Robust 2-DoF PID control for Congestion control of TCP/IP Networks

Internet congestion control and congestion avoidance have been active research interests in the area of networking (see, for example [1] [2] [3]) during the last two decades. It has two components: (1) the end-to-end congestion control protocol, such as TCP [4], and (2) an active queue management (AQM) scheme implemented in routers. AQM signals congestion by discarding or marking packets. When congestion is detected by TCP, it will take actions to reduce the source sending rate. Normally, AQM objectives are: to stabilize the buffer queue length at a given target, thereby achieving predictable queueing delay, and to minimize the occurrences of queue overflow and underflow, thus reducing packet loss and maximizing link utilization. Thus, it is necessary to reduce as much as possible this problem. At present, there are methodologies to deal with this issue [5]: congestion control which is used after the network is overloaded and congestion avoidance which takes action before the problem appears. This paper deals with congestion control because it is where feedback control techniques can be openly and easily applied.