Analysis and Design of AQM for stabilizing TCP

Abstract

In this paper, we propose a unified AQM (Active Queue Management) framework and stabilizing optimal AQMs in stabilizing a given TCP (Transmission Control Protocol) and a real-queue dynamics. Since we formulate the AQM design problem for the given TCP as state-space models, we get three important features. First, we propose a PD-type (Proportional-Derivative) control structure and by applying integral control action technique, a PID-type (Proportional-Integral-Derivative) control structure. Second, we propose memory control structures to compensate explicitly delays in congestion measure by using memory control structures. Third, we propose stabilizing optimal AQMs by minimizing linear quadratic costs on the transients in queue length, aggregate rate, jitter in the aggregate rate, and congestion measure, which are called RHA (Receding Horizon AQM) in this paper. Conversely, we show that any AQM with an appropriate structure solves the same stabilizing optimal control problem with appropriate weighting matrices. Finally, we interpret existing AQMs such as RED (Random Early Detection), REM (Random Exponential Marking), PI (Proportional-Integral) and AVQ as different approximations of the unified AQM structures, and discuss the impact of each structures on performance from the results of the stabilizing optimal AQMs. We illustrate our results through simulation examples for the linearized system of a given nonlinear TCP and queue dynamical system.

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