A novel self-tuning feedback controller for active queue management supporting TCP flows

Wireless access points act as bridges between wireless and wired networks. Since the actually available bandwidth in wireless networks is much smaller than that in wired networks, there is a bandwidth disparity in channel capacity which makes the access point a significant network congestion point. The recently proposed active queue management (AQM) is an effective method used in wired network and wired-wireless network routers for congestion control, and to achieve a tradeoff between channel utilization and delay. The de facto standard, the random early detection (RED) AQM scheme, and most of its variants use average queue length as a congestion indicator to trigger packet dropping. In this paper, we propose a Novel autonomous Proportional and Differential RED algorithm, called NPD-RED, as an extension of RED. NPD-RED is based on a self-tuning feedback proportional and differential controller, which not only considers the instantaneous queue length at the current time point, but also takes into consideration the ratio of the current differential error signal to the buffer size. Furthermore, we give theoretical analysis of the system stability and give guidelines for the selection of feedback gains for the TCP/RED system to stabilize the instantaneous queue length at a desirable level. Extensive simulations have been conducted with ns2. The simulation results have demonstrated that the proposed NPD-RED algorithm outperforms the existing AQM schemes in terms of average queue length, average throughput, and stability.     

随机早期检测主动队列管理算法的改进研究

主动队列管理（Active Queue Management）算法是近几年网络研究的重点。为了改进和完善现有的AQM算法和设计更好的新算法,需要对主动队列管理机制的实现方法和性能特性进行深入研究,详细讨论了随机早期检测（Random Early Detection）主动队列管理机制的关键技术问题,研究了近年来对RED算法的主要改进算法,总结了这几种算法的优缺点及其有待改进之处,并应用网络仿真器（Network Simulator）对实际网络模型进行了仿真实验,检验了改进算法对网络性能的影响。     

Dynamic queue level control of TCP/RED systems in AQM routers

One main TCP congestion control objective is, by dynamically adjusting the source window size according to the router queue level, to stabilize the buffer queue length at a given target, thereby achieving predictable queueing delay, reducing packet loss and maximizing link utilization. One difficulty therein is the TCP acknowledging actions will experience a time delay from the router to the source in a TCP system. In this paper, a time-delay control theory is applied to analyze the mechanism of packet-dropping at router and the window-updating in TCP source in TCP congestion control for a TCP/RED dynamic model. We then derive explicit conditions under which the TCP/RED system is asymptotically stable in terms of the instantaneous queue. We discuss the convergence of the buffer queue lengths in the routers. Our results suggest that, if the network parameters satisfy certain conditions, the TCP/RED system is stable and its queue length can converge to any target. We illustrate the theoretical results using ns2 simulations and demonstrate that the network can achieve good performance and converge to the arbitrary target queues.     

主动队列管理RED算法改进与实验仿真研究

分析了RED及其改进算法的原理和局限性,提出了一种非线性高阶RED拥塞控制机制。该算法利用一个高阶分组丢弃函数,在下限阈值附近以较低的概率标记丢弃分组,在上限阈值附近迅速提高分组的标记丢弃概率。并对网络仿真器NS2进行扩展,通过系列仿真实验验证了改进算法有效提高了网络性能。     

改进的RED队列管理算法：RED-r

为了避免RED缺陷,提出一种改进的RED算法——RED-r。该算法采用二次圆函数来计算丢包概率,减少了RED的设置参数,实现了在网络大延时和小延时时的队列稳定,且在小延时能获得比PID队列更平滑的效果。NS2仿真验证了RED-r算法的有效性。     

基于事件的主动队列管理研究

针对随机早期检测RED存在的对参数过于敏感、时延抖动、队长不稳定等问题,采用特殊事件标记法,通过调整丢弃概率的增减幅度,对RED算法进行了改进。实验表明,改进的算法在稳定性、链路利用率方面有了较好的改善。     

Active Queue Management技术的研究与发展

ActiveQueueManagement(AQM)技术通过有效控制输出队列的丢包时间和丢包方式，对拥塞进行早期通告，这在TCP拥塞控制的实现中至关重要。目前对AQM进行较全面介绍和总结的文献尚不多见，以RandomEarlyDetection(RED)为重点介绍了这种第一代AQM技术的设计思想、优缺点以及为此出现的多种RED变种方法，另外还简单介绍了其它几种与RED设计思路不同的AQM方法，以期对AQM技术的研究和发展进行较全面的总结，并促进国内学者以及设备制造商对这一技术的关注。     

基于路由队列资源自适应的非线性随机早期检测算法

针对随机早期检测(RED)算法在网络拥塞控制中的缺点和复杂性,提出了基于路由队列资源(缓冲)自适应的新算法(ND-RED)。该算法采用非线性丢包策略和动态调整算法参数的方法,使得路由队列长度稳定在参考值附近,从而有效控制了网络拥塞,高效地利用了资源。最后实验结果表明,ND-RED算法具有良好的稳定性,在队列控制和丢包率控制方面优于RED算法。     

A linear system analysis of RED

The random early detection (RED) algorithm proposed by Floyd and Jacobson [IEEE/ACM Trans. Networking 1 (4) (1993) 397] is a simple and quite effective mechanism for active queue management and as a result has been widely implemented in Internet routers. While RED certainly performs better than drop-tail, its parameters are difficult to tune to give good performance under different congestion scenarios. Also, studies have shown that RED does not stabilize the queue lengths in routers, because its equilibrium queue length strongly depends on the number of active TCP connections. As a result numerous variants of RED have been proposed to work around the performance problems of RED. In this paper, using inferences drawn from a linear systems analysis, we provide an insight into why RED is difficult to tune. The same linear systems analysis is used to show that the DRED algorithm proposed in [Computer 36 (2–3) (2001) 203; Comput. Commun. 24 (12) 2001 1170] overcomes the performance limitations of RED [IEEE/ACM Trans. Network. 1 (4) (1993) 397].     

主动队列管理中RQC控制器的设计

基于网络中输入输出速率和队列长度均可帮助决定更精确丢弃概率的思想,提出了根据输入输出速率和队列长度决定包的丢弃标注概率的AQM算法,即RQC算法．通过仿真将该算法与RED和PI算法进行比较,说明了RQC控制算法的优点．     

灰色预测PI主动队列管理拥塞控制策略

提出了一种新颖的基于隐含类型的GM模型的预测PI算法。利用预测队列误差而非瞬时采样值来决定路由器的丢包率。该方法致力于在响应速度与增益两者之间取得一个最佳的折中。仿真结果验证了该灰色预测PI主动队列管理策略的有效性。     

一种基于速率的主动队列管理机制

提出了一种基于速率的主动队列管理机制。主要思想是根据每流过去的输入速率和输出速率预测下一个采样间隔内的输入速率和输出速率,用上一个采样间隔末的每流队列长度、预计输入、预计输出和期望的队长来决定数据包的丢弃概率,达到稳定队列长度和实现公平性的目的：仿真结果证明在多种网络条件下,算法能够实现稳定队列长度和每流公平性两个目的。     

A novel numerical algorithm based on self-tuning controller to support TCP flows

Active queue management (AQM) is an effective method used in Internet routers for congestion control, and to achieve a trade off between link utilization and delay. The de facto standard, the random early detection (RED) AQM scheme, and most of its variants use average queue length as a congestion indicator to trigger packet dropping.     

基于智能预测控制的网络拥塞主动队列管理算法研究

路由队列管理是保证网络性能、避免网络拥塞的重要手段,目前采用的主要队列管理方法为被动式队列管理,同时主动式队列管理已经成为近来的主要研究热点. 随机早侦测(RED)作为最早提出的主动队列管理方法,更获得了普遍的关注. 使用严格的数学模型来描述由端系统和网关组成的系统,并进行队列管理性能分析. 提出一种采用快速广义预测控制的RED控制器( FGPC2RED控制器) ,进行网络拥塞控制的研究. 介绍了系统的结构及系统的辨识, 并通过仿真证明了FGPC算法在路由队列管理中应用的可行性,可以有效控制队列长度,避免路由拥塞及减小往返延迟.     

Active queue management via event-driven feedback control

Active queue management (AQM) is investigated to avoid incipient congestion in gateways to complement congestion control run by the transport layer protocol such as the TCP. Most existing work on AQM can be categorized as (1) ad-hoc event-driven control and (2) time-driven feedback control approaches based on control theory. Ad hoc event-driven approaches for congestion control, such as RED (random early detection), lack a mathematical model. Thus, it is hard to analyze their dynamics and tune the parameters. Time-driven control theoretic approaches based on solid mathematical models have drawbacks too. As they sample the queue length and run AQM algorithm at every fixed time interval, they may not be adaptive enough to an abrupt load surge. Further, they can be executed unnecessarily often under light loads due to the time-driven nature. To seamlessly integrate the advantages of both event-driven and control-theoretic time-driven approaches, we present an event-driven feedback control approach based on formal control theory. As our approach is based on a mathematical model, its performance is more analyzable and predictable than ad hoc event-driven approaches are. Also, it is more reactive to dynamic load changes due to its event-driven nature. Our simulation results show that our event-driven controller effectively maintains the queue length around the specified set-point. It achieves shorter E2E (end-to-end) delays and smaller E2E delay fluctuations than several existing AQM approaches, which are ad hoc event-driven and based on time-driven control theory, while achieving almost the same E2E delays and E2E delay fluctuations as the two other advanced control theoretic AQM approaches. Further, our AQM algorithm is invoked much less frequently than the tested baselines.     

不确定TCP流模型的离散H∞鲁棒主动队列管理算法

针对TCP/IP网络存在参数时变和不确定性下的拥塞控制问题,提出一种新的基于H∞状态反馈控制的离散鲁棒主动列队管理算法(AQM).该方法针对不确定TCP流模型,将短期突发流所占据的带宽作为系统的外部干扰,同时考虑时滞和参数不确定性因素,基于Lyapunov稳定性理论和线性矩阵不等式技术,设计了离散鲁棒状态反馈控制器以保证路由器队列响应的稳定性和鲁棒性.最后,通过NS-2仿真验证了本文方法的有效性.     

A non-equilibrium analysis and control framework for active queue management

We present a non-equilibrium analysis and control approach for the Active Queue Management (AQM) problem in communication networks. Using simplified fluid models, we carry out a bifurcation study of the complex dynamic queue behavior to show that non-equilibrium methods are essential for analysis and optimization in the AQM problem. We investigate an ergodic theoretic framework for stochastic modeling of the non-equilibrium behavior in deterministic models and use it to identify parameters of a fluid model from packet level simulations. For computational tractability, we use set-oriented numerical methods to construct finite-dimensional Markov models, including control Markov chains and hidden Markov models. Subsequently, we develop and analyze an example AQM algorithm using a Markov Decision Process (MDP) based control framework. The control scheme developed is optimal with respect to a reward function, defined over the queue size and aggregate flow rate. We implement and simulate our illustrative AQM algorithm in the ns-2 network simulator. The results obtained confirm the theoretical analysis and exhibit promising performance when compared with well-known alternative schemes under persistent non-equilibrium queue behavior.     

动态网络增强自适应虚拟队列管理新算法

针对动态网络主动队列管理算法中控制参数设置难题,提出了一种增强自适应虚拟队列管理新算法（EPAVQ）。结合TCP流体流模型运用经典控制理论分析自适应虚拟队列管理（AVQ）算法稳定性基础上,利用极点配置技术给出了AVQ算法控制参数的调整规则。同时,针对网络参数时变问题,通过对网络参数的在线估计,利用网络参数与控制器参数的确定关系实时调节控制参数,使得控制器能够适应网络参数的变化。通过ns-2仿真实验与现有的AVQ算法比较,EPAVQ算法具有更快的动态响应,更好的网络性能。     

Internet路由器的AQM策略的研究与分析

分析了几种典型及最新提出的AQM策略算法,并比较了各种策略算法的优缺点,同时对AQM的拥塞指示方式进行了分析,最后给出了几种AQM策略的实验分析结果。     

基于启发式失效率函数的主动队列管理

研究主动队列管理技术的REI)和REM的丢包率和队长稳定性关系;基于启发式丢包处理方法,提出一种 采用启发式失效率函数计算丢弃概率函数以减小丢包率的拥塞控制算法(HFA)。在轻量级负载情况下,该算法性能 和自适应随机早期检测与随机指数标记相当;而在重量级负载情况下,不仅丢包率的均值和方差小,而且瞬时队长在 设定的目标范围,可以明显地减小队列长度的波动性。在N}2上进行的大量实验结果表明,所提算法具有瞬时队长 控制在预期范围、抖动性小、丢包率及丢包率方差小等优点。