Advances in Active Queue Management (AQM) Based TCP Congestion Control

Current end-to-end Internet congestion control under tail-drop (TD) queue management experiences performance degradations such as multiple packet losses, high queueing delay and low link utilization. In this paper, we review recently proposed active queue management (AQM) algorithms for supporting end-to-end transmission control protocol (TCP) congestion control. We focus recently developed control theoretic design and analysis method for the AQM based TCP congestion control dynamics. In this context, we analyze the problems of existing AQM proposals in which congestion is detected and controlled reactively based on current and/or past congestion. Then we argue that AQM based TCP congestion control should be adaptive to the dynamically changing traffic situation in order to detect, control and avoid the current and the incipient congestion proactively. Finally, we survey two adaptive and proactive AQM algorithms, PID-controller and Pro-Active Queue Management (PAQM), designed using classical proportional-integral–derivative (PID) feedback control to overcome the reactive congestion control dynamics of existing AQM algorithms. A comparative study of these AQM algorithms with existing AQM algorithms is given. A simulation study under a wide range of realistic traffic conditions suggests that PID-controller and PAQM outperform other AQM algorithms such as random early detection (RED) [Floyd and Jacobson, 18] and proportional-integral (PI) controller [Hollot et al., 24].     

Simulation comparison of active queue management algorithms in TCP/IP networks

Active Queue Management techniques are recommended to overcome the performance limitations of TCP congestion control mechanisms over drop-tail networks. The main objective of this paper is to present the comparative analysis of the performance of 10 different queue management policies using the OMNeT++ simulator. The AQMs have many parameters which influence their behavior, so some results concerning the parameters selection are given. The algorithms are tested in terms of average queue size, packet delay and packet loss rate in presence of TCP traffic.     

无线误码信道上的拥塞控制策略

主要讨论了无线网络拥塞控制的问题，基于将网络层和传输层策略相结合的思想，一方面在网络层，根据控制论中的不完全微分PID控制器思想设计了一种主动队列管理算法PID—AQM；另一方面，利用TCPW协议作为传输层策略，讨论了将二者相结合在无线网络中的拥塞控制性能。仿真结果表明，两种策略的结合大大提高了无线网络的传输效率。     

AQM controller design for TCP networks based on a new control strategy

When the network suffers from congestion, the core or edge routers signal the incidence of congestion through the active queue management (AQM) to the sources. The time-varying nature of the network dynamics and the complex process of retuning the current AQM algorithms for different operating points necessitate the development of a new AQM algorithm. Since the non-minimum phase characteristics of the network dynamics restrict direct application of the proportional-integral-derivative (PID) controller, we propose a compensated PID controller based on a new control strategy addressing the phase-lag and restrictions caused by the delay. Based on the unstable internal dynamics caused by the non-minimum phase characteristics, a dynamic compensator is designed and a PID controller is then allowed to meet the desired performance objectives by specifying appropriate dynamics for the tracking error. Since the controller gains are obtained directly from the dynamic model, the designed controller does not require to be tuned over the system operating envelop. Moreover, simulation results using ns2 show improvements over previous works especially when the range of variation of delay and model parameters are drastic. Simplicity, low computational cost, self-tuning structure and yet considerable improvement in performance are exclusive features of the proposed AQM for the edge or core routers.     

几种公平的主动队列管理算法的比较研究

主动队列管理是实现网络拥塞控制的一种重要技术,但是多数主动队列算法如RED等对于公平性的考虑不足.近年来,也出现了一些能提供一定的公平性支持的主动队列管理算法,本文对其中几个有代表性的算法进行了对比研究.包括对它们的理论分析,以及在ns2上的仿真实验,并且结合实验结果对算法中存在的问题及其原因进行了深入的分析.文中最后对这几种算法进行了综合的评价,并对算法的改进提出了一些建议,希望能为今后的工作提供一定的支持.     

Stability analysis in an AVQ model of Intemet congestion control algorithm

This paper focuses on the local stability of a classical congestion control model in the Internet,namely adaptive virtual queue(AVQ) algorithm with feedback delay.Firstly,necessary and sufficient stability conditions in terms of key tuning parameters are given,which can provide exact guidelines for setting system parameters.Furthermore,by computing the rightmost characteristic root,the optimal parameter configuration for AVQ is derived,which can guarantee superior stability performance.Finally,some simulation examples are given to illustrate the correctness of the theoretical analysis.     

RED gateway congestion control using median queue size estimates

This paper focuses on the queue size estimation problem in random early detection (RED) gateways. Queue size estimation plays a fundamental role in the congestion control dynamics of RED, as it determines gateways' awareness of network congestion, which in turn determines the packet dropping/marking decision. Conventional RED gateways use exponentially weighted moving averages (EWMA) to estimate the queue size. These infinite impulse response (IIR) filters require very small EWMA weights in order to effectively avoid nonlinear instabilities in RED and to filter out bursty increases in the queue size. While small EWMA weights enable gateways to accommodate transient congestion, they also lead to gateways' failure to closely track rapid queue size depletion and thus causes link under utilization. We investigate the use of simple nonlinear queue size estimators. In particular, we study the congestion control dynamics of a network where adaptive weighted median filters are used for queue size estimation by the gateways. Analytical results for the expected queue size in the steady state are derived. Under this new queue size estimation framework, design guidelines for the remaining RED parameters are provided. Simulation results show that the proposed algorithm provides greater network power, better prevention of global synchronization, and a fairer treatment to bursty traffic than the RED algorithm does.     

互联网中的不确定时滞全局滑模AQM算法

为解决互联网中的拥塞现象,基于全局滑模理论,提出了一种主动队列管理算法.将互联网中的不确定因素等效为拥塞控制模型的参数摄动,并考虑到时变时滞因素,利用线性矩阵不等式设计了渐近稳定的全局滑模面,使系统运动的全程都是滑动模态,显著提高了系统的鲁棒性.并且所设计的控制器能够有效降低路由器中队列长度的稳态振荡.仿真对比表明,所提出的算法具有更高的稳定性和鲁棒性,能够适应复杂多变的互联网环境.     

A fuzzy-logic control algorithm for active Queue Management in IP networks

Active Queue Management （AQM） is an active research area in the Internet community. Random Early Detection （RED） is a typical AQM algorithm, but it is known that it is difficult to configure its parameters and its average queue length is closely related to the load level. This paper proposes an effective fuzzy congestion control algorithm based on fuzzy logic which uses the predominance of fuzzy logic to deal with uncertain events. The main advantage of this new congestion control algorithm is that it discards the packet dropping mechanism of RED, and calculates packet loss according to a preconfigured fuzzy logic by using the queue length and the buffer usage ratio. Theoretical analysis and Network Simulator （NS） simulation results show that the proposed algorithm achieves more throughput and more stable queue length than traditional schemes. It really improves a router＇s ability in network congestion control in IP network.     

一种基于模糊逻辑的主动队列管理算法

主动队列管理 (ActiveQueueManagement,AQM)技术作为Internet拥塞控制的一种有效方法 ,对于提高In ternet的服务质量具有十分重要的作用 .本文根据TCP拥塞控制算法基于数据包丢失的窗口变化机制 ,设计了一种基于模糊逻辑的主动队列管理算法 .该算法依据路由器中队列长度的变化情况 ,根据一定的模糊自校正原则来调整数据包的丢弃概率 ,从而使路由器中的队列长度稳定在参考值附近 .仿真结果表明该算法不但十分有效 ,而且对不同的网络状况具有很好的适应能力 .     

携带虚拟队列长度信息的ABR业务流量控制算法

本文提出了一种新的基于速率检测拥塞的ABR流量控制算法--E-EFCI，它的基本思想是在基于速率检测拥塞的基础上扩展EFCI的功能，使其不仅反映网络阻塞状况，而且还反映网络排队状况。在交换机中通过虚拟队列的长度设置EFCI来传递网络的排队信息。仿真结果表明，本文提出的算法比基本EFCI算法具有更好的控制行为，减小了ACR和排队长度的振荡幅度，提高了链路、缓存利用率，加快拥塞解除，并具有较高的性能价格比。     

基于HTTP的网络服务性能建模与分析

该文将服务器系统和通信访问网络考虑为一个整体建模,给出了一个基于HTTP的Web系统的服务性能模型,并将模型扩展到了多服务器系统;分析了各模型参数对网络服务性能的影响,提出了避免死锁状态的方法和增加服务器的速率原则;最后对比了几种提高服务性能的方法.仿真结果证实了模型的有效性.     

Real-time image processing approach to measure traffic queueparameters

The real-time measurement of various traffic parameters including queue parameters is required in many traffic situations such as accident and congestion monitoring and adjusting the timings of the traffic lights. In case of the queue detection, at least two algorithms have been proposed by previous researchers. Those algorithms are used for queue detection and are unable to measure queue parameters. The authors propose a method based on applying the combination of noise insensitive and simple algorithms on a number of sub-profiles (a one-pixel-wide key-region) along the road. The proposed queue detection algorithm consists of motion detection and vehicle detection operations, both based on extracting edges of the scene, to reduce the effects of variation of lighting conditions. To reduce the computation time, the motion detection operation continuously operates on all the sub-profiles, but the vehicle detection is only applied to the tail of the queue. The proposed algorithms have been implemented on an 80386-based microcomputer system and the whole system works in real-time     

传感器网络拥塞避免与控制的模糊AQM算法

传感器网络节点通信能力有限,当数据到达速率持续超过节点转发能力时网络会发生拥塞;传感器网络是任务型网络,对不同优先级的信息具有不同的服务质量要求.针对传感器网络信息传输的上述特性,提出了一种新的拥塞避免与控制算法FAQM（Fuzzy Active Queue Management）.该算法在综合考虑数据包的随机指数标记概率和优先级权值的基础上,建立了模糊逻辑推理系统,并以数据包丢弃因子作为参量来实现数据流的智能调控.NS2仿真实验结果表明：FAQM算法能减少高优先级数据包的丢弃率和节点间链路的时延,稳定节点队列长度,在有效避免与控制拥塞网络的同时提升网络整体QoS（Quality of Service）性能.     

基于粒子群优化的网络拥塞控制新算法

PI控制器常用于主动队列管理中,但参数整定上的试凑法具有盲目性,算法的瞬态性能也不够理想.本文推导了基于流体流理论的网络简化模型,基于该模型将集群智能中的改进粒子群优化算法(PSO)应用于PID控制器参数优化,定义了一个综合调节时间、上升时间、超调量、系统静态误差、正弦跟踪误差等动静态性能指标函数,在给定的参数空间进行组合优化搜索,迅速求得获取使性能指标优化函数极小化的一组PID控制器参数,将PID控制器应用于网络主动队列管理系统中.仿真结果表明,在大时滞和突发业务流的冲击两种情况下,该方法设计的控制器的动静态性能优于RED、PI算法,超调量均小于5%,调节时间分别小于5秒、4秒,稳态误差分别小于两个数据包和3个数据包.     

PAQM: an adaptive and proactive queue management for end‐to‐end TCP congestion control

Two functions, the congestion indicator (i.e. how to detect congestion) and the congestion control function (i.e. how to avoid and control congestion), are used at a router to support end‐to‐end congestion control in the Internet. Random early detection (RED) (IEEE/ACM Trans. Networking 1993; 1 (4):397–413) enhanced the two functions by introducing queue length averaging and probabilistic early packet dropping. In particular, RED uses an exponentially weighted moving average (EWMA) queue length not only to detect incipient congestion but also to smooth the bursty incoming traffic and its resulting transient congestion. Following RED, many active queue management (AQM)‐based extensions have been proposed. However, many AQM proposals have shown severe problems with detection and control of the incipient congestion adaptively to the dynamically changing network situations. In this paper, we introduce and analyse a feedback control model of TCP/AQM dynamics. Then, we propose the Pro‐active Queue Management (PAQM) mechanism, which is able to provide proactive congestion avoidance and control using an adaptive congestion indicator and a control function under a wide range of traffic environments. The PAQM stabilizes the queue length around the desired level while giving smooth and low packet loss rates and high network resource utilization. Copyright © 2004 John Wiley & Sons, Ltd.     

A compensated PID active queue management controller using an improved queue dynamic model

Beside the major objective of providing congestion control, achieving predictable queuing delay, maximizing link utilization, and robustness are the main objectives of an active queue management (AQM) controller. This paper proposes an improved queue dynamic model while incorporating the packet drop probability as well. By applying the improved model, a new compensated PID AQM controller is developed for Transmission Control Protocol/Internet Protocol (TCP/IP) networks. The non‐minimum phase characteristic caused by Padé approximation of the network delay restricts the direct application of control methods because of the unstable internal dynamics. In this paper, a parameter‐varying dynamic compensator, which operates on tracking error and internal dynamics, is proposed to not only capture the unstable internal dynamics but also reduce the effect of uncertainties by unresponsive flows. The proposed dynamic compensator is then used to design a PID AQM controller whose gains are obtained directly from the state‐space representation of the system with no further gain tuning requirements. The packet‐level simulations using network simulator (ns2) show the outperformance of the developed controller for both queuing delay stability and resource utilization. The improved underlying model leads also to the faster response of the controller. Copyright © 2013 John Wiley & Sons, Ltd.     

一种基于Markov及反馈机制的网络拥塞控制方法

在研究现有网络数据传递拥塞控制问题的基础上,提出了一种基于路由器缓冲区队列长度的网络拥塞预测机制,并以该预测机制为基础提出了一种计费策略(PPBC,Per-Packet Billing Control)来控制网络拥塞.在拥塞控制模式中,将路由器缓冲区队列长度作为拥塞指标,通过马尔可夫链建模预测网络拥塞度.在服务器终端和数据发送方之间建立反馈机制,利用网络拥塞度,通过数据包计费方式控制网络拥塞.最后采用NS2仿真软件对PPBC性能进行仿真测评,仿真结果表明:PPBC不仅能够有效缓解网络拥塞,还能够使网络保持较低的丢包率.     

Random early detection gateways for congestion avoidance

The authors present random early detection (RED) gateways for congestion avoidance in packet-switched networks. The gateway detects incipient congestion by computing the average queue size. The gateway could notify connections of congestion either by dropping packets arriving at the gateway or by setting a bit in packet headers. When the average queue size exceeds a present threshold, the gateway drops or marks each arriving packet with a certain probability, where the exact probability is a function of the average queue size. RED gateways keep the average queue size low while allowing occasional bursts of packets in the queue. During congestion, the probability that the gateway notifies a particular connection to reduce its window is roughly proportional to that connection's share of the bandwidth through the gateway. RED gateways are designed to accompany a transport-layer congestion control protocol such as TCP. The RED gateway has no bias against bursty traffic and avoids the global synchronization of many connections decreasing their window at the same time. Simulations of a TCP/IP network are used to illustrate the performance of RED gateways     

动态权重RED网关

随着网络流量的增加,拥塞控制的重要性日益突出,尤其是链路拥塞控制。IETF推荐RED(Random Early Detection)作为下一代Internet路由器的拥塞控制算法。该文在分析了RED的优点和缺点后,在现在RED算法的基础上通过改进RED算法的平均队列长度计算,使用平均队列长度的均值,判断拥塞的发生和结束,动态调整权重,提高RED对拥塞发生和拥塞结束的反应速度,缩短拥塞时间,维持较低的实际队列长度。最后用仿真验证了该方法。