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Document Type

Original Study

Keywords

Control Engineering

Abstract

Internet represents a shared resource wherein users contend for the finite network bandwidth. Contention among independent user demands can result in congestion, which, in turn, leads to long queuing delays, packet losses or both. Congestion control regulates the rate at which traffic sources inject packets into a network to ensure high bandwidth utilization while avoiding network congestion. In the current Internet, there are two mechanisms which deal with congestion; the end-to-end mechanism which is achieved by the Transmission Control Protocol (TCP) and the intermediate nodes algorithms such as Active Queue Management (AQM) in routers. In this paper, a combined model of TCP and AQM (TCP/AQM) is formulated and first simulated without a controller. The results show that it is unable to track the desired queue size. So, to get better tracking performance, an adaptive PID controller based on wavelet network (AWNPID) is used as AQM in the router queue. The non-adaptive PID controller is also demonstrated, and its weakness to the network dynamic changes is compared to the robustness of adaptive controller (AWNPID). The analytical results for linearized TCP/AQM model are presented in MATLAB version 7.0.

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