Active queue management (AQM) is a congestion control mechanism for the early notification of the incipient congestion pursued by dropping/marking packets. The novelty in our result is that we are able to consider heterogeneous traffic (i.e., multiclass traffic) where each class has its own packet discarding policy, queue size, and bandwidth share. Then, this is so far the first control theory-based approach for the AQM problem on the TCP/IP routers that allows multiclass AQM. Our proposed technique assumes that each class has already a controller, designed a priori, and focuses on designing a static state feedback controller where the proposed design approach is based on the solution of linear matrix inequalities (LMIs). From the theoretical conditions, a new controller design methodology for discrete time systems with multi-delays, saturated inputs, and disturbances is proposed to overcome the obstacle of bilinearity which leads to a quite simple LMI condition that is numerically tractable with any convex optimization algorithm. A numerical example is provided at the end of this paper to show the effectiveness and performances of the proposed approach in the presence of multiclass traffic.
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