Abstract
Active queue management (AQM) is a technique to avoid serious congestion of the transmission control protocol (TCP) flows at a router. AQM based on control theory, which utilizes congestion controllers such as proportional-derivative (PD) controller or proportional-integral-derivative (PID) controller, has been previously proposed. In addition, disturbance observer (DOB) has been utilized to compensate for modeling error of a TCP/AQM congestion control system. However, the DOB-based controllers cannot cope with a large time delay in TCP/AQM networks. Although one of the effective time delay compensators is Smith predictor (SP), the implementation of the DOB and SP in an integrated manner has not been accomplished, because of saturation due to the input limit of packet drop probability. In this paper, a novel TCP/AQM congestion control system with the DOB and SP considering the saturation function is proposed to compensate for the modeling error and time delay simultaneously. Simulation results show that the proposed controller provides better throughput and goodput than conventional controllers. One of the simulations assume that the propagation delay and bottleneck link capacity are set to 100 ms and 100 Mbps, respectively. Under this assumption, it is confirmed that the proposed controller achieves a goodput of 99.55 Mbps whereas the classical PID controller and PD controller with DOB achieve 99.23 Mbps and 99.24 Mbps, respectively.
Highlights
Transmission control protocol (TCP) is often utilized for communications through the Internet, including the communications between sensors and actuators, because of its high reliability
This paper proposes a novel transmission control protocol (TCP)/Active queue management (AQM) congestion control scheme supporting TCP flows by implementing disturbance compensation and time delay compensation in an integrated manner, and avoids serious congestions under large round-trip time (RTT)
The simulations were performed under multiple setups by changing the parameters that mainly affect the behavior of the TCP/AQM network
Summary
Transmission control protocol (TCP) is often utilized for communications through the Internet, including the communications between sensors and actuators, because of its high reliability. We take this input saturation into account and designs a novel TCP/AQM network congestion control system with the DOB and SP, to compensate for the disturbance and time delay simultaneously. A. NONLINEAR TCP/AQM NETWORK MODEL AQM is a congestion control mechanism, which attempts to maintain stable queue length by actively dropping packets. The information of packet drop would be notified to the corresponding sender host by the ACK packet sent from the receiver host, resulting in shrinking of the TCP window size and reduction in the number of packets arriving at the bottleneck link router By these procedures, AQM attempts to maintain the queue length at a constant value.
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