制对ATM网络有效、稳定运行具有重要的作用，在单瓶颈多通道的网络模型下，基于Smith预估原理，提出一种新颖的鲁棒拥塞控制器设计方案，这种基于速率的拥塞控制可以保证ABR的服务质量(QoS)，理论分析和仿真结果表明，所提出方案收敛速度快，对网络的不确定因素具有较强的鲁棒性。     

Discrete time congestion controllers for multi-source connection-oriented communication networks

In this article, a new, discrete time, non-linear flow control strategy for a connection-oriented, multi-source communication network is proposed. The strategy effectively exploits the Smith principle in order to avoid data loss in the network, and to ensure full utilisation of the bottleneck link available bandwidth. The desirable properties of the proposed control strategy are preserved, even though the connection round trip times may be determined imprecisely. Furthermore, an enhanced strategy, which employs extra feed-forward bandwidth compensation, and reduces the influence of the available bandwidth variations on the steady state queue length in the network, is introduced. Finally, the proposed strategy is modified to be appropriate for application when the number of active connections changes during the control process, and new conditions for no data loss and full bandwidth utilisation are formulated and strictly proved. Since the modified strategy allows for arbitrary resource allocation among the controlled virtual circuits, the max–min fairness criteria can be satisfied.     

基于Kalman算法及神经网络预测的网络流量控制

针对通信网络的传播时延会给基于速率反馈的流量控制带来极大的不利影响，提出了基于Kalman算法的反馈控制和神经网络在线预测补偿相结合的复合控制，对ATM网络的ABR流量进行控制，较好地克服了时延对流量控制的快速性和稳定性所产生的不利影响．仿真研究表明：本方案能使信源的发送速率快速响应网络状态的变化，有效地避免拥塞的发生，并使链路带宽得以充分利用．与PID控制方法相比，信元的丢失率更低、链路的利用率更高以及所需的缓冲容量更小．     

A proportional feedback scheme for ATM networks

Available bit rate (ABR) service class is proposed by Asynchronous Transfer Mode (ATM) Forum to provide the “best-effort” services like traditional TCP/IP traffic. It is designed to make use of the remaining bandwidth not used by VBR and CBR. However, the bursty nature of ABR traffic makes it difficult to prevent buffers on ATM switches from overflowing. A number of schemes have been proposed for ABR traffic control. In this paper, a proportional scheme that is rate-based hop-by-hop flow control is proposed. A mathematical model is built to analyze the hop-by-hop flow control scheme. It is shown the scheme can utilize full bandwidth without any cell loss. It is also shown the scheme has low queuing delay and fast transient response.     

Performance analysis of rate-based flow control under a variable number of sources

Rate-based flow control plays an important role for efficient traffic management of ABR service in ATM networks. In this paper, a performance analysis of a rate-based flow control mechanism is presented. In our analytical model, the number of active sources is variable. A new source arrives when a connection is established, and an existing source departs when it has transmitted its data. Hence our model not only reflects the real scenes, but also correctly estimates the effect of the rate-based flow control. Due to this variation, the analysis of the steady state is not enough. Therefore the analysis of transient cycles is also developed. Using the results of both analyses, we derive the equations of cell loss probability and utilization. Numerical results, confirmed by simulation, are given to show that our analysis is accurate. Also an underestimation of over an order of magnitude in cell loss probability is observed when we use the analysis ignoring the transient cycles. We demonstrate that the efficiency of using rate-based control is seriously influenced by the source arrival rate and source departure rate.     

Improving fairness among TCP flows by stateless buffer control with early drop maximum

Transmission control protocol (TCP) has been recognized as the most important transport-layer protocol for the Internet. It is distinguished by its reliable transmission, flow control, and congestion control. However, the issue of fair bandwidth-sharing among competing flows was not properly addressed in TCP. As web-based applications and interactive applications grow more popular, the number of short-lived flows conveyed on the Internet continues to rise. With conventional TCP, short-lived flows will be unable to obtain a fair share of available bandwidth. As a result, short-lived flows will suffer from longer delays and a lower service rate. It is essential for the Internet to come up with an effective solution to this problem in order to accommodate the new traffic patterns.With a more equitable sharing of bottleneck bandwidth as its goal, a stateless queue management scheme featuring early drop maximum (EDM) is developed and presented in this article. The fundamental idea is to drop packets from those flows having more than an equal share of bandwidth. The congestion window size of a TCP sender is carried in the options field on each packet. The proposed scheme will be exercised on routers and make its decision on packet dropping according to the congestion windows. In case of link congestion, the queued packet with the largest congestion window will be dropped from the queue. This will lower the sending rate of its sender and release part of the occupied bandwidth for the use of other competing flows. By so doing, the entire system will approach an equilibrium point with a rapid and fair distribution of bandwidth. As a stateless approach, the proposed scheme inherits numerous advantages in implementation and scalability.Extensive simulations were conducted to verify the feasibility and the effectiveness of the proposed approach. As revealed in the simulation results, the proposed scheme outperforms existing stateless techniques, including Drop-Tail and Random Early Drop, in many respects, such as a fairer sharing of available bandwidth and a shorter response time for short-lived flows.     

MANET中基于速率的流量控制算法研究

由于MANET中网络的动态变化特征,TCP隐含式AIMD流量控制不适应于该领域。本文介绍了基于速率的显式流量控制策略（EXACT）,并分析了它对网络中再路由和带宽变化的反应。在高速动态变化的MANET环境下,通过ns-2系统模拟,本文评价了EXACT在网络传输公平和效率等方面的性能。     

自适应带宽的最大-最小公平性拥塞控制

带宽共享和拥塞控制对于Internet的健壮性和公平性是很重要的研究课题.对交换设备中流量共享拥塞链路的带宽公平分配进行研究,提出一个优化交换设备带宽的设置算法:根据出端口接收速率自适应设置入端口带宽门限,对入端口的带宽进行动态重新分配,提高资源利用率.模拟实验表明,此算法有以下优点:1)高适应性;2)最大最小公平性;3)快速响应网络变化;4)高可靠性;5)稳定性.     

Target bandwidth sharing using endhost measures

Recent congestion control protocols such as XCP and RCP achieve fair bandwidth sharing, high utilization, small queue sizes and nearly zero packet loss by implementing an explicit bandwidth share mechanism in the network routers. This paper develops new quantitative techniques for achieving the same results using only end-host measures. We develop new methods of computing bottleneck link characteristics, a new technique for sharing bandwidth fairly with Reno flows, and a new approach for rapidly converging to bandwidth share. A new transport protocol, TCP-Madison, that employs the new bandwidth sharing techniques is also defined in the paper. Experiments comparing TCP-Madison with FAST TCP, BIC-TCP and TCP-Reno over hundreds of PlanetLab and other live Internet paths show that the new protocol achieves the stated bandwidth sharing properties, is easily configured for near-optimal performance over all paths, and significantly outperforms the previous protocols.     

Feedback-Based Adaptive Packet Marking for Proportional Bandwidth Allocation

Differentiated service (DiffServ) networks have been proposed to assure the achievable minimum bandwidth to aggregate flows. However, analyses in the literature show that the current DiffServ networks are biased in favor of ah aggregate flow that has a smaller committed information rate (CIR) when aggregate flows with different CIRs share a bottleneck link. In order to mitigate this unfairness problem, we propose an adaptive marking scheme which provides the relative bandwidth assurance in proportion to the CIRs of the aggregates. By introducing a virtual target rate (VTR) and adjusting it depending on the provision level of the network, each aggregate can obtain its fair share of the bandwidth, regardless of traffic load. This scheme is based on a feedback approach. It utilizes only two-bit feedback information conveyed in the packet header and can be implemented in a distributed manner. Furthermore, the proposed scheme does not require calculating fair shares of aggregates or any additional signaling protocol. Using steady state analysis and extensive simulations, we show that the scheme can provide aggregate flows with their fair shares of bandwidth, which is proportional to the CIRs, under various network conditions     

A neural-fuzzy system for congestion control in ATM networks

We propose the use of a neural-fuzzy scheme for rate-based feedback congestion control in asynchronous transfer mode (ATM) networks. Available bit rate (ABR) traffic is not guaranteed quality of service (QoS) in the setup connection, and it can dynamically share the available bandwidth. Therefore, congestion can be controlled by regulating the source rate, to a certain degree, according to the current traffic flow. Traditional methods perform congestion control by monitoring the queue length. The source rate is decreased by a fixed rate when the queue length is greater than a prespecified threshold. However, it is difficult to get a suitable rate according to the degree of traffic congestion. We employ a neural-fuzzy mechanism to control the source rate. Through learning, membership values can be generated and cell loss can be predicted from the status of the queue length. Then, an explicit rate is calculated and the source rate is controlled appropriately. Simulation results have shown that our method is effective compared with traditional methods.     

Avoiding request–request type message-dependent deadlocks in networks-on-chips

When an application is running on a network-on-chip (NoC)-based multiprocessor system-on-chip (MPSoC), two types of deadlocks may occur: (i) the routing-dependent deadlocks, and (ii) the message-dependent deadlocks. The former type of deadlocks can be avoided by removing any cyclic paths on the application’s channel dependency graph. The message-dependent deadlocks, caused by mutual dependency of different control and/or data messages, on the other hand, are very complicated to deal with. In this paper, we focus our study on the request–request type message-dependent deadlocks which may appear in a peer-to-peer streaming system. This type of deadlocks can have devastating effects on applications using streaming protocols that often demands real-time processing over continuous data streams. We show that request–request type of deadlocks can be avoided by proper inclusion of virtual channels (VCs) for the links along the selected routing path. These VCs are not bounded to a particular communication path. Instead, they can be shared among multiple existing communication flows. In this paper, we have formally proved a sufficient condition that determines the minimum number of VCs actually needed for each link of a communication flow such that, request–request type message-dependent deadlocks can be completely avoided. Following this sufficient condition, we propose a path selection and minimum VC allocation (PSMV) algorithm to help determine the minimum number of non-uniform VCs for each link. The PSMV algorithm consists of two major steps. In the first step, we attempt to minimize the maximum number of VCs among all the links. This problem is NP-complete in nature, and it is solved using the proposed mixed integral linear programming (MILP)-based algorithm. In the second step, based on the solution suggested in the first step, the minimum number of VCs for each link is finally determined. The PSMV algorithm can literally be integrated with any existing application mapping algorithm to provide deadlock-free mapping results. One such deadlock-free mapping algorithm is suggested in this paper. Our experiments also show that, compared to an existing flow control based deadlock avoidance method (CTC) and a deadlock recovery method (DR), increase of buffers size in PSMV is within 5% compared to a baseline network configuration. The message latency of PSMV is the lowest among all three designs.     

一种有竞争力的自适应Vegas算法

针对TCP Vegas与Reno协议不兼容的问题,提出一种提高Vegas带宽竞争力的算法ACNV,通过估计带宽占有率的变化趋势调节调整源端对带宽资源的抢占力,并采用快速收敛到合理区间的窗口调整策略,达到ACNV与Reno公平分享带宽的目的。实验结果证明,当瓶颈链路带宽由0.1 Mb/s变化到2 Mb/s的过程中时,ACNV与Vegas相比,与Reno共存时平均带宽占有率的平均值从4.3%提高到48.33%。     

基于多令牌桶的组播拥塞控制

IP组播是一种有效的数据传输方式,在过去几年中,组播传输机制已经成为一个活跃的研究领域。但由于其自身特性决定了在组播中实现可靠性和拥塞控制非常困难,组播的拥塞控制问题一直没能得到很好的解决,这成为了其发展的瓶颈,不断增加的UDP数据流恶化了TCP控制拥塞的能力,而且是引起高丢包率的原因之一。文中提出了一种可以对局域网内IP分配固定带宽的扩展令牌桶算法,扩展了令牌桶个数,一个令牌桶控制一个IP,消除了共享带宽的缺点,并通过设计电路,建模仿真结果表明可以对路由器交换节点的组播达到准入控制,防止造成网络拥塞,最大限度保证网络Qos,并且设计的电路占用硬件资源少,能够应用于高速电路当中。     

MediaWorm: a QoS capable router architecture for clusters

With the increasing use of clusters in real-time applications, it has become essential to design high-performance networks with quality-of-service (QoS) guarantees. We explore the feasibility of providing QoS in wormhole switched routers, which are widely used in designing scalable, high-performance cluster interconnects. In particular, we are interested in supporting multimedia video streams with CBR and VBR traffic, in addition to the conventional best-effort traffic. The proposed MediaWorm router uses a rate-based bandwidth allocation mechanism, called Fine-Grained VirtualClock (FGVC), to schedule network resources for different traffic classes. Our simulation results on an 8-port router indicate that it is possible to provide jitter-free delivery to VBR/CBR traffic up to an input load of 70-80 percent of link bandwidth and the presence of best-effort traffic has no adverse effect on real-time traffic. Although the MediaWorm router shows a slightly lower performance than a pipelined circuit switched (PCS) router, commercial success of wormhole switching, coupled with simpler and cheaper design, makes it an attractive alternative. Simulation of a (2/spl times/2) fat-mesh using this router shows performance comparable to that of a single switch and suggests that clusters designed with appropriate bandwidth balance between links can provide required performance for different types of traffic.