【作者】 王福豹；

【导师】 高德远；

【作者基本信息】 西北工业大学 ， 计算机应用， 2002， 博士

【摘要】 自适应比特速率(ABR)业务的流量控制是ATM网络中一种有效的拥塞控制机制和流量管理手段。在高速的ATM网络中，算法的简洁性在很大程度上决定着交换机的性能。尽管二进制ABR流量控制的简洁性具有相当的吸引力，但标准的EFCI算法控制的队列长度和允许信元速率(ACR)却易出现大幅振荡的现象，这势必会降低链路的利用率，严重影响交换机的性能。本文认为现有的基于直觉的启发式算法设计难免带有盲目性和片面性，为此，以现代控制理论为指导，通过仿真试验，对ATM网络的流量控制进行了深入研究，取得了一些成果。 提出并建立了二进制ABR流量控制数学模型，并在稳定工作点对模型进行了局部线性化，得到了ABR流量控制系统的线性模型，作为研究的基础。 在标准的EFCI算法的稳定性分析中，发现了系统振荡的本质原因在于系统中存在非线性环节，进而提出了对EFCI算法的改进，有效克服了系统振荡。 为了进一步克服系统振荡问题，提出采用一种线性的PID控制器来替换标准EFCI算法中的非线性环节，增强了系统的鲁棒性，并实现了队列长度的定点控制，有效地减少了排队延时。 考虑到网络状态参数的时变性，为了使流量控制算法具有较强的抗干扰能力，应用滑模变结构控制器，设计了相应的二进制ABR流量控制算法，适应了网络负载的动态变化，具有更好的鲁棒性。 论文最后通过仿真试验对TCP／IP在ATM网络中的传输性能进行了分析研究，给出了参考建议。更多还原

【Abstract】 Available Bit Rate (ABR) flow control is an effective measure in ATM network congestion control and traffic management. In high-speed ATM networks,the switch performance lies on the algorithm simplicity in some degree. Although the simplicity of binary flow control is very attractive,the queue length and allowed cell rate (ACR) controlled by the standard EFCI algorithm oscillate with great amplitude,which must have negative impact on the performance,so its applicability was doubted. Considering that the intuition-based heuristic algorithm has blindness and one-sidedness,based on the modern control theory,through simulation experiments,the flow control of ATM networks is studied deeply in this paper and some achievements are reached.The binary ABR flow control model is firstly deduced. Subsequently,the nonlinear model is locally linearized about equilibrium point,thus,the linear model is obtained. With this model,the performance of standard EFCI algorithm is evaluated and the conclusion is that oscillations are caused by the nonlinear component existed in EFCI algorithm. Thus,EFCI algorithm is improved and the oscillation is overcome validly.And further,a linear PID controller is designed to replace the nonlinear component in the standard EFCI algorithm,it makes flow control system more robust,at same time,controls the queue length to expected value,which is beneficial to decrease delay in queue.Because the network status is changeable in practice,in order to enhance the ability against disturbance and noise,a novel binary ABR flow control algorithm is put forward using the sliding mode variable structure controller. The simulation results show that new algorithms avoid the self-oscillation induced by the nonlinear component in the standard EFCIalgorithm.Finally,the transmission performance of TCP/IP over ATM is investigated through simulation experiments,and the valuable conclusion and constructive suggestions are drawn.更多还原