Active Queue Management Controller Research Articles

Reduction-based robust active queue management control

This paper is concerned with the design of improved active queue management (AQM) control schemes for time-delay systems taking into account explicitly the presence of delays in the controller design. A robust controller coping with uncertainties on the network parameters such as round-trip time and load variations is proposed. This is based on an appropriate robust reduction method for time-delay systems. A robust observer for time-delay systems is used to estimate online the average transmission window resulting in a robust output feedback stabilization scheme for AQM. The resulting control law is validated and tested firstly through numerical simulations and then pseudo-experimentally by network simulator (NS-2).

Adaptive AQM controllers for IP routers with a heuristic monitor on TCP flows

We propose adaptive proportional (P) and proportional-integral (PI) controllers for Active Queue Management (AQM) in the Internet. We apply the classical control theory in the controller design and choose a proper phase margin to achieve good performance of AQM. We have identified a simple heuristic parameter that can monitor the changes of network environment. Our adaptive controllers would self-tune only when the dramatic change in the network parameters drift the monitoring parameter outside its specified interval. When compared to P controller, a PI controller has the advantage of regulating the TCP source window size by adjusting the packet drop probability based on the knowledge of instantaneous queue size, thus steadying the queue size around a target buffer occupancy. We have verified our controllers by OPNET simulation, and shown that with an adaptive PI controller applied, the network is asymptotically stable with good robustness. Copyright © 2005 John Wiley & Sons, Ltd.

MULTI-RED CONTROLLER FOR ROUTER FAULT ACCOMMODATION

In this work a classical model-based controllers for Active Queue Management(AQM) routers supporting dynamic model of Transmission Control protocol (TCP) flows is developed. Using this model, an AQM control system using Random Early Detection (RED) controller is designed. In first part, the interc0onnection terms of TCP are simplified. Second part, the stability of the closed loop system is studied on the basis of a simplified Internet router model (Misra et al., 2000). In the proposed approach classical RED controller is adapted in order to take into account the network parameters variations. In the last part of the paper, the approach is validated using Matlab Simulation.

Design of AQM controllers for IP routers based on H∞ optimal control

Based on the recently developed feedback control model for the Transport Control Protocol (TCP), this paper has formulated controller design procedures for Active Queue Management (AQM) in Internet Protocol (IP) routers using the H∞ optimal control theory. The H∞ loop-shaping technique is applied to solve the S/U Mixed Sensitivity Problem (MSP) and S/T/U MSP in the controller design. Different weight functions and their impacts on the system performance are evaluated and discussed. The effectiveness of the designed controller is verified through OPNET simulations.

Design of an adaptive PI rate controller for streaming media traffic based on gain and phase margins

An adaptive proportional-integral (PI) rate controller for best-effort streaming media traffic in the Internet is proposed. Classical control theory is employed in the control design, which allows the user to achieve good performance of active queue management (AQM) in the router by specifying the proper gain and phase margins. The proposed adaptive PI rate controller will self-tune only when the number of active controlled source nodes changes or the average round trip time becomes longer. The adaptive PI rate controller located in the router can calculate the advertised source transmission rate for the streaming media traffic based on the instantaneous queue length of the buffer, which clamps the steady value of the queue length around the target buffer occupancy. Every controlled source node always transmits streaming media traffic through IP packets into the network at the maximum allowed transmission rate, thus providing the best-effort service traffic and maximising the bandwidth utilisation of the Internet. Our OPNET simulations demonstrate that the rate-based AQM control system can adapt to the fluctuation of the uncontrolled guaranteed traffic very well, thus providing the network with good stability robustness.

A stable queue-based adaptive controller for improving AQM performance

Active queue management (AQM) mechanisms are designed to provide better support for end-to-end congestion control mechanisms of transmission control protocol (TCP) in TCP/IP networks. This paper introduces a stable queue-based adaptive proportional–integral (Q-SAPI) controller for AQM and presents an implementation. The starting points of our approach are the recently developed fluid-flow modeling and control theoretic interpretation of the TCP/AQM dynamics, and the recently developed fixed-gain proportional–integral (PI) controller for AQM. Q-SAPI aims to improve the transient performance of the fixed-gain PI controller while maintaining its steady-state performance over a wide range of uncertainties in round-trip time (RTT) and the number of active TCP flows. The robustness of Q-SAPI is studied in detail, which provides guidelines for selecting control parameters. Through extensive simulations, we demonstrate the ability of Q-SAPI in controlling queue length in both transient and steady states. Q-SAPI achieves this by adapting the controller gains according to the queue length.

Throughput differentiation using coloring at the network edge and preferential marking at the core

In this paper we introduce an innovation in differentiated services architecture consisting of adaptive two-level coloring at the edge and preferential marking at the core. We identify general properties of these two processes which, when met, guarantee a desirable fixed point for the network; i.e., one where aggregated flow rates meet or exceed given targets in an over-provisioned network. Specific mechanisms realizing the aforementioned properties lead to so-called active rate management controllers for edge coloring, and a preferentially-marking, active queue management controller at the core. We discuss stability of the fixed point for this network, and validate results using ns simulations.

PI-PD Controller for Adaptive and Robust Active Queue Management for Internet Congestion Control

Since random early detection (RED) was proposed in 1993, many active queue management (AQM) algorithms have been proposed to support better end-to-end Transmission Control Protocol (TCP) congestion control. In this article, the authors introduce and analyze a feedback control model of the TCP/AQM dynamics. Then they suggest the concept of an AQM algorithm that can detect and avoid congestion proactively. Finally, they propose the proportional-integral (PI) proportional-derivative (PD) controller using proportional-integral-derivative (PID) feedback control to overcome the reactive control behavior of existing AQM proposals. The PI-PD controller is able to provide proactive congestion avoidance and control using an adaptive congestion indicator and a control function. A comparative simulation study under a variety of network environments shows that the PI-PD controller outperforms RED and the PI controller in terms of the queue length dynamics, the packet loss rates, and the link utilization.

AQM GENERALIZED NYQUIST STABILITY IN MULTIPLE BOTTLENECK NETWORKS

The influence of multiple bottlenecks on the stability of Active Queue Management (AQM) controllers, usually configured on a single bottleneck basis is discussed. We consider a network scenario where RED is configured at each router according to previously developed control theoretic techniques. These configuration rules assure stability in a single bottleneck scenario. We show that instability may arise when two links become congested. We justify this result through a multiple bottleneck model using the Generalized Nyquist stability criterion.

On Designing Self-Tuning Controllers for AQM Routers Supporting TCP Flows Based on Pole Placement

This paper revisits the simple pole placement technique in the classical control theory, and exploits this technique to propose two kinds of controllers for active queue management (AQM) in Internet protocol (IP) routers: the self-tuning proportional controller based on pole placement (ST/spl I.bar/P/spl I.bar/PP) and the self-tuning proportional-plus-integral controller based on pole placement (ST/spl I.bar/PI/spl I.bar/PP). The damping ratio /spl xi/ and undamped natural frequency /spl omega//sub n/ can be appropriately chosen such that: 1) the transient response performance of the system is satisfied and 2) all the poles would lie in the left-half s-plane to guarantee the stability of the control system. The self-tuning controllers can assign proper intervals of /spl xi/ and /spl omega//sub n/ to achieve good AQM performance and thereby adapting the system to significant load changes very well. Furthermore, the ST/spl I.bar/PI/spl I.bar/PP controller can regulate the packet drop probability based on the knowledge of the instantaneous queue size, and clamp the steady value of the queue length to a specified reference value. We verify the effectiveness of these two controllers via OPNET simulation. Our simulation results show the following: 1) choosing appropriate /spl xi/ and /spl omega//sub n/ can successfully satisfy the transient response of the system and 2) when the network load changes, the ST/spl I.bar/P/spl I.bar/PP controller and the ST/spl I.bar/PI/spl I.bar/PP controller exhibit extremely short settling time.

Design a congestion controller based on sliding mode variable structure control

As an effective mechanism acting on the intermediate nodes to support end-to-end congestion control, Active Queue Management (AQM) takes a trade-off between link utilization and delay experienced by data packets. Most existing AQM algorithms are heuristic, and lack a systematic and theoretical design and analysis approach. From the viewpoint of control theory, the AQM system can be regarded as a typical regulating system. Although the PI controller for AQM outperforms the RED algorithm, the mismatches in a simplified TCP flow model inevitably degrade the performance of controller designed using classical control theory. In this paper, a robust controller for AQM is developed based on Sliding Mode Variable Structure Control (SMVS). Because it is insensitive to noise and variance of parameters, it is very suitable for time-varying network systems. The principles and design of the SMVS controller are presented in detail. The integrated performance is evaluated using ns simulations. The results show that the SMVS is responsive and robust against disturbance. At the same time, a complete comparison between SMVS controller and PI controller is made. The conclusion is that both transient and steady performance of the SMVS controller is superior to those of PI controller, thus the SMVS controller can readily achieve to the AQM objectives.

AQM controller design for IP routers supporting TCP flows based on pole placement

The simple pole placement technique in classical control theory is exploited to propose two kinds of controllers for active queue management (AQM) in IP routers: the proportional controller based on pole placement (P―PP controller) and the proportional-plus-integral controller based on pole placement (PI―PP controller). The damping ratio ξ and the undamped natural frequency ω n are appropriately chosen such that the transient response of the system is satisfied and all the poles lie in the left-half s-plane to guarantee the stability of the system. The authors verify the effectiveness of the controllers via extensive simulations using OPNET, including the case of different time-varying round-trip times (RTTs) for different connections. Simulation results show that choosing appropriate values of ξ and ω n can successfully satisfy the transient response of the system. The impact of different values of ξ and ω n on the system performance is also investigated.

A genetic algorithm for the design of a fuzzy controller for active queue management

Active queue management (AQM) policies are those policies of router queue management that allow for the detection of network congestion, the notification of such occurrences to the hosts on the network borders, and the adoption of a suitable control policy. This paper proposes the adoption of a fuzzy proportional integral (FPI) controller as an active queue manager for Internet routers. The analytical design of the proposed FPI controller is carried out in analogy with a proportional integral (PI) controller, which recently has been proposed for AQM. A genetic algorithm is proposed for tuning of the FPI controller parameters with respect to optimal disturbance rejection. In the paper the FPI controller design methodology is described and the results of the comparison with random early detection (RED), tail drop, and PI controller are presented.

Anti-windup compensator for active queue management in TCP networks

In this paper, we apply a dynamic anti-windup scheme for improving the performance of a conventional proportional–integral (PI) controller for active queue management (AQM) supporting TCP flows. When a PI controller is used for AQM, the windup phenomenon of the integral action can cause performance degradation because the packet drop probability is limited between 0 and 1. Therefore we suggest a TCP/AQM model with a saturating actuator and apply a dynamic anti-windup method for improving the performance of the conventional PI AQM scheme. The proposed scheme not only provides graceful performance degradation, but also guarantees the stability of the overall system with the linearized TCP model. We verify the performance of the proposed scheme through ns-2 simulations. The simulation results show that our scheme outperforms the conventional PI controller when the traffic load is not stationary, which is always the case in real network environment.

ACTIVE QUEUE MANAGEMENT ALGORITHM WITH A RATE REGULATOR

In this paper, we propose an efficient control scheme for active queue management (AQM) supporting TCP flows. The proposed controller consists of two parts: a rate controller and a queue size controller. The rate controller is a proportional-integral (PI) controller, which improves the response to dynamic traffic variation and keeps the packet arrival rate around the link capacity. The queue size controller is a proportional (P) controller like the Random Early Detection (RED) algorithm. The rate controller gains are obtained by minimizing the performance index, either the integral square error (ISE) or the integral absolute error (IAE). We compare the performances of the proposed algorithm, the RED algorithm and the PI controller for AQM through ns simulations.

Design of a fuzzy controller for active queue management

As an effective mechanism acting on the intermediate nodes to support end-to-end congestion control, active queue management (AQM) takes a trade-off between link utilization and delay experienced by data packets. From the point of view of the control theory, it is rational to regard AQM as a typical regulating system. Although proportional integral (PI) controller for AQM outperforms traditional RED algorithm, the mismatches in simplified TCP flow model inevitably degrades the performance because the design of PI controller is heavily dependent of the accuracy of the plant, such as, for small buffer the system tends to perform poorly. In this paper, the fuzzy logic controller (FLC) for AQM is designed based on the fuzzy logical control. Its superiority is independent of the model of the plant, which is very suitable to the high variability and uncertainty networks. We present the guidelines and highlights to design the parameters of the FLC. We then compare its performance with the PI controller through simulations, and investigate the impact of the network configuration and operating parameters on the stability and responsibility. The results show that the FLC is rather robust against the noise and disturbance caused by the round-trip time, the link capacity, the number of the active flows and the non-responsive UDP flows, etc., which badly degrade the performance of the PI controller. The transient response and tracking capability of the FLC is superior to that of the PI controller, which is beneficial to achieve the goals of AQM scheme.