【作者】 高妍；

【导师】 关新平；

【作者基本信息】 燕山大学 ， 控制理论与控制工程， 2003， 硕士

【摘要】 未来的计算机网络将是一种能够提供多种不同服务，以支持多种不同应用需求，有着集成支持能力的高速分组交换网络。ATM网络正是支持这种综合业务数字网络的关键技术之一，已被国际电信联盟作为一项典型传输技术加以推广。在ATM网络中，信息流的拥塞及信息的丢失是影响网络业务服务质量的主要原因。为了充分提高ATM网络的性能和服务质量，设计一个高效的拥塞控制系统是一个关键问题。本文正是以此为出发点，将控制理论引入到网络通讯中，解决可控流－ABR业务的拥塞控制问题。本文首先从ATM网络通信基础知识开始，介绍了ATM网络基本原理和ABR业务的反馈机理。给出了一般通讯网络的数字化模型，并且基于Per-flow缓存网络模型，建立了ABR流量反馈控制模型。通过把ABR可用带宽当作系统干扰，在单纯的Smith拥塞控制的基础上，设计出前馈干扰补偿系统，使得队列长度稳定在的初始值之下，提高了链路的利用率。传输时延是影响网络拥塞控制算法的稳定性和性能的一个重要参数。Smith预估补偿是解决纯时延问题的有效工具，但其对预估模型的误差十分敏感。本文基于Per-flow缓存网络模型，提出3种鲁棒Smith预估拥塞控制器。在瓶颈交换机中同时存在不可控流的条件下，通过调整系统参数，使得网络在最糟糕的时延估计情况下，仍然能够保证服务质量和稳定运行。但是多通道共享同一瓶颈交换机的网络模型是不可避免的。本文在假设网络模型下提出了两种鲁棒Smith拥塞控制器。运用小增益定理解决鲁棒稳定性问题，在每个虚路径的往返时延都同时在预估值上下发生变化的情况下，使得交换机中的队列长度能够稳定在给定值，而且抖动都很小。最后，我们把网络拓扑结构模型更加复杂化：假设回路往返时延和虚通道个数随时间变化，提出一种较简单的比例拥塞控制器。最终定理的证明和仿真研究都表明，所设计的拥塞控制器可以保证系统“分段”稳定和网络服务质量。更多还原

【Abstract】 Future computer networks will become a high speed packed switched network that will be able to provide various service so as to support a wide range of network applications. ATM is just one of the key technologies that support the Integrated Service Digital Network (ISDN), which is adopted as a typical technique by the International Telecommunication Union (ITU) and is spread. But congestion of the traffic and the loss of data are main reasons that affect the quality of service. Design of an effective congestion control scheme is critical to the enhancements of the network performance. The paper is based on it and the control theory is introduced to solve the congestion of controllable flow.The paper begins with the foundation of ATM network, and introduces the basic work principle of networks and the feedback mechanism. Then, the normal data networks model is given and ABR feedback control model is set up based on per-flow buffer model. The feedforward disturbance compensation system based on pure Smith congestion control is designed, which regards the ABR bandwidth as the system disturbance. The queue length can be controlled beneath the threshold value and the link utilization is improved.Propagation delays could have an adverse impact on the stability and performance of congestion control algorithm in high-speed ATM networks. Smith principle is a good scheme for overcoming pure time-delay，but it is very sensitive to model estimation error. Therefore the pure Smith controller can’t stable the networks. Three robust Smith congestion controllers based on per-flow buffer model are designed. By regulating the parameters, the QoS (quality of service) of ABR flow could be improved on the condition that there exits uncontrolled traffic flow in the bottlenecked switch, which can guarantee the stability of the networks. But the networks topology model that multiple VCs (virtue circuits) sharing the same bottlenecked switch is popular. Two kinds of robust Smith congestion controllers are proposed under this assumed networks model.<WP=6>Employing the small gain theory can solve the problem of robust stability. Then, when the RTT (Round-trip time) of every VC fluctuates around the estimated value, the steady value of queue could track the specified expected value and the oscillation is very small.In the final, the structure of networks topology is assumed more complex: the RTT and the numbers of VC is changed with time. Based on this assumed networks, a simple proportion congestion controller is designed. At last, by proving the theorem and the simulations, the proposed congestion controllers can guarantee the "piece-wise" stable and the QoS.更多还原