In data networks, a negative phenomenon such as global synchronization can occur. It manifests itself in the form of auto-oscillations, which may capture the whole segment of the network. As a result, the network parameters such as the bandwidth, latency, etc. are degraded. The reason for this phenomenon is the interaction of control elements in the network (for example, active traffic management modules) and protocols such as TCP. To prevent this phenomenon, it is proposed to control the parameters of the network control elements (since the prospects of a radical modification of the TCP protocol seem somewhat illus ory to us). Specifically, we are studying the active traffic control modules of the RED type. To isolate the main parameters on which the occurrence of self-oscillations may depend, we assumed to linearize the m odel with its subsequent investigation. However, the standard linearization leads to the disappearance of the self-oscillatory regime. We suggest to use the method of harmonic linearization, which preserves the self-oscillatory regime. So the method of harmonic linearization is briefly considered in our paper. We also highlight the main criteria that can be used to determine the presence of self-oscillations and to det ermine their parameters. The application of the harmonic linearization method is demonstrated with the help of the RED active traffic control module.