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KEYWORDSHybrid modeling, fluid model, active queue management, random early detection, Modelica ABSTRACTFor the study and verification of our mathematical model of RED-like active traffic management module a discrete simulation model and a continuous analytical model were developed. However, for various reasons, these implementations are not entirely satisfactory. It is necessary to develop a more adequate simulation model, possibly using a different modeling paradigm. In order to modeling of the TCP source, the RED control module, and the process of their interaction it is proposed to use a hybrid (continuous-discrete) approach. For computer implementation of the model the physical modeling language Modelica is used. Because the language Modelica has multiple implementations we have selected the OpenModelica compiler. The hybrid approach allows us to take into account the transitions between different states in the continuous model of the TCP protocol. The hybrid approach simplified the consideration of the model due to the conversion of a differential inclusions into a set of differential equations with discrete transitions. The considered approach allowed to obtain a simple simulation model of interaction between RED module and TCP source. This model has great potential for expansion. It is possible to implement different types of TCP and RED. Furthermore, it is possible to use a hybrid approach not only for the simulation but also for analytical modeling.

Self-oscillation modes in control systems of data transmission networks negatively affect the characteristics of these networks. To investigate the self-oscillation mode for systems with a control module, the analytical model of the active queue management module was developed. The problem of verification of the obtained theoretical results arises in the study. Previously, a software system was developed for software emulation of the router. However, its use has caused some difficulties. Alternatively, the simulation model of network with active queue management module was developed. The paper describes a software package for verifying theoretical calculations based on the NS-2 simulation system. For illustration, a numerical example is given.