基于自相似聚合业务流量的AQM算法性能评价

现有TCP/AQM忽略了非响应业务流量对AQM算法性能的影响,但非响应业务流量约占Internet业务流量的70%～80%.因此,评价非响应业务流量对AQM算法性能的影响具有重要意义.借助于在标准GI/M/1/N排队系统中嵌入AQM算法随机丢包机制的手段,提出了一种利用"扩充的GI/M/1/N排队系统"评价AQM算法在非响应业务流量下的性能的分析方法.最后评价了TD,RED和GRED这3种经典的AQM算法,评价结果与NS-2模拟结果一致,表明该分析方法可能用于评价AQM算法在非响应业务流量下的性能.     

典型AQM算法的性能评价模型

利用GI/M/1/N排队系统和Internet业务流量自相似性的特点建立了一个评价AQM算法在非响应业务流量下性能的分析模型,提出了利用模型的分析计算结果而不是模拟或实验手段评价AQM算法性能的新方法.同模拟或实验手段相比,该方法能更深刻地刻画AQM算法在实际网络环境中的性能.用该模型分析比较3个经典的AQM算法——TD、RED和GRED的性能,所得的结果同其他研究者利用模拟或实验方法所得的结果一致.     

参数自适应的随机早期检测算法

主动队列管理(AQM)算法是最近网络拥塞控制研究的重点,随机早期检测(RED)算法作为 AQM 算法的代表受到广泛的关注.分析了随机早期检测算法的原理和局限性,针对 RED 算法参数配置困难的问题,提出了一种参数自适应的随机早期检测算法.该算法能够根据网络负荷的变化动态的调节 RED 算法的参数,从而能够在突发业务下对拥塞做出及时有效的反应.通过仿真表明该算法能够有效地降低丢包率,降低数据包排队延时,提高了 RED 算法的网络适应性.     

基于Dahlin算法的主动队列管理控制机制研究

主动队列管理 (AQM)是网络中间节点通过一定的分组丢弃策略来达到较低排队时延和较高吞吐量的一种机制。已有多种AQM算法被提出,但绝大多数没有考虑较大的RTT(往返时间)对算法性能的影响。该文针对大RTT的网络环境,实现了一种基于控制理论中Dahlin算法的AQM机制并分析了系统的稳定性和参数选择的准则。仿真实验结果表明,该算法在RTT较大的情况下稳定性、响应速度和鲁棒性都优于随机早期检测(RED)算法和比例－积分(PI)算法。     

模糊自适应算法在网络主动队列管理中的研究

为了改善由于RED算法控制的主动队列管理策略(AQM)系统引起网络响应时间过长,许多文献提出了基于P/PI控制器的AQM策略。但是,由于网络具有非线性特点,论文设计了一种模糊自适应PID控制器的主动队列管理系统,根据队列长度和队列长度变化通过模糊控制规则在线调整PID控制器参数,并用Matlab进行了仿真,验证了当网络出现突发分组时,该算法能够较快的使分组稳定在队列阀值附近,同时不产生队列震荡。     

一种新的主动队列管理算法

提出一种新的主动队列管理（AQM）算法。本算法以V. Misra的TCP流量随机微分方程模型为基础,在计入窗口限制的约束条件下,由局部线性化方法导出本文主动队列管理模型的传递函数,并以其作为受控对象,利用比例积分微分（PID）调节器控制该传递函数输出与理想队列长度之差。仿真分析表明,本算法性能优于RED和ARED算法。     

一种链路负载自适应的主动队列管理算法

随机早检测(random early detection,简称RED)是IETF推荐部署的主动队列管理(active queue management,简称AQM)算法.RED存在参数难以配置、无法得到与流量无关的平均队长等问题.ARED(adaptive RED)是RED的自适应版本,它根据平均队长动态调节最大标记概率参数,从而得到稳定的平均队长.但ARED没有克服瞬时队列长度振荡问题,且在动态流量环境下性能明显降低.分析了ARED性能问题的原因,并提出了一种链路负载自适应的主动队列管理算法LARED(load adaptiveRED).LARED具有两个特点:自适应链路负载、快速响应队长变化.分析和仿真实验表明,与ARED等其他AQM算法相比,LARED在保持高链路利用率和低时延的同时可以得到稳定的瞬时队长,并且具有良好的响应性和鲁棒性.     

TCP/AQM系统大时间尺度模型

网络传输连接的往返时延(round-trip times,RTT)大小各不相同,因此TCP/AQM系统本质为一多时滞回路耦合系统.由于RTT分布范围远大于控制量调节周期,这给准确评估控制效果带来很大困难.已有基于控制理论的主动队列管理(active queue management,AQM)算法多以流体流模型为基础进行设计,没有充分考虑RTT和采样周期对系统性能的影响.对于TCP/AQM系统,合理的评价方法是对调节过程进行评价,而非仅评价单个采样周期内的控制量是否合适.本文结合数据驱动控制思想和系统自身特征,统一从路由视角对TCP与AQM之间的交互进行抽象,通过时间扩展从更大的时间尺度去评价控制量调节过程,然后基于此模型设计自适应AQM算法–—大时间尺度AQM算法(large time scale AQM,LTSAQM).仿真结果表明,该算法收敛速度快,排队时延抖动小,特别是在长时滞网络环境下,性能明显改善.     

基于延时补偿结构的大时滞网络拥塞控制

研究和分析了几种典型的主动队列管理AQM(Active Queue Management)算法在大时滞网络下的稳定性、性能及响应速度,发现如RED、PI等AQM算法在大时滞网络环境下队列出现剧烈的振荡和空队列增多,这些现象直接导致链路利用率降低和丢包率增大.针对上述的大时滞网络,将具有正反馈的延时补偿结构用于TCP/AQM拥塞窗口动态模型,实现对延时的补偿,仿真表明采用该控制结构提高了网络的性能.     

一种基于可变结构的主动队列管理算法

主动队列管理算法(AQM)是近年来网络拥塞控制的研究热点之一,已经提出了许多的主动队列管理算法,例如:RED,ARED,SRED,PI,REM等.文中设计一种基于控制理论的可变结构的主动队列管理.通过分析控制机制对于非线性的TCP/AQM模式的鲁棒性和性能,展示了在不确定的RTT(round-trip time)和活跃的TCP连接个数的情况下,有很好的性能和鲁棒性,这正是主动队列管理最重要的理念.运用网络仿真软件NS对设计进行仿真验证,从不同的角度对其性能与现有队列管理算法进行比较.仿真结果显示,从稳定性和鲁棒性等角度,可变结构控制算法显著胜过现有的AQM算法     

Performance evaluation for DRED discrete-time queueing network analytical model

Due to the rapid development in computer networks, congestion becomes a critical issue. Congestion usually occurs when the connection demands on network resources, i.e. buffer spaces, exceed the available ones. We propose in this paper a new discrete-time queueing network analytical model based on dynamic random early drop (DRED) algorithm to control the congestion in early stages. We apply our analytical model on two-queue nodes queueing network. Furthermore, we compare between the proposed analytical model and three known active queue management (AQM) algorithms, including DRED, random early detection (RED) and adaptive RED, in order to figure out which of them offers better quality of service (QoS). We also experimentally compare the queue nodes of the proposed analytical model and the three AQM methods in terms of different performance measures, including, average queue length, average queueing delay, throughput, packet loss probability, etc., aiming to determine the queue node that offers better performance.     

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。     

Adaptive mechanism-based congestion control for networked systems

In order to assure the communication quality in network systems with heavy traffic and limited bandwidth, a new ATRED (adaptive thresholds random early detection) congestion control algorithm is proposed for the congestion avoidance and resource management of network systems. Different to the traditional AQM (active queue management) algorithms, the control parameters of ATRED are not configured statically, but dynamically adjusted by the adaptive mechanism. By integrating with the adaptive strategy, ATRED alleviates the tuning difficulty of RED (random early detection) and shows a better control on the queue management, and achieve a more robust performance than RED under varying network conditions. Furthermore, a dynamic transmission control protocol–AQM control system using ATRED controller is introduced for the systematic analysis. It is proved that the stability of the network system can be guaranteed when the adaptive mechanism is finely designed. Simulation studies show the proposed ATRED algorithm achieves a good performance in varying network environments, which is superior to the RED and Gentle-RED algorithm, and providing more reliable service under varying network conditions.     

Per-stream loss behavior of ∑MAP/M/1/K queuing system with a random early detection mechanism

In this paper, the matrix-analytic approach is applied to explore the per-stream loss behavior of the multimedia traffic under RED scheme. We constructed a ∑MAP/M/1/K queuing model for the RED mechanism with multimedia traffic which follows a continuous-time Markovian arrival process (MAP). In addition to evaluating the long-term per-stream packet drop probabilities, we examine the bursty nature of per-stream packet drops by means of conditional statistics with respect to dropped periods and the probability that the queuing system stays in the dropped period. The dropped period corresponds to having more than a certain number of packets in router buffer; non-dropped period corresponds to the opposite. These performance measures describe the quality of service provided by the router to particular multimedia traffic streams in the presence of background multimedia traffic.     

LRED: A Robust and Responsive AQM Algorithm Using Packet Loss Ratio Measurement

Active queue management (AQM) is an effective means to enhance congestion control, and to achieve trade-off between link utilization and delay. The de facto standard, random early detection (RED), and many of its variants employ queue length as a congestion indicator to trigger packet dropping. Despite their simplicity, these approaches often suffer from unstable behaviors in a dynamic network. Adaptive parameter settings, though might solve the problem, remain difficult in such a complex system. Recent proposals based on analytical TCP control and AQM models suggest the use of both queue length and traffic input rate as congestion indicators, which effectively enhances stability. Their response time generally increases however, leading to frequent buffer overflow and emptiness. In this paper, we propose a novel AQM algorithm that achieves fast response time and yet good robustness. The algorithm, called Loss Ratio-based RED (LRED), measures the latest packet loss ratio, and uses it as a complement to queue length for adaptively adjusting the packet drop probability. We develop an analytical model for LRED, which demonstrates that LRED is responsive even if the number of TCP flows and their persisting times vary significantly. It also provides a general guideline for the parameter settings in LRED. The performance of LRED is further examined under various simulated network environments, and compared to existing AQM algorithms. Our simulation results show that, with comparable complexities, LRED achieves shorter response time and higher robustness. More importantly, it trades off the goodput with queue length better than existing algorithms, enabling flexible system configurations     

Active Queue Management算法研究

主动队列管理算法对于IP网络的性能影响重大,是网络拥塞控制一个主要手段。介绍了目前主要的主动队列管理算法如RED、改进的RED以及P控制器、PI控制器、模糊控制器、鲁棒控制器、内模控制器。通过对这些算法的分析,指出其中的不足之处,并对AQM算法的设计提出了一些思路。