基于动态输出反馈控制的主动队列管理算法

 针对网络拥塞控制的不确定时滞特性,提出了一种基于动态输出反馈控制(DOFC)的主动队列管理(AQM)算法.建立了TCP/AQM系统的时滞有界模型,给出了判定闭环AQM系统稳定的充分性条件,以及基于线性矩阵不等式的动态输出反馈控制器参数设计方法.仿真结果表明,该算法在大时滞的网络环境中,能迅速地将队列长度收敛到目标长度附近,且在特征参数变化的网络环境中具有较强的鲁棒性.     

一种参数自适应的主动队列管理算法-自适应BLUE

BLUE算法是一种典型的主动队列管理(Active Queue Management,AQM)算法,研究表明BLUE算法优于RED算法.BLUE算法使用丢包事件和链路空闲事件控制网络拥塞.但由于BLUE算法在参数设置方面存在不足,尤其是当TCP连接数突然剧烈变动时,容易导致队列溢出或空闲的频繁发生.该文引进参数自适应机制,提出了自适应BLUE算法,并借鉴了RED算法的早期拥塞检测机制.NS仿真实验表明该算法能有效保持队列长度的稳定,减少队列溢出或空闲现象的发生,在提高链路利用率的同时降低丢包率.     

主动队列管理算法的分类器实现

作为端到端拥塞控制的增强机制,主动队列管理(AQM)通过在网络中间节点有目的地丢弃分组来维持较小的队列长度和较高的链路利用率.已有的大多数主动队列管理算法沿用了随机早期探测(RED)算法首创的概率丢弃机制.本质上,判决是否丢弃分组的过程是一个依赖于网络拥塞状态的决策过程,因此,概率决策不应该是唯一的方法.在本文的研究中,我们首先归纳了理想AQM算法所应具备的品质,然后应用模式识别中分类器的设计思想提出了一种新颖简洁的主动队列管理策略实现框架,并基于Fisher线性判别方法为AQM设计了一个两维两类分类器(TCC).仿真试验表明TCC有效、敏捷、鲁棒,扩展性好,同时实现简单,计算开销小,有利于高速路由器的性能优化.     

有线网络PSO-PID主动队列管理算法稳定性分析

主动队列管理算法的稳定性是实现拥塞控制的基础,针对目前PID-AQM控制器控制参数大多基于经验、缺乏稳定性分析的问题,提出了粒子群优化PID参数的整定策略,同时运用稳定分析论分析PSO-PID队列管理算法的稳定性.考虑TCP/AQM系统的时滞性,将时延系统利用泰勒展开转化为非时延系统进行稳定性判定.通过NS2仿真,结果表明,PSO-PID算法稳定性明显优于PID算法.     

SBlue:一种增强Blue稳定性的主动式队列管理算法

主动式队列管理(AQM)是 IETF 为解决 TCP 端到端拥塞控制机制存在的问题而提出的一种队列管理技术。Blue 是一种常用的 AQM 算法,它使用丢包事件和链路空闲事件来管理拥塞。相比较于 RED 算法,Blue 有很多优点,但由于缺乏早期拥塞检测机制,因此不能维持队列长度的稳定,特别是当 TCP 连接很多或 TCP 连接数发生突变时容易导致队列溢出或空闲。本文为此提出了一种增强 Blue 稳定性的主动式队列管理算法 SBlue。仿真实验表明,SBlue 能有效保持队列长度的稳定,大大减少队列溢出或空闲现象的发生。     

几种主动式队列管理算法的比较研究

主动式队列管理(Active Queue Management,AQM)技术是IETF为了解决Internet拥塞控制问题而提出的一种路由器缓存管理技术.本文对几种主要AQM算法RED、BLUE、ARED和SRED的性能在基于ns-2仿真实验的基础上进行了比较研究.研究的性能包括队列长度、丢包概率、丢包率、连接数对吞吐量的影响及缓冲区大小对链路利用率的影响等.仿真结果表明BLUE、ARED和SRED在这几方面的性能都要优于RED算法.     

一种基于动态阈值的主动队列管理算法

针对BLUE算法缺少早期拥塞检测机制,导致队列溢出或空闲现象频繁发生的问题,通过引进基于动态阈值算法的控制机制,借鉴RED算法所采用的早期拥塞检测机制,提出了DT-BLUE算法。仿真实验表明本文算法能保持队列长度的稳定性,有效降低队列空闲或溢出现象的发生,提高链路的利用率。     

一种顽健的自校正主动队列管理机制

现有基于控制理论的主动队列管理机制（AQM）大多数是根据简化的线性被控对象模型设计的,或者根据特定的网络条件设置算法的参数,当网络条件大范围变化时算法的性能难以保证.为了解决这些问题,提出了一种自校正的主动队列管理机制STR,通过在线估计TCP/AQM闭环系统被控对象模型的参数,并相应地调节报文丢弃概率,使路由器的缓冲区队列长度与期望值之间的方差最小.通过仿真实验验证了当网络条件大范围变化时算法的队列长度、链路利用率、报文丢弃率等性能,实验结果表明该算法具有良好的顽健性.     

基于模糊免疫PID的时滞网络自适应主动队列管理

提出了一种基于灰预测和模糊免疫PID控制的时滞网络自适应主动队列管理（AQM）算法FIGAPID，旨在增强AQM算法动态自适应能力，同时补偿网络时滞，综合提高AQM算法性能。该算法借助免疫反馈机理进行PID参数的在线自适应调整，采用模糊非线性逼近的方法进行免疫反馈函数的确定；采用等维新息滚动灰预测实现路由器队列长度的超前预测，补偿AQM控制的反馈滞后。对比传统PID算法，仿真验证了FIGAPID的有效性，表明算法能快速稳定地适应动态时滞网络环境变化，收敛于路由器队列长度期望值，同时具有较小的数据丢包率。     

TCP-AQM拥塞控制机制的稳定性-时间域方法

文章讨论了TCP—AQM拥塞控制机制的稳定性问题。基于一类为人熟知的TCP非线性模型，我们利用现代控制理论解决了若干网络拥塞控制中的控制器的参数设计问题。文章首先讨论了一类典型的时滞系统，并从此出发．给出了设计在存在网络传输延迟、负载水平变化的情况下的多种控制器的参数设计准则。我们还展望了网络拥塞问题的随机时滞模型。     

Stability and sensitivity for congestion control in wireless mesh networks with time varying link capacities

A critical challenge for wireless mesh networks is the design of efficient transport protocols that provide high bandwidth utilization and desired fairness in the multi-hop, wireless environment. While extensive efforts have been devoted to providing optimization based, distributed congestion control schemes for efficient bandwidth utilization and fair allocation in both wireline and wireless networks, a common assumption therein is fixed link capacities. This unfortunately will limit the application scope in wireless mesh networks where channels are ever changing. In this paper, we explicitly model link capacities to be time varying and investigate congestion control problems in multi-hop wireless networks. In particular we propose a primal–dual congestion control algorithm which is proved to be trajectory stable in the absence of feedback delay. Different from system stability around a single equilibrium point, trajectory stability guarantees the system is stable around a time varying reference trajectory. Moreover, we obtain sufficient conditions for the scheme to be locally stable in the presence of delay. Our key technique is to model time variations of capacities as perturbations to a constant link. Furthermore, to study the robustness of the algorithm against capacity variations, we investigate the sensitivity of the control scheme and through simulations to study the tradeoff between stability and sensitivity.     

A novel adaptive traffic prediction AQM algorithm

In the Internet, network congestion is becoming an intractable problem. Congestion results in longer delay, drastic jitter and excessive packet losses. As a result, quality of service (QoS) of networks deteriorates, and then the quality of experience (QoE) perceived by end users will not be satisfied. As a powerful supplement of transport layer (i.e. TCP) congestion control, active queue management (AQM) compensates the deficiency of TCP in congestion control. In this paper, a novel adaptive traffic prediction AQM (ATPAQM) algorithm is proposed. ATPAQM operates in two granularities. In coarse granularity, on one hand, it adopts an improved Kalman filtering model to predict traffic; on the other hand, it calculates average packet loss ratio (PLR) every prediction interval. In fine granularity, upon receiving a packet, it regulates packet dropping probability according to the calculated average PLR. Simulation results show that ATPAQM algorithm outperforms other algorithms in queue stability, packet loss ratio and link utilization.     

多层卫星网络链路中断容忍路由策略设计

链路中断和接续对卫星网络路由有重要影响,该文针对多层卫星网络,设计了链路中断容忍路由策略,利用非均匀时间段内卫星网络拓扑结构的可预测性进行路由表计算,采取动态的拥塞控制机制和洪泛策略,解决由于卫星运动、通信设备故障引发链路中断情况下的路由问题。仿真结果表明,该路由策略具有较高的链路利用率,能够减少动态路由计算中时延信息收集和星上路由表生成给卫星节点带来的时空开销。     

Cross-layer congestion control in ad hoc wireless networks

The paper presents the problem of performance degradation of transport layer protocols due to congestion of wireless local area networks. Following the analysis of available solutions to this problem, a cross-layer congestion avoidance scheme (C³TCP) is presented, able to obtain higher performance by gathering capacity information such as bandwidth and delay at the link layer. The method requires the introduction of an additional module within the protocol stack of the mobile node, able to adjust the outgoing data stream based on capacity measurements. Moreover, a proposal to provide optional field support to existing IEEE 802.11 protocol, in order to support the presented congestion control solution as well as many other similar approaches, is presented. Achieved results underline good agreement with design considerations and high utilization of the available resources.     

Congestion control for multimedia services

The problem of congestion control in high-speed networks for multimedia traffic, such as voice and video, is considered. It is shown that the performance requirements of high-speed networks involve delay, delay-jitter, and packet loss. A framing congestion control strategy based on a packet admission policy at the edges of the network and on a service discipline called stop-and-go queuing at the switching nodes is described. This strategy provides bounded end-to-end delay and a small and controllable delay-jitter. The strategy is applicable to packet switching networks in general, including fixed cell length asynchronous transfer mode (ATM), as well as networks with variable-size packets     

基于星上处理的卫星ATM中ABR 业务拥塞控制算法研究

卫星ATM是近年来通信领域的研究热点,拥塞控制是其中很关键的一个问题.本文主要研究基于星上处理的卫星ATM网的ABR流量控制,它通过对流量的长时预测来达到控制目的.由于卫星信道的大延时,无法实现精确的长时预测,因而将预测结果直接用于ABR的拥塞控制效果不甚理想.将长时预测同动态利用因子控制的方法结合之后,在链路效率、信元丢失率、不同连接数目和暂态响应等方面都取得很好的结果.     

PDAVQ：一种基于PD控制的自适应虚拟队列管理算法

提出了一种新的基于比例差分控制的自适应虚拟队列管理(AVQ)算法—PDAVQ,用于对网络链路中产生的拥塞进行控制,以达到有效利用网络带宽,使整个网络系统达到稳定,缓解网络拥塞的目的。而且本文对所提算法运用控制理论对系统的稳定性进行了证明,给出了满足系统稳定性条件的参数选择方法和 PDAVQ 算法的具体描述。最后,通过 ns2 仿真实验与现有的 AVQ 算法比较,结果表明,所提 PDAVQ 算法具有较高的吞吐率、较低的链路延迟和数据丢失率,并能更快的使整个网络系统达到稳定,具有较好的网络性能。     

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.     

网络流量控制系统的设计--Kalman算法

在ATM网络的ABR通信中,基于速率反馈的流量控制是防止拥塞和保证高吞吐量的主要手段之一,然而网络的传播时延对其具有很大的不利影响。本文根据网络控制的特点,采用Kalman控制算法对流量控制器进行设计,较好地克服了传播时延所带来的不利影响。理论分析表明该算法保证了网络缓冲器的不溢出及带宽的公平分配和充分利用,动态性能明显优于PID控制器,并得到了仿真结果的验证。     

An Internet friendly transport protocol for continuous media over best effort networks

In this paper, we design and evaluate an Internet friendly transport‐level protocol (IFTP) for solving the TCP‐friendly problem. IFTP has two modes of operation. In the standard mode, the IFTP connection faithfully emulates the behaviour of TCP in order to roughly obtain a bandwidth equal to that of a TCP connection. In the extended mode, a simple modification is used to grant QoS‐differentiated services to selected connections. Connections running in the extended mode can get enhanced bandwidth while still emulating the general behaviour of TCP. We develop an analytical model for the congestion control mechanism of IFTP. We also derive analytically the amount of bandwidth that IFTP may be able to claim from TCP in ideal and non‐ideal environments. We evaluate IFTP through simulation and prove its TCP friendliness as well as provide performance results on some of the important metrics such as packet delay, delay jitter, packet loss and link utilization. Copyright © 2002 John Wiley & Sons, Ltd.