ATM网络拥塞控制中PID控制器的设计

自适应比特（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。在大规模的高速网络中，算法的简洁性对优化交换机的性能是至关重要的。尽管二进制ABR流量控制的简洁性具有相当的吸引力，但显式前向拥塞标识（Explicit Forward Congestion Indication,EFCI)算法控制的队列长度和允许信元速率（Allowed Cell Rate,ACR)大幅振荡，降低了链路利用率，严重的影响了交换机的性能，为此有了相对复杂却有效的显式速率反馈机制，在该文中，引入了拥塞的概率判定机制，并运用经典控制理论为拥塞判定概率的实量更新设计了线性的PID控制器，避免了非线性的控制规律可能诱发的系统自激振荡，在PID控制器的参数整定上，因为使用常用处受到限制，进而给出了一种基于确定稳定裕度的参数整定方法，仿真试验表明：二进制流量控制中的PID算法在保持了算法简洁性的前提下，大幅度地抑制了ACR和队列长度的振荡，提高了链路利用率，减小了队列系统引入的时延抖动，为保证ATM网络中的服务质量（Quality of Service,Qos)提供了必要的技术支持。

PID Controller Design for Congestion Control in ATM Network

Available Bit Rate (ABR) flow control is an effective measure in ATM network congestion control and traffic management. In large scale and high-speed networks, the algorithm simplicity is crucial to optimize the switch. 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 has negative impact on the performance, so its applicability was doubted, and then the explicit rate feedback mechanism, which is relatively complex but effective, was introduced and explored. In this study, we introduce a new detecting/relieving congestion mechanism based on probability, and design the linear PID controller to update the probability depending on the network load status, so the self-oscillation caused by the nonlinear control law will be avoided. Because the common method used in tuning parameters is unstable, a new approach based on the determinate stability margin is put forward. The simulation results show that PID algorithm for binary ABR flow control greatly constrains the oscillations of ACR and queue, improves the link utilization, and decreases the delay jitter introduced by the router queue, which is beneficial to QoS guarantee.