【作者】 田义强；

【导师】 李国勇； 陈晓龙；

【作者基本信息】 太原理工大学 ， 控制理论与控制工程， 2010， 硕士

【摘要】 网络拥塞问题一直困扰着互联网(Internet)发展。基于源端的TCP拥塞控制算法和基于链路端的主动队列管理(AQM)算法相结合是解决拥塞问题的有效途径。本文主要在综述TCP拥塞控制算法中FAST TCP协议参数选择、AQM算法中早期随机检测(RED)算法参数选择和基于滑模控制理论的AQM算法设计研究现状基础上,展开了如下研究:(1)提出更为接近现实网络的FAST TCP拥塞控制模型,在对模型进行稳定性分析基础上得到了更为宽泛的FAST TCP协议参数设计指导方案。首先针对现有FAST TCP模型没有考虑窗口更新间隔参数,并忽略源端在估计拥塞信号时所采用指数平滑滤波稳定性因素的缺陷,改进其网络拥塞控制模型。其次将该模型在其平衡点附近进行线性化,进行Laplace变换后得到FAST TCP系统的开环传递函数。应用Routh判据对系统进行稳定性分析得到其稳定条件,然后提出了一种根据控制器增益参数、窗口更新周期和网络相关参数选择合适协议参数确保系统稳定的指导方案。最后理论计算和NS2仿真验证表明,和相关指导方案相比,该改进方案具有更宽泛的应用范围。(2)提出包含TCP自同步特性的拥塞控制模型,并在稳定性分析基础上给出了更为宽泛的RED参数设置指导方案。TCP自同步特性就是TCP窗口在每接收到一个确认帧后才发送新的数据分组,这样TCP源端数据分组发送速率就不能简单的表示为窗口大小与往返时延的比值,而是由收到的确认帧的瞬时速率决定。本文首先针对现有TCP/RED拥塞控制模型忽略TCP自同步特性缺陷,提出新的包含TCP自同步特性的拥塞控制模型。然后在系统平衡点附近对模型进行线性化,再Laplace变换后得到整个TCP/RED系统的开环传递函数。在应用Nyquist稳定性对系统进行稳定分析后,得到比现有TCP/RED拥塞控制模型更为宽松的RED参数设置范围。最后NS2仿真验证了该模型分析RED参数设置范围的有效性。(3)提出当系统参数扰动不满足匹配条件时基于滑模控制理论的AQM算法设计问题。首先改进了常用的网络拥塞控制模型,并在平衡点线性化后,采用还原算法进行延迟补偿,将该模型转化为无时滞的线性模型。在系统状态矩阵扰动不满足匹配但有界的条件下,采用积分滑模变结构控制算法,基于Lyapunov函数和线性矩阵不等式方法给出了滑模可到达和渐近稳定的可行条件,并根据该条件设计了鲁棒主动队列管理控制器。最后仿真结果验证了该控制器的有效性。更多还原

【Abstract】 The development of Internet has been encumbered with the congestion problem. The combination of TCP congestion control algorithm based on the source side and Active Queue Management (AQM) algorithm based on the link has become a main approach to solve the congestion control problem.Based on the corrent situation in review, which focuses in designing protocol parameter of FAST TCP in TCP congestion control algorithm, parameter selection of Random Early Detection (RED) algorithm in AQM algorithm, and the designing of AQM algorithm based on sliding mode control theory, the main research works and conclusions in this paper are as follows:(1) A more accurate FAST TCP congestion control model is proposed, and a more broadly parameter design guidance is obtained based on the stability analsis of the new model.First of all, aiming at the existing FAST TCP model unconsidering the window update interval parameters exponential smoothing filter which the source uses to estimate congestion signal, this paper improves the network congestion control model. Second, the model is linerarized in the vicinity of the equilibrium point, and FAST TCP open-loop system transfer function is obtained after Laplace transforming. The system stability conditions is obtained with the help of Routh stability criterion, then a preferences guidance scheme was proposed to ensure the network stability according to the controller gain parameter and windows update interval and network related parameter. The theory computing and the NS2 simulation results demonstrate that this improved guidance scheme possesses much extensive application area in contrast to other related scheme.(2) A new congestion control model including TCP self-synchronization is proposed, and a more broadly parameter design guidance is obtained based on the stability analsis of the new model. TCP self-synchronization is that TCP window doesn’t send a new packet to the link until receiving a confirmation frame,so packet sending rate in the source sind cannot simply expressed by the ratio of the window size and RTT, but by receiving the confirmation of the instantaneous speed frame. Aiming at the existing TCP/RED congestion control models ignoring TCP self-synchronization, this paper proposes a new congestion control model including TCP self-synchronization. Then the model is linerarized in the vicinity of the equilibrium point, and the open-loop system transfer function of TCP/RED is obtained after Laplace transforming. The system stability condition is obtained with the help of Nyquist stability criterion, then we receive a more relaxed RED parameters settings scope. At last, NS2 simulation is used to validate the effectiveness of the obtained RED parameters settings scope. (3) AQM algorithm based on sliding mode control theory is proposed when the system parameter perturbation is unmatched. Firstly the model in common use is modified and linearized at the equilibrium. Then the no time-delay linearization model was obtained by the reduction algorithm. The feasible condition with reachable and asymptotic stability of sliding surface was given through the integral sliding mode control algorithm based on the Lyapunov function and LMI method under the condition of the mismatched but bounded perturbation of system state matrix, in which the robust AQM controller was designed. Finally, the effectiveness of the designed controller is validated by simulation.更多还原